Stereotactic body radiotherapy (SBRT) is a technique that allows delivery of very high doses of radiation in a few fractions and requires precise definition of the target and management of target motion. A challenging task in SBRT is fully accounting for the respiratory tumor motion.
Respiratory motion management can be achieved by either using abdominal compression (to reduce breathing motion), or respiratory gating techniques (to “catch” the tumor within a specific window). An abdominal compression device can be added to the stereotactic frame to reduce tumor motion and associated margins, whereas the respiratory gating techniques uses external devices (such as the Varian Respiratory Gating for SCanners (RGSC) system) to predict the phases of the breathing cycle while the patient breathes freely.
Abdominal compression reduces breathing motion, so reducing the size of internal target volume (ITV), then sparing healthy tissue. There is no extra time for treatment delivery. But patient may feel discomfort, it may not be effective if the target is far from the compression. If patient couldn’t tolerance compression, the gated treatment is the choice. The gated treatment including exhale gating, full range gating and deep inspiration breath hold (DIBH). The comparison and corresponding techniques are listed in Table 1.
We compared pros and cons of breathing motion management in patient comfort, workload, treatment planning, treatment delivery and troubleshooting etc. as shown in table 2.
The breathing motion is evaluated with and without the abdominal compression. The abdominal compression can reduce the tumor motion by at least 50%, especially in lower lung tumor. Therefore, a decision was made to use the abdominal compression for all lung SBRT patients unless the patient cannot tolerate the compression. Based on the 4DCT retrospective analysis, the evident based workflow design was given for motion management as shown in Figure 1. For lower lung tumor, using abdominal compression. For patients who can not tolerate the compression or those who are perfect candidates for gated treatment, the gated protocol will be used. For upper lung tumor or the tumor attached to chest wall, patient will have gated treatment if patient can have regular breathing. Depending on the amplitude of motion, patient can have exhale gating or full range gating. If patient could not have regular breathing, but patient could hold breath for 30 seconds, patient could be treated with DIBH. For middle lung tumor, more data is needed. The protocol can also be used for other sites including liver, kidney, pancreas, and adrenal etc.
Breathing motion management impacts patient comfort, workload, treatment complexity, every steps of RT planning, treatment delivery time, finally the quality of the treatment. The optimum workflow design saves treatment unit time and spare normal tissue for patients.
Table 1: Comparison of exhale gating, full range gating and DIBH in motion management, CT scans, Planning, IGRT and Treatment delivery
Table 2: Pros and Cons of Breathing Motion Management (Patient comfort, Workload, Planning, IGRT, Delivery time, Troubleshoot)
Figure 1: The evident based workflow design for motion management (Abdominal compression or gated treatment)