Introduction: Radiotherapy with heavy charged particles such as protons and carbon ions (hadron therapy) has been recognized as an advanced technique for the treatment of various cancers. For some indications such as pediatric and radio-resistant tumors, it is considered the preferred method. However, despite its remarkable benefits, development of hadron therapy centers in the world has always been subject to major constraints due to a number of reasons including the high costs of constructing and maintaining the centers, the need for strong infrastructures, and the lack of adequate research on the estimation of the number of patients eligible for utilizing this technique. Therefore, this study aimed to investigate the initial estimation of the number of patients eligible for hadron therapy in the Fars Province and Iran as a whole. Materials and Methods: In the absence of comprehensive national cancer registry data, the information for the initial estimation of the number of patients residing in the province were collected from the medical records of the patients who were treated at the Radiotherapy Department of Shiraz Namazi Hospital in 2014. First, the patients’ demographic data (place of residence, age, and sex) as well as the type of cancer were extracted according to the patients’ pathology reports. Only the patients residing in Fars were selected. Then, all of the resulting indications were classified based on the methodology proposed in previous studies, and by applying separate coefficients on each, all the indications suitable for the hadron therapy in Fars were determined. Subsequently, by applying a coefficient of 16.4 (the ratio of the total population of the country to that of the Fars Province in 2014), the number of the patients eligible for hadron therapy in the whole country was calculated. Results: Of the total 2,932 cases studied, 1536 patients were residing in Fars, 22.9% of whom were eligible for hadron therapy. Accordingly, the total number of patients in the country was estimated to be 5765 cases/year. Considering similar studies from other countries with such clinics, at least two hadron therapy centers are needed for treating the eligible estimated population. Conclusion: The analysis performed in this study (solely considering patient numbers and treatment indications) suggests that at least two geographically-spread hadron therapy centers are indicated (covering two northern and southern regions of similar populations). The limitations in having access to accurate patient data and the insufficiencies in the national cancer registry system hinders accurate estimations, which potentially lead to underestimation of patient numbers. Also, other economic factors, experience of other countries and expert advice should be considered. The need for extensive cost-benefit studies versus lower-cost radiotherapy equipment before investment is emphasized.