The impact of proton beam therapy on blood cell count nadir during neoadjuvant chemoradiation therapy for esophageal cancer.

Abstract

137 Background: To analyze the blood cell count nadir, particularly grade 4 hematologic toxicities, in patients with esophageal cancer who were treated with neoadjuvant chemoradiation (nCRT) with either Proton Beam Therapy (PBT) or Intensity Modulated Radiation Therapy (IMRT) in a propensity-matched pair analysis. Methods: Esophageal cancer patients (n = 480) treated from 2005-2016 with nCRT with (n = 167) or without (n = 313) induction chemotherapy (ICT) were analyzed. White blood cell, neutrophil, lymphocyte and platelet counts nadir during ICT and CRT were obtained, and graded according to the CTCAE v.4.0. Univariate and multivariable logistic regression models to identify factors associated with increased risk of grade 4 lymphopenia were fitted. By propensity score matching, 136 PBT cases and 136 propensity score matched IMRT controls were selected for comparison. Results: In the entire study cohort during CRT (n = 480), 2 (0.4%), 1 (0.2%), 159 (33%), and 2 (0.4%) patients experienced grade 4 leukopenia, neutropenia, lymphopenia and thrombocytopenia, respectively. This is not seen in patients who received ICT (n = 167), as only 0 (0%), 2 (1.2%), 1 (0.6%) and 0 (0%) patients experienced grade 4 leukopenia, neutropenia, lymphopenia and thrombocytopenia during the ICT phase. Multivariable analyses identified older age (p = 0.0139), larger planning tumor volume (PTV) (p = 0.0213), distal vs upper/mid tumor location (borderline significance, p = 0.0779) and IMRT vs PBT (p < 0.0001) as factors associated with increased risk of grade 4 lymphopenia during CRT. Among the 272 propensity-matched patients treated with either PBT or IMRT, 24 (17.6 %) and 55 (40.4 %) patients experienced grade 4 lymphopenia, respectively (p < 0.001). Grade 4 lymphopenia correlates with poorer survival (p = 0.0587), lower progression free survival (p = 0.0384) and distant metastatic recurrence (p = 0.0185). Conclusions: The use of PBT may be an important modifying factor in altering the incidence of grade 4 lymphopenia during CRT in esophageal cancer. The dosimetric factors that can modulate this risk is a subject of continued investigation.