A simplified technique for delivering total body irradiation (TBI) with improved dose homogeneity.

PURPOSE

Total body irradiation (TBI) with megavoltage photon beams has been accepted as an important component of management for a number of hematologic malignancies, generally as part of bone marrow conditioning regimens. The purpose of this paper is to present and discuss the authors' TBI technique, which both simplifies the treatment process and improves the treatment quality.

METHODS

An AP/PA TBI treatment technique to produce uniform dose distributions using sequential collimator reductions during each fraction was implemented, and a sample calculation worksheet is presented. Using this methodology, the dosimetric characteristics of both 6 and 18 MV photon beams, including lung dose under cerrobend blocks was investigated. A method of estimating midplane lung doses based on measured entrance and exit doses was proposed, and the estimated results were compared with measurements.

RESULTS

Whole body midplane dose uniformity of ±10% was achieved with no more than two collimator-based beam modulations. The proposed model predicted midplane lung doses 5% to 10% higher than the measured doses for 6 and 18 MV beams. The estimated total midplane doses were within ±5% of the prescribed midplane dose on average except for the lungs where the doses were 6% to 10% lower than the prescribed dose on average.

CONCLUSIONS

The proposed TBI technique can achieve dose uniformity within ±10%. This technique is easy to implement and does not require complicated dosimetry and/or compensators.