The value of F-18-fluorodeoxyglucose PET for the 3-D radiation treatment planning of malignant gliomas

Is there any additional benefit of 68Ga-PSMA PET on radiotherapy target volume definition in patients with glioblastoma?

OBJECTIVE

To investigate the contribution of 68Gallium (68Ga)-PSMA (prostate-specific membrane antigen) positron emission tomography (PET) in defining radiotherapy (RT) target volume for glioblastoma and to compare the target volumes defined by Magnetic Resonance Imaging (MRI).

METHODS

RT planning Computed Tomography (CT) images were fused separately with pre-operative MRI and PET/MRI images of 10 glioblastoma patients, retrospectively. The contrast-enhanced area in T1 weighted MRI was contoured as gross tumor volume (GTV) and clinical target volume (CTV1) was obtained by including the cavity and T2/FLAIR hyperintense areas after giving a margin of 2 cm to the GTV. 68Ga-PSMA uptake area was contoured as biological tumor volume (BTV) and CTV2 was obtained with a margin of 2 cm to BTV. Planning target volumes (PTVs) were created with the 3 mm added to the CTVs. Conformity index (CI), dice similarity coefficient (DSC) and overlap volume (OV) were calculated by obtaining the intersection and union volumes. Volumetric comparison, similarity and overlap analyzes were performed statistically by Wilcoxon signed rank and One sample t-test.

RESULTS

The median GTV was 21,96 cc (1,04 - 82,04) and BTV was 25,58 cc (2,43 - 99,47). BTV was on average 47% larger than GTV which was statistically significant (p = 0.03). For GTV-BTV, CTV1-CTV2 and PTV1-PTV2; mean values of CI were 0,56, 0,76 and 0,76; DSC were 0,70, 0,86 and 0,86; OV were 0,88, 0,94 and 0,94, respectively. There was no significant difference on size and spatial similarity between CTV1 and CTV2, PTV1 and PTV2.

CONCLUSION

Altough BTV was larger than GTV, this significance was lost while we gave the same CTV margin including the peripheral edema. It seems that it may help to improve defining non-enhancing tumor part and also recurrent tumor volume.

ADVANCES IN KNOWLEDGE

Recent studies have focused on the role of 68Ga-PSMA PET in imaging of glial tumors. It has been observed that 68Ga-PSMA PET can clearly define the tumor borders and it can be beneficial in target volume delineation, especially in reirradiation of recurrent tumors.

Advanced Imaging Techniques for Radiotherapy Planning of Gliomas

The accuracy of target delineation in radiation treatment (RT) planning of cerebral gliomas is crucial to achieve high tumor control, while minimizing treatment-related toxicity. Conventional magnetic resonance imaging (MRI), including contrast-enhanced T1-weighted and fluid-attenuated inversion recovery (FLAIR) sequences, represents the current standard imaging modality for target volume delineation of gliomas. However, conventional sequences have limited capability to discriminate treatment-related changes from viable tumors, owing to the low specificity of increased blood-brain barrier permeability and peritumoral edema. Advanced physiology-based MRI techniques, such as MR spectroscopy, diffusion MRI and perfusion MRI, have been developed for the biological characterization of gliomas and may circumvent these limitations, providing additional metabolic, structural, and hemodynamic information for treatment planning and monitoring. Radionuclide imaging techniques, such as positron emission tomography (PET) with amino acid radiopharmaceuticals, are also increasingly used in the workup of primary brain tumors, and their integration in RT planning is being evaluated in specialized centers. This review focuses on the basic principles and clinical results of advanced MRI and PET imaging techniques that have promise as a complement to RT planning of gliomas.

A preliminary PET radiomics study of brain metastases using a fully automatic segmentation method

Background

Positron Emission Tomography (PET) is increasingly utilized in radiomics studies for treatment evaluation purposes. Nevertheless, lesion volume identification in PET images is a critical and still challenging step in the process of radiomics, due to the low spatial resolution and high noise level of PET images. Currently, the biological target volume (BTV) is manually contoured by nuclear physicians, with a time expensive and operator-dependent procedure.

This study aims to obtain BTVs from cerebral metastases in patients who underwent L-[¹¹C]methionine (11C-MET) PET, using a fully automatic procedure and to use these BTVs to extract radiomics features to stratify between patients who respond to treatment or not. For these purposes, 31 brain metastases, for predictive evaluation, and 25 ones, for follow-up evaluation after treatment, were delineated using the proposed method. Successively, 11C-MET PET studies and related volumetric segmentations were used to extract 108 features to investigate the potential application of radiomics analysis in patients with brain metastases. A novel statistical system has been implemented for feature reduction and selection, while discriminant analysis was used as a method for feature classification.

Results

For predictive evaluation, 3 features (asphericity, low-intensity run emphasis, and complexity) were able to discriminate between responder and non-responder patients, after feature reduction and selection. Best performance in patient discrimination was obtained using the combination of the three selected features (sensitivity 81.23%, specificity 73.97%, and accuracy 78.27%) compared to the use of all features. Secondly, for follow-up evaluation, 8 features (SUV_mean, SUL_peak, SUV_min, SUL_peak prod-surface-area, SUV_mean prod-sphericity, surface mean SUV 3, SUL_peak prod-sphericity, and second angular moment) were selected with optimal performance in discriminant analysis classification (sensitivity 86.28%, specificity 87.75%, and accuracy 86.57%) outperforming the use of all features.

Conclusions

The proposed system is able i) to extract 108 features for each automatically segmented lesion and ii) to select a sub-panel of 11C-MET PET features (3 and 8 in the case of predictive and follow-up evaluation), with valuable association with patient outcome. We believe that our model can be useful to improve treatment response and prognosis evaluation, potentially allowing the personalization of cancer treatment plans.

The Impact of 18F-deoxyglucose Positron Emission Tomography on Tumor Staging, Treatment Strategy and Treatment Planning for Radiotherapy in a Department of Radiation Oncology

Aims and Background

The study analyzed the potential contribution of positron emission tomography (PET) in patient selection for radiotherapy and in radiation therapy planning.

Methods

Eighty-seven patients with a histological cancer diagnosis were accrued for the study from December 2000 to December 2001. Demographic characteristics included a median age of 54 years and male/female ratio of 51/36. All patients staged by conventional workup who were candidates for radiotherapy had PET imaging and were allocated to a conventional “pre/post-PET stage”. The treatment protocol and the shape and/or size of the portals was directly related to PET results. We examined 26 lung cancers, 15 gastrointestinal tumors, 22 genitourinary cancers and 24 hematologic malignancies.

Results

In the lung cancer group, the stage was modified in 10/26 patients (38.5%) by PET, with a change in management in 13 (50%) and a change in radiotherapy planning in 6 (23.1%). In the hematological group, stage was modified by PET in 8/24 cases (33.3%), with a change in treatment strategy in 9 (37.5%) and a change in radiotherapy planning in 3 (12.5%). In the gastrointestinal group, the stage was modified by PET in 2/15 cases (13.4%), with a change inn treatment strategy in 4 (26.7%) and a change in the decision for radiotherapy in 8 (no radiotherapy in 53.3%). In the mixed group (genitourinary, breast and other), the stage was modified by PET in 6/22 cases (27.3%), with a change in treatment strategy in 11 (50%) and a very low rate of change in radiotherapy planning.

Conclusions

PET contributed to a modification of stage in 26/87 patients (30%), to a changing in treatment strategy in 37/87 (42.5%), and to a substantial change of the shape and/or size of radiotherapy portals in 13/43 (30%) who underwent radiotherapy.

A fully automatic approach for multimodal PET and MR image segmentation in gamma knife treatment planning

BACKGROUND AND OBJECTIVES

Nowadays, clinical practice in Gamma Knife treatments is generally based on MRI anatomical information alone. However, the joint use of MRI and PET images can be useful for considering both anatomical and metabolic information about the lesion to be treated. In this paper we present a co-segmentation method to integrate the segmented Biological Target Volume (BTV), using [¹¹C]-Methionine-PET (MET-PET) images, and the segmented Gross Target Volume (GTV), on the respective co-registered MR images. The resulting volume gives enhanced brain tumor information to be used in stereotactic neuro-radiosurgery treatment planning. GTV often does not match entirely with BTV, which provides metabolic information about brain lesions. For this reason, PET imaging is valuable and it could be used to provide complementary information useful for treatment planning. In this way, BTV can be used to modify GTV, enhancing Clinical Target Volume (CTV) delineation.

METHODS

A novel fully automatic multimodal PET/MRI segmentation method for Leksell Gamma Knife^® treatments is proposed. This approach improves and combines two computer-assisted and operator-independent single modality methods, previously developed and validated, to segment BTV and GTV from PET and MR images, respectively. In addition, the GTV is utilized to combine the superior contrast of PET images with the higher spatial resolution of MRI, obtaining a new BTV, called BTV_MRI. A total of 19 brain metastatic tumors, undergone stereotactic neuro-radiosurgery, were retrospectively analyzed. A framework for the evaluation of multimodal PET/MRI segmentation is also presented. Overlap-based and spatial distance-based metrics were considered to quantify similarity concerning PET and MRI segmentation approaches. Statistics was also included to measure correlation among the different segmentation processes. Since it is not possible to define a gold-standard CTV according to both MRI and PET images without treatment response assessment, the feasibility and the clinical value of BTV integration in Gamma Knife treatment planning were considered. Therefore, a qualitative evaluation was carried out by three experienced clinicians.

RESULTS

The achieved experimental results showed that GTV and BTV segmentations are statistically correlated (Spearman's rank correlation coefficient: 0.898) but they have low similarity degree (average Dice Similarity Coefficient: 61.87 ± 14.64). Therefore, volume measurements as well as evaluation metrics values demonstrated that MRI and PET convey different but complementary imaging information. GTV and BTV could be combined to enhance treatment planning. In more than 50% of cases the CTV was strongly or moderately conditioned by metabolic imaging. Especially, BTV_MRI enhanced the CTV more accurately than BTV in 25% of cases.

CONCLUSIONS

The proposed fully automatic multimodal PET/MRI segmentation method is a valid operator-independent methodology helping the clinicians to define a CTV that includes both metabolic and morphologic information. BTV_MRI and GTV should be considered for a comprehensive treatment planning.

RT_Image: An Open-Source Tool for Investigating PET in Radiation Oncology

Positron emission tomography (PET) has emerged as a valuable imaging modality for the diagnosis and staging of cancer. However, despite evidence that PET may be useful for defining target volumes for radiation therapy, no standardized methodology for accomplishing this task exists. To facilitate the investigation of the utility of PET imaging in radiotherapy treatment planning and accelerate its integration into clinical radiation oncology, we have developed software for exploratory analysis and segmentation of functional imaging datasets.

The application, RT_Image, allows display of multiple imaging datasets and associated three-dimensional regions-of-interest (ROIs) at arbitrary view angles and fields of view. It also includes semi-automated image segmentation tools for defining metabolically active tumor volumes that may aid creation of target volumes for treatment planning. RT_Image is DICOM compliant, permitting the transfer of imaging data and DICOM-RT structure sets between the application and treatment planning software.

RT_Image has been used by radiation oncologists, nuclear medicine physicians, and radiation physicists to analyze over 200 PET datasets. Novel segmentation techniques have been implemented within this programming framework for therapy planning and for evaluation of molecular imaging-derived parameters as prognostic indicators.

RT_Image represents a freely-available software base on which further investigations of the utlity of PET and molecular imaging in radiation oncology may be built. The development of tools such as this is critical in order to realize the potential of molecular imagingguided radiation therapy.

Response Assessment in Neuro-Oncology working group and European Association for Neuro-Oncology recommendations for the clinical use of PET imaging in gliomas

This guideline provides recommendations for the use of PET imaging in gliomas. The review examines established clinical benefit in glioma patients of PET using glucose ((18)F-FDG) and amino acid tracers ((11)C-MET, (18)F-FET, and (18)F-FDOPA). An increasing number of studies have been published on PET imaging in the setting of diagnosis, biopsy, and resection as well radiotherapy planning, treatment monitoring, and response assessment. Recommendations are based on evidence generated from studies which validated PET findings by histology or clinical course. This guideline emphasizes the clinical value of PET imaging with superiority of amino acid PET over glucose PET and provides a framework for the use of PET to assist in the management of patients with gliomas.

Imaging biomarkers in primary brain tumours

We are getting used to referring to instrumentally detectable biological features in medical language as "imaging biomarkers". These two terms combined reflect the evolution of medical imaging during recent decades, and conceptually comprise the principle of noninvasive detection of internal processes that can become targets for supplementary therapeutic strategies. These targets in oncology include those biological pathways that are associated with several tumour features including independence from growth and growth-inhibitory signals, avoidance of apoptosis and immune system control, unlimited potential for replication, self-sufficiency in vascular supply and neoangiogenesis, acquired tissue invasiveness and metastatic diffusion. Concerning brain tumours, there have been major improvements in neurosurgical techniques and radiotherapy planning, and developments of novel target drugs, thus increasing the need for reproducible, noninvasive, quantitative imaging biomarkers. However, in this context, conventional radiological criteria may be inappropriate to determine the best therapeutic option and subsequently to assess response to therapy. Integration of molecular imaging for the evaluation of brain tumours has for this reason become necessary, and an important role in this setting is played by imaging biomarkers in PET and MRI. In the current review, we describe most relevant techniques and biomarkers used for imaging primary brain tumours in clinical practice, and discuss potential future developments from the experimental context.

PET/MR Imaging: A Critical Appraisal

Despite considerable excitement about the potential of PET/MR imaging for the detection, staging, and functional characterization of cancer, this new technology is evolving significantly more slowly than PET/CT. This slower evolution is due partly to ongoing technologic challenges (e.g., accurate attenuation correction of PET images) but also to the complex logistics of combining a whole-body PET scan with whole-body or organ-specific MR imaging. Most PET/MR imaging research published so far has focused on cancer staging and restaging in patients undergoing ¹⁸F-FDG PET/CT as the standard of care. These studies have demonstrated the feasibility of clinical ¹⁸F-FDG PET/MR imaging but so far have not shown substantial improvements in staging. This situation may not be unexpected in view of the fact that MR imaging has not replaced CT for staging of the malignancies for which ¹⁸F-FDG PET/CT is most commonly used. Given the widespread concerns about rising health care costs in general and the costs of advanced imaging techniques in particular, establishing ¹⁸F-FDG PET/MR imaging for whole-body cancer staging may be challenging because it requires more expensive equipment and longer acquisition times than ¹⁸F-FDG PET/CT. An alternative approach to developing clinical PET/MR imaging is to study how stand-alone, organ-specific MR imaging can be improved by PET/MR imaging. Unfortunately, however, ¹⁸F-FDG PET has significant limitations for the tumors that are most commonly studied with MR imaging (brain, liver, pancreatic, and prostate tumors). However, this situation may change with the development of new radiopharmaceuticals, such as prostate-specific membrane or gastrin-releasing peptide receptor ligands for the imaging of prostate cancer. In conclusion, PET/MR imaging has many potential advantages over PET/CT (lower radiation exposure, higher soft-tissue contrast, and multiparametric imaging). Realizing this potential in clinics likely will require new radiopharmaceuticals and applications other than whole-body cancer staging.

Malignant gliomas: current perspectives in diagnosis, treatment, and early response assessment using advanced quantitative imaging methods

Malignant gliomas consist of glioblastomas, anaplastic astrocytomas, anaplastic oligodendrogliomas and anaplastic oligoastrocytomas, and some less common tumors such as anaplastic ependymomas and anaplastic gangliogliomas. Malignant gliomas have high morbidity and mortality. Even with optimal treatment, median survival is only 12–15 months for glioblastomas and 2–5 years for anaplastic gliomas. However, recent advances in imaging and quantitative analysis of image data have led to earlier diagnosis of tumors and tumor response to therapy, providing oncologists with a greater time window for therapy management. In addition, improved understanding of tumor biology, genetics, and resistance mechanisms has enhanced surgical techniques, chemotherapy methods, and radiotherapy administration. After proper diagnosis and institution of appropriate therapy, there is now a vital need for quantitative methods that can sensitively detect malignant glioma response to therapy at early follow-up times, when changes in management of nonresponders can have its greatest effect. Currently, response is largely evaluated by measuring magnetic resonance contrast and size change, but this approach does not take into account the key biologic steps that precede tumor size reduction. Molecular imaging is ideally suited to measuring early response by quantifying cellular metabolism, proliferation, and apoptosis, activities altered early in treatment. We expect that successful integration of quantitative imaging biomarker assessment into the early phase of clinical trials could provide a novel approach for testing new therapies, and importantly, for facilitating patient management, sparing patients from weeks or months of toxicity and ineffective treatment. This review will present an overview of epidemiology, molecular pathogenesis and current advances in diagnoses, and management of malignant gliomas.

High-grade glioma radiation therapy target volumes and patterns of failure obtained from magnetic resonance imaging and 18F-FDOPA positron emission tomography delineations from multiple observers

PURPOSE

The objective of this study was to compare recurrent tumor locations after radiation therapy with pretreatment delineations of high-grade gliomas from magnetic resonance imaging (MRI) and 3,4-dihydroxy-6-[(18)F]fluoro-L-phenylalanine ((18)F-FDOPA) positron emission tomography (PET) using contours delineated by multiple observers.

METHODS AND MATERIALS

Nineteen patients with newly diagnosed high-grade gliomas underwent computed tomography (CT), gadolinium contrast-enhanced MRI, and (18)F-FDOPA PET/CT. The image sets (CT, MRI, and PET/CT) were registered, and 5 observers contoured gross tumor volumes (GTVs) using MRI and PET. Consensus contours were obtained by simultaneous truth and performance level estimation (STAPLE). Interobserver variability was quantified by the percentage of volume overlap. Recurrent tumor locations after radiation therapy were contoured by each observer using CT or MRI. Consensus recurrence contours were obtained with STAPLE.

RESULTS

The mean interobserver volume overlap for PET GTVs (42% ± 22%) and MRI GTVs (41% ± 22%) was not significantly different (P=.67). The mean consensus volume was significantly larger for PET GTVs (58.6 ± 52.4 cm(3)) than for MRI GTVs (30.8 ± 26.0 cm(3), P=.003). More than 95% of the consensus recurrence volume was within the 95% isodose surface for 11 of 12 (92%) cases with recurrent tumor imaging. Ten (91%) of these cases extended beyond the PET GTV, and 9 (82%) were contained within a 2-cm margin on the MRI GTV. One recurrence (8%) was located outside the 95% isodose surface.

CONCLUSIONS

High-grade glioma contours obtained with (18)F-FDOPA PET had similar interobserver agreement to volumes obtained with MRI. Although PET-based consensus target volumes were larger than MRI-based volumes, treatment planning using PET-based volumes may not have yielded better treatment outcomes, given that all but 1 recurrence extended beyond the PET GTV and most were contained by a 2-cm margin on the MRI GTV.

Phase II trial of radiosurgery to magnetic resonance spectroscopy-defined high-risk tumor volumes in patients with glioblastoma multiforme

PURPOSE

To determine the efficacy of a Gamma Knife stereotactic radiosurgery (SRS) boost to areas of high risk determined by magnetic resonance spectroscopy (MRS) functional imaging in addition to standard radiotherapy for patients with glioblastoma (GBM).

METHODS AND MATERIALS

Thirty-five patients in this prospective Phase II trial underwent surgical resection or biopsy for a GBM followed by SRS directed toward areas of MRS-determined high biological activity within 2 cm of the postoperative enhancing surgical bed. The MRS regions were determined by identifying those voxels within the postoperative T2 magnetic resonance imaging volume that contained an elevated choline/N-acetylaspartate ratio in excess of 2:1. These voxels were marked, digitally fused with the SRS planning magnetic resonance image, targeted with an 8-mm isocenter per voxel, and treated using Radiation Therapy Oncology Group SRS dose guidelines. All patients then received conformal radiotherapy to a total dose of 60 Gy in 2-Gy daily fractions. The primary endpoint was overall survival.

RESULTS

The median survival for the entire cohort was 15.8 months. With 75% of recursive partitioning analysis (RPA) Class 3 patients still alive 18 months after treatment, the median survival for RPA Class 3 has not yet been reached. The median survivals for RPA Class 4, 5, and 6 patients were 18.7, 12.5, and 3.9 months, respectively, compared with Radiation Therapy Oncology Group radiotherapy-alone historical control survivals of 11.1, 8.9, and 4.6 months. For the 16 of 35 patients who received concurrent temozolomide in addition to protocol radiotherapeutic treatment, the median survival was 20.8 months, compared with European Organization for Research and Treatment of Cancer historical controls of 14.6 months using radiotherapy and temozolomide. Grade 3/4 toxicities possibly attributable to treatment were 11%.

CONCLUSIONS

This represents the first prospective trial using selective MRS-targeted functional SRS combined with radiotherapy for patients with GBM. This treatment is feasible, with acceptable toxicity and patient survivals higher than in historical controls. This study can form the basis for a multicenter, randomized trial.

Molecular imaging of gliomas with PET: opportunities and limitations

Neuroimaging enables the noninvasive evaluation of glioma and is considered to be one of the key factors for individualized therapy and patient management, since accurate diagnosis and demarcation of viable tumor tissue is required for treatment planning as well as assessment of treatment response. Conventional imaging techniques like MRI and CT reveal morphological information but are of limited value for the assessment of more specific and reproducible information about biology and activity of the tumor. Molecular imaging with PET is increasingly implemented in neuro-oncology, since it provides additional metabolic information of the tumor, both for patient management as well as for evaluation of newly developed therapeutics. Different molecular processes have been proposed to be useful, like glucose consumption, expression of amino acid transporters, proliferation rate, membrane biosynthesis, and hypoxia. Thus, PET might help neuro-oncologists gain further insights into tumor biology by "true molecular imaging" as well as understand treatment-related phenomena. This review describes the method of PET acquisition as well as the tracers used to image biological processes in gliomas. Furthermore, it considers the clinical impact of PET on the use of currently available radiotracers, which were shown to be potentially valuable for discrimination between neoplastic and nonneoplastic tissue, as well as on tumor grading, determinination of treatment response, and providing an outlook toward further developments.

FET-PET for malignant glioma treatment planning

BACKGROUND AND PURPOSE

The aim of this study was to compare MRI-based morphological gross tumour volumes (GTVs) to biological tumour volumes (BTVs), defined by the pathological radiotracer uptake in positron emission tomography (PET) imaging with (18)F-fluoroethyltyrosine (FET), subsequently clinical target volumes (CTVs) and finally planning target volumes (PTVs) for radiotherapy planning of glioblastoma.

PATIENTS AND METHODS

Seventeen patients with glioblastoma were included into a retrospective protocol. Treatment-planning was performed using clinical target volume (CTV=BTV+20mm or CTV=GTV+20mm+inclusion of the edema) and planning target volume (PTV=CTV+5mm). Image fusion and target volume delineation were performed with OTP-Masterplan®. Initial gross tumour volume (GTV) definition was based on MRI data only or FET-PET data only (BTV), secondarily both data sets were used to define a common CTV.

RESULTS

FET based BTVs (median 43.9 cm(3)) were larger than corresponding GTVs (median 34.1cm(3), p=0.028), in 11 of 17 cases there were major differences between GTV/BTV. To evaluate the conformity of both planning methods, the index (CTV(MRT)∩CTV(FET))/(CTV(MRT)∪CTV(FET)) was quantified which was significantly different from 1 (0.73 ± 0.03, p<0.001).

CONCLUSION

With FET-PET-CT planning, the size and geometrical location of GTVs/BTVs differed in a majority of patients. It remains open whether FET-PET-based target definition has a relevant clinical impact for treatment planning.

Radiotherapy planning in high-grade gliomas: a survey of current UK practice

AIMS

Primary brain tumours in adults are rare, with high-grade gliomas (HGG) being the most common and most aggressive type. The clinical management of rare tumours such as HGG can be heterogeneous across different cancer centres. The aim of this survey was to determine current UK practice in the primary management of HGG, particularly in light of the improved outcomes reported recently.

MATERIALS AND METHODS

In February 2009, a questionnaire was sent to 71 consultant clinical oncologists in the UK who were reported to have a neuro-oncology practice. Questions focussed on the radiotherapeutic management of HGG.

RESULTS

In total, 46/71 (65%) completed questionnaires were returned; 31/46 (67%) routinely used magnetic resonance imaging/computed tomography fusion for radiotherapy planning; 34/36 (94%) routinely prescribed 60Gy in 30 fractions in a single phase; 7/36 (19%) would consider 54-55Gy in 30 fractions in selected clinical scenarios; 42/46 (91%) defined the planning target volume (PTV) as the gross tumour volume (GTV)+2-3cm margin and 42/46 (91%) outlined at least one 'organ at risk' (OAR). Accepted tolerance doses varied considerably, e.g. retina range: 30-54Gy. Sixty-four per cent of clinicians (27/42) compromise the PTV and 30% (14/42) the GTV in order to keep OARs within preset tolerances. Nearly one-third (14/42) involve the patient in this decision-making process, e.g. weighing up the risk of late toxicity with the risks of reducing the dose to the PTV.

CONCLUSION

The results of this survey show areas of strong agreement as well as areas of variation in clinical practice of aspects of treatment planning for HGG between UK neuro-oncologists.

The use of FDG-PET to target tumors by radiotherapy

Fluorodeoxyglucose positron emission tomography (FDG-PET) plays an increasingly important role in radiotherapy, beyond staging and selection of patients. Especially for non-small cell lung cancer, FDG-PET has, in the majority of the patients, led to the safe decrease of radiotherapy volumes, enabling radiation dose escalation and, experimentally, redistribution of radiation doses within the tumor. In limited-disease small cell lung cancer, the role of FDG-PET is emerging. For primary brain tumors, PET based on amino acid tracers is currently the best choice, including high-grade glioma. This is especially true for low-grade gliomas, where most data are available for the use of (11)C-MET (methionine) in radiation treatment planning. For esophageal cancer, the main advantage of FDG-PET is the detection of otherwise unrecognized lymph node metastases. In Hodgkin's disease, FDG-PET is essential for involved-node irradiation and leads to decreased irradiation volumes while also decreasing geographic miss. FDG-PET's major role in the treatment of cervical cancer with radiation lies in the detection of para-aortic nodes that can be encompassed in radiation fields. Besides for staging purposes, FDG-PET is not recommended for routine radiotherapy delineation purposes. It should be emphasized that using PET is only safe when adhering to strictly standardized protocols.

[Radiotherapy of brain tumors. New techniques and treatment strategies for]

Through a variety of technical enhancements modern radiotherapy offers the possibility to apply a high dose to an exactly defined target volume while the surrounding normal tissue is optimally spared. This article gives a short overview of new methods and techniques for radiotherapy of patients with brain tumors. Developments in the fields of biological imaging, radiation treatment planning, patient positioning and monitoring during radiotherapy will be especially discussed.

An automatic method for PET target segmentation using a lookup table based on volume and concentration ratio

Accurate evaluation of functionally significant target volumes in combination with anatomic imaging is of primary importance for effective radiation therapy treatment planning. In this study, a method for rapid and accurate PET image segmentation and volumetrics based on phantom measurements and independent of scanner calibration was developed. A series of spheres ranging in volume from 0.5 mL to 95 mL were imaged in an anthropomorphic phantom of human thorax using two commercial PET and CT/PET scanners. The target to background radioactivity concentration ratio ranged from 3:1 to 12:1 in 11 separate phantom scanning experiments. The results confirmed that optimal segmentation thresholding depends on target volume and radioactivity concentration ratio. This information can be derived from a generalized pre-determined "lookup table" of volume and contrast dependent threshold values instead of using fitted curves derived from machine specific information. A three-step method based on the PET image intensity information alone was used to delineate volumes of interest. First, a mean intensity segmentation method was used to generate an initial estimate of target volume, and the radioactivity concentration ratio was computed by a family of recovery coefficient curves to compensate for the partial volume effect. Next, the appropriate threshold value was obtained from a phantom-generated threshold lookup table. Lastly, a threshold level set method was performed on the threshold value to further refine the target contour by reducing the limitation of global thresholding. The segmentation results were consistent for spheres greater than 2.5 mL which yielded volume average uncertainty of 11.2% in phantom studies. The results of segmented volumes were comparable to those determined by contrast-oriented method and iterative threshold method (ITM). In addition, the new volume segmentation method was applied clinically to ten patients undergoing PET/CT volume analysis for radiation therapy treatment planning of solitary lung metastases. For these patients, the average PET segmented volumes were within 8.0% of the CT volumes and were highly dependent on the extension of functionally inactive tumor volume. In summary, the current method does not require fitted threshold curves or a priori knowledge of the CT/MRI target volume. This threshold method can be universally applied to radiation therapy treatment planning with comparable accuracy, and may be useful in the rapid identification and assessment of plans containing multiple targets.

PET-guided delineation of radiation therapy treatment volumes: a survey of image segmentation techniques

Historically, anatomical CT and MR images were used to delineate the gross tumour volumes (GTVs) for radiotherapy treatment planning. The capabilities offered by modern radiation therapy units and the widespread availability of combined PET/CT scanners stimulated the development of biological PET imaging-guided radiation therapy treatment planning with the aim to produce highly conformal radiation dose distribution to the tumour. One of the most difficult issues facing PET-based treatment planning is the accurate delineation of target regions from typical blurred and noisy functional images. The major problems encountered are image segmentation and imperfect system response function. Image segmentation is defined as the process of classifying the voxels of an image into a set of distinct classes. The difficulty in PET image segmentation is compounded by the low spatial resolution and high noise characteristics of PET images. Despite the difficulties and known limitations, several image segmentation approaches have been proposed and used in the clinical setting including thresholding, edge detection, region growing, clustering, stochastic models, deformable models, classifiers and several other approaches. A detailed description of the various approaches proposed in the literature is reviewed. Moreover, we also briefly discuss some important considerations and limitations of the widely used techniques to guide practitioners in the field of radiation oncology. The strategies followed for validation and comparative assessment of various PET segmentation approaches are described. Future opportunities and the current challenges facing the adoption of PET-guided delineation of target volumes and its role in basic and clinical research are also addressed.

Molecular PET/CT imaging-guided radiation therapy treatment planning

The role of positron emission tomography (PET) during the past decade has evolved rapidly from that of a pure research tool to a methodology of enormous clinical potential. (18)F-fluorodeoxyglucose (FDG)-PET is currently the most widely used probe in the diagnosis, staging, assessment of tumor response to treatment, and radiation therapy planning because metabolic changes generally precede the more conventionally measured parameter of change in tumor size. Data accumulated rapidly during the last decade, thus validating the efficacy of FDG imaging and many other tracers in a wide variety of malignant tumors with sensitivities and specificities often in the high 90 percentile range. As a result, PET/computed tomography (CT) had a significant impact on the management of patients because it obviated the need for further evaluation, guided further diagnostic procedures, and assisted in planning therapy for a considerable number of patients. On the other hand, the progress in radiation therapy technology has been enormous during the last two decades, now offering the possibility to plan highly conformal radiation dose distributions through the use of sophisticated beam targeting techniques such as intensity-modulated radiation therapy (IMRT) using tomotherapy, volumetric modulated arc therapy, and many other promising technologies for sculpted three-dimensional (3D) dose distribution. The foundation of molecular imaging-guided radiation therapy lies in the use of advanced imaging technology for improved definition of tumor target volumes, thus relating the absorbed dose information to image-based patient representations. This review documents technological advancements in the field concentrating on the conceptual role of molecular PET/CT imaging in radiation therapy treatment planning and related image processing issues with special emphasis on segmentation of medical images for the purpose of defining target volumes. There is still much more work to be done and many of the techniques reviewed are themselves not yet widely implemented in clinical settings.

The role of PET in target localization for radiotherapy treatment planning

Positron emission tomography (PET) is currently accepted as an important tool in oncology, mostly for diagnosis, staging and restaging purposes. It provides a new type of information in radiotherapy, functional rather than anatomical. PET imaging can also be used for target volume definition in radiotherapy treatment planning. The need for very precise target volume delineation has arisen with the increasing use of sophisticated three-dimensional conformal radiotherapy techniques and intensity modulated radiation therapy. It is expected that better delineation of the target volume may lead to a significant reduction in the irradiated volume, thus lowering the risk of treatment complications (smaller safety margins). Better tumour visualisation also allows a higher dose of radiation to be applied to the tumour, which may lead to better tumour control. The aim of this article is to review the possible use of PET imaging in the radiotherapy of various cancers. We focus mainly on non-small cell lung cancer, lymphoma and oesophageal cancer, but also include current opinion on the use of PET-based planning in other tumours including brain, uterine cervix, rectum and prostate.

Advanced image-guided external beam radiotherapy

The goal of radiation therapy is to eradicate tumor stem cells while sparing healthy tissue. Therefore, the first aim must be to delineate tumor from healthy tissue. Advanced imaging techniques will enable one to reduce the uncertainty of microscopic extension of disease. Ultimately, advanced functional imaging systems correlated with image-registered pathological specimens will allow one to delineate disease extent from normal tissue at the tumor periphery. When it is not possible to determine the CTV margin with reasonable certainty, the margins must remain generous and conformal avoidance methodology could and should be deployed to spare critical normal structures. Of equal importance to defining the CTV is the need to guarantee that this target is indeed treated. For this purpose, image guidance using a variety of systems including portal images, ultrasound devices, and CT scanners at the time of treatment has been implemented. Some image-guided methods, portal images for instance, are more amenable for use with rigid structures such as encountered in the sinus whereas others like ultrasound or CT scanners are able to account for nonrigid setup variations. Several strategies for preventing organ motion from degrading the precision that radiotherapy offers have been described. In particular, a CT scan at the time of treatment delivery can also be used as the basis to reconstruct the dose received by the patient. Dose reconstruction will allow the dose just delivered to be superimposed on the pretreatment CT scan and will allow one to compare the reconstructed delivered dose distribution with the planned dose distribution to assess discrepancies between these. Furthermore, reconstruction of the delivered dose distributions holds the promise of allowing one to accumulate dose delivered to the tumor and normal structures on a fraction per fraction basis. This will ultimately allow for the determination of treatment-specific tumor control probabilities and normal tissue complication probabilities.

From anatomical to biological target volumes: the role of PET in radiation treatment planning

Progress in radiation oncology requires a re-evaluation of the methods of target volume delineation beyond anatomical localization. New molecular imaging techniques for tumour visualisation such as positron emission tomography (PET) provide insight into tumour characteristics and can be complementary to the anatomical data of computed tomography or magnetic resonance imaging. In this review, three issues are discussed: First, can PET identify a tumour more accurately? Second, can biological tumour characteristics be visualised? Third, can intratumoural heterogeneity of these characteristics be identified?

Localization: conventional and CT simulation

Recent developments in imaging and computer power have led to the ability to acquire large three dimensional data sets for target localization and complex treatment planning for radiation therapy. Conventional simulation implies the use of a machine capable of the same mechanical movements as treatment units. Images obtained from these machines are essentially two dimensional with the facility to acquire a limited number of axial slices to provide patient contours and tissue density information. The recent implementation of cone beam imaging on simulators has transformed them into three dimensional imaging devices able to produce the data required for complex treatment planning. The introduction of computed axial tomography (CT) in the 1970s was a step-change in imaging and its potential use in radiotherapy was quickly realised. However, it remained a predominantly diagnostic tool until modifications were introduced to meet the needs of radiotherapy and software was developed to perform the simulation function. The comparability of conventional and virtual simulation has been the subject of a number of studies at different disease sites. The development of different cross sectional imaging modalities such as MRI and positron emission tomography has provided additional information that can be incorporated into the simulation software by image fusion and has been shown to aid in the delineation of tumours. Challenges still remain, particularly in localizing moving structures. Fast multislice scanning protocols freeze patient and organ motion in time and space, which may lead to inaccuracy in both target delineation and the choice of margins in three dimensions. Breath holding and gated respiration techniques have been demonstrated to produce four-dimensional data sets that can be used to reduce margins or to minimize dose to normal tissue or organs at risk. Image guided radiotherapy is being developed to address the interfraction movement of both target volumes and critical normal structures. Whichever method of localization and simulation is adopted, the role of quality control is important for the overall accuracy of the patient's treatment and must be adapted to reflect the networked nature of the process.

Hypoxia imaging-directed radiation treatment planning

Increasing evidence supports the role of the tumor microenvironment in modulating cancer behavior. Tissue hypoxia, an important and common condition affecting the tumor microenvironment, is well established as a resistance factor in radiotherapy. Increasing evidence points to the ability of hypoxia to induce the expression of gene products, which confer aggressive tumor behavior and promote broad resistance to therapy. These factors suggest that determining the presence or absence of tumor hypoxia is important in planning cancer therapy. Recent advances in PET hypoxia imaging, conformal radiotherapy, and imaging-directed radiotherapy treatment planning now make it possible to perform hypoxia-directed radiotherapy. We review the biological aspects of tumor hypoxia and PET imaging approaches for measuring tumor hypoxia, along with methods for conformal radiotherapy and image-guided treatment, all of which provide the underpinnings for hypoxia-directed therapy. As a case example, we review emerging data on PET imaging of hypoxia to direct radiotherapy.

The current status of FDG-PET in tumour volume definition in radiotherapy treatment planning

Positron emission tomography (PET) scan, mainly using 18 F-fluoro-deoxyglucose (FDG) as a tracer, is currently widely accepted as a diagnostic tool in oncology. It may lead to a change in staging and therefore in treatment management. PET can also be used to define the target volume in radiation treatment planning and to evaluate treatment response. In this review, we focused on issues concerning the role of PET in target volume delineation, both for the primary tumour and regional lymph nodes. A literature search was performed using MEDLINE. Furthermore, the following questions were addressed: does PET allow accurate tumour delineation and does it improve the outcome of radiotherapy, in terms of reduced toxicity or a higher tumour control probability? Combined computer tomography (CT) and PET information seems to influence target volume delineation. Using (CT-) PET scan, interobserver variability is being reduced. Only few studies compared delineation based on PET with pathologic examination, showing a complex relation. Preliminary results concerning incorporation of PET information in to target volume delineation varies in different tumour sites. In the field of lung cancer, incorporation of PET seems to improve tumour coverage and spare normal tissues, which may lead to less toxicity or the possibility to escalate dose. In oesophageal cancer and in lymphoma, PET scan can be used to include PET positive lymph nodes in the target volume. In most other tumour sites not enough data are currently available to draw definitive conclusions about the role of PET in radiation treatment planning.

[Analysis of target volumes for gliomas]

Gliomas are the most frequent tumors of the central nervous system of the adult. These intraparenchymal tumors are infiltrative and the most important criterion for definition of GTV and CTV is the extent of infiltration. Delineation of GTV and CTV for untreated and resected glioma remains a controversial and difficult issue because of the discrepancy between real tumor invasion and that estimated by CT or MRI. Is particularly helpful a joint analysis of the four different methods as histopathological correlations with CT and MRI, use of new modality imaging, pattern of relapses after treatment and interobserver studies. The presence of isolated tumor cells in intact brain, oedema or adjacent structures requires the definition of two different options for CTV: i) a geometrical option with GTV defined as the tumor mass revealed by the contrast-enhanced zone on CT or MRI and a CTV with an expanded margin of 2 or 3 cm; ii) an anatomic option including the entire zone of oedema or isolated tumor cell infiltration extending at least as far as the limits of the hyperintense zone on T2-weighted MRI. Inclusion of adjacent structures (such as white matter, corpus callosum, subarachnoid spaces) in the CTV mainly depends on the site of the tumor and size of the volume is generally enlarged.

Target Definition in the Thorax and Central Nervous System

It is the aim of conformal radiotherapy to restrict the high-dose region to the target volume as much as possible, thereby sparing the neighboring healthy tissues. However, to increase the therapeutic range, smaller margins tend to be used. This reduction of safety margins enhances the risk of unsuitable dosage because of mistaken target definition. Central nervous system (CNS) and lung cancers constitute sites that are particularly difficult to irradiate combining a large number of conceptual difficulties, allowing them to be considered as 2 particularly interesting study models. Imaging occupies an increasingly important place in these 2 types of tumors, especially with the development of new radiotherapy techniques. CNS and lung cancers represent an example of clinicopathological correlations. More specifically, CNS cancers represent an excellent model for estimation of new 3-dimensional navigational systems. For lung cancer, there is a combination of ballistic difficulties because of respiratory motion, the number and low tolerance of neighboring organs, and dosimetric difficulties because of the presence of inhomogeneities. This article reviews the main currently accepted criteria of choice justifying the size of gross tumor volume and clinical target volume margins for lung and CNS cancers.

Evaluating changes in tumor volume using magnetic resonance imaging during the course of radiotherapy treatment of high-grade gliomas: Implications for conformal dose-escalation studies

OBJECTIVE

To determine whether changes in tumor volume occur during the course of conformal 3D radiotherapy of high-grade gliomas by use of magnetic resonance imaging (MRI) during treatment and whether these changes had an impact on tumor coverage.

METHODS AND MATERIALS

Between December 2000 and January 2004, 21 patients with WHO Grades 3 to 4 supratentorial malignant gliomas treated with 3D conformal radiotherapy (median dose, 70 Gy) were enrolled in a prospective clinical study. All patients underwent T1-weighted contrast-enhancing and T2-weighted and fluid-attenuated inversion recovery (FLAIR) imaging at approximately 1 to 2 weeks before radiotherapy, during radiotherapy (Weeks 1 and 3), and at routine intervals thereafter. All MRI scans were coregistered to the treatment-planning CT. Gross tumor volume (GTV Pre-Rx) was defined from a postoperative T1-weighted contrast-enhancing MRI performed 1 to 2 weeks before start of radiotherapy. A second GTV (GTV Week 3) was defined by use of an MRI performed during Week 3 of radiotherapy. A uniform 0.5 cm expansion of the respective GTV, PTV (Pre-Rx), and PTV (Week 3) was applied to the final boost plan. Dose-volume histograms (DVH) were used to analyze any potential adverse changes in tumor coverage based on Week 3 MRI.

RESULTS

All MRI scans were reviewed independently by a neuroradiologist (DGH). Two patients were noted to have multifocal disease at presentation and were excluded from analysis. In 19 cases, changes in the GTV based on MRI at Week 3 during radiotherapy were as follows: 2 cases had an objective decrease in GTV (> or =50%); 12 cases revealed a slight decrease in the rim enhancement or changes in cystic appearance of the GTV; 2 cases showed no change in GTV; and 3 cases demonstrated an increase in tumor volume. Both cases with objective decreases in GTV during treatment were Grade 3 tumors. No cases of tumor progression were noted in Grade 3 tumors during treatment. In comparison, three of 12 Grade 4 tumors had tumor progression, based on MRI obtained during Week 3 of radiotherapy. Median increase in GTV (Week 3) was 11.7 cc (range, 9.8-21.3). Retrospective DVH analysis of PTV (Pre-Rx) and PTV (Week 3) demonstrated a decrease in V(95%)(PTV volume receiving 95% of the prescribed dose) in those 3 cases.

CONCLUSIONS

Routine MR imaging during radiotherapy may be essential in ensuring tumor coverage if highly conformal radiotherapy techniques such as stereotactic boost and intensity-modulated radiotherapy are used in dose-escalation trials that utilize smaller treatment margins.

Current imaging paradigms in radiation oncology

The technological revolution in imaging during recent decades has transformed the way image-guided radiation therapy is performed. Anatomical imaging (plain radiography, computed tomography, magnetic resonance imaging) greatly improved the accuracy of delineating target structures and has formed the foundation of 3D-based radiation treatment. However, the treatment planning paradigm in radiation oncology is beginning to shift toward a more biological and molecular approach as advances in biochemistry, molecular biology, and technology have made functional imaging (positron emission tomography, nuclear magnetic resonance spectroscopy, optical imaging) of physiological processes in tumors more feasible and practical. This review provides an overview of the role of current imaging strategies in radiation oncology, with a focus on functional imaging modalities, as it relates to staging and molecular profiling (cellular proliferation, apoptosis, angiogenesis, hypoxia, receptor status) of tumors, defining radiation target volumes, and assessing therapeutic response. In addition, obstacles such as imaging-pathological validation, optimal timing of post-therapy scans, spatial and temporal evolution of tumors, and lack of clinical outcome studies are discussed that must be overcome before a new era of functional imaging-guided therapy becomes a clinical reality.

Proton magnetic resonance spectroscopy imaging in the evaluation of patients undergoing gamma knife surgery for Grade IV glioma

Object. The purpose of this study was to assess the differences in spatial extent and metabolic activity in a comparison of a radiosurgical target defined by conventional strategies that utilize the enhancing lesion and a metabolic lesion defined by proton magnetic resonance spectroscopy (MRS) imaging. The authors evaluated whether these differences manifest themselves in the clinical outcome of patients and assessed the value of incorporating 1H-MRS imaging—derived spatial information into the treatment planning process for gamma knife surgery (GKS).

Methods. Twenty-six patients harboring Grade IV gliomas who had previously been treated with external-beam radiation therapy were evaluated by comparing the radiosurgically treated lesion volume with the volume of metabolically active tumor defined on 1H-MRS imaging. The cohort was evenly divided into two groups based on the percentage of overlap between the radiosurgical target and the metabolic lesion volumes. Patients with a percentage of overlap greater than 50% with respect to the metabolic lesion volume were classified as low risk and those with an overlap less than 50% were classified as high risk.

Kaplan—Meier estimators were calculated using time to progression and survival as dependent variables. The metabolite levels within the metabolic lesion were significantly greater than those within the radiosurgical target (p ≤ 0.001). The median survival was 15.7 months for patients in the low-risk group and 10.4 months for those in the highrisk group. This difference was statistically significant (p < 0.01).

Conclusions. Analysis of the results of this study indicates that patients undergoing GKS may benefit from the inclusion of 1H-MRS imaging in the treatment planning process.

3D MRSI for resected high-grade gliomas before RT: tumor extent according to metabolic activity in relation to MRI

PURPOSE

To evaluate the presence of residual disease after surgery but before radiotherapy (RT) in patients with high-grade glioma by MRI and magnetic resonance spectroscopy imaging (MRSI) and to estimate the impact of MRSI on the definition of postoperative target volumes for RT treatment planning.

METHODS AND MATERIALS

Thirty patients (27 glioblastoma multiforme, 3 Grade III astrocytoma) underwent MRI and MRSI within 4 weeks after surgery but before the initiation of RT. The MRI data were manually contoured; the regions of interest included T(2)-weighted hyperintensity (T(2)), T(1)-weighted contrast enhancement (T(1)), and the resection cavity (RC). Levels of choline and N-acetyl-aspartate (NAA) in the three-dimensional MRSI data were analyzed on the basis of a choline-to-N-acetyl-aspartate index (CNI). The CNI and other metabolic indexes were superimposed on the MRI data as three-dimensional contours. Composite, conjoint, and disjoint volumes were defined for T(1) and T(2), with/without RC, and within the CNI contour, corresponding to a value of 2. In addition, follow-up MRI studies were examined for new onset contrast enhancement and compared with the initial spectroscopic findings obtained before RT.

RESULTS

Substantial variation was found in the spatial relationship between the MRI and MRSI volumes. Ten patients had no contrast enhancement after surgery, and MRSI revealed abnormal metabolic activity in 8 of 10, averaging 20 cm(3) and extending 11-36 mm beyond the RC. In 20 patients with contrast-enhancing lesions, substantial variation was found between T(1) and CNI2; metabolic activity fell outside the contrast enhancement in 19 patients, averaging 21 cm(3) and extending 8-33 mm beyond the contrast enhancement. For all patients, the T(2) encompassed most of the metabolic volume. However, the CNI2 extended beyond the T(2) in 6 of 10 patients without contrast enhancement (mean, 8 cm(3); maximum, 15-23 mm) and in 13 of 20 patients with contrast enhancement (mean, 7 cm(3); maximum, 8-22 mm), representing an increase in the T(2) volume by as much as 180% (median 13%) and 86% (median 14%) for non-contrast-enhancing and contrast-enhancing patients, respectively. Preliminary evaluation of the MRI follow-up examinations revealed correspondence of areas of new contrast enhancement with initial MRSI abnormalities in 8 of 10 non-contrast-enhancing patients. In addition, CNI volumes correlated inversely with the time to onset of new contrast enhancement.

CONCLUSION

MRSI is a valuable diagnostic tool for the assessment of residual disease after surgical resection in high-grade glioma. The incorporation of areas of metabolic abnormality into treatment planning for postoperative patients would produce different sizes and shapes of target volumes for both primary and boost volumes. It also may encourage the use of nonuniform margins to define the extent of tumor cell infiltration, rather than the current use of uniform margins.

Radiation treatment planning with an integrated positron emission and computer tomography (PET/CT): a feasibility study

PURPOSE

To investigate the usefulness of hardware coregistered PET/CT images for target volume definition.

METHODS AND MATERIALS

Thirty-nine patients presenting with various solid tumors were investigated. CT and a FDG-PET were obtained in treatment position in an integrated PET/CT scanner, and coregistered images were used for treatment planning. First, volume delineation was performed on the CT data. In a second step, the corresponding PET data were used as an overlay to the CT data to define the target volume. Delineation was done independently by two investigators.

RESULTS

Coregistered PET/CT showed good fusion accuracy. The GTV increased by 25% or more because of PET in 17% of cases with head-and-neck (2/12) and lung cancer (1/6), and in 33% (7/21) in cancer of the pelvis. The GTV was reduced > or =25% in 33% of patients with head-and-neck cancer (4/12), in 67% with lung cancer (4/6), and 19% with cancer of the pelvis (4/21). Overall, in 56% (22/39) of cases, GTV delineation was changed significantly if information from metabolic imaging was used in the planning process. The modification of the GTV translated into altered PTV changes exceeding >20% in 46% (18/39) of cases. With PET, volume delineation variability between two independent oncologists decreased from a mean volume difference of 25.7 cm(3) to 9.2 cm(3) associated with a reduction of the standard deviation from 38.3 cm(3) to 13.3 cm(3) (p = 0.02). In 16% of cases, PET/CT revealed distant metastasies, changing the treatment strategy from curative to palliative.

CONCLUSION

Integrated PET/CT for treatment planning for three-dimensional conformal radiation therapy improves the standardization of volume delineation compared with that of CT alone. PET/CT has the potential for reducing the risk for geographic misses, to minimize the dose of ionizing radiation applied to non-target organs, and to change the current practice to three-dimensional conformal radiation therapy planning by taking into account the metabolic and biologic features of cancer. The impact on treatment outcome remains to be demonstrated.

Multivariate analysis of clinical prognostic factors in patients with glioblastoma multiforme treated with a combined modality approach

We investigated the influence of various clinical prognostic factors in patients with glioblastoma multiforme (GBM) treated with a combined modality approach. A total of 175 patients with GBM was treated in four consecutive prospective phase II studies using surgery, hyperfractionated or accelerated hyperfractionated radiotherapy (RT) and either adjuvant or concurrent or pre-irradiation chemotherapy (CHT) between January 1988 and December 1993. The median survival time for all 175 patients was 14 months and 1-3-year survival (OS) rates were 57%, 34% and 24%, respectively. The median time to tumour progression was 12 months, and 1-3-year progression-free survival (PFS) rates were 43%, 11% and 7%, respectively. Survival analysis showed that of all investigated prognostic factors, only gender did not influence survival. Patients </=55 years did better than those >55 years; patients with KPS 80-100 did better than those with KPS 50-70; patients with frontal tumours did better than those with tumours in other locations; patients with tumours up to 4 cm did better than those with larger tumours, as did patients with either subtotal or gross total tumour resection when compared to those undergoing biopsy only. Multivariate analysis showed that gender and tumour location did not independently influence survival. When PFS was used as the endpoint, only gender did not influence PFS, as confirmed by multivariate analysis.

Role of fusion in radiotherapy treatment planning

The fusion of functional imaging to traditional imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), is currently being investigated in radiotherapy treatment planning. Most studies that have been reported are in patients with lung, brain, or head and neck neoplasms. There is a potential role for either positron emission tomography (PET) or single photon emission computed tomography (SPECT) to delineate biologically active or tumor-bearing areas that otherwise would not be detected by CT or MRI. Furthermore, target volumes may be modified by using functional imaging, which can have a significant impact in the modern era of three-dimensional radiotherapy. SPECT may also be able to identify "nonfunctional" surrounding tissue and may influence radiotherapy beam arrangement.

Image guidance for precise conformal radiotherapy

PURPOSE

To review the state of the art in image-guided precision conformal radiotherapy and to describe how helical tomotherapy compares with the image-guided practices being developed for conventional radiotherapy.

MATERIALS AND METHODS

Image guidance is beginning to be the fundamental basis for radiotherapy planning, delivery, and verification. Radiotherapy planning requires more precision in the extension and localization of disease. When greater precision is not possible, conformal avoidance methodology may be indicated whereby the margin of disease extension is generous, except where sensitive normal tissues exist. Radiotherapy delivery requires better precision in the definition of treatment volume, on a daily basis if necessary. Helical tomotherapy has been designed to use CT imaging technology to plan, deliver, and verify that the delivery has been carried out as planned. The image-guided processes of helical tomotherapy that enable this goal are described.

RESULTS

Examples of the results of helical tomotherapy processes for image-guided intensity-modulated radiotherapy are presented. These processes include megavoltage CT acquisition, automated segmentation of CT images, dose reconstruction using the CT image set, deformable registration of CT images, and reoptimization.

CONCLUSIONS

Image-guided precision conformal radiotherapy can be used as a tool to treat the tumor yet spare critical structures. Helical tomotherapy has been designed from the ground up as an integrated image-guided intensity-modulated radiotherapy system and allows new verification processes based on megavoltage CT images to be implemented.

[Target-volume selection and delineation in the cervico-maxillo-facial region: beyond the concepts of the ICRU]

Improvement in irradiation techniques, which allows dose distributions sculpting around volumes of very complex shapes, has revealed the limitations in selection and delineation of target volumes. The use of functional imaging (PET, fMRI) in addition to anatomic imaging, will probably bring an extra level of complexity to this issue. In particular, the use of specific markers to visualize biological pathways known to influence response to ionizing radiation (e.g. hypoxia, proliferation) could lead to the delineation of sub-target volumes for delivering an extra boost dose. Such concept of Image-Guided Radiation Therapy still need to be tested in experimental models and in well defined clinical situations before its use in a routine clinical set-up.

Hypoxia imaging in brain tumors

Assessment of the oxygenation status of brain tumors has been studied increasingly with imaging techniques in light of recent advances in oncology. Tumor oxygen tension is a critical factor influencing the effectiveness of radiation and chemotherapy and malignant progression. Hypoxic tumors are resistant to treatment, and prognostic value of tumor oxygen status is shown in head and neck tumors. Strategies increasing the tumor oxygenation are being investigated to overcome the compromising [figure: see text] effect of hypoxia on tumor treatment. Administration of nicotinamide and inhalation of various high oxygen concentrations have been implemented. Existing methods for assessment of tissue oxygen level are either invasive or insufficient. Accurate and noninvasive means to measure tumor oxygenation are needed for treatment planning, identification of patients who might benefit from oxygenation strategies, and assessing the efficacy of interventions aimed to increase the radiosensitivity of tumors. Of the various imaging techniques used to assess tissue oxygenation, MR spectroscopy and MR imaging are widely available, noninvasive, and clinically applicable techniques. Tumor hypoxia is related closely to insufficient blood flow through chaotic and partially nonfunctional tumor vasculature and the distance between the capillaries and the tumor cells. Information on characteristics of tumor vasculature such as blood volume, perfusion, and increased capillary permeability can be provided with MR imaging. MR imaging techniques can provide a measure of capillary permeability based on contrast enhancement and relative cerebral blood volume estimates using dynamic susceptibility MR imaging. Blood oxygen level dependent contrast MR imaging using gradient echo sequence is intrinsically sensitive to changes in blood oxygen level. Animal models using blood oxygen level-dependent contrast imaging reveal the different responses of normal and tumor vasculature under hyperoxia. Normobaric hyperoxia is used in MR studies as a method to produce MR contrast in tissues. Increased T2* signal intensity of brain tissue has been observed using blood oxygen level-dependent contrast MR imaging. Dynamic blood oxygen level-dependent contrast MR imaging during hyperoxia is suggested to image tumor oxygenation. Quantification of cerebral oxygen saturation using blood oxygen level-dependent MR imaging also has been reported. Quantification of cerebral blood oxygen saturation using MR imaging has promising clinical applications; however, technical difficulties have to be resolved. Blood oxygen level dependent MR imaging is an emerging technique to evaluate the cerebral blood oxygen saturation, and it has the potential and versatility to assess oxygenation status of brain tumors. Upon improvement and validation of current MR techniques, better diagnostic, prognostic, and treatment monitoring capabilities can be provided for patients with brain tumors.

Implications of IMT-SPECT for postoperative radiotherapy planning in patients with gliomas

PURPOSE

Using MRI, residual tumor cannot be differentiated from nonspecific postoperative changes in patients with brain gliomas after surgical resection. The goal of this study was to analyze the value of 123I-alpha-methyl-tyrosine-single photon emission CT (IMT-SPECT) in radiotherapy planning of patients with brain gliomas after surgical resection.

METHODS AND MATERIALS

In 66 patients with surgically resected brain gliomas (33 glioblastomas, 20 anaplastic astrocytomas, 7 anaplastic oligodendrogliomas, and 6 low-grade astrocytomas), IMT-SPECT and MRI were performed for radiotherapy planning. On the MRI/IMT-SPECT fusion images, the volume with IMT uptake was compared with the volume of the hyperintensity areas of T(2)-weighted MRI and with the volume of contrast enhancement on T(1)-weighted MRI. The regions with IMT uptake and/or MRI changes (composite Vol-MRI/IMT), regions with overlay of IMT uptake and MRI changes (common Vol-MRI/IMT), area with IMT uptake without MRI changes (increase Vol-MRI/IMT), and area with only MRI changes (Vol-MRI minus IMT) were analyzed separately. The planning target volume and boost volume defined using MRI information alone was compared with the planning target volume and boost volume defined by also using the SPECT information.

RESULTS

Focally increased IMT uptake was observed in 25 (38%) of 66 patients, contrast enhancement on MRI was outlined in 59 (89%) of 66 patients, and hyperintensity areas on T(2)-weighted MRI were found in all 66 investigated patients. The mean composite Vol-T(2)/IMT was 73 cm(3). The relative increase Vol-T(2)/IMT, mean relative common Vol-T(2)/IMT, and mean relative Vol-T(2) minus IMT was 4%, 6%, and 90% of the composite Vol-T(2)/IMT, respectively. The mean composite Vol-T(1)/IMT was 14 cm(3) and the mean relative increase Vol-T(1)/IMT, mean relative common Vol-T(1)/IMT, and mean relative Vol-T(1) minus IMT was 21%, 4%, and 64% of the mean composite Vol-T(1)/IMT, respectively. In 19 (29%) of 66 patients, the focal IMT uptake was located outside the MRI changes. In this subgroup, the mean residual volume defined by focal IMT uptake in MRI/IMT-SPECT images, mean Vol-T(1), and mean Vol-T(2) was 19 cm(3), 10 cm(3), and 70 cm(3), respectively. The mean relative increase T(2)/IMT was 14% and T(1)/IMT was 61%. In this subgroup, the additional information of SPECT led to an increase in boost volume (mean relative increase BV-IMT) by 20%.

CONCLUSION

In patients with surgically resected brain gliomas, the size and location of residual IMT uptake differs considerably from the abnormalities found on postoperative MRI. Because of the known high specificity of IMT uptake for tumor tissue, the findings on IMT-SPECT may significantly modify the target volumes for radiotherapy planning. This will help to focus the high irradiation dose on the tumor area and to spare normal brain tissue.