Interinstitutional Plan Quality Assessment of 2 Linac-Based, Single-Isocenter, Multiple Metastasis Radiosurgery Techniques

Haisong Liu; Evan M Thomas; Jun Li; Yan Yu; David Andrews; James M Markert; John B Fiveash; Wenyin Shi; Richard A Popple

doi:10.1016/j.adro.2019.10.007

Interinstitutional Plan Quality Assessment of 2 Linac-Based, Single-Isocenter, Multiple Metastasis Radiosurgery Techniques

Adv Radiat Oncol. 2019 Dec 2;5(5):1051-1060. doi: 10.1016/j.adro.2019.10.007. eCollection 2020 Sep-Oct.

Authors

Haisong Liu¹, Evan M Thomas², Jun Li¹, Yan Yu¹, David Andrews³, James M Markert⁴, John B Fiveash², Wenyin Shi¹, Richard A Popple²

Affiliations

¹ Department of Radiation Oncology, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, Pennsylvania.
² Department of Radiation Oncology, University of Alabama at Birmingham, Comprehensive Cancer Center, Birmingham, Alabama.
³ Department of Neurosurgery, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, Pennsylvania.
⁴ Department of Neurosurgery, University of Alabama at Birmingham, Birmingham, Alabama.

Abstract

Purpose: Interest and application of stereotactic radiosurgery for multiple brain metastases continue to increase. Various planning systems are available for linear accelerator (linac)-based single-isocenter multiple metastasis radiosurgery. Two of the most advanced systems are BrainLAB Multiple Metastases Elements (MME), a dynamic conformal arc (DCA) approach, and Varian RapidArc (RA), a volumetric modulated arc therapy (VMAT) approach. In this work, we systematically compared plan quality between the 2 techniques.

Methods and materials: Thirty patients with 4 to 10 metastases (217 total; median 7.5; V_min = 0.014 cm³; V_max = 17.73 cm³) were planned with both Varian RA and MME at 2 different institutions with extensive experience in each respective technique. All plans had a single isocenter and used Varian linac equipped with high-definition multileaf collimator. RA plans used 2 to 4 noncoplanar VMAT arcs with 10 MV flattening filter-free beam. MME plans used 4 to 9 noncoplanar DCAs and 6 MV flattening filter-free beam, (minimum planning target volume [PTV_min] = 0.49 cm³; PTV_max = 27.32 cm³; PTV_median = 7.05 cm³). Prescriptions were 14 to 24 Gy in a single fraction. Target coverage goal was 99% of volume receiving prescription dose (D99% ≥ 100%). Plans were evaluated by Radiation Therapy Oncology Group/Paddick conformity index (CI) score, 12 Gy volume (V_12Gy), V_8Gy, V_5Gy, mean brain dose (D_mean), and beam-on time.

Results: Conformity was favorable among RA plans (median: MME CI^RTOG = 1.38; RA CI^RTOG = 1.21; P < .0001). V_12Gy and V_8Gy were lower for RA plans (median: MME V12 = 23.7 cm³; RA V12 = 19.2 cm³; P = .0001; median: MME V_8Gy = 53.6 cm³; RA V_8Gy = 44.1 cm³; P = .024). V_5Gy was lower for MME plans (median: MME V_5Gy = 141.4 cm³; RA V_5Gy = 142.8 cm³; P = .009). Mean brain was lower for MME plans (median: MME D_mean = 2.57 Gy; RA D_mean = 2.76 Gy; P < .0001).

Conclusions: For linac-based multiple metastasis stereotactic radiosurgery, RapidArc VMAT facilitates favorable conformity and V_12Gy/V_8Gy volume compared with the MME DCA plan. MME planning facilitates reduced dose spill at levels ≤V_5Gy.