Clinical studyDifferentiation of tumor recurrence from radiation necrosis in high-grade gliomas using 201Tl-SPECT
Introduction
Management of high-grade gliomas remains one of the greatest challenges in oncology, requiring a multidisciplinary approach, which consists of cytoreductive surgery, radiation therapy and chemotherapy. Nonetheless, these tumors recur almost invariably, with a median survival of 14.6 months in patients with glioblastoma multiforme treated with concurrent radiotherapy and temozolomide followed by 6 months of adjuvant temozolomide.1
Serial MRI is routinely performed in these patients after primary treatment to detect tumor recurrence. However, conventional contrast-enhanced CT scans or MRI cannot reliably distinguish radiation necrosis from recurrent tumor. Both entities can cause extensive edema and blood–brain barrier disruption that result in mass effect and abnormal contrast enhancement.[2], [3] Radiation-induced necrosis often occurs within 2 years after radiation therapy, the same time frame during which tumor recurrence is most frequent.4
Differentiation between tumor progression and radiation necrosis carries obvious prognostic and therapeutic implications. To overcome this problem, several functional and physiological imaging techniques, such as MR spectroscopy (MRS), perfusion-weighted MRI, positron emission tomography (PET), and thallium-201 single-photon emission computed tomography (201Tl-SPECT) have been examined for clinical use.[5], [6], [7], [8], [9], [10], [11], [12] Radiothallium (201Tl) is a monovalent cationic radioisotope with biological properties similar to potassium.13 Experimental evidence suggests that the ionic movement of thallium and potassium are related to active transport through an adenosine triphosphate (ATP) cell membrane pump, and that 201Tl uptake is related to cell growth rates.14 Previous studies showed substantial 201Tl uptake in brain tumors with little uptake in normal brain.[15], [16] In the mid-1980s, noting the disparity between clinical status and CT scan results in patients with gliomas, Kaplan et al. found 201Tl to be superior to CT scans, gallium-67 citrate and technetium-99m gluceptate in identifying viable tumors.11 Subsequently, other studies suggest that 201Tl-SPECT may be a useful method to differentiate between tumor recurrence and radiation necrosis.[12], [17], [18], [19], [20]
We use 201Tl-SPECT in our centre to clarify equivocal MRI findings in patients with post-irradiated brain tumors. Although previous studies have examined the accuracy of 201Tl-SPECT in differentiating radiation necrosis from recurrent tumor, its impact on clinical decision making has not been explored. The aim of this study was to establish the value of 201Tl-SPECT in differentiating radiation necrosis from recurrent tumor, and its influence on therapeutic decision making in a cohort of patients with post-irradiated high-grade gliomas and abnormal MRI findings.
Section snippets
Patients
We identified 19 consecutive patients with primary brain tumors who underwent 201Tl-SPECT at the Royal Melbourne Hospital between March 2004 and May 2007. Two patients had two 201Tl-SPECTs during this time. Therefore, a total of 21 SPECT scans from 19 patients were included in this retrospective analysis. MRIs were performed as routine follow-up evaluation of treated brain tumors, or when there was clinical suspicion of disease recurrence. In all patients, 201Tl-SPECT was prompted either by an
Demographics
Patient characteristics and treatment history of the 19 patients in this study are shown in Table 1. Median age for all patients was 51 (range, 25–78 years), with three patients above 70 years. All patients had histologically confirmed high-grade gliomas. Seven patients had glioblastoma multiforme, seven had anaplastic astrocytoma, and five had anaplastic oligoastrocytoma. Most patients (89%) had undergone either a complete or partial resection of their gliomas, while the remaining two patients
Discussion
Ionizing radiation applied to the central nervous system can result in a localized area of necrosis in the brain. The most common MRI characteristics of radiation necrosis consist of an enhancing mass with a central area of necrosis, which mimics tumor recurrence. The incidence of pure radiation necrosis was 14% in a series of 148 patients with treated malignant gliomas, with another 11% of patients with a mixture of predominantly radiation necrosis intermingled with limited residual and/or
Acknowledgement
The result of this study was presented at the Glioma 2007 Meeting, Sydney, Australia.
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