Development of Colli-DTRT: A Non-Coplanar Intensity Modulated Arc Therapy Technique with Dynamic Collimator Rotation
J Bertholet1*, C Zhu1,2, P-H Mackeprang1, HA Loebner1, G Guyer1, W Volken1, O Elicin1, DM Aebersold1, MFM Stampanoni2, S Mueller1, MK Fix1, P Manser1, (1) Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland, (2) Institute for Biomedical Engineering, ETH Zuerich and PSI, Villigen, Switzerland
Presentations
WE-C1000-IePD-F3-1 (Wednesday, 7/13/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]
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.
Keywords
Treatment Planning, Optimization, Treatment Techniques
Taxonomy
TH- External Beam- Photons: Development (new technology and techniques)
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