Encrypted login | home

Program Information

Total Body Irradiation with Uniform MU and Modulated Arc Segments, UMMS-TBI

B Yi

B Yi*, H Chung , Y Mutaf , K Prado , University of Maryland School of Medicine, Baltimore, MD


TH-EF-BRB-9 (Thursday, August 4, 2016) 1:00 PM - 2:50 PM Room: Ballroom B

To test a novel total body irradiation (TBI) system using conformal partial arc with patient lying on the stationary couch which is biologically equivalent to a moving couch TBI. This improves the scanning field TBI, which is previously presented.

The Uniform MU Modulated arc Segments TBI or UMMS-TBI scans the treatment plane with a constant machine dose rate and a constant gantry rotation speed. A dynamic MLC pattern which moves while gantry rotates has been designed so that the treatment field moves same distance at the treatment plane per each gantry angle, while maintaining same treatment field size (34cm) at the plane. Dose across the plane varies due to the geometric differences including the distance from the source to a point of interest and the different attenuation from the slanted depth which changes the effective depth. Beam intensity is modulated to correct the dose variation across the plane by assigning the number of gantry angles inversely proportional to the uncorrected dose.

Measured dose and calculated dose matched within 1 % for central axis and 3% for off axis for various patient scenarios. Dose from different distance does not follow the inverse square relation as it is predicted from calculation. Dose uniformity better than 5% across 180 cm at 10cm depth is achieved by moving the gantry from -55 to +55 deg. Total treatment time for 2 Gy AP/PA fields is 40-50 minutes excluding patient set up time, at the machine dose rate of 200 MU/min.

This novel technique, yet accurate but easy to implement enables TBI treatment in a small treatment room with less program development preparation than other techniques. The VMAT function of treatment delivery is not required to modulate beams. One delivery pattern can be used for different patients by changing the monitor units.

Contact Email: