(HealthDay News) — For patients receiving radiotherapy for glioblastoma (GBM), use of clinical target volume (CTV) margins as small as 5 mm does not lead to an increase in marginal failures, according to a study published online Dec. 1 in the American Journal of Clinical Oncology.

Anna K. Paulsson, from Wake Forest University in Winston-Salem, N.C., and colleagues assessed patterns of treatment failure in 161 patients with GBM treated with radiotherapy with or without concurrent temozolomide (from August 2000 to May 2010). Results were compared based on CTV margin, use of temozolomide, and use of intensity-modulated radiotherapy (IMRT).

The researchers found that failures in the 60 Gy volume were experienced by 79 percent of patients treated with 5-mm CTV, 77 percent treated with 10-mm CTV, and 86 percent of those treated with 15- to 20-mm CTV. In the 46 Gy volume, the corresponding values were 48, 55, and 66 percent of patients. For patients treated with 5-, 10-, 15- to 20-mm margins, there was no significant difference with regard to 60 Gy failure, 46 Gy failure, or marginal failure. In patients receiving temozolomide, 80 percent experienced failures in the 60 Gy volume. For patients receiving IMRT, there was no increased likelihood of marginal failures.

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“Modern treatment techniques including use of concurrent temozolmide, limited CTV margin size, and IMRT have not greatly changed the patterns of failure of GBM,” the authors write. “Use of CTV margins as small as 5 mm does not seem to lead to an increase in marginal failures.”

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