Intensity-Modulated RT 'Excellent' for Pediatric Low-Grade Glioma

May 09, 2013

By Megan Brooks

NEW YORK (Reuters Health) May 09 - Intensity-modulated radiotherapy (IMRT) provides good local control in children with low-grade glioma, say radiation oncologists at Methodist Hospital, Houston, Texas.

"Despite the reduction of the high doses of radiation to surrounding normal brain tissue, the recurrence rate is no different compared to conventional techniques where more surrounding normal tissue is getting the full dose," Dr. Arnold C. Paulino told Reuters Health.

He also said it's possible to "reduce the clinical target with less than 1 cm margin of surrounding brain tissue with IMRT and have excellent local control."

Dr. Paulino and colleagues evaluated local control and patterns of failure in 39 children (median age 10) with low-grade glioma who received treatment with IMRT after incomplete resection or disease progression at their institution between 1996 and 2012.

According to a report online April 30th in Cancer, tumors were grade one in 32 children (82%) and grade two in seven (18%).

The types of glioma included pilocytic astrocytoma in 26 patients (66.7%), ganglioglioma in six (15.4%), fibrillary astrocytoma in four (10.3%), pilomyxoid astrocytoma in one patient (2.6%), oligodendroglioma in one patient (2.6%), and mixed oligoastrocytoma in one patient (2.6%). The median gross tumor volume (GTV) was 21.7 mL.

The researchers used three methods to delineate the target area. The first was to delineate the gross tumor volume (GTV) and add a 1-cm margin to create the clinical target volume (method one, 19 children). The second was to add a 0.5-cm margin around the GTV to create the clinical target volume (method two, six children). The prescribed dose to the GTV was the same as dose to the clinical target volume for both methods one and two (median, 50.4 Gy).

Method three (14 children) involved dose painting, in which a GTV was delineated with a second target volume created by adding 1 cm to the GTV. Different doses were prescribed to the GTV (median, 50.4 and 41.4 Gy, respectively) and the second target volume.

The eight-year progression-free and 10-year overall survival rates of 78.2% and 93.7%, respectively, compare favorably with previous published reports and indicate that IMRT is "an excellent treatment for pediatric low grade glioma." Dr. Paulino told Reuters Health.

Seven patients (17.9%) had disease progression at a median of 37 months after IMRT. All of these failures were in the high-dose region of the IMRT field.

Multivariate analysis revealed no difference in progression according to the method of target delineation. Only age younger than five at the time of IMRT was associated with worse progression-free survival, consistent with findings in other series, the researchers say.

They note that the question regarding the size of margins around the GTV to create the clinical target volume is controversial and has varied in different studies. Their findings, they say, suggest that 1-cm margins around the GTV "may not be necessary" because "excellent local control" was achieved by adding a 0.5-cm margin (method two) and by dose painting (method three)."

The researchers hope results of the recently completed Children's Oncology Group protocol ACNS0221 will validate their results.

The study had no specific funding and the authors made no disclosures.

SOURCE: http://bit.ly/11Sa78Y

Cancer 2013.

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