Journal Club: Radiation Exposure of Patients Undergoing Whole-Body Dual-Modality 18F-FDG PET/CT Examinations

It’s been a while since the last journal club article. Partly because I hadn’t come across too many articles I thought were interesting enough, mostly because I haven’t had much time to do much journal reading lately. And now from this month’s Journal of Nuclear Medicine come two articles that I found very interesting and informative.

The first one looks at radiation exposures to patients from combined PET/CT scans, an increasingly popular (and quickly becoming ‘standard of care’) method of diagnosing cancer and monitoring therapy efficacy. CT and PET radiation doses were examined at 4 hospitals each employing a variety of techniques: low-dose CT for attenuation correction, diagnostic CT for attenuation correction and localization, contrast and non-contrast studies. Total radiation dose came out to around 25 mSv (about 7 mSv from PET, 18 mSv from CT) and was surprisingly mostly independent of the protocol used.

A handy table of dose coefficients for various organs is also provided, which will make it easy to estimate the radiation dose to various organs from an exam given the injected activity and CTDI from the CT scan.

What was not clear was if any of the scanners had any of the CT dose reduction methods being used in the newest scanners (the ones that dynamically adjust tube current throughout the scan). These have been shown to effectively reduce patient dose while maintaining a desired image quality. I’m sure these methods incorporated into the newest PET/CT units can bring down the radiation dose a little more.

This ought to be a useful paper for any medical physicist or radiologist finding the need to estimate radiation dose from a PET/CT scan, or wanting to optimize their protocols to minimize dose.

Gunnar Brix, PhD, Ursula Lechel, MS, Gerhard Glatting, PhD, Sibylle I. Ziegler, PhD, Wolfgang Münzing, PhD, Stefan P. Müller, MD and Thomas Beyer, PhD, “Radiation Exposure of Patients Undergoing Whole-Body Dual-Modality ¹⁸F-FDG PET/CT Examinations“, JNM 46 608-613 (2005)

Abstract:

We investigated radiation exposure of patients undergoing whole-body ¹⁸F-FDG PET/CT examinations at 4 hospitals equipped with different tomographs. Methods: Patient doses were estimated by using established dose coefficients for ¹⁸F-FDG and from thermoluminescent measurements performed on an anthropomorphic whole-body phantom.
Results: The most relevant difference between the protocols examined was the incorporation of CT as part of the combined PET/CT examination: Separate low-dose CT scans were acquired at 2 hospitals for attenuation correction of emission data in addition to a contrast-enhanced CT scan for diagnostic evaluation, whereas, at the other sites, contrast-enhanced CT scans were used for both purposes. Nevertheless, the effective dose per PET/CT examination was similar, about 25 mSv.
Conclusion: The dosimetric concepts presented in this study provide a valuable tool for the optimization of whole-body ¹⁸F-FDG PET/CT protocols. Further reduction of patient exposure can be achieved by modifications to the existing hardware and software of PET/CT systems.