# Comparative dosimetric evaluation of single-beam dual-arc versus dual-beam single-arc volumetric modulated arc therapy strategies in lung stereotactic body radiotherapy using Monaco

## TL;DR

This study compares two VMAT strategies for lung cancer SBRT and finds that the dual-beam single-arc approach provides better dose distribution and efficiency.

## Contribution

The paper introduces a direct comparison of 1B2A and 2B1A VMAT strategies in lung SBRT using the Monaco system.

## Key findings

- The 2B1A strategy showed significantly lower high-dose parameters for ITV and PTV compared to 1B2A.
- The 1B2A plan required higher monitor units and had greater complexity, indicating lower treatment efficiency.
- Minimal and clinically insignificant differences were found in low-dose lung sparing and OAR dose sparing.

## Abstract

In stereotactic body radiotherapy (SBRT) for lung cancer, the choice of volumetric modulated arc therapy (VMAT) optimization strategy is critical for achieving optimal target dose coverage while minimizing exposure to normal tissues. This study aims to compare the dosimetric performance and plan complexity of two VMAT optimization strategies in Monaco: single-beam dual-arc (1B2A) versus dual-beam single-arc (2B1A).

A retrospective analysis was conducted on 50 lung cancer patients treated with SBRT (prescription dose: 50 Gy in 5 fractions). Two VMAT plans were re-optimized using the Monaco treatment planning system: the 1B2A plan (single-beam dual-arc, collimator angle 10°) and the 2B1A plan (dual-beam single-arc, collimator angles 10° and 350°). Dosimetric parameters, including target dose coverage, conformity index (CI), and gradient index (GI), were evaluated for the internal target volume (ITV) and planning target volume (PTV). Dose metrics for organs at risk (OARs) were also analyzed. Plan complexity was assessed based on monitor units (MU), number of control points, complexity index, and integral dose to normal tissues.

Significant dosimetric differences were observed between the two strategies. When normalized to ensure the prescribed 50 Gy isodose line covers 95% of the PTV volume, the high-dose parameters (D1%, D50%, Dmean) of the ITV and PTV were significantly lower in the 1B2A group compared to the 2B1A group (p < 0.001), indicating superior dose distribution with the 2B1A approach. Although the 1B2A plan exhibited marginally better CI, GI, and low-dose lung sparing (V5–V30), these differences were minimal and clinically insignicant. No substantial dierences were found in the dose sparing of other OARs, including the spinal cord, heart, and ribs. Additionally, the 1B2A plan required signicantly higher MU (+15.5%, p < 0.001) and had greater plan complexity (+9.47%, p < 0.001), suggesting lower treatment efficiency.

In peripheral lung cancer SBRT, the dual-beam single-arc (2B1A) strategy offers superior target dose distribution and treatment efficiency, making it a preferable optimization approach.