Main Session

Sep 29

PQA 07 - Head and Neck Cancer, Lung Cancer/Thoracic Malignancies, and Nursing and Supportive Care

3667 - Linear Energy Transfer-Guided Optimization Enhances High-LETd Coverage in Carbon-Ion Radiotherapy for Locally Advanced Non-Small Cell Lung Cancer

03:45pm - 05:00pm ET

Poster Hall - Exhibit Hall A

Screen: 28

POSTER

Presenter(s)

Kailiang Wu, MD, PhD - Fudan University Shanghai Cancer Center, Shanghai, Shanghai

K. Wu¹, Y. Su², W. Wang², W. C. Hsi², and Y. Li³; ¹Department of Radiation Oncology, Shanghai Proton and Heavy Ion Center, Fudan University Cancer Hospital, Shanghai, China, ²Department of Medical Physics, Shanghai Proton and Heavy Ion Center, Shanghai, China, ³Department of Radiation Oncology, Shanghai Proton and Heavy Ion Center, Shanghai, China

Purpose/Objective(s):

Prior studies indicate that dose-averaged linear energy transfer (LETd) within the internal gross tumor volume (iGTV) correlates with local control of patients with locally advanced non-small cell lung cancer (LA-NSCLC) underwent carbon-ion radiotherapy (CIRT). This study investigates an in-house LET-guided optimization framework for increasing high-LETd coverage of IGTV.

Materials/Methods:

Using the LET-guided optimization, we re-optimized treatment plans of 10 LA-NSCLC patients who experienced local recurrence after the CIR. The LETd modulation was performed by adjusting the maximum relative-biological-effectiveness (RBEmax) of local effect model (LEM) across different LETd intervals. This approach reduced the RBE doses to be in low-LETd =52 keV/µm regions without applying direct LETd constraints. Dosimetric parameters for targets (Dmean, D2%, D50%, D95%, D98%, HI) and organs at risk (Dmean, Dmax, Vx), along with LETd parameters (mean, minimum, percentile LETd; Vx keV/µm; L1cc), were compared between original and optimized plans. Continuous variables are presented as medians with interquartile ranges (IQRs). Normality was assessed with the Shapiro–Wilk test; paired t-tests or Wilcoxon signed-rank tests were used as appropriate, with significance set at *p* < 0.05.

Results:

Compared to original plans, optimized plans exhibited significantly higher LETd values within the iGTV (p < 0.001). The median minimum LETd increased from 29.31 keV/µm (IQR 27.69–31.40) to 38.24 keV/µm (IQR 32.71–39.30; p < 0.001). High-LETd coverage also improved: median LETd98% rose from 36.69 keV/µm (IQR 34.36–38.30) to 44.26 keV/µm (IQR 42.52–45.32; p < 0.001), and V40 keV/µm increased from 92.35% (IQR 88.30–95.82) to 99.94% (IQR 99.39–99.97; p = 0.002). Additionally, median V45 keV/µm improved from 70.48% (IQR 51.96–83.92) to 84.29% (IQR 70.97–93.80; p = 0.0115), providing complementary insight into LETd distribution variability.

Conclusion:

LET-guided optimization successfully achieved the desired LETd parameter values while maintaining target RBE-dose coverage and normal tissue RBE-doses with minimal variation to original plans. Although the V45 keV/µm shows the similar variability as original plan, the underscoring value of V45 keV/µm will be further analysed through the parameter-fitting data.