TBI treatment planning using the ADAC pinnacle treatment planning system

The use of total-body irradiation (TBI) for the purpose of bone marrow transplant is an established procedure at many institutions. In our institution, the TBI monitor unit (MU) calculation starts with the calibration done at the same conditions of the treatment source-axis distance (SAD) = 350 cm for the field size of 40 x 40 cm at a depth of 10 cm). The dose rate in the central axis of the beam at this distance is measured in cGy/MU. A tissue phantom ratio table obtained in the condition of treatment together with off-axis factors is used in the MU calculation for each particular patient. The treatment is done with the patient lying on his/her back and the beam is delivered using right-to-left lateral beams. Due to different thickness' of the patient, a lead compensator is built to compensate for the different parts of the body. Eighteen or 10-MV x-ray photons are used in the TBI treatment, and a 1-cm-thick lucite plate is placed near the patient to increase the dose to the surface. In vivo dosimetry using diodes is done to verify the calculations. The Rando-Phantom was computed-tomography scanned from the head to the abdomen with 1-cm-thick slices covering 70 cm of the phantom. This simulated the TBI treatment and correlated the calculations done by the ADAC treatment planning system to film measurements at the pelvis and lung levels. These results agreed within 5% of the measured dose. The use of the upper arms to reduce the dose to the lungs and optimization of dose using special compensators has been studied using the treatment planning system. Use of the multileaf collimator to compensate the dose received by the patient has been explored in this paper.