In vitro measurement of proton RBE: A multi-centric comparison using a harmonized setup

Area of Science:

• Medical physics
• Radiobiology
• Radiation oncology

Background:

• Harmonized experimental conditions are crucial for multi-center studies in proton therapy.
• Inter-institutional variability can impact the reliability of radiobiological data.
• Accurate relative biological effectiveness (RBE) calculations are essential for precise proton therapy.

Purpose of the Study:

• To compare in vitro cell survival measurements and RBE calculations across six European institutions.
• To assess the impact of harmonized experimental conditions on proton irradiation outcomes.
• To identify challenges in large-scale, multi-center radiobiological experiments.

Main Methods:

• V79-4 cells were irradiated using spread-out Bragg peak (SOBP) proton fields at two dose levels (6 and 8 Gy).
• Standardized protocols and identical phantom designs were used across all participating centers.
• X-ray reference irradiations were performed to determine cell radiosensitivity.

Main Results:

• Significant inter-institutional variability in cell survival measurements was observed, particularly at the distal edge of the SOBP.
• Coefficients of variation reached 43% and 60% for the 6 Gy and 8 Gy plans, respectively.
• Discrepancies in calculated RBE data were noted, though the trend of increasing RBE towards the distal edge was preserved.

Conclusions:

• Minimal biological variation is expected under well-aligned experimental conditions.
• Conducting large-scale, multi-center radiobiological experiments presents significant challenges.
• Inter-comparison of literature data sets requires careful consideration of experimental variability.