In Vitro α/β Ratio Variations in Cervical Cancer, with Consequent Effects on Equivalent Dose in 2 Gy Fraction in...

Area of Science:

• Radiation Oncology
• Medical Physics
• Gynecologic Oncology

Background:

• The alpha/beta (α/β) ratio is a critical parameter in radiobiology, influencing treatment planning and outcome prediction.
• Accurate α/β values are essential for dose calculations, particularly in complex treatments like high-dose-rate brachytherapy (HDR-BT) for cervical cancer.

Purpose of the Study:

• To analyze the distribution of published in vitro α/β values for cervical cancer.
• To determine the impact of α/β value variability on the equivalent dose in 2 Gy fractions (EQD₂) calculations in HDR-BT.
• To provide data-driven recommendations for α/β value selection in cervical cancer treatment planning.

Main Methods:

• Systematic analysis of 98 published α/β values from 31 studies across 23 cervical cancer cell lines.
• Statistical fitting of probability distributions (log-normal) to α/β values, stratified by histology (squamous cell carcinoma, adenocarcinoma).
• Application of derived α/β distributions to representative HDR-BT and external beam therapy (EBT) prescriptions to quantify EQD₂ uncertainties.

Main Results:

• Published α/β values ranged from 1.06 to 34.3 Gy, best fit by a right-skewed log-normal distribution.
• The most probable α/β value for cervical cancer was approximately 4.3 Gy (4.25 Gy for SCC, 4.22 Gy for adenocarcinoma).
• Variability in α/β values introduced significant uncertainties in EQD₂ (ranging from -8.0 to 46.4 Gy), with potential deviations up to 10 Gy and average variations of 8% for a 83.9 Gy EQD₂ prescription.

Conclusions:

• Significant heterogeneity exists in in vitro α/β values for cervical cancer, best represented by a right-skewed log-normal distribution with a most probable value around 4.3 Gy.
• Lower α/β values, characteristic of many cervical cancers, lead to higher EQD₂ compared to higher α/β values, emphasizing the need for precise determination.
• The study underscores the importance of utilizing accurate and potentially lower α/β values for cervical cancer to refine HDR-BT dose prescriptions and improve therapeutic outcomes.