Patient-specific quality assurance and plan dose errors on breast intensity-modulated proton therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• Proton therapy offers precise dose delivery.
• Intensity-modulated proton therapy (IMPT) requires accurate dose calculations.
• Patient-specific quality assurance (QA) is crucial for verifying treatment plans.

Purpose of the Study:

• To determine if Gamma passing rate (GPR) correlates with patient dose error in proton therapy.
• To evaluate if monitor unit (MU) scaling can enhance dose accuracy in IMPT.
• To compare dose errors between plans passing and failing Gamma testing.

Main Methods:

• Retrospective analysis of 20 breast cancer patients treated with IMPT.
• Generation of both pencil-beam (PB) and Monte Carlo (MC) treatment plans.
• Patient-specific QA using 3%/3-mm Gamma analysis to compare calculated vs. measured doses.
• MU scaling applied to improve GPR and subsequent dose error comparison.

Main Results:

• Surprisingly, plans passing Gamma testing exhibited greater dose errors than those that failed.
• MU scaling generally reduced overall dose errors but negatively impacted PTV D99 and D95 in some instances.
• Significant differences in PTV DVH RMSE and PTV ΔDmean were observed between passing and failing groups.

Conclusions:

• Gamma passing rate is not a reliable indicator of reduced dose error for breast IMPT using PB algorithms.
• MU scaling can improve overall dose accuracy for individual plans but requires careful consideration of specific dose metrics.
• Monte Carlo-based plans are recommended over MU-scaled PB plans when MC algorithms are available.