Publication: Evaluating interfraction motion thresholds in image-guided radiotherapy (IGRT) for lung and spine stereotactic body radiotherapy (SBRT)
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Date
2025-07
Authors
Xin, Lau En
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Abstract
Stereotactic body radiotherapy (SBRT) is an advanced technique for small tumour volumes that requires precise dose delivery due to its hypofractionated nature and steep dose gradients. However, tumour motion, particularly respiratory-induced displacement, poses a challenge to treatment accuracy. This study aimed to evaluate interfraction motion thresholds using kilovoltage cone-beam computed tomography (kV-CBCT) in image-guided radiotherapy (IGRT) for lung and spine SBRT at Hospital Pakar Universiti Sains Malaysia (HPUSM). Methods: For seven lung SBRT cases, tumour motion was measured in Eclipse treatment planning system (TPS) by measuring the distance between contours of average gross tumour volume (GTV) and GTV from maximum and minimum respiratory phases using 4D-gated slow CT simulation images. Interfraction motion was quantified using kV-CBCT across 18 lung and spine SBRT patients, evaluating translational and rotational displacements over 3 to 5 treatment fractions. The mean interfraction displacements were evaluated against the AAPM TG-142 recommended thresholds (≤ 1 mm/°). Results: Tumour motion was highest in the superior-inferior (Y) direction during both maximum (mean = 0.3371 ± 0.4043 cm) and minimum (mean = 0.1205 ± 0.1677 cm) phases. A strong correlation (ρ ≥ 0.7) was observed between tumour motion and average GTV volume in most axes but the relationships were not statistically significant (p > 0.05). Interfraction displacement was highest in the lateral axis for lung SBRT (mean = 22.89 ± 33.75 mm) while spine SBRT showed more stable displacements, with the highest in vertical axis (mean = 22.38 ± 27.36 mm). No significant differences in displacement were observed across fractions and between simulation techniques (p > 0.05). The ratio of AAPM TG-142 threshold to actual displacement was approximately 1:20 for translational displacement and nearly 1:1 for rotational displacement. Conclusion: Interfraction motion displacements exceeded AAPM TG-142 translational threshold, highlighting the need of further study for motion management to optimise SBRT delivery.
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