World Journal of Nuclear Medicine

: 2013  |  Volume : 12  |  Issue : 3  |  Page : 3--4

Dosimetry: Does it Really Matter?

David Chee.Eng Ng 
 Senior Consultant, Department of Nuclear Medicine and PET, Singapore General Hospital, Singapore

Correspondence Address:
David Chee.Eng Ng
Senior Consultant, Department of Nuclear Medicine and PET, Singapore General Hospital

How to cite this article:
Ng DC. Dosimetry: Does it Really Matter?.World J Nucl Med 2013;12:3-4

How to cite this URL:
Ng DC. Dosimetry: Does it Really Matter?. World J Nucl Med [serial online] 2013 [cited 2022 Oct 5 ];12:3-4
Available from:

Full Text

This is not meant to be a comprehensive symphony on dosimetry but is a simple plaintive song (joining the growing chorus worldwide) for the increasing recognition of the importance and value of dosimetry, an oft-neglected daughter of nuclear medicine practice, in clinical nuclear medicine practice. I said "oft-neglected"; perhaps, this is too strong a statement. However, there are several reasons why dosimetry is often left behind. First, with the advent of molecular imaging [Positron emission tomography-computed tomography (PET/CT) Positron emission tomography-magnetic resonance (PET/MR), and single-photon emission computed tomography-computed tomography (SPECT/CT)], there is much interest in integrative imaging over the last two decades. Functional/molecular imaging has become the glamour-boy of nuclear medicine. Is it any wonder that more attention is devoted to Nuclear Medicine Imaging than to Therapeutics? Second, there is much progress towards the understanding of basic radiobiological behavior of tissues (and tumors) such as biological effective dose (BED) and principles of dosimetry over the years, leading to a much more complicated picture of dosimetry. This means that learning dosimetry requires extra hard work. Third, there is always a dearth of time, especially in a busy clinical department, and often some things have to give way to the pressing concerns of clinical service. Fourth, there is a lack of trained personnel who knows how to make dosimetry work correctly, and better still, personnel with a facility to innovate and discover new things in this area. More importantly, there seems to be a relative lack of literature-reported evidence on the value of dosimetry and a general skepticism, whether dosimetry really matters when empiric evidence is available.

Traditionally, dosimetry is required for regulatory approval of new radiopharmaceuticals, to calculate patient-based activity for patient safety and to optimize planning of administered activity and post-therapy verification of absorbed doses.

Large chunks of our current nuclear medicine practice use empiric evidence for activity estimation. The result of this is that it is a well-known fact that for some common radiopharmaceutical therapies, there is a wide range of internally absorbed doses delivered to various organs. For example, for the most common therapeutic procedure in nuclear medicine practice worldwide, I-131 thyroidal ablation, absorbed doses can range from 7-3500 Gy in one report [1] and 1.2 to 540 Gy in another. [2] Put in a very crude way, this is akin to giving patients anything from 35-17,500 mg of paracetamol per administration for fever! Of course, this is an exaggeration: The majority of absorbed doses would lie within an appropriate dose range, but the variation is wide.

"Unfortunately, unlike the universal agreement regarding the importance and need for characterizational dosimetry in drug development, dosimetry generally is not used to guide radionuclide therapy, despite the substantial efforts to develop and standardize internal dose methods. There is currently no consensus within the scientific community on the utility of predictive dosimetry, and regulatory agencies do not require its use for determining a treatment activity prescription, because they believe there is a little evidence indicating that dosimetry is predictive of either toxicity or response as compared with simpler administration methods (administered activity or activity adjusted for body mass or surface area)," wrote Michael Stabin, Robert Sharkey, and Jeffry Siegel in the RADAR Commentary: Evolution and current status of dosimetry in Nuclear Medicine. [3]

We as part of the radionuclide therapy community may not be taking a sufficiently proactive role in coupling absorbed dose or BED with other important patient-specific pre-therapy variables in making decisions regarding administration of radiopharmaceuticals. Nonetheless, we are thankful that some of our colleagues have been actively spearheading various initiatives in clinical dosimetry. Perhaps as a community of Nuclear Medicine Physicians, we can look into how we may encourage:

Better and more widespread use of dosimetry in nuclear therapeutics.More training in dosimetry for nuclear medicine physicians and more exposure to dosimetric principles in Nuclear Medicine training programmes.More consensus development of dosimetric practice and collaboration worldwide.More stringent expectations for publications dealing with nuclear therapeutics.More accessible software for use in dosimetric calculations.More research directed at the intricate interactions between dose and other patient variables, leading to better understanding of nuclear medicine radiobiology and its effects on cellular biology and disease.

It is time to consolidate - to put more dosimetric data into our routine therapeutics. I cannot end this editorial without thinking of a quotation from famed Lord Kelvin, Physicist and Scientist, who said in 1883: "I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind. It may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be" (Popular Lectures Vol. I, p. 73).


1O'Connell ME, Flower MA, Hinton PJ, Harmer CL, McCready VR. Radiation dose assessment in radioiodine therapy. Dose-response relationship in differentiated thyroid carcinoma using quantitative scanning and PET. Radiother Oncol 1993;28:16-26.
2Sgouros G, Kolbert KS, Sheikh A, Pentlow KS, Mun EF, Barth A, et al. Patient-specific dosimetry for 131I thyroid cancer therapy using 124I PET and 3-dimensional-internal dosimetry (3D-ID) software. J Nucl Med 2004;45:1366-72.
3Stabin MG, Sharkey RM, Siegel JA. RADAR Commentary: Evolution and current status of dosimetry in Nuclear Medicine. J Nucl Med 2011;52:1156-61.