Contrast-enhanced radiotherapy: feasibility and characteristics of the physical absorbed dose distribution for deep-seated tumors

Abstract

Radiotherapy using kilovoltage x-rays in conjunction with contrast agents incorporated into the tumor, gold nanoparticles in particular, could represent a potential alternative to current techniques based on high-energy linear accelerators. In this paper, using the voxelized Zubal phantom in conjunction with the Monte Carlo code PENELOPE to model a prostate cancer treatment, it is shown that in combination with a 360 degrees arc delivery technique, tumoricidal doses of radiation can be delivered to deep-seated tumors while still providing acceptable doses to the skin and other organs at risk for gold concentrations in the tumor within the range of 7-10 mg-Au per gram of tissue. Under these conditions and using a x-ray beam with 90% of the fluence within the range of 80-200 keV, a 72 Gy physical absorbed dose to the prostate can be delivered, while keeping the rectal wall, bladder, skin and femoral heads below 65 Gy, 55 Gy, 40 Gy and 30 Gy, respectively. However, it is also shown that non-uniformities in the contrast agent concentration lead to a severe degradation of the dose distribution and that, therefore, techniques to locally quantify the presence of the contrast agent would be necessary in order to determine the incident x-ray fluence that best reproduces the dosimetry obtained under conditions of uniform contrast agent distribution.

Gold nanoparticles as novel agents for cancer therapy

“…Furthermore, a commercial kilovoltage X-ray unit with the ability to deliver intensitymodulated radiation is unlikely to be developed. Other studies examined the feasibility of using 150-kVp radiation to treat prostate cancers loaded with a uniform distribution of 1% gold [63]. While it was possible to deliver 72 Gy to the prostate without exceeding tolerance doses to organs at risk (including rectum, bladder, Figure 5.…”

Nanoscale radiation transport and clinical beam modeling for gold nanoparticle dose enhanced radiotherapy (GNPT) using X-rays

“…CERT has been studied by various authors mostly from MC computational and treatment planning standpoints. [30][31][32][33][34][35][36][37][38][39][40] In CERT studies, macroscopic dose enhancement and beam attenuation are computed based on hypothetical planning CT with and without the contrast. Because contrast uptake is typically passive (via tumour microvasculature), endothelial cells are more likely to experience higher dose enhancement than the tumour cells, which are farther away from the microvessels with the contrast.…”

Targeted Radiotherapy with Gold Nanoparticles: Current Status and Future Perspectives

“…Given that the Oraya Therapy system delivers kV energy x-rays and specifically targets the choroidal neovasculature, Ngwa et al proposed and demonstrated in a theoretical study that GNPs would significantly enhance kV stereotactic radiosurgery for neovascular AMD [100], representing a departure from previous GNRT work, mainly focused on potential cancer therapy applications [42,101,154–156]. Justification for pursuing such a targeted RT with GNPs for wet AMD also comes from studies showing that nanoparticles can be specifically targeted to the AMD choroidal neovasculature [143,157,158].…”