LAUSR

PURPOSE/OBJECTIVE(S) We aimed to predict and compare radiation-induced organ-specific secondary solid tumor occurrence risks from conventional total body irradiation (TBI) and from total marrow irradiation (TMI) for patients undergoing hematopoietic cell transplant (HCT). MATERIALS/METHODS We retrospectively selected 20 patients who received TMI treatments prior to HCT. Ten patients (5 male and 5 female) received 12 Gy to the skeletal bones, lymph nodes, and spleen, while the other ten patients (5 male and 5 female) received an escalated dose of 20 Gy to the same targets and 12 Gy to the brain and liver. A conventional TBI treatment plan was generated for each patient with prescription dose of 12 Gy using AP and PA photon beams with lung shielding and chest wall boost using electron beams. Secondary cancer risks were estimated using linear-exponential and plateau models for major organs. RESULTS At the 12 Gy dose level, using the linear-exponential model, the total radiation-induced secondary solid-tumor risks for major organs were 159.3±8.7 for male and 221.5±14.4 for female per 10,000 people per year with the TMI plans, a reduction of 38.8% and 32.9% respectively compared to those with the TBI plans; at the 20 Gy dose level, they were 220.3±8.3 for male and 298.5±9.3 for female with the TMI plans, a reduction of 14.6% and 9.2%, respectively, compared to those with the 12-Gy TBI plans. Significant risk reductions were also found with the TMI plans using the plateau risk model. CONCLUSION At both 12 Gy and 20 Gy prescription dose levels, a conditioning regimen using TMI could significantly lower overall radiation-induced secondary solid tumor risks for major organs compared to a conditioning regimen with standard 12-Gy TBI. Clinical data from long-term follow-up are needed for verification of the model predictions.