Evaluation of bone-seeking novel radiotracer ⁶⁸Ga-NO2AP-Bisphosphonate for the detection of skeletal metastases in carcinoma breast.

Abstract

The successful labelling of bisphosphonates (BP) with ⁶⁸Ga using macrocyclic chelators such as the based triazacyclononane (NO2AP) is a step forward in the in-house availability of a novel bone-seeking PET radiopharmaceutical with dual advantage of PET/CT imaging and generator production. In this study, we compared the novel generator-based skeletal radiotracer ⁶⁸Ga-1,4,7-triazacyclonone-1,4-diacetic acid (⁶⁸Ga-NO2AP-BP) with sodium fluoride (¹⁸F-NaF) for the detection of skeletal metastases in breast cancer patients. In addition, dosimetric analysis of ⁶⁸Ga-NO2AP-BP was performed in a subset of patients. This was a prospective study of histopathologically proven cases of breast cancer patients who were referred for bone scintigraphy and underwent positron emission tomography/computed tomography (PET/CT) with ¹⁸F-NaF and ⁶⁸Ga-NO2AP-BP within a week in random order. The scans of each patient were compared both qualitatively for image quality and quantitatively for number of lesions and SUVmax of lesions. Dosimetric analysis was performed in five patients. Their PET/CT scans were acquired at multiple time points and urine and blood samples were collected. Dosimetric calculations were performed using OLINDA/EXM 1.1 software. Statistical analysis was done using Stata 13 (StataCorp) software package. An agreement analysis regarding number of lesions detected with the two skeletal radiotracers was carried out. The image quality of ⁶⁸Ga-NO2AP-BP PET/CT scans were comparable to that of ¹⁸F-NaF. There was no statistically significant difference in the SUVmax of lesions, normal bone and lesion to background ratio between the two skeletal radiotracers. There was good agreement in the number of lesions detected by both skeletal radiotracers. The mean whole body effective dose for ⁶⁸Ga-NO2AP-BP was 0.00583 mSv/MBq and the effective dose equivalent was 0.0086 mSv/MBq. The excellent lesion detection agreement between ⁶⁸Ga-NO2AP-BP and ¹⁸F-NaF favours the former as an alternative for skeletal scintigraphy in centres without an on-site cyclotron. The favourable dosimetric results and its potential to be used as a theranostic agent makes it an important generator-based skeletal radiotracer.