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Accuracy of XiO Treatment Planning System in Predicting Lateral Penumbra for Different Air Gap and Compensator Thickness in Uniform Scanning Proton Therapy

S Rana

S Rana*, O Zeidan, E Ramirez, M Rains, J Gao, Y Zheng, ProCure Proton Therapy Center, Oklahoma City, OK.

SU-E-T-667 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The purpose of this study is to investigate the accuracy of XiO treatment planning system (TPS) in predicting lateral penumbra (80%-20% distance) for different air gap (AG) and compensator thickness (COMP) in uniform scanning proton therapy.

Methods:First, the dependency of lateral penumbra on AG was investigated for AG 0, 5, 10, 15, 20, 25, 30, and 35 cm using beam parameters of range (R)=16cm, modulation (M)=10cm, COMP=5cm, snout (SNT)=10, and aperture diameter(AP)=10 cm. Second, the dependency of lateral penumbra on COMP was investigated for COMP 0, 5, 10, 15, and 20 cm using beam parameters of R=30cm, M=10cm, AG=5cm, SNT=10, and AP=10cm. Dose calculations were performed in a virtual water phantom using XiO TPS with pencil beam algorithm, whereas measurements were done using solid-water plates and EDR-2 films. Furthermore, depth for all dose calculations and measurements was selected at the center of Spread Out Bragg Peak (SOBP), which coincided with the isocenter of the beam. The OmniPro-I'mRT software was used to analyze the films. The lateral penumbra from the dose computations and measurements were compared for the horizontal and vertical scanning magnets.

Results:Both the TPS and measurements showed an almost linear increase in lateral penumbra with increasing AG. The lateral penumbra results of TPS were larger than measurements, with difference ranged from 0.5 to 1.6 mm for horizontal scanning magnet and from 0.5 to 2.6 mm for vertical scanning magnet. The dependency of lateral penumbra on COMP was less sensitive compared to lateral penumbra versus AG. The discrepancy between lateral penumbra results of TPS and measurements for different COMP ranged from 0.2 to 0.8 mm for horizontal scanning magnet and from 0.9 to 1.7 mm for vertical scanning magnet.

Conclusion:The XiO TPS over-predicted the lateral penumbra compared with the measurements.

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