Implementation of a lateral total body irradiation technique with 6 MV photons: The University of Texas Health Science Center in San Antonio experience

Purpose: Total body irradiation (TBI) involves delivery of marrow-ablative or suppressive dose to the entirety of the marrow habitus. In its current practice, TBI often involves positioning the patient in an uncomfortable upright body position for extended periods of time while delivering radiation dose via anteroposterior/posterioanterior (AP/PA) fields. In an effort to maximize reproducibility and patient comfort, especially for paediatric patients, a supine lateral total body irradiation (LTBI) protocol was implemented as preparatory regimen for bone marrow transplant. Methods and Materials: One hundred and forty-five patient charts were reviewed. Patients were treated in supine position with hands clasped over the upper abdomen in a comfortable position. They were placed in a methylcrylate body box and irradiated with opposed lateral fields at extended distance of 350 cm to the midplane of the patient. Each field delivered 100 cGy with a midplane dose of 200 cGy per fraction. Dose regimes varied from 200 to 1,200 cGy total doses. Custom lead compensating filters were utilized. A 6 MV photon beam produced by a Varian Clinac 600c linear accelerator was applied. In vivo thermoluminescent dosimeter (TLD) readings were taken for anatomical regions of interest (ROI). TLDs were placed in each ROI under a 1.5-cm-thick bolus for maximum dose build-up. Results and Conclusion: The resulting data demonstrate a dosimetric variability of anatomical ROI from reference prescription dose of less than 3%. LTBI has been used for more than ten years in our institution and produced favourable results for more than 100 patients. We suggest this LTBI approach to facilitate successful treatment of children who require TBI while maintaining dose uniformity as recommended by the American Association of Physicists in Medicine Report 17.