Dedicated treatment planning system for the evaluation of the doses delivered to the whole patient body during radiotherapy

Describe the principles and report the preliminary results on dose distributions obtained with a new generation of treatment planning system (TPS) designed to provide, in addition to the dose distributions within the target-volumes, the magnitude of the doses to distant healthy tissues in the course of common radiotherapy procedures. The system is made of (1) a library of adjustable whole-body patient models in radiotherapy treatment position, allowing different patient anatomies to be simulated, (2) a global-beam model allowing the dosimetric data of the irradiation beams to be extended to the whole body and (3) a TPS modified to handle the two first modules in order to produce the dose distributions within the target-volumes and in any organ at distance. Our preliminary results indicate that in an adult male patient treated by radiotherapy for Hodgkin disease using two opposed 6 MV photon beams, the mean doses to distant organs are: 0.9 % of the target volume dose for the pituitary gland, 0.40% to 3.4% for the kidneys, 0.43% for the prostate, and at larger distance, 0.07% and 0.02 % at the level of the knees and the feet respectively. Although the development of our system is still in progress, the preliminary results are encouraging. This systematic evaluation of the low doses delivered at distance of the targetvolumes is a basic requirement for prospective studies of longterm risks of modern radiotherapy procedures.