In vivo film detector for dose verification for IMRT/VMAT techniques

To present the in vivo film detector (IVFD) designed for dose measurement for all teleradiotherapy techniques.

The IVFD was made of Polylactic Acid using a 3D printing technology. The cylinder-shaped detector was constructed in two parts: a film overlay and a thin base. In the overlay in a centrally located air space two pieces of EBT-XD Gafchromic films are placed. Irradiated films were scanned using an EPSON V750PRO flatbed scanner and analyzed using FilmQA Pro (Ashland) software with triple-channel correction method. Validation of the method was performed by comparison of measurements performed with Marcus chamber and with IVFD. Single 6 MV photon static beams and IMRT/VMAT plan were used. To read the reference dose from treatment planning system (TPS) a software was developed. The influence of the presence of the IVFD on the dose distribution was checked. Doses calculated with and without detector were compared.

The uncertainty of measurements performed with IVFD was 1.56 % and for dose read from TPS was 0.56 %. The average discrepancy between measurements and calculations for single beam and for IMRT/VMAT were estimated. The highest value was obtained for single, static beam: 1.6 %. The influence of the detector on the dose distribution was negligible. The maximum difference of mean PTV doses calculated with and without detector was smaller than 2.2 cGy for a 180 cGy fraction.

The film detector allows measurements the dose with high accuracy for dynamic techniques. The presence of the detector has a negligible effect on the dose distribution.