The retrospective binning method improves the consistency of phase binning in respiratory-gated PET/CT.

This study assesses the accuracy of prospective phase-gated PET/CT data binning and presents a retrospective data binning method that improves image quality and consistency. Respiratory signals from 17 patients who underwent 4D PET/CT were analysed to evaluate the reproducibility of temporal triggers used for the standard phase-based gating method. Breathing signals were reprocessed to implement retrospective PET data binning. The mean and standard deviation of time lags between automatic triggers provided by the Real-time Position Management (RPM, Varian) gating device and inhalation peaks derived from respiratory curves were computed for each patient. The total number of respiratory cycles available for 4D PET/CT according to the binning mode (prospective versus retrospective) was compared. The maximum standardized uptake value (SUV(max)), biological tumour volume (BTV) and tumour trajectory measures were determined from the PET/CT images of five patients. Compared to retrospective binning (RB), prospective gating approach led to (i) a significant loss in breathing cycles (15%) and (ii) the inconsistency of data binning due to temporal dispersion of triggers (average 396 ms). Consequently, tumour characterization could be impacted. In retrospective mode, SUV(max) was up to 27% higher, where no significant difference appeared in BTV. In addition, prospective mode gave an inconsistent spatial location of the tumour throughout the bins. Improved consistency with breathing patterns and greater motion amplitude of the tumour centroid were observed with retrospective mode. The detection of the tumour motion and trajectory was improved also for small temporal dispersion of triggers. This study shows that the binning mode could have a significant impact on 4D PET images. The consistency of triggers with breathing signals should be checked before clinical use of gated PET/CT images, and our RB method improves 4D PET/CT image quantification.

Evaluation of the response to therapy of head and neck squamous cell carcinoma by using 3-[123I]iodo-L-alpha-methyl tyrosine and single photon emission tomography.

Early detection of residual tumour tissue offers the possibility for rapid administration of adjuvant treatment. Single photon emission tomography (SPET) with 3-[123I]iodo-L-alpha-methyl tyrosine (IMT) offers the ability to detect recurrence. The aim of this study was to carry out a prospective evaluation of sequential IMT SPET before and after primary therapy and to determine the best timing for scanning in order to establish the response to treatment. Sixteen consecutive patients with histologically proven head and neck cancer (HNC), who underwent IMT SPET before therapy, within 1 week of therapy, and 1 and 3 months after completion of primary therapy were included. Images were classified, according to clinical evaluation, as indicating a high likelihood (HL), intermediate likelihood (IL) and low likelihood (LL) that residual tumoural tissue was present. The definitive clinicopathological diagnosis and follow-up was considered as the 'gold standard'. Based on the definitive clinicopathological outcome, 10 of 16 patients were diagnosed with evidence of local tumour and six without. Nine of 10 patients with evidence of local tumour presented with an HL IMT SPET image after 3 months, seven of whom were from within the first week. In this group, 1/10 patients was considered clinically HS the first week and eventually 4/10 patients became HL, of which there were three at 3 months. Of the six patients diagnosed without local evidence of tumour, with an average follow-up of 15 months, 6/6 were clinically LL in the first week. Three of six had a consistently LL IMT SPET from within the first week. The three other patients had an HL scan the first week, of which one became IL. It is concluded that IMT SPET assessed the response to primary therapy most accurately 3 months after completion of therapy. An IMT SPET image that indicates a high likelihood of residual tumoural tissue may allow earlier stratification of the patients for secondary treatment. If negative, an IMT SPET can exclude residual tumoural tissue from within the first week after completion of therapy.

Diagnosis of recurrent head and neck squamous cell carcinoma with 3-[123I]iodo-L-alpha-methyltyrosine SPET.

The distribution of 3-[123I]iodo-L-alpha-methyltyrosine (123I-3-IMT) in the tumour region of 21 patients with clinically suspected recurrent squamous cell head and neck carcinoma was studied. Single-photon emission tomography (SPET) imaging of the head and neck region was performed 10 min after the injection of 130-170 MBq 123I-3-IMT using a dual-detector gamma camera. Images were interpreted visually and classified as positive or negative for recurrent disease. In addition, target to background ratios (T/B) were measured using semi-automated region of interest analysis. IMT-SPET results were compared with the data derived from clinicopathological follow-up. IMT-SPET detected recurrent disease in 14 of 15 patients (sensitivity 93%). T/B ratios ranged between 1.5 and 2.4 (mean 1.88). One patient with a small tumour (1.2 cm) had a false-negative result. This is attributed to the limited spatial resolution of the SPET system. Five of six patients were correctly diagnosed to be negative for tumour recurrence. T/B ratios ranged between 1.2 and 1.4 (mean 1.30). In one patient IMT-SPET was positive without evidence of recurrence based on clinicopathological follow up. This finding was probably due to uptake into inflammatory tissue. IMT-SPET appears to be a sensitive tool (93%) for the detection of recurrent head and neck squamous cell carcinoma. Further studies with 123I-3-IMT as a metabolic tracer for the detection of head and neck cancer recurrence using SPET are recommended.