The Effect of Needle Number on the Quality of High-dose-rate Prostate Brachytherapy Implants Georgina Fröhlich & Péter Ágoston & József Lövey & Csaba Polgár & Tibor Major Received: 13 August 2009 / Accepted: 17 February 2010 / Published online: 25 March 2010 # Arányi Lajos Foundation 2010 AbstractThe aim of this study is to evaluate the effect of the number of needles on the quality of dose distributions in high-dose-rate (HDR) prostate implantsregarding target coverage, dose homogeneity and dose to organs at risk. Treatment plans of 174 implants were evaluated using cumu- lative dose-volume histograms. The plans were divided into three groups according to the number of implanted needles: <15:LNG (low numbergroup),15–17:MNG (medium number group) and >17: HNG (high number group). Treat- ment planning was based on transrectal ultrasound imaging. Dose-volume parameters for target(V90, V100,V150, V200,D90,D min ) and quality indices (DNR, DHI, CI, COIN) were calculated. Maximaldose in reference points and high dose volumes were determined for rectum and urethra. Nonparametric analysis of variance and correlation was used with regard to needle numbers. Between the groupsdifferenceswerefound only in the following parameters: V p was larger when more needles were used with the values of 22.8 cm 3 , 28.0 cm 3 and 30.9 cm 3 for the three groups, and more needles were used when the central cross-section of the prostate was larger. V200 in MNG was lower than in LNG (12%, 14%). Dose to rectum was higher in MNG than in LNG (D 2 : 51%, 47%). Doses to the urethra were higher in HNG than in MNG (D1: 142%, 137%,and D 0.1 : 128%,125%). There was no significant difference in otherparameters. Differentnumberofneedlesresults significant differences in treatment plans.However,the optimal needle number depends on not only the size of th prostate, but also the individual anatomy of the patient. Based on ourresults, in mostcasesthe use of 15–17 needlesseemstoprovideadosimetricallyacceptable treatment plan in HDR prostate implants. Keywords Dose-volume analysis . High-dose-rate . Prostate brachytherapy . Number of needles . Organs at risk . Treatment planning Abbreviations 3D-CRT three dimensional conformal radiotherapy BT brachytherapy CI coverage index COIN conformal index CTV clinical target volume DHI dose homogeneity index DNR dose nonuniformity ratio DVH dose volume histogram EAU European Association of Urologists GEC/ESTRO Groupe Européen de Curiethérapie/ European Society for Therapeutic Radiology and Oncology HDR high-dose-rate OAR organ at risk PDR pulsed-dose-rate PTV planning target volume RD reference dose RT radiotherapy US ultrasound G. Fröhlich School of PhD Studies, Semmelweis University, Üllői út 26., Budapest 1085, Hungary G. Fröhlich (*) : P. Ágoston : J. Lövey : C. Polgár : T. Major Department of Radiotherapy, National Institute of Oncology, Ráth György u. 7-9., Budapest 1122, Hungary e-mail: gfrohlich@oncol.hu Pathol.Oncol.Res.(2010) 16:593–599 DOI 10.1007/s12253-010-9252-z