TY - JOUR
T1 - Microdosimetric characterization of a clinical proton therapy beam:
T2 - comparison between simulated lineal energy distributions in spherical water targets and experimental measurements with a silicon detector
AU - Parisi, Alessio
AU - Olko, Pawel
AU - Swakoń, Jan
AU - Horwacik, Tomasz
AU - Jablonowski, Nicolai D.
AU - Malinowski, Leszek
AU - Nowak, Tomasz
AU - Struelens, Lara
AU - Vanhavere, Filip
N1 - Score=10
PY - 2022/1/17
Y1 - 2022/1/17
N2 - Objective. Treatment planning based on computer simulations was proposed to account for the increased relative biological effectiveness (RBE) of proton radiotherapy beams near to the edges of the irradiated volume. Since silicon detectors could be used to validate the results of these simulations, it is important to explore the limitations of this comparison. Approach. Microdosimetric measurements with a MicroPlus Bridge V2 silicon detector (thickness = 10 µm) were performed along the Bragg peak of a clinical proton beam. The lineal energy distributions, the dose-mean values, and the RBE calculated with a biological weighting function were compared with PHITS simulations (microdosimetric target = 1 µm water sphere), and published clonogenic survival in vitro RBE data for the V79 cell line. The effect of the silicon-to-water conversion was also investigated by comparing three different methodologies (conversion based on a single value, novel bin-to-bin conversions based on SRIM and PSTAR). Main results. Mainly due to differences in the microdosimetric targets, the experimental dose-mean lineal energy and RBE values at the distal edge were respectively up to 53% and 28% lower than the simulated ones. Furthermore, the methodology chosen for the silicon-to-water
conversion was proven to affect the dose-mean lineal energy and the RBE10 up to 32% and 11% respectively. The best methodology to compensate for this underestimation was the bin-to-bin silicon-to-water conversion based on PSTAR. Significance. This work represents the first comparison between PHITS-simulated lineal energy distributions in water targets and corresponding experimental spectra measured with silicon detectors. Furthermore, the effect of the silicon-to-water conversion on the RBE was explored for the first time. The proposed methodology based on the PSTAR bin-to-bin conversion appears to provide superior results with respect to commonly used single scaling factors and is recommended for future studies.
AB - Objective. Treatment planning based on computer simulations was proposed to account for the increased relative biological effectiveness (RBE) of proton radiotherapy beams near to the edges of the irradiated volume. Since silicon detectors could be used to validate the results of these simulations, it is important to explore the limitations of this comparison. Approach. Microdosimetric measurements with a MicroPlus Bridge V2 silicon detector (thickness = 10 µm) were performed along the Bragg peak of a clinical proton beam. The lineal energy distributions, the dose-mean values, and the RBE calculated with a biological weighting function were compared with PHITS simulations (microdosimetric target = 1 µm water sphere), and published clonogenic survival in vitro RBE data for the V79 cell line. The effect of the silicon-to-water conversion was also investigated by comparing three different methodologies (conversion based on a single value, novel bin-to-bin conversions based on SRIM and PSTAR). Main results. Mainly due to differences in the microdosimetric targets, the experimental dose-mean lineal energy and RBE values at the distal edge were respectively up to 53% and 28% lower than the simulated ones. Furthermore, the methodology chosen for the silicon-to-water
conversion was proven to affect the dose-mean lineal energy and the RBE10 up to 32% and 11% respectively. The best methodology to compensate for this underestimation was the bin-to-bin silicon-to-water conversion based on PSTAR. Significance. This work represents the first comparison between PHITS-simulated lineal energy distributions in water targets and corresponding experimental spectra measured with silicon detectors. Furthermore, the effect of the silicon-to-water conversion on the RBE was explored for the first time. The proposed methodology based on the PSTAR bin-to-bin conversion appears to provide superior results with respect to commonly used single scaling factors and is recommended for future studies.
KW - Microdosimetry
KW - MicroPlus
KW - Proton Therapy
KW - RBE
KW - PHITS
UR - https://ecm.sckcen.be/OTCS/llisapi.dll/open/47772327
U2 - 10.1088/1361-6560/ac4563
DO - 10.1088/1361-6560/ac4563
M3 - Article
SN - 0031-9155
VL - 67
SP - 1
EP - 18
JO - Physics in Medicine and Biology
JF - Physics in Medicine and Biology
M1 - 015006
ER -