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Three-Dimensional Isocenter Verification for Real-Time Tumor-Tracking Radiotherapy System Using a Reusable PVA-I Radiochromic Gel Dosimeter

K Ono1*, T Sera2, T Shiinoki3, S Hayashi4, K Fujino1, Y Akagi1, Y Hirokawa1, (1) Hiroshima Heiwa Clinic, Hiroshima, Japan, (2) Yamaguchi University Hospital, Yamaguchi, Japan, (3) Yamaguchi University, Yamaguchi, Japan, (4) Hiroshima International University, Hiroshima, Japan


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

Room: AAPM ePoster Library

Purpose: To evaluate usefulness of three-dimensional (3D) isocenter verification for a real-time tumor-tracking radiotherapy (RTRT) system, SyncTraX, combined with a TrueBeam linear accelerator using a novel polyvinyl alcohol-iodide (PVA-I) radiochromic gel dosimeter that can be reused after annealing.

Methods: The prepared PVA-I gels were poured into acrylic containers (2 × 2 × 12 cm³), and a fiducial marker (ø2 mm) was embedded in the gels. A PVA-I gel dosimeter as a position detector set to the QUASAR?? Respiratory Motion Platform with a customized rotation stage was moved in a 3D sinusoidal pattern (left?right [LR]: 0.3 cm peak-to-peak, superior?inferior [SI], and anterior?posterior [AP]: 2 cm peak-to-peak) with varying motion periods (3?5 s). The dosimeters were irradiated with four MLC fields (1 × 1 cm²) using the TrueBeam?SyncTraX system when the marker position was within a ±2 mm gating box. In addition, the 3D isocenter verification under the same conditions (period: 4 s) was repeated 20 times by repeated annealing using a dosimeter. Following irradiation, the dosimeters were scanned from the front and lateral sides with a flatbed scanner to analyze the 3D displacements between the marker and the radiation isocenter.

Results: The 3D isocenter displacements obtained from the dosimeters were almost within a ±2 mm gating box with the average values of 1.35 (0.51?2.09), 1.04 (0.35?1.70), and 0.85 (0.34?1.44) mm for the motion periods of 3, 4, and 5 s, respectively. Regarding the repeated 3D isocenter verification, an excellent repeatability (1SD < 0.3 mm) was observed with the results of -0.42 ± 0.23 mm, -1.15 ± 0.22 mm, and 1.36 ± 0.24 mm in the LR, SI, and AP directions, respectively.

Conclusion: The reusable PVA-I gel dosimeter can detect 3D tracking accuracy of the TrueBeam?SyncTraX system easily and reliably; additionally, it is useful for the routine quality assurance of the system.


Gel Dosimeter, 3D, Gating


TH- Radiation Dose Measurement Devices: 3D solid gel/plastic

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