Evaluation of six TPS algorithms in computing entrance and exit doses

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate calculation of radiation doses is crucial for effective cancer treatment delivery.
• Treatment planning systems (TPS) are used to predict radiation doses, and their accuracy must be verified.
• In vivo dosimetry provides a method for verifying treatment accuracy by measuring doses directly on the patient.

Purpose of the Study:

• To evaluate and compare the accuracy of six common TPS algorithms in calculating entrance and exit doses for a 6 MV photon beam.
• To assess the performance of different algorithms using ionization chamber and diode detector measurements in water phantoms.
• To provide a baseline for implementing in vivo dosimetry in clinical settings.

Main Methods:

• Six TPS algorithms were tested: Eclipse PBC, Eclipse AAA, Eclipse AXB, XiO Convolution, XiO Superposition, and Monaco MC.
• Measurements were performed in water phantoms using ionization chambers and diode detectors.
• Comparisons involved central axis point dose, 1D relative profiles, and 2D absolute gamma analysis (3%/3 mm).

Main Results:

• All tested TPS algorithms accurately computed entrance doses within 2% of measured values.
• XiO Convolution, XiO Superposition, Eclipse AXB, and Monaco MC showed good agreement (2%-3%) for exit doses with ionization chamber measurements.
• Eclipse PBC and AAA overestimated exit doses by up to 5.3% and 4.8%, respectively, due to assumptions of full backscatter.
• Monaco MC generally exhibited better 2D gamma pass rates, while Eclipse AXB showed discrepancies in dose profiles beyond 11.5 cm and at field edges.

Conclusions:

• Advanced TPS algorithms like Monaco MC and Eclipse AXB offer improved accuracy for calculating radiation exit doses compared to older algorithms.
• The findings highlight the importance of selecting appropriate TPS algorithms for accurate in vivo dosimetry and treatment verification.
• This study provides valuable data for clinical departments to select and implement TPS algorithms for reliable reference comparisons in radiation therapy.