by Gus Iversen
, Editor in Chief | February 24, 2015
From the January/February issue of HealthCare Business News magazine
Small target precision
Ma, who has nearly 20 years of experience performing SRS, says the latest version of Gamma Knife (Perfexion) retains an advantage over other platforms with regard to dosimetry and accuracy. He also points to the vast amounts of published data on Gamma Knife SRS as an invaluable resource in utilizing the tool responsibly and to its highest potential.
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Ma participated in a study published online earlier this year entitled, Variable Dose Interplay Effects Across Radiosurgical Apparatus in Treating Multiple Brain Metastases, which evaluated the use of Gamma Knife, Novalis, TrueBeam, and CyberKnife at six different clinics to better understand how well each modality spares healthy tissue from radiation. Their findings indicate that treatment by the Gamma Knife did the best job at sparing normal tissue, however, it requires the longest beam-on time (the amount of time that the radiation beam is transmitting radiation to the patient).
“From a physics point of view, the head frame does several important things that people need to know,” says Ma, “Once you target the lesion, it’s easy to be very precise.” He says that the body movements that an image guided platform has to account for—rotational shifts, breathing, sweating, even gravity itself—are infinitely complex and can result in reduced accuracy of the treatment.
When radiation is off-target, it subjects normal tissue to radiation, which can lead to various side effects of varying complexity. For example, when treating trigeminal neuralgia, which affects the fifth cranial nerve, there is precious little room for missing the target.
“You want to zap a little nerve, (1mm by 7mm), with a high dose such as 80 gray,” says Ma, “You better do that with something that can deliver the dose precisely.” Ma says that Gamma Knife is more focused than other platforms and has sharper dose falloff. “The dosimetry using X-ray comes from electrons hitting the target,” says Ma, “Those modalities tend to deliver a factor 2 to 3 times higher in the normal tissue dose, or the skirting dose, than does the Gamma Knife.”
“For other tumors you can make the argument saying those things are tolerable, however, the entire backbone of doing radiosurgery is to be precise,” says Ma. So, for whatever temporary discomfort it implies, he believes the Gamma Knife and its head frame yield better outcomes, especially for the most complex brain cancer cases.
Considerations for throughput and versatility
Alliance Oncology, a technology agnostic and comprehensive network of radiosurgical programs, has Gamma Knifes installed in two of their 29 partnering radiation therapy centers. They also partner with hospitals using modalities from the other major stereotactic manufacturers.