Discovery of prognostic markers in laryngeal cancer treated with radiotherapy
Bruine de Bruin, Leonie
DOI:
10.33612/diss.143832673
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date: 2020
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Bruine de Bruin, L. (2020). Discovery of prognostic markers in laryngeal cancer treated with radiotherapy. University of Groningen. https://doi.org/10.33612/diss.143832673
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum.
Chapter 2
Head and neck tumor hypoxia
imaging by
18
F-fluoroazomycin-arabinoside (
18
F-FAZA)-PET:
a review
GB Halmosa, L Bruine de Bruina,b,†, JA Langendijkd,BFAM van der Laana,#, J Pruimc, RJHM Steenbakkersd
aDepartment of Otorhinolaryngology/Head and Neck Surgery,University of Groningen,
University Medical Center Groningen, Groningen, The Netherlands
bDepartment of Pathology and Medical Biology,University of Groningen, University Medical
Center Groningen, Groningen, The Netherlands
cDepartment of Nuclear Medicine and Molecular Imaging, University of Groningen, University
Medical Center Groningen, The Netherlands and Department of Nuclear Medicine, Tygerberg Hospital, Stellenbosch University, Stellenbosch, South-Africa
dDepartment of Radiation Oncology,University of Groningen, University Medical Center
Groningen, Groningen, The Netherlands †Current affiliation: Department of Otorhinolaryngology/Head and Neck Surgery, Hospital St
Jansdal, Harderwijk/Lelystad, The Netherlands
#Current affiliation: Department of Otorhinolaryngology/Head and Neck Surgery, Haaglanden
Medical Center, The Hague, The Netherlands
ABSTRACT
Tumor hypoxia is known to be associated with poor clinical outcome; therefore, patients with hypoxic tumors might benefit from more intensive treatment approaches. This is particularly true for patients with head and neck cancer. Pre-treatment assessment of hypoxia in tumors would be desirable, not only to predict prognosis but also to select patients for more aggressive treatment.
As an alternative to the invasive polarographic needle electrode method, there is the possibility of using PET with radiopharmaceuticals visualizing hypoxia. Most hypoxia imaging studies on head and cancer have been performed using 18F-labeled
fluoromisonidazole (18F-FMISO). A chemically related molecule, 18
F-fluoroazomycin-arabinoside (18F-FAZA), seems to have superior kinetic properties and may therefore
be the radiopharmaceutical of choice.
This minireview summarizes the published literature on animal and human
18F-FAZA-PET studies. Furthermore, future perspectives on how individualized
treatment could be applied in patients with hypoxic head and neck tumors are discussed, for instance the use of hypoxia sensitizers or special intensity modulated radiation therapy techniques achieving tumor subvolume dose escalation.
2
INTRODUCTION
Tumor hypoxia
Tumor hypoxia is a well-recognized adverse prognostic factor in patients with solid tumors treated with radiotherapy1 and is associated with a number of unfavorable
biological characteristics, including increased genetic instability, increased invasiveness, enhanced metastatic potential and decreased radiosensitivity2,3.
Poorer clinical outcome of hypoxic tumors has been observed in patients with head and neck cancer treated by radiotherapy4,5 and surgery6. From this point of
view, patients with hypoxic tumors might benefit from more intensive treatment approaches to counterbalance the radioresistance. It has been estimated that tumor hypoxia is present in about half of the solid tumors regardless of the tumor volume or histological type7. Unfortunately, patients with head and neck cancer
tend to present themselves with tumors in advanced stages, which increase the likelihood of developing hypoxia8.
Detection of hypoxia
Although tumor hypoxia is usually defined as a tumor region with a partial oxygen pressure (pO2) less than 10 mm Hg9, there is no consensus over the interpretation
and analysis of hypoxia-positive areas of different imaging modalities. For instance, some of the PET studies use the tumor-to-background ratio (T/B), others the tumor-to-muscle ratio (T/M) and there are also self-developed scoring systems. Unfortunately, these differences make it difficult to compare studies.
Polarographic needle electrode sampling is considered the gold standard to assess hypoxia in vivo10,11. However, assessing tumor hypoxia using the Eppendorf
electrodes is invasive, requires sophisticated skills and technical demands and may be subject to sampling error because of the known heterogeneity in tumor hypoxia12,13. In addition, the results of these measurements cannot be used for
radiotherapy treatment planning, for example, for escalating the dose to hypoxic regions within a tumor.
Therefore, assessing tumor hypoxia with metabolic imaging techniques such as PET, using specific radiopharmaceuticals visualizing hypoxia, is an attractive alternative, at least theoretically. Several studies have been published and several different radiopharmaceuticals have been applied. Due to the different analysis techniques applied, however, it is difficult to compare studies even using the same PET radiopharmaceuticals (Table 1).
Table 1. Summary of studies on human 18F-FAZA-PET
Publication No. patients Tumor site (n) Definition of
hypoxic volume Percentage of patients with increased 18F-FAZA uptake
(ie, hypoxia) Grosu et al.16 and
Souvatzoglou et al.43 18 Head and neck (18) T/M ≥ 1.5* 83
Postema et al.44 50 Head and neck
(9) Lymphoma (21) High-grade glioma (7) Lung (13) Visual inspection and T/B ratio ≥ 1.2 6614 100 54 Schuetz et al.45 15 Cervix (15) T/M ≥ 1.2† 33
Shi et al.46 5 Head and neck
(5) Different kinetic models 80 Garcia-Parra et al.47 14 Prostate (14) T/B ratio‡ 0
Mortensen et al.48 40 Head and neck
(40) T/M ≥ 1.4§ 63 Bollineni et al.49 11 Lung (11) T/B ratio ≥ 1.2 and
T/B ratio ≥ 1.4 100 *Tumor SUV/muscle SUVmean ratio ≥ 1.5.
†Tumor SUVmax/muscle SUVmax ratio ≥ 1.2.
‡Tumor SUVmax/benign prostate SUV.
§Tumor SUVmax/muscle SUV mean ratio ≥ 1.4.
18F-FMISO for hypoxia imaging
A number of PET radiopharmaceuticals for hypoxia imaging have been identified, of which the group of nitroimidazoles is the largest. These compounds undergo reduction under hypoxic conditions and form highly reactive oxygen radicals. After binding to intracellular macromolecules, they are trapped inside the hypoxic cells. Among the radiolabeled nitroimidazoles, 18F-FMISO is the most frequently
used. Troost et al.14 found a significant correlation between 18F-FMISO-PET imaging
of tumor hypoxia in head and neck cancer and the extrinsic hypoxic cell marker pimonidazole. Pimonidazole is a nitroimidazole-like robust exogenous hypoxia marker, which needs to be injected 2 hours before biopsy. The distribution of pimonidazole is visualized by immunohistochemistry. In another validation study, only a week correlation was found between 18F-FMISO uptake and pO
2 histography15.
These apparently conflicting results are most likely due to heterogeneity in intratumoral hypoxia16. In a study of 73 patients with head and neck cancer,
hypoxia, defined by increased 18F-FMISO uptake, was found in almost 80% of
the patients. Moreover, increased 18F-FMISO uptake found to be associated with
significant worse overall survival17. Rischin and co-workers18 also found 18F-FMISO
2
tirapazamine (a hypoxic cytotoxin), was found to be effective in patients with hypoxic tumors as assessed by 18F-FMISO-PET. Pre-treatment dynamic 18
F-FMISO-PET scanning has also found to be successful in predicting radiotherapy outcome in non-small cell lung cancer and head and neck cancer19,20. Moreover, a later study
of the same group21 showed that the same imaging technique is also suitable
for following the radio-induced reoxygenation of head and neck cancer during radiotherapy. A recent study by Zips et al.22 investigated the change of hypoxia
and the predictive value of it for survival during radiotherapy in patients with head and neck cancer using 18F-FMISO-PET scan. Each patient has been scanned before
and three times during radiotherapy. The scan parameters performed at week 1 (8-10 Gy) and 2 (18-20 Gy) strongly correlated with the local progression-free survival endpoints, suggesting good prognostic value of 18F-FMISO-PET at these
time points and not at baseline.
Most of the studies investigating hypoxia by PET scans using static scans, as technically static scans are easier to perform. However, dynamic scans are more informative as they allow kinetic modeling and estimation of some rate constants, which can discriminate between tumor and background.
Alternatives to 18F-FMISO
Although hypoxia imaging using 18F-FMISO-PET is feasible and has prognostic value,
there are also some disadvantages using this PET radiopharmaceutical. One of the problems is the relatively short half-life time (110 minutes) of 18F-FMISO, which
hampers late imaging that could enhance good contrast between hypoxia and normal tissues23. There is ongoing intensive research in order to find alternative
hypoxia PET radiopharmaceuticals with better kinetics. 18F-HX4, another new
potential marker for hypoxia PET scanning has recently been described24. Preclinical
studies showed advantageous biodistribution and dosimetry properties, which make 18F-HX4 a promising hypoxia radiopharmaceutical candidate. A pilot PET
study on hypoxia imaging using 18F-HX4 as a radiopharmaceutical in head and neck
cancer patient has recently been published25. Although this study included only 12
patients, the data are promising; higher sensitivity, specificity, faster clearance, and shorter injection-imaging time were found compared to 18F-FMISO. 18F-EF5
is another nitroimidazole that has been evaluated in imaging hypoxia in patients with head and neck squamous cell carcinoma. Data showed that the later uptake and binding of 18F-EF5 are hypoxia specific. The optimal scanning time and the
also been assessed by 18F-FETNIM27. In a later study, high uptake of 18F-FETNIM
seemed to correlate with poorer radiotherapy outcome, although firm conclusions are difficult to draw due to small study population28. Beside these nitroimidazoles,
other molecules have been also tested, like the dithiosemicarbazones. One of them is 64Cu-ATSM, which is also a PET radiopharmaceutical developed to accumulate in
hypoxic tumors. It found to be feasible for radiotherapy planning in a pilot study, and the biokinetic properties seems to be superior to 18F-FMISO, as a hypoxic
tumor subvolume could be identified as early as 10 minutes after injection29.
Purpose of the present review
In this review, we will focus on the possible applicability of PET scanning with a relatively new hypoxia radiopharmaceutical, 18F-FAZA, in radiotherapy treatment
planning based on tumor hypoxia determination in head and neck cancer. More specifically, the purposes of this review are to assess whether hypoxia as determined with 18F-FAZA-PET correlates with histological or biological parameters,
to investigate whether the presence of hypoxia as demonstrated with 18F-FAZA
predicts outcome and to investigate how 18F-FAZA could be used in clinical practice.
PROPERTIES OF
18F-FAZA
18F-FAZA is, like 18F-FMISO, a 2-nitroimidazole compound, but sugar-coupled
(Figure 1). As already mentioned, 2-nitroimidazole compounds undergo reduction under hypoxic conditions, forming highly reactive oxygen radicals. Subsequently, they bind to macromolecules in the intracellular compartment and trapped inside hypoxic cells30. When 18F-FAZA is labeled with the radioisotope 18F, it can be
detected by a PET scanner.
Kumar et al31 were the first that reported on the synthesis of 18F-FAZA by
fluorination of 1-α-D-(2,3-di-O-acetylarabinofuranosyl)-2-nitroimidazole with DAST followed by deprotection. Their main objective was to develop a PET imaging compound that was similar to the SPECT compound 123I-IAZA, but that
was less lipophilic than 18F-FMISO. Theoretically, a less lipophilic compound may
produce higher perfusion and faster clearance from blood resulting in a better hypoxia-background-ratio. In a rat model, they showed that 3H-FAZA had similar
biodistribution, tumor uptake, and pharmacokinetics as 123I-IAZA, but was indeed
2
Figure 1. Molecular structure of 18F-FAZAIN VITRO
18F-FAZA EXPERIMENTS AND
18F-FAZA-PET
XENOGRAFT MODELS
As all new radiopharmaceuticals, 18F-FAZA is also intensively investigated in
both in vitro and in vivo experiments. The detection of hypoxia-dependent radiopharmaceutical accumulation is fundamental, just like exact characterization of pharmacokinetic features.
In the first in vitro study by Busk et al.32, oxygenation-dependent 18F-FAZA
retention was compared to that of 18F-FDG in different carcinoma lines. 18F-FAZA
accumulation was measured after radiopharmaceutical incubation in different oxygenation conditions. Significant 18F-FAZA retention was observed after 3 hours
of anoxia and no binding in nonhypoxic cells. Furthermore, it showed superior in vivo hypoxia specificity compared with 18F-FDG. This study concluded that 18F-FAZA
has excellent in vitro characteristics for hypoxia imaging. Another study33 compared
the hypoxia-selective uptake of 18F-FAZA to that of 18F-FMISO, as the mostly used
hypoxia radiopharmaceutical, and found no differences in the vitro experiments with tumor cell lines, but in the in vivo animal PET study the elimination of
18F-FAZA was found to be faster. This feature seems to be an advantage in imaging,
but the concentration of 18F-FAZA was lower, which suggests a lower sensitivity
of 18F-FAZA. In a later animal PET study, obvious superior biokinetics for 18F-FAZA
were found as compared to 18F-FMISO, for example, significantly higher T/M and tumor-to-blood ratios34.
Beck et al35 evaluated the predictive value of 18F-FAZA in a hypoxic xenograft
tumor model and found that delayed tumor growth by radiotherapy can be further enhanced by adding the hypoxic sensitizer tirapazamine to radiotherapy. This effect has only been observed in hypoxic tumors, but not in normoxic ones. High
18F-FAZA uptake was found to be an independent negative prognostic factor for
tumor progression. Furthermore, 18F-FAZA-PET was able to predict the success of
the hypoxia sensitizing treatment of tirapazamine and radiotherapy.
The distribution of 18F-FAZA in xenograft tumors was examined by Busk et al.36.
The 18F-FAZA-PET images were compared to the spatial distribution of 18F-FAZA using
autoradiography, to polarographic hypoxia mapping using Eppendorf electrode measurements, and to pimonidazole fluorescence imaging. The consistency of
18F-FAZA distribution with hypoxia was verified using these various methods. The
spatial link between 18F-FAZA and pimonidazole was further justified by the same
research group37. Interestingly, the same paper describes substantial spatial overlap
but also areas of mismatch of 18F-FAZA and the endogenous hypoxia marker
GLUT-1. The authors explained these conflicting data by regional blood flow changes in solid tumors and the latency of endogenous hypoxia markers. Namely, acute decrease in tumor perfusion can result in 18F-FAZA retention without accumulation
of GLUT-1, or on the contrary, reoxygenated regions with the presence of GLUT-1 have no 18F-FAZA accumulation. There is of course one more explanation, that is,
the possible unreliable features of endogenous hypoxia markers, which is already described earlier38.
The same research group published their data on dynamic 18F-FAZA-PET imaging
in three squamous cell carcinoma xenograft models39. In this study, 3 hours after 18F-FAZA administration, high tumor-to-reference tissue ratios were found. At the
same time, using pimonidazole and 18F-FAZA autoradiography, a strong correlation
was observed between hypoxic cell density and 18F-FAZA concentration. These
results confirmed that late 18F-FAZA imaging provides a reliable measure of
hypoxia, but the time-activity curves were more dependent on tumor type than on the extent of hypoxia. These conflicting data are explained to be the result of the generic 2-compartment model applied in the study, which assumes homogeneous tumors; however, intratumoral hypoxia is known to be heterogeneous.
An interesting study by Meier et al.40 tried to answer the question whether
different breathing protocols affect oxygenation status of xenograft tumors models. The eventual hypoxic areas have been visualized using 18F-FAZA-PET in
2
visualization of tumor hypoxia, this study also focused on the reversibility of
18F-FAZA binding in normoxic muscle applying three different breathing protocols.
The uptake and clearance of 18F-FAZA has found to be oxygen supply dependent
in both examined carcinomas, but it remained constant in normal muscle tissue.
18F-FAZA accumulation showed correlation with the hypoxia immunostaining.
These results confirm that 18F-FAZA is a reliable hypoxia biomarker.
Recently, a Danish group compared the prognostic value of 18F-FAZA-PET
scanning and Eppendorf needle sampling in an animal model41. Oxygenation status
of subcutaneously grown tumors in mice has been defined with both methods before single dose radiation. Both 18F-FAZA-PET and Eppendorf pO
2 histography
have found to be prognostic of therapy response.
The change of hypoxia during radiotherapy remains an interesting issue. Busk et al.42 monitored tumor hypoxia change in xenograft models before and after
fractionated radiotherapy using 18F-FAZA-PET. Although during treatment, overall
radiopharmaceutical accumulation changed in the experimental animals there was no signs of re-oxygenation. These results prove the high reproducibility of hypoxia PET scanning with 18F-FAZA but contradict the results of other human studies,
where significant changes were observed during therapy22.
Based on these in vitro and xenograft model experiments 18F-FAZA-PET seems
to be a reliable and reproducible imaging technique to visualize hypoxia.
HUMAN
18F-FAZA-PET STUDIES
To the best of our knowledge, only eight studies have been published evaluating
18F-FAZA-PET in humans16,43-49. The main results of these studies are summarized
in Table 1. All 11 head and neck cancer patients included in the publication by Souvatzoglou et al.43 were also analyzed in the publication by Grosu et al.16, but
the latter study included an additional seven patients. Therefore, both publications are considered as one study.
In the study of Grosu et al.16, 18F-FAZA-PET was performed before radiotherapy
in patients with head and neck cancer. Hypoxic areas were identified in the primary tumor in 15 of 18 patients. In four of these patients, the hypoxic area was diffusely dispersed throughout the primary tumor. Therefore, no single area of hypoxia could be identified in these patients. Postema et al.44 found large differences in the
were seen in all patients with high-grade gliomas. For the other tumor sites there were significantly less hypoxic areas, especially in patients with lymphomas; only 14% of these subjects had increased 18F-FAZA uptake. Unfortunately, the reasons
for these large differences in hypoxia between tumor sites are not discussed. In the study by Schuetz et al.45, 18F-FAZA-PET scans were performed before, during
and after external beam radiotherapy in patients with cervical cancer. Five of the 15 patients showed increased 18F-FAZA uptake with inhomogeneous patterns.
Due to the small number of patients, 18F-FAZA-PET could not be used to predict
treatment outcome. In the study by Shi et al.46, five patients with head and neck
cancer were scanned by dynamic PET using 18F-FAZA and 15O-H
2O. The results of
this study show that different kinetic models provide different estimates of tumor hypoxia, and different models may even rank patients differently. Accordingly, although pharmacokinetic analysis may be superior to static scans, additional studies are required in order to assess the true value of kinetic analysis in this respect. In the recently published study using 18F-FAZA-PET by Garcia-Parra et al.47,
14 patients with prostate cancer were scanned before a prostatectomy. They found no existing clinically relevant hypoxic area’s in localized prostate tumors that could be possibly detected by 18F-FAZA-PET, meaning the limited value of 18F-FAZA in
this specific tumor type. A recent human 18F-FAZA-PET study48 investigated the
hypoxia using 18F-FAZA-PET in forty patients with head and neck cancer treated by
(chemo)radiotherapy. Tumors were located at different primary sites and tumor stage varied between patients. Scans were made before and during therapy. There were 25/40 hypoxic tumors before and 6/13 during treatment. Significantly poorer prognosis was observed of patients with hypoxic tumors (disease-free survival, 60%), compared to non-hypoxic counterparts (disease-free survival, 93%). Despite the relatively low patient population and the diversity of the tumors sites that were investigated, this study further strength the idea that 18F-FAZA-PET scan is a reliable
method for hypoxia imaging with prognostic potential. The most recent human
18F-FAZA-PET study compared 18F-FAZA-PET with 18F-FDG-PET scans in 11 patients
with stage III-IV non-small cell lung cancer just before chemoradiotherapy49. They
concluded that 18F-FAZA-PET imaging is able to detect heterogeneous distributions
of hypoxic subvolumes within homogeneous 18F-FDG background. Furthermore,
no correlation between 18F-FAZA and 18F-FDG uptake was found. The authors of this
study claim that 18F-FAZA provides additional information on tumor hypoxia to18
F-FDG and might be used to develop a tool for guiding individualization of treatment of advanced non-small cell lung cancer.
2
FUTURE PERSPECTIVES
Prognosis/patient selection
As shown earlier, 18F-FAZA-PET can be used to identify tumor regions with hypoxia.
Theoretically, such knowledge can be used to make a better estimation of prognosis, but also to select patients for some kind of hypoxia-targeted treatment. For example, accelerated radiotherapy combined with the hyperoxic gas carbogen and nicotinamide (ARCON) is recently investigated in phase 3 trials50-53. For head
and neck cancer, ARCON showed no benefit compared with accelerated radiation, except for regional control in T2-T4 laryngeal cancer51, but a significant gain in
regional control rate was observed among the patients receiving ARCON with equal levels of toxicity53. In this study, no hypoxic imaging has been performed
before the treatment, because at the time of patient selection no hypoxic image tool was available. For the future, 18F-FAZA-PET may be able to select patients with
hypoxic tumors, which might indeed benefit from ARCON and consequently the true value of ARCON defined.
Tirapazamine is a drug with selective cytotoxicity for hypoxic cells. Recently, in a phase 3 trial54, 861 patients with locally advanced head and neck cancer
were randomly assigned to receive chemoradiation or chemoradiation with tirapazamine. No benefit was found in terms of overall survival, failure-free survival, time to locoregional failure, or quality of life. Although in this study no advantage was found, in a substudy18 tirapazamine was found to be effective in
patients with hypoxic tumors as assessed by 18F-FMISO-PET. Again, this finding
suggests that introducing hypoxia imaging would better help selecting patients for additional treatment.
Radiotherapy dose escalation
In the past, several attempts have been made to overcome tumor hypoxia, such as the use of hyperbaric oxygen, radiosensitizers, vasodilators or hypoxic cytotoxins such as tirapazamine combined with (chemo)radiation. Unfortunately, generally speaking, these combined approaches have come to the expense of increased acute and late radiation-induced side-effects55.
Another approach, which may overcome hypoxic tumor resistance, is increasing the radiation dose. However, increasing the radiation dose may also increase radiation-induced side effects, especially in the head and neck area where critical structures, such as the spinal cord, carotid arteries and parotid glands,
are in close proximity to the tumor. Ideally, only hypoxic tumor cells or hypoxic cell islets should receive such a higher dose. Currently, with modern radiotherapy techniques like intensity-modulated radiotherapy, it has become possible to intensify radiation dose in specific subvolumes within the gross tumor volume56.
It has been hypothesized that 18F-FAZA-PET/CT can be used to guide radiotherapy
in order to substantially increase the dose to hypoxic tumor subvolumes16. This
might improve local control and subsequently survival of patients with locally advanced head and neck squamous cell carcinoma. To the best of our knowledge, few clinical data are available so far to prove this hypothesis. In addition, little is known about the way hypoxic areas behave during the radiotherapy course: hypoxic areas may disappear and subsequently appear at different locations. To achieve the most optimal hypoxic tumor subvolume dose escalation, several strategies are developed (e.g., gradual dose escalation using intensity-modulated radiation therapy with a simultaneous integrated boost, intensity modulated arc therapy, stereotactic boost, or protons). Additional information is required with regard to these possible changes.
CONCLUSIONS
Based on this review, we conclude that 18F-FAZA-PET is feasible to detect tumor
hypoxia and to have superior biokinetics compared to 18F-FMISO. 18F-FAZA is a
promising PET radiopharmaceutical for visualization of tumor hypoxia, although clinical studies must still confirm the exact role of 18F-FAZA-PET scanning in
head and neck oncology. Also, the superior hypoxia PET radiopharmaceutical is not known yet. Therefore, a clinical study directly comparing different hypoxia radiopharmaceuticals (e.g., 18F-FMISO, 18F-FAZA, 18F-HX4) in the same patients
2
REFERENCES
1. Vaupel P, Mayer A, Hockel M. Tumor hypoxia and malignant progression. Methods Enzymol. 2004;381:335-354.
2. Harris AL. Hypoxia—a key regulatory factor in tumour growth. Nat Rev Cancer. 2002;2:38-47. 3. Le QT, Denko NC, Giaccia AJ. Hypoxic gene expression and metastasis. Cancer Metastasis Rev.
2004;23:293-310.
4. Vanselow B, Eble MJ, Rudat V, et al. Oxygenation of advanced head and neck cancer: Prognostic marker for the response to primary radiochemotherapy. Otolaryngol Head Neck Surg. 2000;122:856-862. 5. Prosnitz RG, Yao B, Farrell CL, et al. Pretreatment anemia is correlated with the reduced effectiveness
of radiation and concurrent chemotherapy in advanced head and neck cancer. Int J Radiat Oncol Biol
Phys. 2005;61:1087-1095.
6. Isa AY, Ward TH, West CM, Slevin NJ, Homer JJ. Hypoxia in head and neck cancer. Br J Radiol. 2006;79:791-798.
7. Vaupel P, Mayer A. Hypoxia in cancer: Significance and impact on clinical outcome. Cancer Metastasis
Rev. 2007;26(2):225-239.
8. Adam MF, Gabalski EC, Bloch DA, et al. Tissue oxygen distribution in head and neck cancer patients.
Head Neck. 1999;21:146-153.
9. Chitneni SK, Palmer GM, Zalutsky MR, et al. Molecular imaging of hypoxia. J Nucl Med. 2011;52:165-168.
10. Nordsmark M, Overgaard M, Overgaard J. Pretreatment oxygenation predicts radiation response in advanced squamous cell carcinoma of the head and neck. Radiother Oncol. 1996;41:31-39.
11. Brizel DM, Sibley GS, Prosnitz LR, et al. Tumor hypoxia adversely affects the prognosis of carcinoma of the head and neck. Int J Radiat Oncol Biol Phys. 1997;38:285-289.
12. Becker A, Hansgen G, Bloching M, et al. Oxygenation of squamous cell carcinoma of the head and neck: Comparison of primary tumors, neck node metastases, and normal tissue. Int J Radiat Oncol Biol Phys. 1998;42:35-41.
13. Le QT, Kovacs MS, Dorie MJ, et al. Comparison of the comet assay and the oxygen microelectrode for measuring tumor oxygenation in head-and-neck cancer patients. Int J Radiat Oncol Biol Phys. 2003;56:375-383.
14. Troost EG, Laverman P, Kaanders JH, et al. Imaging hypoxia after oxygenation-modification: Comparing [18F]FMISO autoradiography with pimonidazole immunohistochemistry in human xenograft tumors.
Radiother Oncol. 2006;80:157-164.
15. Gagel B, Piroth M, Pinkawa M, et al. pO polarography, contrast enhanced color duplex sonography (CDS), [18F] fluoromisonidazole and [18F] fluorodeoxyglucose positron emission tomography: Validated
methods for the evaluation of therapy-relevant tumor oxygenation or only bricks in the puzzle of tumor hypoxia? BMC Cancer. 2007;7:113.
16. Grosu AL, Souvatzoglou M, Roper B, et al. Hypoxia imaging with FAZA-PET and theoretical considerations with regard to dose painting for individualization of radiotherapy in patients with head and neck cancer. Int J Radiat Oncol Biol Phys. 2007;69:541-551.
17. Rajendran JG, Schwartz DL, O’Sullivan J, et al. Tumor hypoxia imaging with [F-18] fluoromisonidazole positron emission tomography in head and neck cancer. Clin Cancer Res. 2006;12:5435-5441. 18. Rischin D, Hicks RJ, Fisher R, et al. Prognostic significance of [18F]-misonidazole positron emission
tomography-detected tumor hypoxia in patients with advanced head and neck cancer randomly assigned to chemoradiation with or without tirapazamine: A substudy of trans-tasman radiation oncology group study 98.02. J Clin Oncol. 2006;24:2098-2104.
19. Eschmann SM, Paulsen F, Reimold M, et al. Prognostic impact of hypoxia imaging with 18F-misonidazole
PET in non-small cell lung cancer and head and neck cancer before radiotherapy. J Nucl Med. 2005;46:253-260.
20. Thorwarth D, Eschmann SM, Holzner F, et al. Combined uptake of [18F]FDG and [18F]FMISO correlates
21. Eschmann SM, Paulsen F, Bedeshem C, et al. Hypoxia-imaging with (18)F-misonidazole and PET: Changes of kinetics during radiotherapy of head-and-neck cancer. Radiother Oncol. 2007;83:406-410. 22. Zips D, Zophel K, Abolmaali N, et al. Exploratory prospective trial of hypoxia-specific PET imaging
during radiochemotherapy in patients with locally advanced head-and-neck cancer. Radiother Oncol. 2012;105:21-28.
23. Garcia C, Flamen P. Role of positron emission tomography in the management of head and neck cancer in the molecular therapy era. Curr Opin Oncol. 2008;20:275-279.
24. Dubois LJ, Lieuwes NG, Janssen MH, et al. Preclinical evaluation and validation of [18F]HX4, a promising hypoxia marker for PET imaging. Proc Natl Acad Sci U S A. 2011;108:14620-14625.
25. Chen L, Zhang Z, Kolb HC, et al. (1)(8)F-HX4 hypoxia imaging with PET/CT in head and neck cancer: A comparison with (1)(8)F-FMISO. Nucl Med Commun. 2012;33:1096-1102.
26. Komar G, Seppanen M, Eskola O, et al. 18F-EF5: A new PET tracer for imaging hypoxia in head and neck
cancer. J Nucl Med. 2008;49:1944-1951.
27. Lehtio K, Oikonen V, Nyman S, et al. Quantifying tumour hypoxia with fluorine-18 fluoroerythronitroimidazole ([18F]FETNIM) and PET using the tumour to plasma ratio. Eur J Nucl Med
Mol Imaging. 2003;30:101-108.
28. Lehtio K, Eskola O, Viljanen T, et al. Imaging perfusion and hypoxia with PET to predict radiotherapy response in head-and-neck cancer. Int J Radiat Oncol Biol Phys. 2004;59:971-982.
29. Chao KS, Bosch WR, Mutic S, et al. A novel approach to overcome hypoxic tumor resistance: Cu-ATSM-guided intensity-modulated radiation therapy. Int J Radiat Oncol Biol Phys. 2001;49:1171-1182. 30. Reischl G, Ehrlichmann W, Bieg C, et al. Preparation of the hypoxia imaging PET tracer [18F]FAZA:
Reaction parameters and automation. Appl Radiat Isot. 2005;62:897-901.
31. Kumar P, Stypinski D, Xie H, et al. Fluoroazomycin arabinoside (FAZA): Synthesis, 2H and 3H-labelling
and preliminary biological evaluation of a novel 2-nitroimidazole marker of tissue hypoxia. J Label
Compounds Radiopharm. 1999;42:3-16.
32. Busk M, Horsman MR, Jakobsen S, et al. Cellular uptake of PET tracers of glucose metabolism and hypoxia and their linkage. Eur J Nucl Med Mol Imaging. 2008;35:2294-2303.
33. Sorger D, Patt M, Kumar P, et al. [18F]fluoroazomycinarabinofuranoside (18FAZA) and [18F]
fluoromisonidazole (18FMISO): A comparative study of their selective uptake in hypoxic cells and PET
imaging in experimental rat tumors. Nucl Med Biol. 2003;30:317-326.
34. Piert M, Machulla HJ, Picchio M, et al. Hypoxia-specific tumor imaging with 18F-fluoroazomycin
arabinoside. J Nucl Med. 2005;46:106-113.
35. Beck R, Roper B, Carlsen JM, et al. Pretreatment 18F-FAZA PET predicts success of hypoxia-directed
radiochemotherapy using tirapazamine. J Nucl Med. 2007;48:973-980.
36. Busk M, Horsman MR, Jakobsen S, et al. Imaging hypoxia in xenografted and murine tumors with
18F-fluoroazomycin arabinoside: A comparative study involving microPET, autoradiography,
PO2-polarography, and fluorescence microscopy. Int J Radiat Oncol Biol Phys. 2008;70:1202-1212.
37. Busk M, Horsman MR, Jakobsen S, et al. Can hypoxia-PET map hypoxic cell density heterogeneity accurately in an animal tumor model at a clinically obtainable image contrast? Radiother Oncol. 2009;92:429-436.
38. Janssen HL, Haustermans KM, Balm AJ, et al. Hypoxia in head and neck cancer: How much, how important? Head Neck. 2005;27:622-638.
39. Busk M, Munk OL, Jakobsen S, et al.Assessing hypoxia in animal tumor models based on pharmocokinetic analysis of dynamic FAZA PET. Acta Oncol. 2010;49:922-933.
40. Maier FC, Kneilling M, Reischl G, et al. Significant impact of different oxygen breathing conditions on noninvasive in vivo tumor-hypoxia imaging using [(1)(8)F]-fluoro-azomycinarabino-furanoside ([(1)(8)F] FAZA). Radiat Oncol. 2011;6:165,717X-6-165.
41. Mortensen LS, Busk M, Nordsmark M, et al. Accessing radiation response using hypoxia PET imaging and oxygen sensitive electrodes: A preclinical study. Radiother Oncol. 2011;99:418-423.
42. Busk M, Mortensen LS, Nordsmark M, et al. PET hypoxia imaging with FAZA: Reproducibility at baseline and during fractionated radiotherapy in tumour-bearing mice. Eur J Nucl Med Mol Imaging. 2013;40:186-197.
2
43. Souvatzoglou M, Grosu AL, Roper B, et al. Tumour hypoxia imaging with [18F]FAZA PET in head and neckcancer patients: A pilot study. Eur J Nucl Med Mol Imaging. 2007;34:1566-1575.
44. Postema EJ, McEwan AJ, Riauka TA, et al. Initial results of hypoxia imaging using 1-alpha-D: -(5-deoxy-5-[18F]-fluoroarabinofuranosyl)-2-nitroimidazole (18F-FAZA). Eur J Nucl Med Mol Imaging.
2009;36:1565-1573.
45. Schuetz M, Schmid MP, Potter R, et al. Evaluating repetitive 18F-fluoroazomycin-arabinoside (18FAZA) PET in the setting of MRI guided adaptive radiotherapy in cervical cancer. Acta Oncol. 2010;49:941-947. 46. Shi K, Souvatzoglou M, Astner ST, et al. Quantitative assessment of hypoxia kinetic models by a
cross-study of dynamic 18F-FAZA and 15O-H2O in patients with head and neck tumors. J Nucl Med.
2010;51:1386-1394.
47. Garcia-Parra R, Wood D, Shah RB, et al. Investigation on tumor hypoxia in resectable primary prostate cancer as demonstrated by 18F-FAZA PET/CT utilizing multimodality fusion techniques. Eur J Nucl Med
Mol Imaging. 2011;38:1816-1823.
48. Mortensen LS, Johansen J, Kallehauge J, et al. 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.
Radiother Oncol. 2012;105:14-20.
49. Bollineni VR, Kerner GS, Pruim J, et al. PET imaging of tumor hypoxia using 18F-fluorazomycin arabinoside
in stage III-IV non-small cell lung cancer patients. J Nucl Med. 2013;54:1175-1180.
50. Mendenhall WM, Morris CG, Amdur RJ, et al. Radiotherapy alone or combined with carbogen breathing for squamous cell carcinoma of the head and neck: A prospective, randomized trial. Cancer. 2005;104:332-337.
51. Hoskin PJ, Rojas AM, Bentzen SM, et al. Radiotherapy with concurrent carbogen and nicotinamide in bladder carcinoma. J Clin Oncol. 2010;28:4912-4918.
52. Kaanders J, Terhaard C, Doornaert P, et al. Outcome after ARCON for clinical stage T2-4 laryngeal cancer: Early results of a phase III randomized trial. Radiother Oncol. 2010;96(suppl 1):S158.
53. Janssens GO, Rademakers SE, Terhaard CH, et al. Accelerated radiotherapy with carbogen and nicotinamide for laryngeal cancer: Results of a phase III randomized trial. J Clin Oncol. 2012;30:1777-1783.
54. Rischin D, Peters LJ, O’Sullivan B, et al. Tirapazamine, cisplatin, and radiation versus cisplatin and radiation for advanced squamous cell carcinoma of the head and neck (TROG 02.02, HeadSTART): A phase III trial of the trans-tasman radiation oncology group. J Clin Oncol. 2010;28:2989-2995. 55. Hoogsteen IJ, Marres HA, van der Kogel AJ, et al. The hypoxic tumour microenvironment, patient
selection and hypoxia-modifying treatments. Clin Oncol (R Coll Radiol). 2007;19:385-396.
56. Thorwarth D, Eschmann SM, Paulsen F, et al. Hypoxia dose painting by numbers: A planning study. Int