SU‐E‐T‐521: Feasibility Study of a Rotational Step‐And‐Shoot IMRT Treatment Planning Approach

Purpose: Rotational step‐and‐shot IMRT (r‐IMRT) could improve delivery efficiency with good dose conformity, especially if it can leverage the burst mode of the accelerator where radiation is turned on/off momentarily while the gantry rotates continuously. The challenge for the r‐IMRT planning is to minimize the number of beams to achieve a fast and smooth rotational delivery. Methods: Treatment plans for r‐IMRT were created using an in‐house treatment planning system. To generate the plan using a very few beams, gantry angle was optimized by weighting the beam monitoring unit (MU), and beam shape optimization was a combination of column search with k‐means clustering. A prostate case and a head and neck case were planned using r‐IMRT. The dosimetry is compared to s‐IMRT planned with Varian Eclipse treatment planning system. Results: With the same PTV dose coverage D95=100%, the r‐IMRT plans shows comparable sparing as the s‐IMRT plans in the prostate for the rectum D10cc and the bladder Dmean, and in the head and neck for the spinal cord Dmax, the brain stem Dmax, the left/right parotid Dmean, the larynx Dmean, and the mandible Dmean. Both plans meet the established institutional clinical dosimetric criteria. The r‐IMRT plan uses 19 beam/405 MU for the prostate, and 68 beam/880 MU for the head and neck, while the s‐IMRT uses 7 beam/724 MU and 9 beam/1812 MU, respectively. Compared to the corresponding s‐IMRT, r‐IMRT has a reduction of MUs of 44% for the prostate case and 41% for the head and neck case. Conclusions: We have demonstrated the feasibility of a rotational step & shoot IMRT treatment planning approach that significantly shortens the conventional IMRT treatment beam‐on time without degrading the dose comformity.