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- Candela-Juan, C., et al.
(författare)
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Dosimetric characterization of two radium sources for retrospective dosimetry studies
- 2015
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Ingår i: Medical physics (Lancaster). - : American Association of Physicists in Medicine: Medical Physics. - 0094-2405 .- 2473-4209. ; 42:5, s. 2132-2142
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: During the first part of the 20th century, Ra-226 was the most used radionuclide for brachytherapy. Retrospective accurate dosimetry, coupled with patient follow up, is important for advancing knowledge on long-term radiation effects. The purpose of this work was to dosimetrically characterize two Ra-226 sources, commonly used in Sweden during the first half of the 20th century, for retrospective dose-effect studies. Methods: An 8 mg Ra-226 tube and a 10 mg Ra-226 needle, used at Radiumhemmet (Karolinska University Hospital, Stockholm, Sweden), from 1925 to the 1960s, were modeled in two independent Monte Carlo (MC) radiation transport codes: GEANT4 and MCNP5. Absorbed dose and collision kerma around the two sources were obtained, from which the TG-43 parameters were derived for the secular equilibrium state. Furthermore, results from this dosimetric formalism were compared with results from a MC simulation with a superficial mould constituted by five needles inside a glass casing, placed over a water phantom, trying to mimic a typical clinical setup. Calculated absorbed doses using the TG-43 formalism were also compared with previously reported measurements and calculations based on the Sievert integral. Finally, the dose rate at large distances from a Ra-226 point-like-source placed in the center of 1 m radius water sphere was calculated with GEANT4. Results: TG-43 parameters [including gL(r), F(r,theta), Lambda, and s(K)] have been uploaded in spreadsheets as additional material, and the fitting parameters of a mathematical curve that provides the dose rate between 10 and 60 cm from the source have been provided. Results from TG-43 formalism are consistent within the treatment volume with those of a MC simulation of a typical clinical scenario. Comparisons with reported measurements made with thermoluminescent dosimeters show differences up to 13% along the transverse axis of the radium needle. It has been estimated that the uncertainty associated to the absorbed dose within the treatment volume is 10%-15%, whereas uncertainty of absorbed dose to distant organs is roughly 20%-25%. Conclusions: The results provided here facilitate retrospective dosimetry studies of Ra-226 using modern treatment planning systems, which may be used to improve knowledge on long term radiation effects. It is surely important for the epidemiologic studies to be aware of the estimated uncertainty provided here before extracting their conclusions.
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| 2. |
- Loizou, L., et al.
(författare)
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Radiological assessment of local resectability status in patients with pancreatic cancer: Interreader agreement and reader performance in two different classification systems
- 2018
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Ingår i: European Journal of Radiology. - : Elsevier BV. - 0720-048X .- 1872-7727. ; 106, s. 69-76
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: To assess the interreader agreement and reader performance in the evaluation of patients with pancreatic cancer (PC) in two classification systems of local resectability status prior to initiation of therapy, namely the National Comprehensive Cancer Network (NCCN) and Karolinska classification system (KCS). Methods: In this ethics review board-approved retrospective study, six radiologists independently evaluated pancreatic CT-examinations of 30 patients randomly selected from a tertiary referral centre's multidisciplinary tumour board database. Based on well-defined criteria of tumour-vessel relationship, each patient was assigned to one of three NCCN and six KCS categories. We assessed the intraclass correlation coefficient (ICC) and compared the percentages of correct tumour classification of the six readers in both systems (Chi-square test; a P-value < 0.05 was considered significant). The standard of reference was a consensus evaluation of CT-examinations by three readers not involved in the image analysis. Results: The ICC for NCCN and KCS was 0.82 and 0.84, respectively (very strong agreement). The percentages of correct tumour classification at NCCN and KCS were 53-83% and 30-57%, respectively, with no statistically significant differences in the overall reader comparison per classification system. In pair-wise comparison between readers for NCCN/KCS, there were statistically significant differences between reader 5 vs. readers 4 (P = 0.012) and 3 (P = 0.045)/ reader 5 vs. reader 4 (P = 0.037). Conclusion: Interreader agreement in both PC classification systems is very strong. NCCN may be advantageous in terms of reader performance compared to KCS.
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