Proton therapy may have advantages for nasal, sinus cancers

By Megan Brooks

NEW YORK (Reuters Health) - Charged particle therapy is associated with better outcomes than photon therapy for patients with tumors of the nasal cavity or paranasal sinuses, according to a new meta-analysis.

"This is a challenging set of tumors to treat because of their rarity, heterogeneity and where they present. They are located near the anterior skull base abutting many critical structures such as the brain and brainstem, optic structures and cranial nerves," Dr. Samir Patel of Mayo Clinic in Scottsdale, Arizona, told Reuters Health.

"Traditional photon radiation therapy has been utilized but there is difficulty escalating the radiation dose in that area and that can lead to poor tumor control," he explained. "Charged particle therapy is unique in that it has a physical advantage as well as a potential biological advantage in treating tumors in this type of location."

"A good analogy is an egg," Dr. Patel said. "With traditional photon therapy there is no way to just cook the yolk and leave the white uncooked. With charged particle therapy you can deliver radiation, sharply deposit the dose and spare adjacent structures," in essence only cook the yolk, he explained.

In the Lancet Oncology, online June 27, Dr. Patel and colleagues report results of a systemic review and meta-analysis of radiotherapy for patients with nasal cavity and paranasal sinus malignant diseases.

They compared clinical outcomes of 43 cohorts from 41 non-comparative observational studies involving a total of nearly 1,500 patients who underwent charged particle therapy or photon therapy.

Median follow-up was 38 months for the charged particle therapy group and 40 months for the photon therapy group. Pooled overall survival was significantly higher at five years with charged particle therapy (relative risk 1.51; p=0.0038) and at longest follow-up (RR 1.27; p=0.037).

Significant differences favoring charged particle therapy were also seen for disease-free survival and locoregional control.

Subgroup analyses comparing charged particle therapy with intensity-modulated radiotherapy indicated significantly better disease-free survival at five years (p=0.045) and locoregional control at longest follow-up (p=0.011) with charged particle therapy.

"Even looking at the best photon technique compared to proton radiation therapy, patients are living longer without disease with this newer therapy and there is improved control of tumors," Dr. Patel told Reuters Health. "This is the highest-quality data we have at this point to support the use of charged partial therapy."

Charged particle therapy is "an expanding modality but it is not as widely available as photon therapy," Dr. Patel said. The researchers are hopeful that the "growing number of institutions providing charged particle therapy" will "collaborate and report their outcomes."

The author of a comment in Lancet Oncology, Dr. Masashi Koto of the Research Center for Charged Particle Therapy Hospital, National Institute of Radiological Sciences in Chiba, Japan, notes that in the charged particle therapy group, the researchers included heavy ion therapy (e.g., with carbon ions and neon ions).

"This grouping could be inappropriate because heavy ions show greater relative biological effectiveness than protons and photons; heavy ion therapy should be compared with proton beam therapy rather than photon therapy. Conversely, two-dimensional or three-dimensional radiotherapy should not be included in the photon therapy group when compared with charged particle therapy," Dr. Koto says.

"The results of subgroup analyses comparing proton beam therapy with intensity-modulated radiotherapy are remarkable, suggesting that the theoretical advantages of proton beam therapy could be real for treatment of nasal cavity and paranasal sinus tumors," he notes. "However, as discussed by Patel and colleagues, several potential biases exist, including reporting and referral biases."

Dr. Koto concludes, "Findings of prospective comparative studies could clarify the relative merits of charged particle therapy and photon therapy for specific diseases in the future."

"However," he adds, "in the head and neck region, applying the results of prospective studies to individual patients might be difficult because of the complicated anatomical structure. It is more important to offer the most suitable radiotherapy to individual patients rather than to clarify the benefits of charged particle therapy versus photon therapy."

The study was funded by the Mayo Foundation for Medical Education and Research.

SOURCES: http://bit.ly/1riNsD8 and http://bit.ly/1z7HyHo

Lancet Oncol 2014.

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