SU-E-T-413: Dose Verification for Linac-Based SRS Commissioning and Patient Specific QA

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Stereotactic radiosurgery (SRS) program commissioning and quality assurance (QA) traditionally rely on specialized phantoms like the Radiological Physics Center (RPC) Head Neck phantom with TLDs.
• Limited accessibility of the RPC Head Neck phantom restricts routine QA and patient-specific dose verification in many clinics.

Purpose of the Study:

• To propose and validate a simplified SRS dose verification method using widely available clinical instruments.
• To enable both SRS commissioning and patient-specific dose verification.

Main Methods:

• SRS treatment plans were applied to a 14cm solid water phantom with an embedded PTW micro-chamber.
• Treatment couch angles were adjusted to minimize micro-chamber angle dependence and avoid collisions.
• Arc verification plans were recalculated and compared to micro-chamber measurements.
• End-to-end tests using a CyberKnife Head Neck phantom and GAFChromic film served as secondary verification.

Main Results:

• Micro-chamber measurements agreed with calculations within 3% for cone sizes from 10mm to 30mm.
• A 10% underdose was detected with a 5mm cone size, highlighting potential inaccuracies with small cones.
• CyberKnife phantom measurements confirmed dose delivery accuracy within 5%.

Conclusions:

• A straightforward SRS dose verification method employing a micro-chamber and conventional solid water phantom has been successfully presented and validated.
• This accessible approach is valuable for SRS commissioning and ongoing quality assurance.