Physics and Imaging in Radiation Oncology (Oct 2018)

Advantages of intensity modulated proton therapy during hippocampal avoidance whole brain radiation therapy

  • Joshua Stoker,
  • Sujay Vora,
  • Ameet Patel,
  • David Grosshans,
  • Paul D. Brown,
  • Tamara Vern-Gross,
  • Martin Bues,
  • Thomas Daniels,
  • Bryce Allred,
  • Arielle Uejo,
  • Heidi Kosiorek,
  • Marlene Bruso,
  • Sameer Keole

Journal volume & issue
Vol. 8
pp. 28 – 32

Abstract

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Background and purpose: Intensity modulated proton therapy (IMPT) allows for modulation parameterized for individual beamlets by position, intensity, and depth. This modulation capability is ideally suited for sparing organs at risk intermediate of the radiation target, such as hippocampal volumes within the whole brain. This work compared IMPT relative to volumetric modulated arc therapy (VMAT) during hippocampal avoidance whole brain radiation therapy (HA WBRT). Materials and methods: Ten adult and ten pediatric patients previously treated for central nervous system malignancies were identified. IMPT and VMAT treatment plans employing HA WBRT were generated for each patient, delivering 30 GyE (Gray Equivalent) in 10 fractions for adults and 36 GyE in 20 fractions for pediatrics. Dose indices, including dose volume histogram metrics and homogeneity index HI = [D5% − D95%]/[Dmean] × 100, were used to assess plan quality and describe target coverage and normal-tissue sparing. Results: IMPT offered significant benefits relative to VMAT for hippocampal sparing. Hippocampal mean dose was reduced from 13.7 ± 0.8 Gy with VMAT to 5.4 ± 0.3 GyE using IMPT for pediatrics, and was reduced from 11.7 ± 0.9 Gy with VMAT to 4.4 ± 0.2 GyE using IMPT for adults. IMPT similarly lowered left hippocampal mean dose. Dose to 95% of the clinical target volume was statistically equivalent for both groups; however IMPT reduced the homogeneity index by roughly half. Conclusion: This manuscript demonstrates that HA IMPT can match or exceed dosimetric benefits offered with modulated X-rays. Inclusion of IMPT in future prospective studies is warranted. Keywords: Intensity modulated proton therapy, Hippocampal sparing, Whole brain radiation therapy, RTOG 0933