Evaluation of the distribution of activation inside a compact medical cyclotron.

Objective:The aim of this study was to measure occupational exposure doses of technologists who dispense and inject radiopharmaceuticals in 7 positron emission tomography/computed tomography (PET/C...

https://journals.sagepub.com/doi/pdf/10.1177/1559325820938288

Exposure Doses to Technologists Working in 7 PET/CT Departments:

According to the (18)O(p, n) (18)F reaction, fast neutrons produced in the target will cause residual radioactivity in a cyclotron itself and in the concrete walls mainly after thermalization of neutrons.As exploratory work prior to decommissioning of a medical cyclotron facility, surface and core samples of the facility's concrete walls were collected after confirming the external radiation was at a low level based on hollow ionization chamber-type survey meter and glass dosimeter measurements. The residual radioactivity in these samples was measured by gamma-spectrometry. Residual radioactivity was detected in all of the components of the cyclotron. In the concrete, eight residual radioactive nuclides were identified. However, radioactivity concentrations of these radionuclides were less than that of (40)K which may exist generally in a natural environment. A clearance level for radioactive solid waste has not been defined nor implemented at present in Japan, and reliable evaluation will be required to minimize radioactive waste at the time of decommissioning. The present results provide basic data for establishment of regulatory guidelines for decommissioning of medical cyclotrons.

[Evaluation of Radio-activated Compounds Produced in the Walls and Adjacent Areas of a Small Medical Cyclotron].

Time-course study of individual dose equivalents of 2-deoxy-2-[F-18]fluoro-d-glucose positron emission tomography (18F-FDG PET) was conducted in different hospital workers, and the daily work duties were analyzed. For the measurements, a semiconductor dosimeter was used. The values at intervals of 1 min and 1 h, the monthly cumulative and daily cumulative doses, and trend graphs were acquired with dedicated software and displayed on the reader. The following radiation workers with duties involving maximum external exposure work were included: doctors making diagnoses (4.8 μSv/procedure), nurses removing injection needles (3.1 μSv/procedure), pharmacists performing quality control tests (2.9 μSv/procedure), nuclear medicine technologists assisting patient positioning (6.5 μSv/procedure), and cyclotron engineers performing daily checks (13.4 μSv/procedure). The results of analysis of daily work duties revealed the influencing factors of external exposure dose. To reduce the external exposure dose, investigators should shorten the patient’s contact time with the 18F-FDG source or patient tracer.

Time-related study on external exposure dose of 2-deoxy-2-[F-18]fluoro-D-glucose PET for workers' safety.

Objective: [123I] N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-[123I]iodophenyl) nortropane (123I-FP-CIT) or dopamine transporter (DAT) SPECT scan quantitatively depicts striatum dopamine transporter density. The specific binding ratio (SBR) is important for Parkinson's disease (PD) diagnosis. Correction techniques may improve 123I-FP-CIT image quality, but they are currently not standardized. We aim to determine attenuation correction (AC) and scatter correction (SC) influence on 123I-FP-CIT quantitative analysis. Methods: We preformed SPECT imaging on a striatal phantom representing striatum-to-background ratios ranging from 10:1 to 1:1. We used the Chang method for AC and triple energy window for SC. Commercially available software semi-automatically calculated SBR. We performed correlation analysis between SBR and the actual concentration ratio in four groups: no correction (NC), SC, AC, and combined correction (CC), paying particular attention to SBR values below the clinical cut-off (4.5). We applied the same imaging conditions, reconstruction, and corrections on 49 human 123I-FP-CIT SPECT studies. Asymmetric index values (AI) were also analyzed. Receiver operating characteristic (ROC) analysis provided AI diagnostic cut-off values in PD patients. PD patient population whose AI values were above these cut-off value were subject to a correlation study to confirm the association between their clinical symptoms and 123I-FP-CIT SPECT. Results: Phantom study. AC or CC increased SBR 123I-FP-CIT SPECT, making them very close to the standard ratios (AC: y=1.19x ‒ 0.7; R2=0.98; CC: y=1.4x ‒ 1.2; R2=0.98), while NC and SC underestimated SBR at lower values (1 to 4). Clinical study. There was no difference in SBR between NC and SC, while AC and CC produced significantly higher SBR than NC (p<0.0001). Only SC affected AI values (p<0.05). The association between clinical symptoms and 123I-FP-CIT imaging results were maintained only when either NC (n=12, p<0.05) or CC (n=14, p<0.05) was applied. Conclusions: AC increased SBR more than other corrections, while SC increased AI value more than other corrections. The association between clinical symptom and SPECT findings were maintained when either NC or CC was applied. These correction methods should be carefully selected for 123I-FP-CIT SPECT brain imaging.

The Influence of Attenuation and Scatter Corrections on Quantitative Analysis of 123 I-FP-CIT SPECT Brain Imaging

The
acquisition method for planar 67Ga imaging has hardly changed for 30
years. In this study, in order to improve image quality and diagnostic accuracy,
we take steps to optimize the acquisition method, and to choose a scatter
correction. First, we acquired individual images from the 93 keV, 185 keV, and
300 keV photopeak; then the images were added together and compared to the
individual images. Second, we compared results from a low-medium-energy (LME)
collimator with those from a conventional medium-energy (ME) collimator. Also,
we examined whether to combine the data from all three of the usual window
locations (set about 93 keV, 185 keV, and 300 keV) or to use the data from only
two. Third, we compared results from a conventional photopeak ± 10％ window with those from a
photopeak ± 9 keV window. Fourth, for scatter correction we compared results
using the triple energy window (TEW) method with those using the multi-photopeak
dual window (MDW) method. The phantoms studied were cold rods in a uniform
background, and hot spheres within a cylinder containing uniformly radioactive
water. The clinical study involved 22 patients with lung lesions. By the
comparison by the contrast ratio in cold rods phantom, 15.6% is improved in LME
(2 peaks) than ME (3 peaks), and 3.2% is improved in photopeak ± 9 keV than
photopeak ± 10%, 10.2% is improved in TEW than MDW. However, the TEW scatter
correction method recognized unstable to the contrast ratio in a clinical
study. In addition, a body outline might disappear.

/pdf/efforts-to-improve-the-images-from-67-ga-whole-body-38ngdf7ei9.pdf

Takao Kanzaki

Papers

[Evaluation of Radio-activated Compounds Produced in the Walls and Adjacent Areas of a Small Medical Cyclotron].

Time-related study on external exposure dose of 2-deoxy-2-[F-18]fluoro-D-glucose PET for workers' safety.

The Influence of Attenuation and Scatter Corrections on Quantitative Analysis of 123 I-FP-CIT SPECT Brain Imaging

Efforts to Improve the Images from 67 Ga Whole-Body Scintigraphy