Dose reduction in chest CT examination.

Computed tomography (CT) examinations involve relatively high doses to patients. The objectives of this study were to optimise the radiation dose for patient during CT chest scan and to estimate the lifetime cancer risk. A total of 50 patients were studied: control group (A) (38 patients) and optimisation group (B) (12 patients). The optimisation protocol was based on CT pitch increment and lowering tube current. The mean volume CT dose index (CTDI vol) was 21.17 mGy and dose length product (DLP) was 839.0 mGy cm for Group A, and CTDI vol was 8.3 mGy and DLP was 339.7 for Group B. The overall cancer risk was estimated to be 8.0 and 3.0 cancer incidence per million for Groups A and B, respectively. The patient dose optimisation during CT chest was investigated. Lowering tube current and pitch increment achieved a radiation dose reduction of up to 60 % without compromising the diagnostic findings.

Effective dose to staff members in a positron emission tomography/CT facility using zirconium-89.

OBJECTIVE: Positron emission tomography (PET) using zirconium-89 ((89)Zr) is complicated by its complex decay scheme. In this study, we quantified the effective dose from (89)Zr and compared it with fluorine-18 fludeoxyglucose ((18)F-FDG). METHODS: Effective dose distribution in a PET/CT facility in Riyadh was calculated by Monte Carlo simulations using MCNPX. The positron bremsstrahlung, the annihilation photons, the delayed gammas from (89)Zr and those emissions from (18)F-FDG were modelled in the simulations but low-energy characteristic X-rays were ignored. RESULTS: On the basis of injected activity, the dose from (89)Zr was higher than that of (18)F-FDG. However, the dose per scan from (89)Zr became less than that from (18)F-FDG near the patient, owing to the difference in injected activities. In the corridor and control rooms, the (89)Zr dose was much higher than (18)F-FDG, owing to the difference in attenuation by the shielding materials. CONCLUSION: The presence of the high-energy photons from (89)Zr-labelled immuno-PET radiopharmaceuticals causes a significantly higher effective dose than (18)F-FDG to the staff outside the patient room. Conversely, despite the low administered activity of (89)Zr, it gives rise to a comparable or even lower dose than (18)F-FDG to the staff near the patient. This interesting result raises apparently contradictory implications in the radiation protection considerations of a PET/CT facility. ADVANCES IN KNOWLEDGE: To the best of our knowledge, radiation exposure to staff and public in the PET/CT unit using (89)Zr has not been investigated. The ultimate output of this study will lead to the optimal design of the facility for routine use of (89)Zr.