Head and neck compensation for total body irradiation using opposed laterals.

Using shaped brass compensators that follow the coronal profile of a patient's head and neck, we confirm that adequate compensation can be made to prevent overdosing in these regions when delivering total body irradiation using opposed lateral fields. Initially, these compensators were custom made for each patient, but we have shown that the variation from patient to patient is sufficiently small that individual compensators can be used for a number of different patients without compromising the dose distribution. In a subgroup of 35 patients on whom diode measurements were made, 20 used compensators from the library of approximately 40 compensators made for previous patients and 15 required new compensators to be fabricated. No significant difference (3.4% on average) was observed in the dose distribution. By examining the profiles accumulated from 81 patients, we have shown that the primary difference between patients is not in the shape of the head and neck, but in the distance from the top of the head to the suprasternal notch and in the slope of the shoulders; thus, shaped compensators are not necessary and the same quality of dose homogeneity can be achieved using simple flat brass plates. Further, if the arms are supported so that the slope of the shoulders is constant, a relatively small number (15) of square-ended plates of thickness ranging from 4.0 to 11.0 mm would be sufficient to treat all 81 patients in our sample.