Dosimetry of a Small-Animal Irradiation Model using a 6 MV Linear Accelerator

A custom made rat-like phantom was used to measure dose distributions using a 6 MV linear accelerator. The phantom has air cavities that simulate the lungs and cylindrical inserts that simulate the backbone. The calculated dose distributions were obtained with the BrainScan v.5.31 TPS software. For the irradiation two cases were considered: (a) near the region where the phantom has two air cavities that simulate the lungs, and (b) with an entirely uniform phantom. The treatment plan consisted of two circular cone arcs that imparted a 500 cGy dose to a simulated lesion in the backbone. We measured dose distributions using EBT2 GafChromic film and an Epson Perfection V750 scanner working in transmission mode. Vertical and horizontal profiles, isodose curves from 50 to 450 cGy, dose and distance to agreement (DTA) histograms and Gamma index were obtained to compare the dose distributions using DoseLab v4.11. As a result, these calculations show very good agreement between calculated and measured dose distribution in both cases. With a 2% 2 mm criteria 100% of the points pass the Gamma test for the uniform case, while 98.9% of the points do it for the lungs case.