Multi-institutional radiotherapy planning study compared Leksell Gamma Knife Perfexion with three advanced linear-accelerator based stereotactic radiosurgery systems
New York City United States — Wednesday, May 21, 2014
Persons who need radiotherapy for treatment of multiple brain metastases stand to receive as much as a 74 percent lower radiation dose to normal brain tissue if the lesions are treated with Elekta’s Leksell Gamma Knife® Perfexion™ radiosurgery system versus contemporary linear-accelerator-based stereotactic radiosurgery (SRS) systems. These results came from a study1 co-authored by University of California San Francisco physicist Lijun Ma, PhD, and are significant, given the higher likelihood of neurocognitive deficits associated with greater radiation exposure of normal brain tissue.
Dr. Ma’s presentation, based on the treatment planning study recently published online in the International Journal of Computer Assisted Radiology and Surgery, was given at the 17th International Leksell Gamma Knife Society Meeting (May 11-15, New York City).
A follow-up of a previous study2, the latest research: “Variable dose interplay effects across radiosurgical apparatus in treating multiple brain metastases” evaluated peripheral normal brain tissue doses in four systems: Leksell Gamma Knife Perfexion, CyberKnife® (Accuray), Novalis® (Brainlab) linear accelerator with a 3.0 mm multileaf collimator (MLC) and – new for this study – TrueBeam™ (Varian) flattening filter-free linear accelerator with a 2.5 mm MLC. The systems were located at five US and Canadian medical centers that participated in the study.
A multiple (12) metastases SRS case was chosen for independent treatment planning using the delivery systems. Subsets of target combinations with 3, 6, 9 and 12 targets were selected for treatment planning using individual SRS modalities located in different centers, which were selected based on their expertise with the given technology.
“Comparing the volumes of normal brain receiving a radiation dose of 12 Gy, once again – as in the earlier study – the Perfexion system gave the lowest dose to normal brain tissue,” Dr. Ma observes. “The 12 Gy volume, which is a known predictor for symptomatic radionecrosis that could lead to adverse neurocognitive effects, was 180 to 290 percent higher for the TrueBeam, Novalis and CyberKnife treatment plans.”
Furthermore, for every target number and isodose volume (4, 8, 16, 20 Gy) Perfexion outperformed the other three modalities and, overall, had the highest dose conformity.
The study also examined dose interplay – the additional dose delivered to the normal brain surrounding each target as consequence of irradiating the other targets. According to Dr. Ma, the non-coplanar geometry of Gamma Knife radiosurgery
beam delivery helps significantly limit dose interplay effects in comparison to linac-based modalities, particularly as the number of targets increases.
The area in which Perfexion had a significant disadvantage compared to TrueBeam was length of beam-on time, with Perfexion producing the longest beam-on time of 50-148 minutes. TrueBeam yielded the shortest beam-on time of six to nine minutes.
“Although Perfexion had a longer beam-on time than all the other modalities, the frame-based nature of Gamma Knife radiosurgery greatly reduces patient set-up time and treatment planning time can also be significantly shorter,” Dr. Ma says. “In addition, physics and quality assurance work plus treatment planning effort also can be significantly less.”
“Dr. Ma and his group have demonstrated very definitively that Gamma Knife is unparalleled in its ability to treat multiple brain metastases with the greatest conformity and the least amount of dose scatter to the normal brain,” adds Dheerendra Prasad, MD, Medical Director, Department of Radiation Medicine at Roswell Park Cancer Institute (Buffalo, New York). “In our own experience at Roswell of just the last 75 patients and a total of 272 brain tumors, it was possible to spare 98 percent of normal brain tissue with Gamma Knife Perfexion. Any time gained in treatment with other modalities including the flattening filter-free techniques is outweighed by the loss of selectivity of these other methods. Gamma Knife continues to be the gold standard for radiosurgery, both for benign and malignant tumors and the only real contender for radiosurgery of functional disorders.”
1. Ma L, Nichol A, Hossain S, et al. (2014) Variable dose interplay effects across radiosurgical apparatus in treating multiple brain metastases. Int J CARS. Published online: 20 April 2014. doi:10.1007/s11548-014-1001-4
2. Ma L, Petti P, Wang B, et al. (2011) Apparatus dependence of normal brain tissue dose in stereotactic radiosurgery for multiple brain metastases. J Neurosurg 114(6):1580-1584. doi:10.3171/2011.1.JNS101056
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