SU-E-J-127: An Initial Application of Evaluating Lung Tumor Motion Throughout Radiotherapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Imaging

Background:

• Accurate assessment of lung tumor motion is critical for effective radiotherapy planning and delivery.
• Traditional 4D CT (Computed Tomography) scans may not fully capture dynamic intrafraction tumor motion.
• There is a need for real-time or daily evaluation of tumor motion during radiation therapy.

Purpose of the Study:

• To develop and validate a novel method for evaluating lung tumor motion.
• To incorporate data from planning CT, patient localization imaging, and during-treatment imaging.
• To quantify tumor motion patterns and ranges throughout the radiotherapy process.

Main Methods:

• Tumor motion was assessed at three stages: planning (4D CT), pre-treatment localization (CBCT - Cone Beam CT), and during treatment (MV - megavoltage imaging).
• Tumor motion patterns were derived from 4D CT data by contouring and registration.
• Daily tumor motion was evaluated using raw projection data from CBCT scans and MV treatment beam images, employing image registration techniques to track motion components.

Main Results:

• The methodology was applied to five lung cancer patients undergoing radiotherapy.
• Over 5400 MV frames and 24 CBCT scans were analyzed across 12 fractions.
• Observed tumor motion ranges were generally larger than those estimated from 4D CT, with significant variations in motion patterns noted.

Conclusions:

• 4D CT-derived information alone is insufficient for comprehensive lung tumor motion assessment.
• The novel method accurately characterizes daily lung tumor motion without fiducial markers or additional imaging dose.
• This approach enables daily verification of tumor motion within treatment planning margins, enhancing treatment safety and efficacy.