Predicting neutropenia dynamics after radiation therapy in multiple myeloma patients receiving first-line bortezomib-based chemotherapy – a pilot study

Introduction. Radiation therapy (RT) is a useful modality for achieving local control and symptom relief in patients with multiple myeloma (MM), but its use can result in adverse effects such as neutropenia, which may be aggravated by prior chemotherapy. Material and methods. In this retrospective study, we analyzed 530 complete blood count results of 32 MM patients who underwent RT for symptomatic bone pain between cycles or after completing first-line bortezomib-based che­motherapy (VCD). To evaluate the dynamics of neutrophil count (ANC) changes, we developed a generalized additive model (GAM) using initial ANC, dosage (BED10), and treatment volume (PTV) as predictors. Results. Our GAM model demonstrated that ANC nadir after RT can be expected approximately 16 days after treatment initiation. The delivery of 8 Gy in 1 fraction resulted in the lowest ANC nadir, while a dose of 30 Gy in 10–15 fractions was deemed the safest. For PTV = 1000 cm3, an initial ANC level of at least 1.42 × 103/μl was associated with no incidence of severe neutropenia irrespective of the fractionation scheme. Longer courses allowed for treatment delivery without significant neutropenia even with an initial ANC of 1.23 × 103/μl on the day of RT initiation. Conclusions. Our model could aid in optimizing treatment strategies for MM patients receiving RT and chemotherapy. Further research is needed to validate our findings and evaluate the feasibility of implementing this model in clinical practice.