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  4. Impact of Beam Quality On Three-Dimensional Dose Distribution Evaluation Using a Normoxic N-Vinylpyrrolidone-Based Polymer Gel for HDR Brachytherapy

Impact of Beam Quality On Three-Dimensional Dose Distribution Evaluation Using a Normoxic N-Vinylpyrrolidone-Based Polymer Gel for HDR Brachytherapy

M Itano1*, Y Watanabe2 , S Mizukami2 , T Maeyama2 , T Terazaki3 , R Uehara4 , H Tachibana4 , (1) Funabashi municipal medical center, Funabashi, 12, (2) Kitasato University, Sagamihara, ,(3) Yokohama City Minato Red Cross Hospital, Yokohama, ,(4) National Cancer Center Hospital East, Kashiwa,

Presentations

(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: In a gel dosimetry for HDR brachytherapy, the dose response calibration was generally obtained using the same beam quality of Ir-192 source. However, the dose values for the calibration were used from the computed dose profile because direct measurements of dose from the Ir-192 source is difficult. The location uncertainty for region of interest of magnetic resonance image affects the dose uncertainties in dose distribution evaluation because the dose profile is steep. Impact of beam quality on three-dimensional dose distribution evaluation using a normoxic N-vinylpyrrolidone-based polymer gel (VIPET gel) was evaluated when using Ir-192 and high energy X-ray from linear accelerator.

Methods: Two beam qualities of Ir-192 and 6MV-Xray were used. First, doses from 0 to 60 Gy were irradiated to the VIPET gels. The two dose response curves were obtained. Second, a treatment plan was generated using Oncentra planning system (Elekta, Sweden) and was irradiated to the gel. Planar gamma images (Criteria: 3%/2mm) on axial planes and a coronal plane were calculated using the measured dose from the gel and calculated doses from the TPS. The two measured dose distribution were created using the two dose response curves. The two gamma images were compared in terms of gamma pass ratio.

Results: Dose response curves exhibited good agreements. Pass ratios for the two coronal gamma images were same (99.5%). For axial planes, gamma pass ratios were 87.6±15.5% and 87.5±15.1% for 6MV-Xrays and Ir-192 respectively and there was no statistically significant difference of pass ratios for axial images (P = 0.764).

Conclusion: Our results shows no dependence of beam quality in the VIPET gel. Gel dosimetry with the dose response curve generated by direct measurements of dose from linear accelerator may provide 3D dose distribution evaluation with uncertainties of the measurement of high-energy X-rays.

Keywords

Gel Dosimeter, Quality Assurance, Brachytherapy

Taxonomy

TH- Brachytherapy: Dose measurement

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