Purpose: The dose‐related effects of patient setup errors on biophysical indices were evaluated for conventional wedge (CW) and field‐in‐field (FIF) whole breast irradiation techniques. Methods: The treatment plans for 10 patients receiving whole left breast irradiation were retrospectively selected. Radiobiological and physical effects caused by 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 conformity index (CI), homogeneity index (HI), tumor control probability (TCP), and normal tissue complication probability (NTCP) were determined. Results: For “isocenter shift plan” with posterior direction, the D95 of the PTV 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 by about 13% and 1%, respectively, for both techniques. Increasing the gantry angle decreased the TCPs of the PTV by 24.4% (CW) and by 34% (FIF). The NTCPs for the two techniques differed by only 3%. In case of CW, the CIs and HIs were much higher than that of the FIF in all cases. It had a significant difference between two techniques (p<0.01). According to our results, however, the FIF had more sensitive response by set up errors rather than CW in bio‐physical aspects. Conclusions: The radiobiological‐based analysis can detect significant dosimetric errors then, can provide a practical patient quality assurance method to guide the radiobiological and physical effects.
Purpose:Implant‐supported dentures seem particularly appropriate for the predicament of becoming edentulous and cancer patients are no exceptions. As the number of people having dental implants increased in different ages, critical dosimetric verification of metal artifact effects are required for the more accurate head and neck radiation therapy. The purpose of this study is to verify the theoretical analysis of the metal(streak and dark) artifact, and to evaluate dosimetric effect which cause by dental implants in CT images of patients with the patient teeth and implants inserted humanoid phantom.Methods:The phantom comprises cylinder which is shaped to simulate the anatomical structures of a human head and neck. Through applying various clinical cases, made phantom which is closely allied to human. Developed phantom can verify two classes: (i)closed mouth (ii)opened mouth. RapidArc plans of 4 cases were created in the Eclipse planning system. Total dose of 2000 cGy in 10 fractions is prescribed to the whole planning target volume (PTV) using 6MV photon beams. Acuros XB (AXB) advanced dose calculation algorithm, Analytical Anisotropic Algorithm (AAA) and progressive resolution optimizer were used in dose optimization and calculation.Results:In closed and opened mouth phantom, because dark artifacts formed extensively around the metal implants, dose variation was relatively higher than that of streak artifacts. As the PTV was delineated on the dark regions or large streak artifact regions, maximum 7.8% dose error and average 3.2% difference was observed. The averaged minimum dose to the PTV predicted by AAA was about 5.6% higher and OARs doses are also 5.2% higher compared to AXB.Conclusion:The results of this study showed that AXB dose calculation involving high‐density materials is more accurate than AAA calculation, and AXB was superior to AAA in dose predictions beyond dark artifact/air cavity portion when compared against the measurements.
Purpose: To evaluate the dosimetric effects of patients setup errors and breathing movement on whole breast irradiation with conventional hard wedge (HW) and field‐in‐field (FIF) techniques. Methods: A total of 10 patients who received whole breast irradiation were chosen for this study. We performed radiation treatment planning for whole breast irradiation with two techniques; conventional hard wedge (HW) and field‐in‐field (FIF). On the subject of each patients, ‐ original plan‐was created using the general clinical planning technique and then we generated ‐ isocenter shift plan‐and ‐ gantry angle shift plan‐to evaluate dose variation according to change of isocenter and gantry angle. In our study, the isocenter was shifted by 0.6 cm for the right‐left, 0.5 cm for superior‐inferior, and 1.4 cm for anterior‐posterior direction refer to Kinoshita et al. study. Assuming that breast shape changes subtly, the gantry angle was shifted from 1° to 5° each tangential fields. To analysis the plan quality this study calculated a dose‐volume histogram (DVH) and the dose indices that are mean dose of CTV, CTV D95, CTV V95, lung V20, heart V40 and PTV dose improvement (PDI) index. Results: When isocenter of lung and heart shifted in the right‐left and superior‐inferior direction, ‐ isocenter shift plan‐showed no significant variation from ‐ original plan‐for most of the indices. However, a significant difference was found in V95 of CTV with isocenter shift in anterior‐posterior direction by assuming the patient shifted in the posterior direction. Shifts in gantry angle slightly affected lung and heart, and smaller changes were seen in PTV. Conclusions: This study evaluated the dosimetric effects of gantry angle and isocenter shift for simulating patients setup errors and breathing motion. The effects of patient and breast changes during treatment could have influence on dose distribution of OARs as well as that of PTV.
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