ESTRO 2024 - Abstract Book

S1166

Clinical - Haematology

ESTRO 2024

Predicting neutropenia dynamics after RT in first-line Bortezomib-based chemo for MM - a pilot study

Michał Masłowski 1 , Konrad Stawiski 1 , Adam Zięba 1 , Damian Mikulski 2 , Julia Bednarek 3 , Jacek Fijuth 1

1 Copernicus Memorial Hospital in Lodz, Department of Radiotherapy, Lodz, Poland. 2 Copernicus Memorial Hospital in Lodz, Department of Hematology, Lodz, Poland. 3 Medical University of Lodz, Faculty of Medicine, Lodz, Poland

Purpose/Objective:

This pilot study aimed to investigate the dynamics of neutropenia in multiple myeloma (MM) patients receiving radiation therapy (RT) after first-line bortezomib-based chemotherapy. Our goal was to better understand the factors influencing neutrophil count changes in this patient population.

Material/Methods:

We conducted a retrospective analysis of 32 MM patients who underwent RT for symptomatic bone pain. A total of 530 complete blood count results were collected and analyzed. We utilized a generalized additive model (GAM) that considered three key predictors: the initial absolute neutrophil count (ANC), the biologically effective dose (BED10), and the treatment volume (PTV).

Results:

Our GAM model provided several significant insights. First, it indicated that MM patients typically experience their lowest ANC levels, or ANC nadir, approximately 16 days after commencing RT. Notably, patients treated with a single fraction of 8 Gy showed the least severe ANC nadir, while a dose of 30 Gy administered over 10-15 fractions was identified as the safest option. For patients with a PTV volume of 1000 cm³, maintaining an initial ANC level of at least 1.42 × 10³/μl was associated with a lower risk of severe neutropenia, regardless of the fractionation scheme. Longer treatment courses, such as 30 Gy in 10-15 fractions, enabled RT delivery with minimal neutropenia, even when the initial ANC level was as low as 1.23 × 10³/μl on the first day of RT.

Conclusion:

The results of this study offer valuable insights into optimizing treatment strategies for MM patients undergoing a combination of RT and chemotherapy. It is important to note that further research is required to validate these findings and evaluate the feasibility of implementing the predictive model in clinical practice.

Keywords: multiple myeloma, radiotherapy, neutropenia

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