Out with the old, in with the new.

The PARCER trial showed that IMRT reduced late GI toxicity among women receiving adjuvant radiation for cervical cancer. The key to transitioning from conventional fields to IMRT, though, is accurate target volume delineation. PARCER volumes were based on the original RTOG consensus guidelines for post-op volumes. Recently, the NRG/RTOG guidelines have been updated. In this study, gross recurrences from PARCER were contoured and fused with original treatment planning CTs. There were 45 (15%) distant recurrences, 24 (8%) pelvic recurrences, and 9 para-aortic recurrences. For 19 of the patients with pelvic recurrences, target volumes were generated using the updated NRG/RTOG guidelines and compared to coverage from the original PARCER volumes and 2008 RTOG volumes. What was the most notable difference between the old and new volumes? Where the old volumes extended posteriorly to the mesorectal fascia, the updated volumes extend more posterior to cover the anterior third of the mesorectum and anterior wall of the rectum. Of the 19 pelvic recurrences, 9 were covered by the original volumes while 12 were covered by the updated volumes. The 3 additional recurrences were all along the mesorectum–suggesting this simple update could potentially result in an absolute 1% additional reduction in local recurrence. | Mittal, Int J Radiat Oncol Biol Phys 2022