Anatomic and pathologic variability during radiotherapy for a hybrid active breath-hold gating technique

Area of Science:

• Radiation Oncology
• Medical Imaging
• Thoracic Oncology

Background:

• Accurate tumor targeting is crucial in lung cancer radiotherapy.
• Active breath-hold gating techniques aim to minimize respiratory motion artifacts.
• Variability in tumor and lung position and volume can impact treatment accuracy.

Purpose of the Study:

• To evaluate intra- and interfraction variability of tumor and lung volume and position.
• To assess the reproducibility of a hybrid active breath-hold gating technique.
• To identify factors influencing interfraction variability during lung cancer radiotherapy.

Main Methods:

• 159 repeat normal inspiration active breath-hold CTs were acquired weekly for 9 lung cancer patients.
• Gross tumor volume (GTV), lungs, and spinal cord were delineated and contours propagated.
• Intra- and interfraction variability of position and volume, and tumor centroid/border variability were quantified.

Main Results:

• Intrafraction variability of lung and GTV centroid position was <2.0 mm.
• Interfraction GTV centroid variability ranged from 3.6-6.7 mm (systematic) and 3.1-3.9 mm (random).
• Tumor volume regressed by 44.6%, and interfraction GTV variability correlated with tumor and lung volume changes.

Conclusions:

• The hybrid breath-hold technique demonstrated high intrafraction reproducibility (<2 mm).
• Substantial interfraction variability in GTV position and shape was observed due to volume changes.
• Online image guidance is recommended to address interfraction variability in this technique.