Three hundred fifty-nine pretreatment 25-hydroxyvitamin D3 ( 25 [ OH ] D3 ) serum levels from the RICOVER-60 study ( Six Versus Eight Cycles of Biweekly CHOP-14 With or Without Rituximab in Elderly Patients With Aggressive CD20 + B-Cell Lymphomas ) and 63 from the RICOVER-noRTh study ( an amendment to the RICOVER-60 study in which patients received six cycles of cyclophosphamide , doxorubicin , vincristine , and prednisone administered at an interval of 2 weeks plus two cycles of rituximab [ R-CHOP-14 ] , but without radiotherapy ) were determined by chemoluminescent immunoassay .