Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 58 1 2020 06 15 15 20 Christina Nawangsih Department of Radiology, Faculty of Medicine, Diponegoro University, Semarang, Indonesia. Soehartati Gondowihardjo Department of Radiology, Faculty of Medicine, Universitas Indonesia, Jakarta, Indonesia. Sofia Haryana Department of Histology, Faculty of Medicine, Universitas Gadjah Mada, Yogyakarta, Indonesia . Soeharyo Hadisaputro Department,of Internal Medicine, Faculty of Medicine, Diponegoro University, Semarang, Indonesia. Catharina Suharti Department,of Internal Medicine, Faculty of Medicine, Diponegoro University, Semarang, Indonesia. Edi Dharmana Department of Parasitology, Faculty of Medicine, Diponegoro University, Semarang, Indonesia. Hermina Sukmaningtyas Department of Radiology, Faculty of Medicine, Diponegoro University, Semarang, Indonesia. Fifin Rahmi Department of Ophthalmology, Faculty of Medicine, Diponegoro University, Semarang, Indonesia. Ignatius Riwanto Department of Surgery, Faculty of Medicine, Diponegoro University, Semarang, Indonesia. AND Kariadi General Hospital, Semarang, Indonesia. 2019 06 16 2020 04 23 The outcome of inoperable rectal cancer treatment by chemotherapy, radiotherapy, and targeted therapy are still unfavorable. Carbogen is a combination of 98% oxygen and 2% carbon dioxide proven effective as chemoradiosensitizer. The aim of this study is to know the effect of concurrent carbogen and chemoradiotherapy in locally advanced rectal cancer by measuring the shrinkage of the tumor volume. The design of this study was randomized true experimental 2 groups pre and post-test-controlled design. Samples were patients with locally advanced rectal cancer. MRI of the pelvis before and 4-8 weeks after the chemoradiation were examined. A total of 28 subjects were randomized to 14 patients who received concurrent chemoradiation with carbogen (treatment group) and 14 patients chemoradiation (control) The tumor shrinkage in the treatment group (13.08 to 6.08 cm3) was significantly higher compared to the control group (18.00 to 12.83 cm3). Supplementation of carbogen to standard treatment chemoradiation for locally advanced rectal cancer significantly shrinkage the tumor volume. https://acta.tums.ac.ir/index.php/acta/article/view/7956 https://acta.tums.ac.ir/index.php/acta/article/download/7956/5361