Patient-specific QA for the HyperArc technique using gafchromic film with multiple calibration methods

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Dosimetry

Background:

• Accurate pre-treatment verification is crucial for stereotactic radiotherapy (SRT) to ensure patient safety and treatment efficacy.
• EBT-XD films are widely used for patient-specific quality assurance (QA) in radiotherapy, but require precise calibration.
• The HyperArc (HA) technique offers advanced capabilities for SRT, necessitating robust verification methods.

Purpose of the Study:

• To evaluate and compare three distinct calibration methods for EBT-XD films.
• To develop a precise pre-treatment verification protocol for SRT patients treated with the HyperArc technique.
• To assess the accuracy and reliability of EBT-XD film dosimetry for patient-specific QA.

Main Methods:

• EBT-XD films were calibrated using manual, EDW, and PDD calibration approaches.
• Films were digitized using an Epson V850 Pro scanner under a local scanning protocol.
• Patient-specific QA films were irradiated in phantoms and analyzed using gamma analysis to compare film-derived doses with treatment planning system (TPS) calculations.

Main Results:

• Scan-to-scan variation was minimal (≤ 0.2%), and calibration curve accuracy showed deviations ≤ 3% from delivered doses.
• All calibration methods achieved gamma passing rates >94% with clinically relevant criteria.
• EDW calibration showed higher gamma passing rates for single targets (99% ± 1.2%), while PDD calibration improved agreement for multiple targets (99.3% ± 0.8%).

Conclusions:

• The evaluated manual, EDW, and PDD calibration methods are validated for EBT-XD films.
• These methods provide accurate calibration curves essential for pre-treatment patient-specific QA in SRT.
• The study confirms the utility of EBT-XD films for precise dosimetry in advanced radiotherapy techniques like HyperArc.