ABSTRACT
Aim: Several series have already demonstrated that intratumoral subvolumes with high tracer avidity (hotspots) in 18F-flurodesoxyglucose positron-emission tomography (FDG-PET/CT) are preferential sites of local recurrence (LR) in various solid cancers after radiotherapy (RT), becoming potential targets for dose escalation. However, studies conducted on head and neck squamous cell carcinoma (HNSCC) found only a moderate overlap between pre- and post-treatment subvolumes. A limitation of these studies was that scans were not performed in RT treatment position (TP) and were coregistred using a rigid registration (RR) method. We sought to study (i) the influence of FDG-PET/CT acquisition in TP and (ii) the impact of using an elastic registration (ER) method to improve the localization of hotpots in HNSCC. Methods: Consecutive patients with HNSCC treated by RT between March 2015 and September 2017 who underwent FDG-PET/CT in TP at initial staging (PETA) and during follow-up (PETR) were prospectively included. We utilized a control group scanned in non treatment position (NTP) from our previous retrospective study. Scans were registered with both RR and ER methods. Various sub-volumes (AX; x = 30, 40, 50, 60, 70, 80, and 90%SUVmax) within the initial tumor and in the subsequent LR (RX; x = 40 and 70%SUVmax) were overlaid on the initial PET/CT for comparison [Dice, Jaccard, overlap fraction = OF, common volume/baseline volume = AXnRX/AX, common volume/recurrent volume = AXnRX/RX]. Results: Of 199 patients included, 43 (21.6%) had LR (TP = 15; NTP = 28). The overlap between A30, A40, and A50 sub-volumes on PETA and the whole metabolic volume of recurrence R40 and R70 on PETR showed moderate to good agreements (0.41-0.64) with OF and AXnRX/RX index, regardless of registration method or patient position. Comparison of registration method demonstrated OF and AXnRX/RX indices (x = 30% to 50%SUVmax) were significantly higher with ER vs. RR in NTP (p < 0.03), but not in TP. For patient position, the OF and AXnRX/RX indices were higher in TP than in NTP when RR was used with a trend toward significance, particularly for x=40%SUVmax (0.50±0.22 vs. 0.31 ± 0.13, p = 0.094). Conclusion: Our study suggested that PET/CT acquired in TP improves results in the localization of FDG hotspots in HNSCC. If TP is not possible, using an ER method is significantly more accurate than RR for overlap estimation.
ABSTRACT
OBJECTIVE: Following the implementation of single-photon emission computed tomography ventilation/perfusion (SPECT V/Q) in our department, we previously carried out an observational study over the period 2011-2013 that showed the safety of SPECT V/Q to rule out pulmonary embolism (PE). However, PE prevalence (28%) was high compared with some studies. Our hypothesis was that the use of SPECT V/Q may be responsible for an overdiagnosis of PE, especially at the implementation phase of the test. The aim was to carry out a time trend analysis of the evolution over the years of PE diagnosis with SPECT V/Q. PATIENTS AND METHODS: To evaluate the time trend of SPECT V/Q results, the conclusions of all SPECT V/Q scans performed for a suspected acute PE in our department from April 2011 to December 2016 were collected. To confirm the safety of a diagnostic management on the basis of SPECT V/Q to rule out PE, a retrospective observational study of the outcome of patients assessed with SPECT V/Q for suspected acute PE was carried out during the period 2014-2016. SPECT V/Q was interpreted using a diagnostic cutoff of one segmental or two subsegmental mismatches. The final diagnostic conclusion was established by the physician responsible for patient care. The safety of SPECT V/Q was assessed by monitoring the risk of thromboembolic events during the 3-month follow-up period in patients left untreated on the basis of a negative SPECT V/Q. RESULTS: Over the period 2011-2016, an average 16% (95% confidence interval: 10-22%) annual reduction in the proportion of positive SPECT V/Q results was observed. The percentage of positive SPECT V/Q results was 25.3% over the period 2011-2013 compared with 16.3% in 2014-2016 (P<0.0001). Out of the 696 patients analyzed over the period 2014-2016, the SPECT V/Q was positive, indeterminate, and negative in 118, 3, and 575 patients, respectively. The 3-month thromboembolic risk in patients in whom PE was deemed absent according to the SPECT V/Q was 3/543=0.55% (95% confidence interval 0.19-1.61). CONCLUSION: A continuous decrease in the annual proportion of positive SPECT V/Q results was mainly observed while maintaining the safety of the test to rule out PE. Explanatory factors include the introduction of a combined SPECT/CT scan, increased experience and familiarity with the test, and an increased awareness of the risks and consequences of overdiagnosing PE.
