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Session: CBCT-guided Adaptive Radiotherapy [Return to Session]

A Protocol for Implementing CBCT Guided Daily Online Adaptive Radiotherapy Safely and Efficiently to Maximize Patient Benefit

X Ray*, K Kisling, G Kim, K Moore, University of California, San Diego, La Jolla, CA


TU-D1000-IePD-F2-1 (Tuesday, 7/12/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 2

Purpose: To describe our clinically-implemented protocol for CBCT-guided daily online adaptive radiotherapy (ART) using the Varian Ethos™ and the dosimetric improvements from our institution’s first five patients.

Methods: At our clinic, a physicist creates two plans for each adaptive patient: one with standard CTV-to-PTV margins used as a backup reference plan and one with reduced margins whose planning goals are used to re-optimize daily adaptive plans. Both plans are approved by the physician before treatment. The adaptive process consists of six steps: CBCT acquisition, OAR review, target review, plan calculation/selection, plan QA, and repeat CBCT. Therapists acquire CBCT images. The physicist adjusts auto-segmented targets and OARs and performs plan selection and QA. The physician reviews/approves physicist-edited targets every fraction and at the first fraction also approves the adapted plan before treatment. Plan QA includes reviewing verification structures, target coverage, hot spots, OAR metrics, monitor units, and secondary dose calculation. Intrafraction motion is accounted for using in-bore surface monitoring and confirmation CBCTs. Timing data and dose metrics for the first five adaptive patients were collected. Plans included prostate SBRT, three gynecological cancers, and bilateral ovarian ablation.

Results: Using this novel clinical workflow, we safely adapted 62 fractions for five patients. The average time required for the adaptive process (end of CBCT acquisition to plan approval) was 25±9 minutes, and was faster for smaller targets (e.g. prostate 14±1.6 minutes). Margins were reduced for all cases (by 1mm for prostate SBRT, by 15mm for ovarian ablation, and by 2-5mm for gynecological targets). Margin reduction combined with daily adaptive planning reduced OAR dose metrics while increasing daily target coverage.

Conclusion: We successfully implemented a structured workflow to maximize safety of daily adaptation while maintaining high efficiency to minimize on-couch time for patient. Our protocols are useful for clinics looking to implement this technology.

Funding Support, Disclosures, and Conflict of Interest: X. Ray acknowledges honoraria, speaker fees, and a research agreement from Varian Medical Systems. K. Kisling acknowledges honoraria and speaker fees from Varian Medical Systems. K. Moore acknowledges consulting fees and honoraria from Varian Medical Systems.


Treatment Planning, Quality Assurance, Image-guided Therapy


TH- External Beam- Photons: adaptive therapy

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