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‘Cone-down’ radiation boost reduced treatment volume without losing tumor control
A radiation “cone-down” boost was associated with treatment volume reductions of more than 50% in a cohort of patients with pediatric rhabdomyosarcoma.
Bree R. Eaton, MD, of the department of radiation oncology at Winship Cancer Institute at Emory University in Atlanta, and colleagues conducted a retrospective analysis to determine whether a radiation therapy cone-down boost — which is used to reduce high-dose treatment volumes according to tumor response to induction chemotherapy — would have an effect on tumor control.
Bree R. Eaton
Researchers evaluated 55 pediatric patients. Of them, 18 had parameningeal rhabdomyosarcoma and 37 had non-parameningeal disease.
Eligible participants were treated with chemotherapy and radiation between April 2000 and January 2010.
A cone-down boost was administered in 51% of patients.
The high-dose boost volume was reduced by a median of 56% of the initial target volume (range, 5%-91%), according to researchers.
The median time to initiation of radiation was 3 weeks in the parameningeal cohort and 16 weeks in the non-parameningeal cohort (P<.001).
After a median follow-up of 41 months, researchers observed a 9% local failure rate. Two of those patients had received a cone-down boost. There were no marginal failures at this time point.
Intracranial tumor extension occurred in 12 patients (67%) in the parameningeal group. Of this small subgroup, four patients who received the cone-down boost and had at least 3 weeks between chemotherapy and initiation of radiation experienced leptomeningeal failure as their first site of disease progression. Also in this subgroup, a delayed time to initiation of radiation was associated with decreased OS (P=.055).
“A cone-down boost allowed for significant reductions in high-dose [radiation] treatment volume while maintaining excellent tumor control in most patients,” Eaton and colleagues concluded. “However, in the subset of patients with [parameningeal rhabdomyosarcoma] and intracranial tumor extension, early [radiation] initiation and wider margin [radiation] to cover adjacent areas at high risk for meningeal extension may be more important for adequate disease control.”