Implementation and Validation of a Respiratory Gating Program

When a tumor undergoes displacement due to natural physiologic motion such as breathing, the uncertainty of the prescribed dose, volume of healthy cells irritated, and the planned target volume (PTV), increases. Implementation of respiratory-gated treatment over a designated phase of the breathing cycle instead of irradiating the entire trajectory of the tumor motion reduces unnecessary irradiation of healthy cells.

Respiratory-gated treatment allows for a smaller PTV, and dose escalation; however, tumor motion varies and the ability to deliver the treatment at a precise phase of the breathing cycle is difficult and requires validation of the planned treatments versus the treatment delivered. This project utilize a commercially available phantom and an ion chamber detector to explore the efficacy of a recently adopted method of phase base respiratory gated treatment over the 30-70 % of the breathing cycle.

Our results validated the accuracy of the gated treatment to be within 2.5% of the planned vs delivered. In addition, PTV was on order of 41% smaller for the 30-70% phase gated treatment.