Oral & Poster Presentation – Physics Abstracts Archive
UK & Ireland Prostate Brachytherapy Conference 2016
Abstract number 7
Review of the dosimetry of a nine year 125-Iodine seeds prostate brachytherapy programme
Kleefeld C*; Zuchora A*; Fahy L*; Moore M*; Sullivan F*
*University Hospital Galway, Galway, Ireland
AIMS/INTRODUCTION: University Hospital Galway (UHG) commenced 125-Iodine seeds permanent implantations of the prostate in January 2007. In July 2015 the seed model was changed from Oncura/Amersham Model 6711 to Bebig Isoseed 125.S06. A retrospective study is presented reviewing the progression of the implantation dosimetry over time.
MATERIALS/METHODS: The study is based on 463 consecutive monotherapy patients treated with permanent 125-I radioactive seeds. Single seed deposition was performed using a MICK applicator. In an initial approach D90, the dose level covering 90% of the prostate volume, as well as D30 (urethra), the dose level covering 30% of the prostatic urethra volume were chosen as quality parameters. The dose-volume histogram parameters were derived from intraoperative ultrasound images. Annual descriptive statistics, that is, mean, median, and interquartile range have been calculated for the years 2007 to 2015.
RESULTS: With a nominal prescription dose of 160Gy to the prostate capsule, the annual average of D90 in 2007 of 150Gy increases to a plateau value of about 170Gy in the years 2011 to 2014. Over the entire time period the annual spread of D90 expressed as the interquartile range decreases from 40Gy in 2007 to a plateau value of about 10Gy (2011-2015). Similarly, D30 (urethra) levels off to mean values of 175Gy and minimum interquartile ranges of 10Gy (2013-2015).
CONCLUSION: D90 and D30 demonstrate a dosimetric learning effect. However, the D30 mean value was always less than the recommended dose of 181Gy. Following the source model change no differences in D90 and D30 have been observed. The data will be discussed with regard to user variability and treatment protocol changes.