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To Tweak Or Not to Tweak? Prospects for Daily Online Adaptation Using Unedited CBCT Auto-Segmentation

M Moazzezi, K Moore, K Kisling, C Bojechko, X Ray*, University of California San Diego, La Jolla, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Online adaptive radiation therapy (ART) capabilities are becoming more widely available, but the time-consuming nature of clinician-driven target contour editing at the treatment machine limits the numbers of patients who could benefit from this technology. The purpose of this study was to evaluate the impact of daily online ART without manual contour edits on prostate target coverage using a commercially available platform with built-in auto-segmentation and auto-planning on CBCT.

Methods: Planning CTs for 8 retrospective prostate patients treated on our clinic’s Halcyon were re-planned using a Varian EthosTM emulator, 12-field IMRT, with 2Gy fractions. CTV included intact prostate and proximal seminal vesicles. Our clinical asymmetric PTV margins were used: 3mm posterior, 5mm left/right/anterior, and 7mm superior/inferior. The first 10 fractions for each patient were adapted using their daily iterative CBCTs and the emulator’s auto-segmentation and auto-planning workflow without any manual contouring edits (CTVauto). The dose distribution and auto-segmentation was exported to our treatment planning system where the CTVauto contour was reviewed/corrected by human experts to create a CTVtrue. CTV coverage was evaluated for the non-adapted and adapted plans on CTVtrue. This analysis was repeated for a full course of radiotherapy for a single patient to examine intra-patient variability.

Results: A majority (97/100) of daily CTVauto contours required some editing to obtain CTVtrue; edits focused on the seminal vesicles with the prostate generally accurately auto-segmented. Without adaptation, CTVtrue Dmin was greater than 95% for only 45% of fractions; fully-automated adaptation nearly doubled this to 82%. When 27 fractions for a single patient were treated, the CTVtrue Dmin increased for 74% of fractions with fully-automated adaptation.

Conclusion: Online daily adaptation using Ethos can double the fractions of prostate treatments where CTV Dmin>=95% suggesting the Ethos daily adaptive workflow is superior to existing non-adapted workflows even without expert contour review/correction.

Funding Support, Disclosures, and Conflict of Interest: Dr. Ray has a lab services agreement with Varian Medical Systems. Dr. Moore reports income for personal consulting and speaker's honoraria from Varian Medical Systems. This work was supported by an internal grant from the Center for Precision Radiation Medicine.


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