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000020155 0247_ $$2DOI$$a10.1016/j.zemedi.2011.09.002
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000020155 084__ $$2WoS$$aRadiology, Nuclear Medicine & Medical Imaging
000020155 1001_ $$0P:(DE-HGF)0$$aHammes, J.$$b0
000020155 245__ $$aGATE based Monte Carlo simulation of planar scintigraphy to estimate the nodular dose in radioiodine therapy for autonomous thyroid adenoma
000020155 260__ $$aAmsterdam [u.a.]$$bElsevier$$c2011
000020155 300__ $$a290 - 300
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000020155 520__ $$aThe recommended target dose in radioiodine therapy of solitary hyperfunctioning thyroid nodules is 300-400Gy and therefore higher than in other radiotherapies. This is due to the fact that an unknown, yet significant portion of the activity is stored in extranodular areas but is neglected in the calculatory dosimetry. We investigate the feasibility of determining the ratio of nodular and extranodular activity concentrations (uptakes) from post-therapeutically acquired planar scintigrams with Monte Carlo simulations in GATE. The geometry of a gamma camera with a high energy collimator was emulated in GATE (Version 5). A geometrical thyroid-neck phantom (GP) and the ICRP reference voxel phantoms "Adult Female" (AF, 16ml thyroid) and "Adult Male" (AM, 19ml thyroid) were used as source regions. Nodules of 1ml and 3ml volume were placed in the phantoms. For each phantom and each nodule 200 scintigraphic acquisitions were simulated. Uptake ratios of nodule and rest of thyroid ranging from 1 to 20 could be created by summation. Quantitative image analysis was performed by investigating the number of simulated counts in regions of interest (ROIs). ROIs were created by perpendicular projection of the phantom onto the camera plane to avoid a user dependant bias. The ratio of count densities in ROIs over the nodule and over the contralateral lobe, which should be least affected by nodular activity, was taken to be the best available measure for the uptake ratios. However, the predefined uptake ratios are underestimated by these count density ratios: For an uptake ratio of 20 the count ratios range from 4.5 (AF, 1ml nodule) to 15.3 (AM, 3ml nodule). Furthermore, the contralateral ROI is more strongly affected by nodular activity than expected: For an uptake ratio of 20 between nodule and rest of thyroid up to 29% of total counts in the ROI over the contralateral lobe are caused by decays in the nodule (AF 3 ml). In the case of the 1ml nodules this effect is smaller: 9-11% (AF) respectively 7-8% (AM). For each phantom, the dependency of count density ratios upon uptake ratios can be modeled well by both linear and quadratic regression (quadratic: r(2)>0.99), yielding sets of parameters which in reverse allow the computation of uptake ratios (and thus dose) from count density ratios. A single regression model obtained by fitting the data of all simulations simultaneously did not provide satisfactory results except for GP, while underestimating the true uptake ratios in AF and overestimating them in AM. The scintigraphic count density ratios depend upon the uptake ratios between nodule and rest of thyroid, upon their volumes, and their respective position in a non-trivial way. Further investigations are required to derive a comprehensive rule to calculate the uptake or dose ratios based on post-therapeutic scintigraphy.
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000020155 650_2 $$2MeSH$$aAdult
000020155 650_2 $$2MeSH$$aFemale
000020155 650_2 $$2MeSH$$aHumans
000020155 650_2 $$2MeSH$$aIodine Radioisotopes: administration & dosage
000020155 650_2 $$2MeSH$$aIodine Radioisotopes: pharmacokinetics
000020155 650_2 $$2MeSH$$aMonte Carlo Method
000020155 650_2 $$2MeSH$$aPhantoms, Imaging
000020155 650_2 $$2MeSH$$aRadiometry: methods
000020155 650_2 $$2MeSH$$aRadionuclide Imaging: methods
000020155 650_2 $$2MeSH$$aRadiotherapy Planning, Computer-Assisted: methods
000020155 650_2 $$2MeSH$$aThyroid Gland: radiation effects
000020155 650_2 $$2MeSH$$aThyroid Gland: radionuclide imaging
000020155 650_2 $$2MeSH$$aThyroid Neoplasms: radionuclide imaging
000020155 650_2 $$2MeSH$$aThyroid Neoplasms: radiotherapy
000020155 650_2 $$2MeSH$$aThyroid Nodule: radionuclide imaging
000020155 650_2 $$2MeSH$$aThyroid Nodule: radiotherapy
000020155 650_7 $$00$$2NLM Chemicals$$aIodine Radioisotopes
000020155 650_7 $$2WoSType$$aJ
000020155 65320 $$2Author$$aMonte Carlo simulation
000020155 65320 $$2Author$$aGATE
000020155 65320 $$2Author$$ascintigraphy
000020155 65320 $$2Author$$adosimetry
000020155 65320 $$2Author$$aradioiodine therapy
000020155 65320 $$2Author$$asolitary hyperfunctioning thyroid nodule
000020155 7001_ $$0P:(DE-Juel1)VDB2211$$aPietrzyk, U.$$b1$$uFZJ
000020155 7001_ $$0P:(DE-HGF)0$$aSchmidt, M.$$b2
000020155 7001_ $$0P:(DE-HGF)0$$aSchicha, H.$$b3
000020155 7001_ $$0P:(DE-HGF)0$$aEschner, W.$$b4
000020155 773__ $$0PERI:(DE-600)2231492-1$$a10.1016/j.zemedi.2011.09.002$$gVol. 21, p. 290 - 300$$p290 - 300$$q21<290 - 300$$tZeitschrift für Medizinische Physik$$v21$$x0939-3889$$y2011
000020155 8567_ $$uhttp://dx.doi.org/10.1016/j.zemedi.2011.09.002
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