REVIEW OF THE CURRENT PRACTICE OF THE INHALATIONAL USE OF POSITRON EMITTERS

Purpose: In this paper, I am reviewing the current state of art of use of PET imaging in inhalational studies, exploring the potential for this imaging modality in the respiratory field. Inhalational delivery is a commonly used method of drug administration, especially for conditions that affect the lung where optimal lung drug exposure is desired, for example steroids in chronic obstructive pulmonary disease or bronchial asthma (2) or for conditions where the kinetics of systemic therapy has limited access to lungs in conditions such as idiopathic pulmonary fibrosis (3). Approach: I searched the literature, using PubMed and MEDLINE databases, for papers and publications looking into the inhalational use of positron emitters over the last two decades. Results: There has been a quest recently to administer drugs through inhalational methods as an alternative to systemic administration allowing more effective dosing levels with reduced systemic toxicity (4). Nuclear imaging methods such as Single Photon Emission computed tomography (SPECT) and PET, have been used to assess aerosol delivery to the lung. Higher sensitivity, the ability for dynamic acquisition and physiological respiratory gating confers an advantage to PET (7). The biodistribution in the lungs of a number of radiolabeled agents administered via inhalation such as [11C] triamcinolone, [18F] fluticasone, [11C] zanamivir has been evaluated using PET (8-11). Inhalational biodistribution of FDG has also been investigated in conditions such as cystic fibrosis and lung inflammation (11). Conclusions: There are currently continuing advancements in radiotracer development and imaging technologies which offer promising avenues for enhancing drug delivery via inhalation.