MIRD Pamphlet no. 18: Administered cumulated activity for ventilation studies

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiological Dosimetry

Background:

• Lack of a standardized method for calculating administered activity in inhaled radioisotope ventilation studies.
• Uncertainty in actual activity reaching the lungs versus the delivery system.
• Extended administration times complicate activity calculations.

Purpose of the Study:

• To establish a standard calculational approach for administered activity in ventilation studies.
• To define new parameters for quantifying lung activity during inhalation.
• To enable standardization of ventilation protocols across institutions.

Main Methods:

• Review of three primary ventilation procedures: rebreathing systems, continuous-flow generators, and radioaerosol delivery.
• Derivation of analytic expressions for lung administered cumulated activity, A(L)(0,t(a)).
• Definition of mean administered activity for ventilation procedures.

Main Results:

• Introduction of lung administered cumulated activity, A(L)(0,t(a)), representing lung activity during administration.
• Definition of mean administered activity to normalize cumulated activity over the administration period.
• Illustrative examples provided for typical ventilation protocol parameters.

Conclusions:

• The presented models allow evaluation of lung administered cumulated activity using explicit variables.
• Recommended practice: base dose estimates on measured lung cumulated activity, normalized to administered cumulated activity.
• Proposed parameters facilitate consistent and standardized reporting of ventilation study data.