Validation of the Pinnacle³ photon convolution-superposition algorithm applied to fast neutron beams

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Fast neutron therapy offers unique biological advantages but requires accurate dose calculation.
• Commercial treatment planning systems (TPS) often lack specific models for neutron beams.
• Validating existing TPS for neutron dosimetry is crucial for clinical implementation.

Purpose of the Study:

• To evaluate the accuracy of a photon convolution-superposition algorithm in the Pinnacle3 TPS for modeling a fast neutron therapy beam.
• To compare Pinnacle3's calculated neutron doses with measurements and another TPS (Prism).

Main Methods:

• Modeled the Clinical Neutron Therapy System (CNTS) fast neutron beam using Pinnacle3.
• Acquired measured neutron data using an IC30 ion chamber in a water phantom.
• Compared Pinnacle3 dose profiles, central axis, and off-axis doses against Prism TPS and experimental measurements for various field types.

Main Results:

• Pinnacle3's photon model accurately captured key dosimetric features of the CNTS fast neutron beam.
• Dose differences between Pinnacle3, Prism, and measurements were within 3.9 cGy (central axis) and 5 cGy (penumbra) for open/wedged fields.
• Irregular fields showed dose differences up to 9 cGy, with most points below 5 cGy.
• Clinical case comparisons showed average dose differences <0.6% and clinically acceptable dose-volume histograms and spatial dose distributions.

Conclusions:

• The Pinnacle3 TPS, using its photon convolution-superposition algorithm, is suitable for modeling fast neutron therapy beams.
• The model demonstrates sufficient accuracy for clinical use in treatment planning, with variations within acceptable limits.
• This validates the use of Pinnacle3 for neutron dosimetry, potentially expanding its clinical application in radiation oncology.