Abstract：Objective To study the dosimetric effect of styrofoam on intensity-modulated radiotherapy for nasopharyngeal carcinoma.
Methods Firstly, the effect of different thickness of styrofoam on the central point dose was measured. Then 11 patients with early
nasopharyngeal carcinoma who were fixed with head-neck-shoulder thermoplastic mask combined with styrofoam were selected,
two outer contours were drawn for each patient, one sketched the outer contour of normal human skin, and the other sketched the
styrofoam into the outer contour of human body. Two kinds of intensity modulation plans with different skin contours were designed,
the target dose, organ at risk dose and skin dose of the two plans were compared. Results After adding the styrofoam to the outer
contour, the target dose and the dose of the organ at risk of the nasopharyngeal carcinoma intensity modulated radioeheropy plan
were reduced. The maximum dose of the target area was reduced by 0.56%-0.78%, and the average dose was reduced by 0.63%-0.90%.
The maximum doses to the spinal cord, optic chiasm, optic nerve and other organs at risk were reduced by 0.2%-1.1%. The average
dose of posterior cervical skin increased about 0.8-6.0 Gy. Conclusion The application of styrofoam reduced the target dose and
organ at risk dose of nasopharyngeal carcinoma intensity-modulated plan, and increased the skin dose.
