In vivo and in vitro Confirmation of Dose Homogeneity in Total Body Irradiation with Thermoluminescent Dosimeter

Chie, Eui Kyu; Park, Suk Won; Kang, Wee Saing; Kim, Il Han

Abstract

PURPOSE: Total body irradiation (TBI) or whole body irradiation is used to acquire immune suppression, to treat malignant lymphoma and leukemia, and as an conditioning regimen for bone marrow transplantation. For these purposes, many methods were developed to obtain homogenous dose distribution. The objective of this study was to analyze and confirm the accuracy and the homogeneity of the treatment setup, the parallel opposed lateral technique, currently used in Seoul National University Hospital.
MATERIALS AND METHODS
Surface dose data, measured with a thermoluminescent dosimeter, of 8 patients among 10 patients, who were given total body irradiation with the parallel opposed lateral technique between September 1996 to August 1998, at Seoul National University Hospital were analyzed. Surface doses were measured at the head, neck, axilla, thigh, and ankle level. Surface and midline doses were measured with similar set-up and technique in the Humanoid phantom.
RESULTS
Measured surface doses relative to prescribed dose for the head, neck, axilla, thigh, and ankle level were 91.3+/-7.8, 98.3+/-7.5, 95.1+/-6.3, 98.3+/-5.5, and 95.3+/-6.3%, respectively. The midline doses of the head, neck, axilla, thigh, and ankle level estimated from the surface-to-midline ratios in the Humanoid phantom were 103.4+/-9.0, 107.8+/-10.5, 91.1+/-6.1, 93.8+/-4.5, and 104.5+/-9.3%, respectively. Measured surface doses and estimated midline doses ranged from -8.9% to + 7.8%. Midline doses at the neck and the axilla level deviated more than 5% from the prescribed doses. The difference of the estimated midline doses at the neck and the axilla level and the actual doses were attributed to the thickness differences between the Humanoid phantom and the patients.
CONCLUSION
Distribution of the midline doses as well as the surface doses were measured to be within -8.7 - +7.8% range. Actual dose distribution in the patient is expected to be better than the measured dose range mainly attributed to thickness difference between the patient and the Humanoid phantom.