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Comparative Study
. 2025 Mar;43(3):520-529.
doi: 10.1007/s11604-024-01686-1. Epub 2024 Nov 6.

Optimizing normal tissue objectives (NTO) in eclipse treatment planning system (TPS) for stereotactic treatment of multiple brain metastases using non-coplanar RapidArc and comparison with HyperArc techniques

Sivakumar Muthu  1   2 , Gopinath Mudhana  3
Affiliations
Comparative Study

Optimizing normal tissue objectives (NTO) in eclipse treatment planning system (TPS) for stereotactic treatment of multiple brain metastases using non-coplanar RapidArc and comparison with HyperArc techniques

Sivakumar Muthu et al. Jpn J Radiol. 2025 Mar.

Abstract

Purpose: To optimize NTO parameters in non-coplanar RapidArc (RA) stereotactic radiosurgery (SRS) for multiple brain metastases and compare them with HyperArc (HA) plans.

Materials and methods: Thirty patients with multiple brain metastases, receiving 21 Gy prescriptions, were retrospectively enrolled, with lesions ranging from two to eight and volumes between 0.27 and 10.56 cm3. Non-coplanar RapidArc plans utilized manual NTO (RA-mNTO) with varying dose fall-off values (0.1 mm-1, 0.5 mm-1, 1.0 mm-1, 2.0 mm-1, 3.0 mm-1) and end doses (50%, 25% & 10%). Additionally, two HyperArc plans were generated: HA-ALDO used Automatic Lower Dose Objectives with SRS NTO, while HA-mNTO used the same beam geometry with manual NTO parameters optimized from RA-mNTO plans. TrueBeam with High-Definition Multi-leaf Collimators (HDMLC), 6 MV Flattening Filter Free (FFF) Beam at a maximum dose rate of 1400 MU/min, and Eclipse version 16.1 TPS were used. Plans were assessed for Paddick Conformity Index (CI), Gradient Index (GI), Homogeneity Index (HI), normal brain doses (V18Gy, V15Gy, and V12Gy), Monitor Units (MUs), and delivery accuracy using aS1200 Digital Megavolt Imager (DMI) with 2%/2 mm gamma criteria. Statistical analysis utilized integrated scoring and the Wilcoxon signed-rank test.

Results: RA-mNTO plans with 0.5 mm⁻1 dose fall-off and 10% end-dose showed superior dosimetric outcomes: CI (0.85 ± 0.08), GI (3.63 ± 0.87), and HI (0.36 ± 0.06) compared to HA-ALDO (CI 0.84 ± 0.09, GI: 3.97 ± 0.85, HI: 0.39 ± 0.07) and HA-mNTO (CI 0.83 ± 0.08, GI: 3.60 ± 0.93, HI: 0.40 ± 0.06). MUs were comparable: RA-mNTO (9679 ± 1882), HA-ALDO (9509 ± 1315), and higher for HA-mNTO (10,457 ± 1980). RA-mNTO plans exhibited significantly lower normal brain doses (V18Gy: 1.78 ± 1.23, V15Gy: 3.54 ± 2.37, V12Gy: 6.21 ± 4.09) compared to HA-ALDO (V18Gy: 2.02 ± 1.34, V15Gy: 4.09 ± 2.66, V12Gy: 7.15 ± 4.56) and HA-mNTO (V18Gy: 1.85 ± 1.20, V15Gy: 3.68 ± 2.33, V12Gy: 6.36 ± 3.97). All techniques achieved > 98% gamma pass rate.

Conclusion: Non-coplanar RA plans with optimized mNTO settings outperformed HyperArc plans in all studied dosimetric parameters for SRS treatment of multiple brain metastases.

Keywords: Eclipse TPS; HyperArc; Non-coplanar RapidArc; Normal tissue objectives; Stereotactic radiosurgery.

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Conflict of interest statement

Declarations. Conflict of interest: All authors involved in this study declare no conflicts of interest regarding the manuscript. Ethics approval: No human or animal studies were involved, so ethical approval is not applicable.

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