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SU‐E‐J‐67: Evaluation of Adaptive MLC Morphing for Online Correction of Prostate Cancer Radiotherapy
Author(s) -
Sandhu R,
Qin A,
Yan D
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4924154
Subject(s) - image guided radiation therapy , morphing , medicine , radiation treatment planning , radiation therapy , prostate cancer , dosimetry , nuclear medicine , prostate , computer science , medical physics , computer vision , radiology , cancer
Purpose: Online adaptive MLC morphing is desirable over translational couch shifts to accommodate target position as well as anatomic changes. A reliable method of adaptive MLC segment to target during prostate cancer IMRT treatment is proposed and evaluated by comparison with daily online‐image guidance (IGRT) correction and online‐IMRT planning. Methods: The MLC adaptive algorithm involves following steps; move the MLC segments according to target translational shifts, and then morph the segment shape to maintain the spatial relationship between the planning‐target contour and MLC segment. Efficacy of this method was evaluated retrospectively using daily‐CBCT images on seven prostate patients treated with seven‐beam IMRT treatment to deliver 64Gy in 20 fractions. Daily modification was simulated with three approaches; daily‐IGRT correction based on implanted radio‐markers, adaptive MLC morphing, and online‐IMRT planning, with no‐residual variation. The selected dosimetric endpoints and nEUD (normalized equivalent uniform dose to online‐IMRT planning) of each organ of interest were determined for evaluation and comparison. Results: For target(prostate), bladder and rectal‐wall, the mean±sd of nEUD were 97.6%+3.2%, 103.9%±4.9% and 97.4%±1.1% for daily‐IGRT correction; and 100.2%+0.2%, 108.9%±5.1% and 99.8%±1.2% for adaptive MLC morphing, respectively. For daily‐IGRT correction, adaptive MLC morphing and online‐IMRT planning, target D99 was <95% of the prescription dose in 30%, 0% and 0% of 140 fractions, respectively. For the rectal‐wall, D5 exceeded 105% of the planned‐D5 in 2.8%, 11.4% and 0% of 140 fractions, respectively. For the bladder, Dmax exceeded 105% of the planned‐D5 in 2.8%, 5.6% and 0% of 140 fractions, respectively. D30 of bladder and rectal‐wall were well within the planned‐D30 for all three approaches. Conclusion: The proposed method of adaptive MLC morphing can be beneficial for the prostate patient population with large deformation and rotation. It is superior to the daily‐IGRT correction, and comparable to the online‐IMRT planning for dose to the target and rectal‐wall.