Background: In head and neck radiotherapy, immobilization devices can affect dose delivery. In this study, a comprehensive end-to-end test was developed to evaluate the accuracy of radiotherapy treatment. Materials and Methods: An Alderson Radiation Therapy (ART) anthropomorphic phantom with EBT3 film was used to mimic the actual patient treatment process. Ten patients treated for nasopharyngeal carcinomas with IMRT were retrospectively selected. For each patient, the treatment plan, as well as the targets and OARs was transplanted onto the phantom, and the IMRT plan was subsequently recalculated to the phantom with EBT3 film. Two quality assurance (QA) plans were generated, namely “Plan-with” wherein the immobilization device was contoured and “Plan-without” wherein it was omitted. EBT3 measurements were compared with the results of the TPS calculation. Results: With different gamma calculation criteria applied, the results obtained for Plan-with were closer to the dose measured with the EBT3 film. Moreover, 1.8% deviation was observed in the posterior neck skin dose for Plan-with when compared to the film measurements while the value was 33.1% lower for Plan-without. When compared to Plan-without, each target volume in Plan-with exhibited a 1–4% reduction in the maximum dose (D_2%), minimum dose (D_98%) and mean dose (D_mean). Conclusion: Immobilization devices decrease the radiation dose to target volumes while increasing the skin dose and should be included within the body contour to ensure an accurate planning dose. The end-to-end IMRT test using an ART anthropomorphic phantom is a valuable tool to identify discrepancies between calculated and delivered radiation doses.

Background: The purpose of this study was to investigate the dosimetric characteristics of a new type of two-dimensional diode detector array used for quality assurance of stereotactic radiosurgery (SRS). Materials and Methods: The devices used in this study were the SRS MapCHECK detector and the StereoPHAN. The detector has 1013 diode detectors over an area of 77 x 77 mm². The reproducibility, dose linearity, dose rate dependencies, output factors (OPFs) and angular dependencies were investigated as dosimetric characteristics. The OPFs were measured and compared between AP and PA direction ranging from 0.5 x 0.5 to 7 x 7 cm². The angular dependencies were measured using 19 gantry angles. Results: The dose reproducibility and linearities showed sufficient performance of 6 MV and 10 MV. At 40 MU/min, there was a 1.3% difference from the ionization chamber measurements. For the flattening filter-free beam, there was no dose rate dependency from the 400 MU/minute to 2400 MU/minute, and the variation was within 0.5%. For small irradiation fields of 1 cm or less, the measured value of the SMC differed in AP and PA directions by up to 4.5%. The maximum gantry angle dependency of the detector was 5.3%. A maximum difference of -3.1% occurred between the measurements and TPS calculations. Conclusion: Results indicate that the new 2D diode detector is stable and useful for QA and end-to-end testing of SRS due to its excellent dose characteristics, high resolution and ease of handling when combined with the StereoPHAN.