Beam angle optimization using angular dependency of range variation assessed via water equivalent path length (WEPL)...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy

Background:

• Proton therapy offers precise dose delivery but is sensitive to anatomical changes and patient positioning errors.
• Accurate range prediction is crucial for effective proton therapy, especially in complex anatomical regions like the head and neck.
• Water Equivalent Path Length (WEPL) calculations are used to estimate proton range, but their accuracy can be affected by anatomical variations.

Purpose of the Study:

• To investigate how patient anatomy changes and setup errors affect proton range variation.
• To analyze the angular sensitivity of proton range variation using Water Equivalent Path Length (WEPL) calculations.
• To evaluate the impact of different beam angles on proton range accuracy in head and neck cancer patients.

Main Methods:

• WEPL calculations were performed using planning CT (pCT) and scatter-corrected cone-beam CT (cCBCT) images from 11 head and neck cancer patients.
• Proton range variation was quantified as the difference in distal WEPLs between pCT and cCBCT at various beam angles (every 5 degrees).
• The effect of a 10-degree couch kick on mitigating range variations due to anatomical changes and setup errors was assessed.

Main Results:

• Distal WEPL differences were largest for posterior oblique beam angles, suggesting an increased risk of normal tissue overdose.
• The study found a clear angular dependency of WEPL changes in head and neck cancer patients.
• Implementing a couch kick demonstrated a reduction in WEPL differences for specific posterior oblique angles.

Conclusions:

• Proton range variation in head and neck cancer patients exhibits significant angular dependency.
• Careful selection of beam configurations can mitigate range uncertainties caused by anatomical variations and patient setup errors.
• Optimizing beam angles in proton therapy may lead to improved treatment outcomes and reduced toxicity in head and neck cancer patients.