Dosimetric Analysis of Standard vs. IMRT Pelvic Radiation for Post-Operative Treatment of Endometrial and Cervical Cancer in NRG Oncology’s RTOG 1203

Abstract

NRG Oncology’s RTOG 1203 demonstrated improved acute toxicity with post-operative intensity modulated radiation therapy (IMRT) for treatment of cervical and endometrial cancer compared to 3D-conformal (3DCRT) techniques. We aimed to correlate dosimetric parameters with patient reported outcomes from RTOG 1203, in hopes to establish dose constraints for patients receiving IMRT for cervical and endometrial cancers. Two different patient reported outcome assessment tools were used in this study, the PRO-CTCAE and the EPIC questionnaires. These assessments were evaluated in the bowel (GI) and urinary (GU) domains including subdomains of bowel bother, bowel function, urinary bother, urinary function, urinary incontinence, and urinary irritation. These assessments were completed at baseline, 5 weeks, 1 year and 3 years after the start of radiotherapy. Pearson and spearman correlation coefficients were used to correlate the radiation doses and volumes with these EPIC and PRO-CTCAE scores, and receiver operator curve (ROC) analyses were used to identify optimal dosimetric cut points for toxicity prediction. The initial radiation doses considered were mean bowel dose, rectum V40, rectum V45, and bladder mean dose, as they have shown to be significant predictors of toxicity in other retrospective analyses. Out of the 279, 129 patients on the IMRT arm had radiation dose data. Of the 129 IMRT patients, 72%, 69%, and 46% completed the PRO-CTCAE assessment at 5 weeks, 1 year and 3 years respectively, while 85%, 75%, and 53% of patients completed the EPIC assessment at 5 weeks, 1 year and 3 years. The median bowel dose, rectal V40, and rectal V45 were not statistically different between patients with and without GI symptoms including abdominal pain, diarrhea, and fecal incontinence at any time point (p>0.055). Similarly, median bladder dose was not associated with worsening GU symptoms, such as urinary function, bother or irritation, at any time point (p>0.13). Preliminary analysis of patient reported outcomes demonstrated no significant association with mean dose to bowel, rectal and bladder dosimetry in the IMRT cohort of RTOG 1203. Ongoing analysis will include investigating lower dose thresholds and their association with acute and late GI and GU patient reported outcomes, and to include patients from the 3DCRT cohort.