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British Journal of Radiology (2005) Supplement_28, 42-49
© 2005 British Institute of Radiology
doi: 10.1259/bjr/59640473
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British Journal of Radiology Supplement_28 (2005),42-49 ©2005 The British Institute of Radiology

Full Paper

PET for response assessment in oncology: radiotherapy and chemotherapy

W A Weber, MD

Department of Molecular and Medical Pharmacology, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095, USA


   Abstract
Top
 Abstract
Introduction
 Monitoring of tumour response...
 Clinical studies on treatment...
 Prediction of tumour response...
 Conclusion
 References
 
Positron emission tomography (PET) imaging with the glucose analogue fluorodeoxyglucose (FDG) is increasingly used to monitor tumour response in patients undergoing chemotherapy and chemoradiotherapy. Numerous studies have shown that FDG-PET is an accurate test to differentiate between residual viable tumour tissue and therapy-induced fibrosis. Furthermore, quantitative assessment of therapy-induced changes in tumour FDG uptake may allow prediction of tumour response and patient outcome very early in the course of therapy. Treatment may be adjusted according to the chemosensitivity and radiosensitivity of the tumour tissue in an individual patient. Thus, FDG-PET has enormous potential to reduce the side effects and costs of ineffective therapy. This review gives an overview of clinical studies on treatment monitoring with FDG-PET and discusses how the results of PET imaging may be used to change patient management.


   Introduction
Top
 Abstract
 Introduction
Monitoring of tumour response...
 Clinical studies on treatment...
 Prediction of tumour response...
 Conclusion
 References
 
Over the last two decades, enormous progress has been made in defining the molecular alterations that occur in cancer. A multitude of molecular therapeutic targets have been identified and characterised, leading to the emergence of new classes of drugs. In contrast, the drug evaluation process has not kept pace with the discoveries in tumour biology. Treatment responses are still being evaluated from measurements of tumour size prior to and after treatment. In 1981 [1], standardised criteria for treatment monitoring were defined by the World Health Organization (WHO). In these criteria, tumour response was basically defined as a therapy-induced reduction of the product of two perpendicular diameters of the tumour by at least 50%. The theoretical foundation for this was the reproducibility of measurement of tumour size using palpation and callipers [2]. More recently, new "Response Evaluation Criteria for Solid tumours" (RECIST) have been proposed by the National Cancer Institute (NCI) and the European Organisation for Research and Treatment of Cancer (EORTC). In the RECIST criteria, the bidimensional measurements required by the WHO criteria have been replaced by unidimensional measurements [3]. According to RECIST, response is defined as a 30% decrease of the largest diameter of a tumour. For a spherical lesion, this is equivalent to a 50% decrease of the product of two diameters [4]. Thus, when tumours are currently evaluated after therapy by MRI or multislice CT, the criteria for response still stem from data evaluating the accuracy with which physicians could measure tumour size by palpation.

In addition to radiological criteria, tumour response can also be evaluated histopathologically. Histopathologic response is usually defined by the percentage of viable tumour relative to therapy-induced fibrosis. This percentage is expressed as a regression score. The most commonly used histopathologic regression score is probably the Salzer–Kuntschik score for osteosarcomas [5]. Similar scoring systems of tumour response have been established for other tumour types such as non-small cell lung cancer (NSCLC) [6], oesophageal cancer [7] and gastric cancer [8]. Histopathologic regression scores have shown a close correlation with survival. In particular, patients with only minimal (less than 10%) or no residual tumour have been found to have a markedly improved prognosis [6–9]. Therefore, histopathologic response is often used as the gold standard for the evaluation of imaging techniques. However, complete resection of the tumour is necessary for a valid histopathologic response evaluation. Thus, histopathologic response can only be determined at the end of therapy and cannot be used to modify treatment. For these reasons, there is a clear need for techniques that allow non-invasive monitoring of tumour response early in the course of therapy.


   Monitoring of tumour response by fluorodeoxyglucose positron emission tomography (FDG-PET): methodological considerations
Top
 Abstract
 Introduction
 Monitoring of tumour response...
Clinical studies on treatment...
 Prediction of tumour response...
 Conclusion
 References
 
Visual interpretation vs quantitative measurement of tumour glucose utilisation
For staging of malignant tumours, FDG-PET scans are assessed visually, and focally-increased FDG uptake not explained by the normal biodistribution of FDG is considered to be suspicious for metastatic disease. In a similar way, PET scans may also be read after completion of chemotherapy or radiotherapy. FDG uptake should have normalised at this time and focal FGD uptake generally indicates residual viable tumour tissue. As described in the following sections, there are now numerous studies in malignant lymphoma as well as several solid tumours indicating that focal FGD uptake after therapy is a relatively specific sign for viable tumour tissue and is associated with a poor prognosis. Quantitative analysis is frequently not required at this time to make the diagnosis of residual tumour tissue. However, quantitative assessment of tumour metabolism is frequently necessary when FGD-PET scans are performed during treatment in order to predict subsequent tumour response. At this time, the metabolic activity of the tumour tissue has decreased in responders, but generally there will be still considerable residual FGD uptake [10].

Quantitative assessment of tumour glucose use by PET
Quantification of tumour metabolic activity by FDG-PET is complicated by the fact that several factors [11] other than tumour glucose use have an impact on the FGD signal. Partial volume effects can cause a marked underestimation of the true activity concentration within smaller tumours [12]. Of note, the activity concentration may also be considerably underestimated even in large tumours owing to heterogeneous FGD uptake. Furthermore, FGD uptake by malignant tumours is time-dependent and in many cases significantly increases for at least 90 min post injection [13]. Plasma glucose levels have a significant influence on tumour FGD uptake, since FDG and glucose compete for glucose transport and phosphorylation by hexokinase [14]. Considering all these factors, it becomes clear that it is challenging to quantify tumour glucose utilisation by FDG-PET in a clinical setting. Therefore, quantitative measurements of tumour FGD uptake have been criticised and it has been suggested that the commonly used parameter SUV stands for "silly useless value" [15] and not standardised uptake value. However, this does not mean that it is equally difficult to measure relative changes in tumour glucose utilisation over time. In this case, only an intraindividual comparison of two studies is performed. This significantly reduces the number of factors that may confound the FGD signal [16]. Studies have shown that the intraindividual variation in measurements of tumour FGD uptake by serial PET studies is relatively low, with a coefficient of variation of approximately 10% [17, 18]. Based on these data, changes in tumour FGD uptake by more than 20% are unlikely to be due to measurement errors or spontaneous fluctuations of tumour metabolic activity [17, 18]. The 95% normal range for differences in SUVs in serial studies in untreated patients is approximately ± 1. Therefore, changes in SUV should only be considered significant when the difference between the baseline and the follow-up scan is more than 1 [18].

These data establish the minimal effect of treatment on tumour metabolic activity that can be assessed by FDG-PET. However, a measurable change in metabolic activity does not necessarily imply that treatment has a beneficial effect for the patient. Therefore, we have recently evaluated the prognostic implications of a measurable change in tumour glucose utilisation in patients with advanced NSCLC who were treated with palliative platinum-based chemotherapy (Figure 1Go). A "metabolic response" in PET was prospectively defined as a decrease in the SUV of the primary tumour by at least 20%. A total of 57 patients were included in the study and 28 tumours showed a metabolic response after the first chemotherapy cycle. Median progression-free survival of metabolic non-responders was only 1.8 months vs 5.9 months for metabolic responders. Median overall survival of metabolic responders was 8.4 months, but it was only 5.0 months for metabolic non-responders [19]. These data indicate that a measurable change in tumour FGD uptake after the first cycle of chemotherapy is associated with a palliative effect of therapy.



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  		Figure 1. FDG-PET and CT scans of a patient with non-small cell lung cancer demonstrating a good partial response to chemotherapy. There is a 61% decrease in FDG uptake 3 weeks after initiation of chemotherapy. Reproduced with kind permission of the American Society of Clinical Oncology from: Weber WA, et al. Positron emission tomography in non-small-cell lung cancer: prediction of response to chemotherapy by quantitative assessment of glucose use. J Clin Oncol 2003;21:2651–7.

 
Other threshold values for definition of a metabolic response are necessary when chemotherapy is used with curative intent. For example, in patients with high-grade malignant lymphomas, a mean decrease of FGD uptake by more than 45% has been observed within 24 h after the administration of the first dose of chemotherapy [20]. In patients with solid tumours treated by pre-operative chemotherapy, a change in FGD uptake of 35–50% [10, 19, 21, 22] within the first weeks of chemotherapy has been found to provide the highest accuracy for prediction of histopathologically complete or subtotal tumour regression. These differences in the changes in tumour FGD uptake in different clinical situations are not unexpected since the degree of tumour response to treatment is also clearly different. Whilst chemotherapy induces only a minor reduction of tumour size in palliative treatment of NSLCL, it reduces the viable tumour cell mass by more than 90% in patients with a histopathologic response to pre-operative therapy and it cures many patients with high-grade malignant lymphomas (i.e. eliminates 100% of the tumour cells). Thus, the interpretation of a metabolic response in FDG-PET will necessarily depend on the clinical context.

Monitoring radiotherapy or chemoradiotherapy with FDG-PET
Radiotherapy often causes inflammatory reactions, which has raised concerns about using FDG-PET for assessment of tumour response to radiotherapy or chemoradiotherapy. It has frequently been recommended that FDG-PET should not be performed until several months after completion of radiotherapy. However, there is a surprising lack of data to support this recommendation. Although there is no doubt that radiation-induced inflammation accumulates FDG, the intensity of FDG uptake may still be lower than in highly metabolically active untreated primary tumours, such as NSCLC or oesophageal cancer. Furthermore, the configuration of increased FDG uptake in radiation-induced inflammation is often markedly different from a malignant tumour. It is therefore frequently possible to differentiate between radiation-induced inflammation and residual tumour tissue [10, 23], especially when comparing a pre-treatment with a post-treatment PET scan.


   Clinical studies on treatment monitoring with FDG-PET: assessment of tumour response after completion of therapy
Top
 Abstract
 Introduction
 Monitoring of tumour response...
 Clinical studies on treatment...
Prediction of tumour response...
 Conclusion
 References
 
Malignant lymphoma
Anatomical imaging modalities often reveal residual masses after completion of therapy for lymphoma. It is very difficult to assess whether this represents viable tumour or fibrotic scar tissue. Even biopsy may be inaccurate because residual masses frequently contain a mixture of viable tumour cells and fibrosis, which may cause false-negative results. The clinical value of FDG-PET in detecting residual viable tumour tissue has been evaluated for Hodgkin's disease [24, 25] and high-grade non-Hodgkin's lymphoma [26–28], and a similar accuracy has been reported for both diseases. Jerusalem et al were the first to demonstrate in a larger series of patients that focal FGD uptake in a residual mass is associated with a poor outcome [29]. These findings have been confirmed by several studies published in the last 5 years (Table 1Go).


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  		Table 1. Prognostic relevance of residual FDG uptake after completion of chemotherapy or chemoradiotherapy

 
The combination of conventional, predominantly CT-based response assessment according to International Workshop Criteria (IWC) and FDG-PET was recently evaluated in a retrospective analysis of 54 patients with non-Hodgkin's lymphoma [39]. In this analysis, tumour response was classified as complete response (CR) when the FDG-PET scan was negative after treatment even if there were residual lesions on CT. Overall, response assessment according to IWC and IWC + PET was discordant in 21 patients (39%). Tumour response according to both sets of criteria (IWC and IWC + PET) was significantly correlated with patient survival. However, when the two classifications were included in the same multivariate model, only IWC + PET was a statistically significant independent predictor for progression-free survival. In the subgroup of patients with a partial response (PR) according to IWC, the 3-year progression-free survival was 89% in patients with a CR according to IWC + PET and only 33% in the subgroup with no CR in IWC + PET. This suggests that PET scanning identifies two distinct subgroups of patients within the IWC PR group, one with a favourable prognosis and another with an unfavourable prognosis. The biological explanation of this finding is likely related to the fact that the residual radiographic abnormalities represented necrosis and/or fibrosis in most of the PET-negative patients, whereas the abnormalities represented viable tumour in the majority of PET-positive patients [39].

In summary, persistent increased FDG uptake in initially involved tumour sites in patients with Hodgkin's disease or non-Hodgkin's lymphoma is highly predictive for residual or recurrent disease. If PET shows areas of increased FDG outside the initially involved sites, the differential diagnosis includes inflammation, bone marrow stimulation or thymic hyperplasia. Minimal residual disease can still be present in patients with a negative PET scan and can result in subsequent late relapses.

Oesophageal cancer
In patients with oesophageal cancer, residual FDG uptake after chemoradiotherapy appears to be a specific marker for viable tumour tissue and is associated with a poor prognosis [10, 32, 40, 41]. In the largest study published so far, Swisher et al [41] evaluated 103 patients treated by pre-operative chemoradiotherapy followed by surgical resection. The accuracy of FDG-PET to predict histopathologic response was compared with CT and endoscopic ultrasound. Post-chemoradiotherapy PET SUV =>ge; 4 had the highest accuracy for histopathologic response (76%). Univariate and multivariate Cox regression analysis demonstrated that a post-chemoradiotherapy SUV =>ge; 4 was an independent predictor of survival (hazard ratio 3.5; p=0.04). This group has also studied the relationship between the amount of residual tumour tissue and the intensity of FGD uptake. Mean FGD uptake in the tumour bed was not different for patients with no residual viable tumour cells compared with patients with up to 10% viable tumour cells [33]. Thus, FDG-PET cannot rule out residual microscopic disease after chemoradiotherapy of oesophageal cancer.

Lung cancer
MacManus et al [34] studied the use of FDG-PET after chemoradiotherapy in patients with locally advanced NSCLC. Seventy-three patients were prospectively evaluated for tumour response to chemoradiotherapy by CT and FDG-PET. CR in FDG-PET was defined as normalisation of all sites with abnormal FDG uptake, and PR was defined as a significant reduction in FDG uptake of all known lesions without the appearance of new lesions. Tumour response assessed by FDG-PET predicted better patient survival than response by CT criteria, pre-treatment tumour stage or patient performance status. The correlation between tumour FGD uptake after chemoradiotherapy and patient outcome was confirmed in a recent study by Hellwig et al [35]. These investigators studied 47 patients after pre-operative chemoradiotherapy. Patients were classified as responders if the SUV of the primary lesion was <4. Median survival after resection was greater than 56 months for PET responders and 19 months for PET non-responders (p < 0.001). In several studies, FGD uptake after chemoradiotherapy and/or changes during chemoradiotherapy have been correlated with histopathologic tumour regression [42–45]. All these studies report a significant correlation between the findings of FDG-PET and histopathologic tumour regression. The individual values for sensitivity and specificity, however, vary widely (58–100%). This is likely due to the fact that different criteria for a histopathologic response were used (no viable tumour cells, less than 10% viable tumour cells). Furthermore, the number of patients with a histopathologic response was generally small in these studies; as a consequence, the values for specificity of FDG-PET to detect residual tumour tissue (non-responders) must be interpreted with caution.

Other tumours types
The prognostic relevance of FDG-PET after chemotherapy or chemoradiotherapy has been evaluated in several other tumour types. Grigsby et al [38] retrospectively studied 152 patients with carcinoma of the cervix. PET imaging was performed before and after chemoradiotherapy. Patients with a normal FDG-PET scan after therapy were characterised by an excellent prognosis with a 5-year survival rate of 90%. In contrast, 5-year survival was only 45% in patients with persistent FGD uptake at the site of the primary tumour. If the post-therapeutic PET scan demonstrated new metastatic lesions, the prognosis of the patients was poor (5-year survival 15%).

Schuetze et al [36] studied 46 patients with high-grade soft tissue sarcomas before neoadjuvant chemotherapy and again before surgery. Patients with a decrease in FGD uptake by less than 40% were characterised by a poor prognosis. In 90% of these patients, recurrent disease was diagnosed within 4 years. The 2-year overall survival rate was 80% for the 17 patients with a decrease in FGD uptake by at least 40%, but only 40% for patients with a decrease in FGD uptake by less than 40%. In patients with osteosarcoma and Ewing's sarcoma, changes in FGD uptake after neoadjuvant chemotherapy have been shown to be significantly correlated with histological tumour regression, which is one of the most important prognostic factors [46, 47].


   Prediction of tumour response during therapy
Top
 Abstract
 Introduction
 Monitoring of tumour response...
 Clinical studies on treatment...
 Prediction of tumour response...
Conclusion
 References
 
Several studies have indicated that measurements of changes in tumour SUVs during chemotherapy allow prediction of subsequent reduction of the tumour mass as well as of patient survival. The concept of using quantitative changes in tumour metabolism to predict the outcome of therapy goes back to a pioneering study by Wahl et al in 1993 [48] that evaluated tumour glucose utilisation during chemohormonotherapy of breast cancer. The results of this study indicated that metabolic activity in responding tumour markedly changes within the first weeks of therapy. Subsequent studies by Jansson et al [49] in breast cancer and by Findlay et al in colorectal cancer [50] have also suggested that tumour glucose utilisation is rapidly decreased by effective therapy. More recently, the accuracy of FDG-PET to predict response and patient survival has been evaluated in larger studies and other tumour types. The results of these trials are summarised in Table 2Go.


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  		Table 2. Prognostic relevance of quantitative changes in tumour FDG uptake during chemotherapy or chemoradiotherapy

 
In these studies, FDG-PET generally had a high negative predictive value for response, and patients that did not show a significant decrease in FGD uptake early in the course of treatment were unlikely to benefit from continued therapy. Early identification of non-responding patients is of great clinical importance since the response rates of common malignant tumours to chemotherapy are in the range of only 20–30% [57]. This means that the majority of patients will be treated without a significant benefit. Early identification of non-responding patients by PET imaging therefore has the potential to reduce significantly the side effects and costs of ineffective therapy.

Breast cancer
Neoadjuvant chemotherapy is increasingly used to treat patients with locally advanced breast cancer in order to increase the rate of curative resections. Additionally, patients with a histopathologic response have significantly higher disease-free and overall survival rates than non-responders [58].

Smith et al have evaluated the accuracy of FDG-PET in predicting histopathologic response in 30 patients with locally advanced breast cancer undergoing pre-operative chemotherapy [59]. After a single cycle of chemotherapy, PET predicted complete pathological response with a sensitivity of 90% and a specificity of 74%. In another study, Schelling et al compared results from PET imaging with pathological response [60]. As early as after the first course of therapy, responding and non-responding tumours could be differentiated by PET. In contrast, Mankoff et al [61] found a large overlap between changes in metabolic activity in histopathologic responders and non-responders. These discrepant findings may be explained by the different timing of the PET scans. In the study by Mankoff et al, the follow-up PET scans were performed after 2 months of chemotherapy. After that period of time, histopathologic non-responding tumours may demonstrate a relatively large decrease in tumour size and FDG-PET may be unable to differentiate between small absolute differences in the amount of viable tumour cells. Consistent with this explanation, Smith et al [59] also observed a higher accuracy of FDG-PET for prediction of tumour response after the first cycle of chemotherapy than at later points in time. A similar trend has been observed by Wieder et al in oesophageal cancer [10].

Oesophageal and gastric cancer
Most patients with gastric or oesophageal cancer present with locally advanced disease. To improve the rate of curative surgical resections, pre-operative (neoadjuvant) chemotherapy or chemoradiotherapy has been evaluated over many years. However, there is still no consensus as to whether neoadjuvant therapy improves patient survival [62, 63]. Nevertheless, data suggest that in patients responding to pre-operative chemotherapy or chemoradiotherapy survival is significantly improved compared with surgical treatment alone. This beneficial effect appears to be outweighed by the poor prognosis of non-responding patients [64–66]. Therefore, early prediction of tumour response is of particular importance in patients with oesophageal and gastric cancer. We have studied 40 patients with locally advanced adenocarcinomas of the oesophagogastric junction who underwent pre-operative chemotherapy. FDG-PET imaging was performed at baseline and on day 14 of the first cycle of chemotherapy. Changes in tumour FDG uptake were correlated with histopathologic response after 3 months of chemotherapy. Using a threshold of 35% decrease of baseline metabolic activity, histopathologic response could be predicted with a sensitivity and specificity of 89% and 75%, respectively. The 2-year survival of patients responding on FDG-PET imaging was 49% compared with only 9% for PET non-responders [54].

In a more recent study, we have prospectively applied the threshold of 35% SUV decrease from baseline in patients with gastric cancer [22]. Forty-four patients with locally advanced gastric cancer underwent serial FDG-PET imaging; nine patients were excluded from further analysis because of low tumour FDG uptake on the baseline scan. In the remaining 35 patients, the sensitivity and specificity of FDG-PET for prediction of histopathologic response were 77% and 86%, respectively (Figure 2Go). The 2-year survival was 90% for PET responders compared with 25% for PET non-responders (Figure 3Go). These data suggest that changes in tumour metabolic activity may be used to individualise therapy in patients with oesophageal and gastric cancer. PET non-responders may undergo salvage therapy; alternative therapeutic options include chemoradiotherapy or immediate surgical resection. Individualisation of pre-operative chemotherapy for oesophageal cancer is currently being evaluated in the MUNICON trial. An interim analysis of this study has confirmed that FDG-PET allows selection of patients with a high probability of a histopathologic response [67]. As an increasing number of second- and third-line chemotherapy regimens and targeted anticancer treatments are emerging, it will also become more feasible to perform early treatment adjustments in patients who are identified as non-responders on FDG-PET.



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  		Figure 2. FDG-PET and CT studies in patients with gastric cancer treated by pre-operative chemotherapy. The tumour demonstrates intense FGD uptake prior to therapy. Two weeks after initiation of therapy, tumour FGD uptake has been reduced to background levels. Histological evaluation of the resected tumour specimen revealed less than 10% viable tumour cells after 3 months of chemotherapy. Reproduced with kind permission of the American Society of Clinical Oncology from: Ott K, et al. Prediction of response to preoperative chemotherapy in gastric carcinoma by metabolic imaging: results of a prospective trial. J Clin Oncol 2003;21:4604–10.

 


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  		Figure 3. Kaplan–Meier plot showing overall survival of patients with gastric cancer treated by pre-operative chemotherapy (CTx). Patients with a metabolic response 14 days after initiation of therapy are characterised by a markedly better prognosis than patients without a metabolic response. Reproduced with kind permission of the American Society of Clinical Oncology from: Ott K, et al. Prediction of response to preoperative chemotherapy in gastric carcinoma by metabolic imaging: results of a prospective trial. J Clin Oncol 2003;21:4604–10.

 
Other tumour types
Tumour glucose use during chemotherapy was also highly significantly correlated with survival in patients with NSCLC treated by induction chemotherapy followed by surgical resection [56]. In this prospective multicentre study, patients underwent FDG-PET before and after one and three chemotherapy cycles. Tumour metabolic activity after the first and third cycle was highly significantly correlated with overall survival (p=0.0004 and p=0.002, respectively). The prognosis of patients classified as responders on CT and FDG-PET was significantly better than the prognosis of patients classified as responders on CT but not on FDG-PET. Thus, this study confirms in larger group of patients and a multicentre setting that quantitative changes in tumour glucose use may predict patient survival early in the course of therapy. It also shows that tumour response assessment by FDG-PET in NSCLC provides additional prognostic information compared with standard response evaluation by CT.

Since high-grade non-Hodgkin's lymphomas generally respond very rapidly to chemotherapy, visual analysis of the PET scans may be sufficient for treatment monitoring in this tumour type. Three recent studies have indicated that a "negative" PET scan after one to two chemotherapy cycles is highly predictive for a favourable outcome of therapy [51–53]. The classification of PET scans as negative or positive based on visual analysis may appear straightforward and less complicated than quantitative assessment of FGD uptake. However, it also introduces several methodological problems. Whether a lesion is "negative" or "positive" will significantly depend on the performance characteristics of the PET scanner, as well as the acquisition and reconstruction parameters. The higher the spatial resolution and sensitivity of the scanner, the more lesions will be "positive" after one or two cycles of therapy. Increasing the time between injection and imaging and longer acquisition times will increase the signal-to-noise ratio and will also result in more "positive" lesions. Furthermore, background activity may have a significant influence. For example, a lesion located in subcutaneous fat may still be called "mildly positive", whereas a lesion with the same degree of FGD uptake will be called "negative" if it is located in the abdomen because background activity is higher. Finally, there may be a significant interobserver variability in the differentiation of "negative" and "mildly positive" lesions. Therefore, it will be interesting to compare visual and quantitative assessment of tumour FGD uptake in future studies.


   Conclusion
Top
 Abstract
 Introduction
 Monitoring of tumour response...
 Clinical studies on treatment...
 Prediction of tumour response...
 Conclusion
References
 
There is now considerable evidence in the literature that FDG-PET provides accurate assessment of tumour response to chemotherapy and chemoradiotherapy. This has been extensively shown for malignant lymphomas, but also for a variety of solid tumours. There are encouraging data that quantitative assessment of tumour glucose by FDG-PET may allow prediction of tumour response early in the course of therapy. However, it is essential to follow a strict protocol for data acquisition, image reconstruction and data analysis in order to derive robust and reproducible quantitative data from FDG-PET scans.


   References
Top
 Abstract
 Introduction
 Monitoring of tumour response...
 Clinical studies on treatment...
 Prediction of tumour response...
 Conclusion
 References
 

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