Auger electron contribution to bromodeoxyuridine cellular radiosensitization.
Halogenated thymidine analogs become incorporated into the DNA of proliferating cells during S-phase and may be used clinically to radiosensitize tumors that are otherwise poorly responsive to radiation. Although radiosensitization has been studied for years, mechanisms of radiosensitization are poorly understood. One possible mechanism involves the release of short range, high-LET, Auger electrons following photoelectric absorption of an X ray by the K-shell of the incorporated halogen. Such absorption occurs only with X ray energies slightly greater than the K-shell binding energy. We report the results of an experiment designed to measure this effect, in which cultured monolayers of Chinese hamster V79 cells, with 32% replacement of thymidine by bromodeoxyuridine (BUdR), were exposed to monoenergetic X rays just below (13.450 KeV) or above (13.490 KeV) the K-edge (13.475 KeV) of bromine. Enhancement ratios calculated in five different ways were slightly increased (3-12%) above the K-edge compared to below. However, only a calculation using a linear-quadratic fit to the data and a surviving fraction of 0.01 demonstrated a statistically significant increased enhancement ratio (12%) above the K-edge. We conclude that Auger electrons produced following photoelectric absorption of X rays by the K-shell of bromine contribute minimally to observed BUdR cellular radiosensitization.
Larson
D
D
Department of Radiation Oncology, University of California, San Francisco 94143.
Bodell
W J
WJ
Ling
C
C
Phillips
T L
TL
Schell
M
M
Shrieve
D
D
Troxel
T
T
D000818:Animals; D001973:Bromodeoxyuridine / Q000378:metabolism / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004583:Electrons; D007399:Interphase; D011838:Radiation-Sensitizing Agents / Q000378:metabolism / Q000494:pharmacology*
D011838:Radiation-Sensitizing Agents; D001973:Bromodeoxyuridine