R. Cai1, F. Bai2, and J. Zang3; 1Department of Radiotherapy, Xijing Hospital, Fourth Military Medical University, Xian, Shaanxi, China, 2Department of Radiation Oncology, Xijing Hospital, Fourth Military Medical University, xian, Shaanxi, China, 3Department of Radiation Oncology, Xijing Hospital, Air Force Medical University, Xian, China
Purpose/Objective(s): The setup accuracy in patients with limb tumor receiving volumetric-modulated arc therapy remains unclear. Therefore, we designed this multicenter retrospective study to investigate the setup accuracy and provide reference about boundary of planned target volume (PTV) in patients with limb tumor receiving VMAT. Materials/
Methods: Patients with limb tumor receiving VMAT radiotherapy from three large medical institutions in western China were retrospectively reviewed. The off-line Cone beam computed tomography (CBCT) were used to analyze setup errors, and the boundary from CTV to PTV was calculated using formula 2.5?+0.7d. The influence factors were investigated by multivariate linear regression, including age, sex, BMI, KPS score, left or right limb lesions, surgery and the length of the target area. Results: A total of 60 patients were included in the analysis from 2014 to 2023.The median age was 51 years old (ranging from 5 to 80 years). Of all the patients, 31 were males and 28 were females. Seventeen patients had upper limb tumor, 43 patients had lower limb tumor. In patients with upper and lower limb tumors, the translation errors in the left and right were (2.10±1.47 vs 2.23±2.59) mm, p=0.428;the head and foot direction were (1.81±1.39 vs 1.98±1.45) mm, p =0.253; the ventral and dorsal direction were (1.67±1.37 vs 2.09±1.58) mm, p =0.009; the rotation error in the Rz direction were (0.69±0.55 vs 0.54±0.67), p =0.272. The recommendation boundaries for expanding CTV to PTV of the upper limb tumors were 5.21mm, 3.83 mm and 4.22mm in X, Y and Z directions, respectively. The recommendation boundaries for expanding CTV to PTV of lower limb tumors were 5.95mm, 5.66mm and 5.36mm in X, Y and Z directions, respectively. Multivariate analyses found that the setup error was not associated with sex, age, BMI, KPS, left and right limb, surgery and the length of the target. Conclusion: This multicenter retrospective study provides a recommendation about boundaries for expanding CTV to PTV. It was found that the 5mm PTV external boundary of routine VMAT radiotherapy for limb tumors may be insufficient. The lower extremity tumor needs 6mm in three directions, and the upper extremity tumor needs 6mm in the left and right directions, and 5mm is enough in the head, foot and abdominal and dorsal directions. Further studies with large sample are needed to confirm this result.
