Imaging of head and neck tumors with positron emission tomography and [11C]methionine

Non-18F-FDG PET/CT in the management of patients affected by HNC: state-of-the-art

PET/computed tomography with F-fluorodeoxyglucose is considered a powerful molecular imaging technique that can provide useful information in the management of patients affected by head and neck cancer. However, misleading findings have been reported because of nonspecific uptake caused by peritumoural inflammation and physiologic changes in nonmalignant tissues in the head and neck region. More specific β-emitting tracers have been introduced that can track other pathological processes. We aimed to review the existing literature performing the search until June 2015 on non-F-fluorodeoxyglucose PET tracers in head and neck cancer to highlight their role in clinical practice.

Transcriptomic and Immunohistochemical Profiling of SLC6A14 in Pancreatic Ductal Adenocarcinoma

We used a target-centric strategy to identify transporter proteins upregulated in pancreatic ductal adenocarcinoma (PDAC) as potential targets for a functional imaging probe to complement existing anatomical imaging approaches. We performed transcriptomic profiling (microarray and RNASeq) on histologically confirmed primary PDAC tumors and normal pancreas tissue from 33 patients, including five patients whose tumors were not visible on computed tomography. Target expression was confirmed with immunohistochemistry on tissue microarrays from 94 PDAC patients. The best imaging target identified was SLC6A14 (a neutral and basic amino acid transporter). SLC6A14 was overexpressed at the transcriptional level in all patients and expressed at the protein level in 95% of PDAC tumors. Very little is known about the role of SLC6A14 in PDAC and our results demonstrate that this target merits further investigation as a candidate transporter for functional imaging of PDAC.

Metabolism of radiolabeled methionine in hepatocellular carcinoma

PURPOSE

Radiolabeled methionine (Met) promises to be useful in the positron emission tomography (PET) imaging of hepatocellular carcinoma (HCC). However, its metabolic routes in HCC have not yet been fully understood. In this study, the metabolic pathway(s) of radiolabeled Met in HCC were investigated.

PROCEDURES

To simulate the rapid blood clearance of radiolabeled Met, pulse-chase experiments were conducted. L-[methyl-(3)H]-Met or L-[1-(14)C]-Met was pulsed over control or cycloheximide-treated WCH17 cells and rat hepatocytes for 5 min and chased with cold media. The water-soluble, lipid-soluble, DNA, RNA, and protein phases were subsequently extracted and measured from the acid-precipitable and acid-soluble fractions of whole cells. The radioactive metabolites Met, S-adenosylmethionine (SAM), S-adenosylhomocysteine, Met sulfoxide, and Met sulfone were further separated by radio thin layer chromatography.

RESULTS

(1) The uptake of L-[methyl-(3)H]-Met in both cell types was higher than that of L-[1-(14)C]-Met. In rat hepatocytes, the uptake of L-[methyl-(3)H]-Met was significantly higher than that of L-[1-(14)C]-Met, which may contribute to its physiologic accumulation in surrounding hepatic tissues seen in PET imaging of HCC using L-[methyl-(11)C]-Met. Compared to rat hepatocytes, WCH17 cells had significantly higher uptake of both radiotracers. (2) For L-[methyl-(3)H]-Met, the major intracellular uptake was found mostly in the protein phase and, to a lesser degree, in the phosphatidylethanolamine (PE) methylation pathway, which is fairly stabilized within the 55-min chase period (the main metabolites were SAM, Met, Met sulfoxide, and Met sulfone). In contrast, the uptake of Met in rat hepatocytes mainly points to phosphatidylcholine (PC) synthesis through the PE methylation pathway (the main metabolite was PC). (3) Both cell types incorporated L-[1-(14)C]-Met predominantly into protein synthesis. (4) Finally, when the protein synthesis pathway was inhibited, the incorporation of SAM derived from L-[methyl-(3)H]-Met to lipid class (PC was the main metabolite) occurred at a reduced rate in WCH17 cells, suggesting that the route may be impaired in HCC.

CONCLUSIONS

This study demonstrated that different metabolic pathways of radiolabeled Met exist between HCC and surrounding hepatic tissue and contribute to the patterns of increased uptake of radiolabeled Met in HCC.

A Multimodality Imaging Review of Malignant Pleural Mesothelioma Response Assessment

Assessment of response is important to interpret early phase clinical trial results and to guide individual patient management. In malignant pleural mesothelioma (MPM), the circumferential growth pattern of the disease, the presence of pleural effusion and atelectasis, and the common use of pleurodesis make this a challenging task for imaging specialists and clinicians. This article reviews the current evidence for radiological and positron emission tomography (PET) response assessment in MPM, and the pitfalls and challenges in its application. Current research and future directions in radiological and PET response are discussed, including the use of novel radiotracers.

Detection of cervical metastases with (11)C-tyrosine PET in patients with squamous cell carcinoma of the oral cavity or oropharynx: A comparison with (18)F-FDG PET

BACKGROUND

A disadvantage of 2-[(18)F]fluoro-2-deoxy-D-glucose ((18)F-FDG) positron emission tomography (PET) in head and neck cancer is that (18)F-FDG uptake is not specific to malignant tissue. To provide an alternative, radiolabeled amino acids such as L-1-[(11)C]-tyrosine ((11)C-TYR), were introduced because these are less avidly metabolized by inflammatory cells.

METHODS

In this prospective study, we compared both (11)C-TYR PET and (18)F-FDG PET performance in detecting cervical metastases in 27 patients with a squamous cell carcinoma (SCC) of oral cavity or oropharynx.

RESULTS

(11)C-TYR PET sensitivity, specificity, and accuracy for detecting nodal metastases were 33%, 100%, and 81%, respectively. With respect to (18)F-FDG PET, these figures were 67%, 97%, and 89%, respectively. Neck metastases not detected by (11)C-TYR PET were camouflaged by high tracer uptake by salivary glands.

CONCLUSIONS

Because of bilateral accumulation of (11)C-TYR in salivary glands, (11)C-TYR PET is not suitable to replace (18)F-FDG PET in staging SCC of oral cavity and oropharynx.

Localization of medullary thyroid carcinoma after surgery using (11)C-methionine PET/CT: comparison with (18)F-FDG PET/CT

Tumor localization is difficult in patients with medullary thyroid carcinoma (MTC) that have persistent hypercalcitoninemia after thyroidectomy. In this study, the (11)C-methionine positron emission tomography/computed tomography (PET/CT) was compared with the (18)F-FDG PET/CT for diagnostic sensitivity in detecting residual or metastatic disease. (11)C-methionine PET/CT and (18)F-FDG PET/CT were performed on 16 consecutive patients with MTC that had persistent hypercalcitoninemia after surgery in this prospective, single-center study. Patient- and lesion-based analyses were performed using a composite reference standard which was the sum of the lesions confirmed by all combined modalities, including neck ultrasonography (US) with or without fine needle aspiration cytology, CT, bone scan, magnetic resonance imaging (MRI), and surgery. By patient-based analysis, the sensitivities of (11)C-methionine PET/CT and (18)F-FDG PET/CT were both 63%. By lesion-based analysis, the sensitivity of (11)C-methionine PET/CT was similar to (18)F-FDG PET/CT (73% vs. 80%). Excluding hepatic lesions, which could not be detected because of physiological uptake of methionine by the liver, the sensitivity of (11)C-methionine PET/CT was better than (18)F-FDG PET/CT especially for detecting cervical lymph node lesions; however, it was not superior to US. All patients with serum calcitonin levels ≥370 pg/mL showed uptake by (11)C-methionine PET/CT and (18)F-FDG PET/CT. This preliminary data showed that despite its similar sensitivity to (18)F-FDG PET/CT for detecting residual or metastatic MTC, (11)C-methionine PET/CT provided minimal additional information compared to combined (18)F-FDG PET/CT and neck US.

Innovations in radiotherapy planning of head and neck cancers: role of PET

Modern radiotherapy techniques heavily rely on high-quality medical imaging. PET provides biologic information about the tumor, complementary to anatomic imaging. Integrated PET/CT has found its way into the practice of radiation oncology, and (18)F-FDG PET is being introduced for radiotherapy planning. The functional information possibly augments accurate delineation and treatment of the tumor and its extensions while reducing the dose to surrounding healthy tissues. In addition to (18)F-FDG, other PET tracers are available for imaging specific biologic tumor characteristics determining radiation resistance. For head and neck cancer, the potential gains of PET are increasingly being recognized. This review describes the current role of PET and perspectives on its future use for selection and delineation of radiotherapy target volumes and for biologic characterization of this tumor entity. Furthermore, the potential role of PET for early response monitoring, treatment modification, and patient selection is addressed in this review.

Imaging of cell proliferation: status and prospects

Increased cellular proliferation is an integral part of the cancer phenotype. Several in vitro assays have been developed to measure the rate of tumor growth, but these require biopsies, which are particularly difficult to obtain over time and in different areas of the body in patients with multiple metastatic lesions. Most of the effort to develop imaging methods to noninvasively measure the rate of tumor cell proliferation has focused on the use of PET in conjunction with tracers for the thymidine salvage pathway of DNA synthesis, because thymidine contains the only pyrimidine or purine base that is unique to DNA. Imaging with 11C-thymidine has been tested for detecting tumors and tracking their response to therapy in animals and patients. Its major limitations are the short half-life of 11C and the rapid catabolism of thymidine after injection. These limitations led to the development of analogs that are resistant to degradation and can be labeled with radionuclides more conducive to routine clinical use, such as 18F. At this point, the thymidine analogs that have been studied the most are 3'-deoxy-3'-fluorothymidine (FLT) and 1-(2'-deoxy-2'-fluoro-1-beta-d-arabinofuranosyl)-thymine (FMAU). Both are resistant to degradation and track the DNA synthesis pathway. FLT is phosphorylated by thymidine kinase 1, thus being retained in proliferating cells. It is incorporated by the normal proliferating marrow and is glucuronidated in the liver. FMAU can be incorporated into DNA after phosphorylation but shows less marrow uptake. It shows high uptake in the normal heart, kidneys, and liver, in part because of the role of mitochondrial thymidine kinase 2. Early clinical data for 18F-FLT demonstrated that its uptake correlates well with in vitro measures of proliferation. Although 18F-FLT can be used to detect tumors, its tumor-to-normal tissue contrast is generally lower than that of 18F-FDG in most cancers outside the brain. The most promising use for thymidine and its analogs is in monitoring tumor treatment response, as demonstrated in animal studies and pilot human trials. Further work is needed to determine the optimal tracer(s) and timing of imaging after treatment.

Tumor cell metabolism imaging

Molecular imaging of tumor metabolism has gained considerable interest, since preclinical studies have indicated a close relationship between the activation of various oncogenes and alterations of cellular metabolism. Furthermore, several clinical trials have shown that metabolic imaging can significantly impact patient management by improving tumor staging, restaging, radiation treatment planning, and monitoring of tumor response to therapy. In this review, we summarize recent data on the molecular mechanisms underlying the increased metabolic activity of cancer cells and discuss imaging techniques for studies of tumor glucose, lipid, and amino acid metabolism.

O-[18F]fluoromethyl-L-tyrosine is a potential tracer for monitoring tumour response to chemotherapy using PET: an initial comparative in vivo study with deoxyglucose and thymidine

PURPOSE

To compare the utility of a new artificial amino acid, O-[18F]fluoromethyl-L-tyrosine ([18F]FMT), for monitoring cancer chemotherapy with deoxyglucose and thymidine.

METHODS

[18F]FMT, [14C]deoxyglucose ([14C]DG) and [6-3H]thymidine ([3H]Thd) were applied in this study. A 2.5 mg/kg dose of mitomycin (MMC) was administered to AH272 rat hepatoma-bearing Donryu rats. Tumour uptake of each tracer was measured just before (baseline) and on days 1, 3, 5 and 7 after the MMC administration, 1 h after a mixture of [18F]FMT, [14C]DG and [3H]Thd had been injected, and was shown as DURs (% injected dose/gram tissue normalised for the rat body weight). Dual-tracer macroautoradiographs with [18F]FMT and [14C]DG were also prepared.

RESULTS

The tumour uptake for each tracer decreased earlier than did the tumour size. DURs (mean+/-SD) at baseline and on days 1, 3, 5 and 7 were as follows: [18F]FMT: 4.68+/-0.72, 3.34+/-0.66, 3.13+/-0.72, 3.42+/-0.45, 3.01+/-0.32; [14C]DG: 3.26+/-0.40, 3.09+/-0.55, 3.01+/-0.97, 2.28+/-0.35, 1.70+/-0.72; and [3H]Thd: 2.23+/-0.46, 1.54+/-0.45, 1.28+/-0.37, 1.35+/-0.20, 0.94+/-0.12. Decrease in [18F]FMT uptake compared with baseline was significant from day 1 (p<0.01), and the decrease in [3H]Thd uptake was also significant on day 1 (p<0.05) and days 3-7 (p<0.01). However, decrease in [14C]DG uptake was only significant from day 5 (p<0.01). Macroautoradiography suggested that the influence of inflammatory cells on the accumulation of [18F]FMT in tumours is smaller than that on the accumulation of [14C]DG.

CONCLUSION

[18F]FMT uptake shows a rapid and sensitive response to chemotherapy, comparable to that of [3H]Thd, suggesting that it may be applied as a powerful tracer for monitoring of proliferative activity after cancer chemotherapy using PET.

Investigation of thyroid, head, and neck cancers with PET

PET with [(18)F]-fluorodeoxyglucose (FDG) has been accepted as a useful imaging modality for the diagnosis of a variety of malignancies. This article discusses the use of FDG-PET in the management of patients with thyroid and head or neck cancers.

Role of 11-C-methionine positron emission tomography for the delineation of the tumor volume in pharyngo-laryngeal squamous cell carcinoma: comparison with FDG-PET and CT

BACKGROUND AND PURPOSE

Although computed tomography (CT) remains the imaging modality of reference in head and neck squamous cell carcinoma (HNSCC) for the three-dimensional (3D) conformal radiotherapy, its poor soft tissue contrast can hamper precisely delineate the tumor volume. Besides anatomical imaging, 2-[18F] fluoro-2-deoxy-d-glucose-positron emission tomography (FDG-PET) has been shown to enhance the accuracy of the tumor delineation but l-methyl [11C]-methionine-positron emission tomography (MET-PET) has never been tested for this purpose. This study was undertaken to determine the potential added value of MET-PET for the delineation of gross target volume (GTV) in HNSCC, as compared to CT and FDG-PET.

PATIENTS AND METHODS

Twenty-three patients (10 oropharynx, 8 larynx and 5 hypopharynx) presenting with stage II-IV HNSCC were prospectively enrolled. They were treated by primary radiotherapy or by total laryngectomy. Images (CT, FDG-PET and MET-PET) were acquired with a thermoplastic mask and after coregistration, tumor volumes were delineated on CT and using an adaptative threshold-based automatic method on FDG- and MET-PET. Absolute volumes as well as the mismatch between modalities were compared.

RESULTS

For oropharyngeal lesions, FDG volumes were significantly smaller (19.43 ml+/-21.36) than CT (29.04 ml+/-30.97) (P=0.013). On the other hand, MET volumes (24.36 ml+/-20.59) were not different from CT volumes. Similar results were found for laryngeal and hypopharyngeal tumors, with volume of 24.93 ml+/-19.02 for CT, 21.84 ml+/-15.32 for MET-PET and 14.49 ml+/-11.3 for FDG-PET (P=0.003). Large mismatches were observed between modalities, in particular between CT and PET.

CONCLUSIONS

Our study confirms that the use of FDG-PET may result in a significant reduction of GTV's as compared to CT. On the contrary, MET-PET does not have any additional value since MET volumes are not different from CT volumes, probably because of the high uptake of MET by the normal mucosa and salivary glands surrounding the tumor.

Nuclear medicine imaging to predict response to radiotherapy: a review

PURPOSE

To review available literature on positron emission tomography (PET) and single photon emission computerized tomography (SPECT) for the measurement of tumor metabolism, hypoxia, growth factor receptor expression, and apoptosis as predictors of response to radiotherapy.

METHODS AND MATERIALS

Medical literature databases (Pubmed, Medline) were screened for available literature and critically analyzed as to their scientific relevance.

RESULTS

Studies on 18F-fluorodeoxyglucose PET as a predictor of response to radiotherapy in head-and-neck carcinoma are promising but need confirmation in larger series. 18F-fluorothymine is stable in human plasma, and preliminary clinical data obtained with this marker of tumor cell proliferation are promising. For imaging tumor hypoxia, novel, more widely available radiopharmaceuticals with faster pharmacokinetics are mandatory. Imaging of ongoing apoptosis and growth factor expression is at a very early stage, but results obtained in other domains with radiolabeled peptides appear promising. Finally, for most of the tracers discussed, validation against a gold standard is needed.

CONCLUSION

Optimization of the pharmacokinetics of relevant radiopharmaceuticals as well as validation against gold-standard tests in large patient series are mandatory if PET and SPECT are to be implemented in routine clinical practice for the purpose of predicting response to radiotherapy.

Demonstration of [11C] 5-hydroxy-L-tryptophan uptake and decarboxylation in carcinoid tumors by specific positioning labeling in positron emission tomography

In three patients with carcinoid liver and/or lymph node metastases, we studied the process of tumor tracer uptake and decarboxylation by means of positron emission tomography (PET) using 5-hydroxy-L-tryptophan (5-HTP) 11C-labeled in the beta-position (HTP) and later the same day with 5-HTP 11C-labeled in the carboxyl group (HTC). With HTP, in which the 11C-label follows the molecule through decarboxylation to form 11C-serotonin, a high tumor accumulation of the tracer was found. With HTC, in which the label is rapidly eliminated from the tissues as 11CO2 if decarboxylation takes place, there was virtually no uptake by the tumors. By utilizing data from PET scanning with both tracers, we could quantify the decarboxylation rate and tissue accumulation of [11C]-serotonin and hence the enzymatic action of aromatic amino acid decarboxylase.

Evaluation of early response to radiotherapy in head and neck cancer measured with [11C]methionine-positron emission tomography

PURPOSE

To evaluate whether positron emission tomography (PET) with carbon-11-methionine (MET) can be used for detection of early response to external beam radiotherapy (RT) in untreated head and neck cancer using locoregional control and survival as study endpoints.

MATERIALS

Fifteen patients with head and neck cancer underwent a MET PET study before RT and after a median dose of 24 Gy. Fractionation was standard (n = 6) or hyperfractionated (n = 9), and 13 out of 15 patients had planned surgery after RT. SUV was calculated for primary tumor (n = 13) or largest lymph node metastasis in two patients of whom one had his primary excised before study enrollment and one presented with unknown primary tumor syndrome.

METHODS

Attenuation corrected PET scans acquired 20-40 min from tracer injection were used for evaluation of MET uptake in tumors. A quantitative MET uptake index was expressed as standardized uptake value (SUV) or SUV(lean) (corrected for lean body mass). The PET results were correlated with clinical follow-up data. The median follow-up time is currently 28 months (range 22-34).

RESULTS

A total of 13 primary tumors and 12 metastatic lymph nodes were visually identified in MET PET. In the first PET study the median SUV in tumor was 8.6 (range, 5.5-14.0). In the second PET study performed during RT the median SUV decreased to 5.7 (range, 3.1-8.2, P = 0.001). Two out of 15 patients showed no radiation-induced decrease in SUV. The median tumor SUV ratio of patients remaining in local control (CR) after RT was 0.7 (range 0.6-0.8, n = 6), and that of relapsing patients similarly 0.7 (range 0.5-1.0, n = 9, NS). The SUV ratio was not associated with survival time. The MET uptake of submandibular salivary glands decreased in all patients during the first two or three weeks of RT (P = 0.03).

CONCLUSIONS

MET uptake in tumor shows a significant decrease during the first two to three weeks of RT of head and neck cancer. It appears that the rate of decrease in tracer uptake is comparable in relapsing patients and those who remain locally controlled and thus the use of MET PET for prediction of response to RT is limited.

Application of new imaging techniques for the evaluation of squamous cell carcinoma of the head and neck

The past several years have seen dramatic changes in imaging of the head and neck. Technical improvements in CT and MRI coupled with their widespread availability have made cross-sectional imaging an important adjunct in evaluation of patients with disease of the extracranial head and neck. The most recent advances in head and neck imaging are from new metabolic and functional imaging techniques. The intent of this report is to provide an update on the potential role of positron emission tomography, new MRI agents, and magnetic resonance spectroscopy for evaluating squamous cell carcinoma of the extracranial head and neck.

Imaging of olfactory neuroblastoma--an analysis of 17 cases

A total of 17 histologically confirmed olfactory neuroblastomas treated at Helsinki University Central Hospital between 1962 and 1996 were reviewed retrospectively. The tumors displayed a variety of imaging characteristics and aggressiveness. Imaging evolved from plain X-rays at the beginning of the study period to CT and MRI during the latter part of the study. CT provided the best information about the tumor and its local invasion especially into surrounding bony structures. MRI allowed an estimate of tumor spread into surrounding soft-tissue areas, such as the anterior cranial fossa and the retromaxillary space. However, signal intensity characteristics were not specific for olfactory neuroblastomas. Bone scintigraphy and MIBG scan allowed us to detect distant metastases. Olfactory neuroblastoma is an aggressive malignancy and the prognosis is poor in most cases, as shown by the short survival rates (average 45.3 months) in our study group. The tumor can be detected, delineated and its characteristics suspected by modern radiology. Definite diagnosis is based on histopathology. This study proposes general imaging strategies for detecting this disease.

A comparative study of technetium-99m sestamibi and technetium-99m tetrofosmin single-photon tomography in the detection of nasopharyngeal carcinoma

The intention of this prospective study was to compare the diagnostic potential of technetium-99m sestamibi (MIBI) and a novel radiotracer, 99mTc-Tetrofosmin (Tetro), for the assessment of primary nasopharyngeal carcinoma (NPC) and the differentiation of residual disease from post-therapy changes. A total of 38 patients underwent MIBI and Tetro single-photon emission tomography (SPET) imaging at initial presentation (n=22) or following therapy (n=16). The findings were correlated with computed tomography or magnetic resonance imaging (MRI) on a site-by-site basis. Tumour/background (Tm/Bkg) ratios were obtained on coronal sections. Biopsy (nine patients) and/or 12- to 24-month clinical follow-up data were available in the post-therapy group. All primary disease sites were accurately detected by both imaging studies. Although there was no statistical difference between the two imaging techniques in the detection of primary disease, MIBI was superior to Tetro in the detection of regional lymph node metastases (sensitivity: 95% vs 79%). Tetro and MIBI SPET were true-positive in all patients (n=7) with proven residual/recurrent disease. In nine patients who had no evidence of residual/recurrent tumour, MRI was false-positive in five while Tetro and MIBI SPET were false-positive in two and three patients, respectively. Tm/Bkg ratios were </=1.7 in all false-positive cases except one. Tetro, MIBI and MRI had specificities of 78%, 67% and 44%, and accuracies of 87.5%, 81% and 69%, respectively. The results of Tetro and of MIBI SPET were not statistically different from one another with regard to the prediction of residual/recurrent or metastatic NPC.

Oncological applications of positron emission tomography with fluorine-18 fluorodeoxyglucose

Positron emission tomography (PET) is now primarily used in oncological indication owing to the successful application of fluorine-18 fluorodeoxyglucose (FDG) in an increasing number of clinical indications at different stages of diagnosis, and for staging and follow-up. This review first considers the biological characteristics of FDG and then discusses methodological considerations regarding its use. Clinical indications are considered, and the results achieved in respect of various organs and tumour types are reviewed in depth. The review concludes with a brief consideration of the ways in which clinical PET might be improved.

How radiation oncology emerged as a discipline in Finland

The news about the discovery of Röntgen's new rays spread over Finland quite early, and the first Finnish writing about the rays appeared in February 1896. The first x-ray machine was installed in 1897. Proper training of radiologists began, however, at a comparatively late date. For a long time the position of radiologists remained a subordinate one. Radiology had the nature of a spare time hobby, because in most hospitals surgeons treated x-ray machines as a sideline. Because of this, scientific research work was delayed. The specialty of x-ray diagnosis and therapy was, however, established in 1921, and the Finnish Society of Radiology was founded in 1924. The first radiotherapy department with its own beds was opened in 1936 in Helsinki. In 1950, the first professor of medical radiology was appointed at the University of Helsinki. The Finnish Cancer Society played an important role in developing the radiotherapy net in the country by supplying cobalt devises and auxiliary hospital activities in the 1960s. In the early 1960s roentgen diagnosis and radiotherapy were separated into two distinct disciplines. There are now five medical faculties with chairs in radiation oncology. The country is divided into five regions for cancer care. The managing groups in each region are headed by the professor of radiotherapy and oncology. The radiation oncologists in Finland are involved in diagnosis and staging of cancer and are responsible for radiation therapy, chemotherapy and hormones. They are responsible for follow-up of treated patients, their own wards, and the general care of their patients.

Evaluation of response to radiotherapy in head and neck cancer by positron emission tomography and [11C]methionine

PURPOSE

To evaluate the usefulness of positron emission tomography (PET) and L-[methyl-11C]methionine in assessing treatment response to radiotherapy in head and neck cancer.

METHODS AND MATERIALS

Fifteen patients with head and neck cancer (13 with squamous cell carcinoma, 1 with adenocystic carcinoma, and 1 with paranasal plasmocytoma) underwent a PET study with [11C]-methionine both before and after preoperative radiotherapy to the total tumor dose of 61-73 Gy. Twelve primary and 12 metastatic tumor sites were within the field of view. Nineteen of the 24 tumor sites were surgically explored after radiotherapy, and the tumor standardized uptake values (SUVs) of [11C]methionine were compared with histological findings.

RESULTS

All 24 malignant lesions were detectable in the pretreatment study. In all but one case, the tumor SUV decreased after radiotherapy. The median SUV of the tumor site was smaller (1.9, range, 1.3-3.1, n = 7) in cases with histologically verified complete response than in cases with persistent cancer (median 4.1, range, 2.8-7.6, n = 12, p = 0.0008). A complete histological response was verified in none of the 9 cases with a postirradiation SUV larger than the median (3.1), whereas 7 of the 10 cases with a SUV of 3.1 or smaller had complete response (p = 0.003). The preirradiation uptake of [11C]methionine in tumors did not have significant association with histological response (p = 0.45). The PET findings correlated well with follow-up data in five cases with unoperated tumor sites. The [11C]methionine uptake of the submandibular salivary glands decreased after radiotherapy (p = 0.04).

CONCLUSION

PET with [11C]methionine as a tracer may be useful in assessing response to radiotherapy in head and neck cancer. High uptake of [11C]methionine in the postirradiation scan suggests the presence of persistent disease.