The preferred treatment for medically inoperable early-stage endometrial cancer (EC) is definitive radiation therapy (RT), either in the form of brachytherapy (BT) alone or in combination with external beam radiotherapy (EBRT). This case report details a modified brachytherapy approach for a 59-year-old female patient who was known to have multiple comorbidities, poor performance status, and progressive slowness in activities of daily living. She presented with a complaint of post-menopausal bleeding per vaginum, for which she underwent investigations and was diagnosed with a case of endometrial adenocarcinoma, International Federation of Gynecology and Obstetrics (FIGO) stage IA and grade I. After the tumor board discussion, the patient was deemed medically inoperable and planned for radical radiotherapy. She received EBRT via the image-guided intensity-modulated radiotherapy technique, a dose of 50.4 Gy in 28 fractions to the uterus, cervix, and upper 2 cm of the vagina, followed by weekly intracavitary brachytherapy (ICBT), a dose of 4.5 Gy in the first fraction via the Rotte-Y applicator and 5.2 Gy in the second and third fractions each via the modified Rotte-Y applicator. The modified applicator demonstrated better coverage of the target with a lesser dose to the organs at risk (OARs) and underscores its potential use in the future for such cases.