title: A Monte Carlo study of I-125 prostate brachytherapy with gold nanoparticles: dose enhancement with simultaneous rectal dose sparing via radiation shielding.
abstract: We investigate via Monte Carlo simulations a new125I brachytherapy treatment technique for high-risk prostate cancer patients via injection of Au nanoparticle (AuNP) directly into the prostate. The purpose of using the nanoparticles is to increase the therapeutic index via two synergistic effects: enhanced energy deposition within the prostate and simultaneous shielding of organs at risk from radiation escaping from the prostate. Both uniform and non-uniform concentrations of AuNP are studied. The latter are modeled considering the possibility of AuNP diffusion after the injection using brachy needles. We study two extreme cases of coaxial AuNP concentrations: centered on brachy needles and centered half-way between them. Assuming uniform distribution of 30 mg g-1of AuNP within the prostate, we obtain a dose enhancement larger than a factor of 2 to the prostate. Non-uniform concentration of AuNP ranging from 10 mg g-1and 66 mg g-1were studied. The higher the concentration in a given region of the prostate the greater is the enhancement therein. We obtain the highest dose enhancement when the brachytherapy needles are coincident with AuNP injection needles but, at the same time, the regions in the tail are colder (average dose ratio of 0.7). The best enhancement uniformity is obtained with the seeds in the tail of the AuNP distribution. In both uniform and non-uniform cases the urethra and rectum receive less than 1/3 dose compared to an analog treatment without AuNP. Remarkably, employing AuNP not only significantly increases dose to the target but also decreases dose to the neighboring rectum and even urethra, which is embedded within the prostate. These are mutually interdependent effects as more enhancement leads to more shielding and vice-versa. Caution must be paid since cold spot or hot spots may be created if the AuNP concentration versus seed position is not properly distributed respect to the seed locations.
authors.affiliation: Brigham and Women's Hospital, Boston, MA, United States of America. Dana Farber Cancer Institute, Boston, MA, United States of America. Harvard Medical School, Boston, MA, United States of America.
authors.forename: D
authors.initials: D
authors.lastname: Brivio
authors.forename: P L
authors.initials: PL
authors.lastname: Nguyen
authors.forename: E
authors.initials: E
authors.lastname: Sajo
authors.forename: W
authors.initials: W
authors.lastname: Ngwa
authors.forename: P
authors.initials: P
authors.lastname: Zygmanski
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006046:Gold; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000627:therapeutic use*; D008297:Male; D053768:Metal Nanoparticles / Q000737:chemistry / Q000627:therapeutic use*; D009010:Monte Carlo Method; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000627:therapeutic use*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012007:Rectum / Q000528:radiation effects; D014521:Urethra / Q000528:radiation effects
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D006046:Gold