Metal artifact reduction of CT scans to improve PET/CT

In recent years, different metal artifact reduction methods have been developed for CT. These methods have only recently been introduced for PET/CT even though they could be beneficial for interpretation, segmentation, and quantification of the PET/CT images. In this study, phantom and patient scans were analyzed visually and quantitatively to measure the effect on PET images of iterative metal artifact reduction (iMAR) of CT data. Methods: The phantom consisted of 2 types of hip prostheses in a solution of 18F-FDG and water. 18F-FDG PET/CT scans of 14 patients with metal implants (either dental implants, hip prostheses, shoulder prostheses, or pedicle screws) and 68Ga-labeled prostate-specific membrane antigen (68Ga-PSMA) PET/CT scans of 7 patients with hip prostheses were scored by 2 experienced nuclear medicine physicians to analyze clinical relevance. For all patients, a lesion was located in the field of view of the metal implant. Phantom and patients were scanned in a PET/CT scanner. The standard low-dose CT scans were processed with the iMAR algorithm. The PET data were reconstructed using attenuation correction provided by both standard CT and iMAR-processed CT. Results: For the phantom scans, cold artifacts were visible on the PET image. There was a 30% deficit in 18F-FDG concentration, which was restored by iMAR processing, indicating that metal artifacts on CT images induce quantification errors in PET data. The iMAR algorithm was useful for most patients. When iMAR was used, the confidence in interpretation increased or stayed the same, with an average improvement of 28% 6 20% (scored on a scale of 0%–100% confidence). The SUV increase or decrease depended on the type of metal artifact. The mean difference in absolute values of SUVmean of the lesions was 3.5% 6 3.3%. Conclusion: The iMAR algorithm increases the confidence of the interpretation of the PET/CT scan and influences the SUV. The added value of iMAR depends on the indication for the PET/CT scan, location and size/type of the prosthesis, and location and extent of the disease

Interobserver agreement of interim and end-of-treatment18F-FDG PET/CT in diffuse large B-cell lymphoma : Impact on clinical practice and trials

We aimed to assess the interobserver agreement of interim PET (I-PET) and end-of-treatment PET (EoT-PET) using the Deauville score (DS) in first-line diffuse large B-cell lymphoma (DLBCL) patients. Methods: I-PET and EoT-PET scans of DLBCL patients were performed in the HOVON84 study (2007–2012), an international multicenter randomized controlled trial. Patients received R-CHOP14 and were randomized to receive rituximab intensification in the first 4 cycles or not. I-PET was performed after 4 cycles (for observational purposes), and EoT-PET after 6 or 8 cycles. Two independent central reviewers retrospectively scored all scans according to the DS system, masked to clinical outcomes. Results were dichotomized as negative (DS of 1–3) or positive (DS of 4–5). Besides percentage overall agreement (OA), we calculated agreement for positive and negative scores, expressed as positive agreement (PA) and negative agreement (NA), respectively. Results: 465 I-PET and 457 EoT-PET scans were centrally reviewed; baseline18F-FDG PET or PET/CT was available in 75%–77%, and CT in the remaining cases. Percentage OA for I-PET and EoT-PET were 87.7% and 91.7% (P 5 0.049), with NA of 92.0% and 95.0% (P 5 0.091), and PA of 73.7% and 76.3% (P 5 0.656), respectively. Conclusion: Interobserver agreement using DS in DLBCL patients in I-PET and EoT-PET yields high OA and NA. The lower PA suggests that EoT-PET/CT treatment evaluation in daily practice and I-PET–adapted trials may benefit from dual reads and central review, respectively

18F-FDG PET improves baseline clinical predictors of response in diffuse large B-cell lymphoma: The HOVON-84 study

We aimed to determine the added value of baseline metabolic tumor volume (MTV) and interim positron emission tomography (I-PET) to age-adjusted international prognostic index (aaIPI) to predict 2- year progression-free survival (PFS) in diffuse large B-cell lymphoma (DLBCL). Secondary objectives were to investigate optimal I-PET response criteria (using Deauville score (DS) - or quantitative change in maximum Standardized Uptake Value (ΔSUVmax) between baseline and I-PET). Methods: Observational I-PET scans were performed after four cycles R(R)-CHOP14 (I-PET4) in the HOVON-84 randomized clinical trial (EudraCT 2006-005174-42), and centrally reviewed using DS (cut-off 4-5). Additionally, ΔSUVmax (prespecified cut-off 70%) and baseline MTV were measured. Multivariable hazard ratios (HR), positive (PPV), and negative predictive values (NPV) were obtained for 2-year PFS. Results: 513 I-PET4 scans were reviewed according to DS, and ΔSUVmax and baseline MTV were available for 367 and 296 patients. NPV of I-PET ranged between 82% and 86% for all PET response criteria. Univariate HR and PPV were optimal for ΔSUVmax (4·8 and 53%, respectively) compared to DS (3·1 and 38%, respectively). AaIPI and ΔSUVmax independently predicted 2-year PFS (HRs 3·2 and 5·0, respectively); adding MTV slightly improved this. Low/low-intermediate aaIPI combined with ΔSUVmax >70% (37% of patients) yielded a NPV of 93%, and the combination of high-intermediate/high aaIPI and ΔSUVmax=70% a PPV of 65%. Conclusion: In this DLBCL study, I-PET after four cycles R(R)-CHOP14 added predictive value to aaIPI for 2-year PFS, and both were independent response biomarkers in a multivariable Cox model. We externally validated that ΔSUVmax outperformed Deauville score in 2-year PFS prediction

Prognostic value of TARC and quantitative PET parameters in relapsed or refractory Hodgkin lymphoma patients treated with brentuximab vedotin and DHAP

Risk-stratified treatment strategies have the potential to increase survival and lower toxicity in relapsed/refractory classical Hodgkin lymphoma (R/R cHL) patients. This study investigated the prognostic value of serum (s)TARC, vitamin D and lactate dehydrogenase (LDH), TARC immunohistochemistry and quantitative PET parameters in 65 R/R cHL patients who were treated with brentuximab vedotin (BV) and DHAP followed by autologous stem-cell transplantation (ASCT) within the Transplant BRaVE study (NCT02280993). At a median follow-up of 40 months, the 3-year progression free survival (PFS) was 77% (95% CI: 67–88%) and the overall survival was 95% (90–100%). Significant adverse prognostic markers for progression were weak/negative TARC staining of Hodgkin Reed-Sternberg cells in the baseline biopsy, and a high standard uptake value (SUV)mean or SUVpeak on the baseline PET scan. After one cycle of BV-DHAP, sTARC levels were strongly associated with the risk of progression using a cutoff of 500 pg/ml. On the pre-ASCT PET scan, SUVpeak was highly prognostic for progression post-ASCT. Vitamin D, LDH and metabolic tumor volume had low prognostic value. In conclusion, we established the prognostic impact of sTARC, TARC staining, and quantitative PET parameters for R/R cHL, allowing the use of these parameters in prospective risk-stratified clinical trials. Trial registration: NCT02280993