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. 2024 Sep;200(9):815-826.
doi: 10.1007/s00066-024-02249-z. Epub 2024 Jul 8.

Effect of different optimization parameters in single isocenter multiple brain metastases radiosurgery

Angelika Altergot  1 , Carsten Ohlmann  2 , Frank Nüsken  2 , Jan Palm  2 , Markus Hecht  2 , Yvonne Dzierma  2
Affiliations

Effect of different optimization parameters in single isocenter multiple brain metastases radiosurgery

Angelika Altergot et al. Strahlenther Onkol. 2024 Sep.

Abstract

Purpose: Automated treatment planning for multiple brain metastases differs from traditional planning approaches. It is therefore helpful to understand which parameters for optimization are available and how they affect the plan quality. This study aims to provide a reference for designing multi-metastases treatment plans and to define quality endpoints for benchmarking the technique from a scientific perspective.

Methods: In all, 20 patients with a total of 183 lesions were retrospectively planned according to four optimization scenarios. Plan quality was evaluated using common plan quality parameters such as conformity index, gradient index and dose to normal tissue. Therefore, different scenarios with combinations of optimization parameters were evaluated, while taking into account dependence on the number of treated lesions as well as influence of different beams.

Results: Different scenarios resulted in minor differences in plan quality. With increasing number of lesions, the number of monitor units increased, so did the dose to healthy tissue and the number of interlesional dose bridging in adjacent metastases. Highly modulated cases resulted in 4-10% higher V10% compared to less complex cases, while monitor units did not increase. Changing the energy to a flattening filter free (FFF) beam resulted in lower local V12Gy (whole brain-PTV) and even though the number of monitor units increased by 13-15%, on average 46% shorter treatment times were achieved.

Conclusion: Although no clinically relevant differences in parameters where found, we identified some variation in the dose distributions of the different scenarios. Less complex scenarios generated visually more dose overlap; therefore, a more complex scenario may be preferred although differences in the quality metrics appear minor.

Keywords: Brain neoplasms; Elements Multiple Brain Mets; Flat vs FFF beams; Gradient index; Plan complexity.

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Conflict of interest statement

A. Altergot, C. Ohlmann, F. Nüsken, J. Palm, M. Hecht and Y. Dzierma declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Diagram for visualization of all compared scenarios and the corresponding changes made within these scenarios. (DCA dynamic conformal arcs)
Fig. 2
Fig. 2
Boxplots showing the number of monitor units needed for the different scenarios for all plans and the subgroups separately. There was a significant difference between scenario 1 and 2 in subgroup B. (*p = 0.036)
Fig. 3
Fig. 3
Boxplots showing the cumulative V12Gy of the healthy brain minus planning target volume (PTV) for the different scenarios for all plans and the subgroups separately. (* significant at p < 0.05)
Fig. 4
Fig. 4
Boxplots showing the Paddick conformity index (CI), gradient index (GI), the number of missing GIs and the normalized number of missing GIs for the different scenarios for all plans and the subgroups separately. (* significant at p < 0.05)
Fig. 5
Fig. 5
Dose distribution of a patient with 17 lesions for plans according to the scenarios 2, 3 and 4 with an energy of 6 MV (upper row) and scenarios 2 and 3 for 6 MV flattening filter free beams (FFF; lower row). The effects of a larger margin in scenario 4 for more distant metastases can be seen for the lesion in the left hemisphere
Fig. 6
Fig. 6
Number of monitor units needed for 6X FFF compared with 6X and number of monitor units needed for 6X FFF divided by the number of monitor units for 6X in dependence of the distance from the center of the lesion to the isocenter
Fig. 7
Fig. 7
The upper row shows the dose distributions of a plan where extra arcs were added to the lesions farthest from isocenter, the lower row shows scenario 2 with extra arcs for the largest lesions
Fig. 8
Fig. 8
Dose distribution of a patient with 28 lesions for plans according to the scenarios 2, 3 and 4 with an energy of 6 MV (upper row) and scenarios 2 and 3 for 6 MV flattening filter free beams (FFF; lower row)
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