SU-E-T-216: A Clinical Dosimetry Analysis of Total Body Irradiation for Leukemia Patients.

PURPOSE Perform a retrospective dosimetry study of total body irradiation (TBI) on leukemia and bone marrow transplant patients. METHODS The in vivo dosimetry data of 129 patients treated with TBI between 2008 and 2011 were retrieved from the database and analyzed. These patients were mostly treated with the regime of a single fraction or 6 fractions with some exceptions of 8-fraction or 2-fraction treatments depending on the protocols that were applied. For every fraction of treatment, 10 pairs of diode dosimeters were used to monitor the doses to the mid-line of head, neck, arms, mediastinum, left lung, right lung, umbilicus, thigh, knee, and angle for both AP and PA fields. The doses to the midline of the above body parts were considered to be the average of the AP and PA readings of each diode pair. Dose deviation from the prescribed value for each body part was studied by plotting the histogram of the frequency versus deviation and comparing this with the dose delivered to the midline of the umbilicus to where the dose was prescribed. The correlation of dose deviation to body part thickness was also studied. RESULTS The dose differences between measurement and prescription for all body parts are mostly less than 10%. The dose inhomogeneity on different body parts could be manually improved by using compensators but the method is cumbersome. The dose deviation in many histograms ranging from about -10% to 10% indicates some incongruity of dose distribution. This could be due to the method of using lead compensators for a manual dose adjustment which could not ideally compensate different body thicknesses everywhere. CONCLUSION The conventional TBI could give uniform dose to the major body parts under the in vivo dosimetry monitoring at the level of 10%, but the treatment procedure is cumbersome and time consuming.