Adjuvant Bone-Marrow Sparing IMRT in Endometrial Cancer Patients Treated with Sequential Chemotherapy- Does it Help with Completion Rate?

Abstract

Postoperative pelvic IMRT has been shown to have decreased rates of myelosuppression in patients with gynecologic cancers treated with concurrent chemoradiation therapy, when compared to conventional 3D-CRT. However, there is limited data on how marrow sparing IMRT might impact tolerance in the setting of full-dose sequential chemotherapy and extended-field radiotherapy. A retrospective analysis of 158 patients with endometrial cancer treated with adjuvant sequential chemoradiation therapy with marrow sparing IMRT from 2008-2018 was performed. 146 of 158 patients received pre-IMRT chemotherapy, with 14 of 158 receiving post-IMRT chemotherapy. 63 patients were treated with extended field IMRT to include para-aortic lymph nodes, while 95 were treated with pelvic field IMRT including the entire common iliac region. Bone marrow was defined dosimetrically as the pelvic bone, bilateral femoral heads, and lower lumbosacral spine, with goal bone marrow V20 Gy < 80%. Myelosuppressive events were categorized using RTOG criteria. Linear regression analysis was used to assess for correlation between myelosuppression events and bone marrow dose. 157 of 158 (99.4%) patients completed EBRT as prescribed, with 1 discontinuing treatment due to acute GI toxicity. Median EBRT treatment time was 35 days (range 32-60 days). Total EBRT treatment time was 40 days or more in 17 patients (11%), with 4 patients having prolonged EBRT treatment time attributable to myelosuppression (range 42-57 days). All 158 patients had CBCs during treatment (median 4, range 1-8). Results for myelosuppressive events are detailed in the table below. Bone marrow V20 <80% was met in 118/158 (75%) of patients. Median bone marrow mean dose was 29.1 Gy (range 19.4-35.8 Gy). Median bone marrow V20 Gy was 73.9% (range 47.1-91.0%). Linear regression analysis did not reveal statistically significant associations between V20 Gy or mean bone marrow dose with grade 2 myelosuppression events. Grade 3 myelosuppression were rare events, with 2% incidence in pelvic field IMRT and 5% incidence in extended field IMRT. This is the largest series with marrow sparing IMRT in patients with endometrial cancer treated with sequential chemoradiation therapy, showing very low rates of grade III myelosuppression and 99.4% completion rate, with few treatment interruptions. With our goal bone marrow V20 Gy <80% dose met in the majority of patients, we were unable to determine a statistically significant relationship between myelosuppression events and V20 Gy or mean bone marrow dose.Abstract 2808; Table 1Grade 2 Anemia (Hgb<9.5-7.5)Grade 3 Anemia (Hgb <7.5)Grade 2 Neutropenia (ANC <1500-1000)Grade 3 Neutropenia (ANC <1000)Grade 2 Thrombocytopenia (PLT<75-50)Grade 3 Thrombocytopenia (PLT<50)Any Myelosuppression EventAny Grade 3 EventFrequency (n=158)20/158 (13%)0/158 (0%)33/158 (21%)4/158 (3%)8/158 (5%)1/158 (1%)53/158 (34%)5/158 (3%) Open table in a new tab