ESTRO meets Asia 2024 - Abstract Book

S293

Interdisciplinary – Urology

ESTRO meets Asia 2024

JUN WANG 1 , feng LIN 1 , Chao Ming Huang 2 , ying wen zhang 1 , Jie Chu LIN 1,3 , Ngai Chu 1,3 , XIN YAN DONG 1,4 , YANG WANG 1,5,4 1 Radiation Oncology, 1. Guangzhou Chinese Traditional Medicine University Jin-Sha-Zhou Hospital, Guangzhou, China. 2 Radiation Oncology, 1. Guangzhou Chinese Traditional Medicine University Jin-Sha-Zhou Hospital, guangzhou, China. 3 medical physics centre, University of Wollongong, Wollongong, Australia. 4 Medical Physics Centre, University of Wollongong, Wollongong, Australia. 5 Radiation Oncology, Icon-China, Beijing, China

Purpose/Objective:

This study reviewed 22 cases of muscle-invasive bladder cancer (MIBC) treated by Varian Ethos Linac using iCBCT image guided ART, technical challenges for bladder cancer radiotherapy [1] is natural inter-fraction variation for target in shape, volume and position can significantly influences the irradiation accuracy by bladder and rectum fillings conditions. Adaptive Radiotherapy (ART) gives daily on-line contouring adjustments were performed to adapted targets and OARs. Compare with conventional 3D radiotherapy technique, iCBCT guided ART brought higher accuracy and stability improvement to bladder cancer radiotherapy [2] . with significant shorter treatment time compared with MRI based ART [3] , the study obtained convenient benefit in accuracy improvement with better reliability, high local control rate and lower irradiation toxicity.

Material/Methods:

All cases in this study were given 100ml of water 1hr before CT simulation scan, followed PET or MRI image scan for image fusion purpose [4] . Body and OAR contours were delineated using AI tools in Ethos ART planning system. GTV then contoured manually on fusion images, then PTV was created with 3 to 5mm margin from the GTV. Prescription to PTV was 60Gy in 20 fractions to V100(%) and 55Gy optimized to V95(%); and < D45Gy constraint to rectum, small bowel, and sigmoid. Fixed field IMRT treatment technique was chosen for the dose optimization [5] . CT images; then GTV was manually adjusted to match iCBCT anatomically, OARs contours were adjusted by AI function with minor manual adjustment. Dose re-optimization then performed in real-time, and after ART treatment plan completed and delivered, counted total performance time approximately with 15 minutes in average. By reviewing the maximum change ranges of GTV daily adjustment in shape, volume, and position, maximum changes can be up to 1.5cm to 2.0cm, Re-optimized ART dose distribution focused to adapted GTV achieved coverage >D96%. Mean dose to OARs met the constraints of V60<5%, V50 < 10% and V20 <55%, and bladder and rectum Dmean < 30Gy. All patients showed significant lower toxicity throughout the treatment. Reviewing treatment outcome, overall local control rate obtained >97.8%. An accumulated dose distribution for all treatment fractions created by Ethos planning system overlapped with the primary treatment plan, it shows that the accumulated ART dose distributed is much closer to primary treatment plan. However, there is no evidences to show target shape and position stability can be improved by drink water to fill-up bladder before treatment. With normal radiotherapy setup, iCBCT images acquired and fused to primary planning Results:

Conclusion:

An obvious improvement shown this study illustrated iCBCT guided ART dynamically achieving the dose coverage accurately focused to the daily adapted target with satisfied local control rate, low toxicity and in efficient