Cochlear sparing in LINAC-based radiosurgery for vestibular schwannoma: a dosimetric comparison of dynamic conformal arc, IMRT and VMAT treatment plans

• Published in: Radiation oncology (London, England) Vol. 18; no. 1; p. 2
• Main Authors: Khong, Jeremy, Govindaraj, Ramkumar, Ramm, Daniel, Edwards, Suzanne, Roos, Daniel
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 04-01-2023; BioMed Central; BMC
• Subjects: Acoustic nerve; Acoustic neuroma; Analysis; Care and treatment; Cochlear sparing; CT imaging; Diagnosis; Humans; Medical examination; Neuroma, Acoustic - radiotherapy; Patient outcomes; Plan comparison; Radiation dosimetry; Radiosurgery; Radiosurgery - methods; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Intensity-Modulated - methods; Retrospective Studies; Stereotactic radiosurgery; Techniques; Vestibular schwannoma; Australia; Stereotactic radiosurgery; Cochlear sparing; Techniques; Plan comparison; Vestibular schwannoma
• ISSN: 1748-717X; 1748-717X
• DOI: 10.1186/s13014-022-02188-y

Stereotactic radiosurgery (SRS) is the preferred treatment for vestibular schwannoma (VS) in patients with preserved hearing and tumour diameter < 3 cm. Emerging evidence suggests restricting cochlear dose could preserve hearing. This retrospective replanning study aims to compare dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans for superiority of cochlear dose sparing without compromising tumour coverage.
Eligibility criteria included sporadic VS, serviceable hearing and availability of CT and MRI for planning. The original gross tumour volume and brainstem OAR volume were retained; the cochlea was newly contoured on the planning CT scan (bone window). Each case was replanned using the three above techniques, prescribing 12 Gy to the 80% isodose line. No dose constraint was applied to the cochlea.
Eighteen patients were replanned. Mean tumour volume was 2.25 cc. Tumour coverage and tumour mean dose (DCAT: 14.2, IMRT: 14.6, VMAT: 14.5 Gy) were comparable. Paddick and RTOG conformity indices were better for DCAT (0.66 and 1.6) and VMAT (0.69 and 1.5) compared to IMRT (0.56 and 1.9). DCAT had superior gradient index (3.0) compared to VMAT (3.4) and IMRT (3.4). VMAT delivered the lowest mean brainstem maximum dose (8.3 Gy) and decreased the mean cochlear dose (3.4 Gy) by 2.3 and 2.1 Gy, and the mean cochlear maximum dose (3.6 Gy) by 2.4 and 2.5 Gy relative to DCAT and IMRT, respectively.
LINAC-based SRS treatment using VMAT can achieve better cochlear dose sparing than DCAT or IMRT while maintaining tumour coverage.