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Density Scaling of Phantom Materials for a 3D Dose Verification System

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K Tani

K Tani1*, Y Fujita2 , A Wakita3 , R Miyasaka4 , R Uehara5 , D Kawai6 , Y Suzuki3 , A Aikawa3 , N Mizuno7 , H Saitoh1 , (1) Graduate School of Tokyo Metropolitan University, Arakawa, Tokyo, (2) Tokai University School of Medicine, Kanagawa, NA, (3) National Cancer Center Hospital, Tsukiji, Tokyo, (4) Chiba Cancer Center, Chiba, Chiba, (5) National Cancer Center East Hospital, Kashiwa, Chiba, (6) Kanagawa Cancer Center, Yokohama, Kanagawa, (7) St. Luke's International Hospital, Chuo, Tokyo


SU-I-GPD-T-281 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The density of phantom material need to be determined in RTPS for dose verification. The results differ depending on the density. However, the optimum density has not been clarified for a 3D dose verification system. In order to improve the evaluation accuracy of the IMRT dose verification, the density scaling factor of the phantom was determined.

Methods: Tissue-phantom ratios (TPRs) of 6 MV X-ray (Clinac iX, Varian) in PMMA and Plastic Water DT (PWDT) slabs used in the 3D dose verification system (Delta4, ScandiDos) were measured at the field sizes of 10 × 10 cm2 as the reference. RTPS dose calculations were performed with the same geometry. The virtual phantoms consisted of elemental compositions of water and different physical densities. When the slope of TPR in the RTPS most closely matched the slope of the measured TPR, the density assigned in the simulation was decided as the density scaling factor (DSF_RTPS). The dose calculation algorithms were AdaptiveConvolve (Pinnacle), CCC (RayStation), and AcurosXB (Eclipse). The appropriateness of the DSF_RTPS was verified in two plans within three different densities; the nominal physical density, the nominal relative electron density, and DSF_RTPS. The 10 × 10 cm2 with static gantry and TG-119 Mock Head and Neck IMRT plans were used.

Results: DSF_RTPS of AdaptiveConvolve, CCC, and AcurosXB was 1.133, 1.149, and 1.122, respectively, for PMMA and 0.978, 0.979, and 0.967, respectively, for PWDT. DSF_RTPS was showed strongly agreement more than physical and relative electron density in almost all of the verifications.

Conclusion: DSF_RTPS could be the optimum density to assign to the Delta4 phantom materials in RTPS.

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