First experience with I-123-alpha-methyl-tyrosine spect in the 3-D radiation treatment planning of brain gliomas

The Path Toward PET-Guided Radiation Therapy for Glioblastoma in Laboratory Animals: A Mini Review

Glioblastoma is the most aggressive and malignant primary brain tumor in adults. Despite the current state-of-the-art treatment, which consists of maximal surgical resection followed by radiation therapy, concomitant, and adjuvant chemotherapy, progression remains rapid due to aggressive tumor characteristics. Several new therapeutic targets have been investigated using chemotherapeutics and targeted molecular drugs, however, the intrinsic resistance to induced cell death of brain cells impede the effectiveness of systemic therapies. Also, the unique immune environment of the central nervous system imposes challenges for immune-based therapeutics. Therefore, it is important to consider other approaches to treat these tumors. There is a well-known dose-response relationship for glioblastoma with increased survival with increasing doses, but this effect seems to cap around 60 Gy, due to increased toxicity to the normal brain. Currently, radiation treatment planning of glioblastoma patients relies on CT and MRI that does not visualize the heterogeneous nature of the tumor, and consequently, a homogenous dose is delivered to the entire tumor. Metabolic imaging, such as positron-emission tomography, allows to visualize the heterogeneous tumor environment. Using these metabolic imaging techniques, an approach called dose painting can be used to deliver a higher dose to the tumor regions with high malignancy and/or radiation resistance. Preclinical studies are required for evaluating the benefits of novel radiation treatment strategies, such as PET-based dose painting. The aim of this review is to give a brief overview of promising PET tracers that can be evaluated in laboratory animals to bridge the gap between PET-based dose painting in glioblastoma patients.

Magnetic resonance imaging-guided radiation therapy using animal models of glioblastoma

Glioblastoma is the most aggressive and most common malignant primary brain tumour in adults and has a high mortality and morbidity. Because local tumour control in glioblastoma patients is still elusive in the majority of patients, there is an urgent need for alternative treatment strategies. However, to implement changes to the existing clinical standard of care, research must be conducted to develop alternative treatment strategies. A novel approach in radiotherapy is the introduction of pre-clinical precision image-guided radiation research platforms. The aim of this review is to give a brief overview of the efforts that have been made in the field of radiation research using animal models of glioblastoma. Because MRI has become the reference imaging technique for treatment planning and assessment of therapeutic responses in glioblastoma patients, we will focus in this review on small animal radiotherapy combined with MRI.

Molecular PET imaging in adaptive radiotherapy: brain

INTRODUCTION

Owing to their heterogeneity and radioresistance, the prognosis of primitive brain tumors, which are mainly glial tumors, remains poor. Dose escalation in radioresistant areas is a potential issue for improving local control and overall survival. This review focuses on advances in biological and metabolic imaging of brain tumors that are proving to be essential for defining tumor target volumes in radiation therapy (RT) and for increasing the use of DPRT (dose painting RT) and ART (adaptative RT), to optimize dose in radio-resistant areas.

EVIDENCE ACQUISITION

Various biological imaging modalities such as PET (hypoxia, glucidic metabolism, protidic metabolism, cellular proliferation, inflammation, cellular membrane synthesis) and MRI (spectroscopy) may be used to identify these areas of radioresistance. The integration of these biological imaging modalities improves the diagnosis, prognosis and treatment of brain tumors.

EVIDENCE SYNTHESIS

Technological improvements (PET and MRI), the development of research, and intensive cooperation between different departments are necessary before using daily metabolic imaging (PET and MRI) to treat patients with brain tumors.

CONCLUSIONS

The adaptation of treatment volumes during RT (ART) seems promising, but its development requires improvements in several areas and an interdisciplinary approach involving radiology, nuclear medicine and radiotherapy. We review the literature on biological imaging to outline the perspectives for using DPRT and ART in brain tumors.

PET and MRI Guided Irradiation of a Glioblastoma Rat Model Using a Micro-irradiator

For decades, small animal radiation research was mostly performed using fairly crude experimental setups applying simple single-beam techniques without the ability to target a specific or well-delineated tumor volume. The delivery of radiation was achieved using fixed radiation sources or linear accelerators producing megavoltage (MV) X-rays. These devices are unable to achieve sub-millimeter precision required for small animals. Furthermore, the high doses delivered to healthy surrounding tissue hamper response assessment. To increase the translation between small animal studies and humans, our goal was to mimic the treatment of human glioblastoma in a rat model. To enable a more accurate irradiation in a preclinical setting, recently, precision image-guided small animal radiation research platforms were developed. Similar to human planning systems, treatment planning on these micro-irradiators is based on computed tomography (CT). However, low soft-tissue contrast on CT makes it very challenging to localize targets in certain tissues, such as the brain. Therefore, incorporating magnetic resonance imaging (MRI), which has excellent soft-tissue contrast compared to CT, would enable a more precise delineation of the target for irradiation. In the last decade also biological imaging techniques, such as positron emission tomography (PET) gained interest for radiation therapy treatment guidance. PET enables the visualization of e.g., glucose consumption, amino-acid transport, or hypoxia, present in the tumor. Targeting those highly proliferative or radio-resistant parts of the tumor with a higher dose could give a survival benefit. This hypothesis led to the introduction of the biological tumor volume (BTV), besides the conventional gross target volume (GTV), clinical target volume (CTV), and planned target volume (PTV). At the preclinical imaging lab of Ghent University, a micro-irradiator, a small animal PET, and a 7 T small animal MRI are available. The goal was to incorporate MRI-guided irradiation and PET-guided sub-volume boosting in a glioblastoma rat model.

Amino-acid PET versus MRI guided re-irradiation in patients with recurrent glioblastoma multiforme (GLIAA) - protocol of a randomized phase II trial (NOA 10/ARO 2013-1)

Background

The higher specificity of amino-acid positron emission tomography (AA-PET) in the diagnosis of gliomas, as well as in the differentiation between recurrence and treatment-related alterations, in comparison to contrast enhancement in T1-weighted MRI was demonstrated in many studies and is the rationale for their implementation into radiation oncology treatment planning. Several clinical trials have demonstrated the significant differences between AA-PET and standard MRI concerning the definition of the gross tumor volume (GTV). A small single-center non-randomized prospective study in patients with recurrent high grade gliomas treated with stereotactic fractionated radiotherapy (SFRT) showed a significant improvement in survival when AA-PET was integrated in target volume delineation, in comparison to patients treated based on CT/MRI alone.

Methods

This protocol describes a prospective, open label, randomized, multi-center phase II trial designed to test if radiotherapy target volume delineation based on FET-PET leads to improvement in progression free survival (PFS) in patients with recurrent glioblastoma (GBM) treated with re-irradiation, compared to target volume delineation based on T1Gd-MRI. The target sample size is 200 randomized patients with a 1:1 allocation ratio to both arms. The primary endpoint (PFS) is determined by serial MRI scans, supplemented by AA-PET-scans and/or biopsy/surgery if suspicious of progression. Secondary endpoints include overall survival (OS), locally controlled survival (time to local progression or death), volumetric assessment of GTV delineated by either method, topography of progression in relation to MRI- or PET-derived target volumes, rate of long term survivors (>1 year), localization of necrosis after re-irradiation, quality of life (QoL) assessed by the EORTC QLQ-C15 PAL questionnaire, evaluation of safety of FET-application in AA-PET imaging and toxicity of re-irradiation.

Discussion

This is a protocol of a randomized phase II trial designed to test a new strategy of radiotherapy target volume delineation for improving the outcome of patients with recurrent GBM. Moreover, the trial will help to develop a standardized methodology for the integration of AA-PET and other imaging biomarkers in radiation treatment planning.

Trial registration

The GLIAA trial is registered with ClinicalTrials.gov (NCT01252459, registration date 02.12.2010), German Clinical Trials Registry (DRKS00000634, registration date 10.10.2014), and European Clinical Trials Database (EudraCT-No. 2012-001121-27, registration date 27.02.2012).

An innovative iterative thresholding algorithm for tumour segmentation and volumetric quantification on SPECT images: Monte Carlo-based methodology and validation

PURPOSE

Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging play an important role in the segmentation of functioning parts of organs or tumours, but an accurate and reproducible delineation is still a challenging task. In this work, an innovative iterative thresholding method for tumour segmentation has been proposed and implemented for a SPECT system. This method, which is based on experimental threshold-volume calibrations, implements also the recovery coefficients (RC) of the imaging system, so it has been called recovering iterative thresholding method (RIThM). The possibility to employ Monte Carlo (MC) simulations for system calibration was also investigated.

METHODS

The RIThM is an iterative algorithm coded using MATLAB: after an initial rough estimate of the volume of interest, the following calculations are repeated: (i) the corresponding source-to-background ratio (SBR) is measured and corrected by means of the RC curve; (ii) the threshold corresponding to the amended SBR value and the volume estimate is then found using threshold-volume data; (iii) new volume estimate is obtained by image thresholding. The process goes on until convergence. The RIThM was implemented for an Infinia Hawkeye 4 (GE Healthcare) SPECT/CT system, using a Jaszczak phantom and several test objects. Two MC codes were tested to simulate the calibration images: SIMIND and SimSet. For validation, test images consisting of hot spheres and some anatomical structures of the Zubal head phantom were simulated with SIMIND code. Additional test objects (flasks and vials) were also imaged experimentally. Finally, the RIThM was applied to evaluate three cases of brain metastases and two cases of high grade gliomas.

RESULTS

Comparing experimental thresholds and those obtained by MC simulations, a maximum difference of about 4% was found, within the errors (+/- 2% and +/- 5%, for volumes > or = 5 ml or < 5 ml, respectively). Also for the RC data, the comparison showed differences (up to 8%) within the assigned error (+/- 6%). ANOVA test demonstrated that the calibration results (in terms of thresholds or RCs at various volumes) obtained by MC simulations were indistinguishable from those obtained experimentally. The accuracy in volume determination for the simulated hot spheres was between -9% and 15% in the range 4-270 ml, whereas for volumes less than 4 ml (in the range 1-3 ml) the difference increased abruptly reaching values greater than 100%. For the Zubal head phantom, errors ranged between 9% and 18%. For the experimental test images, the accuracy level was within +/- 10%, for volumes in the range 20-110 ml. The preliminary test of application on patients evidenced the suitability of the method in a clinical setting.

CONCLUSIONS

The MC-guided delineation of tumor volume may reduce the acquisition time required for the experimental calibration. Analysis of images of several simulated and experimental test objects, Zubal head phantom and clinical cases demonstrated the robustness, suitability, accuracy, and speed of the proposed method. Nevertheless, studies concerning tumors of irregular shape and/or nonuniform distribution of the background activity are still in progress.

An interindividual comparison of O-(2-[18F]fluoroethyl)-L-tyrosine (FET)- and L-[methyl-11C]methionine (MET)-PET in patients with brain gliomas and metastases

PURPOSE

L-[methyl-(11)C]methionine (MET)-positron emission tomography (PET) has a high sensitivity and specificity for imaging of gliomas and metastatic brain tumors. The short half-life of (11)C (20 minutes) limits the use of MET-PET to institutions with onsite cyclotron. O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) is labeled with (18)F (half-life, 120 minutes) and could be used much more broadly. This study compares the uptake of FET and MET in gliomas and metastases, as well as treatment-induced changes. Furthermore, it evaluates the gross tumor volume (GTV) of gliomas defined on PET and magnetic resonance imaging (MRI).

METHODS AND MATERIALS

We examined 42 patients with pretreated gliomas (29 patients) or brain metastases (13 patients) prospectively by FET- and MET-PET on the same day. Uptake of FET and MET was quantified by standardized uptake values. Imaging contrast was assessed by calculating lesion-to-gray matter ratios. Tumor extension was quantified by contouring GTV in 17 patients with brain gliomas. Gross tumor volume on PET was compared with GTV on MRI. Sensitivity and specificity of MET- and FET-PET for differentiation of viable tumor from benign changes were evaluated by comparing the PET result with histology or clinical follow-up.

RESULTS

There was a strong linear correlation between standardized uptake values calculated for both tracers in cortex and lesions: r = 0.78 (p = 0.001) and r = 0.84 (p < 0.001), respectively. Image contrast was similar for MET- and FET-PET (lesion-to-gray matter ratios of 2.36 ± 1.01 and 2.33 ± 0.77, respectively). Mean GTV in 17 glioma patients was not significantly different on MET- and FET-PET. Both MET- and FET-PET delineated tumor tissue outside of MRI changes. Both tracers provided differentiated tumor tissue and treatment-related changes with a sensitivity of 91% at a specificity of 100%.

CONCLUSIONS

O-(2-[(18)F]fluoroethyl)-L-tyrosine-PET and MET-PET provide comparable diagnostic information on gliomas and brain metastases. Like MET-PET, FET-PET can be used for differentiation of residual or recurrent tumor from treatment-related changes/pseudoprogression, as well as for delineation of gliomas.

[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.

Comparison of T2 and FLAIR imaging for target delineation in high grade gliomas

Background

FLAIR and T2 weighted MRIs are used based on institutional preference to delineate high grade gliomas and surrounding edema for radiation treatment planning. Although these sequences have inherent physical differences there is limited data on the clinical and dosimetric impact of using either or both sequences.

Methods

40 patients with high grade gliomas consecutively treated between 2002 and 2008 of which 32 had pretreatment MRIs with T1, T2 and FLAIR available for review were selected for this study. These MRIs were fused with the treatment planning CT. Normal structures, clinical tumor volume (CTV) and planning tumor volume (PTV) were then defined on the T2 and FLAIR sequences. A Venn diagram analysis was performed for each pair of tumor volumes as well as a fractional component analysis to assess the contribution of each sequence to the union volume. For each patient the tumor volumes were compared in terms of total volume in cubic centimeters as well as anatomic location using a discordance index. The overlap of the tumor volumes with critical structures was calculated as a measure of predicted toxicity. For patients with MRI documented failures, the tumor volumes obtained using the different sequences were compared with the recurrent gross tumor volume (rGTV).

Results

The FLAIR CTVs and PTVs were significantly larger than the T2 CTVs and PTVs (p < 0.0001 and p = 0.0001 respectively). Based on the discordance index, the abnormality identified using the different sequences also differed in location. Fractional component analysis showed that the intersection of the tumor volumes as defined on both T2 and FLAIR defined the majority of the union volume contributing 63.6% to the CTV union and 82.1% to the PTV union. T2 alone uniquely identified 12.9% and 5.2% of the CTV and PTV unions respectively while FLAIR alone uniquely identified 25.7% and 12% of the CTV and PTV unions respectively. There was no difference in predicted toxicity to normal structures using T2 or FLAIR. At the time of analysis, 26 failures had occurred of which 19 patients had MRIs documenting the recurrence. The rGTV correlated best with the FLAIR CTV but the percentage overlap was not significantly different from that with T2. There was no statistical difference in the percentage overlap with the rGTV and the PTVs generated using either T2 or FLAIR.

Conclusions

Although both T2 and FLAIR MRI sequences are used to define high grade glial neoplasm and surrounding edema, our results show that the volumes generated using these techniques are different and not interchangeable. These differences have bearing on the use of intensity modulated radiation therapy (IMRT) and highly conformal treatment as well as on future clinical trials where the bias of using one technique over the other may influence the study outcome.

Non-natural amino acids for tumor imaging using positron emission tomography and single photon emission computed tomography

Amino acids are required nutrients for proliferating tumor cells, and amino acid transport is upregulated in many tumor types. Studies of radiolabeled amino acids in animals and humans demonstrate that amino acid based tracers have advantageous characteristics relative to 2-[(18)F]fluoro-2-deoxyglucose in certain tumors, particularly brain gliomas. Non-natural amino acids for tumor imaging generally have greater metabolic stability and can be labeled with longer-lived radionuclides for positron emission tomography and single photon emission computed tomography such as fluorine-18 and iodine-123. Amino acids enter cells via amino acid transport with varying selectivity based on their chemical structure. This review focuses on the rationale, biological basis, current status and future prospects of radiolabeled non-natural amino acids for tumor imaging and discusses various classes of these compounds including aromatic, alicyclic and alpha,alpha-dialkyl amino acids.

Biological imaging in radiation therapy: role of positron emission tomography

In radiation therapy (RT), staging, treatment planning, monitoring and evaluation of response are traditionally based on computed tomography (CT) and magnetic resonance imaging (MRI). These radiological investigations have the significant advantage to show the anatomy with a high resolution, being also called anatomical imaging. In recent years, so called biological imaging methods which visualize metabolic pathways have been developed. These methods offer complementary imaging of various aspects of tumour biology. To date, the most prominent biological imaging system in use is positron emission tomography (PET), whose diagnostic properties have clinically been evaluated for years. The aim of this review is to discuss the valences and implications of PET in RT. We will focus our evaluation on the following topics: the role of biological imaging for tumour tissue detection/delineation of the gross tumour volume (GTV) and for the visualization of heterogeneous tumour biology. We will discuss the role of fluorodeoxyglucose-PET in lung and head and neck cancer and the impact of amino acids (AA)-PET in target volume delineation of brain gliomas. Furthermore, we summarize the data of the literature about tumour hypoxia and proliferation visualized by PET. We conclude that, regarding treatment planning in radiotherapy, PET offers advantages in terms of tumour delineation and the description of biological processes. However, to define the real impact of biological imaging on clinical outcome after radiotherapy, further experimental, clinical and cost/benefit analyses are required.

Potential value of MR spectroscopic imaging for the radiosurgical management of patients with recurrent high-grade gliomas

Previous studies have shown that metabolic information provided by 3D Magnetic Resonance Spectroscopy Imaging (MRSI) could affect the definition of target volumes for radiation treatments (RT). This study aimed to (i) investigate the effect of incorporating spectroscopic volumes as determined by MRSI on target volume definition, patient selection eligibility, and dose prescription for stereotactic radiosurgery treatment planning; (ii) correlate the spatial extent of pre-SRS spectroscopic abnormality and treatment volumes with areas of focal recurrence as defined by changes in contrast enhancement; and (iii) examine the metabolic changes following SRS to assess treatment response. Twenty-six patients treated with Gamma Knife radiosurgery for recurrent glioblastoma multiforme (GBM) were retrospectively evaluated. All patients underwent both MRI and MRSI studies prior to SRS. Follow-up MRI exams were available for all 26 patients, with MRI/MRSI available in only 15/26 patients. We observed that the initial CNI 2 contours extended beyond the pre-SRS CE in 25/26 patients ranging in volume from 0.8 cc to 18.8 cc (median 5.6 cc). The inclusion of the volume of CNI 2 extending beyond the CE would have increased the SRS target volume by 5-165% (median 23.4%). This would have necessitated decreasing the SRS prescription dose in 19/26 patients to avoid increased toxicity; the resultant treatment volume would have exceeded 20cc in five patients, thus possibly excluding those from RS treatment per our institutional practice. MRSI follow-up studies showed a decrease in Choline, stable Creatine, and increased NAA indicative of response to SRS in the majority of patients. When combined with patient survival data, metabolic information obtained during follow-up MRSI studies seemed to indicate the potential to help to distinguish necrosis from new/recurrent tumor; however, this should be further verified by biopsy studies.

Single-Photon Emission Computed Tomography/Computed Tomography in Brain Tumors

Anatomic imaging procedures (computed tomography [CT] and magnetic resonance imaging [MRI]) have become essential tools for brain tumor assessment. Functional images (positron emission tomography [PET] and single-photon emission computed tomography [SPECT]) can provide additional information useful during the diagnostic workup to determine the degree of malignancy and as a substitute or guide for biopsy. After surgery and/or radiotherapy, nuclear medicine examinations are essential to assess persistence of tumor, to differentiate recurrence from radiation necrosis and gliosis, and to monitor the disease. The combination of functional images with anatomic ones is of the utmost importance for a full evaluation of these patients, which can be obtained by means of imaging fusion. Despite the fast-growing diffusion of PET, in most cases of brain tumors, SPECT studies are adequate and provide results that parallel those obtained with PET. The main limitation of SPECT imaging with brain tumor-seeking radiopharmaceuticals is the lack of precise anatomic details; this drawback is overcome by the fusion with morphological studies that provide an anatomic map to scintigraphic data. In the past, software-based fusion of independently performed SPECT and CT or MRI demonstrated usefulness for brain tumor assessment, but this process is often time consuming and not practical for everyday nuclear medicine studies. The recent development of dual-modality integrated imaging systems, which allow the acquisition of SPECT and CT images in the same scanning session, and their co-registration by means of the hardware, has facilitated this process. In SPECT studies of brain tumors with various radiopharmaceuticals, fused images are helpful in providing the precise localization of neoplastic lesions, and in excluding the disease in sites of physiologic tracer uptake. This information is useful for optimizing diagnosis, therapy monitoring, and radiotherapy treatment planning, with a positive impact on patient management.

Diffusion tensor imaging: possible implications for radiotherapy treatment planning of patients with high-grade glioma

AIMS

Radiotherapy treatment planning for high-grade gliomas (HGG) is hampered by the inability to image peri-tumoural white-matter infiltration. Diffusion tensor imaging (DTI) is an imaging technique that seems to show white-matter abnormalities resulting from tumour infiltration that cannot be visualised by conventional computed tomography or magnetic resonance imaging (MRI). We propose a new term, the image-based high-risk volume (IHV) for such abnormalities, which are distinct from the gross-tumour volume (GTV). For IHV based on DTI, we use the term IHVDTI. This study assesses the value of DTI for the individualisation of radiotherapy treatment planning for patients with HGG.

METHODS

Seven patients with biopsy-proven HGG were included in a theoretical planning exercise, comparing standard planning techniques with individualised plans based on DTI. Standard plans were generated using a 2.5 cm clinical target volume (CTV) margin added to the GTV. For DTI-based plans, the CTV was generated by adding a 1 cm margin to the IHVDTI. Estimates of normal tissue complication probability (NTCP) were calculated and used to estimate the level of dose escalation that could be achieved using the DTI-based plans.

RESULTS

The use of DTI resulted in non-uniform margins being added to the GTV to encompass areas at high risk of tumour involvement, but, in six out of seven cases, the IHVDTI was encapsulated by the standard CTV margin. In all cases, DTI could be used to reduce the size of the planning-target volume (PTV) (mean 35%, range 18-46%), resulting in escalated doses (mean 67 Gy, range 64-74 Gy), with NTCP levels that matched the conventional treatment plans.

CONCLUSION

DTI can be used to individualise radiotherapy target volumes, and reduction in the CTV permits modest dose escalation without an increase in NTCP. DTI may also be helpful in stratifying patients according to the degree of white-matter infiltration.

Reirradiation of recurrent high-grade gliomas using amino acid PET (SPECT)/CT/MRI image fusion to determine gross tumor volume for stereotactic fractionated radiotherapy

PURPOSE

To develop a valid treatment strategy for recurrent high-grade gliomas using stereotactic hypofractionated reirradiation based on biologic imaging and temozolomide.

PATIENTS AND METHODS

The trial included a total of 44 patients with recurrent high-grade gliomas (1 patient with anaplastic oligodendroglioma, 8 with anaplastic astrocytoma, 33 with glioblastoma multiforme, and 2 with gliosarcoma) after previous surgery and postoperative conventional radiotherapy +/- chemotherapy. For fractionated stereotactic radiotherapy (SFRT) treatment planning, the gross tumor volume was defined by (11)C-methionine positron emission tomography (MET-PET) or (123)I-alpha-methyl-tyrosine (IMT) single-photon computed emission tomography (SPECT)/computed tomography (CT)/magnetic resonance imaging (MRI) fusion in 82% of the patients and by CT/T1+gadolinium-MRI image fusion in 18% of the patients. Six fractions of 5 Gy were administered in 6 days. In 29 of 44 patients (66%), chemotherapy with temozolomide (200 mg/m(2) body surface/day) was given in one to two cycles before and four to five cycles after SFRT. The patients were evaluated in follow-up by clinical investigators and MRI or CT every 3 months after SFRT until death. In cases suspicious for radiation necrosis, a MET-PET or IMT-SPECT investigation was performed.

RESULTS

The median survival time in the whole group was 8 months. Treatment planning based on PET(SPECT)/CT/MRI imaging was associated with improved survival in comparison to treatment planning using CT/MRI alone: median survival time 9 months vs. 5 months (p = 0.03, log-rank). Median survival time were 11 months for patients who received SFRT based on biologic imaging plus temozolomide and significantly lower, 6 months for patients treated with SFRT without biologic imaging, without temozolomide or without both (p = 0.008, log rank). The most important prognostic factor in univariate analysis was a long interval between initial diagnosis and recurrence (p = 0.0002, log-rank). In the multivariate model, time interval to retreatment (p = 0.006) and temozolomide (p = 0.04) remained statistically significant. No acute neurologic toxicity Grade 3 or higher and no Grade 4 hematologic toxicity was observed.

CONCLUSION

This is the first study of biologic imaging optimized SFRT plus temozolomide in recurrent high-grade gliomas. It demonstrates the feasibility and safety of this approach. The most striking result of the trial is the statistically significant longer survival time in the univariate analysis for patients reirradiated using MET-PET or IMT-SPECT/CT/MRI image fusion in the treatment planning, in comparison to patients treated based on MRI/CT alone. Multivariate analysis confirmed a significant survival benefit from multimodal treatment (i.e., addition of temozolomide), despite the limited number of patients. Whether treatment planning with SPECT/PET independently influences survival has to be studied in a larger series of patients.

Biological imaging in radiation oncology

The goal of this study was to discuss the value of integrating biological imaging (PET, SPECT, MRS etc.) in radiation treatment planning and monitoring. Studies in patients with brain tumors have shown that, compared to CT and MRI alone, the image fusion of CT/MRI and amino acid SPECT or PET allows a more correct delineation of gross tumor volume (GTV) and planning target volume (PTV). For FDG-PET comparable results with different techniques are reported in the literature also for bronchial carcinoma, ear-nose-and-throat tumors, and cervical carcinoma, or, in the case of MRS, for prostate cancer. Imaging of hypoxia, cell proliferation, apoptosis, tumor angiogenesis, and gene expression leads to the identification of differently aggressive areas of a biologically inhomogeneous tumor mass that can be individually and more appropriately targeted using innovative IMRT. Thus, a biological, inhomogeneous dose distribution can be generated, the so-called dose painting. In addition, the biological imaging can play a significant role in the evaluation of the therapy response after radiochemotherapy. Clinical studies in ear-nose-and-throat tumors, bronchial carcinoma, esophagus carcinoma, and cervical carcinoma suggest that the sensitivity and specificity of FDG-PET for the therapy response are higher compared to anatomical imaging (CT and MRI). Clinical and experimental studies are required to define the real impact of these investigations in radiation treatment planning, and especially in the evaluation of therapy response.

L-(methyl-11C) methionine positron emission tomography for target delineation in resected high-grade gliomas before radiotherapy

PURPOSE

Using magnetic resonance imaging (MRI), residual tumor cannot be differentiated from nonspecific postoperative changes in operated patients with brain gliomas. The higher specificity and sensitivity of L-(methyl-11C)-labeled methionine positron emissions tomography (MET-PET) in gliomas has been demonstrated in previous studies and is the rationale for the integration of this investigation in gross tumor volume delineation. The goal of this trial was to quantify the affect of MET-PET vs. with MRI in gross tumor volume definition for radiotherapy planning of high-grade gliomas.

METHODS AND MATERIALS

The trial included 39 patients with resected malignant gliomas. MRI and MET-PET data were coregistered based on mutual information. The residual tumor volume on MET-PET and the volume of tissue abnormalities on T1-weighted MRI (gadolinium [Gd] enhancement) and T2-weighted MRI (hyperintensity areas) were compared using MET-PET/MRI fusion images.

RESULTS

The MET-PET vs. Gd-enhanced T1-weighted MRI analysis was performed on 39 patients. In 5 patients (13%), MET uptake corresponded exactly with Gd enhancement, and in 29 (74%) of 39 patients, the region of MET uptake was larger than that of the Gd enhancement. In 27 (69%) of the 39 patients, the Gd enhancement area extended beyond the MET enhancement. MET uptake was detected up to 45 mm beyond the Gd enhancement. MET-PET vs. T2-weighted MRI was investigated in 18 patients. MET uptake did not correspond exactly with the hyperintensity areas on T2-weighted MRI in any patient. In 9 (50%) of 18 patients, MET uptake extended beyond the hyperintensity area on the T2-weighted MRI, and in 18 (100%), at least some hyperintensity on the T2-weighted MRI was located outside the MET enhancement area. MET uptake was detected up to 40 mm beyond the hyperintensity area on T2-weighted MRI.

CONCLUSION

In operated patients with brain gliomas, the size and location of residual MET uptake differs considerably from abnormalities found on postoperative MRI. Because postoperative changes cannot be differentiated from residual tumor by MRI, MET-PET, with a greater specificity for tumor tissue, can help to outline the gross tumor volume with greater accuracy.

[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.

The American Society for Therapeutic Radiology and Oncology (ASTRO) evidence-based review of the role of radiosurgery for malignant glioma

PURPOSE

To systematically review the evidence for the use of stereotactic radiosurgery or stereotactic fractionated radiation therapy in adult patients with malignant glioma.

METHODS

Key clinical questions to be addressed in this evidence-based review were identified. Outcomes considered were overall survival, quality of life or symptom control, brain tumor control or response and toxicity. MEDLINE (1990-2004 June Week 2), CANCERLIT (1990-2003), CINAHL (1990-2004 June Week 2), EMBASE (1990-2004 Week 25), and the Cochrane library (2004 issue 2) databases were searched using OVID. In addition, the Physician Data Query clinical trials database, the proceedings of the American Society of Clinical Oncology (1997-2004), ASTRO (1997-2004), and the European Society of Therapeutic Radiology and Oncology (ESTRO) (1997-2003) were searched. Data from the literature search were reviewed and tabulated. This process included an assessment of the level of evidence.

RESULTS

For patients with newly diagnosed malignant glioma, radiosurgery as boost therapy with conventional external beam radiation was examined in one randomized trial, five prospective cohort studies, and seven retrospective series. There is Level I evidence that the use of radiosurgery boost followed by external beam radiotherapy and carmustine (BCNU) does not confer benefit with respect to overall survival, quality of life, or patterns of failure as compared with external beam radiotherapy and BCNU. There is Level I-III evidence of toxicity associated with radiosurgery boost as compared with external beam radiotherapy alone. The results of the prospective and retrospective studies may be influenced by selection bias. Radiosurgery used as salvage for recurrent or progressive malignant glioma after conventional external beam radiotherapy failure was reported in zero randomized trials, three prospective cohort studies, and five retrospective series. The available data are sparse and insufficient to make absolute recommendations. Stereotactic fractionated radiation therapy has been reported as boost therapy with external beam radiotherapy for patients with newly diagnosed malignant glioma in only three prospective studies. As primary therapy alone without conventional external beam radiotherapy for newly diagnosed malignant glioma patients, stereotactic fractionated radiation therapy has been reported in only one prospective study. There were only three prospective series and two retrospective studies reported for patients with recurrent or progressive malignant glioma.

CONCLUSIONS

For patients with malignant glioma, there is Level I-III evidence that the use of radiosurgery boost followed by external beam radiotherapy and BCNU does not confer benefit in terms of overall survival, local brain control, or quality of life as compared with external beam radiotherapy and BCNU. The use of radiosurgery boost is associated with increased toxicity. For patients with malignant glioma, there is insufficient evidence regarding the benefits/harms of using radiosurgery at the time progression or recurrence. There is also insufficient evidence regarding the benefits/harms in the use of stereotactic fractionated radiation therapy for patients with newly diagnosed or progressive/recurrent malignant glioma.

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.

Multimodal metabolic imaging of cerebral gliomas: positron emission tomography with [18F]fluoroethyl-L-tyrosine and magnetic resonance spectroscopy

OBJECT

The purpose of this study was to determine the predictive value of [18F]fluoroethyl-L-tyrosine (FET)-positron emission tomography (PET) and magnetic resonance (MR) spectroscopy for tumor diagnosis in patients with suspected gliomas.

METHODS

Both FET-PET and MR spectroscopy analyses were performed in 50 consecutive patients with newly diagnosed intracerebral lesions supposed to be diffuse gliomas on contrast-enhanced MR imaging. Lesion/brain ratios of FET uptake greater than 1.6 were considered positive, that is, indicative of tumor. Results of MR spectroscopy were considered positive when N-acetylaspartate (NAA) was decreased in conjunction with an absolute increase of choline (Cho) and an NAA/Cho ratio of 0.7 or less. An FET lesion/brain ratio, an NAA/Cho ratio, and signal abnormalities on MR images were compared with histological findings in neuronavigated biopsy specimens. The FET lesion/brain ratio and the NAA/Cho ratio were identified as significant independent predictors for the histological identification of tumor tissue. The accuracy in distinguishing neoplastic from nonneoplastic tissue could be increased from 68% with the use of MR imaging alone to 97% with MR imaging in conjunction with FET-PET and MR spectroscopy. Sensitivity and specificity for tumor detection were 100 and 81% for MR spectroscopy and 88 and 88% for FET-PET, respectively. Results of histological studies did not reveal tumor tissue in any of the lesions that were negative on FET-PET and MR spectroscopy. In contrast, a tumor diagnosis was made in 97% of the lesions that were positive with both methods.

CONCLUSIONS

In patients with intracerebral lesions supposed to be diffuse gliomas on MR imaging, FET-PET and MR spectroscopy analyses markedly improved the diagnostic efficacy of targeted biopsies.

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.

Characterization of uptake of 3-[131I]iodo-α-methyl-L-tyrosine in human monocyte-macrophages

The radiopharmaceutical 3-[(123)I]iodo-alpha-methyl-L-tyrosine ([(123)I]IMT) can be used to study amino acid transport by single-photon emission tomography (SPET). In order to evaluate the potential contribution of [(123)I]IMT accumulation in macrophages to overall uptake values measured in neoplastic lesions in vivo, we studied the mechanisms governing the uptake of this tracer by human monocyte-macrophages (HMMs). HMMs were isolated from healthy human donors by density gradient centrifugation using Ficoll methods. The human glioblastoma cell line U-138 MG (GLIOs) was obtained from American Type Culture Collection. Using multiwell dishes, cells were incubated in phosphate buffered saline or an equivalent sodium-free buffer with 50 kBq [(131)I]IMT per well. [(131)I]IMT uptake was quantified as % injected dose per mass of protein within each culture well. Several natural and artificial amino acids were used as potential transport inhibitors both in sodium-containing and sodium-free medium. [(131)I]IMT uptake was significantly lower in HMMs than in GLIOs (34 +/- 2 %/mg (40 min) vs. 507 +/- 50 %/mg at 30 minutes of incubation, respectively; p < 0.01). Endotoxin (LPS) significantly increased [(131)I]IMT uptake in HMMs by a factor of approximately 2. Transport into non-stimulated HMMs was exclusively sodium-independent and inhibitable by BCH, but not by MeAIB. Under LPS stimulation exclusively, there was in addition also a sodium-dependent inhibition of [(131)I]IMT uptake by L-arginine and MeAIB, albeit to a minor extent. [(131)I]IMT accumulation in HMMs is mainly mediated via an L-like amino acid transport system and increases on HMM activation by LPS. LPS may induce an additional Na(+)-dependent transport system in HMMs. The considerably lower [(131)I]IMT uptake in HMMs than in GLIOs suggests that overall uptake values of this tracer measured by SPET in tumors are not significantly affected by [(123)I]IMT accumulation in macrophages within the neoplastic lesion.

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.

Validation of a method for automatic image fusion (BrainLAB System) of CT data and 11C-methionine-PET data for stereotactic radiotherapy using a LINAC: first clinical experience

PURPOSE

(a) To implement a fully automatic method to integrate (11)C-methionine positron emission tomography (MET-PET) data into stereotactic radiation treatment planning using the commercially available BrainLAB System, by means of CT/MET-PET image fusion. (b) To validate the fully automatic CT/MET-PET image fusion technique with respect to accuracy and robustness. (c) To give a short glance at the clinical consequences for patients with brain tumors.

METHODS AND MATERIALS

In 12 patients with brain tumors (9 meningeomas, 3 gliomas), CT, MRI, and MET-PET were performed for stereotactic fractionated radiation treatment planning. The CT and MET-PET investigations were performed using a relocatable mask for head fixation. Fifteen external reference markers (5 on each lateral and 5 on the frontal localizer plate) that could be identified in CT and MET-PET were applied on the stereotactic localizer frame; the marker positions were exactly defined for both investigations. The MRI/CT fusion was done completely automatically. The CT/MET-PET fusion was performed using two different methods: The gold standard was the CT/PET fusion based on the reference markers, and the test method was the automatic, intensity-based CT/PET fusion, independent of the external markers. The markers visible on CT and transmission PET were matched using a point-to-line matching algorithm. To quantify the amount of misregistration, the two fusion methods were compared by calculating the mean value of deviation between corresponding points inside a cubic volume of interest of > or =512 cm(3) defined within the cranial cavity. The gross tumor volume (CT/MRI) outlined on CT and T1-MRI with contrast medium was compared with the gross tumor volume (PET) defined in the reoriented MET-PET data sets. The clinical impact of MET-PET in tumor volume definition for stereotactic radiotherapy will be discussed.

RESULTS

The fully automatic integration of MET-PET into stereotactic radiation treatment planning was successfully realized in all patients investigated. Mean deviation of the intensity-based automatic CT/PET fusion compared with the external marker-based gold standard was 2.4 mm; the standard deviation was 0.5. The algorithm's robustness was evaluated, and the discrepancy of fusion results due to different initial image alignments was determined to be below 1 mm inside the test volume of interest. In patients with meningiomas and gliomas, MET-PET was shown to deliver additional information concerning tumor extension.

CONCLUSION

The precision of the automatic CT/PET image fusion was high. A mean deviation of 2.4 mm is acceptable, considering that it is approximately equal to the pixel size of the PET data sets. MET-PET improves target volume definition for stereotactic fractionated radiotherapy of meningiomas and gliomas.

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.

Stereotactic imaging for radiotherapy: accuracy of CT, MRI, PET and SPECT

CT, MRI, PET and SPECT provide complementary information for treatment planning in stereotactic radiotherapy. Stereotactic correlation of these images requires commissioning tests to confirm the localization accuracy of each modality. A phantom was developed to measure the accuracy of stereotactic localization for CT, MRI, PET and SPECT in the head and neck region. To this end. the stereotactically measured coordinates of structures within the phantom were compared with their mechanically defined coordinates. For MRI, PET and SPECT, measurements were performed using two different devices. For MRI, T1- and T2-weighted imaging sequences were applied. For each measurement, the mean radial deviation in space between the stereotactically measured and mechanically defined position of target points was determined. For CT, the mean radial deviation was 0.4 +/- 0.2 mm. For MRI, the mean deviations ranged between 0.7 +/- 0.2 mm and 1.4 +/- 0.5 mm, depending on the MRI device and the imaging sequence. For PET, mean deviations of 1.1 +/- 0.5 mm and 2.4 +/- 0.3 mm were obtained. The mean deviations for SPECT were 1.6 +/- 0.5 mm and 2.0 +/- 0.6 mm. The phantom is well suited to determine the accuracy of stereotactic localization with CT, MRI, PET and SPECT in the head and neck region. The obtained accuracy is well below the physical resolution for CT, PET and SPECT, and of comparable magnitude for MRI. Since the localization accuracy may be device dependent, results obtained at one device cannot be generalized to others.

[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.

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.

Metabolic imaging of low-grade gliomas with three-dimensional magnetic resonance spectroscopy

PURPOSE

The role of radiotherapy (RT) seems established for patients with low-grade gliomas with poor prognostic factors. Three-dimensional (3D) magnetic resonance spectroscopy imaging (MRSI) has been reported to be of value in defining the extent of glioma infiltration. We performed a study examining the impact MRSI would have on the routine addition of 2-3-cm margins around MRI T2-weighted hyperintensity to generate the treatment planning clinical target volume (CTV) for low-grade gliomas.

METHODS AND MATERIALS

Twenty patients with supratentorial gliomas WHO Grade II (7 astrocytomas, 6 oligoastrocytomas, 7 oligodendrogliomas) underwent MRI and MRSI before surgery. The MRI was contoured manually; the regions of interest included T2 hyperintensity and, if present, regions of contrast enhancement on T1-weighted images. The 3D-MRSI peak parameters for choline and N-acetyl-aspartate, acquired voxel-by-voxel, were categorized using a choline/N-acetyl-aspartate index (CNI), a tool for quantitative assessment of tissue metabolite levels, with CNI 2 being the lowest value corresponding to tumor. CNI data were aligned to MRI and displayed as 3D contours. The relationship between the anatomic and metabolic information on tumor extent was assessed by comparing the CNI contours and other MRSI-derived metabolites to the MRI T2 volume.

RESULTS

The limitations in the size of the region "excited" meant that MRSI could be used to evaluate only a median 68% of the T2 volume (range 38-100%), leaving the volume T2c. The CNI 2 volume (median 29 cm(3), range 10-73) was contained totally within the T2c in 55% of patients. In the remaining patients, the volume of CNI 2 extending beyond the T2c was quite small (median 2.3 cm(3), range 1.4-5.2), but was not distributed uniformly about the T2c, extending up to 22 mm beyond it. Two patients demonstrated small regions of contrast enhancement corresponding to the regions of highest CNI. Other metabolites, such as creatine and lactate, seem useful for determining less and more radioresistant areas, respectively.

CONCLUSION

Metabolically active tumor, as detected by MRSI, is restricted mainly to the T2 hyperintensity in low-grade gliomas, but can extend outside it in a limited and nonuniform fashion up to 2 cm. Therefore, a CTV including T2 and areas of CNI extension beyond the T2 hyperintensity would result in a reduction in the size and a change in the shape of the standard clinical target volumes generated by adding uniform margins of 2-3 cm to the T2 hyperintensity.

3-[(123)I]Iodo-alpha-methyl-L-tyrosine: uptake mechanisms and clinical applications

3-[(123)I]Iodo-alpha-methyl-L-tyrosine (IMT) is an artificial amino acid which has gained considerable interest in Nuclear Medicine in the last two decades. Although the tracer is not incorporated into proteins it exhibits high uptake in brain tumors and appears to be a valuable tool especially for the diagnostic evaluation and therapy planning of patients with cerebral gliomas. In this paper the present knowledge of the uptake mechanisms and the clinical applications of IMT are reviewed and the clinical perspectives discussed.

Image fusion between 18FDG-PET and MRI/CT for radiotherapy planning of oropharyngeal and nasopharyngeal carcinomas

PURPOSE

Accurate diagnosis of tumor extent is important in three-dimensional conformal radiotherapy. This study reports the use of image fusion between (18)F-fluoro-2-deoxy-D-glucose positron emission tomography (18FDG-PET) and magnetic resonance imaging/computed tomography (MRI/CT) for better targets delineation in radiotherapy planning of head-and-neck cancers.

METHODS AND MATERIALS

The subjects consisted of 12 patients with oropharyngeal carcinoma and 9 patients with nasopharyngeal carcinoma (NPC) who were treated with radical radiotherapy between July 1999 and February 2001. Image fusion between 18FDG-PET and MRI/CT was performed using an automatic multimodality image registration algorithm, which used the brain as an internal reference for registration. Gross tumor volume (GTV) was determined based on clinical examination and 18FDG uptake on the fusion images. Clinical target volume (CTV) was determined following the usual pattern of lymph node spread for each disease entity along with the clinical presentation of each patient.

RESULTS

Except for 3 cases with superficial tumors, all the other primary tumors were detected by 18FDG-PET. The GTV volumes for primary tumors were not changed by image fusion in 19 cases (89%), increased by 49% in one NPC, and decreased by 45% in another NPC. Normal tissue sparing was more easily performed based on clearer GTV and CTV determination on the fusion images. In particular, parotid sparing became possible in 15 patients (71%) whose upper neck areas near the parotid glands were tumor-free by 18FDG-PET. Within a mean follow-up period of 18 months, no recurrence occurred in the areas defined as CTV, which was treated prophylactically, except for 1 patient who experienced nodal recurrence in the CTV and simultaneous primary site recurrence.

CONCLUSION

This preliminary study showed that image fusion between 18FDG-PET and MRI/CT was useful in GTV and CTV determination in conformal RT, thus sparing normal tissues.

Clinical value of iodine-123-alpha-methyl-L-tyrosine single-photon emission tomography in the differential diagnosis of recurrent brain tumor in patients pretreated for glioma at follow-up

PURPOSE

To assess the clinical potential of iodine-123-alpha-methyl-L-tyrosine (IMT) and single-photon emission tomography (SPET) in the differential diagnosis of recurrences in patients pretreated for gliomas at follow-up.

PATIENTS AND METHODS

Seventy-eight patients were examined after primary therapy over 36 months. Histopathologic diagnoses of all patients was known at first treatment; magnetic resonance and/or computed tomography examination was performed in addition to IMT-SPET. Cerebral SPET images were acquired 20 minutes after intravenous application of 190 +/- 10 MBq of IMT. SPET images were classified as positive or negative for recurrent tumor visually and by calculating the ratios between tracer accumulation in the lesion and the unaffected contralateral regions of reference using region of interest. Final diagnoses were based on prospective clinicopathologic findings obtained independently of IMT-SPET.

RESULTS

IMT-SPET detected all high-grade recurrent gliomas (grade 4; sensitivity, 100%). A difference could be demonstrated in grade 2 and 3 recurrences (sensitivity, 84% and 92%, respectively). Moreover, benign posttherapeutic lesions (postoperative scars, radiation necrosis) were correctly diagnosed as negative for tumor recurrence. In general, IMT uptake in grade 2 (1.45 +/- 0.24) was significantly lower than that in grades 3 (1.70 +/- 0.41) and 4 (1.88 +/- 0.32). However, it was difficult to evaluate tumor grade only from the IMT accumulation in individual cases.

CONCLUSION

IMT-SPET seems highly useful for detecting and delineating recurrent gliomas and differentiating between benign posttherapeutic lesions and malignant tumor tissue. It may be a valuable clinical tool to diagnose recurrences in patients pretreated for gliomas at follow-up. However, it showed limitations in determining histologic tumor grade.

Registration of magnetic resonance spectroscopic imaging to computed tomography for radiotherapy treatment planning

The incorporation of multiple imaging modalities into radiotherapy treatment planning offers the potential to improve identification of regions of pathology. This work outlines and evaluates a methodology for registration of magnetic resonance images (MRI) and spectroscopic images (MRSI) to computed tomography (CT) images, and visualization of the multimodality data on the treatment planning workstation. Volumetric magnetic resonance images were acquired during an examination prior to the initiation of radiotherapy. Registration between these images and the treatment planning computed tomography images was performed using an automated alignment routine, and was improved manually using an interactive registration tool. The parameters of the alignment were then used to transform the spectroscopic images into the same reference frame. The spectroscopy data were represented in terms of a statistical measure of abnormality, and embedded within the MRI data as overlaid contours. These images were sent via DICOM transfer to the treatment planning workstation. An analysis of the reproducibility of the

MR-spectroscopy guided target delineation for high-grade gliomas

PURPOSE

Functional/metabolic information provided by MR-spectroscopy (MRSI) suggests MRI may not be a reliable indicator of active and microscopic disease in malignant brain tumors. We assessed the impact MRSI might have on the target volumes used for radiation therapy treatment planning for high-grade gliomas.

METHODS AND MATERIALS

Thirty-four patients (22 Grade III; 12 Grade IV astrocytomas) were evaluated; each had undergone MRI and MRSI studies before surgery. MRI data sets were contoured for T1 region of contrast enhancement (T1), region of necrosis, and T2 region of hyperintensity (T2). The three-dimensional MRSI peak parameters for choline (Cho) and N-acetylaspartate (NAA), acquired by a multivoxel technique, were categorized based on an abnormality index (AI), a quantitative assessment of tissue metabolite levels. The AI data were aligned to the MRI and displayed as three-dimensional contours. AI vs. T conjoint and disjoint volumes were compared.

RESULTS

For both grades, although T2 estimated the region at risk of microscopic disease as being as much as 50% greater than by MRSI, metabolically active tumor still extended outside the T2 region in 88% of patients by as many as 28 mm. In addition, T1 suggested a lesser volume and different location of active disease compared to MRSI.

CONCLUSION

The use of MRSI to define target volumes for RT treatment planning would increase, and change the location of, the volume receiving a boost dose as well as reduce the volume receiving a standard dose. Incorporation of MRSI into the treatment-planning process may have the potential to improve control while reducing complications.