Probabilities for secondary cancer incidence have been estimated for a patient 
with Hodgkin's disease for whom treatment has been planned with different 
radiation modalities using photons and protons. The ICRP calculation scheme has 
been used to calculate cancer incidence from dose distributions. For this 
purpose, target volumes as well as critical structures have been outlined in the 
CT set of a patient with Hodgkin's disease. Dose distributions have been 
calculated using conventional as well as intensity-modulated treatment 
techniques using photon and proton radiation. The cancer incidence has been 
derived from the mean doses for each organ. The results of this work are: (a) 
Intensity-modulated treatment of Hodgkin's disease using nine photon fields (15 
MV) results in nearly the same cancer incidence as treating with two opposed 
photon fields (6 MV). (b) Intensity-modulated treatment using nine proton fields 
(maximum energy 177.25 MeV) results in nearly the same cancer incidence as 
treating with one proton field (160 MeV). (c) Irradiation with protons using the 
spot scanning technique decreases the avoidable cancer incidence compared to 
photon treatment by a factor of about two. This result is independent of the 
number of beams used. Our work suggests that there are radiotherapy indications 
in which intensity-modulated treatments will result in little or no reduction of 
cancer incidence compared to conventional treatments. However, proton treatment 
can result in a lower cancer incidence than photon treatment.