Target delineation in high-grade glioma do CTV margins make a difference? ESTRO ACROP versus RTOG guidelines a comparative dosimetric study

Background and purpose: There exist two major consensus guidelines for target delineation in glioblastoma (GBM). Namely the established radiation therapy oncology group (RTOG) and the recently redefined European society for radiation oncology (EORTC)-advisory committee on radiation oncology practice (ACROP). Clinical studies evaluating the pattern of recurrence with relation to the CTV margins have as of date not evidenced statistically significant difference in relation to the two guidelines. However, considering the standardization of concurrent chemo-radiation with Temozolomide nearly 20% off patients can be expected to survive 2years or beyond. Quality of life issues will play a higher role in defining the better protocol. In the current study, we have dosimetrically compared these guidelines in both perspectives. Material and methods: Thirty patients of GBM who had been planned for conformal radiotherapy from Jan 2017 to Feb 2019 were considered. Each patient dataset contoured with ESTRO-ACROP guidelines to create PLAN A and RTOG guidelines to create PLAN B. Both plans were compared to evaluate the volumetric difference in terms of PTV and the relative proximity to critical normal structures. Results: The median volume of brain irradiated to high doses (60Gy) was significantly greater in PLAN B, 566cc vs 398 ccs (p 400cc and with tumor in Parietal or Temporal regions wouldn’t benefit from PLAN A. Conclusion: The use of target delineation based on a single step plan, excluding expanded edema (ESTRO-ACROP) could potentially reduce high dose target volumes and significantly spare brainstem, optic-chiasma, and hippocampus. Patients with tumor volume <400 cc and frontal lesions are most likely to benefit.