Photon vs. Proton Whole Ventricular Radiotherapy for Non-Germinomatous Germ Cell Tumors

Abstract

<h3>Purpose/Objective(s)</h3> The hypothesis is that dose to normal CNS structures is lower for children treated with proton therapy, as compared to photon therapy for children receiving whole ventricular radiotherapy (WVRT) for non-germinomatous germ cell tumors (NGGCT). We present data from patients enrolled in stratum 1 of the Children's Oncology Group study ACNS1123. <h3>Materials/Methods</h3> Dosimetric data for NGGCT patients on ACNS1123 who received 30.6 Gy WVRT were compared in a post-hoc analysis. Target segmentation was standardized using a contouring atlas as per the study protocol. The PTV was created by creating a 3-5mm geometric expansion from the CTV. Doses to cranial organs-at-risk (OARs) were compared between proton and photon treatments. Clinically relevant dose-volume parameters that were compared included mean dose and dose to 40% of the OAR volume (D40). A subgroup analysis of patients treated with 3 mm PTV margins was performed. Dosimetric comparisons between proton and photons plans were conducted using two-sided Wilcoxon's rank sum test for continuous variables. <h3>Results</h3> Fifty-eight patients had WVRT dosimetry available and were included; 13 (22%) received proton treatment and 45 (78%) received photon treatment. Median age was 10 years old (range 0-21). Mean and D40 doses to the supratentorial brain, cerebellum (see Table), and bilateral temporal, parietal and frontal lobes were statistically significantly lower amongst proton-treated patients compared to photon-treated patients. In a subgroup analysis of patients uniformly treated with a 3 mm planning target volume, patients who received proton therapy continued to have statistically significantly lower doses to brain OARs. <h3>Conclusion</h3> Children treated with proton therapy for WVRT had lower doses to normal brain structures when compared to those treated with photon therapy. Future work will help elucidate whether this dosimetric advantage of proton therapy translates to a reduction in toxicities for these patients.