PETRA: A pencil beam trimming algorithm for analytical proton therapy dose calculations with the dynamic collimation...

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Biology

Background:

• The Dynamic Collimation System (DCS) offers superior proton therapy treatment plans compared to uncollimated pencil beam scanning (PBS).
• Clinical adoption of DCS requires a validated dose calculation algorithm for commercial treatment planning systems (TPS).

Purpose of the Study:

• To introduce the analytical Pencil bEam TRimming Algorithm (PETRA) for DCS proton therapy.
• To implement and validate PETRA within the Astroid TPS, with and without a range shifter.

Main Methods:

• PETRA was developed by adapting an existing pencil beam model to incorporate DCS-specific effects like trimmer blurring and range shifter interactions.
• The algorithm was tuned and validated against a measurement-validated Dynamic Collimation Monte Carlo (DCMC) model.
• Calibration followed IAEA TRS-398 guidelines for monitor unit calculations.

Main Results:

• PETRA demonstrated excellent agreement with DCMC for integral depth dose curves (99.99% pass rate at 1%/1 mm gamma criteria).
• Median 2D gamma pass rates for lateral dose profiles were 99.99% (1.5%/1.5 mm) at various depths.
• Minimum pass rates remained high, exceeding 97.5% even at critical depths.

Conclusions:

• The PETRA algorithm is a robust and validated tool for DCS dose calculations.
• PETRA's successful implementation in a commercial TPS facilitates clinical use of advanced proton therapy techniques.