Radiobiological Characterization of the Radiosensitization Effects by Gold Nanoparticles for Megavoltage Clinical Radiotherapy Beams

Gold nanoparticles (AuNPs) have been experimentally proven to induce radiosensitization effects particularly for kilovoltage photon beam. Theoretically, AuNPs bombarded with kilovoltage photon beam would increase the photoelectric interactions cross section and hence increase cell death. Despite the intriguing finding, this type of beam is not common in clinical radiotherapy and possesses limited application compare to megavoltage beams. In this study, quantification of the radiosensitization effects acquired from clinical megavoltage photon, electron, and high-dose rate (HDR) gamma rays from Ir-192 source were conducted. In addition, radiobiological characterization of the cell survival curves that are commonly described by linear-quadratic (LQ) model was also evaluated using multi-target (MT) and repairable conditionally repairable (RCR) model. Significant sensitization enhancement ratios (SER) were obtained particularly for 15 MeV electron beams in which the amplification of radiation effects by AuNPs is up to the factor of 1.78. The results also demonstrate validity of experimental models to describe the cell survival curve and determine the radiosensitization effects. However, slight variation was observed for SER values computed from each model which indicate the importance to specify the quantification method. Adoption of radiobiological models and their parameters could also be employed as indicator to explain the mechanistic events in the AuNPs’ radiosensitization effects. As conclusion effective radiosensitization by megavoltage clinical radiotherapy beams could be achieved and precise radiobiological characterization drawn from radiobiological models may provide insight towards radiobiological impacts induced by AuNPs.