Extension of CadPlan algorithm to model the dose distribution under a motorized wedge

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Treatment Planning

Background:

• The CadPlan treatment planning system uses an equivalent water thickness model for wedged fields.
• This model accurately predicts dose distribution for uniform wedges but struggles with tapered motorized wedges.
• Motorized wedges in Elekta accelerators have tapered thickness, leading to inaccuracies in the CadPlan model.

Purpose of the Study:

• To evaluate and improve the accuracy of the CadPlan treatment planning system for modeling off-axis ratios (OAR) in wedged fields from Elekta motorized accelerators.
• To address the limitations of the existing CadPlan model which assumes uniform wedge thickness.
• To achieve accurate dose distribution modeling for radiation therapy planning.

Main Methods:

• The study adapted the CadPlan algorithm by modifying effective water thickness values at off-axis distances.
• The modified algorithm was tested for 4, 6, and 18 MV beams on Elekta accelerators.
• Off-axis ratio (OAR) predictions from the modified model were compared against measured values.

Main Results:

• The original CadPlan model showed significant over/underestimations of OAR for Elekta motorized wedges (up to 10%).
• The modified CadPlan algorithm successfully modeled the OAR in the non-wedged direction.
• The enhanced model achieved accuracy within 2.5% of measured OAR values for tested beams and accelerators.

Conclusions:

• The CadPlan system requires modification to accurately model dose distributions for Elekta motorized wedges.
• Adjusting effective water thickness at off-axis positions significantly improves OAR prediction accuracy.
• The enhanced CadPlan model provides a more reliable tool for radiotherapy treatment planning with Elekta motorized wedges.