Proton therapy is an effective treatment for chondrosarcomas of the skull bone and cervical spine, offering high local control at the base of the skull and high overall survival rates with acceptable toxicity.
That conclusion comes from a study developed at Loma Linda University Medical Center in Loma Linda, CA, and the National Cancer Center in Goyang, South Korea, and presented at the 2008 American Society for Therapeutic Radiology and Oncology (ASTRO) meeting in Boston.
Chondrosarcoma, which develops in cartilage cells, is the second most common form of bone cancer. Proton therapy may be a more viable option to surgery for some patients, given that chondrosarcoma does not often respond favorably to radiation and chemotherapy.
Researchers retrospectively analyzed the records of 63 patients with chondrosarcomas of the skull base and cervical spine who were treated with proton therapy at Loma Linda's James M. Slater Proton Treatment and Research Center between 1992 and May 2004.
Tumor location
The decision to evaluate the efficacy of proton therapy for this rare tumor at the base of the skull was "a natural choice," said Dr. Reinhard Schulte, co-author and associate professor of translational science at Loma Linda University. "These are tumors that are locally aggressive; they do not metastasize. You need very high doses for control. That's where we could show a difference by escalating the dose and increasing the control, which had been difficult in the past."
The median total dose was 72 cobalt grey equivalent (CGE) delivered in dose fractions of 1.8 CGE. Local control and overall survival rates were calculated using the Kaplan-Meier method. Treatment-related toxicity was assessed according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE).
With a median follow-up of 84 months, ranging from 19 to 171 months, researchers found that nine patients had developed local recurrences of chondrosarcoma. The actuarial local control rates were 86% and 83.1% at five and 10 years, respectively, and overall survival was 93% and 77% at five and 10 years, respectively.
On univariate analysis of prognostic clinical parameters affecting local control, previous treatment, tumor location, and extent of surgery were statistically significant. On multivariate analysis, only tumor location remained as a significant factor for the local control rate.
Unexpected results
Schulte said that researchers were surprised to see tumors in the cervical spine perform much worse in regard to control compared to the same tumors at the base of the skull, even though they have the same histology. "We do not have a good answer as to what could explain it," he said, but added that it is probably the location of the tumor, rather than its biology.
"It is not a far distance from the base of the skull to the cervical spine; it is adjacent, but there are differences," Schulte said. "Maybe the surgery is not quite as radical. You can spare a lot of your base of skull and still function, but if you resect the spine, there is nothing to hold the head."
There is the issue of metal homogeneity -- for example, with a titanium implant in the cervical spine -- which makes radiation treatment planning more difficult, as radiation oncologists are likely to be more conservative when dealing with the cervical spinal cord. "Because of the metal artifacts, you tend to be more conservative," Schulte said. "This is something one has to look at more closely, but this is not acceptable to have only 40% to 50% control" for chondrosarcomas at the cervical spine.
Proton therapy's future
While chondrosarcomas are rare, Schulte said that proton use has been successful in treating these tumors in this particular location. Proton therapy, he opined, has "a downside in that many people in the community of radiation oncologists still think that protons are to be used on rare and special tumors, which, of course, is not the case. This research shows that it can make a difference; it doesn't mean that you can't use protons on other sites."
The future of proton therapy will depend on several factors, including greater interest and access to the technology within the radiation oncology industry. "I think there is still a lot of technology that can be developed around protons and intensity-modulated proton therapy," Schulte said.
Protons also must become more affordable, he added, and training of users also is an important factor in proton therapy's future utilization.
By Wayne Forrest
AuntMinnie.com staff writer
September 29, 2008
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