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Pediatric Cranio-Spinal Axis Irradiation: Comparison of Radiation-Induced Secondary Malignancy Estimations Based On Three Methods of Analysis for Three Different Treatment Techniques

P Myers*, S Stathakis, P Mavroidis, C Esquivel, A Gutierrez, W Jones, T Eng, C Ha, N Papanikolaou, University of Texas HSC SA, San Antonio, TX

SU-E-T-281 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
Pediatric cranio-spinal axis irradiation (CSI) is a valuable treatment for many central nervous system diseases, but due to the life expectancies and quality of life expectations for children, minimizing the risk of radiation-induced secondary malignancies must be a high priority. This study compares CSI risk estimates based on three methods for three delivery techniques.

Methods:
Twenty-four (n=24) pediatric patients previously treated with CSI for tumors of the CNS were retrospectively planned using three different treatment techniques: 3D-CRT, SmartArc, and Tomotherapy. Each plan was designed to deliver 23.4Gy (1.8 Gy/fraction) to the target which was defined as the entire brain and spinal column with a 3mm expansion. The mean doses as well as the dose volume histogram (DVH) data for specific organs were analyzed for secondary malignancy risk according to three different methods: effective dose equivalence (EDE), excess relative risk (ERR), and linear quadratic (LQ) model.

Results:
Using the EDE method, the average secondary-risk was highest for the 3D plans, 37.6%, compared to SmartArc, 28.1%, and Tomotherapy, 27.9%. The ERR method showed similarly that the 3D plans had significantly higher risk (10.8%) than SmartArc and Tomotherapy, which almost equally showed lower risks (7.1% and 7.1%). The LQ model requires organ-specific cell survival parameters found in literature of which the lungs, heart, and breast values were found and studied. The lung risk for secondary malignancy was found to be 1.0, 2.0, and 2.1% for 3D, SmartArc, and Tomotherapy respectively. The secondary cancer risk for the breasts was estimated to be 0.1, 0.2, and 0.3% and for heart it was 9.8, 6.0, 6.3% for the 3D, SmartArc, and Tomotherapy, respectively.

Conclusion:
Based on three methods of secondary malignancy calculations, 3D plans produced highest radiation-induced secondary malignancy risk, and SmartArc and Tomotherapy plans had nearly equally lowered risk.

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