(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: Recent studies have shown that patient lymphocyte depletion is associated with radiation therapy. Moreover, severe lymphopenia has been shown to be strongly associated with poor outcomes. However, dose distribution patterns from protons and photons can be greatly different. In this study, we aim to assess the possible outcome in terms of lymphocyte depletion in esophageal cancer patients for three treatment modalities: intensity-modulated radiation therapy (IMRT), passive scattering proton therapy (PSPT) and intensity-modulated proton therapy (IMPT).
Methods: Ten esophageal cancer patients treated with PSPT at our institution were included in this study. IMRT and IMPT plans were created with comparable target coverage to the existing PSPT plan for each patient with a prescription of 50.4 Gy for 28 fractions. Based on dose distributions in the same treatment volume for each patient, we estimated the absolute lymphocyte count (ALC) after treatment based on an approximate piecewise-linear relationship between lymphocyte survival and dose per fraction for each modality. This estimation assumes that all circulating blood cells receive doses after the treatment volume is irradiated after all fractions.
Results: The average mean body doses (MBD) for the ten patients were 7.71 Gy, 5.12 Gy and 3.98 Gy for IMRT, PSPT and IMPT plans, respectively. The average predicted ALCs after treatment were 0.30 K/μL, 0.39 K/μL and 0.42 K/μL for IMRT, PSPT and IMPT plans, respectively.
Conclusion: Proton plans were shown reduced risk of lymphopenia after the treatment course compared to photon plans. The difference between PSPT and IMPT in estimated ALC depletion is relatively small.
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