title: Cluster pattern analysis of energy deposition sites for the brachytherapy sources 103Pd, 125I, 192Ir, 137Cs, and 60Co.
abstract: Analysing the pattern of energy depositions may help elucidate differences in the severity of radiation-induced DNA strand breakage for different radiation qualities. It is often claimed that energy deposition (ED) sites from photon radiation form a uniform random pattern, but there is indication of differences in RBE values among different photon sources used in brachytherapy. The aim of this work is to analyse the spatial patterns of EDs from 103Pd, 125I, 192Ir, 137Cs sources commonly used in brachytherapy and a 60Co source as a reference radiation. The results suggest that there is both a non-uniform and a uniform random component to the frequency distribution of distances to the nearest neighbour ED. The closest neighbouring EDs show high spatial correlation for all investigated radiation qualities, whilst the uniform random component dominates for neighbours with longer distances for the three higher mean photon energy sources (192Ir, 137Cs, and 60Co). The two lower energy photon emitters (103Pd and 125I) present a very small uniform random component. The ratio of frequencies of clusters with respect to 60Co differs up to 15% for the lower energy sources and less than 2% for the higher energy sources when the maximum distance between each pair of EDs is 2 nm. At distances relevant to DNA damage, cluster patterns can be differentiated between the lower and higher energy sources. This may be part of the explanation to the reported difference in RBE values with initial DSB yields as an endpoint for these brachytherapy sources.
authors.affiliation: Department of Radiology, Oncology, and Radiation Science, Section of Medical Radiation Physics, Uppsala University. Sjukhusfysik. Akademiska Sjukhuset, SE-75185 Uppsala, Sweden.
authors.forename: Fernanda
authors.initials: F
authors.lastname: Villegas
authors.forename: Nina
authors.initials: N
authors.lastname: Tilly
authors.forename: Gloria
authors.initials: G
authors.lastname: Bäckström
authors.forename: Anders
authors.initials: A
authors.lastname: Ahnesjö
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D002588:Cesium Radioisotopes / Q000627:therapeutic use; D016000:Cluster Analysis; D003037:Cobalt Radioisotopes / Q000627:therapeutic use; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D010165:Palladium / Q000627:therapeutic use; D011879:Radiotherapy Dosage
chemical_list: D002588:Cesium Radioisotopes; D003037:Cobalt Radioisotopes; D007457:Iodine Radioisotopes; D007496:Iridium Radioisotopes; D010165:Palladium