Correlation of PET images of metabolism, proliferation and hypoxia to characterize tumor phenotype in patients with cancer of the oropharynx

Association between maximum standarised uptake value (SUV) and local control in patients with oropharyngeal carcinoma treated with radiotherapy

OBJECTIVE

To analyse the prognostic ability of the maximum standardised uptake value (SUVmax) on local disease control in patients with oropharyngeal carcinoma treated with radiotherapy.

MATERIAL AND METHODS

Retrospective study of 105 patients with oropharyngeal carcinomas treated with radiotherapy, including chemo- and bio-radiotherapy, and who had a PET-CT scan prior to the start of treatment.

RESULT

Patients with a SUVmax value higher than 17.2 at the primary tumour site had a significantly higher risk of local recurrence. The 5-year local recurrence-free survival for patients with SUVmax less than or equal to 17.2 (n = 71) was 86.5% (95% CI 78.2-94.7 %), and for patients with SUVmax greater than 17.2 (n = 34) it was 55.8% (95% CI 36.0-75.6 %) (P = 0.0001). This difference in local control was maintained regardless of patients' HPV status. Specific survival was similarly lower for patients with a SUV greater than 17.2. The 5-year specific survival for patients with SUVmax greater than 17.2 was 39.5% (95% CI: 20.6-58.3 %), significantly shorter than that of patients with SUVmax equal to or less than 17.2, which was 77.3% (95% CI: 66.9-87.6 %) (P = 0.0001).

CONCLUSIONS

Patients with oropharyngeal carcinomas treated with radiotherapy with a SUVmax greater than 17.2 at the level of the primary tumour site had a significantly higher risk of local recurrence.

Prognostic and predictive values of baseline and mid-treatment FDG-PET in oropharyngeal carcinoma treated with primary definitive (chemo)radiation and impact of HPV status: review of current literature and emerging roles

BACKGROUND AND PURPOSE

This study provides a review of the literature assessing whether semiquantitative PET parameters acquired at baseline and/or during definitive (chemo)radiotherapy ("prePET" and "iPET") can predict survival outcomes in patients with oropharyngeal squamous cell carcinoma (OPC), and the impact of human papilloma virus (HPV) status.

MATERIAL AND METHODS

A literature search was carried out using PubMed and Embase between 2001 to 2021 in accordance with PRISMA.

RESULTS

The analysis included 22 FDG-PET/CT studies^1-22, 19 pre-PET and 3 both pre-PET and iPET^14,18,20,. The analysis involved 2646 patients, of which 1483 are HPV-positive (17 studies: 10 mixed and 7 HPV-positive only), 589 are HPV-negative, and 574 have unknown HPV status. Eighteen studies found significant correlations of survival outcomes with pre-PET parameters, most commonly primary or "Total" (combined primary and nodal) metabolic tumour volume and/or total lesional glycolysis. Two studies could not establish significant correlations and both employed SUVmax only. Two studies also could not establish significant correlations when taking into account of the HPV-positive population only. Because of the heterogeneity and lack of standardized methodology, no conclusions on optimal cut-off values can be drawn. Ten studies specifically evaluated HPV-positive patients: five showed positive correlation of pre-PET parameters and survival outcomes, but four of these studies did not include advanced T or N staging in multivariate analysis^1,6,15,22, and two studies only showed positive correlations after excluding high risk patients with smoking history⁷ or adverse CT features²². Two studies found that prePET parameters predicted treatment outcomes only in HPV-negative but not HPV-positive patients^10,16. Two studies found that iPET parameters could predict outcomes in HPV-positive patients but not prePET parameters^14,18.

CONCLUSION

The current literature supports high pre-treatment metabolic burden prior to definitive (chemo)radiotherapy can predict poor treatment outcomes for HPV-negative OPC patients. Evidence is conflicting and currently does not support correlation in HPV-positive patients.

Advances in PET and MRI imaging of tumor hypoxia

Tumor hypoxia is a complex and evolving phenomenon both in time and space. Molecular imaging allows to approach these variations, but the tracers used have their own limitations. PET imaging has the disadvantage of low resolution and must take into account molecular biodistribution, but has the advantage of high targeting accuracy. The relationship between the signal in MRI imaging and oxygen is complex but hopefully it would lead to the detection of truly oxygen-depleted tissue. Different ways of imaging hypoxia are discussed in this review, with nuclear medicine tracers such as [¹⁸F]-FMISO, [¹⁸F]-FAZA, or [⁶⁴Cu]-ATSM but also with MRI techniques such as perfusion imaging, diffusion MRI or oxygen-enhanced MRI. Hypoxia is a pejorative factor regarding aggressiveness, tumor dissemination and resistance to treatments. Therefore, having accurate tools is particularly important.

Imaging of Tumor Hypoxia With Radionuclide-Labeled Tracers for PET

The hypoxic state in a solid tumor refers to the internal hypoxic environment that appears as the tumor volume increases (the maximum radius exceeds 180-200 microns). This state can promote angiogenesis, destroy the balance of the cell’s internal environment, and lead to resistance to radiotherapy and chemotherapy, as well as poor prognostic factors such as metastasis and recurrence. Therefore, accurate quantification, mapping, and monitoring of hypoxia, targeted therapy, and improvement of tumor hypoxia are of great significance for tumor treatment and improving patient survival. Despite many years of development, PET-based hypoxia imaging is still the most widely used evaluation method. This article provides a comprehensive overview of tumor hypoxia imaging using radionuclide-labeled PET tracers. We introduced the mechanism of tumor hypoxia and the reasons leading to the poor prognosis, and more comprehensively included the past, recent and ongoing studies of PET radiotracers for tumor hypoxia imaging. At the same time, the advantages and disadvantages of mainstream methods for detecting tumor hypoxia are summarized.

Mid-treatment Fluorodeoxyglucose Positron Emission Tomography in Human Papillomavirus-related Oropharyngeal Squamous Cell Carcinoma Treated with Primary Radiotherapy: Nodal Metabolic Response Rate can Predict Treatment Outcomes

AIMS

To evaluate whether biomarkers derived from fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) performed prior to (prePET) and during the third week (interim PET; iPET) of radiotherapy can predict treatment outcomes in human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinoma (OPC).

MATERIALS AND METHODS

This retrospective analysis included 46 patients with newly diagnosed OPC treated with definitive (chemo)radiation and all patients had confirmed positive HPV status (HPV+OPC) based on p16 immunohistochemistry. The maximum standardised uptake value (SUV_max), metabolic tumour volume (MTV) and total lesional glycolysis (TLG) of primary, index node (node with the highest TLG) and total lymph nodes and their median percentage (≥50%) reductions in iPET were analysed, and correlated with 5-year Kaplan-Meier and multivariable analyses (smoking, T4, N2b-3 and AJCC stage IV), including local failure-free survival, regional failure-free survival, locoregional failure-free survival (LRFFS), distant metastatic failure-free survival (DMFFS), disease-free survival (DFS) and overall survival.

RESULTS

There was no association of outcomes with prePET parameters observed on multivariate analysis. A complete metabolic response of primary tumour was seen in 13 patients; the negative predictive value for local failure was 100%. More than a 50% reduction in total nodal MTV provided the best predictor of outcomes, including LRFFS (88% versus 47.1%, P = 0.006, hazard ratio = 0.153) and DFS (78.2% versus 41.2%, P = 0.01, hazard ratio = 0.234). More than a 50% reduction in index node TLG was inversely related to DMFFS: a better nodal response was associated with a higher incidence of distant metastatic failure (66.7% versus 100%, P = 0.009, hazard ratio = 3.0).

CONCLUSION

The reduction (≥50%) of volumetric nodal metabolic burden can potentially identify a subgroup of HPV+OPC patients at low risk of locoregional failure but inversely at higher risk of distant metastatic failure and may have a role in individualised adaptive radiotherapy and systemic therapy.

Role of Non-FDG-PET/CT in Head and Neck Cancer

Head and neck cancers are commonly encountered malignancies in the United States, of which the majority are attributed to squamous cell carcinoma. ¹⁸F-FDG-PET/CT has been well established in the evaluation, treatment planning, prognostic implications of these tumors and is routinely applied for the management of patients with these cancers. Many alternative investigational PET radiotracers have been extensively studied in the evaluation of these tumors. Although these radiotracers have not been able to replace ¹⁸F-FDG-PET/CT in routine clinical practice currently, they may provide important additional information about the biological mechanisms of these tumors, such as foci of tumor hypoxia as seen on hypoxia specific PET radiotracers such as ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO), which could be useful in targeting radioresistant hypoxic tumor foci when treatment planning. There are multiple other hypoxia-specific PET radiotracers such as ¹⁸F-Fluoroazomycinarabinoside (FAZA), ¹⁸F-Flortanidazole (HX4), which have been evaluated similarly, of which ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO) has been the most investigated. Other radiotracers frequently studied in the evaluation of these tumors include radiolabeled amino acid PET radiotracers, which show increased uptake in tumor cells with limited uptake in inflammatory tissue, which can be useful especially in differentiating postradiation inflammation from residual and/or recurrent disease. ¹⁸F-Fluorothymidine (FLT) is localized intracellularly by nucleoside transport and undergoes phosphorylation thereby being retained within tumor cells and can serve as an indicator of tumor proliferation. Decrease in radiotracer activity following treatment can be an early indicator of treatment response. This review aims at synthesizing the available literature on the most studied non-FDG-PET/CT in head and neck cancer.

Comparison of DCE-MRI kinetic parameters and FMISO-PET uptake parameters in head and neck cancer patients

Purpose

Tumor hypoxia is a major cause of radiation resistance, often present in various solid tumors. Dynamic [¹⁸F]‐fluoromisonidazole (FMISO) PET imaging is able to reliably assess tumor hypoxia. Comprehensive characterization of tumor microenvironment through FMISO‐PET and dynamic contrast enhanced (DCE) MR multimodality imaging might be a valuable alternative to the dynamic FMISO‐PET acquisition. The aim of this work was to explore the correlation between the FMISO‐PET and DCE‐MRI kinetic parameters.

Methods

This study was done on head and neck cancer patients (N = 6), who were imaged dynamically with FMISO‐PET and DCE‐MRI on the same day. Images were registered and analyzed for kinetics on a voxel basis. FMISO‐PET images were analyzed with the two‐tissue compartment three rate‐constant model. Additionally, tumor‐to‐muscle ratio (TMR) maps were evaluated. DCE‐MRI was analyzed with the extended Tofts model. Voxel‐wise Pearson's coefficients were calculated for each patient to assess pairwise parameter correlations.

Results

Median correlations between FMISO uptake parameters and DCE‐MRI kinetic parameters varied across the parameter pairs in the range from −0.05 to 0.71. The highest median correlation of r = 0.71 was observed for the pair V_b−v_p, while the K₁−K^trans median correlation was r = 0.45. Median correlation coefficients for the K₁−v_p and the K_i−K^trans pairs were r = 0.42 and r = 0.32, respectively. Correlations between FMISO uptake rate parameter K_i and DCE‐MRI kinetic parameters varied substantially across the patients, whereas correlations between the FMISO and DCE‐MRI vascular parameters were consistently high. Median TMR‐K₁ and TMR‐K^trans correlations were r = 0.52 and r = 0.46, respectively, but varied substantially across the patients.

Conclusions

Based on this clinical evidence, we can conclude that the vascular fraction parameters obtained through DCE‐MRI kinetic analysis or FMISO kinetic analysis measure the same biological property, while other kinetic parameters are unrelated. These results might be useful in the design of future clinical trials involving FMISO‐PET/DCE‐MR multimodality imaging for the assessment of tumor microenvironment.

Evolution of [18F]fluorodeoxyglucose and [18F]fluoroazomycin arabinoside PET uptake distributions in lung tumours during radiation therapy

BACKGROUND

Dose painting (DP) aims to improve radiation therapy (RT) outcome by targeting radioresistant tumour regions identified through functional imaging, e.g., positron emission tomography (PET). Importantly, the expected benefit of DP relies on the ability of PET imaging to identify tumour areas which could be consistently targeted throughout the treatment. In this study, we analysed the spatial stability of two potential DP targets in lung cancer patients undergoing RT: the tumour burden surrogate [¹⁸F]fluorodeoxyglucose (FDG) and the hypoxia surrogate [¹⁸F]fluoroazomycin arabinoside (FAZA).

MATERIALS AND METHODS

Thirteen patients with unresectable lung tumours underwent FDG and FAZA 4D-PET/CT before (pre), and during the second (w2) and third (w3) weeks of RT. All PET/CT were reconstructed in their time-averaged midposition (MidP) for further analysis. The metabolic tumour volume (MTV: FDG standardised uptake value (SUV) > 50% SUV_max) and the hypoxic volume (HV: FAZA SUV >1.4) were delineated within the gross tumour volume (GTV_CT). The stability of FDG and FAZA PET uptake distributions during RT was subsequently assessed through volume-overlap analysis and voxel-based correlation analysis.

RESULTS

The volume-overlap analysis yielded median overlapping fraction (OF) of 0.86 between MTV_pre and MTV_w2 and 0.82 between MTV_pre and MTV_w3. In patients with a detectable HV, median OF was 0.82 between HV_pre and HV_w2 and 0.90 between HV_pre and HV_w3. The voxel-based correlation analysis yielded median Spearman's correlation coefficient (r_S) of 0.87 between FDG_pre and FDG_w2 and 0.83 between FDG_pre and FDG_w3. Median r_S was 0.78 between FAZA_pre and FAZA_w2 and 0.79 between FAZA_pre and FAZA_w3.

CONCLUSIONS

FDG and FAZA PET uptake distributions were spatially stable during the 3 first weeks of RT in patients with unresectable lung cancer, both based on volume- and voxel-based indicators. This might allow for a consistent targeting of high FDG or FAZA PET uptake regions as part of a DP strategy.

Early and delayed evaluation of solid tumours with 64Cu-ATSM PET/CT: a pilot study on semiquantitative and computer-aided fractal geometry analysis

OBJECTIVE

The aim of this study was to analyse early and delayed acquisition on copper-64 diacetyl-bisN4-methylthiosemicarbazone (Cu-ATSM) PET/CT in a small cohort of patients by comparing semiquantitative and computer-aided fractal geometry analyses.

PATIENTS AND METHODS

Five cancer patients, including non-small-cell lung cancer and head and neck cancer, were investigated with Cu-ATSM PET/CT. Participants received an intravenous injection of Cu-ATSM according to body size and were imaged 60 min (early) and 16 h (delayed) later on hybrid PET/CT. Reconstructed images were visualized on advanced workstations for the definition of semiquantitative parameters: standardized uptake value (SUV)max, SUVratio-to-muscle, SUVmean, hypoxic volume (HV) and hypoxic burden (HB=HV×SUVmean). DICOM data retrieved from both scans were analysed using an ad-hoc computer program to determine the mean intensity value, SD, relative dispersion, three-dimensional histogram fractal dimension and three-dimensional fractal dimension.

RESULTS

All tumour lesions showed increased uptake of Cu-ATSM at early evaluation, with a median SUVratio-to-muscle of 4.42 (range: 1.58-5.62), a median SUVmax of 5.3 (range: 1.9-7.3), a median SUVmean of 2.8 (range: 1.5-3.9), a median HV of 41.6 cm (range: 2.8-453.7) and a median HB of 161.5 cm (range: 4.4-1112.5). All semiquantitative data obtained at 1 h were consistent with the parameters obtained on delayed imaging (P>0.05). A borderline statistically significant difference was found only for SUVmax of the muscle (P=0.045). Fractal geometry analysis on DICOM images showed that all parameters at early imaging showed no statistically significant difference with late acquisition (P>0.05).

CONCLUSION

Our findings support the consistency of Cu-ATSM PET/CT images obtained at early and delayed acquisition for the assessment of tumour lesions.

Assessing Tumor Oxygenation for Predicting Outcome in Radiation Oncology: A Review of Studies Correlating Tumor Hypoxic Status and Outcome in the Preclinical and Clinical Settings

Tumor hypoxia is recognized as a limiting factor for the efficacy of radiotherapy, because it enhances tumor radioresistance. It is strongly suggested that assessing tumor oxygenation could help to predict the outcome of cancer patients undergoing radiation therapy. Strategies have also been developed to alleviate tumor hypoxia in order to radiosensitize tumors. In addition, oxygen mapping is critically needed for intensity modulated radiation therapy (IMRT), in which the most hypoxic regions require higher radiation doses and the most oxygenated regions require lower radiation doses. However, the assessment of tumor oxygenation is not yet included in day-to-day clinical practice. This is due to the lack of a method for the quantitative and non-invasive mapping of tumor oxygenation. To fully integrate tumor hypoxia parameters into effective improvements of the individually tailored radiation therapy protocols in cancer patients, methods allowing non-invasively repeated, safe, and robust mapping of changes in tissue oxygenation are required. In this review, non-invasive methods dedicated to assessing tumor oxygenation with the ultimate goal of predicting outcome in radiation oncology are presented, including positron emission tomography used with nitroimidazole tracers, magnetic resonance methods using endogenous contrasts (R₁ and R2*-based methods), and electron paramagnetic resonance oximetry; the goal is to highlight results of studies establishing correlations between tumor hypoxic status and patients’ outcome in the preclinical and clinical settings.

Molecular Imaging and Precision Medicine in Head and Neck Cancer

The concept of using tumor genomic profiling information has revolutionized personalized cancer treatment. Head and neck (HN) cancer management is being influenced by recent discoveries of activating mutations in epidermal growth factor receptor and related targeted therapies with tyrosine kinase inhibitors, targeted therapies for Kristen Rat Sarcoma, and MET proto-oncogenes. Molecular imaging using PET plays an important role in assessing the biologic behavior of HN cancer with the goal of delivering individualized cancer treatment. This review summarizes recent genomic discoveries in HN cancer and their implications for functional PET imaging in assessing response to targeted therapies, and drug resistance mechanisms.

Prognostic Evaluation of Disease Outcome in Solid Tumors Investigated With 64Cu-ATSM PET/CT

PURPOSE

Cu-ATSM is a very promising PET radiopharmaceutical for tumor imaging of hypoxia. One of the advantages of this compound compared with other hypoxia-avid tracers is the high tumor-to-background signal offered, which guaranties facilitated tumor delineation. This study analyzes optimal semiquantitative and quantitative parameters obtained by Cu-ATSM PET/CT in the same cohort of patients with special focus on their correlation to disease outcome.

PATIENTS AND METHODS

A prospective recruitment of 18 consecutive patients (M:F, 13:5; mean age, 60.7 years) with locally advanced non-small cell lung cancer (n = 7) or head and neck cancer (HNC) was performed. Each participant received 105 to 500 MBq of tracer according to body size and was scanned in a 3-dimensional mode PET/CT 60 minutes after tracer injection. PET images were reconstructed and visualized on a GE Advanced 4.6 workstation for the definition of semiquantitative and quantitative parameters: SUVmax, SUVratio-to-muscle, hypoxic tumor volume (HTV), and hypoxic burden (HB = HTV × SUVmean). These data were subsequently correlated to disease outcome, expressed in terms of progression-free survival calculated on a follow-up period with a median of 14.6 months.

RESULTS

All patients showed a moderately to highly increased uptake of Cu-ATSM in tumor lesions, with a mean SUVmax of 5.2 (range, 1.9-8.3) and mean SUVratio of 4.4 (range, 1.6-6.8). In addition, a broad range of HTV and HB was defined as mean values of 99.3 cm (range, 2.5-453.7 cm) and 301 (4.2-1134), respectively. Receiver operating characteristic analysis identified as reference cutoffs with respect to disease outcome with the following values: SUVmax >2.5 (AUC, 0.57; sensitivity, 88.9%; specificity, 50%), SUVratio ≤4.4 (AUC, 0.60; sensitivity, 50; specificity, 83.3%), HTV >160.7 cm (AUC, 0.61; sensitivity, 55.6%; specificity, 75%), and HB >160.7 (AUC, 0.67; sensitivity, 58.3%; specificity, 83.3%). In our cohort, HB showed a statistically significant difference in terms of mean values on the analysis of variance test with respect to disease progression (P = 0.04). On univariate analysis, Cox regression confirmed these findings and showed a significant correlation to progression-free survival for HB (P = 0.05) and HTV (P = 0.02).

CONCLUSIONS

In our cohort, the definition of optimal semiquantitative and quantitative parameters on Cu-ATSM PET/CT seems feasible and in line with previously published data. However, when considering the prognostic role with respect to disease outcome, the more robust parameters are represented by HTV and HB.

Multiparametric imaging of patient and tumour heterogeneity in non-small-cell lung cancer: quantification of tumour hypoxia, metabolism and perfusion

Purpose

Multiple imaging techniques are nowadays available for clinical in-vivo visualization of tumour biology. FDG PET/CT identifies increased tumour metabolism, hypoxia PET visualizes tumour oxygenation and dynamic contrast-enhanced (DCE) CT characterizes vasculature and morphology. We explored the relationships among these biological features in patients with non-small-cell lung cancer (NSCLC) at both the patient level and the tumour subvolume level.

Methods

A group of 14 NSCLC patients from two ongoing clinical trials (NCT01024829 and NCT01210378) were scanned using FDG PET/CT, HX4 PET/CT and DCE CT prior to chemoradiotherapy. Standardized uptake values (SUV) in the primary tumour were calculated for the FDG and hypoxia HX4 PET/CT scans. For hypoxia imaging, the hypoxic volume, fraction and tumour-to-blood ratio (TBR) were also defined. Blood flow and blood volume were obtained from DCE CT imaging. A tumour subvolume analysis was used to quantify the spatial overlap between subvolumes.

Results

At the patient level, negative correlations were observed between blood flow and the hypoxia parameters (TBR >1.2): hypoxic volume (−0.65, p = 0.014), hypoxic fraction (−0.60, p = 0.025) and TBR (−0.56, p = 0.042). At the tumour subvolume level, hypoxic and metabolically active subvolumes showed an overlap of 53 ± 36 %. Overlap between hypoxic sub-volumes and those with high blood flow and blood volume was smaller: 15 ± 17 % and 28 ± 28 %, respectively. Half of the patients showed a spatial mismatch (overlap <5 %) between increased blood flow and hypoxia.

Conclusion

The biological imaging features defined in NSCLC tumours showed large interpatient and intratumour variability. There was overlap between hypoxic and metabolically active subvolumes in the majority of tumours, there was spatial mismatch between regions with high blood flow and those with increased hypoxia.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-015-3169-4) contains supplementary material, which is available to authorized users.

64Cu-CTS: A Promising Radiopharmaceutical for the Identification of Low-Grade Cardiac Hypoxia by PET

The subtle hypoxia underlying chronic cardiovascular disease is an attractive target for PET imaging, but the lead hypoxia imaging agents (64)Cu-2,3-butanedione bis(N4-methylthiosemicarbazone) (ATSM) and (18)F-fluoromisonidazole are trapped only at extreme levels of hypoxia and hence are insufficiently sensitive for this purpose. We have therefore sought an analog of (64)Cu-ATSM better suited to identify compromised but salvageable myocardium, and we validated it using parallel biomarkers of cardiac energetics comparable to those observed in chronic cardiac ischemic syndromes.

METHODS

Rat hearts were perfused with aerobic buffer for 20 min, followed by a range of hypoxic buffers (using a computer-controlled gas mixer) for 45 min. Contractility was monitored by intraventricular balloon, energetics by (31)P nuclear MR spectroscopy, lactate and creatine kinase release spectrophotometrically, and hypoxia-inducible factor 1-α by Western blotting.

RESULTS

We identified a key hypoxia threshold at a 30% buffer O2 saturation that induces a stable and potentially survivable functional and energetic compromise: left ventricular developed pressure was depressed by 20%, and cardiac phosphocreatine was depleted by 65.5% ± 14% (P < 0.05 vs. control), but adenosine triphosphate levels were maintained. Lactate release was elevated (0.21 ± 0.067 mmol/L/min vs. 0.056 ± 0.01 mmol/L/min, P < 0.05) but not maximal (0.46 ± 0.117 mmol/L/min), indicating residual oxidative metabolic capacity. Hypoxia-inducible factor 1-α was elevated but not maximal. At this key threshold, (64)Cu-2,3-pentanedione bis(thiosemicarbazone) (CTS) selectively deposited significantly more (64)Cu than any other tracer we examined (61.8% ± 9.6% injected dose vs. 29.4% ± 9.5% for (64)Cu-ATSM, P < 0.05).

CONCLUSION

The hypoxic threshold that induced survivable metabolic and functional compromise was 30% O2. At this threshold, only (64)Cu-CTS delivered a hypoxic-to-normoxic contrast of 3:1, and it therefore warrants in vivo evaluation for imaging chronic cardiac ischemic syndromes.

Exploring spatial overlap of high-uptake regions derived from dual tracer positron emission tomography-computer tomography imaging using 18F-fluorodeoxyglucose and 18F-fluorodeoxythymidine in nonsmall cell lung cancer patients: a prospective pilot study

Interest is growing in radiotherapy to nonuniformly boost radioresistant regions within nonsmall cell lung cancer (NSCLC) using molecular imaging techniques. The complexity of tumor behavior is beyond the ability of any single radiotracer to reveal. We hold dual tracer positron emission tomography-computer tomography (PET/CT) imaging with fluorodeoxyglucose (FDG) and fluorodeoxythymidine (FLT) for NSCLC patients to offer an integrated overlook of tumor biological behaviors quantitatively and localizationally, which may help biological target volume delineation and subvolume boost.Pathological confirmed that NSCLC patients were eligible. FDG and FLT PET/CT were performed for each patient before anticancer treatment and coregistrated for analysis. Maximum and mean standardized uptake values (SUVmax and SUVmean) were calculated automatically. Metabolic volumes (MVs) were delineated by a fixed 50% of SUVmax in FDG PET/CT and proliferative volumes (PVs) were delineated by 50% to 90% of SUVmax with 10% interval in FLT PET/CT. Overlap ratio (OR) were determined as overlapped volume between MV and PV divided PV. Conventional contrast-enhanced CT-based intensity-modulated radiotherapy (IMRT) plans with and without additional PET/CT-guided subtarget boost were made for each of the 5 typical NSCLC patients. Dosimetric parameters derived from dose-volume histogram, tumor control probability (TCP), and normal tissue complication probability (NTCP) of lung, esophagus, heart, and spinal cord were calculated and compared.Thirty-one patients were prospectively included and 23 were selected for analysis. Totally, 23 primary diseases, 41 metastatic lymph nodes, and 15 metastatic lesions were positive in dual PET/CTs and included for analysis. Median ORs increased from 58.61% to 93.12% under thresholds of 50% of SUVmax in FDG PET/CT and increased thresholds from 50% to 90% of SUVmax in FLT PET/CT. Based on conventional IMRT, additional boost to union of high FDG (determined by 50% SUVmax) and FLT (determined by 80% SUVmax) uptake subtargets exhibited higher TCP without significant elevated NTCP of lung, esophagus, spinal cord, and heart.Dual tracer PET/CT of FDG and FLT is suggested for NSCLC patients to guide tumor target delineation in clinical practice. FDG PET/CT is necessary whereas FLT PET/CT may be optional when guiding tumor target delineation clinically. Additional information from randomized trials is required to validate.

Imaging and dosimetric errors in 4D PET/CT-guided radiotherapy from patient-specific respiratory patterns: a dynamic motion phantom end-to-end study

Effective positron emission tomography / computed tomography (PET/CT) guidance in radiotherapy of lung cancer requires estimation and mitigation of errors due to respiratory motion. An end-to-end workflow was developed to measure patient-specific motion-induced uncertainties in imaging, treatment planning, and radiation delivery with respiratory motion phantoms and dosimeters. A custom torso phantom with inserts mimicking normal lung tissue and lung lesion was filled with [(18)F]FDG. The lung lesion insert was driven by six different patient-specific respiratory patterns or kept stationary. PET/CT images were acquired under motionless ground truth, tidal breathing motion-averaged (3D), and respiratory phase-correlated (4D) conditions. Target volumes were estimated by standardized uptake value (SUV) thresholds that accurately defined the ground-truth lesion volume. Non-uniform dose-painting plans using volumetrically modulated arc therapy were optimized for fixed normal lung and spinal cord objectives and variable PET-based target objectives. Resulting plans were delivered to a cylindrical diode array at rest, in motion on a platform driven by the same respiratory patterns (3D), or motion-compensated by a robotic couch with an infrared camera tracking system (4D). Errors were estimated relative to the static ground truth condition for mean target-to-background (T/Bmean) ratios, target volumes, planned equivalent uniform target doses, and 2%-2 mm gamma delivery passing rates. Relative to motionless ground truth conditions, PET/CT imaging errors were on the order of 10-20%, treatment planning errors were 5-10%, and treatment delivery errors were 5-30% without motion compensation. Errors from residual motion following compensation methods were reduced to 5-10% in PET/CT imaging, <5% in treatment planning, and <2% in treatment delivery. We have demonstrated that estimation of respiratory motion uncertainty and its propagation from PET/CT imaging to RT planning, and RT delivery under a dose painting paradigm is feasible within an integrated respiratory motion phantom workflow. For a limited set of cases, the magnitude of errors was comparable during PET/CT imaging and treatment delivery without motion compensation. Errors were moderately mitigated during PET/CT imaging and significantly mitigated during RT delivery with motion compensation. This dynamic motion phantom end-to-end workflow provides a method for quality assurance of 4D PET/CT-guided radiotherapy, including evaluation of respiratory motion compensation methods during imaging and treatment delivery.

Phase 1 trial of bevacizumab with concurrent chemoradiation therapy for squamous cell carcinoma of the head and neck with exploratory functional imaging of tumor hypoxia, proliferation, and perfusion

PURPOSE

A phase 1 trial was completed to examine the safety and feasibility of combining bevacizumab with radiation and cisplatin in patients with locoregionally advanced squamous cell carcinoma of the head and neck (HNSCC) treated with curative intent. Additionally, we assessed the capacity of bevacizumab to induce an early tumor response as measured by a series of biological imaging studies.

METHODS AND MATERIALS

All patients received a single induction dose of bevacizumab (15 mg/kg) delivered 3 weeks (±3 days) before the initiation of chemoradiation therapy. After the initial dose of bevacizumab, comprehensive head and neck chemoradiation therapy was delivered with curative intent to 70 Gy in 33 fractions with concurrent weekly cisplatin at 30 mg/m(2) and bevacizumab every 3 weeks (weeks 1, 4, 7) with dose escalation from 5 to 10 to 15 mg/kg. All patients underwent experimental imaging with [(18)F]fluorothymidine positron emission tomography (FLT-PET) (proliferation), [(61)Cu]Cu-diacetyl-bis(N4-methylthiosemicarbazone) PET (Cu-ATSM-PET) (hypoxia), and dynamic contrast-enhanced computed tomography (DCE-CT) (perfusion) at 3 time points: before bevacizumab monotherapy, after bevacizumab monotherapy, and during the combined therapy course.

RESULTS

Ten patients were enrolled. All had stage IV HNSCC, all achieved a complete response to treatment, and 9 of 10 remain alive, with a mean survival time of 61.3 months. All patients experienced grade 3 toxicity, but no dose-limiting toxicities or significant bleeding episodes were observed. Significant reductions were noted in tumor proliferation (FLT-PET), tumor hypoxia (Cu-ATSM-PET), and DCE-CT contrast enhancement after bevacizumab monotherapy, with further decreases in FLT-PET and Cu-ATSM-PET during the combined therapy course.

CONCLUSIONS

The incorporation of bevacizumab into comprehensive chemoradiation therapy regimens for patients with HNSCC appears safe and feasible. Experimental imaging demonstrates measureable changes in tumor proliferation, hypoxia, and perfusion after bevacizumab monotherapy and during chemoradiation therapy. These findings suggest opportunities to preview the clinical outcomes for individual patients and thereby design personalized therapy approaches in future trials.

Imaging tumour hypoxia with positron emission tomography

Hypoxia, a hallmark of most solid tumours, is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. Given its prominent role in oncology, accurate detection of hypoxia is important, as it impacts on prognosis and could influence treatment planning. A variety of approaches have been explored over the years for detecting and monitoring changes in hypoxia in tumours, including biological markers and noninvasive imaging techniques. Positron emission tomography (PET) is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels. This review provides an overview of imaging hypoxia with PET, with an emphasis on the advantages and limitations of the currently available hypoxia radiotracers.

Positron emission tomography to assess hypoxia and perfusion in lung cancer

In lung cancer, tumor hypoxia is a characteristic feature, which is associated with a poor prognosis and resistance to both radiation therapy and chemotherapy. As the development of tumor hypoxia is associated with decreased perfusion, perfusion measurements provide more insight into the relation between hypoxia and perfusion in malignant tumors. Positron emission tomography (PET) is a highly sensitive nuclear imaging technique that is suited for non-invasive in vivo monitoring of dynamic processes including hypoxia and its associated parameter perfusion. The PET technique enables quantitative assessment of hypoxia and perfusion in tumors. To this end, consecutive PET scans can be performed in one scan session. Using different hypoxia tracers, PET imaging may provide insight into the prognostic significance of hypoxia and perfusion in lung cancer. In addition, PET studies may play an important role in various stages of personalized medicine, as these may help to select patients for specific treatments including radiation therapy, hypoxia modifying therapies, and antiangiogenic strategies. In addition, specific PET tracers can be applied for monitoring therapy. The present review provides an overview of the clinical applications of PET to measure hypoxia and perfusion in lung cancer. Available PET tracers and their characteristics as well as the applications of combined hypoxia and perfusion PET imaging are discussed.

In vivo quantification of hypoxic and metabolic status of NSCLC tumors using [18F]HX4 and [18F]FDG-PET/CT imaging

PURPOSE

Increased tumor metabolism and hypoxia are related to poor prognosis in solid tumors, including non-small cell lung cancer (NSCLC). PET imaging is a noninvasive technique that is frequently used to visualize and quantify tumor metabolism and hypoxia. The aim of this study was to perform an extensive comparison of tumor metabolism using 2[(18)F]fluoro-2-deoxy-d-glucose (FDG)-PET and hypoxia using HX4-PET imaging.

EXPERIMENTAL DESIGN

FDG- and HX4-PET/CT images of 25 patients with NSCLC were coregistered. At a global tumor level, HX4 and FDG parameters were extracted from the gross tumor volume (GTV). The HX4 high-fraction (HX4-HF) and HX4 high-volume (HX4-HV) were defined using a tumor-to-blood ratio > 1.4. For FDG high-fraction (FDG-HF) and FDG high-volume (FDG-HV), a standardized uptake value (SUV) > 50% of SUVmax was used. We evaluated the spatial correlation between HX4 and FDG uptake within the tumor, to quantify the (mis)match between volumes with a high FDG and high HX4 uptake.

RESULTS

At a tumor level, significant correlations were observed between FDG and HX4 parameters. For the primary GTV, the HX4-HF was three times smaller compared with the FDG-HF. In 53% of the primary lesions, less than 1 cm(3) of the HX4-HV was outside the FDG-HV; for 37%, this volume was 1.9 to 12 cm(3). Remarkably, a distinct uptake pattern was observed in 11%, with large hypoxic volumes localized outside the FDG-HV.

CONCLUSION

Hypoxic tumor volumes are smaller than metabolic active volumes. Approximately half of the lesions showed a good spatial correlation between the PET tracers. In the other cases, a (partial) mismatch was observed. The addition of HX4-PET imaging has the potential to individualize patient treatment.

The clinical importance of assessing tumor hypoxia: relationship of tumor hypoxia to prognosis and therapeutic opportunities

Tumor hypoxia is a well-established biological phenomenon that affects the curability of solid tumors, regardless of treatment modality. Especially for head and neck cancer patients, tumor hypoxia is linked to poor patient outcomes. Given the biological problems associated with tumor hypoxia, the goal for clinicians has been to identify moderately to severely hypoxic tumors for differential treatment strategies. The "gold standard" for detecting and characterizing of tumor hypoxia are the invasive polarographic electrodes. Several less invasive hypoxia assessment techniques have also shown promise for hypoxia assessment. The widespread incorporation of hypoxia information in clinical tumor assessment is severely impeded by several factors, including regulatory hurdles and unclear correlation with potential treatment decisions. There is now an acute need for approved diagnostic technologies for determining the hypoxia status of cancer lesions, as it would enable clinical development of personalized, hypoxia-based therapies, which will ultimately improve outcomes. A number of different techniques for assessing tumor hypoxia have evolved to replace polarographic pO2 measurements for assessing tumor hypoxia. Several of these modalities, either individually or in combination with other imaging techniques, provide functional and physiological information of tumor hypoxia that can significantly improve the course of treatment. The assessment of tumor hypoxia will be valuable to radiation oncologists, surgeons, and biotechnology and pharmaceutical companies who are engaged in developing hypoxia-based therapies or treatment strategies.

Parametric imaging of ¹⁸F-fluoro-3-deoxy-3-L-fluorothymidine PET data to investigate tumour heterogeneity

PURPOSE

[(18)F]Fluoro-3'-deoxy-3'-L-fluorothymidine ([(18)F]FLT) is a tissue proliferation marker which has been widely validated as a tumour-specific imaging tracer for PET. [(18)F]FLT uptake in breast cancer is generally quantified at the region level or through first-order statistical descriptors (mean or maximum value), approaches that ignore the known complexity and heterogeneity of cancer tissues. Our aims were: (1) to validate a robust and reproducible voxel-wise approach to the quantification of [(18)F]FLT PET data in breast cancer patients, and (2) to exploit the entire distribution of the [(18)F]FLT retention estimates and their variability in the tumour region for the prediction of early treatment response.

METHODS

The dataset was derived from 15 patients with stage II-IV breast cancer, scanned twice before chemotherapy and once 1 week after therapy. Using RECIST criteria (after 60 days) nine patients were categorized as responders or nonresponders to treatment. Kinetic modelling (compartmental modelling, Patlak analysis and spectral analysis with iterative filter), tissue-to-plasma ratio and standardized uptake value were applied at the voxel level. Test-retest estimates were used to assess reproducibility and reliability of the [(18)F]FLT uptake values before and after therapy for responder/nonresponder prediction.

RESULTS

All the methods provided a measure of [(18)F]FLT uptake that was reliable and reproducible with ICC >0.94. Moreover, a very strong correlation was found among the methods (R (2) > 0.81). All the methods provided a limited number of outliers (<20 % in tumour), with the exception of compartmental modelling (>25 %) which was therefore excluded from the prediction analysis. Differences between before and after therapy in mean voxel-wise uptake in tumour did not allow a complete responder/nonresponder classification. In contrast, considering the full estimate distributions within the tumour (changes in median and mode between before and after therapy) improved therapy response for all the analysed methods.

CONCLUSION

We showed that kinetic modelling (Patlak and spectral analysis with iterative filter) applied voxel-wise allows appropriate [(18)F]FLT uptake estimation in breast cancer with good reproducibility. Notably, this study indicated that a more comprehensive statistical investigation could improve tumour characterization and prediction of treatment response.

Spatiotemporal stability of Cu-ATSM and FLT positron emission tomography distributions during radiation therapy

PURPOSE

In dose painting, in which functional imaging is used to define biological targets for radiation therapy dose escalation, changes in spatial distributions of biological properties during treatment can compromise the quality of therapy. The goal of this study was to assess the spatiotemporal stability of 2 potential dose painting targets--hypoxia and proliferation--in canine tumors during radiation therapy.

METHODS AND MATERIALS

Twenty-two canine patients with sinonasal tumors (14 carcinoma and 8 sarcoma) were imaged before hypofractionated radiation therapy with copper(II)-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) positron emission tomography/computed tomography (PET/CT) for hypoxia and 3'-deoxy-3'-(18)F-fluorothymidine (FLT) PET/CT for proliferation. The FLT scans were repeated after 2 fractions and the Cu-ATSM scans after 3 fractions. Midtreatment PET/CT images were deformably registered to pretreatment PET/CT images. Voxel-based Spearman correlation coefficients quantified the spatial stability of Cu-ATSM and FLT uptake distributions between pretreatment and midtreatment scans. Paired t tests determined significant differences between the patients' respective Cu-ATSM and FLT correlations coefficients. Standardized uptake value measures were also compared between pretreatment and midtreatment scans by use of paired t tests.

RESULTS

Spatial distributions of Cu-ATSM and FLT uptake were stable through midtreatment for both sarcomas and carcinomas: the population mean ± standard deviation in Spearman correlation coefficient was 0.88 ± 0.07 for Cu-ATSM and 0.79 ± 0.13 for FLT. The patients' Cu-ATSM correlation coefficients were significantly higher than their respective FLT correlation coefficients (P=.001). Changes in Cu-ATSM SUV measures from pretreatment to midtreatment were histology dependent: carcinomas experienced significant decreases in Cu-ATSM uptake (P<.05), whereas sarcomas did not (P>.20). Both histologies experienced significant decreases in FLT uptake (P<.05).

CONCLUSIONS

Spatial distributions of Cu-ATSM were very stable after a few fractions of radiation therapy. FLT spatial distributions were generally stable early in therapy, although they were significantly less stable than Cu-ATSM distributions. Canine tumors had significantly lower proliferative activity at midtreatment than at pretreatment, and they experienced histology-dependent changes in Cu-ATSM uptake.

Systematic analysis of 18F-FDG PET and metabolism, proliferation and hypoxia markers for classification of head and neck tumors

Background

Quantification of molecular cell processes is important for prognostication and treatment individualization of head and neck cancer (HNC). However, individual tumor comparison can show discord in upregulation similarities when analyzing multiple biological mechanisms. Elaborate tumor characterization, integrating multiple pathways reflecting intrinsic and microenvironmental properties, may be beneficial to group most uniform tumors for treatment modification schemes. The goal of this study was to systematically analyze if immunohistochemical (IHC) assessment of molecular markers, involved in treatment resistance, and ¹⁸F-FDG PET parameters could accurately distinguish separate HNC tumors.

Methods

Several imaging parameters and texture features for ¹⁸F-FDG small-animal PET and immunohistochemical markers related to metabolism, hypoxia, proliferation and tumor blood perfusion were assessed within groups of BALB/c nu/nu mice xenografted with 14 human HNC models. Classification methods were used to predict tumor line based on sets of parameters.

Results

We found that ¹⁸F-FDG PET could not differentiate between the tumor lines. On the contrary, combined IHC parameters could accurately allocate individual tumors to the correct model. From 9 analyzed IHC parameters, a cluster of 6 random parameters already classified 70.3% correctly. Combining all PET/IHC characteristics resulted in the highest tumor line classification accuracy (81.0%; cross validation 82.0%), which was just 2.2% higher (p = 5.2×10^-32) than the performance of the IHC parameter/feature based model.

Conclusions

With a select set of IHC markers representing cellular processes of metabolism, proliferation, hypoxia and perfusion, one can reliably distinguish between HNC tumor lines. Addition of ¹⁸F-FDG PET improves classification accuracy of IHC to a significant yet minor degree. These results may form a basis for development of tumor characterization models for treatment allocation purposes.

Biologic targets identified from dynamic 18FDG-PET and implications for image-guided therapy

PURPOSE

The outcome of biologic image-guided radiotherapy depends on the definition of the biologic target. The purpose of the current work was to extract hyperperfused and hypermetabolic regions from dynamic positron emission tomography (D-PET) images, to dose escalate either region and to discuss implications of such image guided strategies.

METHODS

Eleven patients with soft tissue sarcomas were investigated with D-PET. The images were analyzed using a two-compartment model producing parametric maps of perfusion and metabolic rate. The two image series were segmented and exported to a treatment planning system, and biological target volumes BTVper and BTVmet (perfusion and metabolism, respectively) were generated. Dice's similarity coefficient was used to compare the two biologic targets. Intensity-modulated radiation therapy (IMRT) plans were generated for a dose painting by contours regime, where planning target volume (PTV) was planned to 60 Gy and BTV to 70 Gy. Thus, two separate plans were created for each patient with dose escalation of either BTVper or BTVmet.

RESULTS

BTVper was somewhat smaller than BTVmet (209 ± 170 cm(3) against 243 ± 143 cm(3), respectively; population-based mean and s.d.). Dice's coefficient depended on the applied margin, and was 0.72 ± 0.10 for a margin of 10 mm. Boosting BTVper resulted in mean dose of 69 ± 1.0 Gy to this region, while BTVmet received 67 ± 3.2 Gy. Boosting BTVmet gave smaller dose differences between the respective non-boost DVHs (such as D98).

CONCLUSIONS

Dose escalation of one of the BTVs results in a partial dose escalation of the other BTV as well. If tumor aggressiveness is equally pronounced in hyperperfused and hypermetabolic regions, this should be taken into account in the treatment planning.

Heterogeneity in intratumor correlations of 18F-FDG, 18F-FLT, and 61Cu-ATSM PET in canine sinonasal tumors

Intratumor heterogeneity in biologic properties and in relationships between various phenotypes may present a challenge for biologically targeted therapies. Understanding the relationships between different phenotypes in individual tumor types could help inform treatment selection. The goal of this study was to characterize spatial correlations of glucose metabolism, proliferation, and hypoxia in 2 histologic types of tumors.

METHODS

Twenty canine veterinary patients with spontaneously occurring sinonasal tumors (13 carcinomas and 7 sarcomas) were imaged with (18)F-FDG, (18)F-labeled 3'-deoxy-3'-fluorothymidine ((18)F-FLT), and (61)Cu-labeled diacetyl-bis(N(4)-methylthiosemicarbazone) ((61)Cu-ATSM) PET/CT on 3 consecutive days. Precise positioning and immobilization techniques coupled with anesthesia enabled motionless scans with repeatable positioning. Standardized uptake values (SUVs) of gross sarcoma and carcinoma volumes were compared by use of Mann-Whitney U tests. Patient images were rigidly registered together, and intratumor tracer uptake distributions were compared. Voxel-based Spearman correlation coefficients were used to quantify intertracer correlations, and the correlation coefficients of sarcomas and carcinomas were compared. The relative overlap of the highest uptake volumes of the 3 tracers was quantified, and the values were compared for sarcomas and carcinomas.

RESULTS

Large degrees of heterogeneity in SUV measures and phenotype correlations were observed. Carcinoma and sarcoma tumors differed significantly in SUV measures, with carcinoma tumors having significantly higher (18)F-FDG maximum SUVs than sarcoma tumors (11.1 vs. 5.0; P = 0.01) as well as higher (61)Cu-ATSM mean SUVs (2.6 vs. 1.2; P = 0.02). Carcinomas had significantly higher population-averaged Spearman correlation coefficients than sarcomas in comparisons of (18)F-FDG and (18)F-FLT (0.80 vs. 0.61; P = 0.02), (18)F-FLT and (61)Cu-ATSM (0.83 vs. 0.38; P < 0.0001), and (18)F-FDG and (61)Cu-ATSM (0.82 vs. 0.69; P = 0.04). Additionally, the highest uptake volumes of the 3 tracers had significantly greater overlap in carcinomas than in sarcomas.

CONCLUSION

The relationships of glucose metabolism, proliferation, and hypoxia were heterogeneous across different tumors, with carcinomas tending to have high correlations and sarcomas having low correlations. Consequently, canine carcinoma tumors are robust targets for therapies that target a single biologic property, whereas sarcoma tumors may not be well suited for such therapies. Histology-specific PET correlations have far-reaching implications for the robustness of biologic target definition.

Hypoxia imaging with [¹⁸F]HX4 PET in NSCLC patients: defining optimal imaging parameters

BACKGROUND AND PURPOSE

[(18)F]HX4 is a promising hypoxia PET-tracer. Uptake, spatio-temporal stability and optimal acquisition parameters for [(18)F]HX4 PET imaging were evaluated in non-small cell lung cancer (NSCLC) patients.

MATERIALS AND METHODS

[(18)F]HX4 PET/CT images of 15 NSCLC patients were acquired 2h and 4h after injection (p.i.). Maximum standardized-uptake-value (SUV(max)), tumor-to-blood-ratio (TBR(max)), hypoxic fraction (HF) and contrast-to-noise-ratio (CNR) were determined for all lesions. To evaluate spatio-temporal stability, DICE-similarity and Pearson correlation coefficients were calculated. Optimal acquisition-duration was assessed by comparing 30, 20, 10 and 5 min acquisitions.

RESULTS

Considerable uptake (TBR >1.4) was observed in 18/25 target lesions. TBR(max) increased significantly from 2 h (1.6 ± 0.3) to 4 h p.i. (2.0 ± 0.6). Uptake patterns at 2 h and 4 h p.i. showed a strong correlation (R=0.77 ± 0.10) with a DICE similarity coefficient of 0.69 ± 0.08 for the 30% highest uptake volume. Reducing acquisition-time resulted in significant changes in SUV(max) and CNR. TBR(max) and HF were only affected for scan-times of 5 min.

CONCLUSIONS

The majority of NSCLC lesions showed considerable [(18)F]HX4 uptake. The heterogeneous uptake pattern was stable between 2 h and 4 h p.i. [(18)F]HX4 PET imaging at 4 h p.i. is superior to 2 h p.i. to reach highest contrast. Acquisition time may be reduced to 10 min without significant effects on TBR(max) and HF.

Is there room for combined modality treatments? Dosimetric comparison of boost strategies for advanced head and neck and prostate cancer

The purpose of the study was to determine the dosimetric difference between three emerging treatment modalities--volumetric-modulated arc therapy (VMAT), intensity-modulated proton beam therapy (IMPT) and intensity-modulated carbon ion beam therapy (IMIT)--for two tumour sites where selective boosting of the tumour is applied. For 10 patients with locally advanced head and neck (H&N) cancer and 10 with high-risk prostate cancer (PC) a VMAT plan was generated for PTV initial that included lymph node regions, delivering 50 Gy (IsoE) for H&N and 50.4 Gy (IsoE) for PC patients. Furthermore, separate boost plans (VMAT, IMPT and IMIT) were created to boost PTV boost up to 70 Gy (IsoE) and 78 Gy (IsoE) for H&N and PC cases, respectively. Doses to brainstem, myelon, larynx and parotid glands were assessed for H&N cases. Additionally, various OARs (e.g. cochlea, middle ear, masticator space) were evaluated that are currently discussed with respect to quality of life after treatment. For PC cases, bladder, rectum and femoral heads were considered as OARs. For both tumour sites target goals were easily met. Looking at OAR sparing, generally VMAT + VMAT was worst. VMAT + IMIT had the potential to spare some structures in very close target vicinity (such as cochlea, middle ear, masticator space ) significantly better than VMAT + IMPT. Mean doses for rectal and bladder wall were on average 4 Gy (IsoE) and 1.5 Gy (IsoE) higher, respectively, compared to photons plus particles scenarios. Similar results were found for parotid glands and larynx. Concerning target coverage, no significant differences were observed between the three treatment concepts. Clear dosimetric benefits were observed for particle beam therapy as boost modality. However, the clinical benefit of combined modality treatments remains to be demonstrated.