Multichannel film dosimetry vs 2D-array seven29 for vmat lung sbrt

Abstract

Introduction Volumetric Modulated Arc Therapy (VMAT) can achieve high conformation and gradient levels required to deliver Stereotactic Body Radiation Therapy (SBRT). Quality Assurance (QA) usually includes a 2D gamma analysis. Here we compare two different QA procedures for VMAT lung SBRT treatments. Materials and methods Fourteen patients were selected. Dose per fraction ranged between 7.5 and 18 Gy. OCTAVIUS phantom (PTW) was used in both QA arrangements: 1. PTW 2D-ARRAY seven29 consists of a matrix of 729 cubic vented ionization chambers spaced 1 cm. To duplicate the resolution from 1 to 0,5 cm the “Merge” algorithm included in Verisoft software was used. 2. EBT3 radiochromic film with multichannel dosimetry was used. Also we applied the “efficient protocol” (Lewis, Mike and Yu, 2012) that provides specific calibration curves for each individual irradiation. Scanning was made with an Epson 10000XL, resolution was 72 dpi. Dose maps were created with Matlab. Gamma analysis criteria of 3%/3 mm and 2%/2 mm relative to maximum (MD) and local (LD) doses were performed. Results 3%/3 mm criteria: MD analysis produced averaged pass rates of 100% in both test. LD analysis gave 99.1% for EBT3 and 97.2% for 2D-array. A. 2%/2 mm criteria: MD analysis for EBT3 gave 98.9% and 90.8% for 2D-array. Also LD analysis gives 93.5% and 86.8% respectively. EBT3 provides more resolution and gives higher pass rates compared with 2D array. 3%/3 mm seems not to be an appropriate criterion. 2%/2 mm was more sensitive and gives pass rates above 96% and 91% for maximum and local dose respectively. Conclusion 2%/2 mm local dose gamma analysis of EBT3 using multichannel dosimetry gives excellent results for VMAT lung SBRT. Disclosure None.