A dosimetric study of skin toxicity induced by 3-D conventional and intensity-modulated radiotherapy techniques using immobilization mask for treatment of head-and-neck (nasopharyngeal cancer) carcinoma: a prospective study

Background

The purpose of this study was to investigate variations in surface dose, with and without the use of a Klarity® Mask (Orfit Industries America, Wijnegem, Belgium), using intensity-modulated radiotherapy (IMRT) and 3-D conventional radiotherapy (3D-CRT).

Materials and methods

Thermoluminescent dosimeters (TLDs) together with a phantom were used to examine acute skin toxicity during nasopharyngeal cancer treatment. These plans were sequentially delivered to the perspex phantom. Dosimeters were placed in five fixed regions over the skin. A Klarity mask for immobilization was used for covering the head, neck, and shoulder. The phantom was irradiated with and without a Klarity Mask, using IMRT and 3D-CRT, respectively.

Results

The Klarity mask increased the skin doses for IMRT and 3D-CRT approximately 18·6% and 8·6%, respectively, from the prescribed maximum skin dose using treatment planning system (TPS). Additionally, the average percentage dose between IMRT and 3D-CRT received on the surface region was 30·9%, 24·9% with and without Klarity mask respectively. The average percentage dose received on surfaces from the total therapeutic dose 70 Gy, without using the mask was 7·7% and 5·7%, for IMRT and 3D-CRT, respectively. The TPS overestimated the skin dose for IMRT planning by 20%, and for 3D-CRT by 16·6%, compared with TLD measurements.

Conclusions

The results of this study revealed that IMRT significantly increases acute skin toxicity, compared with CRT. Although it is recommended to use Klarity mask as a sparing tool of normal tissue, it increases the risk of skin toxicity. In conclusion, skin dose is an important issue of focus during radiotherapy.