title: Transit dose comparisons for60Co and192Ir HDR sources.
abstract: The goal of this study is to evaluate the ambient dose due to the transit of high dose rate (HDR)60Co sources along a transfer tube as compared to192Ir ones in a realistic clinical scenario. This goal is accomplished by evaluating air-kerma differences with Monte Carlo calculations using PENELOPE2011. Scatter from both the afterloader and the patient was not taken into account. Two sources, mHDR-v2 and Flexisource Co-60, (Elekta Brachytherapy, Veenendaal, the Netherlands) have been considered. These sources were simulated within a standard transfer tube located in an infinite air phantom. The movement of the source was included by displacing their positions along the connecting tube from z  =  -75 cm to z  =  +75 cm and combining them. Since modern afterloaders like Flexitron (Elekta) or Saginova (BEBIG GmbH) are able to use equally192Ir and60Co sources, it was assumed that both sources are displaced with equal speed. Typical HDR source activity content values were provided by the manufacturer. 2D distributions were obtained with type-A uncertainties (k  =  2) less than 0.01%. From those, the air-kerma ratio60Co/192Ir was evaluated weighted by their corresponding typical activities. It was found that it varies slowly with distance (less than 10% variation at 75 cm) but strongly in time due to the shorter half-life of the192Ir (73.83 d). The maximum ratio is located close to the tube. It reaches a value of 0.57 when the typical activity of the sources at the time when they were installed by the vendor was used. Such ratio increases up to 1.28 at the end of the recommended working life (90 d) of the192Ir source.60Co/192Ir air-kerma ratios are almost constant (0.51-0.57) in the vicinity of the source-tube with recent installed sources. Nevertheless, air-kerma ratios increase rapidly (1.15-1.29) whenever the192Ir is approaching the end of its life. In case of a medical event requiring the medical staff to access the treatment room, these ratios indicate that the dosimetric impact on the medical team will be lower, with a few exceptions, in the case of60Co-based HDR brachytherapy as compared to192Ir-based one when typical air-kerma strength values are considered.
authors.affiliation: Department of Atomic, Molecular and Nuclear Physics, University of Valencia, 46100 Burjassot, Spain.
authors.forename: Vicent
authors.initials: V
authors.lastname: Giménez-Alventosa
authors.forename: Javier
authors.initials: J
authors.lastname: Vijande
authors.forename: Facundo
authors.initials: F
authors.lastname: Ballester
authors.forename: Jose
authors.initials: J
authors.lastname: Perez-Calatayud
mesh_terms: D001918:Brachytherapy; D003037:Cobalt Radioisotopes; D007496:Iridium Radioisotopes; D009010:Monte Carlo Method; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*
chemical_list: D003037:Cobalt Radioisotopes; D007496:Iridium Radioisotopes