Comparative Proton and Photon Treatment Planning in Pediatric Patients with Various Diagnoses

Purpose: Radiation therapy with protons, owing to its physical properties, can beadvantageous for the treatment of children. This study was conducted in order to quantify the advantages of proton therapy from a treatment planning point of view in a consecutive, realistic, and mixed pediatric/adolescent population with varying diagnoses and target locations.Patients and Methods: Forty-five patients treated with conventional 3 dimensional conformal radiation therapy photon radiation therapy were retrospectively re-planned with scanned proton beams. Treatment sites represented were the central nervous system, head and neck, thorax, and abdomen. Median age was 8 years (range, 2-18 years). All plans were optimized with intensity-modulated proton therapy (multi-field optimization). We analyzed a number of dose-volume descriptors for planned targetvolumes (PTVs). Organ-specific mean doses and relevant DV -values were derived fororgans at risk. In addition, homogeneity index, conformity index, treated volume, and integral dose were calculated for each treatment plan. The Wilcoxon matched-pairs signed rank test was used for studying differences between these variables for the 2 treatment modalities.Results: Planned target volume coverage (V95%) was similar when comparing photons and protons. Conformity and homogeneity indices were similar or better for protons for most cases. In general, doses to organs at risk were lower with protons. In cases with organs at risk in close vicinity to the PTV, the gain with protons is less.Conclusions: The patient cohort benefits from reduced integral dose with protons compared with photons. Patients with tumors in the central nervous system, head and neck, upper mediastinum, and some abdominal locations will gain significantly if treated with protons compared with photons. For 7 of the 45 consecutive patients studied (whole brain, whole lung, whole abdomen, flank treatment), we found no gain with protons (difference in integral dose less than 8%)