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Evaluation of Measurement-Guided 4D Dose Reconstruction with Motion as a Perturbation Using IPAGAT Polymer Gel Dosimeter

K Ono

K Ono1*, S Fujimoto1 , S Hayashi2 , K Hioki3 , M Miyazawa4 , Y Akagi1 , Y Hirokawa1 , (1) Hiroshima Heiwa Clinic, Hiroshima, JP, (2) Hiroshima International University, Hiroshima, JP, (3) Hiroshima University Hospital, Hiroshima, JP, (4) R-TECH.INC, Tokyo, JP,


SU-I-GPD-T-271 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To evaluate the dosimetric accuracy of Respiratory MotionSim™ (RMS) as measurement-guided 4D dose reconstruction with motion as a perturbation using customized polymer gel dosimeter during the delivery of volumetric-modulated arc therapy (VMAT).

Methods: Several PET vials (φ4 cm, 100 mL) filled with PAGAT polymer gel dosimeter with improved dose sensitivity (iPAGAT) were prepared. The 3D-printed lung insert with iPAGAT dosimeter for the QUASAR™ respiratory motion phantom (Modus) was moved as superior-inferior direction in a sinusoidal pattern (peak-to-peak: 2 cm, period: 2 sec/4 sec) during VMAT delivery. VMAT plan was generated for the PTV considering target motion of the GTV as a 2 cm diameter sphere. The 4D dose reconstruction was performed by the RMS with ArcCHECK and 3DVH system (Sun Nuclear) simulating these target motion, and the measured 3D dose was read out by 3.0T MRI system. These dose distributions and homogeneity index (HI = D₂-D₉₈/D₉₅ × 100) of the PTV were compared by gamma index and DVH analysis using in-house developed software.

Results: A good agreement of the dose distributions between the RMS and iPAGAT dosimeter was observed in the coronal and sagittal planes, and the mean pass rate by gamma index analysis (3%/3 mm, global normalization) were 97.2 ± 1.4%. HI value of the planned PTV dose without target motion was 5.92, in contrast HI values of the PTV dose with target motion by the RMS and iPAGAT dosimeter were 30.89 and 35.31 (2 sec), and 31.06 and 32.79 (4 sec), respectively.

Conclusion: Although the dose homogeneity of PTV with the RMS was reduced caused by interplay and gradient effect compared to the planned dose, a good agreement of the 3D dose was observed compared to the measured dose. Therefore it is suggested that the RMS with ArcCHECK and 3DVH system is useful for the clinical application.

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