Target and organ dose estimation from intensity modulated head and neck radiation therapy using 3 deformable image...

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• Accurate dose accumulation is crucial for effective head and neck radiation therapy.
• Deformable image registration (DIR) algorithms are used to account for anatomical changes during treatment.
• Cone beam CT (CBCT) images have limitations like small field of view and Hounsfield unit uncertainties.

Purpose of the Study:

• To evaluate and compare the accuracy of three DIR algorithms in estimating delivered radiation doses to targets and organs at risk.
• To assess the dosimetric impact of anatomical variations during head and neck cancer treatment.

Main Methods:

• Retrospective analysis of five head and neck cancer patients with daily CBCT data.
• Deformable registration of planning CT to CBCT images with a 4.2-cm expansion.
• Calculation and accumulation of daily doses onto the planning CT using three DIR algorithms.
• Comparison of dosimetric indices from dose-volume histograms with planned values.

Main Results:

• No significant differences were found among the three DIR algorithms for cumulative dose-volume histograms.
• Mean dose deviation for planning target volumes and gross tumor volumes was within 2% of the planned dose.
• Parotid gland mean dose showed significant variation (up to 33% deviation), partly due to patient weight loss.
• Mean dose deviations were 1.0 ± 1.6% for PTV, 1.6 ± 2.3% for GTV, 7.3 ± 9.6% for left parotid, 10.3 ± 11.9% for right parotid, and 3.3 ± 4.7% for mucosa.

Conclusions:

• Estimated target doses are generally within 2% of the intended dose with a 5-mm planning margin.
• Adaptive radiotherapy planning may be necessary to prevent excessive doses to organs like the parotid glands.
• DIR algorithms provide reliable dose estimation for targets, but organ-at-risk dose variations require attention.