Dosimetric comparison of linear accelerator-based stereotactic radiosurgery systems

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• Stereotactic radiosurgery (SRS) utilizes 3-D narrow photon beams for intracranial lesion irradiation, avoiding surgery.
• Linear accelerator-based SRS systems (X-Knife) employ tertiary collimators like circular cones and micro multileaf collimators (mMLC).

Purpose of the Study:

• To compare dosimetric characteristics (output factor, tissue maximum ratio, off-axis ratio) of different collimators used in SRS.
• To validate the suitability of mMLC-based SRS systems for clinical use.

Main Methods:

• Measured output factor (S(t)), tissue maximum ratio (TMR), and off-axis ratio (OAR) for BrainLab/Radionics circular cones and BrainLab mMLC.
• Utilized ionization chambers (CC01, Pinpoint, Markus), thermoluminescent dosimeters (TLD), and radiochromic film for measurements.
• Compared measured data with existing data for other mMLC X-Knife systems.

Main Results:

• Ionization chamber measurements indicated no need for further reduction in chamber size for SRS/SRT dosimetry.
• Output factors for BrainLab and Radionics cones were similar, but differed from mMLC fields.
• TMR values were comparable across all three SRS systems.
• OARs for Radionics cone and BrainLab mMLC were within 2%, and BrainLab cone OARs were within 4%.

Conclusions:

• Dosimetric characteristics of mMLC-based SRS systems are comparable to traditional cone-based systems.
• The transition to mMLC for SRS/SRT is supported by these dosimetric findings.
• mMLC offers a viable alternative for precise intracranial radiotherapy delivery.