Working thresholds for in-vivo dosimetry in EPIGray based on a clinical, anatomically-stratified study

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• In vivo dosimetry is crucial for verifying radiation dose delivery during treatment.
• The Electronic Portal Imaging Device (EPID)-based EPIgray system offers a method for real-time dose monitoring.

Purpose of the Study:

• To establish tolerance levels for the EPIgray in vivo dosimetry system.
• To analyze dose differences between planned and delivered radiation therapy across various anatomical regions.

Main Methods:

• Analysis of 5,791 treatment fractions across gastro-intestinal, urological, gynecological, breast, head and neck, and lung regions.
• Assessment of dose difference symmetry and distribution, including linear regression for temporal drift in specific regions.
• Phantom studies using water and water-polystyrene interfaces to determine system-intrinsic dose differences and radiochromic film verification.

Main Results:

• Dose differences did not follow a normal distribution in any region, and only two regions exhibited symmetry around zero.
• Mean dose differences varied by region, with notable positive deviations in lung (5.63 ± 5.48%), breast (3.48 ± 4.00% for 3DCRT), and head and neck (0.70 ± 3.20%).
• The EPIgray system demonstrated sensitivity to dose variations, with specific mean dose differences reported for each anatomical site.

Conclusions:

• Tolerance levels for the EPIgray system should accommodate asymmetric deviations from zero, especially for lung, breast, and head and neck treatments.
• The system's capability to detect dose variations during treatment can aid in identifying changes in tumor volume.
• Further research may refine tolerance levels based on these observed asymmetric dose distributions.