SU-E-T-384: An Easy Use Anthropomorphic Phantom for Lung IMRT QA.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Lung IMRT plans are calculated with CT heterogeneity correction.
• Patient-specific validation often uses homogeneous solid media, which may not accurately reflect patient anatomy.
• There is a need for realistic, heterogeneous phantoms for precise lung IMRT validation.

Purpose of the Study:

• To develop and evaluate a heterogeneous phantom for measurement-based validation of lung IMRT plans.
• To assess the accuracy of IMRT plan calculations against phantom measurements.
• To provide a practical tool for routine clinical quality assurance of lung IMRT.

Main Methods:

• Constructed two heterogeneous phantoms (Hetero-1, Hetero-2) using anthropomorphic RANDO phantom slabs and virtual water.
• Employed a 2D diode array detector (MapCHECK) and ion chamber for dose measurements.
• Generated two lung IMRT plans and compared point and planar doses with phantom measurements and Treatment Planning System (TPS) calculations.

Main Results:

• MapCHECK measurements for Hetero-1 showed high passing rates (93.5%-98.5%) under 3%/3mm Gamma criteria.
• Hetero-2 measurements yielded passing rates of 96.3%-98.5%, even with shifts including more lung material.
• Ion chamber measurements showed minimal differences (1.2%-1.71%) compared to TPS calculations, with TLD results within 98%-99% agreement.

Conclusions:

• An easily assembled heterogeneous phantom using anthropomorphic phantom slabs is feasible for lung IMRT QA.
• This phantom serves as a convenient and efficient tool for routine clinical validation of lung IMRT.
• The developed phantom enables accurate, patient-specific quality assurance for lung IMRT plans.