CME 2 Session - EANM'16

Dosimetry & Radionuclide Therapy: Dosimetry for Clinical Trials

Educational objectives:
  1. Physical requirements for activity quantification methods to perform dosimetry in clinical trials
  2. Legal requirements for dosimetry assessments of investigative radiopharmaceuticals
  3. Dosimetry calculations according to the MIRD-scheme
  4. Patient-averaged dose assessments in diagnostics and patient-specific dosimetry in therapy
  5. The impact of age and clinical condition on dosimetry
  6. Impact of dosimetry in planning and performing clinical trials with radiopharmaceuticals

Quantitative imaging and radioactivity measurements are essential in performing dosimetry studies.

Calculations of absorbed doses are mostly carried out according to the Medical Internal Radiation Dosimetry (MIRD) scheme.

Dosimetry should be based on the pharmacokinetics of the radiolabelled substance. Initially animal pharmacokinetic data can be extrapolated to man for estimating tissue and whole body absorbed doses. Ideal time-points should be chosen for organ activity quantification according to the expected pharmacokinetics.

Pharmacokinetic studies of the investigative radiopharmaceutical should be performed in suitable patients, rather than in healthy volunteers. Patient-averaged doses can be used for diagnostic radiopharmaceuticals, but are often irrelevant for therapeutic agents. For diagnostics the effective dose is the main quantity and it is calculated using the tissue weighting factors established by the International Commission for Radiological Protection (ICRP). The effective dose, however, is only intended to calculate the risk for an age-independent reference person not the individual risk. The applicability of this quantity to patients and for pediatric Nuclear Medicine will be discussed.

For therapeutic radiopharmaceuticals the absorbed dose to specific organs can be influenced significantly by pathophysiological changes induced by the disease process. Patient-specific dosimetry methods needed for tailored radionuclide therapies are explained.

Clinicians are facing increasing legal requirements for dosimetry when performing clinical trials with radiopharmaceuticals. Continuous dialogue between physicists and clinicians is mandatory for a better understanding of the respective needs.  

Key Words:

Diagnostic dosimetry, absorbed dose calculation, effective dose, Patient-specific dosimetry

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