2368 - Motion Management in Pediatric Radiotherapy: Assessment of Intrafraction Motion Using an Audio/Visual Distraction Method

Purpose/Objective(s): Immobilization for pediatric cancer patients often requires the use of general anesthesia (GA) to ensure safe setup and minimize the risk of intrafraction motion; however, daily anesthesia can incur significant medical risk and healthcare cost. We hypothesized that the use of the Audio-Visual Assisted Therapeutic Ambience in Radiotherapy (AVATAR) audio/visual distraction technique would produce acceptable intrafraction motion management compared to the use of general anesthesia thereby reducing anesthesia-related risks.

Materials/Methods: A retrospective analysis was conducted on 30 patients with local stage III Wilms tumor (20 AVATAR, 10 GA) treated at a single institution between 2019 and 2025 with anterior posterior (AP) and/or posterior anterior (PA) treatment fields. Intrafraction motion was quantified by measuring the displacement of the treatment isocenter relative to stable vertebral landmarks using paired daily kilovoltage setup (AP or PA image) and megavoltage field verification images (AP or PA) obtained on the first day of treatment. Measurements were independently verified by two reviewers. Differences in horizontal (lateral) and vertical (superior-inferior) shifts between the two cohorts were analyzed using independent t-tests. The time between setup imaging and field verification imaging on the first day; and setup imaging and completion of treatment delivery for the third and fifth fraction was captured from the record and verify system.

Results: No statistically significant difference in intrafraction motion was observed between the two modalities. Mean horizontal displacement was 1.1 +/- 1.7 mm for AVATAR vs. 0.6 +/- 0.7 mm for GA (p=0.20). Mean vertical displacement was 0.9 +/- 1.2 mm for AVATAR vs. 0.6 +/- 0.04 mm for GA (p=0.23). Inter-observer variability was minimal (average 0.8 mm). The average time between setup imaging and field verification imaging on the first day (intrafraction motion measured in this study) was greater than the average time from setup imaging to completion of treatment delivery at the 3rd and 5th fraction (Table).

Conclusion: The AVATAR system demonstrated effective intrafraction immobilization for patients with stage III Wilms tumor with average vertical and horizontal displacement well below acceptable PTV margins. In addition, we demonstrate that the intrafraction measurement points in this study effectively estimate the actual treatment delivery time for these patients. These findings support AVATAR as a safe, non-invasive standard of care for select pediatric Wilms tumor patients, offering a viable alternative that mitigates the physiological and logistical burdens of daily anesthesia.