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Session: Multi-Disciplinary General ePoster Viewing [Return to Session]

Optimal QACT Frequency During Proton Therapy: A Single Institution Study

N C Biswal*, E Nichols, R Mogilnay, M E Witek, B Yi, University of Maryland School of Medicine, Baltimore, MD


PO-GePV-M-81 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Patients treated with proton beam therapy (PBT) undergo routine quality assurance CT (QACT) scans during their course of treatment, which determines whether the initial plan remains accurate for the whole course of treatment or needs to be re-planned based on their QACT findings. The objective of this study was to optimize QACT frequency while maintaining treatment quality. Benefits of reducing QACT frequency include reducing imaging dose and optimizing use of patient time and staff resources.

Methods: We performed a retrospective IRB-approved single-institution review of 2471 patients, who were treated with PBT between 2017 and 2021. For each anatomic site, QACT and re-planning patterns were analyzed to identify the optimal frequency for QACTs for different anatomical sites, while maintaining the same quality of care as before.

Results: Weekly QACTs are recommended for head-and-neck (HN) patients treated twice per day. Every-other-week QACTs are required for lung and HN treatments treated once per day, whereas first-week and half-way-through-treatment QACTs are necessary for abdomen, pelvis, bladder, rectum, and anus treatments. QACTs for gynecologic, spines, and prostate with seminal vesicles (SVs) and pelvic lymph nodes (LNs) with sequential treatments require QACTs in the first week and a week before the boost plan starts. Liver, pancreas, kidney, stomach, prostate, and prostate with SVs require QACTs in the first week of treatment. Brain treatments need QACTs on the second week of treatment, and Breast patients require QACTs half-way through treatment. No QACTs are required for craniospinal irradiation and extremity tumors. Following these new guidelines, a total of 7023 QACTs could be effectively reduced by 2750 QACTs (~39% reduction) over 5 years.

Conclusion: The above newly proposed QACT patterns for all anatomic sites are optimal and maintain treatment quality. Following this analysis, we have adopted a new clinical paradigm for decreased routine QACTs.


Protons, Quality Assurance


TH- External Beam- Particle/high LET therapy: Proton therapy – adaptive therapy

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