ESTRO 37 Abstract book

S1232

ESTRO 37

conjunction with vaginal packing is recommended when clinically feasible during tandem and ovoids applicator placement. No significant bladder dose reduction is found in this study when rectal spacer is employed. EP-2229 Evaluation of Apparent diffusion coefficient(ADC) in Image guided brachytherapy for cervical cancer R. Kumar 1 , P. Kala 2 , G. Narayanan 2 1 Vydehi Institute of Medical Sciences, Radiation Oncology, gurgaon, India 2 Vydehi Institute of Medical Sciences, Radiation Oncology, Bangalore, India Purpose or Objective For IGABT T2W MRI is the gold standard, but studies have shown that target delineation with the same results in uncertainties, poor interobserver variabilities and low conformity indices for high risk clinical target volume (HRCTV) contours. This variation is largest for cases with large parametrial disease pre EBRT who end up having near complete response pre brachytherapy. We aimed to investigate the presence or absence of abnormal ADC outside the HRCTV(High Risk clinical target volume) contours as defined by GEC ESTRO I and to objectively define the extent of HRCTV contours in the suspicious grey zones with the help of ADC maps derived from Diffusion weighted imaging (DWI) Material and Methods We identified 30 biopsy proven squamous cell cervical carcinoma patients who were selectively divided in two groups based on commonly experienced clinical scenarios. 1st being patients with parametrial disease at diagnosis and no parametrial disease post teletherapy and 2nd being parametrial disease at diagnosis with persistent parametrial disease at the time of brachytherapy. All patients underwent a MRI of the abdomen and pelvis along with DWI. ADC maps were derived using three levels of b values 0, 400, 800 s/mm2. ADC for the following regions were calculated, Tumor, tumor edge and 1cm lateral to tumor edge on both diagnostic and brachytherapy scans. An Abnormal ADC was calculated for every patient and was set as a threshold. Microsoft excel was used to calculate the mean and difference of mean for the recorded values. Paired t-test was used as the test of significance to test the change in ADC from diagnostic to brachytherapy MRI in the same patient. Unpaired t – test was used as the test of significance to compare group 1 and group 2. Results There was a significant increase in ADC values across all measured areas from diagnosis to brachytherapy(p=.00001). No abnormal ADC was present outside the HRCTV contours. The threshold ADC was present either inside or on the HRCTV contours with a mean distance of 3mm (+3/-3) inside the HRCTV contours. This mean distance was more for patients in group 1 (-3.4mm) as compared to patients in group 2 (- 2.5mm) but this increase was not significant (p-value 0.13)