Clinico-Dosimetric Correlation for Acute and Chronic Gastrointestinal Toxicity in Patients of Locally Advanced Carcinoma Cervix Treated With Conventional Versus IMRT: An Analysis from a Prospective Randomized Trial Rath GK 1, Gandhi AK 1, Sharma DN 1, Kumar S 2, Julka PK 1 1 Department of Radiation Oncology, 2 Department of Gynecology & Obstetrics, All India Institute of Medical Sciences, New Delhi, India Session title: GYN; Date/Time: :45 Location: Room D-2 Monitor number: 5

Introduction Radiation therapy with conventional technique leads to a acute and chronic gastrointestinal (GI) toxicity of >20-30% and > 5- 10% respectively Intensity Modulated Radiotherapy (IMRT) has shown to reduce both acute and chronic GI toxicity with good clinical outcome We earlier reported 1 results of our prospective randomized study comparing conventional pelvic radiotherapy (CRT) to Intensity modulated radiotherapy (IMRT) In our study reported earlier 1,IMRT arm had significantly fewer acute ≥ Grade 2 GI toxicity (31.8% vs. 63.6%), ≥ Grade 3 GI toxicity (4.5% vs. 27.3%) as well as lesser chronic gastrointestinal toxicity (13.6% vs. 50%) 1. Gandhi AK, Sharma DN, Rath GK et al. Int J Radiat Oncol Biol Phys Nov 1;87(3):542-8

Aims & Statistical Analysis The purpose of this study is to correlate reported acute and chronic GI toxicity in our study with Dosimetric parameters. Acute GI Toxicity: Assessed from start of treatment till 3 months of completion of treatment as per CTCAE (Version 3.0) Chronic GI toxicity : Assessed from 6 months after the completion of Brachytherapy until the last follow-up visit as per RTOG late morbidity scoring criteria Volume of rectum and small bowel (SB) receiving 40% (V40), 90% (V90) and 100% (V100) of the prescription dose and Volume of SB receiving ≥ 45 Gray (V45) were noted. Bowel loops were contoured as peritoneal cavity and not individually.

Gastrointestinal Toxicity CRT (%)IMRT(%) Acute ≥ Grade 2 GI Toxicity (p=0.034) Acute ≥ Grade 3 GI Toxicity (p=0.047) Chronic ≥ Grade 2 GI Toxicity Chronic ≥ Grade 3 GI Toxicity Overall GI Toxicity (p=0.011)

Mean V 90 and V 100 of SB in CRT and IMRT arm was vs ml and vs ml respectively. V 90, V 100 and V 45 >180 cc of SB correlated with acute GI toxicity (p=0.04, p=0.031 and p= 0.036) but not with chronic GI toxicity. Volume of the rectum did not correlate significantly with either acute or chronic gastrointestinal toxicity.

Conclusion IMRT in locally advanced carcinoma cervix (LACC) leads to significantly lesser acute and chronic GI toxicities as compared to Conventional radiotherapy. V 90, V 100 and V 45 >180 cc of SB significantly correlates with acute gastrointestinal toxicity in patients of locally advanced carcinoma cervix treated with IMRT and should be used in prospective clinical trials. Further follow up is required for assessment of clinic- dosimetric correlation of chronic gastrointestinal toxicity.