Authors: Pham Tuan Anh, Nguyen Van Han, Ha Ngoc Son, Nguyen Trung Hieu, Nguyen Van Nam, Chu Van Dung, Doan Trung Hiep, Tran Ba Bach, Nguyen Dinh Long.
Research published in: Vietnam Journal of Oncology, No. 5/2019, pp. 243-248.
SUMMARY
Purpose: Evaluation of patient setting errors before treatment with separate fixation devices for different anatomical regions using the OBI system, including the head and neck, thorax, abdomen, and pelvis.
Subjects and methods: A total of 45 patients were randomly selected for the VMAT treatment plan, divided equally into 3 anatomical regions assigned for radiotherapy at Vinmec Times City International General Hospital from January 2018 to August 2019. Patients were scanned with simulated CT on the CT Optimal 580 (GE Medical System, Milwaukee, Wisconsin, USA), planned on Eclipse software (ver 13.0) of Varian (USA). Patients were scanned with 2D-KV images (daily) and 3D-CBCT images (Monday and Thursday or all days of the week for 4D-VMAT) analyzed directly on OBI software and compared with DRR images from the plan, from which the errors were evaluated and recorded in 3 directions: AP (anterior and posterior); SI (upper and lower); LR (left and right).
Results: A total of 1220 pairs of 2D - kV images were performed in all 3 radiation areas before daily treatment.
For head and neck radiation, the average setting errors in the AP, SI, and LR directions were: (1 ± 1.41mm); (1.09 ± 1.41mm); (1 ± 1.33mm).
For thoracic and abdominal radiation, they are: (1.27 ± 1.84mm); (0.93 ± 2.39mm); (1.58 ± 1.81mm).
For pelvic radiation, they are: (1.30 ± 2.02mm); (1.62 ± 3.24mm); (1.47 ± 1.60mm).
Conclusion: Pre-treatment image verification using the OBI system helps reduce setup errors, increase dose delivery to the tumor, and reduce unwanted side effects. Through the research results, we propose a margin setup for head and neck radiation therapy at our hospital: 4mm (AP), 4mm (SI), and 4mm (LR). For thoracic and abdominal radiation therapy: 5mm (AP), 5mm (SI), 6mm (LR). For pelvic radiation therapy: 5mm (AP), 6.5mm (SI), 5mm (LR).
