Dose to specific subregions of pelvic bone marrow defined with FDG-PET as a predictor of hematologic nadirs during concomitant chemoradiation in anal cancer patients

To test the hypothesis that irradiated volume of specific subregions of pelvic active bone marrow as detected by ¹⁸FDG-PET may be a predictor of decreased blood cells nadirs in anal cancer patients undergoing concurrent chemoradiation, we analyzed 44 patients submitted to IMRT and concurrent chemotherapy. Several bony structures were defined: pelvic and lumbar-sacral (LSBM), lower pelvis (LPBM) and iliac (IBM) bone marrow. Active BM was characterized employing ¹⁸FDG-PET and characterized in all subregions as the volume having standard uptake values (SUVs) higher than SUV_mean. All other regions were defined as inactive BM. On dose–volume histograms, dosimetric parameters were taken. Endpoints included white blood cell count (WBC), absolute neutrophil count (ANC), hemoglobin (Hb) and platelet (Plt) nadirs. Generalized linear modeling was used to find correlations between dosimetric variables and blood cells nadirs. WBC nadir was significantly correlated with LSBM mean dose (β = −1.852; 95 % CI −3.205/−0.500; p = 0.009), V₁₀ (β = −2.153; 95 % CI −4.263/−0.721; p = 0.002), V₂₀ (β = −2.081; 95 % CI −4.880/−0.112; p = 0.003), V₃₀ (β = −1.971; 95 % CI −4.748/−0.090; p = 0.023) and IBM V₁₀ (β = −0.073; 95 % CI −0.106/−0.023; p = 0.016). ANC nadir found to be significantly associated with LSBM V₁₀ (β = −1.878; 95 % CI −4.799/−0.643; p = 0.025), V₂₀ (β = −1.765; 95 % CI −4.050/−0.613; p = 0.030) and IBM V₁₀ (β = −0.039; 95 % CI −0.066/−0.010; p = 0.027). Borderline significance was found for correlation between Plt nadir and LSBM V₃₀ (β = −0.056; 95 % CI −2.748/−0.187; p = 0.060), V₄₀ (β = −0.059; 95 % CI −3.112/−0.150; p = 0.060) and IBM V₃₀ (β = −0.028; 95 % CI −0.074/−0.023; p = 0.056). No inactive BM subsites were found to be correlated with any blood cell nadir. ¹⁸FDG-PET is able to define active bone marrow within pelvic osseous structures. LSBM is the strongest predictor of decreased blood cells nadirs in anal cancer patients undergoing concurrent chemoradiation.