Exhibit Hall | Forum 3
Purpose: To optimize table angle, gantry-angle range and dynamic collimator rotation for non-coplanar dynamic-collimator trajectory radiotherapy (colli-DTRT).
Methods: The number of arcs, their table angle, and gantry-angle range are determined on Gantry-Table cost-maps quantifying target/organ-at-risk (OAR) overlap in beam’s-eye¬-view. Candidate arcs spanning more than 50° gantry-angle range are selected on the thresholded cost-map and ranked by cost (lowest to highest) and gantry-angle range (longest to shortest). Final selection is based on the candidates’ summed ranks and user-defined desired total gantry-angle range. Dynamic-collimator rotation is determined to minimize field width in the x-direction. Intensity modulation is optimized using the VMAT photon optimizer (Varian Medical Systems). Dose distributions achieved with colli-DTRT were compared to coplanar-VMAT with static collimator for seven head-and-neck (HN) cases on an anthropomorphic phantom.
Results: colli-DTRT had an average [min-max] gantry-angle range of 349.2° [295.2°-392.4°], using 2.8 [2.0-3.5] partial arcs per full VMAT arc (360°). Estimated delivery times (including time between arcs) were 1.54 [1.15-2.06] times longer for colli-DTRT.Target coverage was acceptable for the two techniques in all cases. For three locoregionally advanced oropharyngeal carcinomas and one adenoid-cystic carcinoma (all sequential boost), mean dose to salivary glands, pharynx and oral cavity was reduced by 2.2 Gy on average with colli-DTRT compared to VMAT. For a nasopharyngeal carcinoma, D0.03cc to optic nerves (ON, tolerance: 54 Gy) was 54.8 Gy (VMAT) and 53.1 Gy (colli-DTRT) for left-ON and 31.4 Gy (VMAT) and 19.0 Gy (colli-DTRT) for right-ON. For a single vocal cord irradiation case, mean dose to the contralateral vocal cord and arytenoid were reduced by 4.4 and 9.8 Gy respectively with colli-DTRT compared to VMAT. Both techniques showed similar results for a stage-II laryngeal carcinoma.
Conclusion: colli-DTRT has the potential to improve OAR sparing compared to VMAT, with efficient and accurate delivery on conventional linacs.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by Varian Medical Systems.