Thallium-201 SPECT: the optimal prediction of response in glioma therapy

CT-based quantitative SPECT for the radionuclide ²⁰¹Tl: experimental validation and a standardized uptake value for brain tumour patients

We have previously reported on a method for reconstructing quantitative data from 99mTc single photon emission computed tomography (SPECT) images based on corrections derived from X-ray computed tomography, producing accurate results in both experimental and clinical studies. This has been extended for use with the radionuclide ²⁰¹Tl. Accuracy was evaluated with experimental phantom studies, including corrections for partial volume effects where necessary. The quantitative technique was used to derive standardized uptake values (SUVs) for ²⁰¹Tl evaluation of brain tumours. A preliminary study was performed on 26 patients using ²⁰¹Tl SPECT scans to assess residual tumor after surgery and then to monitor response to treatment, with a follow-up time of 18 months. Measures of SUVmax were made following quantitative processing of the data and using a threshold grown volume of interest around the tumour. Phantom studies resulted in the calculation of concentration values consistently within 4% of true values. No continuous relation was found between SUVmax (post-resection) and patient survival. Choosing an SUVmax cut-off of 1.5 demonstrated a difference in survival between the 2 groups of patients after surgery. Patients with an SUVmax<1.5 had a 70% survival rate over the first 10 months, compared with a 47% survival rate for those with SUVmax>1.5. This difference did not achieve significance, most likely due to the small study numbers. By 18 months follow-up this difference had reduced, with corresponding survival rates of 40% and 27%, respectively. Although this study involves only a small cohort, it has succeeded in demonstrating the possibility of an SUV measure for SPECT to help monitor response to treatment of brain tumours and predict survival.

Tumor shrinkage and objective response rates: gold standard for oncology efficacy screening trials, or an outdated end point?

Phase II clinical trials have long been used to screen new cancer therapeutics for antitumor activity ("efficacy") worthy of further evaluation. Traditionally, the primary end point used in these screening trials has been objective response rate (RR), with the desired rate being arbitrarily set by the researchers before initiation of the trial. For cytotoxic agents, especially in common tumor types, response has been a reasonably robust and validated surrogate of benefit. Phase II trials with response as an end point have a modest sample size (15-40 patients) and are completed rapidly allowing early decisions regarding future development of a given agent. More recently, a number of new agents have proven successful in pivotal phase III studies, despite a low or very modest RR demonstrated in early clinical trials. Researchers have postulated that these novel agents, as a class, may not induce significant regression of tumors, and that the use of RR as an end point for phase II studies will result in false negative results, and point out that not all available data is used in making the decision. Others have pointed out that even novel agents have proven unsuccessful in pivotal trials if objective responses are not demonstrated in early clinical trials. We review here the historical and current information regarding objective tumor response.

Diagnostic accuracy of 201Thallium-SPECT and 18F-FDG-PET in the clinical assessment of glioma recurrence

PURPOSE

Reliable differential diagnosis between tumour recurrence and treatment-induced lesions is required to take advantage of new therapeutic approaches to recurrent gliomas. Structural imaging methods offer a high sensitivity but a low specificity, which might be improved by neurofunctional imaging. This study aimed to test the hypothesis that incorporation of 18-fluoro-deoxy-glucose positron emission tomography (FDG-PET) increases the accuracy of this differential diagnosis obtained with 201Tl chloride-single-photon emission computed tomography (201Tl-SPECT).

MATERIALS AND METHODS

Seventy-six patients (mean age 47.72 +/- 16.19 years) under suspicion of glioma recurrence, 42% with low-grade and 58% with high-grade lesions, were studied by (201)Tl-SPECT and FDG-PET, reporting results under blinded conditions using visual analysis. Tumour was confirmed by histological confirmation (23 patients) or clinical and structural neuroimaging follow-up (mean of 2.6 years).

RESULTS

This population had a high disease prevalence (72%). Globally, highest sensitivity was obtained using 201Tl-SPECT assessed with MRI (96%) and highest specificity using FDG-PET + MRI (95%). FDG-PET appeared slightly better for confirming tumour recurrence, whereas 201Tl-SPECT was superior for ruling out possible recurrence (disease present in 38% of FDG-PET negative explorations). In the high-grade subgroup, there were no false-positive examinations (specificity: 100%), but sensitivity differed among techniques (201Tl-SPECT : 94%; 201Tl-SPECT + MRI: 97%; FDG-PET + MRI: 83%). In the low-grade subgroup, 201Tl-SPECT + MRI showed highest sensitivity (95%) and lowest posttest negative probability (9%); FDG-PET + MRI offered highest specificity (92%) with a posttest negative probability of 35%.

CONCLUSIONS

FDG-PET does not clearly improve the diagnostic accuracy of (201)Tl-SPECT, which appears to be a more appropriate examination for the diagnosis of possible brain tumour recurrence, especially for ruling it out.

Cerebral necrosis after 25Gy radiotherapy in childhood followed 28 years later by 54Gy radiotherapy

The development of brain necrosis is life-long risk of repeat radiation therapy, even after a long time interval and a moderate radiation dose. We report on a 34-year-old patient who had prophylactic cranial irradiation with 25Gy and adjuvant chemotherapy in childhood for leukaemia and in adulthood, 28 years later, therapeutic radiotherapy with 54Gy for an atypical (WHO grade II) meningioma. About 2 years later he developed a contrast-enhancing lesion on MRI-scan that was indicative of a tumor according to a thallium-201 ((201)Tl) SPECT scan. Histopathology of the operated contrast-enhancing lesion showed extensive radionecrosis. Radiation necrosis is a small but serious risk after repeat radiation therapy, even after a very long-term interval, the delivery of small fractions and an average cumulative total dose. Patients undergoing repeat radiotherapy therefore need to be followed life-long for potential late radiation toxicity.

Thallium-201SPECT assessment in the detection of recurrences of treated gliomas and ependymomas

INTRODUCTION

The aim of this study was to establish the value of thalium-(201) single-photon emission computed tomography ((201)Tl-SPECT) in the detection of recurrences in the follow-up of patients with treated primary neuroepithelial tumours.

MATERIAL AND METHODS

Sixty-three (201)Tl-SPECT were performed in 36 patients with glioma (12 males, mean age of 46 +/- 13 years). All patients underwent surgery and adjuvant radiotherapy (and some of them received chemotherapy). All patients were submitted to morphological neuroimaging techniques as well (and (201) Tl-SPECT). Mean follow-up was 18.3 +/- 14.6 months. Gold standard was based on clinical follow-up, therapeutical decisions (at least 4 months after (201)Tl-SPECT) and imaging features.

RESULTS

Sensitivity and specificity of (201)Tl-SPECT to detect glioma recurrences were 90% and 100% respectively and 93% accuracy. Sensitivity and specificity for high grade tumours, were 100% respectively. Due to 4 false negatives, sensitivity and specificity for low grade gliomas were 78% and 100%. In the positive (201)Tl-SPECT group of patients overall survival was 13.64% at the end of the study. The negative (201)Tl-SPECT group had 84.62% overall survival at the end of the study (p = 0.0003). CONCLUSIONS. (201)Tl-SPECT is a valuable and noninvasive diagnostic procedure to detect recurrence or progression disease for treated gliomas and ependymomas. (201)Tl-SPECT has a good correlation with short term prognosis with excellent diagnostic accuracy.