2010 - Quantification of Respiration-Induced Segmental Lung Motion: Toward Personalized Margins for Radiotherapy Planning

Purpose/Objective(s): Respiratory-induced tumor motion poses significant challenges in thoracic radiotherapy planning, especially in settings where respiratory gating or deep inspiration breath-hold (DIBH) are not feasible due to patient-related factors or resource limitations. This study aims to comprehensively quantify tumor movement across broncho-pulmonary segments (BPS) and assess the relationship between tumor location and movement to guide individualized planning target volume (PTV) margins.

Materials/Methods: This retrospective study analyzed 219 tumors distributed across the entire range of BPS. Expiratory and inspiratory radiotherapy planning scans were retrieved from the hospital PACS. Tumors abutting the chest wall and patients with severe COPD or interstitial lung disease (ILD) were excluded. Tumor movement was quantified as the Euclidean distance between expiration and inspiration positions based on 3D coordinates. Movements were summarized by lung side (right/left), lobe (upper/middle/lower), and BPS. Descriptive statistics, including mean, standard deviation (SD), and range (min-max), were reported for each BPS. Statistical comparisons were performed to assess variations across different lung regions and also to assess any significant change.

Results: Tumor motion varied significantly across BPS. Mean movement ranged from 0.43 ± 0.18 cm in the apical segment of the right upper lobe to 1.83 ± 0.76 cm in the anterior segment of the right lower lobe. Tumors in the lower lobes exhibited greater movement than those in the upper lobes. In the right lung, mean tumor movement was 0.87 ± 0.32 cm in the upper lobe, 1.22 ± 0.44 cm in the middle lobe, and 1.33 ± 0.26 cm in the lower lobe. In the left lung, mean tumor movement was 0.66 ± 0.12 cm in the upper lobe and 1.28 ± 0.32 cm in the lower lobe. Overall, tumor motion in the right lung (1.12 ± 0.18 cm) was higher than in the left lung (0.90 ± 0.16 cm). These findings highlight the heterogeneity of tumor motion across different lung regions, reinforcing the need for location-specific margin adaptation.

Conclusion: Tumor motion varies significantly based on location within the lung. These findings support the need for individualized PTV margins, particularly in settings where respiratory motion management is not feasible.