PV QA 3 - Poster Viewing Q&A 3
Purpose/Objective(s): Craniospinal irradiation (CSI) is a key component of therapy for many pediatric central nervous system (CNS) malignancies. There has been increased availability and utilization of proton therapy for CSI which offers dosimetric advantages due to reduced normal tissue exposure because of the lack of exit dose. For maximal tissue sparing, protons can target the thecal sac alone, but this results in a dose gradient across the vertebral bodies, and raises concerns about partial coverage resulting in uneven growth in growing pediatric patients with possible lordosis. For this reason, some physicians target the entire vertebral body, while others will allow a dose gradient to better spare organs at risk. This study was done in order to assess current practice patterns regarding vertebral body coverage for pediatric patients undergoing CSI.
Materials/Methods: Pediatric radiation oncologists who treat with proton therapy were identified from membership in the Particle Therapy Co-Operative Group pediatric sub-committee or by affiliation with U.S. proton centers. An IRB approved, anonymized web-based survey was distributed by email to these physicians on June 21st, 2017 with a follow-up email on October 10th, 2017. The survey included up to 11 questions regarding practice patterns relating to vertebral body coverage/sparing in the treatment of children with CSI, and utilized skip logic to focus relevant follow-up questions based on initial responses.
Results: Thirty-three physicians responded to the survey, five of whom were excluded for lack of recent pediatric proton CSI experience. Of the 28 included responses, 23 physicians sometimes treat the entire vertebral body. Five physicians report always treating the entire vertebral body and zero report never treating the entire vertebral body. Most common responses regarding anterior CTV expansion beyond the thecal sac were no expansion (n=9) and 3-4 mm (n=8). The majority of physicians report modification of the anterior margin for some structures, most commonly the esophagus (n=15), thyroid (n=6), heart (n=5), bowel (n=4) and pharynx (n=2).
Conclusion: Vertebral body coverage in proton based CSI varies amongst radiation oncologists in respect to target delineation, CTV expansions and modifications for ventral organs at risk with many factors influencing this decision. These data suggest an opportunity for developing a more standardized approach to vertebral body coverage in pediatric proton based CSI.
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