SU-E-T-417: Tomotherapy Isocentricity: Is it Good Enough for Stereotactic Radiosurgery?

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Stereotactic radiosurgery (SRS) demands high precision in radiation delivery.
• Accurate isocenter alignment is critical for effective SRS treatments.

Purpose of the Study:

• To assess the accuracy of the TomoTherapy linear accelerator's radiation beam isocenter relative to its mechanical axis.
• To determine the suitability of the TomoTherapy system for SRS applications.

Main Methods:

• A simplified Winston-Lutz test was performed using a BrainLab pointer on the TomoTherapy couch.
• Four static radiation plans were delivered with specific jaw and multi-leaf collimator (MLC) settings.
• Gafchromic EBT films were used to record radiation delivery, with subsequent image analysis using ImageJ to determine isocenter displacement.

Main Results:

• Isocenter accuracy was evaluated at two distances from the isocenter (11cm and 25cm).
• Average displacements were 0.73mm at 11cm and 0.75mm at 25cm.
• These results indicate precise alignment between the radiation and mechanical isocenters.

Conclusions:

• The TomoTherapy system demonstrates isocenter accuracy within the 1mm tolerance required for SRS.
• The system's performance suggests it is well-suited for stereotactic radiosurgery procedures.