Abstract
Depth dose distribution of a proton beam with the best quality has been calculated for a small field. The normal tissue dose around a target irradiated by a proton beam was estimated based on irradiation conditions for a few typical cases of small lung cancer treated by multi-portal irradiation. The surface dose at each port was estimated to be below 10% of the maximum dose when 6 portal irradiations doses were applied to a target smaller than 3 cm in diameter. However the relative dose averaged for a “dose increasing region” was calculated to exceed 10%. Rusults indicate the need for a precise rotational irradiation system when designing a dedicated proton radiotherapy facility.
