Geometrical reconstruction and manual dosimetry of interstitial iridium implants

The dosimetric calculations in several planes using treatment planning systems give a clear perception of dose distribution of the implant. It is impractical to do the complete dosimetry where the facility of treatment planning system is not available or in case of failure of such system. Taking this into consideration a method of reconstruction of geometry of implant using orthogonal films and manual method of dosimetry are described based on Paris System. Initially a double plane implant geometry was constructed in a phantom and sets of orthogonal films were taken by orienting the phantom at different angles in order to simulate possible implant geometry inside the patient. Using the set of orthogonal X-rays the X and Z coordinates were obtained. The Plot of X versus Z will give the reconstructed geometry of the implant. This was found to match fairly with the transverse section taken from CT scan. Later the method was also confirmed with actual clinical implants. (author). 8 refs., 2 figs., 1 tab