Efficacious patient-specific QA for Vertebra SBRT using a high-resolution detector array SRS MapCHECK: AAPM TG-218...

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Vertebra stereotactic body radiation therapy (SBRT) involves highly modulated small fields, creating challenges for patient-specific quality assurance (PSQA) due to steep dose gradients.
• Accurate PSQA is critical to ensure effective treatment delivery and minimize toxicity to the spinal cord.

Purpose of the Study:

• To evaluate the efficacy of the SRS MapCHECK® (SRSMC) device for PSQA in vertebra SBRT.
• To explore the correlation between plan complexity metrics and measurement accuracy.
• To establish appropriate tolerance and action limits for SRSMC in vertebra SBRT PSQA based on AAPM TG-218 methodology.

Main Methods:

• Forty vertebra SBRT plans (M-MLC and HD-MLC) were analyzed.
• Measurements were performed using Gafchromic EBT3 film and SRSMC in the StereoPHAN phantom.
• Plan complexity was assessed using MCS, EM, modulation factor, and ALPO; dose gradients were analyzed; and TG-218 methodology was applied to derive SRSMC-specific limits.

Main Results:

• SRSMC demonstrated accurate measurement of high dose gradients, comparable to film (R² > 0.86).
• No significant correlation was found between film and SRSMC gamma-pass rates (p > 0.05).
• HD-MLC plans exhibited steeper dose gradients than M-MLC plans.
• SRSMC-specific tolerance (97%) and action (96%) limits for 4%/1mm (β=6) were determined.

Conclusions:

• The SRS MapCHECK® is a suitable tool for vertebra SBRT PSQA.
• Standard AAPM TG-218 limits may not be optimal for vertebra SBRT; process-based limits are recommended.
• Implementation of TG-218 methodology allows for the establishment of specific, effective action and tolerance limits for SRSMC in vertebra SBRT.