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Impact of Intra-Fractional Motion on Dose Distributions in Lung IMRT
Mikhail A Chetvertkov1, Oleg N Vassiliev1, Jinzhong Yang1
1Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, 1400 Pressler St., Houston, TX 77030, USA.
Journal of Radiotherapy in Practice
|June 25, 2021
Summary
Intra-fractional motion during lung cancer radiation therapy reduces target coverage and affects organ doses. Treatment planning systems using average CT scans overestimate doses to organs at risk.
Area of Science:
- Radiation Oncology
- Medical Physics
- Radiotherapy
Background:
- Intensity-modulated radiation therapy (IMRT) is a common treatment for lung cancer.
- Accurate dose delivery is crucial for effective cancer treatment and minimizing side effects.
- Intra-fractional motion, particularly respiratory motion, can significantly impact dose distribution during IMRT.
Purpose of the Study:
- To evaluate the impact of intra-fractional motion on dose distribution in patients undergoing IMRT for lung cancer.
- To compare actual dose distributions with those predicted by standard treatment planning.
- To assess the effect of motion on planning target volume (PTV) coverage and organ-at-risk (OAR) doses.
Main Methods:
- Retrospective analysis of 20 non-small cell lung cancer patients treated with IMRT.
- Acquisition of four-dimensional computed tomography (4D-CT) datasets.
- Dose re-calculation across 10 respiratory phases and combination using deformable image registration.
- Comparison of cumulative dose distributions with clinical treatment plans based on average CT.
Main Results:
- Intra-fractional motion consistently reduced PTV coverage (median 3.4% reduction in prescription isodose volume; D98 reduced by 3.1 Gy).
- Organs at risk (OARs) generally received lower doses than predicted: heart dose reduced (median 0.22 Gy), spinal cord unaffected, esophagus dose reduced.
- Lung V20 increased in most patients (median 1.6%), indicating potential for increased lung toxicity.
Conclusions:
- Intra-fractional motion significantly degrades PTV coverage in lung cancer IMRT.
- Standard treatment planning overestimates OAR doses, potentially leading to overly conservative treatment margins.
- Accurate accounting for intra-fractional motion is necessary for optimizing IMRT for lung cancer.
