Experimental validation of absorbed dose-to-medium calculation algorithms in heterogeneous media

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Radiotherapy Physics

Background:

• Validating advanced type-b dose calculation algorithms requires accurate absorbed dose-to-medium (Dm,Qclinm,fclin) determination.
• Detector readings in heterogeneous media necessitate correction factors (hQclin,Qreffclin,frefdetm,w) for precise algorithm validation.
• The impact of detector orientation on these correction factors in diverse media is not fully understood.

Purpose of the Study:

• To determine heterogeneous correction factors (hQclin,Qreffclin,frefdetm,w) for various detectors and media.
• To validate absorbed dose-to-medium (Dm,Qclinm,fclin) calculation algorithms using these correction factors.
• To investigate the influence of detector orientation on correction factors in heterogeneous environments.

Main Methods:

• Calculated hQclin,Qreffclin,frefdetm,w factors for four detectors (PinPoint T31016, microDiamond T60019, microSilicon T60023, EBT3 film).
• Evaluated factors in various media (cortical bone, lung, adipose tissue, Teflon, RW3) for a 6 MV beam.
• Applied corrections to detector measurements at different depths in heterogeneous phantoms.

Main Results:

• Correction factors primarily depend on the medium, with significant variations in high-density media like cortical bone (0.911–0.934).
• Detector orientation dependence was observed, particularly in high-density media, except for the PinPoint T31016.
• Excellent agreement (≤1.5%) was achieved between calculated Dm,Qclinm,fclin and corrected detector readings across all phantoms.

Conclusions:

• The study provides essential hQclin,Qreffclin,frefdetm,w factors for medical physicists validating dose calculation algorithms.
• Detector orientation significantly impacts readings in heterogeneous media, challenging assumptions based on water-only studies.
• Accurate interpretation of detector readings and comparison with Dm,Qclinm,fclin calculations mandate the use of these correction factors.