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; Gopinath Mudhana

doi:10.1007/s11604-024-01686-1

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

Jpn J Radiol. 2024 Nov 6. doi: 10.1007/s11604-024-01686-1. Online ahead of print.

Authors

Sivakumar Muthu^{1

2}, Gopinath Mudhana³

Affiliations

¹ Department of Physics, School of Advanced Sciences, Vellore Institute of Technology (VIT), Chennai Campus, Vandalur - Kelambakkam Road, Chennai, Tamil Nadu, 600 127, India.
² Department of Radiation Oncology, Sri Shankara Cancer Hospital & Research Centre, Bangalore, 560 004, India.
³ Department of Physics, School of Advanced Sciences, Vellore Institute of Technology (VIT), Chennai Campus, Vandalur - Kelambakkam Road, Chennai, Tamil Nadu, 600 127, India. [email protected].

PMID: 39503823
DOI: 10.1007/s11604-024-01686-1

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 (V_18Gy, V_15Gy, and V_12Gy), 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 (V_18Gy: 1.78 ± 1.23, V_15Gy: 3.54 ± 2.37, V_12Gy: 6.21 ± 4.09) compared to HA-ALDO (V_18Gy: 2.02 ± 1.34, V_15Gy: 4.09 ± 2.66, V_12Gy: 7.15 ± 4.56) and HA-mNTO (V_18Gy: 1.85 ± 1.20, V_15Gy: 3.68 ± 2.33, V_12Gy: 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.