This study is a single-center,blinded, efficacious, phase III randomized clinical trial initiated by investigators. The primary objective is to investigate the use of Surface Guided Radiation Therapy (SGRT) in combination with Deep Inspiration Breath Hold (DIBH) technique for left breast cancer treatment, compared to traditional laser alignment with free breathing treatment. This approach offers superior positioning accuracy and improved heart protection without any increase in radiation or adverse reactions.

This is an investigator-initiated blinded, efficacious, phase III randomized clinical trial study. The study hypothesis is that the use of Surface Guided Radiation Therapy (SGRT) in combination with the Deep Inspiration Breath Hold (DIBH) technique for left breast cancer treatment can improve positioning accuracy and heart protection without any increase in radiation or adverse reactions. The primary endpoint of this study is the accuracy of the treatment location and incidence of patient coronary events/myocardial perfusion decline.

Inclusion Criteria:

1. Patients who have undergone breast-conserving surgery or modified radical mastectomy for left breast cancer;
2. Planned whole-breast ± supraclavicular region, chest wall ± supraclavicular region radiotherapy;
3. Able to perform deep inspiration breath-hold technique with breath-holding time >35s and can repeat it continuously for more than 6 times;
4. Patients who have not received neoadjuvant chemotherapy or breast reconstruction surgery;
5. No active heart disease, myocardial infarction, congestive heart failure or other cardiac diseases at baseline;
6. Patients are fully voluntary and able to sign the informed consent form 30 days before enrollment.

Exclusion Criteria:

1. Bilateral breast cancer;
2. No pathological diagnosis;
3. Remote metastasis;
4. Receiving neoadjuvant chemotherapy or breast reconstruction;
5. Have received mediastinal radiotherapy in the past;
6. Previous history of abdominal or pelvic radiotherapy;
7. Previous or secondary primary malignant tumor;
8. Serious cardiac insufficiency; Myocardial infarction or uncorrected unstable arrhythmia or uncorrected unstable angina pectoris occurred in the last 3 months; Pericardial disease.

aged 18-70, with an expected lifespan of >5 years

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