The Brain Centre upgrades to Leksell Gamma Knife Icon, expanding treatment options for individuals with poor prognoses
Living up to its name and reputation, The Brain Centre (Hong Kong) upgraded its Gamma Knife® system in June 2016 to Leksell Gamma Knife® Icon™, refining and expanding its Gamma Knife radiosurgery capabilities. Today, frameless fractionated radiosurgery with Icon – maintaining the extreme accuracy for which frame-based Gamma Knife® radiosurgery is renowned – is benefitting up to four patients each week at The Brain Centre.
Clinicians at The Brain Centre – China’s first Icon installation – have treated thousands of patients with Gamma Knife radiosurgery over the years. Now with Icon, reserving frameless, fractionated treatments mainly for patients with disease recurrences, patients who are medically unfit for surgery or repeat surgery and those with pathology close to or abutting critical structures. (see box)
New hope for “hopeless” cases
“The first indication is salvage cases, patients who have undergone all of the standard treatments and still have recurrences of their lesion, whether it be a glioblastoma, malignant meningioma or craniopharyngioma,” says CP Yu, a neurosurgeon at The Brain Centre. “They seem like hopeless cases, but often the patients respond rather unexpectedly well.”
“We’re able to provide excellent control of symptoms and prolongation of life. These are the cases that give us confidence to increasingly use fractionation.”
Frameless fractionated treatments have been delivered in 39 percent of the total Icon cases and 8 Gy X 4 (over one week) and 4 Gy X 10 (over two weeks) are the most common dose/fraction regimes. Frame-based single-fraction Icon treatments are performed when the therapy session will be more than 30 minutes long, which increases the likelihood of patient head movement.
“An example of a frameless single-session treatment we did was a 90-year-old patient with a meningioma that was inoperable because it had invaded the sagittal sinus,” Dr. Yu says. “We also didn’t need the supreme accuracy that the G-frame would afford.”
For all but exceptional cases. Dr. Yu and his team avoid delivering full course fractionation – 25 fractions – because the treatment becomes unnecessarily protracted.
“We have used full fractionation in only two cases, one of which involved a meningioma wrapping around the optic nerve,” he reports. “We were able to deliver a very tiny, homogenous dose to the tumor over five weeks.”
A combined approach
While Elekta promotes the fractionation of large tumors as a key frontline indication for Icon, at The Brain Centre frameless radiosurgery typically is the second phase of a two-part treatment combining surgery and radiosurgery. Frontline radiosurgery is only an option for patients who are too frail or medically unfit to undergo open surgery.
For large lesions, the tumor is initially surgically de-bulked, such as the reduction of a 4 cm acoustic neuroma to a 1 cm remnant.
“In this example, we resect the part of the lesion that is compressing the brain stem and leave the remnant inside the internal auditory canal to avoid damaging hearing and the facial nerve. We then treat the remnant with fractionated radiosurgery,” Prof. Yu explains. “For pituitary adenomas we also want to remove as much as we can so that the tumor is falling away from the optic chiasm. And we avoid going into the cavernous sinuses to eliminate the potential for damaging the carotid and the third cranial nerve. Before Icon, we couldn’t have offered Gamma Knife radiosurgery because this particular lesion was so close to the optic chiasm. But now with Icon, we can treat these tumors rather easily after surgery.”
Over the last several months, the availability of fractionated intracranial radiosurgery at The Brain Centre has attracted the attention of university hospitals seeking to reduce the backlog of cases on their linacs, according to Dr. Yu.
“We are getting referrals from these centers precisely because they also can use a linear accelerator to treat intracranial diseases and disorders, but they are so busy and their waiting lists are so long that they see an opportunity to reserve their treatment systems for body indications,” he notes. “This is a trend that is accelerating.”
While the referring centers benefit by a less hectic, back up schedule, the biggest beneficiary – in Dr. Yu’s estimation – are the referred patients who will receive treatment on a system that provides a gentler therapy experience while also featuring gold standard accuracy.
“In my opinion, the beauty of Icon is that accuracy is superior to other linac-based systems,” he says. “Secondly, the mean dose delivered to the tumor is significantly higher. The maximum dose is almost double because we use the 50 percent prescription isodose lines, so that the maximum dose and the mean dose are a lot higher than linac-based systems. In addition, surrounding tissue protection is much better. The dose fall-off is steep and the gradient index we always maintain below three – this is not achievable with linacs. Lastly and perhaps most important, over the last 11 months we have not seen any major side effects.”
Recent frameless Icon cases at The Brain Centre
- Meningioma, 76-year-old female, WHO grade 1, located at left petrous bone.
- Volume: 31 cc
- Dose: 25 Gy @ 45% in 5 fractions to GTV to preserve the acoustic and facial nerve
- Pituitary adenoma, 48-year-old male
- Dose: 1.8 Gy @80% in 25 fractions to avoid over-exposing the optic chiasm.
- Pituitary macro-adenoma with normal vision, 76-year-old patient
- Dose: 1.8 Gy in 25 fractions for total marginal dose of 45 Gy at 59% isodose level, total of 22 shots. 60 Gy line at least 3 mm from optics.
- New large volume posterior fossa metastases (2), from breast cancer
- Previous WBRT + posterior fossa boost
- Dose: 8 Gy X 4, beam-on time 24.8 min., tumor shrinkage from 4.38 cc to 1.05 cc in two months.