Investigation of Collapsed-cone Algorithm Accuracy in Small Fields and Heterogeneous Environments

Area of Science:

• Medical Physics
• Radiotherapy
• Dosimetry

Background:

• Advanced radiotherapy utilizes small radiation fields, increasing dose calculation complexity.
• Accurate dose delivery is critical for patient treatment outcomes.
• Evaluating commercial treatment planning system (TPS) algorithms is essential.

Purpose of the Study:

• To assess the accuracy of the Collapsed-Cone dose calculation algorithm within the Isogray treatment planning system.

Main Methods:

• Experimental dosimetry using a Pinpoint detector in solid water phantoms with lung and bone heterogeneities.
• Irradiations performed with 6, 10, and 18 MV photon beams across various field sizes (1x1 cm² to 5x5 cm²).
• Comparison of experimental dose measurements with TPS calculations.

Main Results:

• Maximum deviations observed in small fields (1x1 cm²) and in water-bone heterogeneity.
• Deviations up to 5% in homogeneous water and lung phantoms for fields up to 2x2 cm².
• Good agreement between TPS and experimental dosimetry for fields 3x3 cm² and larger.

Conclusions:

• The Collapsed-Cone algorithm meets standard audit criteria.
• Caution is advised when using this algorithm in bone heterogeneity, particularly at lower photon energies.