Set-up Errors and Determination of Planning Target Volume Margins Protocol for Different Anatomical Sites in a Newly Established Tertiary Radiotherapy Centre in India

Abstract

Objective Our study aimed to assess the set-up errors for image-guided radiotherapy at a newly established tertiary radiation center in India and to establish the departmental protocol of clinical target volume–planning target volume (CTV–PTV) margins for different anatomical sites. Materials and Methods This study enrolled the first 200 patients who were treated with curative intent at All India Institute of Medical Sciences, Patna, from February 2019 to September 2019. Number of patients were 53, 26, 53, 11, 6, 47, and 4 for head and neck, brain, breast, thorax, abdomen, pelvis, and craniospinal irradiation (CSI), respectively. The translational vectors for total 1,463 kV cone-beam computed tomography (CBCT) images were collected from the treatment record. Results For the systematic error, the largest value is found for the thoracic subset on the X and Y directions, and for breast patients on Z axis, whereas the smallest values were found for CSI. For random error, the largest value was found for pelvic in the X, Y direction, and for breast subset on Z axis, whereas the smallest values on X and Z axes were found in the brain and for head and neck on the Y axis. Largest value for systemic error is smaller than 5 mm in all directions and for all anatomical subsets. The highest random error value is 5.07 mm in Y axis for pelvic subset. The largest values for CTV–PTV margin are found for thoracic subset and the smallest for CSI followed by the brain. Significant reduction of set-up error observed for the last hundred patients as compared to the first half of the patient population. Conclusion Use of thermoplastic cast along with breast board and respiratory motion management should be recommended to reduce set-up error for breast and thoracic subset. Six degrees of freedom robotic couch system can also further rectify the set-up error in image-guided radiotherapy.