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Absolute Film Dosimetry for Stereotactic Radiosurgery and Stereotactic Body Radiotherapy Quality Assurance Using Gafchromic EBT3 Films

S Lu

S Lu*, N Wen , J Kim , Y Qin , Y Huang , B Zhao , I Chetty , Henry Ford Health System, Detroit, MI


PO-BPC-Exhibit Hall-9 (Saturday, March 5, 2016)  Room: Exhibit Hall

To evaluate the absolute dosimetric uncertainties of EBT3 films coupled with a flat-bed document scanner for IMRT and VMAT based SRS/SBRT Quality Assurance

In this study, 93 SRS/SBRT patient specific quality assurances were performed with Gafchromic EBT3 films and an Epson Expression 10000XL flat-bed scanner. An integrated film dosimetry protocol was established with in-house software to streamline a nine dose pattern delivery for dose calibration, calibration curve fitting, dose mapping from multiple color channels, and profile/gamma analysis. The acrylic phantom consisting of two 5 cm slabs (30cm x 30cm) was used for patient QA. The phantom was setup to measure the dose plane in the coronal direction for all the cases except spinal tumors, where the dose plane was measured axially to capture dose drop off from the vertebral body to the cord. Point dose was measured in the high dose region within the target using a PTW pin point ion chamber. 3%/1mm gamma passing rate was used for film analysis. A one-way ANOVA was used to evaluate if any of the variables (volume size, treatment site, treatment delivery technique) had a statistically significant effect on the gamma index.

The percentage of points passing the 3%/1mm gamma criteria, averaged over all tests was 94.5 ± 5.7, with a corresponding 95% CLs between 93.4 and 95.8. No variables (volume size, treatment site, treatment delivery technique) were found to have a statistically significant impact on the gamma index based on the one-way ANOVA test.

Our film dosimetry protocol can offer a highly efficient solution for absolute dose commissioning and routine SRS/SBRT PSQA.

Funding Support, Disclosures, and Conflict of Interest: The work was supported by a research scholar grant, RSG-15-137-01-CCE from the American Cancer Society.

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