Analysis of MRI Volumetric Changes After Hypofractionated Stereotactic Radiation Therapy for Benign Intracranial Neoplasms

Abstract

PurposeTo quantitatively assess volumetric changes after hypofractionated stereotactic radiation therapy (HFSRT) in patients treated for vestibular schwannomas and meningiomas.Methods and materialsWe retrospectively reviewed records of patients treated with HFSRT at our institution from 2002 to 2014. Patients received a median dose of 25 Gy in 5 fractions. After treatment, they underwent clinical and radiologic follow-up with magnetic resonance imaging (MRI) at 3- to 12-month intervals. Gross tumor volume was outlined on each thin slice of contrast-enhanced T1 series before and on each scan after HFSRT. Volumetric changes were calculated and compared with neuroradiologist interpretations.ResultsForty-three patients underwent 182 MRI scans. Tumor types included vestibular schwannoma (n = 34) and meningioma (n = 9). Median follow-up time was 29 months. Median gross tumor volume was 3.1 cm3. Local control was 81.4% for the entire cohort at the time of last follow-up. Transient volume expansion was noted in 17 patients (50%) with vestibular schwannoma and 2 (22%) with meningioma. For all patients, transient volume expansion and subsequent regression occurred at a median time of 5.5 and 12 months, respectively. Neuroradiologist agreement with regard to tumor regression, progression, or stability occurred in 155 of 182 total reports (85%). The largest discordance identified was a stable finding on the MRI interpretation when the measured volumetric change exceeded 20% (n = 24 [13%]).ConclusionsHFSRT is associated with excellent local control and a low incidence of toxicity. With volumetric MRI measurement, transient volume expansion was a common finding and was associated with temporary adverse effects. Although the neuroradiologist’s interpretation generally agreed with the volumetric MRI measurement, the overall 15% discordance rate emphasizes the potential benefit of considering volumetric measurements, which may help clinicians correlate posttreatment symptoms with MRI findings.

Longitudinal Radiographic Outcomes of Vestibular Schwannoma in Single and Fractionated Stereotactic Radiosurgery: A Retrospective Cohort Study

“…Earlier studies of pseudoprogression, such as the report by Flickinger et al, demonstrate pseudoprogression rates of less than 2%, whereas more recent groups have reported rates up to 50%, though imaging varied among these studies. 16,24,25 Our definition of pseudoprogression, as a transient 3D volumetric increase, is more sensitive compared with pseudoprogression defined as planar growth in earlier studies and is closer to rates reported in more contemporary studies.…”

Long-term volumetric analysis of vestibular schwannomas following stereotactic radiotherapy: Practical implications for follow-up

“…While the radiological follow-up after a surgical tumor resection is unambiguous, interpretation of serial magnetic resonance imaging (MRI) following radiotherapy remains a matter of debate. Transient tumor enlargement, also called pseudoprogression, and loss of central contrast enhancement were described in 5–74% of patients in the first three years after SRS [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] . These well-known phenomena are of no or little relevance for the patient, since they are rarely symptomatic.…”

“…Several studies showed that transient tumor enlargement usually peaks at 6 months after SRS and resolves in 12–18 months [4] , [6] , [8] , [9] , [10] , [12] , [13] , [16] , [18] , [20] , [21] , [23] , [24] . But its resolution may require years for some patients.…”

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“…Several comparative studies suggested improved hearing and facial preservation rates along with better quality of life parameters with utilization of radiosurgery [62][63][64]. Nevertheless, response to radiosurgery in terms of tumor size may be variable particularly in the postintervention period as addressed in several studies [1,[65][66][67][68][69][70][71][72][73][74][75]. Transient volume changes during the postradiosurgical period have been referred to as transient expansion, tumor pseudoprogression, and transient tumor enlargement which may occur due to radiation induced swelling with several mechanisms.…”

“…The authors reported that transient expansion of VS frequently occurs at 6 to 18 months after radiosurgery whereas tumor growth seems to develop approximately at 3-4 years [72]. In a comprehensive analysis of MRI volumetric changes following HFSRT for benign intracranial neoplasms, Fega et al reported that transient volume expansion was a frequent finding after HFSRT of VS which was in association with temporary adverse effects [73]. The authors reported an overall 15% discordance rate regarding the neuroradiologist interpretation and volumetric MRI measurements, which underscores importance of incorporating volumetric measurements as part of detailed assessments to aid in decision making [73].…”