Effect of random seed placement error in permanent transperineal prostate seed implant.
OBJECTIVE
Random seed placement error may adversely effect dose distribution in transperineal prostate seed implants. In this study, we investigated the extent to which individual seed activity influences dose-distribution degradation due to random seed placement error.


METHODS
Separate initial treatment plans were prepared for three prostate sizes, 27.3, 43.2 and 48.9 cc, using 0.35, 0.55 and 0.75 mCi iodine-125 seeds. All stated activities are understood to be apparent activities. The combinations produced a total of nine treatment plans. Each initial treatment plan was subjected to 1000 stochastic three-dimensional Gaussian perturbations of seed location, with a standard deviation of 4mm for a total of 9000 treatment plans. The resulting plans were evaluated for target coverage and urethra involvement.


RESULTS
Satisfactory initial treatment plans were prepared for all prostate sizes and seed activities. All 9000 perturbed treatment plans showed acceptable target coverage under the D90/90 criterion. Some of the perturbed plans for the 27.3 and 43.2 cc prostates with 0.55 and 0.75 mCi seeds failed the V100/90 criterion. Some of the randomly perturbed seed distributions showed significantly increased doses to the urethra relative to the unperturbed treatment plan. This effect was more pronounced with greater seed activity.


CONCLUSIONS
There may be a higher probability of unfavorable target coverage due to random seed placement error when performing transperineal iodine-125 prostate seed implants using seeds with activity greater than 0.35 mCi. There may also be a higher probability of unfavorable urethra involvement when using higher activity seeds.
Bues
Martin
M
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, 77030, USA. mbues@mdanderson.org
Holupka
Edward J
EJ
Meskell
Paul
P
Kaplan
Irving D
ID
D001918:Brachytherapy / Q000379:methods*; D005069:Evaluation Studies as Topic; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D019300:Medical Errors; D011467:Prostate / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000009:adverse effects*; D011881:Radiotherapy, Computer-Assisted
D007457:Iodine Radioisotopes