114. Pelvic bone marrow dosimetric parameters analysis relating to hematologic toxicity in gynecological tumors patients treated with volumetric modulated arc therapy

Purpose To test the hypothesis that the volume of pelvic bone marrow (PBM) receiving 10–20-30–40 Gy (V10-V20-V30-V40) and median dose is associated with hematologic toxicity (HT) in gynecological cancer patients treated with concurrent chemoradiotherapy. Methods and materials We analyzed 29 consecutive gynecological cancer patients (21 only RT and 8 with concurrent chemotherapy) and volumetric-modulated-arc radiation therapy at the Varese Hospital between 2013 and 2015. The median radiation dose prescribed was 50.4 Gy (1,8 Gy daily fractions). The external contour of the PBM was delineated on the planning CT using bone windows was defined as the region extending from the iliac crests to the ischial tuberosities, including the os coxae, lumbosacral spine and proximal femora, and the relative dose volume histogram (DVHs) were calculated. HT was graded according to CTCAE and endpoints included the white blood cell count, absolute neutrophil count, hemoglobin, and platelet count nadirs. Results Non-parametric test for independent samples (Mann–Whitney test) show that the difference between the two groups was not significant for any Vx (p = 0.49). The Table 1 shows the mean values referred all patients in relation to the dose constraints used in the treatment planning. We identified only one patient associated with acute HT G3 (Table 1). Conclusion Techniques to limit PBM irradiation may reduce HT in cervical cancer patients. Only one patient developed acute HT G3, however, the values of DVH(Vx) related to pelvic bone structures are within the dose constraints. V40 results the most critical volume, this value is above the limit in 58.6% of patients, but none of them has developed acute HT. The Vx proposed by the scientific community are valid and safe for HT. We’re working on calculating cumulative DVH area-equivalent using the Lymann algorithm in order to evaluate if this parameter is capable of describing toxicity better than usual indexes like V10-V40.