Breathing adapted radiotherapy of breast cancer: Investigation of two different gating techniques and visual guidance, using optical surface scanning and pressure monitoring

Abstract: Background and purpose: Post-operative adjuvant radiotherapy of left-sided breast cancer patients is associated with cardiac and pulmonary complication. By utilizing different respiratory gating techniques the absorbed dose to the heart and lung can decrease. The purpose of this study was to evaluate and compare enhanced inspiration gating (EIG) and deep inspiration breath hold (DIBH). The use of visual guidance for both the techniques was also evaluated. Material and methods: Twenty healthy female volunteers were included in the study.The volunteers performed both EIG and DIBH, with and without visual guidance. A 3 mm gating window was introduced at an individual amplitude, based on a practice session, for both EIG and DIBH. To monitor the breathing and to have access to visual guidance the Catalyst(C-RAD positioning AB, Uppsala, Sweden) was used. Parameters such as reproducibility, stability and attendance in the gating window (PGW) were evaluated. Possible advantages of a pre-set delay of the irradiation when the patient’s chest entered the gating window were also investigated. The study also included pressure measurements with the I-scan system and sensor model 9801 (Tekscan Inc., South Boston, USA) which was placed under the patients scapulars. These novel pressure measurements were used to evaluate if there was any risk of patient lifting to enter the gating window, and thus not increase the spatial distance between the heart and the target volume. One last step in the study was to see how long the volunteers were able to hold their breath in the gating window. Results: Spontaneously, without visual guidance, the volunteers breathe significantly deeper using DIBH compared to EIG, and thus increased the distance between the heart and the target volume. Theaverage chest amplitude for EIG was 10.8 ± 4.7mm (1 SD) and for DIBH 12.9 ± 5.8 mm. The reproducibility and PGW improved for both techniques when visual guidance was used. The stability did not indicate any particular trend. The pressure measurements showed that there was a possible risk that the volunteerslifted from the couch, which was more prominent for high amplitudes (∼2.5 cm) and when visually guided. The volunteers where able to hold their breath 57.2 ± 22.5 s on average. Conclusion: According to this study there are major advantages using DIBH and visual guidance. DIBH resulted in higher amplitudes which could result in cardiac and pulmonary dose sparing. To prevent patient lifting, patients should not be pushed to perform too high amplitudes. There are no benefits of changing gating method from EIG to DIBH if no visual guidance can be provided regarding reproducibility, stability and PGW.