Implications of radiation induced apoptosis on calculated radial cell inactivation for a linear 192Ir source.
The cell inactivation probability as a function of the radial distance from a 4 cm linear, low dose rate (LDR) 192Ir source was calculated using a modified linear-quadratic (LQ) equation, taking into account the effect of radiation induced apoptosis. As a measure of the therapeutic range of the source, the radial distance from the midpoint of the central axis of the source to the point of 50% inactivation probability was calculated. It was found that the therapeutic range increased with increasing values of the maximal radiation induced apoptotic fraction, Fa; but only as long as the ratio between the apoptotic cell kill susceptibility, zeta, and the alpha value is larger than unity. If the ratio was smaller than unity, a decrease in therapeutic range was found. The slope of the radial cell inactivation probability curve was measured as the distance between the point of 10% and 90% inactivation probability. The slope was found to be fairly independent of the repair half-time, T(1/2), but became steeper with decreasing values of Fa.
Olsen
D R
DR
Department of Medical Physics, The Norwegian Radium Hospital, The College of Oslo, Norway. d.r.olsen@dnr.uio.no
D017209:Apoptosis / Q000528:radiation effects*; D001918:Brachytherapy; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D007496:Iridium Radioisotopes / Q000008:administration & dosage*; D011853:Radiobiology; D011879:Radiotherapy Dosage
D007496:Iridium Radioisotopes