In the era of cloud-based healthcare and the Internet of Medical Things (IoMT), securing medical images is essential to protect patient privacy and ensure data integrity. This paper proposes a robust encryption scheme tailored for medical images, incorporating a 3D chaos-based system with layered security mechanisms. The approach integrates chaotic sequence generation, histogram equalization, spatial permutation, DNA- based encoding, and secure XOR operations. By employing chaotic maps for both key generation and permutation, alongside dynamically selected DNA rules, the method achieves high levels of confusion and diffusion. Experimental evaluations demonstrate strong performance in entropy, resistance to statistical and differential attacks, and robustness against brute-force and chosen-plaintext attacks. The proposed system offers a secure and efficient solution for protecting sensitive medical data in IoMT environments.