Abstract book - ESTRO meets Asia

S36 ESTRO meets Asia 2018

Conclusion This is the first study demonstrating a significant prediction of tumor grading by a CT-based radiomic classifier. Further studies should evaluate the feasibility of differentiating low risk from high risk sarcomas as well as the potential superior performance of an MRI-based radiomic model. Poster viewing: Quality management and verification (RTT) PV-089 Comparison of two immobilization devices used for treatment of breast and abdomen regions P. Umbarkar 1 , S. Deshpande 1 , S. Naidu 1 , S. Shinde 1 , N. Parmar 1 , J. Ashiwini 1 , P. Kamble 1 , S. Ullagaddi 1 , O. Jadhav 1 , K. Venkatesan 1 , V. Anand 1 , R. Bajpai 1 , V. Babu 1 , V. Mittal 1 1 P D Hinduja Hospital, Radiation Oncology, Mumbai, India Purpose or Objective Proper immobilization is important for the accurate and precise delivery of radiotherapy. Wide variety of immobilization devices are available for any given treatment site. Technologists play an important role in the selection of these devices as per patient needs during simulation stage. This study aimed to compare the effectiveness of the commonly used immobilization device with a new device for treatment of breast and abdomen regions. Material and Methods Daily treatment set-up data for 475 (including DIBH) patients treated on true Beam (Varian medical system USA) were analysed. These patients were treated with two different immobilization systems. Out of total 475 patients analysed, 337 were breast patients and 138 were abdomen patients. Of the 337 breast patients, 206 patients were treated using AIO and 131 patients were treated using vacuum cushion and of the total 131 abdomen patients, 80 patients were treated using AIO and 58 patients were treated using vacuum cushion. Five images per patient were analysed in this study. Statistical Methods: Margins along each of the three directions (AP, SI and ML) were generated from the recipes of Van Herk, Stroom and ICRU 62 for both set of patients i.e. patients treated with AIO and vacuum cushion. Systematic errors were the standard deviation of mean errors as calculated for each patient in various sub groups. Random errors were the root mean square values of the standard deviation of errors recorded in all three directions for each patient in a sub group. Mean systematic and random errors of lateral, longitudinal and vertical directions were calculated and compared between immobilization systems for each region. Results

Conclusion Both the immobilization devices, AIO and vacuum cushion did not show statistically significant differences in set up accuracy when used along with online guidance, thus for the treatment of breast and abdomen regions both the methods of immobilization can be considered equivalent. However differences were noted in the ML direction in the breast group treated with vacuum cushion as compare to those treated with AIO device. Setup with AIO device has an added advantage of lesser setup time compare to vacuum cushion PV-090 Setup errors in brain tumor patients with et and cbct imaging. P. Nayyar 1 , R.K. Munjal 1 , D. Kumar 1 , M. Simar 1 1 max superspeciality hospital, radiation oncology, New Delhi, India Purpose or Objective The Exactrac system (ET) is mainly an integration of 2 sub- systems. An infrared (IR) based optical positioning system and a radiographic KV x ray imaging system (x ray 6D). The infrared system consists of 2 IR cameras which are used to monitor IR reflective body markers placed on the patient body to asses in patient positioning and setup, an IR reflective reference star, which is attached to the treatment couch to assess in patient’s setup. It can assist in couch movement with spatial resolution better then 0.3 mm. The radiographic KV x ray imaging system devices consist of 2 semi orthogonal oblique x ray tubes to obtain high quality radiographic images for patient position verification and adjustment. The position verification is made by fusion of the radiograph with DRR created from simulation CT images using 6 degree of freedom (6D) fusion algorithm. The position adjustment is performed using the infrared system according to the verification result. Material and Methods This was a retrospective analysis of 40 brain tumor patients who were treated from July 2017 to December 2017 at our institute and monitored with ET and CBCT. We calculated mean shifts in X,Y,Z axis and in pitch, roll, Yaw with ET and applied the shifts. We subsequently performed a CBCT to verify correction of setup errors by ET and calculated the mean difference in shifts for all 6 degree of freedom for all patients. Results Mean shift for all patient with ET were in X axis (- 0.16±0.22 cm), Y axis (0.0±0.22 cm), Z axis (-0.04 ± 0.40 cm), yaw degree (1.05±1.18°) Roll degree (-0.14±1.40°), Pitch degree (0.35±1.53°), the mean difference in between ET and CBCT was X axis (0.03±0.07cm), Y axis (0.09±0.09cm), Z axis (-0.05±0.09cm). Mean difference in shifts between CBCT and ET were all < 1 mm. Conclusion ET based image verification alone can achieve sufficient accuracy for IGRT of patients with intracranial malignancies. This has the advantage of reducing overall treatment time, radiation exposure of the patients and increase machine throughput. ET based imaging protocol should be considered in future for such patient after initial verification of accuracy.