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Effects of the time interval between prostate brachytherapy and postimplant dosimetric evaluation in community
Peter F Orio1, Gregory S Merrick, Peter Grimm
1Department of Radiation Oncology, Brooke Army Medical Center, Ft Sam Houston, TX, USA.
Objective:
To evaluate the influence of postimplant dosimetric timing on prostate brachytherapy quality in community practice.
Materials And Methods:
The Pro-Qura database was stratified by multiple time intervals between the implant and postimplant dosimetric analysis. Postimplant dosimetry was performed in a standardized fashion. Criteria for implant adequacy included V(100) >80%, D(90) >90%, and V(150) <60% for I-125 and <75% for Pd-103. Implants with V(100) <80% and D(90) <90% were deemed "too cool." Implants were considered "too hot" if D(90) >140% of prescription dose and/or V(150) >150% for I-125 and >75% for Pd-103.
Results:
For I-125, the average V(100) and D(90) increased from 88.6% to 89.8%, and 102.8% to 103.1% for day 0 and day 30 dosimetry. For Pd-103 implants the change was more pronounced, with V(100) and D(90) increasing from 81.6% to 87.8% (P < 0.001) and 88.7% to 100.0% (P < 0.001) for day 0, and day 30, respectively. The percentage of implants considered too cool based on a V(100) and D(90) criteria decreased from 18.8% and 26.9% on day 0 to 11.0% and 19.7% on day 30, respectively. Implants determined to be too hot based on a V(150) >60% (I-125)/>75% (Pd-103) or D(90) >140% were 16.4% and 2.2% on day 0 and 16.0% and 0.7% on day 30, respectively.
Conclusion:
In community-based brachytherapy programs, postimplant dosimetry performed at day 30 resulted in a statistically and clinically significant improvement in postimplant dosimetry compared with day 0. The influence of timing is substantially greater for Pd-103 than I-125.
