Use of lung treatment plans to evaluate DIR algorithms

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Processing

Background:

• Accurate radiation dose calculation in lung cancer treatment requires accounting for respiratory motion.
• Four-dimensional computed tomography (4DCT) and deformable image registration (DIR) are advanced techniques used to address this challenge.

Purpose of the Study:

• To evaluate the accuracy of two DIR algorithms in dose summation for lung cancer patients.
• To assess the impact of DIR on dose distributions for '4D' planned and '4D optimal' intensity modulated radiation therapy (IMRT) plans.

Main Methods:

• Developed 4DCT step-and-shoot IMRT plans for ten lung cancer patients, dividing the breathing cycle into ten phases.
• Registered each phase's CT images to the average intensity projection (AIP) CT using DIR algorithms.
• Calculated composite dose distributions by summing deformed doses from all phases for both '4D' and '4D optimal' plans.

Main Results:

• DIR successfully mapped dose distributions across breathing phases in lung cancer patients.
• DIR method and tumor characteristics (motion, size, location) influenced dose distribution differences.
• Despite aiming for 95% target coverage, DIR methods occasionally failed to achieve this in '4D optimal' plans.

Conclusions:

• Composite deformed dose calculation using DIR is feasible and acceptably accurate for lung cancer radiotherapy.
• Tumor motion and body deformation must be considered, particularly for small or lower lobe lung tumors.
• The choice of DIR method significantly impacts the accuracy of dose summation and treatment planning.