We investigated the stability of serrated gold coils (Visicoil) implanted within the prostate glands of patients undergoing definitive external beam radiotherapy for prostate cancer. Radiopaque Visicoils of diameter 0.75 mm and median length 3 cm (range 2–4 cm) were implanted, one into each lobe of the prostate glands of 30 patients planned for external beam treatment. The coils were visualized on CT simulation and again after 25 fractions of treatment (5WK). Data from 30 patients were studied, of whom 19 also received androgen ablation therapy. The average change in the distance between the two coils over five weeks of treatment was 0.8 mm (± 0.6 mm), with a maximum of 2.5 mm in one patient. Average residual errors (standard deviations) for the positions of individual coil segments after five weeks of therapy were only 0.7 mm LAT, 0.6 mm AP, and 0.4 mm SI. The average change in distance between the coils over five weeks compared favorably with published data regarding marker seed stability. Overall, less than a 2 mm margin (i.e., 2 standard deviations) would adequately compensate for positioning uncertainty of the coils in more than 95% of cases.PACS number: 87.55.kh
Brass compensators for beam modulation present an alternative method for IMRT treatment planning to traditional dynamic leaf modulation. In this work, we present a detailed method to commission the Pinnacle treatment planning system for IMRT using brass compensators. Beam attenuation from various brass thicknesses were measured using an ion chamber, as well as a MapCHECK device, for a representative seven‐field IMRT plan. We show that Pinnacle's parameters for compensators can be optimized to match the measured results while still maintaining the original open‐beam model. Only Pinnacle's modified scatter factor and brass density value were adjusted. Beam attenuation in several brass slabs were optimized by minimizing a χ2 function of measured and modeled data for several depths in solid water. Using MapCHECK, Pinnacle's parameters were optimized by minimizing the number of points that fail during a gamma analysis of seven fields in a typical IMRT plan. Our results show that Pinnacle's 10X beam is best modeled using a brass density of 7.8 g/cm3 and a modified scatter factor of 0.1 cm−1.PACS numbers: 87.56.N, 87.56.ng, 87.55.kh, 87.55.de
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.