Respiratory Gating for Radiotherapy: Main Technical Aspects and Clinical Benefits

Abstract

Respiratory-gated radiotherapy offers a significant potential for improvement in the irradiation of tumor sites affected by respiratory motion such as lung, breast, and liver tumors. An increased conformality of irradiation fields leading to decreased complication rates of organs at risk is expected. Five main strategies are used to reduce respiratory motion effects: integration of respiratory movements into treatment planning, forced shallow breathing with abdominal compression, breath-hold techniques, respiratory gating techniques, and tracking techniques. Measurements of respiratory movements can be performed either in a representative sample of the general population, or directly on the patient before irradiation. Reduction of breathing motion can be achieved by using either abdominal compression, breath-hold techniques, or respiratory gating techniques. Abdominal compression can be used to reduce diaphragmatic excursions. Breath-hold can be achieved with active techniques, in which airflow of the patient is temporarily blocked by a valve, or passive techniques, in which the patient voluntarily breath-holds. Respiratory gating techniques use external devices to predict the phase of the breathing cycle while the patient breathes freely. Another approach is tumor-tracking technique, which consists of a real-time localization of a constantly moving tumor. This work describes these different strategies and gives an overview of the literature.

Quality Assurance for Respiratory-Gated Radiotherapy Using the Real-Time Tumor-Tracking Radiotherapy System

“…In general, the respiratory gating system is used based on the external surrogate signal [15]- [17]. In external gating, the tumor position is derived using the external breathing signal.…”

Continuous generation of volumetric images during stereotactic body radiation therapy using periodic kV imaging and an external respiratory surrogate

“…A patient would be set up for treatment according to clinical standard of care, with the addition of a respiratory monitoring device such as an abdominal marker block (e.g. as in the RPM system [1,46,47,48,49,50,51]) or spirometry device [23,52,53,54,55]. Additionally, during treatment the kV imaging panel would be deployed and would acquire kV images every 3 seconds (this is the current maximum frame rate of the in-treatment kV image functionality in clinical mode on the Varian TrueBeam accelerators used in our clinic).…”

Real-time Tumor Tracking with Respiratory Motion Based on Short-term Prediction

“…The displacement of the epigastric surface is commonly detected with the depth-based camera [7], respiration belt [8], and mostly infra-red devices [3,9]. For example, the RPM system can monitor the respiration by locating a cube placed on the patient's abdomen [10]. However, for the purpose of capturing the movements as comprehensive as possible, multiple markers should be placed on the thorax and/or abdomen of the subject.…”