Abstract
Osteonecrosis is the death of bone cells due to insufficient blood supply; radiotherapy for various underlying malignancies is one of the uncommon causes. Microvascular damage or underlying tissue fibrosis, which leads to an ischemic environment and cell death, is a proposed mechanism. Factors influencing risk of radiation induced AVN include type of radiation whether external beam radiotherapy or brachytherapy, age of the patient, included body part and concomitant additional steroid or chemotherapy treatment. In this case report we brought a case of 40-year-old male patient with right proximal thigh leiomyosarcoma who underwent surgical resection and adjuvant radiotherapy, about a year later when Pelvic MR was done for evaluation of surgical bed and tumor progress right femoral head AVN was detected, the patient was asymptomatic. The exact cut-off radiation dose that causes AVN is unknown and varies across studies, necessitating a cautious study of joints included in the radiation field even in asymptomatic patients for early diagnosis and to prevent morbidity associated with delayed diagnosis.