SU-E-T-526: Evaluation of Dose Mapping Errors via Use of a Volume-Based Dose Mapping Method

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• 4D treatment planning accounts for organ motion during radiation delivery.
• Accurate dose mapping is crucial for ensuring precise radiation delivery in lung cancer patients.
• Point-based dose mapping methods are commonly used but may contain errors.

Purpose of the Study:

• To quantify dose mapping errors (DMEs) of a point-based dose mapping method for 4D lung cancer treatment plans.
• To compare the accuracy of point-based dose mapping against a volume-based dose mapping method.
• To evaluate the impact of different deformation vector field (DVF) versions on dose mapping accuracy.

Main Methods:

• Dose mapping errors (DMEs) were calculated as the difference between point-based and volume-based mapped doses.
• Deformation vector fields (DVFs) from Pinnacle treatment planning system (versions 8.1y and 9.100) were utilized.
• Ten 4D lung cancer cases were analyzed, with DMEs computed for various breathing phases and accumulated doses.

Main Results:

• The largest DMEs were observed in regions of steep dose or density gradients.
• Using Pinnacle 9.100 DVFs, the mean DME was 0.3% ± 4.8%, with a range of -41% to 32%.
• Accumulated mean DMEs across ten 4D lung cases were within ±0.07%, with standard deviations of 1-5% and a range of -102% to 64%.

Conclusions:

• Volume-based dose mapping provides a reliable method for quantifying errors in point-based dose mapping due to its integral dose conservation.
• Although mean DMEs were small, approximately 5% of voxels exhibited dose mapping errors, these errors were not located within the primary tumor targets.
• The findings suggest that current point-based dose mapping methods are generally acceptable for 4D lung cancer treatment planning, as critical structures are not significantly affected by these errors.