Potential of Proton Therapy to Reduce Acute Hematologic Toxicity in Concurrent Chemoradiation Therapy for Esophageal Cancer

PURPOSE: Radiation therapy dose escalation using a simultaneous integrated boost (SIB) is predicted to improve local tumor control in esophageal cancer; however, any increase in acute hematologic toxicity (HT) could limit the predicted improvement in patient outcomes. Proton therapy has been shown to significantly reduce HT in lung cancer patients receiving concurrent chemotherapy. Therefore, we investigated the potential of bone marrow sparing with protons for esophageal tumors. METHODS AND MATERIALS: Twenty-one patients with mid-esophageal cancer who had undergone conformal radiation therapy (3D50) were selected. Two surrogates for bone marrow were created by outlining the thoracic bones (bone) and only the body of the thoracic vertebrae (TV) in Eclipse. The percentage of overlap of the TV with the planning treatment volume was recorded for each patient. Additional plans were created retrospectively, including a volumetric modulated arc therapy (VMAT) plan with the same dose as for 3D50; a VMAT SIB plan with a dose prescription of 62.5 Gy to the high-risk subregion within the planning treatment volume; a reoptimized TV-sparing VMAT plan; and a proton therapy plan with the same SIB dose prescription. The bone and TV dose metrics were recorded and compared across all plans and variations with respect to PTV and percentage of overlap for each patient. RESULTS: The 3D50 plans showed the highest bone mean dose and TV percentage of volume receiving ≥30 Gy (V(30Gy)) for each patient. The VMAT plans irradiated a larger bone V(10Gy) than did the 3D50 plans. The reoptimized VMAT62.5 VT plans showed improved sparing of the TV volume, but only the proton plans showed significant sparing for bone V(10Gy) and bone mean dose, especially for patients with a larger PTV. CONCLUSIONS: The results of the present study have shown that proton therapy can reduced bone marrow toxicity.