title: Impact of interseed attenuation and tissue composition for permanent prostate implants.
abstract: The purpose is to evaluate the impact of interseed attenuation and prostate composition for prostate treatment plans with 125I permanent seed implants using the Monte Carlo (MC) method. The effect of seed density (number of seeds per prostate unit volume) is specifically investigated. The study focuses on treatment plans that were generated for clinical cases. For each plan, four different dose calculation techniques are compared: TG-43 based calculation, superposition MC, full MC with water prostate, and full MC with realistic prostate tissue. The prostate tissue description is from the ICRP report 23 (W. S. Snyer, M. J. Cook, E. S. Nasset, L. R. Karkhausen, G. P. Howells, and I. H. Tipton, "Report of the task group on reference man," Technical Report 23, International Commission on Radiological Protection, 1974). According to the comparisons, the seed density has an influence on interseed attenuation. A plan with a typical low seed density (42 0.6 mCi seeds in a 26 cm3 prostate) suffers a 1.2% drop in the CTV D90 value due to interseed attenuation. A drop of 3.0% is calculated for a higher seed density (75 0.3 mCi seeds, same prostate). The influence of the prostate composition is similar for all seed densities and prostate sizes. The difference between MC simulations in water and MC simulations in prostate tissue is between 4.4% and 4.8% for the D90 parameter. Overall, the effect on D90 is ranging from 5.8% to 12.8% when comparing clinically approved TG-43 and MC simulations in prostate tissue. The impact varies from one patient to the other and depends on the prostate size and the number of seeds. This effect can reach a significant level when reporting correlations between clinical effect and deposited dose.
authors.affiliation: Département de Radio-Oncologie et Centre de Recherche en Cancérologie, CHUQ Pavillon L'Hôtel-Dieu de Québec, 11 Côte du Palais, Québec, Quebec G1R 2J6, Canada. francois.carrier.chum@ssss.gouv.qc.ca
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Carrier
authors.forename: Luc
authors.initials: L
authors.lastname: Beaulieu
authors.forename: François
authors.initials: F
authors.lastname: Therriault-Proulx
authors.forename: René
authors.initials: R
authors.lastname: Roy
mesh_terms: D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D003198:Computer Simulation; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D008954:Models, Biological; D009010:Monte Carlo Method; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011874:Radiometry / Q000379:methods*; D012062:Relative Biological Effectiveness; D014867:Water / Q000737:chemistry
chemical_list: D007457:Iodine Radioisotopes; D014867:Water