3D gamma analysis between treatment plans for nominally beam-matched medical linear accelerators using PyMedPhys.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Beam-matched linear accelerators (linacs) are crucial for flexible patient scheduling and efficient radiation therapy delivery, especially during unexpected machine downtime.
• Ensuring accurate dose delivery and patient safety during treatment transfers between matched linacs is paramount.

Purpose of the Study:

• To evaluate the feasibility of using the 3D gamma index as an additional metric for assessing radiation therapy plan consistency between nominally matched linacs.
• To determine if 3D gamma index analysis can improve the efficiency and confidence in evaluating treatment plans for safe patient transfer.

Main Methods:

• Seventeen 3D conformal radiotherapy (3DCRT) and thirty-six volumetric-modulated radiation therapy (VMAT) plans were evaluated.
• An in-house script automated plan creation and dose calculation on a target linac using original plan parameters.
• 3D gamma analysis with 2%/2 mm and 1%/1 mm criteria was performed using PyMedPhys to compare dose distributions.

Main Results:

• All 3DCRT plans achieved >99.99% pass rate for 2%/2 mm gamma criteria. The 1%/1 mm criteria had a median pass rate of 99.86%, with two failures.
• VMAT plans showed median 2%/2 mm and 1%/1 mm pass rates of 99.43% and 92.02%, respectively.
• Ten VMAT cases failed the 1%/1 mm criteria, highlighting potential plan variations.

Conclusions:

• 3D gamma index analysis is a feasible and valuable tool for evaluating treatment plan consistency between beam-matched linacs.
• This method offers an additional layer of confidence for ensuring safe patient transfer and treatment continuity.
• The findings support the integration of 3D gamma index into routine quality assurance protocols for linac networks.