Fraction-variant beam orientation optimization for spatiotemporal fractionation schemes

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Spatiotemporal fractionation (STF) aims to deliver partial hypofractionation to tumors while ensuring uniform fractionation in surrounding normal tissues.
• This technique involves distinct dose distributions across multiple fractions, targeting complementary tumor regions with high doses and sparing normal tissues.

Purpose of the Study:

• To extend STF schemes by incorporating non-coplanar beam orientations for each fraction.
• To investigate the potential benefits of varied beam angles in STF for treating different target volume regions.

Main Methods:

• Developed a novel biologically effective dose (BED)-based direct aperture optimization (DAO) algorithm for STF treatments.
• Optimized multiple dose distributions, multileaf collimated apertures, and monitor unit weights simultaneously for each fraction.
• Implemented fraction-specific non-coplanar dynamic trajectories with 360° gantry arcs and dynamic couch rotation.
• Demonstrated the approach using stereotactic body radiotherapy (SBRT) for liver metastases and stereotactic radiotherapy (SRT) for arteriovenous malformation (AVM).

Main Results:

• STF treatments achieved highly non-uniform dose distributions tailored to specific fractions.
• Fraction-specific non-coplanar trajectories led to significant reductions in mean liver BED3 (13.7%) and brain BED2 (18.4%) compared to coplanar VMAT.
• These improvements were observed for both liver metastases and AVM cases, maintaining target coverage.

Conclusions:

• Selecting different non-coplanar beam orientations in each fraction enhances the dosimetric quality of STF treatments.
• This approach offers significant advantages for treating specific regions within the target volume, improving therapeutic ratio.