Spinal stereotactic body radiation therapy (SBRT) can be used to deliver a high dose of noninvasive radiation as part of spinal tumor treatment. Vertebral compression fractures are a common complication associated with SBRT, and development of an in vivo model is "crucial to fully understand how focal radiation treatment affects vertebral integrity and biology at various dose fractionation regiments," noted the authors of a recent study that examined the impact of single-dose versus fractionated radiation treatment on spinal bone structure, cell conditions, and the mechanics of structure (Int J Radiat Oncol Biol Phys 2021; https://doi.org/10.1016/j.ijrobp.2021.04.050).
Conducted by a team led by researchers from Johns Hopkins Medicine, the research finds evidence that delivering radiation therapy in a series of sessions, as opposed to a single radiation treatment, could help prevent vertebral compression fractures in patients with spinal tumors.
Noting that radiation and tumors can weaken the bones in the spine, and acknowledging that bone fractures lessen the quality of patients' lives and add a degree of difficulty to their treatment, the researchers sought to find "the ideal way of delivering radiation" to target the tumor while mitigating the effects of treatment on bone strength and quality, according to researchers at Johns Hopkins Medicine.
Study Details
To achieve this goal, the study authors analyzed the microstructure and morphology of the bones in the irradiated areas, tested stiffness and fracture load of the exposed vertebrae, and examined the bone cellular features from those sites. The researchers treated the L5 vertebra of New Zealand white rabbits with either a 24-Gy single dose of focused radiation or three fractionated 8-Gy doses throughout 3 consecutive days via the Small Animal Radiation Research Platform.
The study found that fractionated high-dose radiation therapy impacts bone less compared to single-dose irradiation to treat spinal tumors. For example, a single radiation dose showed greater detrimental effects than hypofractionation on the microarchitectural, cellular, and biomechanical characteristics of irradiated vertebral bodies, according to the study authors.
More specifically, localized single-dose radiation led to decreased vertebral bone volume and trabecular number and a subsequent increase in trabecular spacing and thickness at L5. Hypofractionation of the radiation dose similarly led to reduced trabecular number and increased trabecular spacing and thickness, yet it preserved normalized bone volume, according to the authors.
In addition, the correlation the research team found between radiologic measurements and biomechanical properties supported the reliability of this animal model of radiation-induced vertebral compression fracture, a finding that the authors say can be applied to future studies of preventative measures.
"The beauty of this model is that we can look at the three-dimensional structure of the bone to measure its quality, its density, and the interconnectedness of its structure," said study co-author Christina Holmes, PhD, former Johns Hopkins Medicine postdoctoral fellow and current Assistant Professor of Chemical and Biomedical Engineering at Florida State University.
Looking ahead, the Johns Hopkins research team plans to study the timeline of bone fractures during radiation to gain a better understanding of how and why they occur. The researchers say that insight will ultimately enable them to start considering preventive therapies.
In the meantime, the findings from this study suggest that fractionated radiation doses could potentially lower spinal tumor patients' risk for spinal column breaks, as well as preserving bone strength in the spinal column, according to Timothy Witham, MD, Director of the Johns Hopkins Neurosurgery Spinal Fusion Laboratory and the study's lead author.
"There are different ways to deliver radiation to the spinal column to treat spinal column tumors. It can be done with a single dose of high-intensity radiation, such as stereotactic radiosurgery or stereotactic body radiotherapy," said Witham.
He noted the other method is fractionated radiotherapy, which relies on smaller doses of radiation spread out over time and in multiple treatments or doses.
"What our research shows is that fractionating the radiation doses-the latter technique-may reduce the side effects on bone in the clinical setting," he said. "This may lessen the risk of subsequent spinal column fractures and may help to maintain the strength of the bone in the spinal column."
Mark McGraw is a contributing writer.