Dose planning for prostate cancer with a three-dimensional image

Treatment planning for ultrasound-guided transperineal I-125 permanent prostatic implants is a time consuming task, because this treatment uses many seeds (e.g. 50-80) and there are many solutions (seed positions) for optimizing the dose distribution. In conventional treatment planning for brachytherapy the locations of sources are usually input into a computer manually with reference to two X-ray films. We use so many sources in this treatment planning that we can hardly obtain accurate location of each source. That is, the identification of each seed with two X-ray films is very difficult. Even though we can use X-ray CT images for deciding on the source position, there are artifacts due to the high attenuation material. This paper proposes a method for obtaining accurate locations of radioactive sources from a few projection data (e.g. RPO 60, 30, LPO 60, 30 and 0 deg.) with a reconstruction method. In our method for obtaining actual source positions we use iterative image reconstruction techniques. With these source positions we made a treatment planning system with a personal computer. In this paper we show our preliminary results obtained with the proposed system.