Clinical evidence on PET–CT for radiation therapy planning in head and neck tumours

A pilot study of [68Ga]Ga-fibroblast activation protein inhibitor-04 PET/CT in renal cell carcinoma

OBJECTIVES

As a promising positron emission tomography (PET) tracer, [68Ga]Ga-fibroblast activation protein inhibitor-04([68Ga]Ga-FAPI-04) performs better than 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) at diagnosing primary and metastatic lesions in patients with various types of cancer. We investigated the utility of [68Ga]Ga-FAPI-04 PET/CT for the detection of primary and metastatic lesions in renal cell carcinoma (RCC). [18F]FDG PET/CT were used for comparison.

METHODS

Twenty-two patients with suspected RCC or recurrent RCC were enrolled in our study. Among these patients, 14 were newly diagnosed with RCC, 3 had recurrent RCC, and 5 were excluded from further analysis due to having benign renal tumours. Seventeen patients with RCC underwent [68Ga]Ga-FAPI-04 PET/CT, and 6 of them also received [18F]FDG PET/CT. The positive detection rates were calculated and compared with those in patients who underwent both scans.

RESULTS

Data from 17 patients with RCC (median age: 60.5 years, interquartile range [IQR]: 54-70 years) were evaluated. The positive detection rate of [68Ga]Ga-FAPI-04 PET/CT for RCC was 64.7% (11/17). Lymph node metastases (n = 44), lung metastasis (n = 1), and bone metastasis (n = 1) were detected. Six patients with RCC underwent [68Ga]Ga-FAPI-04 and [18F]FDG PET/CT. [68Ga]Ga-FAPI-04 PET/CT showed a higher positive detection rate than [18F]FDG PET/CT in detecting RCC (83.3% [5/6] vs. 50% [3/6], P = 0.545). Additionally, [68Ga]Ga-FAPI-04 PET/CT has higher SUVmax (3.20 [IQR: 2.91-5.80 vs. 2.71 [IQR: 2.13-3.10], P = 0.116) and tumour-to-background ratio (TBR) values (1.60 [IQR: 1.33-3.67] vs. 0.86 [0.48-1.21], P = 0.028) than [18F]FDG PET/CT.

CONCLUSIONS

These findings suggest that [68Ga]Ga-FAPI-04 PET/CT has potential value in RCC diagnosis. Further studies are warranted to validate these results.

ADVANCES IN KNOWLEDGE

Clinical utility of [68Ga]Ga-FAPI-04 in RCC remains unclear, and there are not many similar studies in the literature. We evaluated the role of [68Ga]Ga-FAPI-04 in diagnosing RCC.

Head and neck MRI-based T stage and [18F]FDG PET/CT-based N/M stage improved prognostic stratification in primary nasopharyngeal carcinoma

OBJECTIVES

To evaluate whether MRI-based T stage (TMRI), [18F]FDG PET/CT-based N (NPET/CT), and M stage (MPET/CT) are superior in NPC patients' prognostic stratification based on long-term survival evidences, and whether TNM staging method involving TMRI + NPET/CT + MPET/CT could improve NPC patients' prognostic stratification.

METHODS

From April 2007 to December 2013, 1013 consecutive untreated NPC patients with complete imaging data were enrolled. All patients' initial stages were repeated based on (1) the NCCN guideline recommended "TMRI + NMRI + MPET/CT" ("MMP") staging method; (2) the traditional "TMRI + NMRI + Mconventional work-up (CWU)" ("MMC") staging method; (3) the single-step "TPET/CT + NPET/CT + MPET/CT" ("PPP") staging method; or (4) the "TMRI + NPET/CT + MPET/CT" ("MPP") staging method recommended in present research. Survival curve, ROC curve, and net reclassification improvement (NRI) analysis were used to evaluate the prognosis predicting ability of different staging methods.

RESULTS

[18F]FDG PET/CT performed worse on T stage (NRI =  - 0.174, p < 0.001) but better on N (NRI = 0.135, p = 0.004) and M stage (NRI = 0.126, p = 0.001). The patients whose N stage upgraded by [18F]FDG PET/CT had worse survival (p = 0.011). The "TMRI + NPET/CT + MPET/CT" ("MPP") method performed better on survival prediction when compared with "MMP" (NRI = 0.079, p = 0.007), "MMC" (NRI = 0.190, p < 0.001), or "PPP" method (NRI = 0.107, p < 0.001). The "TMRI + NPET/CT + MPET/CT" ("MPP") method could reclassify patients' TNM stage to a more appropriate stage. The improvement is significant in patients with more than 2.5-years follow-up according to the time-dependent NRI values.

CONCLUSIONS

The MRI is superior to [18F]FDG PET/CT in T stage, and [18F]FDG PET/CT is superior to CWU in N/M stage. The "TMRI + NPET/CT + MPET/CT" ("MPP") staging method could significantly improve NPC patients' long-term prognostic stratification.

CLINICAL RELEVANCE STATEMENT

The present research provided long-term follow-up evidence for benefits of MRI and [18F]FDG PET/CT in TNM staging for nasopharyngeal carcinoma, and proposes a new imaging procedure for TNM staging incorporating MRI-based T stage and [18F]FDG PET/CT-based N and M stage, which significantly improves long-term prognostic stratification for patients with NPC.

KEY POINTS

• The long-term follow-up evidence of a large-scale cohort was provided to evaluate the advantages of MRI, [18F]FDG PET/CT, and CWU in the TNM staging of nasopharyngeal carcinoma. • A new imaging procedure for TNM stage of nasopharyngeal carcinoma was proposed.

Biological target volume based on fluorine-18-fluorode-oxyglucose positron emission tomography/computed tomography imaging: a spurious proposition?

PURPOSE

To assess whether the high metabolic region of fluorine-18-fluorode-oxyglucose (¹⁸F-FDG) in the primary lesion is the crux for recurrence in patients with nasopharyngeal carcinoma (NPC), to assess the feasibility and rationale for use of biological target volume (BTV) based on ¹⁸F-FDG positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT).

METHODS

The retrospective study included 33 patients with NPC who underwent ¹⁸F-FDG-PET/CT at the time of initial diagnosis as well as the time of diagnosis of local recurrence. Paired ¹⁸F-FDG-PET/CT images for primary and recurrent lesion were matched by deformation coregistration method to determine the cross-failure rate between two lesions.

RESULTS

The median volume of the V_pri (primary tumor volume using the SUV thresholds of 2.5), the V_high (the volume of high FDG uptake using the SUV50%max isocontour), and the V_recur (the recurrent tumor volume using the SUV thresholds of 2.5) were 22.85, 5.57, and 9.98 cm³, respectively. The cross-failure rate of V_recur∩high showed that 82.82% (27/33) of local recurrent lesions had < 50% overlap volume with the region of high FDG uptake. The cross-failure rate of V_recur∩pri showed that 96.97% (32/33) of local recurrent lesions had > 20% overlap volume with the primary tumor lesions and the median cross rate was up to 71.74%.

CONCLUSION

¹⁸F-FDG-PET/CT may be a powerful tool for automatic target volume delineation, but it may not be the optimal imaging modality for dose escalation radiotherapy based on applicable isocontour. The combination of other functional imaging could delineate the BTV more accurately.

Survival effect of pretreatment FDG-PET-CT on nasopharyngeal cancer

BACKGROUND/PURPOSE

Accurate staging is the first step for optimal treatment selection in patients with nasopharyngeal carcinoma (NPC). In this propensity-score-matched, population-based cohort study, we investigated the survival effects of pretreatment 8-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸FDG-PET-CT) on patients with NPC.

METHODS

We included patients with stage I-IVA NPC receiving radiotherapy or concurrent chemoradiotherapy and categorized them into two 1:1 propensity score-matched groups according to whether or not they underwent pretreatment ¹⁸FDG-PET-CT and compared their outcomes.

RESULTS

Of the 10,756 patients, propensity score matching yielded 4366 patients in each group. According to multivariable Cox regression analyses, the most prominent correlation between pretreatment ¹⁸FDG-PET-CT and all-cause death was observed in patients with stage II NPC (adjusted hazard ratio [aHR], 0.77; 95% confidence interval [CI], 0.60-0.90; P = .0433), followed by patients with stage III NPC (aHR, 0.81; 95% CI, 0.69-0.94; P = .0071) and patients with stage IVA NPC (aHR, 0.88; 95% CI, 0.79-0.97; P = .0091). This association was not significant in patients with stage I NPC (aHR, 1.20; 95% CI, 0.75-1.93; P = .4426).

CONCLUSION

Pretreatment ¹⁸FDG-PET-CT is associated with longer survival in patients with clinical stage II-IVA NPC but not in stage I NPC.

Stereotactic body radiotherapy plus cetuximab for previously irradiated un-resectable head and neck cancer

BACKGROUND

The aim of the study was to explore the treatment outcomes and prognostic factors for patients with previously irradiated but unresectable recurrent head and neck squamous cell carcinoma (rHNSCC) treated by stereotactic body radiotherapy (SBRT) plus cetuximab at a single institute in Taiwan.

METHODS

From February 2016 to March 2019, 74 patients with previously irradiated but unresectable rHNSCC were treated with SBRT plus cetuximab. All patients received irradiation to the gross tumor and/or nodal area with 40-50 Gy in five fractions, with each fraction interval ≥ 2 days over a 2-week period by using the CyberKnife M6 machine. An¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) scan was performed before treatment for treatment target delineation (n = 74) and 2 months later for response evaluation (n = 60). The median follow-up time was 9 months (range 1-36 months).

RESULTS

The treatment response rate was complete response: 25.0%, partial response: 41.7%, stable disease: 11.7%, and progressive disease: 21.7% based on the criteria of the Response Evaluation Criteria in Solid Tumors (n = 72) and complete metabolic response: 21.7%, partial metabolic response: 51.7%, stable metabolic disease: 13.3%, and progressive metabolic disease: 13.3% based on PET-CT (n = 60), respectively. The 1-/2-year overall survival (OS) and progression-free survival (PFS) rates were 42.8%/22.0% and 40.5%/19.0%, respectively. In the logistic regression model, a re-irradiation interval > 12 months was observed to be the only significant prognostic factor for a favorable treatment response. In the Cox proportional hazards model, a re-irradiation interval > 12 months and gross tumor volume (GTV) ≦ 50 ml were favorable prognostic factors of OS and PFS.

CONCLUSION

SBRT plus cetuximab provides a promising salvage strategy for those patients with previously irradiated but unresectable rHNSCC, especially those with a re-irradiation interval > 12 months or GTV ≦ 50 ml.

Accuracy of metabolic volume and total glycolysis among six threshold-based target segmentation algorithms

OBJECTIVE

This study aimed to evaluate the accuracy of six threshold-based segmentation methods with different target-to-background ratios (TBR), images with different voxel sizes and image noise, in measuring metabolic volume (MV) and total glycolysis (TG).

METHODS

A standard body phantom consisting of six spheres (inner diameters of 37, 28, 22, 17, 13, and 10 mm) was filled with ¹⁸F-FDG solution. The background radioactivity level was 2.65 kBq/mL, and the TBRs were 4 and 8. PET data were acquired for 30 min with list mode. PET data for 30 and 3 min were reconstructed with a three-dimensional ordered subset expectation maximization algorithm plus time-of-flight information with images with 2 and 4 mm isotropic voxels. The six methods examined were absolute standardized uptake value (SUV) of 2.5 (SUV_2.5), 41%, 50%, adaptive 41%, and adaptive 50% thresholds of maximum SUV (Th₄₁, Th₅₀, ThA₄₁, and ThA₅₀, respectively); and the contrast-oriented algorithm (Th_COA). Segmented MV and TG were compared with the actual inner volume and expressed as percentages (%MV_seg and %TG_seg, respectively). In addition, the segmented MV was converted to the diameter, and the differences of it from the reference diameter were compared among six methods.

RESULTS

The Th_COA method yielded the most accurate measurements of %MV_seg and %TG_seg; the difference between %MV_seg or %TG_seg and its reference were smaller than 10% in 30-min and 15% in 3-min images, but the segmented contour was almost the same as the reference diameter. Measurements with Th₅₀ and Th_COA were highly accurate for both %MV_seg and %TG_seg in the large spheres, and the adaptive threshold methods, including ThA₄₁, ThA₅₀, and Th_COA, were also highly accurate in the small spheres. The voxel sizes affected the accuracy of %MV_seg and %TG_seg with a TBR of 4 in any threshold-based methods.

CONCLUSIONS

Of the six threshold-based segmentation methods studied, Th_COA was the most accurate method for evaluating MV and TG and had only minor dependence on TBRs and sphere size. The small voxel sizes improved the variation of the accuracy in low TBR.

Correlation Between FDG Hotspots on Pre-radiotherapy PET/CT and Areas of HNSCC Local Relapse: Impact of Treatment Position and Images Registration Method

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 (PET_A) and during follow-up (PET_R) 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 (A_X; x = 30, 40, 50, 60, 70, 80, and 90%SUVmax) within the initial tumor and in the subsequent LR (R_X; x = 40 and 70%SUVmax) were overlaid on the initial PET/CT for comparison [Dice, Jaccard, overlap fraction = OF, common volume/baseline volume = A_XnR_X/A_X, common volume/recurrent volume = A_XnR_X/R_X].

Results: Of 199 patients included, 43 (21.6%) had LR (TP = 15; NTP = 28). The overlap between A₃₀, A₄₀, and A₅₀ sub-volumes on PET_A and the whole metabolic volume of recurrence R₄₀ and R₇₀ on PET_R showed moderate to good agreements (0.41–0.64) with OF and A_XnR_X/R_X index, regardless of registration method or patient position. Comparison of registration method demonstrated OF and A_XnR_X/R_X 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 A_XnR_X/R_X 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.

Fibroblast activation protein inhibitor (FAPI) PET for diagnostics and advanced targeted radiotherapy in head and neck cancers

Purpose

Cancer-associated fibroblasts (CAFs) expressing fibroblast activation protein (FAP) have been associated with the aggressive nature of head and neck cancers (HNCs). These tumours grow diffusely, leading to extremely challenging differentiation between tumour and healthy tissue. This analysis aims to introduce a novel approach of tumour detection, contouring and targeted radiotherapy of HNCs using visualisation of CAFs: PET-CT with ⁶⁸Ga-radiolabeled inhibitors of FAP (FAPI).

Methods

FAPI PET-CT was performed without complications prior to radiotherapy in addition to contrast enhanced CT (CE-CT) and MRI on 14 patients with HNC. First, for tissue biodistribution analysis, volumes of interest were defined to quantify SUV_mean and SUV_max in tumour and healthy parenchyma. Secondly, using four thresholds of three-, five-, seven- and tenfold increase of FAPI enhancement in the tumour as compared with normal tissue, four different gross tumour volumes (FAPI-GTV) were created automatically. These were compared with GTVs created conventionally with CE-CT and MRI (CT-GTV).

Results

The biodistribution analysis revealed high FAPI avidity within tumorous lesions (e.g. primary tumours, SUV_max 14.62 ± 4.44; SUV_mean 7.41 ± 2.39). In contrast, low background uptake was measured in healthy tissues of the head and neck region (e.g. salivary glands: SUV_max 1.76 ± 0.31; SUV_mean 1.23 ± 0.28). Considering radiation planning, CT-GTV was of 27.3 ml, whereas contouring with FAPI resulted in significantly different GTVs of 67.7 ml (FAPI × 3, p = 0.0134), 22.1 ml (FAPI × 5, p = 0.0419), 7.6 ml (FAPI × 7, p = 0.0001) and 2.3 ml (FAPI × 10, p = 0.0001). Taking these significant disparities between the GTVs into consideration, we merged FAPI-GTVs with CT-GTVs. This resulted in median volumes, that were, as compared to CT-GTVs, significantly larger with FAPI × 3 (54.7 ml, + 200.5% relative increase, p = 0.0005) and FAPI × 5 (15.0 ml, + 54.9%, p = 0.0122). Furthermore, FAPI-GTVs were not covered by CE-CT-based planning target volumes (CT-PTVs) in several cases.

Conclusion

We present first evidence of diagnostic and therapeutic potential of FAPI ligands in head and neck cancer. Larger studies with histopathological correlation are required to validate our findings.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04859-y) contains supplementary material, which is available to authorized users.

Impact of positron emission tomography with computed tomography for image-guided radiotherapy

Therapeutic effectiveness in radiotherapy is partly related to correct staging of the disease and then precise therapeutic targeting. Positron emission tomography (PET) allows the stage of many cancers to be determined and therefore is essential before deciding on radiation treatment. The definition of the therapeutic target is essential to obtain correct tumour control and limit side effects. The part of adaptive radiotherapy remains to be defined, but PET by its functional nature makes it possible to define the prognosis of many cancers and to consider radiotherapy adapted to the initial response allowing an increase over the entire metabolic volume, or targeted at a subvolume at risk per dose painting, or with a decrease in the dose in case of good response at interim assessment.

The effect of different segmentation methods on primary tumour metabolic volume assessed in 18F-FDG-PET/CT in patients with cervical cancer, for radiotherapy planning

Introduction

Gynaecological cancers, including cervical cancer, often require a multidisciplinary approach that includes external beam radiotherapy, chemotherapy, and/or surgical treatment. Biological parameters of the tumour evaluated in ¹⁸F-FDG-PET/CT are used for target volume delineation in radiotherapy planning. The choice of segmentation method may affect the assessment of metabolic tumour volume (MTV) in ¹⁸F-FDG-PET/CT.

Aim of the study

To find the optimal segmentation method for the assessment of primary MTV in ¹⁸F-FDG-PET/CT in cervical cancer patients for radiotherapy planning.

Material and methods

Retrospective analysis was performed on a group of 30 patients with newly diagnosed, histologically confirmed cervical cancer. The primary MTVs were assessed by SUV_max and SUV_mean values; three segmentation methods were used to assess the primary MTV: constant threshold of SUV_max of 2.5, threshold of SUV_max 35%, and threshold of SUV _max 45%. The MTVs were compared with the tumour volumes obtained in magnetic resonance imaging (MRI), which was the "gold standard", to select the best optimal segmentation method reflecting the tumour size. Wilcoxon-Mann-Whitney and t-test were used for statistical analysis.

Results

Depending on the segmentation method chosen, significant differences in the MTVs were obtained (p < 0.001). The highest volumes were obtained using the method based on constant SUV_max of 2.5, while the smallest in case of threshold of SUV_max of 45%. Regarding the volume determined by MRI, a 35% SUV_max threshold was chosen as the most reliable method.

Conclusions

The choice of appropriate segmentation method has a significant impact on the primary MTV assessment in ¹⁸F-FDG-PET/CT in patients with cervical cancer.

18F-FDG PET/CT in staging and delineation of radiotherapy volume for head and neck cancer

PURPOSE

The aim is to investigate the use of ¹⁸F-FDG (fluorine-18 fluorodeoxyglucose) PET/CT in head and neck cancer (HNC) staging and its effect on the therapeutic strategy and radiotherapy (RT) planning.

METHODS AND MATERIALS

One hundred patients with HNC were included. Primary tumor sites: 18% oral cavity, 20% oropharynx, 12% hypopharynx, 11% nasopharynx, 37% larynx, 2% paranasal sinuses. Patients were staged according to the American Joint Committee of Cancer 7th edition. Stage: 5% stage I, 7% stage II, 14% stage III, 61% stage IVA, 7% stage IVB and 6% stage IVC. A contrast-enhanced CT and a ¹⁸F-FDG PET/CT acquired under RT position were performed. Both exams were compared to analyze patients' staging reclassification. Changes in therapeutic strategy were analyzed.

RESULTS

¹⁸F-FDG PET/CT detected 6 distant metastases and treatment intention changed to palliative. Eight synchronous tumors were detected; one received palliative treatment. ¹⁸F-FDG PET/CT reclassified cTNM staging in 27patients. Tumor extension changed in 28 (14% up-staged; 14% down-staged), implying a change in GTV (Gross Tumor Volume) delineation. Nodal detection was reclassified in 47 patients: 8 patients down-staged (N2C to N2A/N2B/N1) and 2 were false positive. Nineteen patients were false negatives and 5 staged as N+(N1/N2A/N2B) turned out into N2C. These staging modifications imply adapting the nodal volume to be irradiated.

CONCLUSIONS

¹⁸F-FDG PET/CT reclassification was higher than 10% in almost all categories studied (cTNM, tumor extension and nodal disease) and detects more metastases and synchronous tumors than conventional studies, which has an impact on the therapeutic patient management and RT planning.

Use of baseline 18F-FDG PET scan to identify initial sub-volumes with local failure after concomitant radio-chemotherapy in head and neck cancer

Introduction

Head and neck squamous cell carcinoma (HNSCC) treated by radio-chemotherapy have a significant local recurrence rate. It has been previously suggested that 18F-FDG PET could identify the high uptake areas that can be potential targets for dose boosting. The purpose of this study was to compare the location of initial hypermetabolic regions on baseline scans with the metabolic relapse sites after radio-chemotherapy in HNSCC.

Results

The initial functional tumor volume was significantly higher for patients with proven local recurrence or residual disease (23.5 cc vs. 8.9 cc; p = 0.0005). The overlap between baseline and follow-up sub-volumes were moderate with an overlap fraction ranging from 0.52 to 0.39 between R40 and I30 to I60.

Conclusion

In our study the overlap between baseline and post-therapeutic metabolic tumor sub-volumes was only moderate. These results need to be investigated in a larger cohort acquired with a more standardized patient repositioning protocol for sequential PET imaging.

Methods

Pre and post treatment PET/CT scans of ninety four HNSCC patients treated with radio-chemotherapy were retrospectively reviewed. Follow-up 18F-FDG PET/CT images were registered to baseline scans using a rigid body transformation. Seven metabolic tumor sub-volumes were obtained on the baseline scans using a fixed percentage of SUV_max (I30, I40, I50, I60, I70, I80, and I90) and were subsequently compared with two post-treatment sub-volumes (R40, R90) in 38 cases of local recurrence or residual metabolic disease. Overlap fraction, Dice and Jaccard indices, common volume/baseline volume and common volume/recurrent volume were used to determine the overlap of the different estimated sub-volumes.

[PET-CT in head and neck cancer]

The importance of ¹⁸F-fluorodesoxyglucose positron-emission tomography (FDG-PET) for the diagnosis of malignant disease is increasing. On one hand, this is due to the high sensitivity of this method, on the other, because the entire body can be examined. FDG-PET can be particularly advantageous for the diagnosis of head and neck tumors, where tumor staging is an important prognostic parameter and essentially determines the therapeutic regimen. This article presents the different possibilities for combined evaluation with PET and computed tomography (CT) for the diagnosis of patients with head and neck cancer. Special focus is placed on primary staging and tumor follow-up, as well as on the role of PET-CT in the diagnosis of patients with cancer of unknown primary origin (CUP). The use of PET-CT for radiotherapy planning and new aspects of PET technology are also discussed.

Effect of different segmentation algorithms on metabolic tumor volume measured on 18F-FDG PET/CT of cervical primary squamous cell carcinoma

Background and purpose

It is known that fluorine-18 fluorodeoxyglucose PET/computed tomography (CT) segmentation algorithms have an impact on the metabolic tumor volume (MTV). This leads to some uncertainties in PET/CT guidance of tumor radiotherapy. The aim of this study was to investigate the effect of segmentation algorithms on the PET/CT-based MTV and their correlations with the gross tumor volumes (GTVs) of cervical primary squamous cell carcinoma.

Materials and methods

Fifty-five patients with International Federation of Gynecology and Obstetrics stage Ia∼IIb and histologically proven cervical squamous cell carcinoma were enrolled. A fluorine-18 fluorodeoxyglucose PET/CT scan was performed before definitive surgery. GTV was measured on surgical specimens. MTVs were estimated on PET/CT scans using different segmentation algorithms, including a fixed percentage of the maximum standardized uptake value (20∼60% SUV_max) threshold and iterative adaptive algorithm. We divided all patients into four different groups according to the SUV_max within target volume. The comparisons of absolute values and percentage differences between MTVs by segmentation and GTV were performed in different SUV_max subgroups. The optimal threshold percentage was determined from MTV_20%∼MTV_60%, and was correlated with SUV_max. The correlation of MTV_{iterative adaptive} with GTV was also investigated.

Results

MTV_50% and MTV_60% were similar to GTV in the SUV_max up to 5 (P>0.05). MTV_30%∼MTV_60% were similar to GTV (P>0.05) in the 5<SUV_max≤10 group. MTV_20%∼MTV_60% were similar to GTV (P>0.05) in the 10<SUV_max≤15 group. MTV_20% and MTV_30% were similar to GTV (P>0.05) in the SUV_max of at least 15 group. MTV_{iterative adaptive} was similar to GTV in both total and different SUV_max groups (P>0.05). Significant differences were observed among the fixed percentage method and the optimal threshold percentage was inversely correlated with SUV_max. The iterative adaptive segmentation algorithm led to the highest accuracy (6.66±50.83%). A significantly positive correlation was also observed between MTV_{iterative adaptive} and GTV (Pearson’s correlation r=0.87, P<0.0001).

Conclusion

MTV_{iterative adaptive} is independent of SUV_max, more accurate, and correlated with GTV. Iterative adaptive algorithm segmentation may be more suitable than the fixed percentage threshold method to estimate the tumor volume of cervical primary squamous cell carcinoma.

Correlation between fluorodeoxyglucose hotspots on pretreatment positron emission tomography/CT and preferential sites of local relapse after chemoradiotherapy for head and neck squamous cell carcinoma

BACKGROUND

The potential benefits of ¹⁸ F-fluoro-2-deoxy-D-glucose-positron emission tomography/CT (FDG-PET/CT) imaging for radiotherapy (RT) treatment planning of head and neck squamous cell carcinoma (HNSCC) are increasingly being recognized. It has been suggested that intratumoral subvolumes with high FDG avidity ("hotspots") are potential targets for selected dose escalation. The purposes of this study were to demonstrate that pre-RT FDG-PET/CT can identify intratumoral sites at increased risk of local relapse after RT and to determine an optimal threshold to delineate smaller RT target volumes that would facilitate RT dose escalation without impaired tolerance.

METHODS

Seventy-two consecutive patients with locally advanced HNSCC treated by RT ± chemotherapy were included in this study. All patients underwent FDG-PET/CT at initial staging (PET_A ) and during systematic follow-up (PET_R ). FDG-PET/CT was coregistered on the initial CT scan with a rigid method. Various subvolumes (A_X ; × = 30%, 40%, 50%, 60%, 70%, 80%, and 90% standardized uptake value maximum [SUVmax] thresholds) within the primary tumor and in the subsequent local relapse (R_X ; × = 40% and 70% SUVmax thresholds) were compared together (Dice, Jaccard, overlap fraction, common volume/baseline volume, and common volume/recurrent volume).

RESULTS

Nineteen patients (26%) had local relapses. Using a 40% SUVmax threshold, the initial metabolic tumor volume was significantly higher in patients with local relapses than in controlled patients (10.4 ± 8.6 vs 5.1 ± 4.9 cc; p = .002) as well as total lesion glycolysis (117.9 ± 88.6 vs 60.6 ± 80.4; p = .013). For both methods, the overlap index among A₃₀ , A₄₀ , and A₅₀ subvolumes on PET_A and the whole metabolic volume of recurrence R₄₀ and R₇₀ on PET_R showed a moderate agreement (0.52 to 0.43).

CONCLUSION

Our study does not find high overlap index values between the initial tumor and recurrence subvolumes, probably because of a suboptimal coregistration. Our results also confirm that metabolic tumor volume and total lesion glycolysis are independently correlated with recurrence-free survival in patients with HNSCC. Further larger prospective studies with FDG-PET/CT performed in the same RT position and with a validated elastic registration method are needed. © 2017 Wiley Periodicals, Inc. Head Neck 39: 1155-1165, 2017.

An enhanced random walk algorithm for delineation of head and neck cancers in PET studies

An algorithm for delineating complex head and neck cancers in positron emission tomography (PET) images is presented in this article. An enhanced random walk (RW) algorithm with automatic seed detection is proposed and used to make the segmentation process feasible in the event of inhomogeneous lesions with bifurcations. In addition, an adaptive probability threshold and a k-means based clustering technique have been integrated in the proposed enhanced RW algorithm. The new threshold is capable of following the intensity changes between adjacent slices along the whole cancer volume, leading to an operator-independent algorithm. Validation experiments were first conducted on phantom studies: High Dice similarity coefficients, high true positive volume fractions, and low Hausdorff distance confirm the accuracy of the proposed method. Subsequently, forty head and neck lesions were segmented in order to evaluate the clinical feasibility of the proposed approach against the most common segmentation algorithms. Experimental results show that the proposed algorithm is more accurate and robust than the most common algorithms in the literature. Finally, the proposed method also shows real-time performance, addressing the physician's requirements in a radiotherapy environment.

Radiation Oncology--New Approaches in Squamous Cell Cancer of the Head and Neck

The many advances in radiotherapy for squamous cell cancer of the head and neck described in this article will have significant effects on the ultimate outcomes of patients who receive this treatment. The technological and clinical advances should allow one to maintain or improve disease control, while moderating the toxicity associated with head and neck radiation therapy.

Influence of FDG-PET on primary nodal target volume definition for head and neck carcinomas

BACKGROUND

The role of 2-[¹⁸F]-fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography (PET)/computed tomography (CT) in routine diagnostic staging remains controversial. In case of discordance between FDG-PET and CT, a compromise has to be made between the risk of false positive FDG-PET and the risk of delaying appropriate salvage intervention. Second, with intensity modulated radiation therapy (IMRT), smaller radiation fields allow tissue sparing, but could also lead to more marginal failures.

METHODS

We retrospectively studied 283 patients with head and neck carcinoma scheduled for radiotherapy between 2002 and 2010. We analyzed the influence of FDG-PET/CT versus CT alone on defining nodal target volume definition and evaluated its long-term clinical results. Second, the location of nodal recurrences was related to the radiation regional dose distribution.

RESULTS

In 92 patients, CT and FDG-PET, performed in mold, showed discordant results. In 33%, nodal staging was altered by FDG-PET. In 24%, FDG-PET also led to an alteration in nodal treatment, including a nodal upstage of 18% and downstage of 6%. In eight of these 92 patients, a regional recurrence occurred. Only two patients had a recurrence in the discordant node on FDG-PET and CT and both received a boost (high dose radiation).

CONCLUSION

These results support the complementary value of FDG-PET/CT compared to CT alone in defining nodal target volume definition for radiotherapy of head and neck cancer.

FDG and Beyond

Although many PET tracers are in use, FDG still is the most widely used in clinical oncology practice. FDG therefore deserves an in-depth discussion, which is even more interesting because of the huge increase in the molecular biology of glucose metabolism. Obviously, other tracers are of increasing importance as well, and these will be discussed in short.

Molecular Imaging to Plan Radiotherapy and Evaluate Its Efficacy

Molecular imaging plays a central role in the management of radiation oncology patients. Specific uses of imaging, particularly to plan radiotherapy and assess its efficacy, require an additional level of reproducibility and image quality beyond what is required for diagnostic imaging. Specific requirements include proper patient preparation, adequate technologist training, careful imaging protocol design, reliable scanner technology, reproducible software algorithms, and reliable data analysis methods. As uncertainty in target definition is arguably the greatest challenge facing radiation oncology, the greatest impact that molecular imaging can have may be in the reduction of interobserver variability in target volume delineation and in providing greater conformity between target volume boundaries and true tumor boundaries. Several automatic and semiautomatic contouring methods based on molecular imaging are available but still need sufficient validation to be widely adopted. Biologically conformal radiotherapy (dose painting) based on molecular imaging-assessed tumor heterogeneity is being investigated, but many challenges remain to fully exploring its potential. Molecular imaging also plays increasingly important roles in both early (during treatment) and late (after treatment) response assessment as both a predictive and a prognostic tool. Because of potentially confounding effects of radiation-induced inflammation, treatment response assessment requires careful interpretation. Although molecular imaging is already strongly embedded in radiotherapy, the path to widespread and all-inclusive use is still long. The lack of solid clinical evidence is the main impediment to broader use. Recommendations for practicing physicians are still rather scarce. (18)F-FDG PET/CT remains the main molecular imaging modality in radiation oncology applications. Although other molecular imaging options (e.g., proliferation imaging) are becoming more common, their widespread use is limited by lack of tracer availability and inadequate reimbursement models. With the increasing presence of molecular imaging in radiation oncology, special emphasis should be placed on adequate training of radiation oncology personnel to understand the potential, and particularly the limitations, of quantitative molecular imaging applications. Similarly, radiologists and nuclear medicine specialists should be sensitized to the special need of the radiation oncologist in terms of quantification and reproducibility. Furthermore, strong collaboration between radiation oncology, nuclear medicine/radiology, and medical physics teams is necessary, as optimal and safe use of molecular imaging can be ensured only within appropriate interdisciplinary teams.

Spatio-temporal stability of pre-treatment 18F-Fludeoxyglucose uptake in head and neck squamous cell carcinomas sufficient for dose painting

BACKGROUND

The pre-treatment 18F-Fludeoxyglucose (FDG) avid subvolume of the tumor has shown promise as a potential target for dose painting in patients with in head and neck squamous cell carcinomas (HNSCC).

PURPOSE

The purposes of this study are: 1) to assess the pre-treatment spatio-temporal variability of FDG PET/CT target volumes and 2) to assess the impact of this variability on dose distribution in dose painting plans in patients with HNSCC.

MATERIAL AND METHODS

Thirty patients were enrolled and scanned twice, three days apart, days prior to treatment. Delineation of the FDG avid subvolume of the tumor and lymph nodes on both scans was performed by a specialist in nuclear medicine yielding GTVPET1 and GTVPET2 and segmentation based on SUV iso-contours were constructed yielding two metabolic target volumes, MTV1 and MTV2. Images were co-registered rigidly and dose painting plans with dose escalation up to 82 Gy to GTVPET1 were planned and GTVPET2 was copied from the co-registered images to the dose planning scan. Variation in dose to the target and modeled tumor control probability were assessed as measures of the impact of imaging variations in a dose painting scenario.

RESULTS

Twenty-four patients were available for full analysis. The median mismatch between GTVPET1 and GTVPET2 was 14.2% (1.7 cm(3)). The median difference in dose to the FDG planning target volume was 0.3 Gy (PTVPET) and 0.4 Gy (PTVMTV). Median difference in the modeled tumor control probability (TCP) was < 0.2% and 23 of 24 patients had a difference in expected TCP < 1%.

CONCLUSIONS

Pre-treatment FDG PET/CT target volumes were stable and day-to-day variability had no relevant impact on dose distribution and expected tumor control in dose painting plans.

Variability of dynamic 18F-FDG-PET data in breast cancer xenografts

BACKGROUND

A murine breast cancer xenograft model was employed to evaluate inter- and intra-variability of various parameters derived from dynamic positron emission tomography with [18F]-fluorodeoxyglucose as tracer (FDG-PET).

MATERIAL AND METHODS

Seventeen female athymic nude foxn1/nu mice with bilaterally implanted triple-negative basal-like ductal carcinoma (MAS98.12) breast cancer xenografts underwent a dynamic PET scan over an hour after injection of approximately 10 MBq FDG. Inter-animal data were obtained from the entire animal cohort, while intra-animal data were from four mice receiving an additional scan after one or two days. Standardised uptake values (SUVmax, SUVmean and SUVmedian) were estimated for all tumours at different time points. Tumour uptake was analysed with a kinetic two-compartment model for estimation of pharmacokinetic parameters. The coefficient of variation (CV) was calculated for all PET-derived metrics.

RESULTS

The CVs for SUVmean and SUVmedian were typically 10-20% for the tumours, depending on the time post-injection and group (intra vs. inter). The CV for SUVmax was mostly higher. The variability in the pharmacokinetic parameters ranged from 23 to almost 150%.

CONCLUSIONS

SUVmean and SUVmedian show less variability than SUVmax. The pharmacokinetic tumour metrics again display much greater variability than the SUV-based metrics. However, it is generally not known which of these metrics that best represents cancer aggressiveness and their use may still depend on the research questions addressed.

Variability of Gross Tumor Volume in Nasopharyngeal Carcinoma Using 11C-Choline and 18F-FDG PET/CT

This study was conducted to evaluate the variability of gross tumor volume (GTV) using ¹¹C-Choline and ¹⁸F-FDG PET/CT images for nasopharyngeal carcinomas boundary definition. Assessment consisted of inter-observer and inter-modality variation analysis. Four radiation oncologists were invited to manually contour GTV by using PET/CT fusion obtained from a cohort of 12 patients with nasopharyngeal carcinoma (NPC) and who underwent both ¹¹C-Choline and ¹⁸F-FDG scans. Student’s paired-sample t-test was performed for analyzing inter-observer and inter-modality variability. Semi-automatic segmentation methods, including thresholding and region growing, were also validated against the manual contouring of the two types of PET images. We observed no significant variation in the results obtained by different oncologists in terms of the same type of PET/CT volumes. Choline fusion volumes were significantly larger than the FDG volumes (p < 0.0001, mean ± SD = 18.21 ± 8.19). While significantly consistent results were obtained between the oncologists and the standard references in Choline volumes compared with those in FDG volumes (p = 0.0025). Simple semi-automatic delineation methods indicated that ¹¹C-Choline PET images could provide better results than FDG volumes (p = 0.076, CI = [–0.29, 0.025]). ¹¹C-Choline PET/CT may be more advantageous in GTV delineation for the radiotherapy of NPC than ¹⁸F-FDG. Phantom simulations and clinical trials should be conducted to prove the possible improvement of the treatment outcome.

Effectiveness of PET/CT with (18)F-fluorothymidine in the staging of patients with squamous cell head and neck carcinomas before radiotherapy

AIM

The aim of our study was to compare the staging of the disease declared before anticancer treatment was begun with the staging that was found after the planning PET/CT scanning with (18)F-FLT was performed.

BACKGROUND

PET/CT in radiotherapy planning of head and neck cancers can facilitate the contouring of the primary tumour and the definition of metastatic lymph nodes.

MATERIALS AND METHODS

Between November 2010 and November 2013, 26 patients suffering from head and neck carcinomas underwent planning PET/CT examination with (18)F-FLT. We compared the staging of the disease and the treatment strategy declared before and after (18)F-FLT-PET/CT was performed.

RESULTS

The findings from (18)FLT-PET/CT led in 22 patients to a change of staging: in 19 patients it led to upstaging of the disease and in 3 patients it led to downstaging of the disease. In one patient, a secondary malignancy was found.

CONCLUSIONS

We have confirmed in this study that the use of (18)F-FLT-PET/CT scanning in radiotherapy planning of squamous cell head and neck carcinomas has a great potential in the precise evaluation of disease staging and consequently in the precise determination of target volumes.

Use of PET/CT instead of CT-only when planning for radiation therapy does not notably increase life years lost in children being treated for cancer

BACKGROUND

PET/CT may be more helpful than CT alone for radiation therapy planning, but the added risk due to higher doses of ionizing radiation is unknown.

OBJECTIVE

To estimate the risk of cancer induction and mortality attributable to the [F-18]2-fluoro-2-deoxyglucose (FDG) PET and CT scans used for radiation therapy planning in children with cancer, and compare to the risks attributable to the cancer treatment.

MATERIALS AND METHODS

Organ doses and effective doses were estimated for 40 children (2-18 years old) who had been scanned using PET/CT as part of radiation therapy planning. The risk of inducing secondary cancer was estimated using the models in BEIR VII. The prognosis of an induced cancer was taken into account and the reduction in life expectancy, in terms of life years lost, was estimated for the diagnostics and compared to the life years lost attributable to the therapy. Multivariate linear regression was performed to find predictors for a high contribution to life years lost from the radiation therapy planning diagnostics.

RESULTS

The mean contribution from PET to the effective dose from one PET/CT scan was 24% (range: 7-64%). The average proportion of life years lost attributable to the nuclear medicine dose component from one PET/CT scan was 15% (range: 3-41%). The ratio of life years lost from the radiation therapy planning PET/CT scans and that of the cancer treatment was on average 0.02 (range: 0.01-0.09). Female gender was associated with increased life years lost from the scans (P < 0.001).

CONCLUSION

Using FDG-PET/CT instead of CT only when defining the target volumes for radiation therapy of children with cancer does not notably increase the number of life years lost attributable to diagnostic examinations.

Alterations in anatomic and functional imaging parameters with repeated FDG PET-CT and MRI during radiotherapy for head and neck cancer: a pilot study

Background

The use of imaging to implement on-treatment adaptation of radiotherapy is a promising paradigm but current data on imaging changes during radiotherapy is limited. This is a hypothesis-generating pilot study to examine the changes on multi-modality anatomic and functional imaging during (chemo)radiotherapy treatment for head and neck squamous cell carcinoma (HNSCC).

Methods

Eight patients with locally advanced HNSCC underwent imaging including computed tomography (CT), Fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)-CT and magnetic resonance imaging (MRI) (including diffusion weighted (DW) and dynamic contrast enhanced (DCE)) at baseline and during (chemo)radiotherapy treatment (after fractions 11 and 21). Regions of interest (ROI) were drawn around the primary tumour at baseline and during treatment. Imaging parameters included gross tumour volume (GTV) assessment, SUV_max, mean ADC value and DCE-MRI parameters including Plasma Flow (PF). On treatment changes and correlations between these parameters were analysed using a Wilcoxon rank sum test and Pearson’s linear correlation coefficient respectively. A p-value <0.05 was considered statistically significant.

Results

Statistically significant reductions in GTV-CT, GTV-MRI and GTV-DW were observed between all imaging timepoints during radiotherapy. Changes in GTV-PET during radiotherapy were heterogeneous and non-significant. Significant changes in SUV_max, mean ADC value, Plasma Flow and Plasma Volume were observed between the baseline and the fraction 11 timepoint, whilst only changes in SUV_max between baseline and the fraction 21 timepoint were statistically significant. Significant correlations were observed between multiple imaging parameters, both anatomical and functional; 20 correlations between baseline to the fraction 11 timepoint; 12 correlations between baseline and the fraction 21 timepoints; and 4 correlations between the fraction 11 and fraction 21 timepoints.

Conclusions

Multi-modality imaging during radiotherapy treatment demonstrates early changes (by fraction 11) in both anatomic and functional imaging parameters. All functional imaging modalities are potentially complementary and should be considered in combination to provide multi-parametric tumour assessment, to guide potential treatment adaptation strategies.

Trial Registration

ISRCTN Registry: ISRCTN34165059. Registered 2nd February 2015.

Reproducibility of (18)F-FDG PET uptake measurements in head and neck squamous cell carcinoma on both PET/CT and PET/MR

OBJECTIVE

To investigate reproducibility of fluorine-18 fludeoxyglucose ((18)F-FDG) uptake on (18)F-FDG positron emission tomography (PET)/CT and (18)F-FDG PET/MR scans in patients with head and neck squamous cell carcinoma (HNSCC).

METHODS

30 patients with HNSCC were included in this prospective study. The patients were scanned twice before radiotherapy treatment with both PET/CT and PET/MR. Patients were scanned on the same scanners, 3 days apart and according to the same protocol. Metabolic tumour activity was measured by the maximum and peak standardized uptake value (SUVmax and SUVpeak, respectively), and total lesion glycolysis from the metabolic tumour volume defined from ≥50% SUVmax. Bland-Altman analysis with limits of agreement, coefficient of variation (CV) from the two modalities were performed in order to test the reproducibility. Furthermore, CVs from SUVmax and SUVpeak were compared. The area under the curve from cumulative SUV-volume histograms were measured and tested for reproducibility of the distribution of (18)F-FDG uptake.

RESULTS

24 patients had two pre-treatment PET/CT scans and 21 patients had two pre-treatment PET/MR scans available for further analyses. Mean difference for SUVmax, peak and mean was approximately 4% for PET/CT and 3% for PET/MR, with 95% limits of agreement less than ±20%. CV was small (5-7%) for both modalities. There was no significant difference in CVs between PET/CT and PET/MR (p = 0.31). SUVmax was not more reproducible than SUVpeak (p = 0.09).

CONCLUSION

(18)F-FDG uptake in PET/CT and PET/MR is highly reproducible and we found no difference in reproducibility between PET/CT and PET/MR.

ADVANCES IN KNOWLEDGE

This is the first report to test reproducibility of PET/CT and PET/MR.

PET/CT-guided treatment planning for paediatric cancer patients: a simulation study of proton and conventional photon therapy

OBJECTIVE

To investigate the impact of including fluorine-18 fludeoxyglucose ((18)F-FDG) positron emission tomography (PET) scanning in the planning of paediatric radiotherapy (RT).

METHODS

Target volumes were first delineated without and subsequently re-delineated with access to (18)F-FDG PET scan information, on duplicate CT sets. RT plans were generated for three-dimensional conformal photon RT (3DCRT) and intensity-modulated proton therapy (IMPT). The results were evaluated by comparison of target volumes, target dose coverage parameters, normal tissue complication probability (NTCP) and estimated risk of secondary cancer (SC).

RESULTS

Considerable deviations between CT- and PET/CT-guided target volumes were seen in 3 out of the 11 patients studied. However, averaging over the whole cohort, CT or PET/CT guidance introduced no significant difference in the shape or size of the target volumes, target dose coverage, irradiated volumes, estimated NTCP or SC risk, neither for IMPT nor 3DCRT.

CONCLUSION

Our results imply that the inclusion of PET/CT scans in the RT planning process could have considerable impact for individual patients. There were no general trends of increasing or decreasing irradiated volumes, suggesting that the long-term morbidity of RT in childhood would on average remain largely unaffected.

ADVANCES IN KNOWLEDGE

(18)F-FDG PET-based RT planning does not systematically change NTCP or SC risk for paediatric cancer patients compared with CT only. 3 out of 11 patients had a distinct change of target volumes when PET-guided planning was introduced. Dice and mismatch metrics are not sufficient to assess the consequences of target volume differences in the context of RT.

Quality assurance for the EORTC 22071-26071 study: dummy run prospective analysis

Purpose

The phase III 22071–26071 trial was designed to evaluate the addition of panitumumab to adjuvant chemotherapy plus intensity modulated radiotherapy (IMRT) in locally advanced resected squamous cell head and neck cancer. We report the results of the dummy run (DR) performed to detect deviations from protocol guidelines.

Methods and Materials

DR datasets consisting of target volumes, organs at risk (OAR) and treatment plans were digitally uploaded, then compared with reference contours and protocol guidelines by six central reviewers. Summary statistics and analyses of potential correlations between delineations and plan characteristics were performed.

Results

Of 23 datasets, 20 (87.0%) GTVs were evaluated as acceptable/borderline, along with 13 (56.5%) CTVs and 10 (43.5%) PTVs. All PTV dose requirements were met by 73.9% of cases. Dose constraints were met for 65.2-100% of mandatory OARs. Statistically significant correlations were observed between the subjective acceptability of contours and the ability to meet dose constraints for all OARs (p ≤ 0.01) except for the parotids and spinal cord. Ipsilateral parotid doses correlated significantly with CTV and PTV volumes (p ≤ 0.05).

Conclusions

The observed wide variations in treatment planning, despite strict guidelines, confirms the complexity of development and quality assurance of IMRT-based multicentre studies for head and neck cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13014-014-0248-9) contains supplementary material, which is available to authorized users.

PET-based radiation therapy planning

In this review, we review the literature on the use of PET in radiation treatment planning, with an emphasis on describing our institutional methodology (where applicable). This discussion is intended to provide other radiation oncologists with methodological details on the use of PET imaging for treatment planning in radiation oncology, or other oncologists with an introduction to the use of PET in planning radiation therapy.

Prognostic value of tumour blood flow, [¹⁸F]EF5 and [¹⁸F]FDG PET/CT imaging in patients with head and neck cancer treated with radiochemotherapy

PURPOSE

In order to improve the treatment of squamous cell carcinoma of the head and neck, precise information on the treated tumour's biology is required and the prognostic importance of different biological parameters needs to be determined. The aim of our study was to determine the predictive value of pretreatment PET/CT imaging using [(18)F]FDG, a new hypoxia tracer [(18)F]EF5 and the perfusion tracer [(15)O]H₂O in patients with squamous cell cancer of the head and neck treated with radiochemotherapy.

METHODS

The study group comprised 22 patients with confirmed squamous cell carcinoma of the head and neck who underwent a PET/CT scan using the above tracers before any treatment. Patients were later treated with a combination of radiochemotherapy and surgery. Parametric blood flow was calculated from dynamic [(15)O]H₂O PET images using a one-tissue compartment model. [(18)F]FDG images were analysed by calculating standardized uptake values (SUV) and metabolically active tumour volumes (MATV). [(18)F]EF5 images were analysed by calculating tumour-to-muscle uptake ratios (T/M ratio). A T/M ratio of 1.5 was considered a significant threshold and used to determine tumour hypoxic subvolumes (HS) and hypoxic fraction area. The findings were finally correlated with the pretreatment clinical findings (overall stage and TNM stage) as well as the outcome following radiochemotherapy in terms of local control and overall patient survival.

RESULTS

Tumour stage and T-classification did not show any significant differences in comparison to the patients' metabolic and functional characteristics measured on PET. Using the Cox proportional hazards model, a shorter overall survival was associated with MATV (p = 0.008, HR = 1.108), maximum [(18)F]EF5 T/M ratio (p = 0.0145, HR = 4.084) and tumour HS (p = 0.0047, HR = 1.112). None of the PET parameters showed a significant effect on patient survival in the log-rank test, although [(18)F]EF5 maximum T/M ratio was the closest (p = 0.109). By contrast, tumour blood flow was not correlated with any of the clinical endpoints. There were no statistically significant correlations among [(18)F]FDG SUVmax, [(18)F]EF5 T/M ratio and blood flow.

CONCLUSION

Our study in a limited number of patients confirmed the importance of MATV in the prognosis of locally advanced squamous cell carcinoma of the head and neck. It is of interest that high uptake of the hypoxia tracer [(18)F]EF5 showed a stronger correlation with a poor clinical outcome than [(18)F]FDG uptake. This confirms the importance of hypoxia in treatment outcome and suggests that [(18)F]EF5 may act as a surrogate marker of radioresistance.

Is FDG -PET-CT a valuable tool in prediction of persistent disease in head and neck cancer

OBJECTIVES

To evaluate accuracy of FDG-PET CT in prediction of persistent disease in head and neck cancer cases and to determine prognostic value of metabolic tumor response.

MATERIALS AND METHODS

Between 2009 and 2011, 46 patients with squamous cell carcinoma of head and neck receiving PET-CT were treated with definitive radiotherapy, with or without chemotherapy. There were 29 nasopharyngeal, 11 hypopharyngeal, 3 oropharyngeal and 3 laryngeal cancer patients, with a median age of 50.5 years (range 16-84), 32 males and 14 females. All patients were evaluated with PET-CT median 3-5 months (2.4-9.4) after completion of radiotherapy.

RESULTS

After a median 20 months of follow up, complete metabolic response was observed in 63% of patients. Suspicious residual uptake was present in 10.9% and residual metabolic uptake in 26.0% of patients. The overall sensitivity, specificity, positive predictive value and negative predictive value of FDG-PET-CT for detection of residual disease was 91% and 81%, 64% and 96% respectively. Two year LRC was 95% in complete responders while it was 34% in non-complete responders.

CONCLUSIONS

FDG PET CT is a valuable tool for assessment of treatment response, especially in patients at high risk of local recurrence, and also as an indicator of prognosis. Definitely more precise criteria are required for assessment of response, there being no clear cut uptake value indicating residual disease. Futhermore, repair processes of normal tissue may consume glucose which appear as increased uptake in control FDG PET CT.

[Radioanatomy of rhinopharyngeal carcinoma]

Rhinopharyngeal cancer is one of the best indications for conformal radiotherapy with modulated intensity. Due to the high dose gradient, accurate delineation of target volumes and organs at risk is a critical success factor with this technology. This requires a good knowledge of rhinopharyngeal radioanatomy and optimal imaging techniques.

Efficacy of FDG-PET for defining gross tumor volume of head and neck cancer

We analyzed the data for 53 patients with histologically proven primary squamous cell carcinoma of the head and neck treated with radiotherapy between February 2006 and August 2009. All patients underwent contrast-enhanced (CE)-CT and (18)F-fluorodeoxyglucose (FDG)-PET before radiation therapy planning (RTP) to define the gross tumor volume (GTV). The PET-based GTV (PET-GTV) for RTP was defined using both CE-CT images and FDG-PET images. The CE-CT tumor volume corresponding to a FDG-PET image was regarded as the PET-GTV. The CE-CT-based GTV (CT-GTV) for RTP was defined using CE-CT images alone. Additionally, CT-GTV delineation and PET-GTV delineation were performed by four radiation oncologists independently in 19 cases. All four oncologists did both methods. Of these, PET-GTV delineation was successfully performed in all 19 cases, but CT-GTV delineation was not performed in 4 cases. In the other 15 cases, the mean CT-GTV was larger than the PET-GTV in 10 cases, and the standard deviation of the CT-GTV was larger than that of the PET-GTV in 10 cases. Sensitivity of PET-GTV for identifying the primary tumor was 96%, but that of CT-GTV was 81% (P < 0.01). In patients with oropharyngeal cancer and tongue cancer, the sensitivity of CT-GTV was 63% and 71%, respectively. When both the primary lesions and the lymph nodes were evaluated for RTP, PET-GTV differed from CT-GTV in 19 cases (36%). These results suggested that FDG-PET is effective for defining GTV in RTP for squamous cell carcinoma of the head and neck, and PET-GTV evaluated by both CE-CT and FDG-PET images is preferable to CT-GTV by CE-CT alone.

The reliability of quantitative thresholding methods for PET aided delineation of GTVs in Head and Neck tumours

Introduction: PET–CT scans are commonly used for the purpose of gross tumour volume (GTV) delineation in head and neck cancers. Qualitative visual methods (QVM) are currently employed in most radiotherapy departments but these are subject to inter- and intra-observer variability. Quantitative thresholding methods which appear in the published literature are evaluated with respect to their reliability for delineation of GTVs in head and neck cancers.

Discussion: Image segmentation involves the application of a distinct value to all pixels or voxels in an image dataset. This is a complex process affected by numerous variables. Some of the following segmentation thresholds may be applied to automatically delineate specified regions. Standardised uptake value (SUV) is commonly used to apply a threshold for GTV delineation, however this leads to inappropriately large GTVs. A further common quantitative threshold is based on the maximum signal on the PET image relative to the background uptake, known as signal to background ratio (SBR). This method generates GTVs that correlate well with surgically removed tumour volumes. Applying a fixed threshold of a percentage of the maximal intensity uptake is also documented in the literature but was found to be unsuitable for the purpose of head and neck GTV contouring. Systems based on the physical features of the PET-CT images are also discussed and are found to produce very promising results.

Conclusion: A number of quantitative techniques are evaluated and currently the most suitable is found to be SBR, however even this method was not found to be entirely reliable. More promising techniques need further evaluation before they could be implemented clinically and a Radiation Oncologist or Nuclear Medicine Radiologist must still validate all GTVs produced by quantitative methods.

A gel tumour phantom for assessment of the accuracy of manual and automatic delineation of gross tumour volume from FDG-PET/CT

INTRODUCTION

Our primary aim was to make a phantom for PET that could mimic a highly irregular tumour and provide true tumour contours. The secondary aim was to use the phantom to assess the accuracy of different methods for delineation of tumour volume from the PET images.

MATERIAL AND METHODS

An empty mould was produced on the basis of a contrast enhanced computed tomography (CT) study of a patient with a squamous cell carcinoma in the head and neck region. The mould was filled with a homogeneous fast-settling gel that contained both (18)F for positron emission tomography (PET) and an iodine contrast agent. This phantom (mould and gel) was scanned on a PET/CT scanner. A series of reference tumour contours were obtained from the CT images in the PET/CT. Tumour delineation based on the PET images was achieved manually, by isoSUV thresholding, and by a recently developed three-dimensional (3D) Difference of Gaussians algorithm (DoG). Average distances between the PET-derived and reference contours were assessed by a 3D distance transform.

RESULTS

The manual, thresholding and DoG delineation methods resulted in volumes that were 146%, 86% and 100% of the reference volume, respectively, and average distance deviations from the reference surface were 1.57 mm, 1.48 mm and 1.0, mm, respectively.

DISCUSSION

Manual drawing as well as isoSUV determination of tumour contours in geometrically irregular tumours may be unreliable. The DoG method may contribute to more correct delineation of the tumour. Although the present phantom had a homogeneous distribution of activity, it may also provide useful knowledge in the case of inhomogeneous activity distributions.

CONCLUSION

The geometric irregular tumour phantom with its inherent reference contours was an important tool for testing of different delineation methods and for teaching delineation.

Changes in functional imaging parameters following induction chemotherapy have important implications for individualised patient-based treatment regimens for advanced head and neck cancer

BACKGROUND

When induction chemotherapy (IC) is used prior to chemoradiotherapy (CRT) in head and neck cancer (HNC), functional imaging (FI) may inform adaptation of treatment plans with the aim of optimising outcomes. Understanding the impact of IC on FI parameters is, therefore, essential.

PURPOSE

To prospectively evaluate the feasibility of acquiring serial FI ((18)F-FDG-PET, diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) MRI) and its role in defining individualised treatment regimens following IC in HNC.

METHODS AND MATERIALS

Ten patients with stage III and IV HNC underwent conventional (CT and MRI) and functional (DW, DCE-MRI and (18)F-FDG-PET/CT) imaging at baseline and following two cycles of IC prior to definitive CRT.

RESULTS

One patient withdrew due to claustrophobia. Seven out of nine patients had a complete metabolic response to IC on (18)F-FDG-PET imaging. DCE-MRI showed a significant fall in transfer constant (K(trans)) (0.209 vs 0.129 min(-1)P<0.01) and integrated area under gadolinium curve at 60s (IAUGC6O) (18.4 vs 11.9 mmol/min, P<0.01) and DW-MRI a rise in ADC (0.89 vs 1.06 × 10(-3) mm(2)/s, P<0.01) following IC.

CONCLUSIONS

Acquiring FI sequences is feasible in HNC. There are marked changes in FI parameters following IC which may guide adaptation of individualised treatment regimens.

Current oncologic concepts and emerging techniques for imaging of head and neck squamous cell cancer

The incidence of head and neck squamous cell carcinoma (HNSCC) is increasing and currently they account for 5% of all malignancies worldwide. Inspite of ongoing developments in diagnostic imaging and new therapeutic options, HNSCC still represents a multidisciplinary challenge.One of the most important prognostic factors in HNSCC is the presence of lymph node metastases. Patients with confirmed nodal involvement have a considerable reduction of their 5-year overall survival rate. In the era of individually optimised surgery, chemotherapy and intensity modulated radiotherapy, the main role of pre- and posttherapeutic imaging remains cancer detection at an early stage and accurate follow-up. The combined effort of early diagnosis and close patient monitoring after surgery and/or radio-chemotherapy influences disease progression and outcome predicition in patients with HNSCC.This review article focuses on currrent oncologic concepts and emerging tools in imaging of head and neck squamous cell cancer. Besides the diagnostic spectrum of the individual imaging modalities, their limitations are also discussed. One main part of this article is dedicated to PET-CT which combines functional and morphological imaging. Furthermore latest developments in MRI are presented with regard to lymph node staging and response prediction. Last but not least, a clinical contribution in this review explains, which information the head and neck surgeon requires from the multimodality imaging and its impact on operation planning.

Recommendations of the Spanish Societies of Radiation Oncology (SEOR), Nuclear Medicine & Molecular Imaging (SEMNiM), and Medical Physics (SEFM) on (18)F-FDG PET-CT for radiotherapy treatment planning

Positron emission tomography (PET) with (18)F-fluorodeoxyglucose (FDG) is a valuable tool for diagnosing and staging malignant lesions. The fusion of PET and computed tomography (CT) yields images that contain both metabolic and morphological information, which, taken together, have improved the diagnostic precision of PET in oncology. The main imaging modality for planning radiotherapy treatment is CT. However, PET-CT is an emerging modality for use in planning treatments because it allows for more accurate treatment volume definition. The use of PET-CT for treatment planning is highly complex, and protocols and standards for its use are still being developed. It seems probable that PET-CT will eventually replace current CT-based planning methods, but this will require a full understanding of the relevant technical aspects of PET-CT planning. The aim of the present document is to review these technical aspects and to provide recommendations for clinical use of this imaging modality in the radiotherapy planning process.

FAZA PET/CT hypoxia imaging in patients with squamous cell carcinoma of the head and neck treated with radiotherapy: results from the DAHANCA 24 trial

PURPOSE

Hypoxia is a cause of resistance to radiotherapy, especially in patients with head and neck squamous cell carcinoma (HNSCC). The purpose of this study was to evaluate (18)F-fluoroazomycin arabinoside (FAZA) positron emission tomography (PET)/computed tomography (CT) hypoxia imaging as a prognostic factor in HNSCC patients receiving radiotherapy.

MATERIAL AND METHODS

Forty patients with HNSCC treated with radiotherapy (66-76 Gy) were included. Static FAZA PET/CT imaging 2h post injection was conducted prior to irradiation. The hypoxic volume (HV) was delineated using a tumor-to-muscle value ≥ 1.4. In 13 patients, a repetitive FAZA PET/CT scan was conducted during the radiotherapy treatment.

RESULTS

A hypoxic volume could be identified in 25 (63%) of the 40 tumors. FAZA PET HV varied considerably with a range from 0.0 to 30.9 (median: 0.3) cm(3). The T(max)/M(med) ranged from 1.1 to 2.9 (median: 1.5). The distribution of hypoxia among the Human Papillomavirus (HPV) positive (12/16) and negative (13/24) tumors was not significant different. In the FAZA PET/CT scans performed during radiotherapy, hypoxia could be detected in six of the 13 patients. For these six patients the location of HV remained stable in location during radiotherapy treatment, though the size of the HV decreased. In 30 patients a positive correlation was detected between maximum FAZA uptake in the primary tumor and the lymph node. During a median follow up of 19 months a significant difference in disease free survival rate with 93% for patients with non hypoxic tumors and 60% for patients with hypoxic tumors could be detected.

CONCLUSION

This study emphasizes the role of FAZA PET/CT imaging as a suitable assay with prognostic potential for detection of hypoxia in HNSCC.

Radiotherapy for head and neck tumours in 2012 and beyond: conformal, tailored, and adaptive?

Intensity-modulated radiation therapy (IMRT) is a conformal irradiation technique that enables steep dose gradients. In head and neck tumours this approach spares parotid-gland function without compromise to treatment efficacy. Anatomical and molecular imaging modalities may be used to tailor treatment by enabling proper selection and delineation of target volumes and organs at risk, which in turn lead to dose prescriptions that take into account the underlying tumour biology (eg, human papillomavirus status). Therefore, adaptations can be made throughout the course of radiotherapy, as required. Planned dose increases to parts of the target volumes may also be used to match the radiosensitivity of tumours (so-called dose-painting), assessed by molecular imaging. For swift implementation of tailored and adaptive IMRT, tools and procedures, such as accurate image acquisition and reconstruction, automatic segmentation of target volumes and organs at risk, non-rigid image and dose registration, and dose summation methods, need to be developed and properly validated.

Hypoxia imaging with the nitroimidazole 18F-FAZA PET tracer: a comparison with OxyLite, EPR oximetry and 19F-MRI relaxometry

BACKGROUND AND PURPOSE

(18)F-FAZA is a nitroimidazole PET tracer that can provide images of tumor hypoxia. However, it cannot provide absolute pO(2) values. To qualify (18)F-FAZA PET, we compared PET images to pO(2) measured by OxyLite, EPR oximetry and (19)F-MRI.

MATERIALS AND METHODS

Male WAG/Rij rats grafted with rhabdomyosarcoma were used. Tumor oxygenation was modified by gas breathing (air or carbogen). The same day of PET acquisition, the pO(2) was measured in the same tumor either by OxyLite probes (measurement at 10 different sites), EPR oximetry using low frequency EPR or (19)F-relaxometry using 15C5 on an 11.7T MR system.

RESULTS

There was a good correlation between the results obtained by PET and EPR (R = 0.93). In the case of OxyLite, although a weaker correlation was observed (R = 0.55), the trend for two values to agree was still related to the inverse function theoretically predicted. For the comparison of (18)F-FAZA PET and (19)F-MRI, no change in T(1) was observed.

CONCLUSIONS

A clear correlation between (18)F-FAZA PET image intensities and tumor oxygenation was demonstrated, suggesting that (18)F-FAZA PET is a promising imaging technique to guide cancer therapy.

Improving target definition for head and neck radiotherapy: a place for magnetic resonance imaging and 18-fluoride fluorodeoxyglucose positron emission tomography?

Defining the target for head and neck radiotherapy is a critical issue with the introduction of steep dose gradients associated with intensity-modulated radiotherapy. Tumour delineation inaccuracies are a major source of error in radiotherapy planning. The integration of 18-fluoride fluorodeoxyglucose positron emission tomography ((18)FDG-PET) and magnetic resonance imaging directly into the radiotherapy planning process has the potential to greatly improve target identification/selection and delineation. This raises a range of new issues surrounding image co-registration, delineation methodology and the use of functional data and treatment adaptation. This overview will discuss the practical aspects of integrating (18)FDG-PET and magnetic resonance imaging into head and neck radiotherapy planning.