Irradiation of cochlear structures during vestibular schwannoma radiosurgery and associated hearing outcome

Abstract

During GKS for VSs, relatively high doses of radiation can be delivered to the cochlea. Worsening of hearing after GKS can be the consequence of either radiation injury to the cochlea or the irradiation dose delivered into the auditory canal, or both.

Preserving normal facial nerve function and improving hearing outcome in large vestibular schwannomas with a combined approach: planned subtotal resection followed by gamma knife radiosurgery

“…On the other hand, several large series of radiosurgery for the treatment of small and medium benign skull-base lesions have demonstrated adequate long-term tumor control, along with very low neurological morbidity and improved preservation of functions, especially with regard to the risk for cranial nerve deficit, compared with surgery [20, 39, 41, 59, 66]. In large tumors, radical surgery alone yields a high risk for neurological deficit, and radiosurgery cannot be used safely as a first line of treatment because of the high risk for radiation-induced complications associated with large-volume tumors.…”

Critical appraisal of RapidArc radiosurgery with flattening filter free photon beams for benign brain lesions in comparison to GammaKnife: a treatment planning study

“…Mean cochlea doses below 3.7 and 4.8 Gy are reported to be safe for retaining useful hearing [8]. QUANTEC guideline recommends maximum dose to be limited to 12-14 Gy for hearing preservation [9].…”

Critical neurological structure sparing radiosurgery of vestibular schwannoma: Dosimetric comparison of different techniques and dose prescription methods

“…However, the methodology for measurement of the dose to the cochlea was not mentioned. The first publication of the importance of the cochleae dose to hearing preservation after GKS for VS was by Massager et al, [9] In their retrospective study of 82 patients treated with a fixed margin dose of 12 Gy, they reported a mean cochleae dose of 4.33 Gy (range 1.30-10 Gy). Unlike other previous publication, they measured the mean cochlea dose averaged over the whole 3D volume of the cochlea and found that those with preserved hearing had a mean cochlea dose of 3.7 Gy versus 5.33 Gy in those who lost useful hearing.…”

“…We have reported minimum, mean, maximum doses and D 5 for all CNSs. Although none of the technique fulfills the cochleae threshold dose (3.7 Gy) for preserved hearing as suggested by Massager, [9] prescription of dose at 50% isodose and IMRS_80% plan maintained the mean dose below the upper threshold (5.33 Gy) for lost of useful hearing. While the mean maximal dose to cochlea in our study (range 9.02 Gy for SCF_50% to 10.15 Gy for DCA_80%) was less than that of gamma knife plan, [10] it was well above the threshold dose (6 Gy) suggested in a recent review article for hearing preservation.…”

“…[9,10] Concurrently, the risk of facial and trigeminal neuropathy is associated with the irradiated length of CN and brainstem dose. [11][12][13][14] A few studies have reported retrospective measurement of radiation doses to some of the critical neurological structures (CNSs) such as cochleae, CN and brainstem separately during gamma knife radiosurgery (GKS) of VS. [9,10,[14][15][16] However, dosimetry data on these CNSs from a single treatment plan is rather limited to correlate with the toxicity profile. Radiosurgery treatment planning and delivery techniques of VS is still evolving and need further improvement in regards to reduction of dose to the CNSs without compromising target coverage.…”