Validation of a modern second-check dosimetry system using a novel verification phantom.

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate radiation dose calculation is critical in modern cancer treatment.
• Independent verification of treatment planning systems (TPS) enhances patient safety.
• The Mobius second-check dosimetry system offers an independent dose calculation and verification solution.

Purpose of the Study:

• To evaluate the Mobius second-check dosimetry system's accuracy by comparing its calculations to ionization-chamber measurements.
• To compare Mobius calculations against the Varian Eclipse treatment planning system (TPS) with the AcurosXB dose algorithm.
• To assess the clinical performance of the Mobius system by comparing patient doses calculated by Mobius and Eclipse.

Main Methods:

• Seventeen intensity-modulated clinical treatment plans were analyzed.
• Dose was recalculated using Mobius and Eclipse on the Mobius Verification Phantom™ (MVP).
• Calculated doses were compared to measurements from an A1SL ionization chamber in the MVP. Gamma analysis and dose metrics (target mean dose, D95%) were used for comparison.

Main Results:

• Mobius dose calculations agreed with measurements with an average difference of 0.3 ± 1.3%.
• Varian Eclipse calculations showed an average difference of -1.2 ± 0.7% compared to measurements.
• For pre-clinical cases, Mobius and Eclipse target mean dose differed by 1.0 ± 1.1%, with an average global gamma pass rate of 94.4% (3%, 2mm criteria).

Conclusions:

• The Mobius system accurately calculates dose, agreeing with measurements within 3.5% across all tested intensity-modulated plans.
• The Mobius system's dose calculation accuracy and independence make it suitable for rigorous second-check verification of TPS.
• Clinical implementation results were consistent with pre-clinical findings, demonstrating the system's reliability in practice.