Abstract
IMPT plans with various multi-angle beams were planned by the Varian Eclipse treatment planning system for one case of brain cancer. Dose distributions for each plan, along with the associated linear energy transfer distributions, were recomputed using an in-house fast Monte Carlo dose calculator with a FRBE of 1.1 or with a previously published VRBE model. We then compared dosimetric parameters obtained by the VRBE with those obtained by the FRBE. Biological doses obtained by the VRBE for the clinical target volume in all plans were 1% - 2% larger than those obtained by the FRBE. The minimum dose obtained by the VRBE for the right optic nerve in the MFO IMPT with 4 fields was 70% larger than that obtained by the FRBE, but the difference was only 18.1 cGy (RBE). The difference in maximum dose for the right optic nerve in the MFO IMPT with 5 fields was less than 10.4%, but the difference was 131.8 cGy (RBE). The mean difference in maximum dose was less than 2% for all other organs at risk. We found that biological dose with the FRBE had any dose errors in IMPT with various multi-angle beams.
Highlights
Proton beam therapy can enhance tumor control while minimizing irradiation to surrounding normal tissues in cancer care owing to the Bragg peak, with a sharp distal fall-off [1] [2]
The single-field optimization (SFO) intensity-modulated proton therapy (IMPT) plans obtained by the fixed relative biological effectiveness (FRBE) and by the variable RBE (VRBE) models differed by a mean (±standard deviation) of 1.5% ± 0.3% in maximum dose and 1.3% ± 0.0% in mean dose (Figure 2)
The minimum dose obtained by the VRBE for the right optic nerve in multi-field optimization (MFO) plan H was 70% larger than that obtained by the FRBE, the mean differences in maximum dose were less than 2% for all other organs at risk (OARs)
Summary
Proton beam therapy can enhance tumor control while minimizing irradiation to surrounding normal tissues in cancer care owing to the Bragg peak, with a sharp distal fall-off [1] [2]. In the latest proton beam therapy, beam scanning technique [5] [6] [7] has been widely used. Intensity-modulated proton therapy (IMPT), in which scanning beam lets of protons, used to “paint” radiation dose on the target, can be exploited to safely bend beams around complex critical structures, allowing improved sparing of these structures without compromising target coverage [8]. Two types of IMPT optimization exist, namely, single-field optimization (SFO) and multi-field optimization (MFO). The SFO optimizes individually each field to create a uniform dose distribution from each beam, and the MFO optimizes simultaneously spots from all the fields to get highly conformal dose distributions
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