Development of Simple Methods to Reduce the Exposure of the Public to Radiation from Patients Who Have Undergone 18F-FDG PET/CT

Which modality is better to diagnose high-grade transformation in retroperitoneal liposarcoma? Comparison of computed tomography, positron emission tomography, and magnetic resonance imaging

BACKGROUND

Survival in patients with retroperitoneal liposarcoma (RPLS) depends on the surgical management of the dedifferentiated foci. The present study investigated the diagnostic yield of contrast-enhanced CT, ¹⁸F-fluorodeoxyglucose positron emission tomography (PET), and diffusion-weighted MRI in terms of dedifferentiated foci within the RPLS.

METHODS

Patients treated with primary or recurrent RPLS who underwent the above imaging between January 2010 and December 2021 were retrospectively reviewed. The diagnostic accuracy of the three modalities for histologic subtype of dedifferentiated liposarcoma (DDLS) and French Federation of Cancer Center (FNCLCC) grade 2/3 were compared using receiver operating characteristic curves and areas under the curves (AUCs).

RESULTS

The cohort involved 32 patients with 53 tumors; 30 of which exhibited DDLS and 31 of which did FNCLCC grades 2/3. The optimal thresholds for predicting DDLS were mean CT value of 31 Hounsfield Unit (HU) (AUC = 0.880, 95% CI 0.775-0.984; p < 0.001), maximum standardized uptake value (SUVmax) of 2.9 (AUC = 0.865 95% CI 0.792-0.980; p < 0.001), while MRI failed to differentiate DDLS. The cutoff values for distinguishing FNCLCC grades 1 and 2/3 were a mean CT value of 24 HU (AUC = 0.858, 95% CI 0.731-0.985; p < 0.001) and SUVmax of 2.9 (AUC = 0.885, 95% CI 0.792-0.978; p < 0.001). MRI had no sufficient power to separate these grades.

CONCLUSIONS

Contrast-enhanced CT and PET were useful for predicting DDLS and FNCLCC grade 2/3, while MRI was inferior to these two modalities.

DESIGN, COMMISSIONING AND OPERATION OF PROGRAMMABLE DRAINAGE SYSTEM FOR PET-CT: AN OPTIMIZED APPROACH TO PROTECT PERSONNEL AND ENVIRONMENT IN NUCLEAR MEDICINE FACILITIES

Nuclear medicine facilities are considered one of the most important practices associated with potential radiological risks to personnel and the environment due to the significant amounts of solid and liquid radioactive waste generated from these facilities. Whenever possible and applicable, the licensee shall apply the most up-to-date technological advances to ensure that such radioactive waste is safely discharged to the public sewage. To date, there is no specific technical safety requirement endorsed by regulatory body in Egypt regarding drainage system design for nuclear medicine facilities. This paper discusses the design, commissioning and operation of a programmable drainage system in a Positron Emission Tomography/Computed Tomography (PET-CT) unit for collecting and draining sewage contaminated with the radioactive isotope 18F. The system operates automatically without the need for human intervention. The system has been tested using clean water and found to be working efficiently in accordance with the design parameters. The proposed system concept can be applied in other nuclear medicine facilities after scaling it up/down according to all radionuclides in use and the expected volume of associated radioactive waste. Based on the system's demonstrated performance, regulatory bodies are highly recommended to embrace such approach as a safety requirement to assist the licensees in complying with the safety standards during the planning and construction of PET-CT facilities.

Reducing Radiation Exposure from PET Patients

Objective: This study measured the typical emitted radiation rate from the urinary bladder of PET patients after their scan and investigated simple methods for reducing the emitted radiation before discharge. Methods: The study included 83 patients, 63 [¹⁸F]FDG and 20 [¹⁸F]NaF. Emitted radiation from the patients' urinary bladder was measured with an ionization survey meter at a 1-meter distance, presuming the urinary bladder to be the primary source of radiation. The measurements were taken at different time points after PET image acquisition: immediate (pre-void 1), voided (post-void 1), after waiting 30 min in the uptake room while drinking 500 mL of water (pre-void 2) and voided again (post-void 2). Results: For [¹⁸F]FDG patients, the reduction of emitted radiation due to drinking water and voiding alone from pre-void 1 to decay corrected post void 2 was an average of 22.49 ± 7.48% (13.65 ± 3.42 µSv/h to 10.48 ± 2.37 µSv/h, P = 0). As for [¹⁸F]NaF patients, the reduction was an average of 25.80 ± 10.03% (9.83 ± 2.01 µSv/h to 7.23 ± 1.49 µSv/h, P = 0). Conclusion: In addition to the physical decay of the radiotracers, utilizing the biological clearance properties have resulted in a significant decrease of the emitted radiation in this study. Implementing additional water consumption to facilitate voiding with 30 minutes of wait time before discharging certain [¹⁸F]FDG and [¹⁸F]NaF patients that need to be in close contact with others such as elderly, caregivers and inpatients, might facilitate lowering their emitted radiation by an average of 22-25% due to voiding, not counting in the physical decay which should add an additional 17% reduction.

NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR NUCLEAR MEDICINE IN KUWAIT

The diagnostic reference level (DRL) is an optimization tool of patients exposure used to evaluate and provide guidance for radiation doses in medical imaging. In the past few decades, there has been a global increase in the number of diagnostic imaging procedures, including nuclear medicine procedures, and consequently the patient radiation exposure. This has encouraged international and national healthcare organizations to take actions and keep up with such changes to meet the expectations of an increasing use of ionizing radiation in medicine. The DRL in Kuwait was established by investigating the administered activity of radiopharmaceuticals and computed tomography (CT) radiation doses in hybrid imaging systems. The DRL were determined based on the 75th percentile of radiopharmaceuticals administered activity distribution as recommended by the international commission on radiation protection (ICRP). This study presents the establishment process and results of the first national DRLs for nuclear medicine procedures in Kuwait as a way to optimize radiation exposure. The DRLs determined in Kuwait are in good agreement with other published DRLs in Europe, Japan, Korea, Australia and the US.