AAPM: NC-IMAT promising for pediatric brain tumors

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Double non-coplanar-intensity modulated arc therapy (NC-IMAT) can improve treatment for pediatric posterior fossa tumors compared to NC-IMRT (non-coplanar-intensity modulated radiation therapy), and it may provide dose reduction to critical structures and surrounding tissue, according to a study presented at the 52nd Annual Meeting of the American Association of Physicists in Medicine (AAPM) in Philadelphia on July 18.

The study compared different treatment strategies including IMAT in order to determine whether the therapy had any clinical benefit over NC-IMRT for pediatric brain tumors. "Anything we can do to reduce that dose is obviously better," said Chris Beltran, PhD, from St. Jude Children's Hospital in Memphis, who presented the study authored with Medical Physicist Jonathan M. Gray, MS, also of St. Jude Children's Hospital. 

The researchers selected nine pediatric patients ranging in age from 6.1 to 15.1 years for inclusion in the study. Each patient had been treated with IMRT within the past year at the institution.

For each patient, treatment plans were re-planned with 54Gy to the planning target volume with five different methods: eight-field NC-IMRT; single-coplanar IMAT; double-coplanar IMAT; single NC-IMAT; and double NC-IMAT.

For each method, the dose to 95 percent of the planning target volume was held constant, and as a result, dose to surrounding critical structures could be minimized, explained the authors. The treatment plans for each patient were then compared based on conformality index, monitor units and dose to surrounding normal tissue.

The body V5 and brain organ volume (D50) for IMAT and double IMAT were reduced compared to NC-IMRT, and the body V5 and D50 to the cochleae were increased. For IMAT, the conformality index and monitor units were decreased. For NC-IMAT, the V5 was increased but the D50 to the right cochlea and both temporal lobes was decreased, offered the authors.

The body V5 and D50 to both cochleae and temporal lobes were decreased for double IMAT; however, the body V5 and monitor units were increased. In addition, the conformality index for the double NC-IMAT was found to have improved. Four patients had NC-IMRT plans where both cochleae received greater than 25Gy. The average dose was increased for IMAT (32.7Gy) and double IMAT (31.0Gy). For the NC-IMAT, on the other hand, the researchers noted a decrease to 22.5Gy and double NC-IMAT also saw a decrease (20.0Gy).

Double NC-IMAT can improve treatment for these tumors in pediatric patients and over non-coplanar IMRT and could help spare the sensitive surrounding tissues, found the study. “This method has merit and should be considered alongside IMRT for these patients,” concluded Beltran.