Exhibit Hall | Forum 4
Purpose: Intensity modulated proton therapy (IMPT) with single-energy Bragg peak (SEBP) beams (IMPT-SEBP) for FLASH has been previously proposed to eliminate the exit dose beyond the target, which can achieve superior OAR sparing compared to proton transmission delivery technique. We aim to examine the robustness of the IMPT-SEBP and compare it with clinical intensity-modulated proton therapy (IMPT-Clinical) in hypofractionated liver radiotherapy.Materials and
Methods: An in-house platform was developed to enable inverse IMPT-SEBP planning on 10 liver patient cases with prescription doses as 50 Gy in 5 fractions. We adopted a similar or identical beam arrangement to the conventional proton SBRT-Clinical plans. Minimum MUs of 400 and 800 constraints were used for IMPT-SEBP treatment plans to meet sufficient FLASH dose rate coverage. The setup errors are ±5 mm in all three directions, and the CT HU to RSP conversion uncertainty is ± 3.5%. There are a total of 12 perturbation scenarios to assess the robustness of the IMPT-SEBP plans.
Results: There is no significance between the SBRT and Bragg peak plans in liver-GTV and heart dose metrics. For the chest wall, the IMPT-SEBP-800MU plans result in 18.3% higher D2cc than proton SBRT-Clinical ones (p < 0.05). For the CTV Dmax, the SBRT plans result in 11.9% (p<0.01) less than IMPT-SEBP-400MU plans and 18.8% (p<0.01) less than IMPT-SEBP-800MU plans. The median D95(%) of SBRT-Clinical, IMPT-SEBP-400MU, IMPT-SEBP-800MU are 95.5%, 92.5% and 96.0% (no significance) for the 10 liver cases.
Conclusion: IMPT-SEBP plans can yield comparable plan quality in most OARs in liver hypofractionated treatment planning. The clinically acceptable target coverage using second worst-case scenarios indicates the IMPT-SEBP plans can maintain a robust dose coverage when range and setup uncertainties are present.
Not Applicable / None Entered.