Background: Acute haematologic toxicity is the most common side effect of chemoradiotherapy in patients with locally advanced cervical cancer .We aim to test the efficacy of single-photon emission computed tomography-defined active bone marrow-sparing volumetric-modulated arc therapy in reducing grade 3+ acute hematologic toxicity (HT) in locally advanced cervical cancer patients treated with chemoradiotherapy. Methods: This was a prospective, single-center, open label, randomized clinical trial that enrolled locally advanced cervical cancer patients. Participants were randomized to the ^99mTc sulfur colloid SPECT-defined ABMS VMAT (ABMS group) or control group, who received weekly cisplatin concurrently with volumetric-modulated arc therapy followed by high-dose-rate intracavitary brachytherapy. The ABMS group additionally received SPECT-defined ABM dose constraints. The primary endpoint was the incidence of grade 3+ acute hematologic toxicity.Secondary objectives included acute gastrointestinal toxicity, planning Target Volume (PTV) coverage, dosimetric parameters of organs at risk (OARs), progression-free survival (PFS), overall survival (OS). Results: A total of 192 FIGO stage IB-IIIB patients were randomized treated (96 each in the ABMS control groups). The median follow-up was 24.0 months. The incidence of grade 3+ acute hematologic toxicity in the ABMS group was significantly lower than that in the control group (32.3% vs 53.1%, p<0.01). The number of patients completing five cycles of cisplatin was 88.5% in the ABMS group and 75% in the control group, and the difference was significant (p=0.02). There were no significant differences in the mean dose to 95%, 97% and 99%of the PTV between the ABMS group (45.1 Gy, 44.6 Gy, and 43.3 Gy, respectively) and the control group (45.4 Gy, 44.8 Gy, and 43.6 Gy). There were no differences in dosimetric parameters of OARs ,acute gastrointestinal toxicity, 2-year PFS or 2-year OS between the two groups. Patients in the control group had nonsignificantly worse 2-year distant metastasis than patients in the ABMS group (17.8% vs. 11.1%, p=0.19). Conclusions: ABMS VMAT significantly reduced grade 3+ acute HT and improved chemotherapy delivery compared with the control treatment. We found weak evidence of the effect of ABMS VMAT on distant metastasis. Clinical trial information: ChiCTR-IOR-16010214.