After obtaining consent and verifying eligibility requirements, the patients will be randomized to one of three doses for prophylactic platelet transfusions (lower, medium, or higher dose). The dosage is based on the patient's body surface area (BSA). The dose targets are as follows: 1) the lower dose is 1.1 x 10^11/m²; 2) the medium dose is 2.2 x 10^11/m²; and 3) the higher dose is 4.4 x 10^11/m². A dose within 25% of this value in either direction is considered to be in the target range. For many adult patients, the typical dose of one unit of apheresis platelets would fall in the target range for the medium dose. All prophylactic transfusions provided while the patient is in the study will be given according to the randomized target dose range. Only blood bank staff, not clinical staff, will have access to the target dose range for each patient.