Setup time analysis for stereotactic body radiotherapy in O-ring linear accelerator without rotational correction.

This study analyse setup time (ST) and frequency of on-board imaging for stereotactic abdomen (liver, stomach), lung, and spine radiotherapy in the absence of automatic rotational correction. Total 53 stereotactic body radiotherapy (SBRT) patients, 28 of abdomen, 19 lung, and 6 spine treated for 230 sessions in O-ring gantry accelerator were evaluated for ST analysis. The mean setup time for all patients, abdomen, lung, and spine cases were 7.7 ± 7.4 min, 9.2 ± 9.2 min, 6.3 ± 4.1 min, and 5.5 ± 3.3 min, respectively. Median number CBCT was 2. 96% of cases had a CBCT between 1 and 3, and 9 (4%) had ≥ 4 CBCTs. Overall, 38.1%, 35.5%, 22.1%, 2.2%, and 2.2% of setup time fall into window of 0-5 min, 5-10 min, 10-20 min, 20-30 min, and > 30 min. Most difficult challenge is to negotiate with unknown rotational errors. It will be easy to dealt with them without automatic rotational correction if values are known.