Internal radiation dose estimation using multiple D-shuttle dosimeters for positron emission tomography (PET): A validation study using NEMA body phantom

PurposeInternal 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. MethodsRadioactivity 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 F-18-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 MBq/mL and 1.32 MBq/mL, respectively. The initial radioactivities of the torso cavity and six spheres (treated as source organs) were 15.9 MBq (torso cavity), 34.7 MBq (37 mm sphere), 15.1 MBq (28 mm sphere), 7.27 MBq (22 mm sphere), 3.26 MBq (17 mm sphere), 1.54 MBq (13 mm sphere), and 0.697 MBq (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. ResultsRadioactivity 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 MBq (torso cavity), 33.0 +/- 0.624 MBq (37 mm sphere), 15.7 +/- 0.189 MBq (28 mm sphere), 7.11 +/- 0.738 MBq (22 mm sphere), 4.17 +/- 0.083 MBq (17 mm sphere), 1.48 +/- 0.469 MBq (13 mm sphere), and 0.865 +/- 0.313 MBq (10 mm sphere), which were very close to the actual initial radioactivity measurements for each source organ. ConclusionsThe phantom study showed that our technique worked successfully. This technique could be used to estimate internal radiation dosimetry in a clinical PET study.