ESTRO 2024 - Abstract Book

S1080

Clinical - Gynaecology

ESTRO 2024

Jeevanshu Jain 1 , Kamalnath J 2 , Anjana A K 2 , Ankita Gupta 1 , Nilesh Ranjan 3 , Mayuri Charnalia 1 , Prachi Mittal 3 , Supriya Chopra 1 1 Advanced Centre for Treatment, Research & Education in Cancer, Tata Memorial Centre, Homi Bhabha National Institute, Department of Radiation Oncology, Navi Mumbai, India. 2 Tata Memorial Hospital, Tata Memorial Centre, Homi Bhabha National Institute, Department of Medical Physics, Mumbai, India. 3 Tata Memorial Hospital, Tata Memorial Centre, Homi Bhabha National Institute, Department of Radiation Oncology, Mumbai, India

Purpose/Objective:

PARCER was a phase III randomized control trial (RCT) designed to compare the incidence of moderate to severe late gastrointestinal (GI) toxicity in patients receiving postoperative image-guided intensity-modulated radiotherapy (IG-IMRT) to three-dimensional conformal radiation therapy (3D-CRT) for cervical cancer. The phase III RCT prospectively deployed V 15Gy and V 40Gy bowel dose constraints in the IG-IMRT arm. Though the phase III RCT reported a 21% reduction in grade≥2 late GI toxicity in IG-IMRT arm [1] , no dosimetric predictors of late GI toxicity could be identified while using standard dose volume histogram (DVH) analysis dichotomized across population medians. [1] The present work was undertaken to investigate if there was a difference in DVH quartiles in patients with and without grade≥2 late GI toxicity. Furthermore, we also wanted to investigate if DVH- area under the curve (AUC) allows better discrimination of such events. In addition, we compared differences, if any, in DVH quartiles and DVH-AUC characteristics in patients who had persistent vs. non-persistent late diarrhoea or GI toxicity using previously described month and severity score (MOSES) [2] . Patients from IG-IMRT arm were included. The bowel bag (BB) V 15Gy , V 30Gy , and V 40Gy were determined. Additionally, the AUC from 15Gy to 45Gy (AUC 15-45Gy ) (dose range of prospective constraints) was calculated in intervals of 5Gy using the equation: (AUC 15-45Gy = AUC 15-20Gy +AUC 20-25Gy +AUC 25-30Gy +AUC 30-35Gy +AUC 35-40Gy +AUC 40-45Gy ) where AUC x-yGy is defined as: AUC x-yGy = [(y-x) x V y ] + [0.5(y-x) x (V x -V y )] ; V x & V y are volumes receiving x Gy and y Gy dose, respectively. The CTCAE grades for late diarrhoea and GI toxicity, MOSES for late diarrhoea, and cumulative MOSES (C-MOSES) for GI toxicity were obtained from the trial database. Patients were grouped into 2 categories; the first group included patients with grade 0-1 (CTCAE) and the second included those with ≥ grade 2 diarrhoea and GI toxicity. Similarly, patients were also categorised on the basis of symptom persistence (MOSES cut-off of 0.2 for single symptom (diarrhoea) and C-MOSES cut-off 0.7 for GI symptoms). In the first step, the median and percentile values were compared for V 15Gy , V 30Gy and V 40Gy for those with and without grade≥2 diarrhoea and GI toxicity. Subsequently, the same parameters were evaluated for symptom persistence. Additionally, DVH-AUC (cc.Gy) values for those with and without grade≥2 diarrhoea and GI toxicity, and those with and without symptom persistence were compared. Recommendations for future bowel DVH characteristics are made based on categorical cut-offs and DVH-AUC. Material/Methods:

Results:

Complete dosimetric details were available for 88/151 patients. Of these, 14/88 patients (16%) had late grade≥2 GI toxicity and 5/88 had late grade≥2 diarrhoea (5.6%). Overall, 15/88 patients (17%) had persistent GI symptoms (C-MOSES>0.7) and 6/88 (6.8%) had persistent diarrhoea (MOSES>0.2). As seen in Figure1 the patients who experienced grade≥2 diarrhoea, the median V 15Gy , V 30Gy , and V 40Gy for BB was 1109cc, 560cc and 341cc as compared to 955cc, 544cc and 325cc in those who did not. The median V 15Gy values, of those with and without grade≥2 diarrhoea, were separated by 154cc. Furthermore, the 25th percentile values were lower by 141cc in cohort that did not have grade≥2 diarrhoea. For patients with non-persistent compared to persistent diarrhoea (MOSES >0.2) the median V 15Gy was lower by 140cc and 25th percentile value was lower by 117cc. This suggests that future dose