Muscle cramps refer to muscle spasms, which are not usually caused by breast cancer radiation therapy and may be caused by other reasons. The main causes of muscle cramps include dehydration, muscle fatigue, cold stimulation or caused by certain diseases. 1. Dehydration: because a large amount of water loss will lead to electrolyte balance disorders, increased muscle excitability can cause muscle spasms. 2. Muscle fatigue: because muscle fatigue leads to a decrease in motor coordination, excessive or unreasonable force can cause muscle spasm. 3. Cold stimulation: in the cold environment, it can lead to muscle excitability increase, resulting in muscle tonic contraction and muscle spasm, while radiotherapy for breast cancer generally does not lead to muscle spasm. 4. Disease factors: for example, lack of calcium, high fever, epilepsy, rabies, tetanus, etc. can cause muscle spasm. Breast cancer patients with muscle spasms after radiotherapy should actively consult the doctor, patients should not use their own medication to avoid adverse results.