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Enhanced Sparing of Organs at Risk with the Single-Energy-Modulated Proton Arc Therapy (SEM-PAT); A Proof of Concept in Central Lung and Pelvis

A Modiri1*, S Mossahebi1, P Mohindra1, R Miller1, A Sawant1, S Chen1, B Yi1, (1) University of Maryland School of Medicine, Baltimore

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
To explore feasibility of a novel intensity-modulated proton arc technique that uses a single energy with a tertiary energy modulator (TEM) and to demonstrate the dosimetric improvement in target coverage and sparing of organs at risk (OARs).

Methods:
For two patient cases, a pelvis (GYN) and a central lung, we simulated SEM-PAT in Eclipse-V15.6. An arc with 10-degree gantry-spacing delivered the dose to orthogonal (isocenter) planes in the direction of the rotating beam. The energy requested from cyclotron in SEM-PAT stays the same for the entire arc with the incident energy of the beam being varied by a modulator located at the nozzle.

Results:
For the pelvis case, in arc plan versus clinical plan, mean doses to left/right femoral head, bladder and small bowel were reduced by 62%/69%, 9% and 33%, respectively. An increase of 6% in rectum mean dose was noted without an increase in the clinically relevant high doses. For the lung case, mean doses to spinal cord, trachea, lung and great vessels were reduced by 80%, 25%, 14% and 10%, respectively, while doses to carina and esophagus stayed equivalent. In both sites, target dose conformity was achieved and OAR volumes receiving =75% of prescribed dose were either reduced or stayed comparable. The ranges of energy modulations were 42-59 MeV and 64-89 MeV for the pelvis and the lung cases, respectively. These energy variations are less than 10 cm of water equivalent depth (WET) for the incident energies used in this planning study, 166–186 MeV.

Conclusion:
Significant OARs sparing in proton therapy was achieved using the novel proton arc technology, SEM-PAT, for the plans used in this study. Range of the energy modulations during the SEM-PAT was less than 10 cm WET, which is practically easy to deliver, demonstrating the SEM-PAT’s potential translatability into clinical routine.

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