Real-Time Treatment Planning Optimisation for Brachytherapy

In this paper, we present an integrated system for real-time dose distribution calculation and treatment planning optimisation for brachytherapy of prostate cancer, with a special emphasis on the visual integration of the dosimetry and target images obtained from the open magnetic resonance system. This system involves a fast method to calculate dose distributions of multiple concurrent radioactive sources, based on the combination of elements from a database of pre-calculated dose distribution maps for single sources, combined linearly to provide the final dose distribution map. Simulated annealing, in conjunction with the inverse planning method, is used to determine the source dwell times at pre-selected locations in order to optimally irradiate thetumour while preserving the surrounding healthy tissues. This algorithm, implemented in FORTRAN, is integrated into a computer-assisted treatment planning tool, written in JAVA, using the runtime class and RMI API of Java. The whole system is now under clinical testing at the Geneva University Hospital

Absolute depth-dose-rate measurements for an 192Ir HDR brachytherapy source in water using MOSFET detectors

Reported MOSFET measurements concern mostly external radiotherapy and in vivo dosimetry. In this paper, we apply the technique for absolute dosimetry in the context of HDR brachytherapy using an 192Ir source. Measured radial dose rate distributions in water for different planes perpendicular to the source axis are presented and special attention is paid to the calibration of the R and K type detectors, and to the determination of appropriate correction factors for the sensitivity variation with the increase of the threshold voltage and the energy dependence. The experimental results are compared with Monte Carlo simulated dose rate distributions. The experimental results show a good agreement with the Monte Carlo simulations: the discrepancy between experimental and Monte Carlo results being within 5% for 82% of the points and within 10% for 95% of the points. Moreover, all points except two are found to lie within the experimental uncertainties, confirming thereby the quality of the results obtained

Characterisation of MCP-7s- material for use as a beta extremity dosemeter

LiF:Mg,Cu,P phosphors (commercially designated as MCP-N) are very sensitive thermoluminescent detectors and are considered by many laboratories to hold great promise for low level radiation monitoring. It is their high efficiency relative to TLDs based on LiF:Mg,Ti which make MCP-N particularly attractive for low dose measurements. The currently investigated detector material made of LiF:Mg,Cu,P bears the code name MCP-7s and has a very thin active layer and consequently an improved response to low energy beta radiation. Detailed studies have been carried out to characterise MCP-7s detectors in terms of glow curve, beta and gamma response, reusability, batch homogeneity and fading. Based on the positive outcome of these investigations, the dosimetry service at PSI plans to replace the TL material LiF:Mg,Ti presently used for extremity dosimetry with MCP-7

144Ce as a potential candidate for interstitial and intravascular brachytherapy

To investigate the suitability of 144Ce for both interstitial and intravascular brachytherapy applications. Monte Carlo calculations of radial dose rate distributions in water were performed for 144Ce in a spring-shaped source and compared with two commonly used interstitial and intravascular sources, 192Ir and 32P. The numeric simulations were checked experimentally with a calibrated ionization chamber in a water phantom. Other source characteristics, such as half-life and specific activity, were also compared. For interstitial brachytherapy, 144Ce presents dosimetric advantages over 192Ir in terms of higher dose rate at shorter distances and lower irradiation of organs outside the tumor. The source size and shape reduce the anisotropy and the number of dwell positions necessary. The longer half-life of 144Ce might also be advantageous over 192Ir. For intravascular brachytherapy, 144Ce permits the treatment of larger arteries as compared with 32P, compensates centering errors more effectively, and has a more suitable half-life. The experimental validation showed good agreement (within 10%) with the Monte Carlo simulated dose rate distributions. There are certain potential advantages of using 144Ce as a source for both interstitial and intravascular brachytherapy. The basis for this finding is provided by the Monte Carlo radial dose rate comparisons with 192Ir and 32P, as well as by such characteristics as half-life and specific activity. [All rights reserved Elsevier

Comparison of Monte Carlo simulations of photon/electron dosimetry in microscale applications

It is important to establish reliable calculational tools to plan and analyse representative microdosimetry experiments in the context of microbeam radiation therapy development. In this paper, an attempt has been made to investigate the suitability of the MCNP4C Monte Carlo code to adequately model photon/electron transport over micron distances. The case of a single cylindrical microbeam of 25-micron diameter incident on a water phantom has been simulated in detail with both MCNP4C and the code PSI-GEANT, for different incident photon energies, to get absorbed dose distributions at various depths, with and without electron transport being considered. In addition, dose distributions calculated for a single microbeam with a photon spectrum representative of the European Synchrotron Radiation Facility (ESRF) have been compared. Finally, a large number of cylindrical microbeams (a total of 2601 beams, placed on a 200-micron square pitch, covering an area of 1 cm2) incident on a water phantom have been considered to study cumulative radial dose distributions at different depths. From these distributions, ratios of peak (within the microbeam) to valley (mid-point along the diagonal connecting two microbeams) dose values have been determined. The various comparisons with PSI-GEANT results have shown that MCNP4C, with its high flexibility in terms of its numerous source and geometry description options, variance reduction methods, detailed error analysis, statistical checks and different tally types, can be a valuable tool for the analysis of microbeam experiments