ESTRO 2020 Abstract book

S293 ESTRO 2020

PH-0483 Acuros XB Dose Calculation algorithm: Dosimetric evaluation for computed tomography metal artifacts C.H. Lee 1 , M. Yeom 1 , C. Kim 1 , I. Yun 1 , H. Song 1 , G. Back 1 1 Asan Medical Center, radiation oncology, seoul, Korea Republic of Purpose or Objective Calculation of the radiation dose is important in radiation therapy. The dose calculation algorithm for radiation therapy has improved rapidly in the last few decades. The Acuros XB (AXB) algorithm was recently implemented in the Eclipse treatment planning system. Computed tomography (CT) is commonly used for treatment planning. However, metal artifacts in CT reduce the accuracy of dose calculation. This study aimed to evaluate dose calculation for metal artifacts in CT, caused by metal implants, using the AXB algorithm. Material and Methods We designed two customized phantoms using a 3D printer. One phantom had no metal implants while the other had metal implants for the evaluation of metal artifacts. We acquired CT images of the two phantoms for treatment planning and set a planning target volume (PTV) and four regions of interest (ROIs). Volumetric modulated arc therapy was used for treatment planning, and the daily dose was 200 cGy. We calculated the dose using the AXB algorithm and compared treatment plans between the two phantoms.

phantoms were 0.5%, 1.6%, 0.4%, and 0.2%. An average 0.7%-higher mean dose was measured in the no-metal phantom.

Conclusion The HI and CI were similar regardless of the presence of metal artifacts. Furthermore, there was no significant difference of four regions in metal artifact. Calculation of dose on metal artifact region and no metal artifact region using AXB was within 1% of measurements. AXB calculated the best dose distribution, regardless of the presence of metal artifacts. Thus, AXB may be regarded as a crucial algorithm in metal artifact regions. PH-0484 Evaluation of AI based contouring tools in prostate cancer RT A. Borkvel 1 , E. Gershkevitsh 1 , M. Adamson 1 , K. Kolk 1 , D. Zolotuhhin 1 1 North Estonia Medical Centre, Radiotherapy Centre, Tallinn, Estonia Purpose or Objective OAR and target contouring is a labour intensive step in an RT treatment planning process. Recently multiple vendors have introduced a segmentation algorithms based on artificial intelligence (AI) to reduce the amount of manual work. In this study, the accuracy and efficiency gain for prostate cancer patient contouring when using AI based contouring tools from two vendors was assessed. Material and Methods Contouring accuracy was evaluated for 37 patients by comparing manually contoured structures to automatically segmented structures using MVison contouring tool. Standard Imaging StructSure software was used to evaluate the difference in structure volumes and Dice similarity coefficient. The following structures were segmented and evaluated for all patients: bladder, rectum, prostate, seminal vesicles, femoral heads and penile bulb. To assess the efficiency gain, two experienced RTTs produced manual contours for 18 patients and recorded the time required for outlining. Different set of 15 patients was automatically segmented, then manually edited by the same RTTs and time required recorded. Use of TPS semi-automatic segmentation tools was allowed. Average time per patient was calculated for manual contouring and editing task. To compare 2 different vendors the same 4 prostate patients were segmented using MVision and Mirada Medical contouring tools. Results Table 1 shows results of the automatic segmentation. Difference in volume for bladder and rectum is less than 10% and Dice coefficient is higher than 0.8. For the rest of the structures the difference in volumes is greater (27.0%- 69.5%) and reflected in a poorer Dice coefficient results (0.44-0.78). For prostate, MVision contouring tool systematically added extra contour on one CT slice above and below those outlined manually. The larger difference

Results In the metal phantom, the homogeneity index (HI) and conformity index (CI) of PTV were 0.984 and 1.102, respectively. In the no-metal phantom, the HI and CI of PTV were 0.98 and 1.107, respectively. The differences in HI and CI were 0.4% and 0.5%, respectively. In the metal phantom, the mean doses to the metal artifacts in the four ROIs were 38.9, 44.4, 50.1, and 89.2 cGy. In the no-metal phantom, the mean doses to the metal artifacts in the four ROIs were 39.1, 45.1, 50.3, and 89.4 cGy. The differences in the mean dose between the no-metal and metal