Dosimetric and microdosimetric study of contrast-enhanced radiotherapy with kilovolt x-rays

Abstract

Kilovolt x-rays are clearly suboptimal compared to MV photon beams for radiotherapy of deep-seated tumours because of the increased attenuation in tissue, causing a rapid dose fall-off. This picture could change drastically when tumours can be labelled with contrast medium, containing high atomic number elements. This causes a significant dose enhancement to the tumour by exploiting the high cross sections for the photo-electric effect for kV x-rays. In this work, we have investigated the dosimetric and microdosimetric characteristics of kV contrast-enhanced radiation therapy (CERT) for different photon energies, contrast-medium concentrations and types (I and Gd). Two idealized patient treatment plans (head and lung) for irradiation with CT-arc beams were calculated. It is shown that the dose enhancement in tumours can be highly significant (up to about sixfold for realistic 80-120 kVp x-ray spectra and an iodine concentration of 50 mg ml-1) but that dose homogeneity in the tumour depends on photon energy, contrast-medium concentration and type, and irradiation scheme. An attempt to optimize the irradiation scheme is discussed. The microdosimetric study of the dose mean lineal energy shows that radiation quality changes in the contrast-medium-labelled region compared to homogeneous tissue are fairly small and limited to 10%. It is concluded that kV-CERT is a promising radiotherapy technique, provided contrast medium can be delivered reliably to tumours.

Silver nanoparticles outperform gold nanoparticles in radiosensitizing U251 cells in vitro and in an intracranial mouse model of glioma

“…32 It is widely accepted that the use of low-energy kilovoltage beams could maximize tumor dose enhancement; 33,34 however, their inherent shallow penetration and significant dose heterogeneity inside the target tumor hinder the translation of this technology to the clinic. 35 Compared with kilovoltage, the clinically relevant megavoltage X-ray energies have relatively limited application in the field of nanoparticle-based radiotherapy. In this study, we demonstrated the efficacies of AuNPs and AgNPs in conjunction with a single moderate dose of 6 MV radiation with the latter being the stronger.…”

Increased apoptotic potential and dose‐enhancing effect of gold nanoparticles in combination with single‐dose clinical electron beams on tumor‐bearing mice

“…In theory, loading high Z materials into the tumor could result in greater photoelectric absorption within the tumor than in surrounding tissues, and thereby enhance the dose delivered to a tumor during radiation therapy. At least 20 years ago, it was noted in vitro that this effect might be employed to enhance radiotherapy for cancer.(1) Accumulating studies have demonstrated the dose enhancement caused by high Z materials in kilovoltage beams (2)(3)(4) and in megavoltage beams.(5-8) Moreover, enhanced cell killing was also observed when cells were irradiated adjacent to high Z materials by kilovoltage X-rays. (9)(10)(11)(12) In clinical practice, electron beams from linear accelerators have increasingly taken the place of kilovoltage X-ray beams for skin and subcutaneous tumors because they offer distinct advantages in terms of dose uniformity in the target volume and in minimizing the dosage to deeper tissues.…”

“…(1) Accumulating studies have demonstrated the dose enhancement caused by high Z materials in kilovoltage beams (2)(3)(4) and in megavoltage beams.…”

“…At least 20 years ago, it was noted in vitro that this effect might be employed to enhance radiotherapy for cancer. (1) Accumulating studies have demonstrated the dose enhancement caused by high Z materials in kilovoltage beams (2)(3)(4) and in megavoltage beams. (5)(6)(7)(8) Moreover, enhanced cell killing was also observed when cells were irradiated adjacent to high Z materials by kilovoltage X-rays.…”

“…The use of kilovoltage X-rays produces significant dose heterogeneity inside the target tumor. (4,14) To be clinically useful, a radiosensitizer and/or dose enhancer should significantly increase the therapeutic ratio and should be readily available, easily utilized, and non-toxic. Gold (Au; Z = 79) or nanogold (gold nanoparticles, AuNP) showed doseenhancing effects in cell experiments, (15) the murine model, (16) and through Monte Carlo calculations.…”