Purpose: This work employs the Monte Carlo method to recompute the IMRT dose distributions from three TPS to provide a platform for independent comparison and evaluation of the plan quality in terms of target conformity and delivery efficiency. Method and Materials: Three prostate cases were planned with Corvus, Xio and Eclipse TPS using appropriate optimization parameters and dose constraints. The plans were recalculated by Monte Carlo using leaf sequences and MUs for individual plans. Dose‐volume histograms and isodose distributions were compared. Other quantities such as Dmin (the minimum dose received by 99% of CTV/PTV), Dmax (the maximum dose received by 1% of CTV/PTV), the volume of rectum and bladder receiving 65 and 40Gy (V65, V40), and the volume of femur receiving 50Gy (V50) were evaluated. Results: Special care must be taken to reproduce the dose distributions from different TPS due to their implementation of effective leaf positions. This may introduce up to a few percent differences in the absolute dose between treatment plans. The Monte Carlo results agreed with the dose distributions from all the TPS to within 5%/5mm. Both XiO and Eclipse plans show less target dose heterogeneity (smaller Dmax) and lower V65 and V40 for the rectum and bladder than the Corvus plans. The PTV Dmin is about 2Gy lower for XiO plans than Corvus and Eclipse plans while the XiO and Eclipse plans have slightly higher V50 for the femur than the Corvus plans. The Eclipse and XiO plans require significantly less MUs to deliver than the Corvus plans. Conclusion: We have tested an independent Monte Carlo dose calculation system for dose reconstruction and plan evaluation. This system provides a platform for the fair comparison and evaluation of treatment plans to facilitate clinical decision making in selecting TPS and beam delivery systems for particular treatment sites.
Purpose: Image‐guided radiation therapy (IGRT) is one of the major treatment of esophageal cancer. Gray value registration and bone registration are two kinds of image registration, the purpose of this work is to compare which one is more suitable for esophageal cancer patients. Methods: Twenty three esophageal patients were treated by Elekta Synergy, CBCT images were acquired and automatically registered to planning kilovoltage CT scans according to gray value or bone registration. The setup errors were measured in the X, Y and Z axis, respectively. Two kinds of setup errors were analysed by matching T test statistical method. Results: Four hundred and five groups of CBCT images were available and the systematic and random setup errors (cm) in X, Y, Z directions were 0.35, 0.63, 0.29 and 0.31, 0.53, 0.21 with gray value registration, while 0.37, 0.64, 0.26 and 0.32, 0.55, 0.20 with bone registration, respectively. Compared with bone registration and gray value registration, the setup errors in X and Z axis have significant differences. In Y axis, both measurement comparison results of T value is 0.256 (P value > 0.05); In X axis, the T value is 5.287(P value < 0.05); In Z axis, the T value is −5.138 (P value < 0.05). Conclusion: Gray value registration is recommended in image‐guided radiotherapy for esophageal cancer and the other thoracic tumors. Manual registration could be applied when it is necessary. Bone registration is more suitable for the head tumor and pelvic tumor department where composed of redundant interconnected and immobile bone tissue.
Purpose: To appreciate the difference of electron dose distributions calculated from the Monte Carlo and Electron 3D algorithms of radiotherapy in a heterogeneous phantom. Methods: A phantom consisted of two different materials (lungs mimicked by low‐density cork and others by polystyrene) with an 11×16 cm field size (SSD = 100 cm) was utilized to estimate the two‐dimensional dose distributions under 6 and 18 MeV beams. On behalf of two different types of tissue, the heterogeneous phantom was comprised of 3 identical slabs in the longitudinal direction with a thickness of 1 cm for each slab and 2 with a thickness of 2.5 cm. The Monte Carlo/MCTP application package constituted of five codes was performed to simulate the electron beams of a Varian Clinac 23IX. A 20×20 cm2 type III (open walled) applicator was used in these simulations. It has been shown elsewhere that the agreement of the phase space data between the calculation results of MCTP application package and the measured data were within 2% on depth‐dose and transverse profiles, as well as output factor calculations. The electron 3D algorithm owned by Pinnacle 8.0m and the MCTP application package were applied for the two‐dimensional dose distributions calculation. The curves at 50% and 100%‐prescribed dose were observed for 6 and 18 MeV beams, respectively. Results: The MC calculations results were compared with the electron 3D calculations in terms of two‐dimensional dose distributions for 6 and 18 MeV beams showed excellent agreement except in distal boundary where it was the very junction of the high and low‐density region. Conclusions: The Monte Carlo/MCTP method could be used to better reflect the dose variation caused by heterogeneous tissues. Conclusion: A case study showed that the Monte Carlo/MCTP method could be used to better reflect the dose variation caused by heterogeneous tissues.
Purpose: To measure the setup errors by using cone beam computed tomography (CBCT) and to analyze the effect of the setup errors on the physics dose of targets and peripheral organs at risk (OARs) for cervical Cancer undergoing the intensity modu1ated radiation therapy (IMRT). Methods: Ten cervical Cancer cases were chosen at random. CBCT was performed before radiotherapy.The acquired CBCT were co‐ registered with the planning CT for online set‐up correction and errors of isocenter positions on x、y、z axes were obtained .Those were simulated in actual therapy on the treatment planning system (TPS),and recalculated their dose distribution.A series of relative targets and OAR dose parameters were analyzed,and obtained the impact of the setup errors on the physics dose. Results: (1)A total of 126 CBCT scans were performed on 10 patients.The detection rates of deviation of ≤0.3cm were 92.86% in left‐ to‐right (X) direction,83.33% in superior‐to‐inferior (Y) direction, and 91.26% in anterior‐to ‐posterior (Z)direction;The setup errors on X,Y and Z axes direction were(0.24±0.21)cm 2289;(0.28±0.32)cm 2289;(0.10士0.23)c m. (2) Dose and volumes index of CTV were no significant difference between simulated plans and actual plans. (3) V45、V50 of bladder and V30、V40、V45、V50 of rectum in simulated plans were significantly larger than those in actual plans,especially V45、V50 of rectum(P<0.005). Conclusions: The CBCT plays key ro1e in the guarantee of accurate delivery of IMRT for cervical Cancer,especially peripheral OARs.
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