A preliminary comparison of total skin electron treatment techniques to demonstrate the application of a mid-torso phantom for measurement of dose penetration

Abstract

Objectives: In the UK, the treatment of patients with mycosis fungoides using total skin electron (TSE) beam therapy is undertaken using a number of different irradiation techniques. As part of a review of these techniques, a comparative set of measurements would be useful to determine how the techniques differ in terms of dose distribution. A dose penetration intercomparison method that could be used as part of such a study is presented here.

Methods: The dose penetrations for six treatment techniques currently or recently used in four centres in the UK were measured. The variation of dose with skin depth was measured in a WT1 solid water mid-torso phantom. The phantom is portable and suitable to be used in all the techniques. It is designed to hold four small radiochromic film dosemeters to investigate the variation in dose around the mid-torso. For each treatment technique, the phantom was irradiated using the clinical set-up.

Results: The phantom performed well and was able to measure dose penetration and the uniformity of penetration for several treatment techniques.

Conclusion: These preliminary results demonstrate that there is some variation in dose distribution between different TSE treatment techniques and that the phantom could be used in a more comprehensive intercomparison. The results are not intended to demonstrate comprehensively the range of penetration that can be achieved in clinical practice as, for one of the treatment techniques, the penetration is customised for the extent of the disease.

Figure 1

Schematic diagram of the Coventry total skin electron phantom showing radiochromic film positions.

Figure 2

Comparison between MD-55 film measurements and thermoluminescent dosemeter measurements using the rotational technique.

Figure 3

Comparison of mean original depth–dose measurements with those from a repeated exposure by the total skin electron centre.

Figure 4

Comparison of MD-55 film measurements with the standard depth–dose curve for the total skin electron beam.

Figure 5

The depth–dose curves relative to the surface dose at position A for the arcing total skin electron technique.

Figure 6

The depth–dose curves relative to the surface dose at position A for the translational betatron total skin electron technique.

Figure 7

The depth–dose curves relative to the surface dose at position A for the dual angle total skin electron technique.

Figure 8

The depth–dose curves relative to the mean surface dose for the static four-field total skin electron technique.

Figure 9

The depth–dose curves relative to the mean surface dose for the static smoothed total skin electron technique.

Figure 10

The depth–dose curves relative to the surface dose at position A for the rotational total skin electron technique.