Patterns of Relapse After Adjuvant Chemoradiation for Cervical Cancer in a Phase 3 Clinical Trial (PARCER): An Evaluation of Updated NRG Oncology/RTOG Target Delineation Guidelines

The Radiation Therapy Oncology Group (RTOG) under NRG Oncology recently published updated contouring guidelines for intensity modulated radiation therapy in postoperative treatment for endometrial and cervical cancer. The present study was designed to evaluate the implications of newly published guidelines.We recruited 300 patients in a phase 3 randomized controlled trial of adjuvant chemoradiation therapy for cervical cancer (NCT01279135) to understand patterns of relapse. For those patients with pelvic relapse, we imported radiation therapy structure sets, treatment plans, and diagnostic images at relapse on the treatment planning system. We performed rigid registration with treatment planning images that contained the delineated planning target volume and radiation dose information. We delineated gross tumor volume at time of relapse on the diagnostic scans and superimposed it on the radiation therapy treatment scans. We categorized the site of pelvic relapse as "within field of old RTOG/[Postoperative Adjuvant Radiation in Cervical Cancer (PARCER)] target delineation guidelines" or "within field of new NRG/RTOG guidelines," or both, and compared proportions of recurrences contained within the 2 guidelines. We consider a P value of <.05 statistically significant. Additionally, we generated intensity modulated radiation therapy treatment plans based on the new guidelines for a limited set of patients to see if these new guidelines increased the organ at risk doses.Most common form of relapse was distant metastasis (15%). Pelvic relapse rate in our study was 8%. Overall, 9 out of 19 relapses were encompassed in the contouring guidelines of the old RTOG/ Postoperative Adjuvant Radiation in Cervical Cancer (PARCER) trial, and 12 out of 19 were encompassed within the new RTOG 2021 contouring guidelines. This corresponded to a further 1% reduction in local relapses (P = .007). Dose to rectum was marginally increased with the new contouring, with no difference in other organs at risk. Salvage treatment was offered in 25 out of 60 patients who relapsed. Patients who received local treatment after relapse had a mean survival after relapse of 27.2 months compared with 8 months among those who received supportive care alone.Our study supports the use of newly published NRG/RTOG contouring guidelines in patients with cervical cancer who have undergone hysterectomy. Further data are needed to ascertain if anterior extension of the clinical target volume is needed as in the Postoperative Adjuvant Radiation in Cervical Cancer trial.