Jonathan Saleeby MS, Presenter: Nothing to Disclose

Ruth Ebert BS, Abstract Co-Author: Nothing to Disclose

TJ Fitzgerald MD, Abstract Co-Author: Nothing to Disclose

Charles S Mayo PhD, Abstract Co-Author: Nothing to Disclose

Richard S. Pieters MD, FACR, Abstract Co-Author: Nothing to Disclose

Purpose/Objective(s): Protocol ACNS0232 of the Children?s Oncology Group calls for pediatric patients with occult multi-focal or localized CNS germinoma to receive whole-ventricular irradiation to 24 Gy as part of their treatment regimen. The protocol provides treatment guidelines but does not specify a required treatment technique. In this study, we examine dose distributions in the ventricular planning target volume (PTV) and normal brain structures resulting from three treatment techniques: opposed laterals, 3D conformal, and IMRT. Materials/Methods: CT scans of five pediatric patients with normal brain anatomy were selected. Anatomical structures and the ventricular PTV were contoured in the Eclipse planning system. As defined by the protocol, the PTV encompassed the lateral, third, and fourth ventricles with a 1.5 cm margin. Three 6 MV treatment plans were completed for each patient using opposed laterals, 8-field 3D conformal, and 7-field IMRT planning techniques. Plans were created with the intent of covering the PTV with the 100% isodose line while keeping the dose to the lenses under 200 cGy. 3D conformal plans were coplanar except where avoidance of patient lenses required the use of non-coplanar fields. IMRT plans used five coplanar fields and two vertex fields. Dose volume histograms (DVHs) of the PTV and of the cerebrum, cerebellum, and brain stem (all with the PTV subtracted) were created for each patient. For each structure, an average DVH per planning technique was calculated. Results: Defining the heterogeneity index (HI) as D5%/D95%, the mean HI of the PTV for the opposed laterals, 3D conformal, and IMRT plans each was 1.04 ñ 0.01. Defining the conformity index (CI) as VD100%/VPTV, the mean CI of the PTV for the opposed laterals, 3D conformal, and IMRT plans was 2.60 ñ 0.24, 1.50 ñ 0.07, and 1.08 ñ 0.02 respectively. For the non-target cerebrum and non-target cerebellum, IMRT plans spared more tissue from higher doses (doses > 60% of the prescription) while opposed lateral plans spared more tissue from lower doses (< 50%). 3D conformal plans provided intermediate tissue sparing for both structures. For the non-target brain stem, IMRT plans spared more tissue at doses above 90%. Below 90%, all three techniques were nearly equivalent. Pituitary, hypothalamus, thalamus, and optic chiasm all fell within the PTV and thus received full prescription dose. Conclusions: Opposed laterals, 3D conformal, and IMRT techniques for whole-ventricular irradiation provide similar dose homogeneity within the PTV. IMRT allows maximum sparing of non-target tissue from high doses while opposed laterals allows maximum sparing of non-target tissue from low doses. 3D conformal allows intermediate sparing of non-target tissue from both high and low doses.

Saleeby, J, Ebert, R, Fitzgerald, T, Mayo, C, Pieters, R, Whole-Ventricular Irradiation of Pediatric Patients Using Opposed Laterals, 3D Conformal, and IMRT Techniques: A Dose Volume Histogram Comparison.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8502050.html