Computer calculations in interstitial seed therapy: II. Dose control after seed implantation

After seed implantation exact dose control is desirable. In clinical practice a measurement of dose in a depth of tissue is hardly possible. A measurement may be possible by the method of three-dimensional reconstruction of the seed arrangement in water. To reconstruct an identical seed arrangement one must know the co-ordinates of the seeds. How can one measure the co-ordinates of the seeds in tissue? Several methods are given in the literature (Adams and Meurk, 1964; Nuttall and Spiers, 1946; Pierquin et al, 1960) but all seem to be somehow imperfect, because of the difficulties in correcting faults of projection and identifying individual seeds. The laborious procedure of correcting manually for projection enlargement, identifying of seeds and correcting for adjustment faults in making radiographs may be the reason for such methods not being used in routine practice. A computer programme has been written to correct central projection, to correct the two most important adjustment faults and to identify seeds in perpendicular radiographs. The method of determining the dose distribution after seed implantation consists of two parts, a manual part and a computer part. The manual part has three working steps: (1) Making radiograms in perpendicular planes of the subject, (2) Measuring co-ordinates of seed pictures in the radiographs, (3) Feeding the measured and other data into the computer