Treatment planning for particle radiation therapy

Fast neutrons beams from the new medically dedicated cyclotrons in the US have depth dose characteristics comparable to photon beams from a 6-MV linear accelerator, at best. Treatment planning will have specific difficulties related to the relatively increased radiosensitivities of the brain, spinal cord, lens of the eye, and salivary gland. Therefore, exploitation of the potential biologic advantages compared to high energy photons will extract the price of increased difficulties in treatment planning. Dosimetric advantages of protons and helium ions compared to high energy photons are real and make possible the high-dose irradiation of cancers immediately adjacent to sensitive critical normal structures. Treatment planning and delivery with a precision of less than 2 mm is necessary. Such methods are already operational. Particle radiation therapy facilities are national resources, which can help the clinical radiation oncologist in the unique management of a few, specific problems.