Use of thermoluminescent dosimetry to verify dose compensation in total body irradiation

For Total Body Irradiation (TBI) the midline dose along the long axis of the body should vary by no more than +/- 10% compared to the dose received at the prescription point. Compensating filters are often made to compensate for contour irregularities. This paper describes an experimental method using Thermoluminescent Dosimetry (TLD) to verify the appropriateness of dose compensation provided by compensating filters. An AP/PA treatment geometry was used with an 18 MV photon beam. TLDs were placed in the midplane and on the surface of an anthropomorphic phantom in five different areas. Three different lead compensating filters were designed to provide proper compensation, overcompensation, and undercompensation. The TLD readings were compared with calculated doses and the measurements correlated favorably. The measurements were sensitive enough to detect dose variations due to improper compensation. These results demonstrate that TLD is a reliable method of verifying dose compensation provided by compensating filters in TBI.