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Is a loose-seed nomogram still valid for prostate brachytherapy in a stranded-seed era?
Rajat J Kudchadker1, David A Swanson, Deborah A Kuban
1Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA.
Purpose:
To characterize the amount of activity required to treat the prostate with stranded (125)I radioactive seeds and compare our stranded data with the amount of activity recommended when individual seeds are implanted using a Mick applicator.
Methods And Materials:
Data from two groups of patients at The University of Texas M. D. Anderson Cancer Center who were treated with prostate brachytherapy as monotherapy were analyzed. The first group included 100 patients implanted with individual seeds in 2000 and 2001. The second group comprised 81 patients for whom stranded seeds were implanted in 2006 and 2007. Seeds in both groups were (125)I seeds with an air kerma strength of 0.497 U per seed (0.391 mCi per seed). The prescribed dose to planning target volume was 145 Gy.
Results:
The total implanted activity and the number of seeds used were significantly lower in the second group (p < 0.0001) than in the first group. The reduction in activity in the stranded-seed group was approximately 23% for a 20-cm(3) prostate and approximately 15% for a 60-cm(3) prostate. With equivalent activity between the two groups, the stranded-seed treatment covered a larger treatment volume with the prescribed dose.
Conclusions:
The amount of activity required to effectively treat a prostate of a given volume was lower with stranded seeds than with loose seeds. Our experience suggests that prostate brachytherapy that uses stranded seeds leads to a more efficient implant with fewer seeds and lower overall activity, resulting in improved homogeneity.
