VERIFICATION OF LUNG ATTENUATOR POSITIONING BEFORE TOTAL-BODY IRRADIATION USING AN ELECTRONIC PORTAL IMAGING DEVICE

Purpose: We report the first clinical experience with an electronic po rtal imaging device for lung attenuator positioning before delivery of total body irradiation. We demonstrate a technique for lung attenuato r placement which reduces the dose to the patient during setup, reduce s the patient setup time, and increases the accuracy of lung attenuato r positioning. Methods and Materials: Patients are treated with total body irradiation using a dedicated dual source irradiation facility pr ior to receiving bone marrow transplantation. The dose rate to the pat ient's midline is limited to 0.10 Gy/min, and partial transmission lun g blocks are used to minimize radiation induced pneumonitis while deli vering adequate dose to the regions under the blocks. Lung blocks are placed on the patient's back and chest wall, and portal images are use d to verify proper block placement before the remaining treatment dose is delivered. Results: We report the use of a liquid ionization chamb er matrix electronic portal imaging device for imaging total body irra diation patient setups. Conclusion: The dose to the patient using the EPID for portal imaging is a factor of 7.5 lower than that needed for film. Image quality is superior to that of film due to digital process ing. Since less time and dose are needed for imaging, it is demonstrat ed that better and more efficient final placement of the lung blocks c an be achieved.