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Technical Note: Spot characteristic stability for proton pencil beam scanning.

Chin-Cheng Chen¹, Chang Chang¹, Michael F Moyers²

¹ProCure Treatment Center, Somerset, New Jersey 08873.

Medical Physics

|February 5, 2016

Summary

Proton pencil beam scanning (PBS) spot characteristics were analyzed over 16 months. Regular quality assurance checks are recommended after any system updates or interventions to maintain precise beam delivery.

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Area of Science:

Medical Physics
Radiation Oncology
Particle Therapy

Background:

Proton pencil beam scanning (PBS) enables precise radiation delivery.
Consistent quality assurance (QA) is crucial for maintaining the accuracy of PBS systems.

Purpose of the Study:

To analyze proton pencil beam scanning spot characteristics over a 16-month period.
To establish QA frequency and tolerances for PBS based on measured data.

Main Methods:

Generated asymmetric 9-spot patterns for 18 proton energies (100.0-226.0 MeV).
Measured delivered fluence distribution using a CCD camera at three planes.
Analyzed spot sizes and positional deviations using in-house programs.

Main Results:

16-month averaged spot size deviations at isocenter were 2.30% (x) and 1.38% (y).
Positional deviations were within 1.5 mm after isocenter optimization.
A site configuration update caused a 6 mm spot position deviation until parameters were restored.

Conclusions:

Monthly spot size and position checks are recommended for PBS systems.
Perform checks after any database update or cyclotron intervention.
A spot size deviation tolerance of <15% is achievable; positional deviations <2 mm are maintained.