Minimizing the number of implantation needles for prostate (125)I brachytherapy: an investigation of possibilities and implications.
OBJECTIVE
Reduction of the number of implantation needles for prostate brachytherapy will shorten the duration of implantation procedures and possibly reduce trauma-related morbidity. The purpose of this study was to investigate possibilities for the minimization of the number of needles and to investigate the consequences for the dose distribution.


METHODS
A planning study for six different prostate volumes was performed. The number of needles was minimized by changing fixed 1cm interseed spacing to free interseed spacing within the needles and by increasing the seed activity. Dose-volume parameters of prostate and organs at risk (OAR) bladder, rectum, and urethra were determined. For plans with different needle and seed configurations, the sensitivity for random seed placement inaccuracies was tested. Dose distributions of realized implants based on fixed (n=21) and free interseed spacing (n=21) were compared.


RESULTS
The average number of needles (±1 standard deviation) could be reduced from 18.8±3.6 to 12.7±2.9 (-33%) when changing from fixed interseed spacing to free interseed spacing and subsequently to 7.3±1.0 (-42%) by increasing the seed strength from 0.57U to 1.14U. These needle reductions resulted in increased dose inhomogeneity within the prostate and increased sensitivity of dose-volume parameters of the OAR for random geometrical inaccuracies. Introduction of free interseed spacing in our clinic resulted in very satisfactory dose coverage of the prostate (D(90)=172±17Gy), while the average number of needles was reduced by 30%.


CONCLUSIONS
Substantial reduction of the number of implantation needles is possible without compromising adequate dose coverage of the prostate. However, the chance of an unpredicted high dose to the OAR increases as fewer needles are used.
Steggerda
Marcel J
MJ
Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands. m.steggerda@nki.nl
van der Poel
Henk G
HG
Moonen
Luc M F
LM
D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000627:therapeutic use*; D008297:Male; D009339:Needles; D058958:Organs at Risk / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects; D014521:Urethra / Q000528:radiation effects; D001743:Urinary Bladder / Q000528:radiation effects
D007457:Iodine Radioisotopes