Abstract
Total skin electron irradiation (TSEI) is a complex technique which requires many nonstandard measurements and dosimetric procedures. The purpose of this work was to validate measured dosimetry data by Monte Carlo (MC) simulations using EGSnrc‐based codes (BEAMnrc and DOSXYZnrc). Our MC simulations consisted of two major steps. In the first step, the incident electron beam parameters (energy spectrum, FWHM, mean angular spread) were adjusted to match the measured data (PDD and profile) at SSD=100 cm for an open field. In the second step, these parameters were used to calculate dose distributions at the treatment distance of 400 cm. MC simulations of dose distributions from single and dual fields at the treatment distance were performed in a water phantom. Dose distribution from the full treatment with six dual fields was simulated in a CT‐based anthropomorphic phantom. MC calculations were compared to the available set of measurements used in clinical practice. For one direct field, MC calculated PDDs agreed within 3%/1 mm with the measurements, and lateral profiles agreed within 3% with the measured data. For the OF, the measured and calculated results were within 2% agreement. The optimal angle of 17° was confirmed for the dual field setup. Dose distribution from the full treatment with six dual fields was simulated in a CT‐based anthropomorphic phantom. The MC‐calculated multiplication factor (B12‐factor), which relates the skin dose for the whole treatment to the dose from one calibration field, for setups with and without degrader was 2.9 and 2.8, respectively. The measured B12‐factor was 2.8 for both setups. The difference between calculated and measured values was within 3.5%. It was found that a degrader provides more homogeneous dose distribution. The measured X‐ray contamination for the full treatment was 0.4%; this is compared to the 0.5% X‐ray contamination obtained with the MC calculation. Feasibility of MC simulation in an anthropomorphic phantom for a full TSEI treatment was proved and is reported for the first time in the literature. The results of our MC calculations were found to be in general agreement with the measurements, providing a promising tool for further studies of dose distribution calculations in TSEI.PACS number(s): 87.10. Rt, 87.55.K, 87.55.ne
Highlights
419 Nevelsky et al.: Validation of Total skin electron irradiation (TSEI) data by Monte Carlo (MC) simulationTSEI, which is commonly performed with a 6 MeV beam
Various techniques have been developed for TSEI; their descriptions can be found in the AAPM Report 23, “Total Skin Electron Therapy: Technique and Dosimetry”.(6) According to the recommendations of this report, a uniform dose distribution in an area of 200 cm in height and 80 cm in width should be available
The results of our Monte Carlo calculations were found to be in general agreement with the measurements, providing a promising tool for further studies of dose distribution calculations in TSEI
Summary
419 Nevelsky et al.: Validation of TSEI data by MC simulationTSEI, which is commonly performed with a 6 MeV beam. Bremsstrahlung X-ray contamination should be low and the dose rate at the patient should be high (at least 0.25 Gy/min, practically over 1 Gy/min) To achieve these recommendations, we use the Stanford technique developed by Karzmark and colleagues.[7] This technique has been considered as a safe and effective treatment, and has been selected by a majority of institutions in the last 20 years as the preferred modality.[2] The Stanford technique is characterized by the use of: 1) an extended SSD (more than 3 m); 2) dual large electron fields with central axis angled by approximately ± 20° from the horizontal; and 3) six patient positions relative to each of the two large angled TSEI beams (anterior, posterior, and four lateral obliques). The application of MC for TSEI beams has been limited, primarily because it involves time-consuming, large-scale electron transport simulations
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