ESTABLISHMENT OF LOCAL DIAGNOSTIC REFERENCE LEVELS (LDRL) FOR WHOLE BODY GALLIUM-68 (GA-68) FAPI PET/CT IMAGING: THE FIRST PRELIMINARY STUDY IN INDONESIA

Abstract

The radiopharmaceutical Gallium-68 Fibroblast Activation Protein Inhibitor (Ga-68 FAPI) offers high diagnostic superiority in nuclear oncology. However, as a modality that has only recently been adopted in Indonesia, there is currently a lack of reference dose data or Diagnostic Reference Levels (DRLs) to guide radiation protection optimization. Consequently, this study aims to establish LDRLs for injected activity and CT dose parameters (CTDIvol and DLP) specifically for Ga-68 FAPI PET/CT examinations using a Whole Body protocol. A retrospective study was conducted on 46 patients (15 males, 31 females; mean age 57 years) who underwent examinations at the Department of Nuclear Medicine between September 17 and November 26, 2025. All examinations were performed using a GE Discovery IQ Gen 2 PET/CT system. The LDRL was determined as the 75th percentile value (P75) of the dose distribution. The mean patient body weight was 54.68 kg. The established LDRL values are Injected Activity of 118.23 MBq, CTDIvol of 6.75 mGy, and DLP of 917.45 mGy.cm. Based on the DLP/CTDIvol ratio, the mean scan length was estimated at 135.9 cm. This study presents the first LDRL for Ga-68 FAPI in Indonesia. The results demonstrate the use of low and optimized radiation doses, facilitated by high-sensitivity detector technology and low-dose CT protocols.