Radiosurgery safe, effective for small vestibular schwannomas
A Singapore study reports evidence of the efficacy and safety of radiosurgery (RS) for small vestibular schwannomas (VSs) or as an adjunct therapy after microsurgery.
“[S]mall, uncomplicated but enlarging VSs should be treated with RS, although observation is an option for a selected subgroup, especially older patients or those with small, asymptomatic and slow-growing tumours,” researchers said.
Forty-six patients underwent single-fraction RS and 31 hypofractionated RS, with a median follow-up of 40.6 months. Prior surgery was conducted in 29 patients to remove the tumour (median size, 1.68 cm3). A conservative treatment was given to one patient with symptomatic increase in tumour size (>20 percent in largest diameter), who subsequently showed stable disease on magnetic resonance imaging (MRI). There was a 98.7-percent progression-free survival. [Singapore Med J 2018;59:590-596]
In another case, ventriculoperitoneal shunt insertion was required in a patient with symptomatic oedema. Among patients (n=11) who had serviceable hearing prior to radiotherapy, 72.7 percent retained useful hearing (mean decline in pure tone average, 20.1 dB). Furthermore, >90 percent of patients had preserved their facial and trigeminal nerve functions and sense of equilibrium.
“This study has shown that with careful patient selection, especially with regard to tumour size, patient outcomes were excellent, with freedom from progression and freedom from surgery both at 98.7 percent,” researchers said.
Other larger studies support the safety of single-fraction RS, while fewer and smaller studies have reported on hypofractionated RS. [Radiother Oncol 2015;114:378-383; Int J Radiat Oncol Biol Phys 2001;50:1265-1278; Clin Oncol (R Coll Radiol) 2014;26:309-315; Neurosurgery 2005;57:60-70; J Neurosurg 2013;118:557-565; Neurochir Suppl 2008;101:169-173; Strahlenther Onkol 2014;190:798-805; Comput Aided Surg 2011;16:112-120; Jpn J Clin Oncol 2013;43:805-812]
“Bearing the pros and cons of the various treatment options in mind, observation may sometimes be a valid and the most reasonable option for some patients, given the indolent natural history of VS, especially in patients with a limited estimated lifespan or poorer performance status, or those who are asymptomatic or incidentally diagnosed during brain MRI,” researchers noted.
The present study was a retrospective review of case notes and MRI of VS patients treated with RS. Treatment was administered as either a single 13 Gy session or 25 Gy in five sessions. Only larger or higher Koos grade VSs were routinely treated with hypofractionated RS.
Researchers used RECIST criteria and Gardner-Robertson scale to evaluate tumour response and hearing, respectively. They also assessed other toxicities using physical examination and history-taking. The Kaplan-Meier method was used to estimate freedom from radiological progression.
“Going forward, prospective trials comparing the different treatment modalities are required, although with high tumour control and low toxicity rates across all treatment options, obtaining statistically significant results may be difficult, as a large number of patients will be needed,” researchers said.
“To better compare between studies, standardizing the reporting of tumour size (cm3 or maximal diameter) and tumour control, such as RECIST criteria and toxicity reporting, should be undertaken for future trials or cohort reporting,” they added.