Intrafraction geometric uncertainties in frameless image-guided radiosurgery.

Area of Science:

• Radiation Oncology
• Medical Physics
• Neurosurgery

Background:

• Frameless radiosurgery enables precise radiation delivery but is susceptible to intrafraction patient movement.
• Movement during treatment can lead to underdosage of the target volume.
• Accurate target coverage is crucial for effective radiosurgery outcomes.

Purpose of the Study:

• To compare alignment errors and their impact on target coverage between fixed and dynamic alignment techniques in frameless radiosurgery.
• To evaluate the effectiveness of intrafraction corrections in mitigating movement-related underdosage.

Main Methods:

• Analysis of 577 records of intrafraction patient movement during frameless cranial and spinal radiosurgery.
• Calculation of average misalignment per fraction.
• Estimation of necessary planning margins using hyperfractionated radiotherapy formulae to maintain target coverage.

Main Results:

• Dynamic alignment reduced fractions with >2 mm mean misalignment from ~20% to near zero.
• Estimated optimal margins for fixed alignment were 3.6-4.5 mm.
• Estimated optimal margins for dynamic alignment were 1.2-1.6 mm.

Conclusions:

• Dynamic alignment effectively corrects for systematic intrafraction shifts, significantly reducing required planning margins.
• Margins for dynamic alignment approach traditional radiosurgery tolerances, while fixed alignment requires margins three times larger.
• Intrafraction motion substantially impacts target coverage, highlighting the benefit of dynamic alignment strategies.