Unlocking Precision: Surface and Target Motion Monitoring in Lung, Liver and Breast Radiotherapy

For the last three years, the clinical staff at Klinik Donaustadt’s Department of Radiation Oncology have been employing C-RAD’s Catalyst⁺ HD Surface Image Guided Radiation Therapy (SGRT) and Sentinel 4DCT optical surface scanning system. These solutions have been indispensable in ensuring accurate treatments for the center’s SBRT lung and breast cancer patients, where significant target motion is often expected. Currently, the center treats approximately 140 patients per day with four Elekta linear accelerators. SGRT is currently used in approximately 30 percent of these cases.

“The benefit we can see in the C-RAD system is that we can surveil the position and movement of the patient without applying any additional radiation to the patient,” says Lukas Bauer, a medical physicist at Klinik Donaustadt. “C-RAD is very good from a motion management perspective and the Sentinel system with its 4DCT capability allows us to more accurately account for patient breathing motion, which is particularly important for high dose SBRT treatments.”

Before C-RAD, the department used markers and tattoos for positioning the patient according to room lasers. They employed an offset vector and shifted the couch accordingly, then marked the position with a water-proof pen.

For the 140 patients the clinic treats each day over four linear accelerators, the staff uses SGRT for approximately one-third of the patients, primarily lung, breast and liver treatments and “pretty much anything that has to do with extremities,” Bauer says. “It is really good for control – basically, we use it for anything where we believe the surface is a good indicator for tumor and organs-at-risk position.”

At Klinik Donaustadt, a significant number of lung and liver patients are already treated via SBRT, where, depending on the patient, the tumor position and, thus, on the respiratory tumor motion, they use either a 4DCT free breathing or a DIBH workflow for their SBRT treatments.

Sentinel 4DCT isolates target within the breathing cycle

Sentinel 4DCT gives clinicians the opportunity to take 4DCT scans during CT simulation to determine motion and help design an accurate plan for employing precise standard or gated (DIBH) therapy.

“This has been critical for us in numerous lung and liver SBRT treatments,” Bauer says. “On the CT scanner, we take a breathing curve and reconstruct the image accordingly. Then we mark the tumor with an ITV [internal target volume] approach. During treatment at the linac, we then position the patient, making sure that the patient breathes in the same way as for the CT scan.”

He adds that after the 4DCT scan, they examine the breathing curve and set boundaries such that the patient cannot breathe in a different way during treatment at the linac.

“We confirm that the tumor motion is within the planned target volume,” Bauer notes. “Sentinel 4DCT enables us to track tumor motion within the breathing cycle. The synergy with Catalyst is also really great here.”

Visual coaching solutions

The department prefers to use a tablet for visual respiration coaching for all DIBH treatments.

“We use the tablet for all DIBH treatments, because particularly for DIBH it is vital that patients receive feedback on their breathing. We use small margins and it’s difficult to do the treatment without this feedback,” he explains. “Conversely, for free-breathing treatments, we don’t use the tablet, as it sometimes causes patients to control their breathing too much.”

“One of the benefits that we experience is that – for the cPositioning module – we do have the option to send the shift of the patient position directly to the couch,” Bauer adds. “This reduces treatment time because we don’t have to redo CBCT scans due to large discrepancies.”

SGRT success

Without Catalyst⁺ HD, Bauer asserts that his department would not be able to perform DIBH treatments for indications affected by tumor motion.

“For certain SBRT treatments we do use DIBH if the treated volume would become too great,” he says. “If we would treat the patient in free-breathing mode, some liver metastases, for instance, would be impacted due to diaphragm motion. In such treatments, we would use DIBH. This would not be possible otherwise.”

“Also, any 4D CT scan that we do would simply not be achievable,” Bauer continues. “Most of our stereotactic lung treatments would not be feasible. We would have to use standard fractionation schemes and greater margins. With Catalyst+HD and Sentinel 4DCT, therefore, treatment time is significantly reduced – not just for patients, but also for the staff – because we don’t have to deliver as many fractions.”

Bottom line

The ability to hypo-fractionate patients by virtue of optimal target and patient position monitoring has been a key patient benefit.

“The advantage for the patient is that in comparison to conventional fractionation, the treatment course is shorter for them and also for us, so we can treat more patients,” he says. “If we need to do a DIBH – because otherwise, it would lead to a greater toxicity for the patient – it allows us to reduce these margins and, thus, dose to adjacent tissue and organs-at-risk. That means we’re able to treat more tumors and also ones with increased respiratory motion without going overboard on the risk for healthy tissues and organs.”