Treatment planning considerations in contrast-enhanced radiotherapy: energy and beam aperture optimization

Abstract

It has been shown that the use of kilovoltage x-rays in conjunction with a contrast agent incorporated into the tumor can lead to acceptable treatment plans with regard to the absorbed dose distribution produced in the target as well as in the tissue and organs at risk surrounding it. In this work, several key aspects related to the technology and irradiation techniques necessary to clinically implement this treatment modality are addressed by means of Monte Carlo simulation. The Zubal phantom was used to model a prostate radiotherapy treatment, a challenging site due to the depth of the prostate and the presence of bony structures that must be traversed by the x-ray beam on its way to the target. It is assumed that the concentration levels of the enhancing agent present in the tumor are at or below 10 mg per 1 g of tissue. The Monte Carlo code PENELOPE was used to model a commercial x-ray tube having a tungsten target. X-ray energy spectra for several combinations of peak electron energy and added filtration were obtained. For each energy spectrum, a treatment plan was calculated, with the PENELOPE Monte Carlo code, by modeling the irradiation of the patient as 72 independent conformal beams distributed at intervals of 5° around the phantom in order to model a full x-ray source rotation. The Cimmino optimization algorithm was then used to find the optimum beam weight and energy for different treatment strategies. It is shown that for a target dose prescription of 72 Gy covering the whole tumor, the maximum rectal wall and bladder doses are kept below 52 Gy for the largest concentration of contrast agent of 10 mg per 1 g of tissue. It is also shown that concentrations of as little as 5 mg per 1 g of tissue also render dose distributions with excellent sparing of the organs at risk. A treatment strategy to address the presence of non-uniform distributions of the contrast agent in the target is also modeled and discussed.

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.…”

Combined Megavoltage and Contrast-Enhanced Radiotherapy as an Intrafraction Motion Management Strategy in Lung SBRT

“…13 X-rays of 220 kVp were used as we have previously shown that a X-ray beam with 220-kVp spectrum is an optimal compromise between penetration at depth and sizable fluence in the energy interval that maximized the absorption of the incident beam by the GNPs. 22…”

Feasibility of robotic stereotactic body radiotherapy of lung tumors with kilovoltage x-ray beams

“…A detailed description of how this algorithm is applied to optimization of radiotherapy treatment plans is given in 14 and. 15 Briefly, the algorithm solves the following set of equations:…”