Poster — Thur Eve — 38: Feasibility of a Table‐Top Total Body Irradiation Technique using Robotic Couch Motion

Abstract

Purpose:To develop and test the feasibility of a table‐top implementation for total body irradiation (TBI) via robotic couch motion and coordinated monitor unit modulation on a standard C‐arm linac geometry.Methods:To allow for collision free delivery and to maximize the effective field size, the couch was rotated to 270° IEC and dropped to 150 cm from the vertical radiation source. The robotic delivery was programmed using the TrueBeam STx Developer Mode using custom XML scripting. To assess the dosimetry of a sliding 30×20 cm2 field, irradiation on a solid water phantom of varying thickness was analyzed using EDR2 radiographic film and OSLDs. Beam modulation was achieved by dividing the couch path into multiple segments of varying dose rates and couch speeds in order to deliver 120 cGy to the midline.Results:The programmed irradiation in conjunction with coordinated couch motion was successfully delivered on a TrueBeam linac. When no beam modulation was employed, the dose difference between two different phantom sections was 17.0%. With simple beam modulation via changing dose rates and couch speeds, the desired prescription dose can be achieved at the centre of each phantom section within 1.9%. However, dose deviation at the junction was 9.2% due to the nonphysical change in the phantom thickness.Conclusions:The feasibility of robotic table‐top TBI on a C‐arm linac geometry was experimentally demonstrated. To achieve a more uniform dose distribution, inverse‐planning allowing for a combination of dose rate modulation, jaw tracking and MLC motion is under investigation.