Hypofractionated image-guided radiotherapy for the treatment of acoustic neuromas: A dosimetrically acceptable alternative to stereotactic radiosurgery in a resource-constrained environment

Hester Burger,Ross Balchin,Jeannette D Parkes,Hannelie Mac Gregor

doi:10.4102/sajo.v1i0.19

Hester Burger, Ross Balchin + Show 2 more

Open Access

https://doi.org/10.4102/sajo.v1i0.19

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Abstract

Purpose: Treatment options for acoustic neuromas (ANs) are limited in low- and middle-income countries. The aim of this study was to investigate whether hypofractionated image-guided radiotherapy (IGRT) is a clinically acceptable treatment option for departments where no other radiosurgery options are available. Methods and materials: Fifteen dynamic conformal arc plans that had been clinically utilised were evaluated against the Radiation Therapy Oncology Group (RTOG) radiosurgery criteria and published indices. Analysis involved evaluating critical structure doses and the volume of normal tissue receiving 12 and 10 Gy single fraction equivalent dose (V12Eq and V10Eq). Results: Overall, there was only one RTOG protocol deviation in the whole patient group, where quality of coverage was compromised in order to achieve brainstem tolerance. Conformity indices were within clinically acceptable limits (CIPaddick ≥ 0.6) despite being inferior to the published Universitair Ziekenhuis Brussel (UZB) Gamma Knife and CyberKnife results (p &lt; 0.0001). Homogeneity was superior to the Gamma Knife (p &lt; 0.0001) and Novalis dynamic conformal arc (p = 0.0002) results. Gradient index results were inferior to all published techniques, but doses to the normal structures were well controlled with the exception of the cochlea. The V10Eq data showed increased sensitivity when compared with V12Eq. Conclusion: Dynamic arc IGRT allows for good coverage of AN lesions, but the dose fall-off is not as steep as that obtained with mainstream radiosurgery systems. Contouring and planning should include detailed critical structures analysis. For normal brain parenchyma analysis, V10Eq is a superior risk indicator when compared to V12Eq for this technique. Dynamic arc IGRT offers a dosimetrically acceptable treatment alternative for patients without serviceable hearing, in departments where there are no mainstream radiosurgery treatment options available.

Highlights

Acoustic neuromas (ANs) or vestibular schwannomas are benign neoplasms associated with the vestibular cranial nerve
The remaining plans were fully compliant with Radiation Therapy Oncology Group (RTOG) radiosurgery criteria (Figure 1)
The Groote Schuur Hospital (GSH) dynamic conformal arc (DCA) technique was compliant with the RTOG radiosurgery criteria with the exception of a single largevolume treatment, where dose reduction and decreased tumour coverage were accepted in order to obtain critical structure tolerance

Summary

Introduction

Acoustic neuromas (ANs) or vestibular schwannomas are benign neoplasms associated with the vestibular cranial nerve. Benign, untreated lesions may cause symptoms because of local nerve compression of the auditory, vestibular, facial or, less commonly, the trigeminal nerve.[1,2] Very large lesions may become life-threatening because of brainstem compression. Surgery was considered the treatment of choice, but the introduction of stereotactic radiosurgery in the latter half of the 20th century allowed for significantly lower levels of morbidity and similar or better levels of tumour control.[3] Radiosurgery is less invasive than surgery and can be performed on outpatients, making it the preferred choice for many. Radiosurgery is commonly used as the favoured treatment option for small to medium ANs.[4]

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