# Segmented jaw‐locking in IMRT for upper thoracic esophageal cancer: A plan complexity‐driven approach to lung dose reduction

## TL;DR

This study introduces a new radiotherapy planning method for esophageal cancer that reduces lung dose while maintaining treatment effectiveness.

## Contribution

The study introduces a novel IMRT planning strategy (SJL-IMRT) that reduces lung dose without compromising target coverage.

## Key findings

- SJL-IMRT lowers geometric complexity and improves dose fall-off compared to EF-IMRT.
- SJL-IMRT significantly reduces mean lung dose and lung complication probabilities.
- SJL-IMRT plans have higher delivery accuracy and more compact high-dose areas.

## Abstract

Extended‐field intensity‐modulated radiotherapy (EF‐IMRT) used for elective nodal irradiation (ENI) in upper thoracic esophageal cancer frequently results in excessive intermediate‐to‐low‐dose pulmonary irradiation. This study presented a practical and reproducible planning strategy (segmented Jaw‐locking IMRT, SJL‐IMRT) for optimizing dose distributions to ENI target volumes, and assessed its impact on plan complexity and lung parenchyma sparing.

In a paired planning study (n = 40), EF‐IMRT and SJL‐IMRT plans were generated per patient under identical target coverage objectives. SJL‐IMRT partitioned the longitudinal ENI volume into cervical‐supraclavicular and upper‐mediastinal segments via coordinated orthogonal collimators, and multi‐leaf collimator (MLC)‐defined apertures locked within each segment. The evaluation was based on multifaceted criteria, including metrics for: (i) plan complexity: the aperture‐based edge‐area metric (EAM) and the sequence‐level modulation complexity score (MCS); (ii) dosimetry: conformity index (CI), homogeneity index (HI), gradient measure (GM), pulmonary parameters (mean lung dose [MLD], V5∼V30), and spinal cord maximum dose (Dmax); (iii) radiobiological effects: tumor control probability (TCP) and normal tissue complication probability (NTCP). The delivery accuracy of SJL‐IMRT and EF‐IMRT was validated with a PTW OCTAVIUS 729 2D ionization chamber array and RW3 phantom, using γ analysis (3.0%/3.0 mm criterion, global normalization, 10% dose threshold). Statistical analysis was performed using Wilcoxon signed‐rank test.

Both SJL‐IMRT and EF‐IMRT satisfied prescription dose objectives for planning target volume (PTV). No significant differences were observed in CI and HI (p = 0.347 and p = 0.173, respectively). SJL‐IMRT demonstrated lower geometric complexity and simpler sequencing: EAM 8.610 ± 2.951 vs. 20.824 ± 4.944 (paired Δ = −12.214; p = 0.00195) and MCS 0.243 ± 0.015 vs. 0.203 ± 0.036 (paired Δ = +0.040; p = 0.0193), respectively. Compared with EF‐IMRT, SJL‐IMRT (i) reduced gradient measures (GM) by 0.215 cm (p < 0.01), indicating a steeper dose fall‐off; (ii) decreased MLD by 1.62 Gy (left) and 2.64 Gy (right); (iii) lowered left lung V5 and V20 by 19.96%, 3.63%, right lung V5 and V20 by 25.27%, 3.05%, respectively (all p < 0.01); (iv) exhibited a marginally higher mean γ passing rate (99.4 ± 0.72% vs. 98.8 ± 0.75%, p = 0.048), no dose cold/hot spots in the 2‐cm feathered overlap, and a more compact high‐dose area; (v) demonstrated a longer mean delivery time (10.9 vs. 8.8 min, p = 0.021) and higher total monitor units (MUs: 2893 vs. 2066; p = 0.026). (vi) translated these dosimetric gains into significant NTCP reductions for both lungs (left −1.30%, right −1.29%; p < 0.01). TCP values were numerically higher for SJL‐IMRT, but these differences were not statistically significant; Dmax to the spinal cord followed the same pattern.

SJL‐IMRT reduces plan complexity (EAM↓, MCS↑) and lowers intermediate‐to‐low lung dose compared with EF‐IMRT for ENI in upper thoracic esophageal cancer, without compromising target coverage, supporting SJL‐IMRT as a pragmatic approach to improving dosimetric quality and delivery simplicity. Confirmation in larger cohorts is warranted.