Elongated beamlets: a simple technique for segment and MU reduction for sMLC IMRT delivery on accelerators utilizing...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• Intensity-modulated radiation therapy (IMRT) is a standard technique for prostate cancer treatment.
• Optimizing IMRT plans involves balancing dose conformity, treatment efficiency, and patient safety.
• Current planning often utilizes square beamlets, which may lead to increased treatment complexity.

Purpose of the Study:

• To evaluate the efficacy of using elongated beamlets in IMRT for prostate cancer.
• To compare dose conformity and treatment efficiency between elongated and square beamlets.
• To determine if elongated beamlets can maintain clinical acceptance criteria while reducing treatment parameters.

Main Methods:

• Ten prostate cancer patient plans were created using IMRT.
• Three beamlet configurations were used: 5x5 mm² (default), 10x5 mm² (parallel to prostate-rectum interface), and 10x5 mm² (perpendicular to prostate-rectum interface).
• Plans were evaluated for dose distribution metrics (R65, R40, conformity index), number of segments, monitor units (MU), and modified modulation scaling factor (MSFmod).

Main Results:

• Both elongated beamlet schemes reduced the average number of segments by approximately 49%.
• The total MU required decreased by about 34.6%, and MSFmod decreased by 34.3%.
• Elongated beamlets oriented perpendicular to the prostate-rectum interface (scheme 2) met clinical acceptance criteria without degrading dose distribution compared to the default scheme.

Conclusions:

• Strategically oriented elongated beamlets can achieve dose conformity and critical structure sparing similar to 5x5 mm² beamlets.
• This technique reduces MSFmod, leading to decreased patient leakage dose and shorter treatment times.
• Elongated beamlets offer a viable method for optimizing IMRT delivery in prostate cancer treatment.