Dose delivery accuracy on helical tomotherapy for 4-dimensional tumor motion - a phantom study

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-Guided Therapy

Background:

• Helical tomotherapy (HT) is advanced for lung cancer treatment due to image guidance and conformal dose delivery.
• Respiratory motion poses a challenge to accurate dose delivery in HT.
• Phantom studies are crucial for evaluating motion effects on radiation therapy.

Purpose of the Study:

• To quantify the impact of respiratory motion on delivered dose accuracy in helical tomotherapy.
• To assess the influence of varying motion amplitudes, directions, and delivery interruptions on treatment fidelity.

Main Methods:

• A dynamic phantom simulating lung tumor motion (COS4 pattern) was used with 4D CT.
• Treatment plans were generated, and film dosimetry with gamma analysis assessed dose accuracy.
• Varied parameters included target motion (superior-inferior, anteroposterior, lateral), breathing cycle time, and delivery interruptions.

Main Results:

• Gamma pass rate (3%, 2mm criteria) significantly decreased from 97.5% to 54.4% with increasing superior-inferior motion (3mm to 8mm).
• Combined motion (S-I 8mm, L-R/A-P 3mm) and three delivery interruptions reduced the gamma pass rate by 74%.
• These findings highlight the sensitivity of HT dose delivery to respiratory motion.

Conclusions:

• The internal target volume (ITV) approach in HT is suitable for shallow breathing (<5mm S-I, <3mm L-R/A-P motion).
• Significant deviations from these limits necessitate careful treatment planning and potentially adaptive strategies.
• Motion management is critical for ensuring accurate dose delivery in HT for lung cancer.