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MO‐D‐T‐6E‐08: Derivation of the Relative Biological Effectiveness of High Dose Rate 252Cf Brachytherapy
Author(s) -
Rivard M,
Zinkin H,
Melhus C
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1998278
Subject(s) - relative biological effectiveness , neutron , nuclear medicine , dosimetry , radiobiology , physics , radiochemistry , irradiation , nuclear physics , chemistry , medicine
Purpose: While there is significant clinical experience using both low‐ and high‐dose rate (HDR)252 Cf brachytherapy, there is minimal data regarding values for the neutron relative biological effectiveness (RBE) with both modalities. The aim of this research was to derive a radiobiological model for252 Cf neutron RBE and to compare these results with neutron RBE values used clinically in Russia. Method and Materials: The linear‐quadratic (L‐Q) model was used as the basis to characterize cell survival following irradiation, with identical cell killing rates (S N = Sγ) between252 Cf neutrons and photons used for derivation of RBE. Using this equality, a relationship among neutron dose and L‐Q radiobiological parameter (i.e., α N , β N , α γ , β γ ) was obtained without need to specify the photon dose. These results were used to derive the252 Cf neutron RBE which was then compared with Russian neutron RBE values. The252 Cf neutron RBE was determined after incorporating the L‐Q radiobiological parameters obtained from cell survival studies with fast neutrons and teletherapy photons. Results: For single‐fraction HDR neutron doses of 0.5, 1.0, and 1.5 Gy, the total (neutron plus photon) doses were 3.5, 6.0, and 8.1 Gy, with252 Cf neutron RBE values of 6.4, 5.5, and 4.9, respectively. Russian clinicians obtained HDR252 Cf neutron RBE values ranging from 7 to 3 for similar doses and fractionation schemes, and observed that252 Cf neutron RBE increases with the number of fractions and is dose rate dependent. A value of 5 was obtained for HDR252 Cf neutron RBE. Conclusion: The methodology presented herein presents a reasonable technique to utilize well‐characterized radiobiology parameters from radiation sources having similar radiobiological properties towards obtaining calculated values for RBE. Using these relationships, results were in general concordance with252 Cf RBE values obtained from Russian clinical experience.