Feasibility study of multi-purpose quality assurance phantom for pretreatment verification of volumetric modulated arc therapy

Background: The purpose of this study was to evaluate the feasibility of a multi-purpose quality assurance (QA) phantom for pretreatment verification of volumetric modulated arc therapy (VMAT). Materials and Methods: The QA phantom was constructed with polymethyl methacrylate (PMMA) to perform relative dosimetry using EBT3 film and MapCHECK, as well as absolute dosimetry using an ionization chamber. The QA phantom was constructed to perform relative dosimetry using EBT3 film and MapCHECK, as well as the absolute dosimetry using ionization chamber. In order to verify the pretreatment plans, 25 patients treated with VMAT were selected. The pretreatment plans were calculated in the Eclipse treatment planning system using the Acuros XB dose calculation algorithm and CT images for the QA phantom, with the same beam setup and monitor units (MUs) as those for patient treatment. All plans were delivered to the Varian TrueBeam accelerator equipped with a high-definition multi-leaf collimator. Results: The multi-purpose QA phantom is developed for convenient VMAT dose verification. By using the QA phantom, all 25 cases passed +/- 3% acceptability criteria in absolute dosimetry with an ionization chamber for pretreatment verification. The relative dosimetry using EBT3 film and MapCHECK system also showed high agreement of more than 90% for 2%/2-mm and 3%/3-mm criteria. Conclusion The results of this study demonstrated the good multi-purpose capabilities of the phantom for the absolute and relative dosimetry. Therefore, the developed multi-purpose QA phantom was applied in our institution for routine VMRT dose verification.