Room: Exhibit Hall
Purpose: This work deals with dosimetric corroboration brain intensity modulated radiotherapy (IMRT) plans using the 6 and 15 MV photon beams. Gafchromic EBT film was used in the quality assurance (QA).
Methods: Sixteen brain patients were planned using the 5-field IMRT technique with 6 and 15 MV photon beams produced by a dual-energy DHX linac. Treatment plans were created using the Eclipse treatment planning system with dose distributions calculated by the anisotropic analytical algorithm. For patient-specific QA, dose comparison between the planned and measured dose using the Gafchromic EBT3 film was carried out based on the gamma analysis. Dose comparison parameters such as gamma dose distribution, distance-to-agreement (DTA) and dose difference (DD) were determined. Three different gamma criteria of DD/DTA (i.e. 3%/2 mm, 3%/3mm and 5%/3mm) were used for superlative comparison. Irradiated EBT films were evaluated using the film QA Pro software, which used the signals from all three color channels (Red, Green, and Blue). These criteria were evaluated while suppressing the dose of 5% from dose distribution. Criterion validity accepted as section with gamma value less than or equal to 1 (Î³ â‰¤ 1) to be 90%.
Results: Comparing dose distributions obtained from the treatment planning system and EBT3 film, the DTA criteria of 3%/2mm shows less dose deviation with pixels passing rate up to 93% for the 6 MV photon beam. For the 15 MV photon beam, however, the relaxed DTA criteria of 5%/3mm are consistent regarding the dose deviation acceptability criteria of 95% pixels passing rate. If the range of criteria was increased, the compatibility increased and reached 100%.
Conclusion: Our results suggested that the 6 MV photon beam and gamma criteria of 3%/2mm may be relatively suitable for IMRT QA of brain treatment plan.