Acute clinical adverse radiation effects after Gamma Knife surgery for vestibular schwannomas

Abstract

OBJECTIVEVestibular schwannomas (VSs) represent a common indication of Gamma Knife surgery (GKS). While most studies focus on the long-term morbidity and adverse radiation effects (AREs), none describe the acute clinical AREs that might appear on a short-term basis. These types of events are investigated, and their incidence, type, and outcomes are reported in the present paper.METHODSThe included patients were treated between July 2010 and March 2016, underwent at least 6 months of follow-up, and presented with a disabling symptom during the first 6 months after GKS that affected their quality of life. The timing of appearance, as well as the type of main symptom and outcome, were noted. The prescribed dose was 12 Gy at the margin.RESULTSThirty-five (22%) of 159 patients who fulfilled the inclusion criteria had acute clinical AREs. The mean followup period was 30 months (range 6–49.2 months). The mean time of appearance was 37.9 days (median 31 days; range 3–110 days). In patients with de novo symptoms, the more frequent symptoms were vertigo (n = 4; 11.4%) and gait disturbance (n = 3; 8.6%). The exacerbation of a preexisting symptom was more frequently related to hearing loss (n = 10; 28.6%), followed by gait disturbance (n = 7; 20%) and vertigo (n = 3, 8.6%). In the univariate logistic regression analysis, the following factors were statistically significant: age (p = 0.002; odds ratio [OR] 0.96), hearing at baseline by Gardner-Robertson (GR) class (p = 0.006; OR 0.21), pure tone average at baseline (p = 0.006; OR 0.97), and Koos grade at baseline (with Koos Grade I used as a reference) (for Koos Grade II, OR 0.17 and p = 0.002; for Koos Grade III, OR 0.42 and p = 0.05). The following were not statistically significant but showed a tendency toward significance: the number of isocenters (p = 0.06; OR 0.94) and the maximal dose received by the cochlea (p = 0.07; OR 0.74). Fractional polynomial regression analysis showed a nonlinear relationship between the outcome and the radiation dose rate (minimum reached at a cutoff of 2.5 Gy/minute) and the maximal vestibular dose (maximum reached at a cutoff of 8 Gy), but the small sample size precludes a detailed analysis of the former. The clinical acute AREs disappeared in 32 (91.4%) patients during the first 6 months after appearance. Permanent and somewhat disabling morbidity was found in 3 cases (1.9% from the whole series): 1 each with complete hearing loss (GR Class I before and V after), hemifacial spasm (persistent but alleviated), and dysgeusia.CONCLUSIONSAcute effects after radiosurgery for VS are not rare. They concern predominantly de novo vertigo and gait disturbance and the exacerbation of preexistent hearing loss. In de novo vestibular symptoms, a vestibular dose of more than 8 Gy is thought to play a role. In most cases, none of these effects are permanent, and they will ultimately improve or disappear with steroid therapy. Permanent AREs remain very rare.

Gamma Knife radiosurgery for intravestibular and intracochlear schwannomas

“…Beside the previous, only a small number of papers have described this particular and rare pathology, in non-radiosurgical setting, in the frame of case reports or small series [10]. In our experience, we report no acute or subacute adverse radiation effects in this indication, both for ICS and for IVS, as we have previously reported in our overall series of VSs treated with GKR [21]. Symptom stability was confirmed on four out of five cases.…”

“…During dosimetry planning, special attention was given to the dose received by the cochlea in patients with functional hearing at baseline [14]. Due to the particular anatomical location, we also defined the vestibule, as the structure that is very close anatomically to the cochlea, and which might be subjected to dose increase when limiting the dose to the cochlea, as in our previously described methodology [21].…”

When Should We Stop Scanning Older Patients with Vestibular Schwannomas?

“…For instance, one consideration would be if there was an increased incidence of treatment side effects or their functional impact with aging. This may happen if there are existing balance problems, for instance, (more likely in the elderly) which may be exacerbated with both surgical or radiotherapy treatment 14 and lead to loss of independence. Also, because of decreased remaining life expectancy with aging, there is simply less time to accrue bad outcomes from the underlying disease or indeed from its treatment (e.g., malignant change from radiotherapy).…”

Letter: A Retrospective Cohort Study of Longitudinal Audiologic Assessment in Single and Fractionated Stereotactic Radiosurgery for Vestibular Schwannoma

“…In the same sense, what would be the equivalent of the single fraction maximal cochlear dose corresponding to the 3 and 5 fraction cases, if we would have considered 5 Gy as the upper limit for one fraction? It is now well acknowledged that while treating VSs with serviceable hearing with SRS, the maximal dose received by the cochlea should be kept below 5 Gy, so as to give maximal chances to preserve hearing on short and long-term basis [4][5][6][7] . In this sense, hearing loss is not really astonishing in the single fraction group.…”