Quantitative analysis of setup errors in lung SBRT with R624-SCF immobilization equipment

Abstract

Objective KV-CBCT was utilized to evaluate the setup errors in lung SBRT with R624-SCF immobilization equipment, quantitatively analyze the percentage of all types of errors in the cumulative errors and unravel the main sources of setup errors. Methods The CBCT data weekly and QA data monthly from 32 patients diagnosed with lung neoplasms were collected to quantitatively analyze the setup errors. The cumulative errors were calculated by statistical model. The proportion and source of each type of setup error was analyzed. Results All 32 patients received a total of 420 times of CBCT.The setup errors of immobilization equipment in the lateral, supine-inferior, anterior-posterior directions were (0.03±0.72) mm, (0.73±1.16) mm and (-0.21±0.95) mm, respectively. The errors of tumor motion in three directions were (0.71±2.61) mm, (-0.80±2.60) mm and (0.075±1.77) mm, respectively. According to the calculation formula proposed by Vance Keeling, the proportion of the cumulative error was 54.55%, 9.21% for immobilization equipment, 12.97% for tumor motion, 2.55% for couch sagging, 5.70% for Gantry radiation isocenter, 4.73% for Collimator radiation isocenter, 4.61% for couch radiation isocenter and 5.70% for X-ray field isocenter, respectively. Conclusions The main factors of setup errors during SBRT treatment for lung cancer are setup random, tumor motion, immobilization equipment, couch sagging and machine isocenter. During radiotherapy, targeted control of tumor motion is of significance for minimizing the cumulative errors. Key words: Lung neoplasm/radiotherapy; Setup error; Cumulative error