Background: Adherence to radiotherapy with curative intent is essential to achieve optimal tumour control and improve survival. In low and middle-income countries, particularly in rural and multicultural settings, structural and sociocultural barriers can significantly compromise treatment completion.

Objective: To identify the social and clinical factors associated with non-adherence to radiotherapy with curative intent and its impact on progression-free survival in patients treated at a Peruvian cancer centre.

Methods: A retrospective observational study was conducted that included 254 patients treated with radiotherapy with curative intent between 2020 and 2021. Data were obtained through structured review of medical records and validated surveys. Multivariate logistic regression and survival analysis using Kaplan–Meier curves were applied.

Results: Non-adherence was significantly associated with belonging to an indigenous ethnic group (odds ratio (OR): 10.45; 95% confidence interval (CI): 2.34–46.67), lack of access to paved roads (OR: 2.19; 95% CI: 1.10–4.36) and incomplete secondary education (OR: 2.31; 95% CI: 1.33–4.01). These factors were also associated with reduced progression-free survival.

Conclusions: Structural and sociocultural determinants significantly influence adherence to radiotherapy in underserved populations. Tailored interventions—such as transport support, intercultural health education and the implementation of hypofractionated protocols—are urgently needed to improve equity in cancer care.