Conformal external radiotherapy of prostatic carcinoma: requirements and preliminary results

The aim of conformal radiotherapy is to deliver with a high precision, a specific dose (which may be a high dose) to a planning target volume, concurrently with irradiating as little as possible healthy tissue and organs at risks. Radiation therapy may suffer from a number of problems that results in both over or under-sizing the irradiation fields, simplifying the irradiation ballistics and delivering an insufficient tumoral dose (to spare critical organs and reduce toxicity). One of these problems lies in the accurate positioning of the planning target volume with respect to the irradiation system, thence in the correct execution of the ballistics. In this paper, we describe a system aiming at achieving a higher overall accuracy in the delivery of prostatic boost for carcinoma of the prostate. The system is based on the use of '2.5D' ultrasonic images for measuring the actual position of the prostate just before the irradiation. Since these images are registered with pre-operative (CT or MRI) images, the position and orientation of the planning target volume is computed with respect to the irradiation system, and can be corrected accordingly. 10 figs