ABSTRACT
Background: the purpose of this study was to evaluate the feasibility of a multipurpose 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 Map CHECK, as well as absolute dosimetry using an ionization chamber. The QA phantom was constructed to perform relative dosimetry using EBT3 film and Map CHECK, 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 True Beam 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 Map CHECK 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 multipurpose 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
ABSTRACT
Background: The dose-related effects of patient setup errors on bio-physical indices were evaluated for the conventional wedge [CW] and field-in-field [FIF] whole breast irradiation techniques [WBI]
Materials and Methods: The treatment plans of 10 patients receiving left WBI were retrospectively selected for evaluation. The bio-physical effects of dose variations were evaluated by shifting the isocenters and gantry-angles of the treatment plans. Dose-volume histograms of the planning target volume [PTV], heart, and lungs were generated, and the conformity index [Cl], homogeneity index [HI], tumor control probability [TCP], and normal tissue complication probability [NTCP] were determined
Results: The D95 of the PTV for an [isocenter shift plan] with a posterior direction decreased by approximately 15%, and the TCP of the PTV decreased by approximately 50% for the FIF technique and by 40% for the CW; however, the NTCPs of the lungs and heart increased for both techniques. Increasing the gantry-angle decreased the TCPs of the PTV by 24.4% [CW] and by 34% [FIF]. The NTCPs of the lungs and heart for the two techniques differed by only 3%. The CIs and His for the CW case were higher than the corresponding values obtained for the FIF case. Significant differences were observed between the two techniques [p<0.01]
Conclusion: Our results revealed that the biophysical properties of the FIF case were more sensitive to setup errors than those in the CW case. The radiobiological-based analysis could be detected significant dosimetric errors and provided a practical patient quality assurance method for guiding the bio-physical effects?