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

Abstract

<strong>Purpose:</strong> 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.<br /><strong>Methods and materials:</strong> 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 (V12<sub><span style="font-size: small;">Eq</span></sub> and V10<sub><span style="font-size: small;">Eq</span></sub>).<br /><strong>Results:</strong> 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 (CI<sub><span style="font-size: small;">Paddick</span></sub> ≥ 0.6) despite being inferior to the published Universitair Ziekenhuis Brussel (UZB) Gamma Knife and CyberKnife results (<em>p</em> < 0.0001). Homogeneity was superior to the Gamma Knife (<em>p</em> < 0.0001) and Novalis dynamic conformal arc (<em>p</em> = 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 V10<sub><span style="font-size: small;">Eq</span></sub> data showed increased sensitivity when compared with V12<sub><span style="font-size: small;">Eq</span></sub>.<br /><strong>Conclusion:</strong> 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, V10<sub><span style="font-size: small;">Eq</span></sub> is a superior risk indicator when compared to V12<sub><span style="font-size: small;">Eq</span></sub> 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.