ESTRO 37 Abstract book

S1077

ESTRO 37

741cGy for T2W and DWI respectively (p value .006), HRCTV D100- 441.05 and 444.5 for T2W and DWI plans respectively (.006). This superior coverage could be achieved without significantly increasing dose to the bladder, rectum and sigmoid.

Figure 2; A scalp skin cancer treatment. The position of the lesion and the initial setup of the patient made it particularly challenging to find the good gantry and couch rotation angles using the 3D visualization tool. Conclusion This tool has proved to be an efficient way to produce fast and accurate perpendicular beam arrangements for electrons patients. It has shown great usefulness for challenging patient anatomies. EP-1977 Comparative study of Diffusion & T2- Weighted MRI for delineation & planning-Cervix brachytherapy R. Kumar 1 , 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 Brachytherapy (BT) plays a crucial role in the management of invasive cervix cancer from stages I to IV. GEC ESTRO recommends the use image-based brachytherapy as it has resulted in better local control and organ sparing . The use of T2W MRI is the gold standard for image-guided adaptive brachytherapy but few studies have shown uncertainties, poor interobserver variabilities and low conformity index for target delineation. Functional imaging with DWI can improve cervical tumor distinction as it is more sensitive than T2W MRI even in detecting parametrial invasion. Addition of DWI as a supplement to T2W imaging has also decreased the interobserver variability. Hence we intended to compare target delineation using these two imaging modalities. Material and Methods A total of 50 patients with squamous cell carcinoma who were suitable for intracavitary brachytherapy were included for the study from Jan 2015 to june 2016. Patients were subjected to MRI based brachytherapy post EBRT using GEC ESTRO working group guidelines. Along with a T2W sequence a diffusion weighted sequence was also taken using b values 0, 400, and 800. After importing the images to brachy vision software by varian, GTV, HRCTV and IRCTV were contoured on both T2W MRI and DWI along with bladder rectum and sigmoid. D2cc for all the organs at risk (OAR) and HRCTV D90, D100 were recorded after generating 2 plans, one for each imaging modality. Treatment was given using the plan generated from T2W images Results GTVBT, HRCTV and IRCTV contours on DWI were different when compared with T2W, mean GTVBT on T2W and DWI was 5.25 and 5.23 respectively (p value 0.8). Mean HRCTV on T2W and DWI was 28.3 and 27cc respectively (p value .003) with Mean HRCTV on DWI being significantly lower. Mean IRCTV on T2W and DWI was 68.1 and 65cc respectively with mean IRCTV on DWI being significantly lower (p value .003). planning on the above volumes resulted in a superior coverage in terms of HRCTV D90 and D100 for DWI based plan, HRCTV D90 – 735.1 and

Conclusion GEC ESTRO based contouring guidelines cover all the functionally abnormal areas on DWI. In this study DWI based plans when compared to T2W plans resulted in smaller HRCTV and IRCTV volumes leading to better coverage without increasing dose to the organs at risk. But care must be taken in using DWI as a standalone imaging for planning and contouring, due to its poor anatomic visualization and distortions there is a huge risk of geometric and applicator reconstruction uncertainties. If at all DWI has to be used for planning, image fusion with T2W is a must. Hence we recommend that DWI