Evaluation of Amplitude-Gated IMRT for Respiratory Motion Management in Right Breast Radiotherapy Using RGSC
Authors: Major Md Khairul Islam
Institution: Combined Military Hospital (CMH) Dhaka
Introduction
Respiratory induced chest wall movement during breast radiotherapy can introduce positional uncertainty and compromise target localization. To account for this motion, larger clinical target volume (CTV)-to-planning target volume (PTV) margins may be required during free-breathing treatment, potentially increasing the irradiated volume and dose to surrounding organs at risk (OARs). Respiratory Gating for Scanners (RGSC) system enables respiratory amplitude monitoring and gated radiation delivery within a predefined motion window.
Methods
A comparative treatment planning evaluation was performed for right breast radiotherapy using free-breathing and RGSC-based amplitude-gated IMRT. Respiratory-related chest wall motion was considered when defining target margins. The planning target volume (PTV), total irradiated volume, ipsilateral lung V20, ipsilateral lung mean dose (Dmean), and heart Dmean were compared between the two techniques. The PTV volume was 1337 cc for free-breathing IMRT and 1196.25 cc for amplitude-gated IMRT.
Results
Compared with free-breathing IMRT, amplitude-gated IMRT reduced PTV volume by 10.5% and total irradiated volume by 24.3%. Ipsilateral lung V20 decreased by 8.64 percentage points, representing a relative reduction of 28.2%. Ipsilateral lung Dmean decreased by 23.5%, from 17 Gy to 13 Gy. Heart Dmean decreased by 40.6%, from 4.21 Gy to 2.5 Gy. These findings demonstrate a substantial reduction in the volume of normal tissue exposed to radiation and improved dosimetric sparing of the ipsilateral lung and heart with amplitude-gated planning.
Conclusion
RGSC-based amplitude-gated IMRT demonstrated dosimetric advantages over free-breathing IMRT for right breast radiotherapy, including reduced PTV and irradiated volumes and lower doses to the ipsilateral lung and heart. Respiratory amplitude monitoring may help account for chest wall motion and reduce the need for larger motion-related PTV margins in appropriately selected patients. Further evaluation of respiratory reproducibility, setup uncertainty, target coverage, and intrafraction motion is necessary to establish the clinical safety and generalizability of this approach.
