Lili Wu MS, Presenter: Nothing to Disclose

Hong Chen BS, Abstract Co-Author: Nothing to Disclose

Jiayang Lu MS, Abstract Co-Author: Nothing to Disclose

Blake Rowedder PhD, Abstract Co-Author: Nothing to Disclose

Yu Kuang PhD, Abstract Co-Author: Nothing to Disclose

Purpose/Objective(s): The dose delivery accuracy of IMRT is primarily dependent on how well the leaf motion pattern calculated by the leaf motion calculator (LMC) algorithm matches the optimized field fluence map with MLC constraints. The Smart LMC (SLMC) in Eclipse treatment planning system is an advanced fluence delivery modeling algorithm as it takes into account fine MLC features including inter-leaf leakage, rounded leaf tips, non-uniform leaf thickness, and the spindle cavity etc. In this study, SLMC and traditional Varian leaf motion calculator (VLMC) algorithms were investigated, for the first time, in dose delivery accuracy of sliding window (SW) IMRT using three patient specific quality assurance (QA) tools.Materials/Methods: The SW IMRT plans of 51 cancer cases (including 10 nasopharynges, 10 esophaguses, 9 breasts, 12 lungs, and 10 cervixes) were included to evaluate dose delivery accuracy from leaf motion calculated by SLMC and VLMC. The leaf trajectories of each plan were derived from the same optimal fluence map by SLMC and VLMC, respectively. All plans were delivered using a Varian TrueBeam linear accelerator. Three-dimensional (3D) bi-planar diode array Delta4 and portal dosimetry from a high resolution 2D array electronic portal imaging device (EPID) were used to measure the delivered dose distribution. Independent dose calculation software IMSure was also used to verify the dose distribution. Gamma index was employed to compare the planned dose distribution calculated by both LMC algorithms and delivered dose distribution with the criteria of 3%/3mm and 2%/2mm. The MUs was also analyzed.Results: Gamma analysis shows an excellent agreement between the planned dose distribution calculated by both LMC algorithms and delivered dose distribution measured by three QA tools in all plans at 3%/3 mm, leading to a mean passing rate exceeding 97%. The IMSure calculation results show that the mean fraction of pixels with gamma < 1 was 97.0% ± 1.9% for SLMC and 98.9% ± 0.8% for VLMC. The Delta4 measurement results are in line with those of IMSure calculation. However, with the highest spatial resolution, EPID portal dosimetry demonstrates that gamma passing rate of SLMC was slightly higher than that of VLMC. The complex cases such as nasopharynx and cervical plans had the lowest gamma passing rate in the IMSure results, but showed a highest passing rate in portal dosimetry. Significant differences in the MUs were observed between these two LMCs (p  < 0.001).Conclusions: The study suggests that SLMC is modestly more accurate than VLMC in modeling advanced MLC features, which may lead to a more accurate dose delivery in SW IMRT. Current clinical tools might not be specific enough to differentiate the dosimetric discrepancies at the millimeter level calculated by these two LMC algorithms and complex cases.

Wu, L, Chen, H, Lu, J, Rowedder, B, Kuang, Y, Evaluation Of Dose Delivery Accuracy In Leaf Motion Calculator Algorithms For Sliding Window IMRT.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14043612.html