| The use of a shell has made it unnecessary to mark the skin in radiation therapy for head and neck cancers. However, a serious problem is that secondary electrons from the shell frequently cause radiation dermatitis. The increase in surface dose is a major problem in using a shell, and several trials have been carried out to overcome this problem. In this study, the result of measurement with 6 MV x-rays demonstrated that the use of a shell caused the surface dose to increase 2.9 times in a 5 x 5 cm2 field and 2.3 times in a 10 x10 cm2 field. With a pair of lateral opposed fields for neck cancers, the angle of incidence was approximately 45 degrees. In a comparison of the perpendicular incidence of an open field and 45-degree incidence of a shell field, it was found that the surface dose increased 3.6 times in the 5x5 cm2 field and 2.9 times in the 10 x10 cm2 field. Considering patients' quality of life, we decided to remove the shell from the radiation field and also not to mark the skin, and devised a new method of precutting the shell and developed supplemental equipment. The result of measurement of the shell with our supplemental devices suggested that it would be useful in decreasing surface dose in patients with head and neck cancers. |
