Speaker
Description
Particle therapy has many advantages over conventional photon therapy, particularly for treating deep-seated solid tumours due to its greater conformal energy deposition achieved in the form of the Bragg peak (BP). The benefits of spatially fractionated radiation fields leading to increased healthy tissue dose tolerance have been demonstrated with high intensity photon microbeam studies. The aim of particle mini-beam therapy is to incorporate the highly conformal dose delivery of ion beams with healthy tissue sparing in the entrance channel due to spatially fractionated radiation fields. This may allow the therapeutic index in ion beam therapy to be increased and thereby reduce damage to healthy tissue proximal to the target volume and the risks of secondary cancer. Successful treatment with conventional protons and heavy ions as well as mini beam particle therapy depends largely on knowledge of the relative biological effectiveness (RBE) of the radiation produced by primary and secondary charged particles. A SOI microdosimeter with 3D micron sized sensitive volumes (SVs) mimicking dimensions of cells, known as the “Mushroom” microdosimeter developed by the Centre for Medical Radiation Physics (CMRP), University of Wollongong was used to evaluate the RBE of various ions [3] and were successfully utilised for validation of treatment planning system (TPS) in multiple ion therapy at Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan [4].
An experimental and simulation response of the SOI microdosimeter at varying positions throughout the 12C ion minibeam radiation therapy (MBRT) field produced with a clinical broad beam and a brass multi-slit collimator (MSC) was studied and the corresponding dose-mean lineal energies and RBE for 10% cell survival (RBE10) were calculated using the modified Microdosimetric Kinetic Model (MKM) [5]. An increase in the average RBE10 of ∼30% and 10% was observed in the plateau region compared to broad beam for experimental and simulation values, respectively. The experimental collimator misalignment was determined to be 0.7° by comparison between measured and simulated microdosimetric spectra at varying collimator angles. The simulated dose-mean lineal energies in the valley region between minibeams were found to be higher on average than in the minibeams due to higher LET particles being produced in these regions from the MSC.
A pixelated silicon detector prototype known as the dose magnifying glass (DMG) developed at the CMRP was used to measure depth dose profile of proton scanning beam. The linear array of small sensitive volumes allowed for accurate point and high spatial resolution one-dimensional profile measurements of small radiation fields in real time to be completed with minimal impact from partial volume averaging.
References:
[1] Rosenfeld A., Nucl. Instrum. Methods., Phys. Res. A 809, 156–170, February 2016
[2] Linh T. Tran et. al, IEEE Transactions on Nuclear Science, Volume: 65, Issue: 1, 467-472, Jan. 2018.
[3] Linh T. Tran, et. al., Medical Physics, 2018, DOI10.1002/mp.12874.
[4] Lee et al., Phys. Med. Biol. 66 045017 2021.
