Second Workshop on Particle Minibeam Therapy

20 Mar 2024, 15:00 → 22 Mar 2024, 17:00 Europe/Berlin

Casino (Universität der Bundeswehr München)

Judith Reindl

Following the success of the first workshop last year in Paris, we are glad to announce the 2nd International Particle Minibeam Therapy Workshop taking place in Munich on the 20th-22nd of March 2024!

There will be experts from all related disciplines (physics, biology, clinics etc.) offering more stimulating and comprehensive discussions. In the workshop, plenty of people involved in the minibeam research community will give interesting talks, while also young researchers will have the chance to present their work and get beneficial feedback from experienced researchers.

The topics covered in this workshop are:

• Technologies of Particle Minibeam production and application
• Dosimetry of Particle Minibeams
• Biological mechanisms of the effect of Particle Minibeams
• Pre-clinical studies on Particle Minibeam Therapy
• Medical applications

 

Additionally we are pleased to announce that the ErUM-Data-Hub features the special topic about: Digitization and machine learning in particle minibeam therapy.

Furthermore, we are aiming in enlarging the network of collaboration and the interdisciplinarity of the field and increase accesibility for beamtime. We therefore especially invite people from the other ErUM Comittees and from facilities offering beamtime to join the workshop.

Please also visit our website: https://www.pmbt-group.org/workshop2024/overview

Register and join us in Munich.

Judith Reindl

(Conference Chair)
 

 

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Wednesday 20 March

Welcome Reception and impulse debate

Conveners: Judith Reindl, Dr Stefanie Girst

Thursday 21 March

08:00 Coffee and Drinks

Welcome

Convener: Judith Reindl

Biological Mechanisms of the effect of Particle Minibeams

Convener: John Eley (Vanderbilt University)

1 Invited talk: TBA

Speaker: Dr Lorrea Itturi

2 Assessing the biomolecular effects of carbon minibeam radiation therapy via synchrotron-based infrared microspectroscopy

A higher therapeutic index might be achieved in carbon therapy when used in combination with Minibeam Radiation Therapy (CMBRT). Nevertheless, the biochemical effects underlying CMBRT are not profoundly known. This work aims to study the nature of these effects by employing synchrotron-based Fourier Transform Infrared microspectroscopy (SR-FTIRM).
Cancer cell irradiations (LM8 mouse osteosarcoma) were carried out at the GSI (Germany). Broad beam (BB) and minibeam (MB) irradiations were performed with two mean doses (2 and 8 Gy). SR-FTIRM measurements were held at ALBA synchrotron. Principal Component Analysis (PCA) was used to evaluate spectral modifications related to proteins, nucleic acids, and lipids.
PCA score plots indicate that the biochemical signatures obtained from the BB-treated cells are closer to control cells, while CMBRT infrared spectral features clearly differ from BB for both peak and valley MB groups. The peaks that contribute the most to BB-MB data separation in the PCA score plot are Amide I (1598-1710 cm−1), Amide II (1483-1590 cm−1), Phosphate I (1240 cm−1), and Phosphate III (970 cm−1). Changes in the amides have been previously related to protein secondary structure modifications, while Phosphate I might account for cell death, oxidative stress, or DNA backbone modifications. Phosphate III has been related with deoxyribose damage, backbone single and double strand breaks, and crosslinks. Regarding lipids, changes in the CH2 and CH3 vibrational modes (3000-2800 cm-1) were detected, which were previously correlated with changes in the lipid chain length, oxidative stress and membrane alterations. Several differences were also encountered between MB peak and valley groups. Specifically, in the Amide I and Phosphate II regions, as well as in the ester vibration mode located at 1740 cm-1.
The above-described changes suggested distinct biochemical effects on irradiated tumor cells, adverting differences in the impact of CMBRT against homogeneous radiation.

Speaker: Martina Cots-Costa (Universitat Autònoma de Barcelona)

3 Infrared microspectroscopy to uncover the in vivo biochemical effects of proton minibeam radiation therapy

Background: the biology underlying proton minibeam radiation therapy (pMBRT) is not fully known yet. Therefore, this study reports on the in vivo biochemical mechanisms following pMBRT irradiations using Fourier Transform Infrared Microspectroscopy (FTIRM). This technique can reveal details of the biochemical structure of the main biomolecules and their possible modifications by measuring infrared absorbance spectra.

Materials and methods: radiotherapy (RT) was performed at Institut Curie Proton Therapy Center using 100 MeV proton beams. Both healthy and tumour-bearing (F98 cell line) Fischer rats were subjected to conventional (BB) proton RT and pMBRT, delivering 30 Gy to whole brains (excluding the olfactory bulb and cerebellum). Brain sections were fixed at 2 and 24 hours post-RT. FTIRM measurements were then conducted at ALBA Synchrotron, where infrared raster scanning maps of the sections were collected for each sample and irradiation condition. Data analysis included hyperspectral imaging and assessment of spectral markers of biochemical modifications.

Results: in healthy animals, a large absorbance increase of protein-related spectral bands was observed in the brain cortex at 2 hours post-RT, indicating modifications in the secondary structure of proteins. Conversely, a reduced absorbance of nucleic acid bands was indicative of the radiation-induced damage to the DNA and carbohydrates, especially for BB-RT. Most of pMBRT damage was reduced 24 hours after treatment. Phosphate bands were altered in the tumours of glioma-bearing rats one day post pMBRT, indicating enhanced DNA damage. In the lipid spectral region, both RT modalities produced similar hydrocarbon chain modifications.

Conclusions: this is the first study to report in vivo biochemical modifications resulting from pMBRT. Spectral differences were dependent on the brain region, irradiation configuration and fixation time. In healthy rats, almost all early damage induced by pMBRT decreased after one day, while greater DNA damage due to pMBRT was observed in the tumours of glioma-bearing rats.

Speaker: Roberto González Vegas (Autonomous University of Barcelona)

4 Migration behavior of U87 glioblastoma cells after irradiation with varying LET

Glioblastoma multiforme is the most common malignant brain tumor with a very poor prognosis. High infiltration rates, uncontrolled cell growth, and a strong ability to develop therapy resistance are components of the aggressive nature of this type of cancer. Despite multimodal treatment, the tumor often recurs within 1-2 cm of the primary tumor.
In this study, the migration behavior of U87 glioblastoma after low and high LET irradiation is analyzed to determine whether migration is enhanced or otherwise affected by radiation exposure.
For the migration assay, cells were seeded in Ibidi Culture-Inserts 2-well to create a cell-free gap of approximately 500 µm between two cell populations. Targeted irradiation was performed with 55 MeV carbon ions and 20 MeV protons at the ion microprobe SNAKE (Superconducting Nanoprobe for Nuclear Physics Experiments) at the 14 MV tandem accelerator in Garching (GER). The closure of the gap after irradiation was observed by phase-contrast microscopy under live-cell conditions.
Differences in the migration behavior of the cells in terms of speed and direction are visible. Cells irradiated with high-LET protons tend to be faster but have lost all orientation. Low-LET proton irradiation also causes a loss of orientation but has almost no effect on the speed of the cells. When only the cell population on one side of the gap is irradiated, the cells are better oriented regardless of the type of irradiation. However, one-sided proton irradiation leads to a deceleration of the cells.
Our results show that the migration behavior changes with different irradiation conditions. In particular, the behavior changes when only a part of the cells is irradiated. These results indicate that the close presence of non-irradiated cells has a strong effect on the migration behavior of the whole population.

Speaker: Nicole Matejka (Universität der Bundeswehr München)

5 Hypoxic radioresistance in particle minibeam tumor response: in vitro study to inform optimal peak dose and treatment planning protocols

The existence of severe hypoxia in locally advanced tumors is well characterized. In terms of particle minibeam applications, few studies have considered the dose that may be required to completely sterilize tumor tissue that falls within the peak dose volumes. Instead, peak doses are mostly decided at random and dictated by valley dose treatment goals or anatomic constraints depending on the tumor position. Unfortunately, without thresholds/min/max data for each tumor type, the clinical team is left to design somewhat random treatment plans that do not account for important biology such as hypoxic resistance, vascular damage and indirect effects thereof, or intrinsic radiation resistance of each tumor type. We have begun a study to compare the hypoxic radiation response of F98 rat glioma cells when given graded doses of photons or protons in the Bragg peak or plateau regions to understand the predicted total single dose that would be required to eliminate all hypoxic cells. When this value is determined, beam width and spacing to allow desired valley doses for immune activation or other goals can be directly calculated and a consistent protocol for tumor treatment can be established. Our initial studies using photons suggest that while a dose of 15-20 Gy can eliminate over 8 logs of tumor cells in fully aerobic conditions, a dose of 90-100 Gy or more will be required to eliminate the same order of magnitude of hypoxic tumor cells in a peak dose volume. We surmise that protons of differing energies/dose rates that possess increased LET and RBE may allow the peak dose target to be reduced compared to photons. Plans to assess other particle minibeams with greater RBE with collaborating institutions and instrument platforms are underway.

Speaker: Robert Griffin (Institut Curie)

10:50 Coffee, Cake and Posters

Treatment planning and simulations

Convener: Prof. Juergen Meyer (University of Washington)

6 Invited talk: TBA

7 MC-IMPT: A multi-collimator intensity-modulated PVDR-optimized treatment planning method for proton minibeam radiotherapy

Purpose: The clinical translation of proton minibeam radiation therapy (pMBRT) is non-trivial, for which the proper treatment planning technique remains an open question: on one hand, the uniform target dose is desirable for anti-tumor efficacy and the easy acceptance of pMBRT as a standalone treatment modality; on the other hand, high peak-to-valley dose ratio (PVDR) is also desirable in organs-at-risk (OAR) for normal tissue sparing, which however can be challenging for these OAR distal to beam entrance or require patient-specific collimators. This work proposes a novel pMBRT treatment planning method that can achieve uniform dose at target and high PVDR at OAR simultaneously, via multi-collimator intensity-modulated PVDR-optimized inverse optimization method called MC-IMPT.

Methods: MC-IMPT utilizes a set of generic and premade multi-slit collimators with different center-to-center distances, and does not need patient-specific collimators. The collimator selection per field is OAR-specific and tailed to maximize PVDR in OAR. Then the inverse optimization method with intensity modulation and PVDR optimization is utilized to jointly optimize target dose uniformity, PVDR, and other dose objectives, which is solved by iterative convex relaxation optimization algorithm.

Results: The efficacy of MC-IMPT is demonstrated using clinical abdomen, lung, and head-and-neck cases. Compared to CONV, MC-IMPT had similar target dose uniformity and plan quality, while providing unique PVDR in OAR. It was also shown that the use of PVDR optimization further improved PVDR for MC-IMPT.

Conclusions: A novel pMBRT treatment planning method called MC-IMPT is proposed that utilizes a set of generic and premade collimators and PVDR optimization algorithm to optimize OAR-specific PVDR and target dose uniformity simultaneously.

Speaker: Hao Gao (University of Kansas Medical Center)

8 Facility presentation

Speaker: Gerd Datzmann

12:45 Lunch, Coffee, Cake and Posters

Postersession

Convener: Judith Reindl

9 A Linac-based hardron minibeam irradiation facility

Minibeam therapy faces challenges in preserving deep-seated normal tissue due to the lateral spreading of minibeams caused by small-angle scattering. Unlike proton minibeams, helium or carbon minibeams experience less spreading, potentially reducing side effects. Studies with proton beams indicate that reaching full therapeutic potential of minibeam therapy requires high beam brightness. Assuming a similar need for helium and carbon beams, circular accelerator-based irradiation facilities are not ideal for preclinical and clinical helium or carbon minibeam therapy studies. With clinical treatment or combinations of minibeam and flash therapy, this demand increases as the irradiation time is inversely proportional to the beam brillance. This manuscript introduces a concept for a hardron minibeam therapy facility based on a Linac design for conventional carbon therapy. The Linac beam is focused into submillimeter minibeams by a quadrupole triplet. A scanning unit and dosimetry unit are included to navigate the minibeam across the target area and monitor the applied dose. TRAVEL simulations optimize the beamline, while TOPAS simulations evaluate beam-component interactions and resulting parameters at the focal plane. For carbon energies between 100 MeV/u and 430 MeV/u (approximately 3 cm and 30 cm range in water), the facility achieves a transverse beamwidth of < 100 µm (sigma) and a peak-to-valley (energy) dose ratio of > 1000, with an average beam current of around 30 nA.

Speaker: Michael Mayerhofer (Univeristät der Bundeswehr München)

10 Beyond Proton Minibeam Therapy: Exploring Boron-Proton-Capture effect for Enhanced Tumor Control

The primary aim of radical radiotherapy is to effectively treat tumors while minimizing damage to normal tissues. Hadron therapy, utilizing heavy particles such as protons, alpha particles, and carbon ions, provides a unique advantage over conventional photon therapy, which can be increased by the use of spatial fractionation. The focus of this research project is to further enhance the effect of Proton Minibeam Therapy by the additional use of Boron Proton Capture therapy aiming to enhance the effectiveness of treatment with respect to tumor control. The boron-proton interaction generates short-lived excited states, releasing alpha particles with higher energy than conventional protons, intensifying damage to tumor cells while preserving healthy tissue.
The methodology consists of introducing boron compounds into tumor cells and then irradiating them with proton particles. Subsequently, the ionizing radiation induced foci (IRIF) staining tests, capture the interaction and alpha particle emission, employing high-resolution confocal microscopy for analysis. Another experimental phase involves the micronuclei test, evaluating and comparing the radiotoxicity of proton and alpha particles in terms of inducing micronuclei in cells. The cell line used in this research project is the PANC1 cell line.
Preliminary results from ionizing radiation induced foci microscopy demonstrated the successful capture of the interaction between boron compounds and proton particles. However, further improvements in boron compound synthesis are crucial for successful localization within tumor cell nuclei. This ongoing research signifies a notable step toward advancing proton therapy, providing valuable insights into the potential of Boron-Proton-Capture therapy for enhancing tumor control while minimizing the impact on healthy tissues.

Speaker: Asieh Amarlou (TUM School of Medicine, Technical university of Munich, Munich, Germany)

11 Comparison of particle types in longitudinally heterogeneous irradiation treatment plan simulations for Particle Minibeam Radiotherapy

Proton minibeam therapy (pMBT) using sub-millimeter beams spaced a few millimeters apart has demonstrated the ability to reduce side effects in normal tissues and possible increase of the therapeutic ratio. Preclinical studies also indicate that FLASH irradiation, delivering ultra-high dose rates (>40 Gy/s), minimizes tissue toxicity while maintaining effective tumor control. However, integrating the FLASH technique with pMBT and Spread-Out Bragg Peak (SOBP) presents technical challenges. Previous simulations proposed investigating a single-energy distal-edge Bragg Peak from opposing directions to reduce toxicity further while enabling successful FLASH application. Additionally, heavy ion minibeams, such as helium or carbon, might offer similar advantages, potentially improving tissue sparing in deeper tissue due to reduced angle scattering compared to protons.
This study compares longitudinally heterogeneous irradiation modes of different particle minibeams: protons, helium, and carbon ions. A 25 cm-thick water phantom, with a 5cm-thick tumor, was irradiated in TOPAS (Tool for Particle Simulation) with varying beam sizes (σ = 0.05 mm, σ = 0.1 mm, and σ = 0.2 mm) for each scenario. The minimum prescribed dose within the tumor volume was achieved through the overlay of minibeams from two opposing directions using the same single energy from each direction for each particle type. From the resulting dose distributions, the normal tissue-sparing effect was estimated and compared through calculated mean clonogenic cell survival using the linear-quadratic model, employing averaged model parameters from PIDE (Particle Irradiation Data Ensemble) database for each particle type.
Helium ions may offer the best balance in tissue sparing between protons and carbon ions, attributed to their smaller beam spread relative to protons and smaller fragmentation tail, smaller uncertainty in Relative Biological Effectiveness (RBE) prediction compared to carbon ions.

Speaker: Thandar Aung (Technical University of Munich/ University of Bundeswehr)

12 Design study of a ridge filter for FLASH application of Proton minibeam radiotherapy

Proton minibeam radiation therapy (pMBT) and FLASH radiotherapy (FLASH-RT) have attracted the interest of scientists due to the better sparing of healthy tissue compared to conventional modalities. Combining these methods may lead to further reduction of the induced side effects. In this proof-of-principle study, the feasibility of designing a ridge filter (RF) for the FLASH application of pMBT has been investigated. The simulations were performed in TOPAS using a 68.5 MeV magnetically focused planar proton minibeam. An RF was designed to create a spread-out Bragg peak (SOBP) in a water phantom with a tumor at 2.88 - 3.88 cm depth. It is made by an asymmetrical carbon unit with 10 steps of equal thicknesses and different widths, which is repeated in space vertically to the axis of the incoming beam. The distance from the middle of one unit to the other is equal to twice the sigma (σ) of the non-degraded beam at the position of the RF. The dose fluctuation in the SOBP region, the dose homogeneity of the tumor, and the beam size at the phantom entrance were evaluated and a robustness analysis related to the RF positioning has been done. The dose fluctuation in the tumor region is almost ±2% and also the application of 10 beams with a center-to-center distance (ctc) of 1.4 mm, creates a dose distribution in the tumor meeting the ICRU criteria. The preservation of small beam sizes at the entrance, with a high peak-to-value dose ratio (PVDR) is possible. The robustness analysis revealed the sensitivity in movements and that precise positioning is needed to always fulfill the homogeneity standards. The simulation study has shown that the designed RF enables the generation of a SOBP in pMBT. In future research, the fabrication method and an accurate positioning system should be investigated.

Speaker: Aikaterini Rousseti (Universität der Bundeswehr München)

13 Employing Deep Learning for automated evaluation of microscope recordings through the object detection model CeCILE

Automated detection and tracking of living cells in microscopy recordings by deep learning algorithms may considerably speed up and facilitate evaluation compared to manual post-processing. However, the performance of such algorithms on individual sets of cell data and their generalizability differ significantly. One approach is to use a deep learning object detection model, which identifies areas in images containing cell depictions, and sorts them into predefined classes based on morphological features. Such a model (CeCILE) was developed at the University of the Bundeswehr Munich by fine-tuning a pretrained model from the TensorFlow 2 Object Detection API on a custom dataset. The latter contains videos of unstained irradiated and non-irradiated cells of four cell lines obtained with phase-contrast microscopy. An application programming interface (API) provides an easy-to-use framework, but modification, addition and removal of code is challenging. Additionally, the Tensorflow Object Detection API is deprecated. Further development of CeCILE can therefore hardly be addressed directly within the model code. For example, CeCILE detects and labels cells only in individual video frames, neglecting their temporal dependence, which is especially important for tracking cell divisions. Therefore, CeCILE is currently under revision and being rewritten with another programming library, PyTorch, without a dedicated object detection API. This approach is expected to increase flexibility and user-friendliness while maintaining the localization and classification accuracy previously achieved with CeCILE. Also, the addition of further features will be attempted, for example to leverage the temporal information in the videos of the dataset. Overall, the approach contributes to achieve more goals more quickly with less data. This work will introduce the concept of deep learning-based object detection, give an overview of CeCILE’s functionalities and insights into the current development. Additionally, results of applying CeCILE to data generated from experiments with spatially fractionated minibeams will be presented.

Speaker: Laura Stepanek (Universität der Bundeswehr München)

14 Improved Imaging of a Biological Model for a Preclinical Proton Minibeam Radiotherapy Facility

In collaboration with the Helmholtz Zentrum Berlin (HZB) a new pMBT facility, called MINIBEE, is currently under construction. The facility will include a small animal radiation research platform (SARRP) for positioning small animals or in vitro samples, X-ray irradiation, onboard CT-imaging, and treatment planning. Additionally, there will be a microscope that enables imaging of samples during irradiation. However, since the late 1950s, the 3R Principle (Replace, Reduce, Refine animal experiments) has been established as a guideline for scientific work using animal models. This work discusses the development of a biological cancer model to be used as a preliminary stage of animal models at this pMBT facility, in order to follow this principle and reduce or replace the number of animal experiments. Compared to animal experiments, 3D models also result in easier handling, lower costs and less time expenditure.
This work shows spheroids as a 3D tumor model. The use of spheroids, is particularly beneficial in mimicking tumor behavior due to their similarity to tumors in terms of oxygen, nutrient and waste product distribution. The study of three-dimensional models comes with issues in microscopy, such as scattering and the range of the laser, which makes it hard to image the whole 3D body. These issues are mainly caused by the large size of the spheroids and the dense packing of the cells.
In this work, we discuss methods to improve the imaging of spheroids as a 3D culture model. It focuses on two basic states in which the spheroids can be studied: living and dead. Spheroid Clearing can provide better images without killing the spheroids, allowing for continued observation of the living spheroid. An alternative method would be to cut the spheroid, which would allow a complete microscopy of the spheroid, but would also definitively and irreversibly destroy it.

Speaker: Ms Anne-Sophie Krull (UniBw)

15 In vitro exploration of the biochemical processes underlying neon minibeam radiation therapy using synchrotron-based infrared microspectroscopy

Healthy tissue toxicity limitations of neon beams may be overcome by combining such ions with the remarkable normal tissue sparing that spatially fractionated radiotherapies provide. The present study explores the biochemical effects involved at a single-cell level in neon minibeam radiation therapy (NeMBRT) using synchrotron-based Fourier transform infrared microspectroscopy (SR-FTIRM). This tool can unveil specific biochemical characteristics of samples by analysing their IR absorbance spectra.

Irradiations were performed at HIMAC (Japan). Both healthy (BJ fibroblasts) and tumour (B16-F10 melanoma) cell lines were subjected to conventional neon RT (NeBB) and NeMBRT. 230 Mev/u neon beams were employed to deliver mean doses of 2, 4 and 8 Gy. Biochemical effects were assessed right after irradiations and 24 hours later. SR-FTIRM measurements were conducted at ALBA Synchrotron (Spain). Differences between treatment configurations were assessed with principal component analysis (PCA).

PCA scores separated samples according to their different IR biochemical signatures resulting from irradiations. In fibroblasts, a clear segregation between NeBB and NeMBRT groups was observed, with the latter remaining closer to control samples. The main IR bands affected by irradiations were the amides, suggesting protein secondary structure alterations. NeBB also affected the ester and phosphate bands, pointing to oxidative stress and DNA backbone damage. For the tumour cell line, modifications of IR bands led to separate PCA clusters of all irradiation modalities; NeMBRT peak group was the most segregated from controls, mostly altering IR bands associated with amide substructures. DNA- and lipid-associated spectral regions were also affected by NeBB and NeMBRT peak groups, which might have resulted from DNA and RNA conformational changes or oxidative stress.

The SR-FTIRM capabilities allowed to uncover the biochemical responses of healthy and cancerous cell lines to NeMBRT, suggesting the activation of distinct effects for both. Specific spectral differences between irradiation configurations were dose-, time- and cell line-dependent.

Speaker: Roberto González Vegas (Universitat Autònoma de Barcelona (UAB))

16 Investigating the effect of spatial and temporal fractionation of proton irradiation to the blood in a blood-flow simulation chamber

Radiotherapy is one of three methods used to fight against cancer along with surgery and chemotherapy, and has currently attracted a lot of scientific interest particularly due to novel techniques, like Proton Minibeam Radiotherapy (pMBT) and FLASH therapy. The latter can deliver an ultra-high dose rate of radiation to the target (>40 Gy/s). From a biological aspect, the main target of radiotherapy, is the DNA of the cancer cells due to its radiosensitivity. Simultaneously, the gold standard for radiotherapy is, achieving optimal tumor control, with minimal healthy tissue complications. Finally, it has been shown that other biological factors, like cell oxygenation and the irradiated blood volume, are contributing aspects to better understanding the effects of radiation on cancerous and healthy tissues alike. Here, we investigate the outcomes of different types of radiation, and different dose rates, on the simulated flow of a specific blood volume.

Collaboratively with Helmholtz-Zentrum Dresden-Rossendorf (HZDR), we create an artificial capillary of materials, selected after running simulations of desired cases on TOPAS (Tool for Particle Simulation), through which, blood cells will flow during irradiation at the 10 MeV proton beam at HZDR, to simulate real-time blood flow irradiation. This might also apply to dose rates used for FLASH therapy, because of the short irradiation times which could mean that a considerably smaller blood volume receives a potentially better tolerated dose compared to doses given at conventional radiotherapeutic sessions. This project aims to test the possible correlation between irradiated blood volumes, different dose distributions within the blood volume, and side effects of radiotherapy, possibly due to that depending on the amount of blood volume that receives a certain dose at a specific dose rate, the corresponding amount of blood components like white cells, receive doses, probably critical to their survival, thus making the side effects more severe.

Speaker: Nikolaos Mallousis (University of the Bundeswehr Munich)

17 Investigation of the Radiation Induced Bystander Effect in pMBRT

LhARA (Laser-hybrid Accelerator for Radiobiological Applications) is conceived as a novel, uniquely flexible facility dedicated to the study of the biological response to ionising radiation. The design for LhARA offers versatility, allowing for the production of spatially fractionated radiation therapy (SFRT) at the in-vitro and in-vivo end stations.

Background

SFRT aims to minimise radiation exposure to healthy tissues by separating the incident beam into fractions. The delivery of SFRT and the measurement of the dose distribution present a variety of challenges that must be explored to optimise the design of LhARA end stations. For example, a current body of research predicts that cells that have not been directly exposed to radiation still show biological changes in a process labelled the radiation-induced bystander effect. In reference to SFRT, this suggests that damage could accumulate in the valleys (unirradiated regions) over time.

Methods

An in-vitro experiment was carried out at the Birmingham MC40 beamline to investigate any indirect biological response FaDu tumour cells. Cells were irradiated, stained and imaged at different times post proton SFRT, detecting the 𝛄h2AX foci damage repair changes over time in the peaks and valleys to see if the damage migrates to the space between the directly irradiated regions.

Results

The preliminary in-vitro investigation saw evidence of damage increase in the valleys over time, most prominently at 10Gy for this cell line, though more experiments are required to establish significant results. The study is to be concluded ahead of the conference, finishing a full set of repeats in February 2024.

Conclusions

The observed increase in valley damage suggests a potential observation of the 'bystander effect,' emphasising the necessity for additional experiments to refine our understanding and formulate a comprehensive theory, warranting the study's timely conclusion before the upcoming conference.

Speaker: Ms Josie McGarrigle (Imperial College London)

18 Microbeam Radiation Therapy controls in vivo tumors more effectively than conventional radiation treatment

Introduction
Microbeam Radiotherapy (MRT) and Minibeam Radiotheraoy (MBRT) have proven to not only increase normal tissue tolerance but also the ability to combat tumors more effectively. The latter aspect is the focus of our research, where we are interested in the tumor control probability of MRT and MBRT compared to conventional uniform doses.

Methods
A549 cells were injected subcutaneously into the right flank of immunocompromised CD-1 Foxn1nu mice. Once the tumors had reached a volume of >= 60mm³ they were irradiated with either MRT or uniform doses. All irradiations were performed using a self-developed setup within the small animal irradiator XenX platform. For microbeams the radiation dose was determined using the concept of the equivalent uniform dose (EUD) based on the linear quadratic model (LQM. The dosimetry for both radiation modalities was carried out using Gafchromic EBT3 films and a daily quality assurance protocol was established utilizing the PTW microdiamond detector.

Results
Fitting the preliminary data using logistic regression shows a significant shift in the TCD50 value, where 50% of the tumors are controlled. For MRT the TCD50 value was found to be (19.6±1) Gy, whereas the value for conventional treatment was (28.8±4.6) Gy. Furthermore, the slope of tumor control probability increase is steeper for MRT than for uniform dose.

Conclusion and outlook
This study was the first demonstrating the effective tumor control probability of MRT in a xenograft mouse model performed at a small animal irradiator. The TCD50 value for MRT was found to be substantially lower compared to conventional radiation therapy from our preliminary results, indicating an increase in the therapeutic window for lung cancer treatment.
Further, experiments including groups irradiated with different Minibeam doses are already being carried out and will provide the tumor control probability of MBRT.

Speaker: Mabroor Ahmed (IRM)

19 Modification of a Medical Isotope Production Cyclotron Beamline for in-vitro proton therapy studies

Background and Objectives: The 18 MeV medical cyclotron at Bern University Hospital (Inselspital) is designed for routine radiopharmaceutical production. It is equipped with a Beam Transfer Line (BTL), accessible in a separate bunker, for research in medical applications of particle physics. In an effort to make pre-clinical proton therapy studies more accessible to research groups, the BTL has been adapted to generate a proton beam suitable for in-vitro irradiations at both conventional and FLASH dose rates. In upcoming tests, we aim to modify the delivered beam to be suitable for spatially fractionated proton therapy (SFPT) studies.

Methods: The beam is passively scattered and shaped to deliver a uniform dose to a target in air. The delivered dose rate is measured in real time, using an in-beam ionization chamber (IC) paired with fiber-coupled scintillators to ensure reliable dosimetry over a large range of dose rates. For SFPT, the use of several collimator configurations is being investigated to optimize the spatial distribution of the delivered beam.

Results: The beam is extracted into air at 15.2 MeV, with a dose uniformity of 6% within a 1.5 cm diameter, extending to 15% uniformity within a 5 cm diameter. The real-time IC current has been calibrated to delivered dose rate from 0.027 Gy/s to 160 Gy/s, and will also be used in the SFPT configuration to measure the average dose rate over the entire beam field.

Conclusion: Successful adaptation of the BTL enables the production of a flat proton beam with variable dose rates, accommodating both conventional and FLASH applications. Initial cell irradiation experiments at conventional rates in collaboration with the University of Bern Institute of Anatomy have been conducted, with plans for further experiments at FLASH rates and SFPT.

Speaker: Eva Kasanda (Universität Bern)

20 Nanoparticle-assisted electron minibeam radiotherapy

Preclinical and clinical studies have shown that radiation delivery at ultra-high dose rate (UHDR, > 40 Gy/s) and sufficiently high total dose elicits the FLASH effect that maintains anti-tumor efficacy and spares normal tissue as compared with conventional dose rate (0.05 Gy/s), used in RT clinical practice. The 22 MeV electron PITZ beam delivers radiation at both UHDR up to unique 10^14 Gy/s and conventional dose rate. FLASHlab@PITZ – a multidisciplinary R&D platform in collaboration with Technical University of Applied Sciences Wildau opens new territory of UHDR radiation with high bunch charges and bunch lengths in the picosecond time range, single bunch doses and dose rates up to extremely high levels and flexible choice of bunch timing structure and beam manipulation.
The concept of electron radiation combination with fullerene/cisplatin/gold nanoparticle-assisted near infrared (NIR)-luminescence imaging is being proposed. A generic multifunctional stimuli-responsive nanomedicine proposes chief attraction in high selectivity, imaging and switchable toxicity under exposure to electron radiation. The PITZ electron beam is very well controlled, its flexible single bunch charge and beam energy allows electron spot sizes from a few centimeters down to about ~100 µm. A kicker system distributes single bunches to different transverse locations, thus can “paint” the tumor within 1 ms. The dose per bunch can be freely adjusted in the range from 0.02 to 1000 Gy in 1 mm^3 volume that gives an opportunity to run a diagnostic imaging of tumor tissue location to guide its irradiation. For that first low-charged diagnostic bunch train can be used to scan the tumor for NIR-luminescence signal, based on which second high-charge therapeutic bunch train can be used to irradiate positive areas within 0.1-1 s. Combined imaging-guided UHDR dose delivery and tissue radiosensitization has a potential to improve cancer treatment efficiency.

Speaker: Dr Anna Grebinyk (PITZ DESY)

21 PARTREC Facility

After 25 years of successful research in the nuclear and radiation physics and biology domain, the KVI-CART research center in Groningen has been re-focussed and re-established as the open access UMCG PARticle Therapy Research Center (PARTREC). Using the superconducting cyclotron AGOR and being embedded within the University Medical Center Groningen, it operates in synergy with the clinical Groningen Proton Therapy Center, providing an integrated bench to bed and back approach. PARTREC uniquely combines radiation physics, medical physics, radiation biology and radiotherapy research with an R&D program to improve hadron therapy technology and advanced radiation therapy for cancer. A number of further upgrades, scheduled for completion in 2023, will establish a wide range of irradiation modalities, such as pencil beam scanning, shoot-through with high energy protons and SOBP for protons, helium and carbon ions. Delivery of spatial fractionation (GRID) and dose rates over 300 Gy/s (FLASH) are envisioned, while FLASH beams (over 60 Gy/s) have been already realized. In addition, PARTREC delivers a variety of proton, light and heavy ion beams delivered in three separatee beamlines, as well as infrastructure for radiation hardness experiments conducted by academic and industrial communities, and nuclear science research in collaboration with the Faculty of Science and Engineering of the University of Groningen.

Speaker: Alexander Gerbershagen (PARTREC, UMCG, University of Groningen (NL))

22 Proton minibeam radiation therapy and immune response

roton minibeam radiation therapy (pMBRT) is a novel therapeutic approach offering great promise for the treatment of radioresistant tumors based on the spatial fractionation of the dose. pMBRT applies a high dose modulation consisting of high doses (peaks) deposited in the paths of millimetric planar beams and low doses (valleys) in the rest of the tissue. This distinct dose delivery leads to different radiobiology effects than conventional protontherapy, associated to bystander cell communication, vascular remodeling and immune response. As a result, pMBRT has demonstrated in several preclinical experiments to lead to a superior tumor control compared to conventional protontherapy while remarkably sparing normal tissues.
The pivotal role of the immune system in the anti-tumor response of minibeam radiation therapy was recently shown[1], centered on T and B cells from the adaptive immunity system that confers long-term anti-tumor immunity to the cancerous cells. The advances in single cell analysis and next-generation sequencing have allowed us a better understanding to pMBRT immune mechanisms. pMBRT is able to produce a significant acute inflammatory response in glioblastoma via specific signaling pathways. Taking advantage of flow cytometry phenotyping, transcriptomic and proteomic analysis of irradiated rat brain healthy tissue and glioblastoma, we will discuss the latest evidence in proton minibeam radiobiology and its relationship with immune response in order to shed light on the anti-tumor response mechanisms underlying this innovative technique.
[1] Bertho A. & Iturri L. et al., IJROBP 2022

Speaker: Lorea Iturri (Institut Curie)

Technologies of Particle Minibeam production and application

Convener: Günther Dollinger (Universität der Bundeswehr München)

23 Invited talk: TBA

Speaker: Aikaterini Rousseti (Universität der Bundeswehr München)

24 Past Research and Future Possibilities of Research on Spatially Fractionated Beams at UMCG PARTREC

The radiation biology research at the UMCG PARTREC accelerator facility was pivotal in providing pre-clinical evidence for introduction of proton therapy as a cancer treatment modality in the Netherlands. UMCG PARTREC (formerly known as KVI-CART) operates the unique superconducting cyclotron AGOR that provides customizable ion beams of all stable elements, that are employed for a wide range of mainly medically oriented experiments. These experiments included the topics related to spatial fractionation, examining the influence of adjacent low-dose fields on tolerance to high doses of protons in rat cervical spinal cords. A major upgrade of a beamline for high precision radiation biology irradiations is under construction, to become available to the scientific community by the end of 2024. This infrastructure will permit customized sub-millimetric highly conformal pre-clinical proton, ion and photon beam irradiations with individualized irradiation planning. Such ultra-high dose delivery precision can be utilized to deliver scanned or scattered minibeams to cell lines, spheroids, organoids, tissue slices, mice, rats and other pre-clinical models. These minibeams can be precisely controlled and modified in order to examine the exact parameters influencing the irradiation outcomes. In addition, an extensive experimental and simulational FLASH program for proton and helium ion beams is ongoing, focusing a.o. on the comparison and minimization of the beam penumbra due to multiple scattering. The newly implemented Twin Beam capability of precisely replicating the parameters of the clinical beams can be used in conjunction with the short lived isotope PET reconstruction and proton radiography for dose delivery verification.

Speaker: Alexander Gerbershagen (PARTREC, UMCG, University of Groningen (NL))

25 The INFN MIRO (MInibeam RadiOtherapy) project for a systematic investigation of the minibeam effect

The main parameters for minibeams that seem to affect the magnitude of the sparing effect are the peak/valley dose ratio, the FWHM and the distance between peaks. The quantitative dependencies of the minibeam effect on these parameters are not yet fully understood. Therefore, a systematic investigation of the variations of the biological effects in vitro and in vivo (small animals) as a function of the minibeam parameters would be of crucial importance for achieving a deeper understanding of the effect in the perspective of a future clinical translation.
The MIRO (MInibeam RadiOtherapy) project, recently funded by the INFN 5th Committee, aims to address various inquiries to assess the potential clinical implications of the minibeam effect. To accomplish this goal, the project brings together a team of over fifty researchers from diverse disciplines (beam delivery, dosimetry, radiobiology, computing) and will make use of two electron facilities (7-9 MeV at the CPFR in Pisa and 18 MeV at the Physics Department in Turin) and a proton one (at the Trento Proton Therapy Centre). The goals of the MIRO project are the following: i) to study the quantitative dependencies of the minibeam effect on the beam parameters (by creating flexible minibeams), ii) to understand the underlying radiobiological mechanisms with quantitative in-vitro/in-vivo experiments (using advanced fluorescence microscopy techniques) and theoretical modeling methods, iii) to develop a clinical protocol for minibeams (by developing a new dosimetric and developing new suitable dosimeters), iv) to study clinical perspectives for minibeam radiotherapy (by developing a radiobiological planning), v) to investigate possible synergistic effects with the FLASH effect, thanks to the possibility of combining the two approaches at a dedicated facility.
Beyond a project overview, the first dosimetric tests demonstrating the feasibility of combining both the minibeam and FLASH effects will be shown.

Speaker: Francesco Romano (INFN Catania Division)

26 A compact x-ray source for microbeam and minibeam radiation therapy in the making

Purpose:
Microbeam and minibeam radiotherapy are the most extreme forms of spatially fractionated photon radiotherapy. Both techniques may improve cancer treatment substantially because they preclinically demonstrated high dose tolerances of normal tissue at similar tumor control rates as conventional radiotherapy. However, until now, suitable clinical treatment facilities are lacking, which produce high-dose rate orthovoltage x-rays shapeable into planar, micrometer-wide beamlets. The line-focus x-ray tube (LFxT) is the only suitable compact treatment machine for clinical translation.

Methods:
We developed and built a preclinical prototype of the LFxT, designed to a power of 90 kW at a 300 kVp spectrum. By exploiting the heat capacity limit, the prototype can deliver dose rates >10 Gy/s from a 50 µm-wide focal spot without destroying the rapidly (>200 Hz) rotating x-ray target. We designed multi-slit collimators and a robotic arm on a linear stage to characterize the x-ray field.

Results:
We installed the LFxT prototype that we currently put into operation. We have reached an ultra-high vacuum (<10-8 mbar), performed high-voltage conditioning, target rotation and balancing, and cathode heating. The multi-slit collimators split the x-ray field into microbeams or minibeams with high-dose peaks (40 µm or 200 µm wide) separated by low-dose valleys (peak-to-peak distance 320 µm or 800 µm). The collimator slits account for the divergent beam and the viewing angle onto the focal spot of 45°. Monte Carlo simulations resulted in a peak-to-valley dose ratio for microbeam radiotherapy of >25 throughout 50 mm water.

Conclusion:
We will combine all subsystems to create the first x-ray beam, characterize the microbeam and minibeam fields, and start with biological proof-of-principal experiments. The robotic arm will serve as a sample holder for in-vitro and in-vivo experiments. This lays the foundation for a more powerful clinical LFxT at dose rates >100 Gy/s with a 600 kVp spectrum.

Speaker: Dr Johanna Winter (Department of Radiation Oncology, School of Medicine and Health and Klinikum rechts der Isar, Technical University of Munich (TUM), Munich, Germany)

27 Ask the expert

Speaker: Judith Reindl

18:30 Dinner

Friday 22 March

08:00 Coffee and Drinks

Welcome

Convener: Judith Reindl

Medical Applications of Particle Minibeam Therapy

Convener: Stephanie E. Combs (IRM)

28 Invited talk: TBA

Speaker: Dr Emanuelle Jouglar

ErUM Data Featured Session: Digitization and machine learning in Particle Minibeam Therapy

Convener: Judith Reindl

10:00 Coffee, Brezn and Poster

Dosimetry of Particle Minibeam production and application

Convener: Dr Peracchi Stefania (Australia's Nuclear Science and Technology Organisation)

29 Invited talk: TBA

Speaker: Dr Tran Thuy Linh

30 Application of a primary-standard level calorimeter for absolute dosimetry in monoenergetic proton radiation therapy (pMBRT) beams

Using TRS-398, primary standard level dose measurements for calibrating ionisation chambers are currently realised in a 60Co beam. The upcoming UK IPEM Code of Practice for Proton Radiotherapy will provide a new protocol for the direct calibration of ionization chambers in a proton beam using the NPL Primary Standard Portable Calorimeter (PSPC) reducing the uncertainty on reference absorbed dose measurements by approximately 50%. In this study, an exploratory investigation was conducted to determine if is possible to apply the PSPC to proton minibeam radiotherapy (pMBRT) for primary standard level dosimetry.

Measurements were conducted at Institut Curie, utilising the PSPC, which was irradiated with a 100 MeV monoenergetic proton beam. The calorimeter core (16 mm diameter) was positioned at the isocentre, at 2 cm water equivalent depth. Monte Carlo derived correction factors were determined using TOPAS v3.6 to convert the measured dose to graphite core, to dose to water; using phase space data scored before the collimator (Figure1 ).

The PSPC was able to measure radiation- induced temperature rise (Figure2) in both quasi-adiabatic and isothermal modes. However, the pMBRT dose profile introduces large uncertainties associated with the position of the PSPC (Figure3). Additionally, experimental variations in alignment of the collimator introduce further uncertainty with lowered repeatability.

Primary standard level dosimetry in pMBRT is possible with sufficient signal-to-noise ratio observed in raw data, however with significantly larger uncertainties than clinical proton beams. Additional research is ongoing to analyse and simulate collected Spread-Out Bragg peak pMBRT data, and the viability of other calorimeters for pMBRT dosimetry.

Speaker: Samuel Flynn (National Physical Laboratory)

31 Realization and dosimetric characterization of a mini-beam/flash electron beam at the Centro Pisano Flash Radiotherapy (CPFR)

This work presents the realization and complete characterization of a low energy electron mini-beam flash beam. This beam can vary the Flash parameters (Dose per pulse, average dose rate, intra-pulse dose rate) and the mini-beam parameters (Peak-to-Valley Dose Ratio (PVDR), FWHM and center-to-center (ctc) distance) independently from one and another. We utilize the Triode-Gun equipped ElectronFlash linac by SIT at the Centro Pisano FLASH Radiotherapy (CPFR), thanks to special funding from Fondazione Pisa, operating at 7 and 9 MeV with an average dose rate of up to 5,000 Gy/s. The linac's flexibility enables the independent variation of main parameters without altering the experimental setup.

To create Ultra-High Dose Rate (UHDR) mini-beams, Monte Carlo simulations are employed to design collimator templates, utilizing tungsten for its high atomic number to prevent electron bleed-through. Various hole structures and ctc in the templates are explored to study different mini-beam effects. Spatial distribution comparisons are conducted using radiochromic gafchromic films and three independent Monte Carlo simulation codes (EGSnrc, Geant4, and FLUKA). Despite inherent limitations in dose reading accuracy, the radiochromic films demonstrate agreement with Monte Carlo simulations.

The results highlight minor discrepancies in valley dose among Monte Carlo codes and generally falling within the uncertainty range of gafchromic films. Manipulating ctc influences valley dose, PVDR (above 30 in some configurations), and mini-beam zone size, providing versatility for different experimental setups. The proposed mini-beam generation method, combined with flash capabilities, establishes a robust platform for quantitative experiments, allowing the independent variation of spatial and temporal parameters. The mini-beam and mini-beam-flash operating beams emerge as valuable tools for radiobiological experiments, offering insights into quantitative dependencies and underlying mechanisms. This research contributes to advancing a comprehensive understanding of these novel techniques and their potential application in radiotherapy, providing a foundation for future clinical protocols and treatment planning systems.

Speaker: Dr Jake Harold Pensavalle (Centro Pisano Multidisciplinare Sulla Ricerca e Implementazione Clinica Della Flash Radiotherapy (CPFR), Pisa, Italy)

32 Impact of positioning uncertainty of detectors on the dosimetry of Particle Minibeam Therapy.

An experimental campaign was conducted at Institut Curie, France, to perform dosimetry with the Primary Standard Proton Calorimeter (PSPC) developed by the National Physical Laboratory (NPL), UK, in proton minibeams. The minibeams were produced using a collimator with 400µm wide slits of 5cm length and 4mm separation. Dosimetry was also performed with EBT3 radiochromic film and PTW Roos chambers.

The dose distribution was determined from EBT3 radiochromic film, and the integrated dose calculated over the sensitive area of each detector in the centre of this distribution. The dose in the same sized region was then calculated after applying a lateral offset, representing experimental positioning uncertainty of the detector. This calculation was also performed for PTW Advanced Markus and PTW Bragg Peak chambers for additional comparison.

The dose was found to increase by approximately 8% when applying a 2mm offset to the position of the calorimeter and PTW Roos chambers compared to that when aligned centrally. In comparison, the dose decreased by approximately 8% in the case of the PTW Advanced Markus chamber, and decreased by <1% for the PTW Bragg Peak chamber.

The significant difference in the dose when applying a small lateral offset highlights the difficulties in performing reference dosimetry for minibeams. The results also demonstrate there is an interplay effect between the size of the sensitive region of the detector and the specific configuration of the minibeams. A much larger sensitive region demonstrated a much-reduced effect, highlighting that encapsulating more of the beam when performing dosimetry would reduce the uncertainty on the measurement. A device such as a Dose-Area-Product calorimeter currently under development at NPL could help address this for the purpose of primary standard dosimetry of spatially fractionated radiotherapy.

Fig[1]: https://drive.google.com/file/d/1lZ9GUHlmy2FdkUQ5XYIR-Rzw8xsTUQDN/view?usp=drive_link "Dose over the detectors' sensitive area with lateral offset, relative to that with zero offset."

Speaker: Dr John Cotterill (Medical Radiation Science Group, National Physical Laboratory, Teddington TW11 0LW, United Kingdom)

12:00 Lunch

Pre-Clinical studies on Particle Minibeam Therapy

Convener: Yolanda prezado

33 Invited talk: TBA

Speaker: Mrs Angela Corvino

34 Correlation between dosimetry quantities and cell survival for microbeam radiation therapy

Spatially fractionated radiation therapy (SFRT) has shown promise in increasing the therapeutic window compared to conventional irradiation techniques. However, which dose parameter best correlates highly modulated dose distributions with cellular and clinical endpoints remains unresolved. The aim of this work was to determine the predictive value of several physical and biological dose quantities with regard to cell survival. A human fibroblast cell line (MRC5) and two tumor cell lines (LN18 and A549) were irradiated with 225kV x-rays over a range of doses with uniform and microbeam radiation therapy (MRT). The MRT field had a slit width of 50µm and a center-to-center spacing of 400µm. Cell survival for uniform and MRT irradiation were analyzed in terms of average dose, peak dose, valley dose and the equivalent uniform dose (EUD). Dose uncertainties were evaluated through measurements and error modeling. Cell survival plotted as a function of EUD matched uniform irradiation within the estimated uncertainties and was the most predictive quantity followed by the valley dose. Average and peak doses showed poor correlation with invitro cell survival. Enhanced cell killing was observed for both tumor cell lines (1.1 for LN18 and 1.3 for A549 at 8 Gy EUD) for MRT compared to uniform irradiation. Normal human fibroblasts showed reduced cell killing for MRT relative to uniform irradiation (0.6 for MRC5). Modeling revealed that EUD uncertainties are strongly dominated by valley dose uncertainties, especially at high doses, highlighting the importance of accurate dosimetry. EUD is preferred over physical dose quantities for comparisons of SFRT and uniform irradiation. The results suggest an increase in survival of normal-human fibroblast cells and reduced survival for both tumor cell lines after SFRT relative to uniform irradiation. Further work is required to independently confirm these findings for different beam types and MRT geometries.

Speaker: Prof. Juergen Meyer (University of Washington)

35 Round table: Are we ready for Clinical Trials

Speaker: Judith Reindl

15:10 Conclusion and Fare well with Coffee and Cake