Abstract: This bolus, which is for radiation therapy, can be deformed to match the shape of a human body surface, and has little deformation during therapy. The bolus forming material is a rubber composition containing ethylene-propylene rubber and a temperature-sensitive material. The bolus forming material has a JIS type A hardness of 20 or higher at 30° C., and thus is not susceptible to deformation. The bolus forming material has a JIS type E hardness of 10 to 60 at 70° C., and thus easily deforms. The bolus forming material shifts the peak of the percentage depth dose for electron beams and X-rays in the beam source direction at 0.8 to 1.2 times the thickness thereof. Therefore, the bolus forming material has dose characteristics in the depth direction that are substantially the same as a human body. After a sheet of the bolus forming material is heated to around 70° C., the sheet deforms.