Source localization from axial image sets by iterative relaxation of the nearest neighbor criterion.

The use of axial image sets has become widely used to localize interstitial brachytherapy sources. One application of this method of localization is to perform post-implant dosimetry following transperineal interstitial permanent prostate brachytherapy (TIPPB) where the target structure and the source locations are displayed on the same image. The design of an appropriate scanning sequence often results in abutting slices of an intermediate slice width (3, 4, or 5 mm). Because a single source may be imaged on more than one slice, the resultant scans always show many more source locations than actual sources implanted. The physicist is then faced with the tedious task of determining which sources appear on more than one slice and deciding which source locations to eliminate from the data set. We have developed an algorithm, similar to one employed by Roy et al., which automates this process by relaxing the nearest neighbor criterion until the number of sources is reduced to either the number of sources implanted or the number counted on a projection radiograph. This paper details this algorithm and the results of its application to phantom studies, comparing to known source locations, as well as clinical studies, comparing to orthogonal film source localization, on a series of ten patients. Phantom studies demonstrate the superiority of the algorithm over orthogonal film reconstruction, locating 100% of the sources within 5 mm of the actual location as compared to 66% for the paired radiographs. The clinical study findings are commensurate with these results, with 72% of the sources on average located within 5 mm of the corresponding source in the other data set. The positive correlation of the quality of the orthogonal film reconstruction results with the quality of the coregistration results suggests that differences in registration between the two data sets may be due primarily to the uncertainties in the orthogonal film reconstruction.

[1]  R L Siddon,et al.  Two-film brachytherapy reconstruction algorithm. , 1985, Medical physics.

[2]  G T Chen,et al.  A new source localization algorithm with no requirement of one-to-one source correspondence between biplane radiographs. , 1996, Medical physics.

[3]  M A Moerland,et al.  Evaluation of permanent I-125 prostate implants using radiography and magnetic resonance imaging. , 1997, International journal of radiation oncology, biology, physics.

[4]  M D Altschuler,et al.  Rapid, accurate, three-dimensional location of multiple sees in implant radiotherapy treatment planning. , 1983, Physics in medicine and biology.

[5]  H. A. Hughes.  Accuracy of foreign body localisation from tube-shift radiographs. , 1956, The British journal of radiology.

[6]  H I Amols,et al.  A three-film technique for reconstruction of radioactive seed implants. , 1981, Medical physics.

[7]  J J Prete,et al.  Comparison of MRI- and CT-based post-implant dosimetric analysis of transperineal interstitial permanent prostate brachytherapy. , 1998, Radiation oncology investigations.

[8]  L. Fitzgerald,et al.  Analysis of errors in three-dimensional reconstruction of radium implants from stereo radiographs. , 1975, Radiology.

[9]  M S Rosenthal,et al.  An automatic seed identification technique for interstitial implants using three isocentric radiographs. , 1983, Medical physics.

[10]  C C Ling,et al.  A CT-based evaluation method for permanent implants: application to prostate. , 1993, International journal of radiation oncology, biology, physics.

[11]  B. Prestidge,et al.  Clinical impact of implementing the recommendations of AAPM Task Group 43 on permanent prostate brachytherapy using 125I. American Association of Physicists in Medicine. , 1998, International journal of radiation oncology, biology, physics.

[12]  M D Altschuler,et al.  Semiautomated matching and seed position location for implanted ribbons. , 1994, Medical physics.

[13]  C A Kelsey,et al.  The effect of geometric errors in the reconstruction of iridium-192 seed implants. , 1982, Medical physics.

[14]  D D Leavitt,et al.  Computed tomography treatment planning in IR-192 brachytherapy in the head and neck. , 1992, International journal of radiation oncology, biology, physics.

[15]  P J Biggs,et al.  Geometric reconstruction of seed implants using a three-film technique. , 1983, Medical physics.

[16]  L. Anderson,et al.  Dosimetry of interstitial brachytherapy sources: Recommendations of the AAPM Radiation Therapy Committee Task Group No. 43 , 1995 .

[17]  P. Schönemann,et al.  A generalized solution of the orthogonal procrustes problem , 1966 .