Clinical Comparison of Beam-Specific Planning Target Volume Single-Field Uniform Dose and Robust Intensity-Modulated...

Area of Science:

• Radiation Oncology
• Medical Physics
• Prostate Cancer Treatment

Background:

• Ultra-hypofractionated (UHF) proton therapy offers a shorter treatment course for localized prostate cancer.
• Ensuring plan robustness against various uncertainties is critical for effective treatment delivery.

Purpose of the Study:

• To compare the robustness of beam-specific planning target volume (bs-PTV)-based single-field uniform dose (SFUD) and robustly optimized intensity-modulated proton therapy (IMPT) plans.
• To evaluate plan performance against setup, range, and anatomical uncertainties in UHF proton therapy for prostate cancer.

Main Methods:

• Generated SFUD and IMPT plans for ten prostate cancer patients receiving 36.25 GyE in 5 fractions.
• Simulated 20 error scenarios including isocenter shifts and Hounsfield Unit variations to assess robustness.
• Recalculated doses using virtual CT derived from weekly CBCT to account for anatomical changes.

Main Results:

• Both SFUD and IMPT plans maintained stable target coverage within accepted criteria under all evaluated uncertainties.
• IMPT plans showed smaller dose variations for organs at risk (OARs) and achieved lower low- and intermediate-dose metrics for the rectum and bladder.
• A statistically significant but small difference in worst-case CTV D99 was observed between SFUD and IMPT.

Conclusions:

• Both bs-PTV SFUD and robustly optimized IMPT plans are adequate for UHF proton therapy in prostate cancer.
• IMPT offers a modest dosimetric benefit due to improved OAR sparing and robustness, likely from planning technique and uncertainty management differences.