Exhibit Hall | Forum 4
Purpose: To investigate differences in linear energy transfer (LET) in intensity-modulated proton therapy (IMPT) brain treatment plans produced by two proton beamlines.
Methods: IMPT plans were created for 20 brain cases for two proton platforms, P1 and P2. P1 is based on a synchrocyclotron and modulates energy via range-shifter plates, while P2 is cyclotron-based and incorporates slit-based energy selection with an option for mounting a range-shifter to the snout. Identical beam geometries and optimization objectives were used for both models, and P2 plans were created 1) without and 2) with range-shifter (P2RS). Dose and LET were calculated via Monte Carlo simulation with 2% statistical uncertainty. Mean dose-weighted LET (LETd) and LETd2% were calculated in each target volume, and in a set of 5 mm rinds extending from target border to 15 mm away and overlapping brain (R1, R2, R3). Tests of significant differences in distributions between P1 and P2/P2RS were performed via two-sided Wilcoxon rank-sum tests.
Results: Significant differences for mean LETd were observed only between P1 and P2 within R2 (p = 0.004), whereas for LETd2% significant differences were identified between P1 and P2 within R1 (p = 0.012), R2 (p = 0.0003), and R3 (p = 0.0003). No significant differences were observed between P1 and P2RS. Median (inter-quartile range) LETd2% values in keV/μm in each rind were R1) 5.27 (1.00) and 5.34 (0.96), R2) 6.63 (1.57) and 7.19 (1.45) and R3) 7.48 (1.74) and 8.31 (1.57) for P1 and P2, respectively.
Conclusion: Significant differences in LETd2% were identified between P1 and P2 in rinds adjacent to targets. Mean LETd values were similar within CTV and rinds for both beamlines, with significant differences observed only between P1 and P2 in R2. Future work will investigate how optimization strategies can be adjusted to produce similar LET distributions between platforms.
Funding Support, Disclosures, and Conflict of Interest: Dr. Stephanie Perkins served as a paid member of the medical advisory committee for MEVION Medical Systems. Dr. Shahed Badiyan received a speakers honoraria from MEVION in 2021.