Establishment of Provisional Multicenter Local Diagnostic Reference Levels for Adult V/Q SPECT/CT: A South African Pilot Study

Abstract The aim of this study was to establish facility-specific and provisional multicenter local diagnostic reference levels (LDRLs) for adult ventilation–perfusion (V/Q) single-photon emission computed tomography (SPECT)/computed tomography (CT) examinations in South African nuclear medicine facilities using a structured multicenter approach consistent with international DRL methodology. A retrospective study was conducted between 2021 and 2024 across three South African nuclear medicine facilities. Adult patients (≥18 years) undergoing either 2-day V/Q SPECT/CT or 1-day perfusion-only SPECT/CT were included. Facility median administered activities and CT dose metrics including volume computed tomography dose index (CTDIvol) and dose-length product (DLP) were calculated. Provisional multicenter LDRLs were derived as the 75th percentile of facility median values. Owing to the limited number of participating facilities (n = 3), the resulting values are presented as preliminary multicenter optimization benchmarks rather than nationally representative DRLs. A total of 175 adult studies were analyzed (median age 50 years; interquartile range: 33.0–67.5). One facility performed 2-day V/Q imaging using Technegas and 99mTc-MAA, whereas all three facilities performed 1-day perfusion-only protocols using 99mTc-MAA. For the 2-day V/Q protocol, provisional benchmark values derived from a single participating facility were 500 MBq for ventilation activity, 185 MBq for perfusion activity, 3.9 mGy for CTDIvol, and 142 mGy·cm for DLP. For 1-day perfusion-only studies, the provisional LDRLs were 285 MBq for perfusion activity, 4.6 mGy for CTDIvol, and 172 mGy·cm for DLP. Substantial interfacility variability was observed, particularly for CT dose metrics. This study established the first provisional multicenter LDRLs for adult V/Q SPECT/CT in South Africa. Considerable interfacility variability in CT dose metrics was observed, reflecting differences in scanner technology, exposure-control strategies, protocol implementation, and scan-length selection. The proposed protocol-specific optimization benchmarks, comprising provisional multicenter LDRLs for 1-day perfusion-only imaging and provisional benchmarks for the 2-day V/Q protocol, provide practical guidance for dose harmonization across participating facilities. Elevated administered activities observed for 1-day perfusion-only protocol exceeded internationally recommended activity ranges and therefore represent an important target for protocol optimization. Further multicenter expansion will be required to support the future development of nationally representative diagnostic reference levels for adult V/Q SPECT/CT practice in South Africa.