Effect of External Targeted Radiotherapy on Dosimetry Due to Rapid Clearance of Gold Nanoparticles
Progress in the application of gold nanoparticles (GNPs) in the biomedical research of small animals has substantially advanced in recent years. Studies suggest a high potential of applying nanoparticle technology to the targeted drug delivery and sensitization system for external beam radiotherapy. Therefore, a scenario of integrated cancer therapy is highly expected, in which patients are treated with administration of GNP media and external beam radiotherapy simultaneously. However, a possible problem is that GNPs may be rapidly transported through the circulatory system to the kidneys, accumulating in the bladder. As a consequence, dosimetric variations could occur as GNP media are absent in the treatment planning, but present in the bladder at a high density during treatment delivery. This study investigates the effect of the rapid clearance of GNPs on dosimetric variations and biological consequences. A prostate phantom and five clinical cases are included. Intensity-modulated radiation therapy (IMRT) and RapidArc are used as the treatment techniques. Dose-volume histograms show that the amounts of dose delivered to the prostate planning target volume (PTV), bladder, and rectum decrease. Linear correlations between the concentration of GNP media in the bladder and the corresponding percentage changes of mean dose at the PTV are formulated. For biological consequences, high-dose regions in the mucosal areas of the bladder and rectum are identified. To manage a dosimetric variation of less than 3 % for the prostate PTV, the phantom study results suggest an upper threshold of 97.48 mg-Au/mL with IMRT and 168.22 mg-Au/mL with RapidArc, whereas the clinical study suggests 131.58 mg-Au/mL with RapidArc.