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. 2025 Feb 26:64:319-325.
doi: 10.2340/1651-226X.2025.41924.

Adaptation of dose-prescription for vestibular schwannoma radiosurgery taking body contouring method and heterogeneous material into account

Marcus Fager  1 , Michael Gubanski  2 , Åsa Carlsson Tedgren  3 , Hamza Benmakhlouf  4
Affiliations

Adaptation of dose-prescription for vestibular schwannoma radiosurgery taking body contouring method and heterogeneous material into account

Marcus Fager et al. Acta Oncol. .

Abstract

Background: Majority of vestibular schwannoma (VS) patients have undergone gamma-knife radiosurgery (GKRS) with favorable results. Clinical evidence is derived from doses calculated with a type-a algorithm, which in this case assumes all material to be water. A type-b algorithm (Convolution algorithm [CA]) taking tissue heterogeneity into account is available. Historically, body contour is defined using a 16-point approximation, whereas modern softwares generate the body from Magnetic Resonance Imaging (MRI). The accuracy in dose-calculation algorithms (DCA) and contouring method (CM) will have a significant influence in the relation between clinical outcome and dosimetric data. The objective was to investigate the impact of DCA and CMs on dose distribution while preserving treatment conditions.

Methods: Treatment plans for 16 VS patients were recalculated in terms of DCA and CM. The difference in the dose covering 99% of the VS (DVS99%) depending on CM and DCA was estimated. The difference in DVS99% was used to adopt the prescription of new CA-based plans. CA-plans were recalculated to TMR10 to evaluate clinical treatability, as clinical evidence is derived from TMR10-doses.

Results: Both CM and DCA had a significant impact on the dose to VS and surrounding structures. CM altered the doses homogenously by 2.1-3.3%, whereas DCA heterogeneously by 5.0-10.7%. An increase of 9.1[8.1, 10.0]% was found for DVS99% and the CA-plans recalculated into TMR10 resulted in clinically treatable plans.

Interpretation: We conclude that transferring to more modern algorithms that take tissue heterogeneity into account heterogeneously alter dose distributions. This work establishes a safe pathway to adopt prescription dose for VS while preserving clinical treatability.

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Conflict of interest statement

The authors report there are no competing interests to declare.

Figures

Figure 1
Figure 1
Shows the typical anterior 1 mm expansion we have used in our study as a pseudo-volume in order to estimate the possible differences in doses to the facial nerve.
See this image and copyright information in PMC

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