Pretransplant Splenic Irradiation in Patients With Myeloproliferative Neoplasms.

Purpose: Allogeneic hematopoietic cell transplantation (HCT) serves as the only curative treatment option for patients with myelofibrosis and other myeloproliferative neoplasms. Splenomegaly commonly manifests in patients with myeloproliferative neoplasms and can lead to delayed or poor engraftment, increased transfusion burden, and worse survival. Methods to decrease the effect of splenomegaly include splenectomy and splenic irradiation. We sought to report on clinical outcomes for patients treated with splenic irradiation as part of their transplant conditioning. Methods and Materials: Patients with splenomegaly measuring greater than 22 cm were referred for splenic irradiation. They received radiation to the entire spleen to 10 Gy in 5 fractions using 3-dimensional conformal radiation with anteroposterior/posteroanterior or opposed tangent fields. Blood counts were monitored closely on treatment. Changes in splenic size were measured using first and last treatment image guided radiation therapy and pre- and posttransplant diagnostic imaging. Results: Seventeen patients completed pretransplant splenic irradiation between 2012 and 2021. Median platelet, white blood cell, and hemoglobin levels decreased on treatment. One patient required platelet transfusion and 3 required packed red blood cell transfusions. Mean decrease in spleen size during radiation was -8.5% in the craniocaudal dimension. Prolonged decreases, measured 2 to 12 months after transplant, averaged 14.64%. All patients engrafted. Fourteen (82.4%) were alive at time of analysis with median follow-up of 4.2 years from hematopoietic cell transplantation. Conclusions: Splenic irradiation offers a safe method of managing significant splenomegaly as part of transplant conditioning. Transplant outcomes in this series were excellent. Prospective data may be beneficial to determine the absolute benefit of this addition to pretransplant conditioning in this patient population.