α/β for Hepatocellular Carcinoma Tumors Treated With Radiation Therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Research

Background:

• Fractionated radiation therapy is a common treatment for primary Hepatocellular Carcinoma (HCC).
• The linear-quadratic (LQ) model is crucial for comparing different fractionation schemes and predicting local recurrence rates in HCC tumors.

Purpose of the Study:

• To determine the alpha/beta (α/β) ratio within the LQ model that best predicts recurrence rates for HCC treated with fractionated radiation.
• To analyze lesion-level data and published meta-analysis data to estimate the α/β ratio.

Main Methods:

• Analysis of two datasets: 390 HCC lesions (2008-2021) with factors like GTV, fractionation, DVH, and time between doses.
• Utilized Cox proportional hazards and linear models with autoregressive covariance structure for α/β estimation.
• Meta-analysis of 4,313 lesions from 41 publications on 46 fractionation schemes.

Main Results:

• Lesion-level data suggested an α/β ratio between 37.5-52 Gy, with a wide confidence interval (3.4, ∞).
• Fractionation regimen and elapsed time significantly impacted recurrence hazard (p<0.001), while elapsed time alone did not.
• Meta-analysis yielded an α/β estimate of 161.4 Gy (CI: 4.7, ∞); lower DVH doses were better predictors than mean dose.

Conclusions:

• Both analyses indicate a high α/β ratio (≥37.5 Gy) for HCC, though precise estimation remains challenging.
• For practical purposes, α/β ratios >20 Gy result in similar rankings of fractionation schemes.
• More precise α/β estimates necessitate datasets with more patients receiving fractionated radiation doses of 2.0-2.9 Gy per fraction.