Skin dose distributions between Stanford and rotational techniques in total skin electron therapy (TSET).

PURPOSE

Total skin electron therapy (TSET) has proven to be one of the most effective treatments for advanced-stage cutaneous T-cell lymphoma. Two most used techniques are the Stanford six-field and rotational techniques. This study compares patient skin dose distributions as a function of depth between these two techniques.

METHODS

The EGSnrc system was used to simulate electron beams and calculate patient dose distributions. The calculations assumed the same patient standing on a platform, and the patient's different postures were ignored for the Stanford technique in the comparison of dose distributions. The skin doses were analyzed as a function of skin depth-dose coverage and evaluated using dose-volume-histograms (DVH). The comparisons were performed in three realistic clinical settings in which dual-field were used for patients treated at extended distances of 316 and 500 cm, and a single field was used at 700 cm. In all cases the realistic patient treatment beam delivery geometry was simulated.

RESULTS

Although small dose differences were observed in some local areas, no clinically significant differences were found in the patient 3D dose distributions between the Stanford and rotational techniques. Virtually the same DVH curves between two the techniques were observed for mean dose to skin depth of 0-5, 5-10, and 10-15 mm from the skin surface, respectively. It is found that the skin depth dose coverage is 2 mm shallower for patient treatment at 500 cm compared to at 316 cm due to the additional air attenuation. However, very similar dose coverage and uniformity can be achieved at these two different extended treatment distances by adjusting the thickness of acrylic scatter plate. Adequate thickness of a scattering plate improves the skin dose uniformity.

CONCLUSION

Both the Stanford and rotational techniques deliver very similar skin dose coverage in DVH plots, and only small differences are seen in local areas. It is worth to emphasize that the DVH is a graphical representation of the distribution of dose within a structure, and it does not contain spatial information. Therefore, comparison of entire skin dose using DVH may mask some variations at different locations of the surface area. In addition, the comparison did not consider different patient postures of the Stanford technique. Including the different patient postures in the calculation may affect the result of doses to the limbs.