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Internal radiation dose estimation using multiple D‐shuttle dosimeters for positron emission tomography ( PET ): A validation study using NEMA body phantom
Author(s) -
Islam Md. Shahidul,
Watanuki Shoichi,
Tashiro Manabu,
Watabe Hiroshi
Publication year - 2018
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.13124
Subject(s) - imaging phantom , dosimeter , torso , nuclear medicine , dosimetry , physics , positron emission tomography , materials science , standardized uptake value , monte carlo method , spheres , biomedical engineering , medicine , mathematics , statistics , anatomy , astronomy
Purpose Internal radiation dosimetry plays an important role in ensuring the safe use of positron emission tomography ( PET ) technology and is a legal requirement in most countries. We propose a new technique to estimate the internal radiation dose in PET studies by means of multiple D‐shuttle dosimeters attached on the body surface of the patient. Methods Radioactivity in a source organ was estimated iteratively using measurements from multiple D‐shuttle dosimeters with a maximum‐likelihood expectation‐maximization ( MLEM ) algorithm with dose response from a source to a D‐shuttle dosimeter computed by Monte Carlo simulation. To validate our technique, we performed a phantom study using a National Electrical Manufacturers Association ( NEMA ) body phantom. The fillable compartments (torso cavity and six spheres) of the phantom were filled with 18 F‐ FDG mixed with pure water using an 800:1 sphere‐to‐background radioactivity concentration ratio. The radioactivity concentrations present in the torso cavity and six spheres were 0.00165 MB q/ mL and 1.32 MB q/ mL , respectively. The initial radioactivities of the torso cavity and six spheres (treated as source organs) were 15.9 MB q (torso cavity), 34.7 MB q (37 mm sphere), 15.1 MB q (28 mm sphere), 7.27 MB q (22 mm sphere), 3.26 MB q (17 mm sphere), 1.54 MB q (13 mm sphere), and 0.697 MB q (10 mm sphere). Eleven D‐shuttle dosimeters were attached to the NEMA body phantom surface to obtain information on body surface dose and a mathematical NEMA body phantom has been modeled in the Heavy Ion Transport Code System ( PHITS ) Monte Carlo simulation code. Results Radioactivity was estimated in 2 min intervals over a 110‐min total dose time using our proposed technique. A significant correlation (R 2 = 0.992) was found between actual radioactivity and estimated radioactivity at every 2 min interval for each source organ. The estimated initial radioactivity (mean with standard deviation) was 16.5 ± 0.311 MB q (torso cavity), 33.0 ± 0.624 MB q (37 mm sphere), 15.7 ± 0.189 MB q (28 mm sphere), 7.11 ± 0.738 MB q (22 mm sphere), 4.17 ± 0.083 MB q (17 mm sphere), 1.48 ± 0.469 MB q (13 mm sphere), and 0.865 ± 0.313 MB q (10 mm sphere), which were very close to the actual initial radioactivity measurements for each source organ. Conclusions The phantom study showed that our technique worked successfully. This technique could be used to estimate internal radiation dosimetry in a clinical PET study.