Room: ePoster Forums
Purpose: Evaluate the pass rate for irradiations of the anthropomorphic liver phantom using proton and photon beams.
Methods: The phantom has one insert that represents the liver and two targets mimicking non-coplanar liver metastases. The insert is made of polystyrene for photon beams and Standard Imaging Blue Water for proton beams. PTV1 is an ovoid 2 cm in diameter and 2.5 cm long. PTV2 is a 3 cm diameter sphere. There is one TLD and 2 planes of radiochromic film in each PTV. The phantom includes a motion table to simulate 1 cm respiratory motion in the superior-inferior direction. Institutions were instructed to design and deliver a plan that delivers 6 Gy/ 6 Gy(RBE) to â‰¥95% of each PTV.
Results: The mean TLD/TPS values were 0.99 (Â±0.03) and 0.96 (Â±0.02) for photons and protons, respectively, which were statistically different (ANOVA:p<<0.05). While the photon TLD values were statistically different by TPS algorithm (ANOVA:p<0.05), the pass rates were not different by algorithm. Proton irradiations showed no statistical difference between TPS algorithm. The mean percent of pixels passing the 7%/4mm gamma analysis were 91% (Â±9%) and 82% (Â±14%) for photons and protons, respectively, which were statistically different (Kruskal-Wallis:p<<0.05). The pass rate was 72.8% and 37.5% for photons and protons, respectively. For photon irradiations, the pass rate was statistically worse for phantom irradiations using an ITV technique compared to other motion-management techniques (Chi-square:p=0.05). Proton data was not analyzed by motion technique as most centers used the ITV technique.
Conclusion: While both modalities have low pass rates, photon centers perform better irradiating the liver phantom. The ITV technique of motion management performs worse than other motion-mitigation techniques. All centers could potentially improve their pass rate with implementation of tracking, gating, or breath-hold techniques. Proton centers should strive to improve their planning system dose calculations.
Funding Support, Disclosures, and Conflict of Interest: This work received funding from the NIH/NCI grant #CA180803.