from eight sites, including the survey authors, were collected for the survey of QC practices for gamma cameras and SPECT/CT. The locations and types of the participating sites and the roles of the survey respondents are summarised in Table 2.
State-wide medical physics and radiation safety services are provided to public hospitals by single organisations in both Queensland and South Australia. The respondent from Queensland was based at a single site, while the respondent from South Australia worked across several sites. The latter also confirmed that the sites overall follow the same QC testing schedule. For simplification, the network of public hospitals in South Australia have been combined into a single survey response.
A QC manual, which included a recommended testing schedule, was available for the network of public hospitals in Queensland. The creation of the manual was aided by SPECT/CT systems across all sites being from the same vendor. It was noted that the testing schedule included a series of tests that are performed as an annual QC testing program. The respondent, however, commented that they cannot ascertain if the tests or frequencies were always followed at individual sites.
All participating sites operated up to 3-4 gamma cameras and SPECT/CT systems, except for the sites in South Australia for which data was not readily available.
For reporting purposes, the tests identified during the analyses were categorised as either being part of daily or periodic QC testing programs. Fig. 1 summarises the basis or reference for the development of the daily and periodic QC programs across all sites. For daily QC, all participating sites followed the schedules recommended by the vendors. In relation to periodic QC schedules, three of the sites followed the vendors’ recommendations, while the remaining five sites used a combination of recommendations from vendors and self-designed schedules. The self-designed schedules varied across sites due to factors such as availability and experience of physicists/technologists and overall scanner stability.
Table 3 compares the daily QC tests performed at the participating sites. A comparison of the periodic QC schedules and the professional group(s) responsible for performing each test across the participating sites is provided in Table 4. It was noted that some of the participating sites performed annual physics surveys, which included several tests, on their gamma cameras and SPECT/CT systems.
Gamma Camera – Planar Tests
Daily QC tests at all participating sites involved flood-field uniformity verification without photomultiplier tube (PMT) tuning and the execution of the daily CT test function available on the scanner software. The method for flood-field uniformity verifications (intrinsic or extrinsic/system) and the daily CT tests (phantom-based image quality or CT air dose calibrations) depended on vendor specifications
In contrast to daily QC tests, variations in testing schedules for periodic QC tests between the participating sites were observed.
In addition to being performed on a daily basis, intrinsic or system uniformity verifications without tuning were conducted weekly at Site 4 and was part of the annual physics survey at Site 3. High-count (at least 50 million counts) intrinsic uniformity verifications without tuning were performed by medical physicists before and after monthly PMT tuning and 200-million counts uniformity calibrations at Site 8. High-count uniformity verifications without tuning were performed as part of the annual physics survey at Site 1.
Weekly intrinsic flood-field uniformity verifications post-tuning were performed at Sites 1, 2, 3, 4 and 7, mostly by nuclear medicine technologists. More thorough tuning with high-count flood-field uniformity calibrations were performed monthly at all sites, except at Site 4. Across all sites, the tests were performed either by nuclear medicine technologists or by medical physicists. The respondent at Site 4 noted that service engineers performed PMT tuning when daily and weekly flood-field uniformity tests results fell outside of passing limits or when artefacts were observed.
Intrinsic uniformity tests using off-peak energy windows to check for crystal hydration and PMT tuning were performed as part of annual physics surveys at Sites 1 and 3, and on an ad-hoc basis at Site 8. The respondent at Site 1 commented that crystal hydration was a recurring issue with gamma cameras at the site.
System energy resolution, multiple window spatial resolution and collimator hole alignment testing were performed only at Site 3 as part of their annual physics survey. Site 3 also performed qualitative and quantitative system spatial resolution tests monthly and annually, respectively. System spatial resolution tests were performed annually at Sites 1 and 6, and on an ad-hoc basis at Site 7.
System planar sensitivity was performed monthly at Site 6, annually at Sites 1 and 4 and on an ad-hoc basis at Sites 5, 7, and 8. The respondent from Site 7 noted that the test was also performed after every scanner service. The test was performed by medical physicists across all sites.
Gamma Camera – Whole Body Tests
Whole-body spatial resolution, count rate variability and exposure time correction tests were performed only at Site 3 as part of their annual physics survey.
SPECT Tests
Centre of rotation (COR) offset verifications were performed monthly at Sites 2, 3, 5 and 8, quarterly at Site 1, and on an ad-hoc basis at Site 7. Site 4 performed the test on a weekly basis or after a collimator change. Additionally, it is noted that Site 1 switched to a quarterly COR offset check from monthly checks due to the stability of SPECT systems observed over a period of time. This test was performed either by nuclear medicine technologists or medical physicists at the participating sites.
SPECT image quality testing was performed at Sites 4, 5 and 8 on an ad-hoc basis and six-monthly at Site 1. Site 3 performed the test as part of the annual physics survey. The respondent from Site 4 commented that SPECT image quality testing was typically performed when requested for research trials. This test was performed by medical physicists across the participating sites.
SPECT spatial resolution and SPECT uniformity and sensitivity were performed as part of annual physics surveys at Sites 1 and 3.
SPECT/CT Tests
Vendor service engineers performed SPECT/CT alignment calibrations and verifications during preventative maintenance service across all participating sites. Ad-hoc verifications were performed by medical physicists at Sites 3, 4 and 8, and after major services/repairs at Site 2. The respondent from Site 1 noted that they would not repeat an alignment check during their annual physics survey if they were able to review the service report from the engineers.
CT Tests
Testing of the CT component of hybrid SPECT/CT systems in accordance with CT compliance requirements was performed annually at Sites 2 and 8, and biennially at Sites 5 and 7. CT compliance testing was also performed after major CT service or repair at Sites 7 and 8.
Analyses of QC Results
The outcomes of daily and periodic QC tests at the participating sites were based on vendor-set or locally-set pass/fail criteria (Fig. 2). For daily QC tests, the decision to proceed with patient imaging or to initiate investigation was based on vendor-set passing limits at all sites, except for two sites which used a pass/fail criteria based on locally-determined passing limits. At one of the two sites, the passing limits for daily flood-field uniformity tests were based on the experience of the local medical physicist. At the other site, the passing limits were determined from a standard deviation analysis of daily flood-field uniformity tests. For periodic QC tests, five sites used passing limits set by the vendors, while three used locally-set criteria which were mainly based on baselines set at acceptance testing.
As part of their local QA programs, four sites performed further analyses of daily flood-field uniformity QC results. Quarterly and annual reviews were each performed at two sites, while trend analyses and monthly reviews were each performed at single sites (Fig. 3). Only two sites reviewed periodic tests results, with one performing monthly reviews while the other performing annual reviews (Fig. 3). Oversight and review of QC results were performed by medical physicists at the sites.
Phantoms
Information on the phantoms available for gamma camera and SPECT/CT QC tests were obtained from seven of the eight surveyed sites. Fig. 4 summarises the number of sites possessing commonly used phantoms for gamma camera and SPECT/CT tests. It was noted that the SPECT image quality test in the latest NEMA NU-1 publication [17] requires the PET IEC Body phantom.
Vendor-specific phantoms for daily CT, periodic SPECT/CT alignment and COR tests were available at all sites but were not included in Fig. 4. Additional phantoms such as Wilke phantoms for CT laser alignment check, anthropomorphic phantoms, and Kyoto fillable phantoms with hard insert were also not included.