mARC prostate treatment planning with Varian Eclipse for flat vs. FFF beams

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• The modulated arc (mARC) technique is a rotational intensity-modulated radiation therapy (IMRT) delivery method utilizing burst mode.
• Varian's Eclipse treatment planning system (TPS) now includes an mARC planning option, necessitating systematic evaluation.
• Flattening-filter-free (FFF) beams offer potential advantages in radiation delivery efficiency and dose reduction.

Purpose of the Study:

• To systematically evaluate the mARC technique for prostate cancer treatment planning using the Eclipse TPS.
• To compare mARC with conventional IMRT using both 6MV and flattening-filter-free (FFF) 7MV beam energies.
• To assess plan quality, organ-at-risk sparing, out-of-field dose, and treatment delivery times.

Main Methods:

• Ten prostate cancer patients underwent standardized re-contouring and re-planning to 76Gy.
• Intensity-modulated radiation therapy (IMRT) and mARC plans were created using 6MV and FFF 7MV beams.
• Plans were compared based on plan quality indices, and delivered on an anthropomorphic phantom for dosimetry and time measurements.

Main Results:

• No significant difference in planning-target-volume (PTV) coverage between mARC and IMRT techniques.
• mARC demonstrated improved bladder sparing up to 75Gy; IMRT showed better sparing above this dose.
• The combination of FFF 7MV beams and mARC significantly reduced out-of-field dose and treatment time by a factor of three compared to 6MV IMRT.

Conclusions:

• All investigated modalities produced highly conformal treatment plans.
• The combination of high dose rate FFF beams with mARC is the preferable option for prostate cancer radiotherapy.
• This preferred approach offers significant reductions in treatment time and out-of-field dose.