Selection Strategy of Jaw Tracking in VMAT Planning for Lung SBRT

Wuji Sun; Yinghua Shi; Yu Li; Chao Ge; Xu Yang; Wenming Xia; Kunzhi Chen; Libo Wang; Lihua Dong; Huidong Wang

doi:10.3389/fonc.2022.820632

Selection Strategy of Jaw Tracking in VMAT Planning for Lung SBRT

Front Oncol. 2022 Feb 8:12:820632. doi: 10.3389/fonc.2022.820632. eCollection 2022.

Authors

Wuji Sun¹, Yinghua Shi¹, Yu Li¹, Chao Ge¹, Xu Yang¹, Wenming Xia¹, Kunzhi Chen¹, Libo Wang¹, Lihua Dong^{1

2

3}, Huidong Wang^{1

2}

Affiliations

¹ Department of Radiation Oncology and Therapy, The First Hospital of Jilin University, Changchun, China.
² Jilin Provincial Key Laboratory of Radiation Oncology and Therapy, Department of Radiation Oncology and Therapy, The First Hospital of Jilin University, Changchun, China.
³ National Health Commission (NHC) Key Laboratory of Radiobiology, School of Public Health, Jilin University, Changchun, China.

Abstract

Purpose: This study aimed to investigate the dosimetric effect and delivery reliability of jaw tracking (JT) with increasing planning target volume (PTV) for lung stereotactic body radiation therapy (SBRT) plans. A threshold of PTV was proposed as a selection criterion between JT and fixed-jaw (FJ) techniques.

Methods: A total of 28 patients with early-stage non-small-cell lung cancer were retrospectively included. The PTVs ranged from 4.88 cc to 68.74 cc, prescribed with 48 Gy in four fractions. Three-partial-arc volumetric modulated arc therapy (VMAT) plans with FJ and with JT were created for each patient with the same optimization objectives. These two sets of plans were compared using metrics, including conformity index (CI), V_50%, R_50%, D_2cm, dose-volume parameters of organs at risk, and monitor units (MUs). The ratio of small subfields (<3 cm in either dimension), %SS, was acquired as a surrogate for the small-field uncertainty. Statistical analyses were performed to evaluate the correlation between the differences in these parameters and the PTV.

Results: The V_50%, R_50%, D_2cm, and V_20Gy, D_1,500cc, and D_1,000cc of the lung showed a statistically significant improvement in JT plans as opposed to FJ plans, while the number of MU in JT plans was higher by an average of 1.9%. Between FJ and JT plans, the PTV was strongly correlated with the differences in V_50%, moderately correlated with those in V_20Gy of the lung, and weakly correlated with those in D_2cm and D_1,500cc of the lung. By using JT, %SS was found to be negatively correlated with the PTV, and the PTV should be at least approximately 12.5 cc for an expected %SS <50%, which was 15 cc for a %SS <20% and 20 cc for a %SS <5%.

Conclusions: Considering the dosimetric differences and small-field uncertainties, JT could be selected using a PTV threshold, such as 12.5, 15, or 20 cc, on the basis of the demand of delivery reliability for lung SBRT.

Keywords: jaw tracking technique; planning target volume; small field; stereotactic body radiation therapy; volumetric modulated arc therapy.