Room: AAPM ePoster Library
Purpose: Single-energy modulated proton arc therapy (SEM-PAT) has the potential to improve dose conformality, reduce RBE and LET concerns, thereby improving the quality of proton radiotherapy. SEM-PAT uses a single-energy proton beam and modulates the energy using an energy modulator at the nozzle. If the beam characteristics of the modulated energy (ME), such as the depth-dose profile, differs from the single energy (SE) providing the same proton range, treatment planning optimization becomes a challenge and requires a new beam data commissioning. This study compares the beam characteristic of the ME and SE providing the same proton range.
Methods: Three proton beam energies, 230MeV, 200MeV, and 160MeV were used as the initial energies for ME. The range of each energy was reduced by 5.4, 6.3, 7.2, 8.0, 8.9, and 10.6cm water-equivalent-distance using high-density polyethylene blocks, and the depth-dose profile of each scenario was measured using a multi-layer ion chamber. Beam characteristics (R90, R80, dose fall-off) of ME proton beams were compared to the SE proton beam with the same proton range.
Results: The depth-dose profile of ME beams using higher energy proton beam showed better agreement with the corresponding SE beams. For all three energies, the difference between R90 and R80 of ME and SE were within 0.7mm. The difference between R20 and dose fall-off (R20-R80) of ME and SE were within 0.5, 1.0, and 2.0mm for 230, 200, and 160MeV, respectively. For all energies of ME, higher entrance doses were observed compared to the corresponding SE (max: 230MeV=4.5%, 200MeV=6.5%, 160MeV=11.5%).
Conclusion: Beam characteristics of the ME match within 2mm to the corresponding SE proton beam, which is insignificant considering SEM-PAT delivers dose only to the center of the target from each gantry angle. Beam characteristics of the SE can be used in ME for the optimization of SEM-PAT plans.