Radiation therapy to the breast has remained a standard practice for breast conserving therapy. Because of the location of the heart and lungs when patients are positioned face-up, whole breast radiation therapy has been reported to increase the risk of damage to the heart a few years after treatment until at least 20 years after exposure, and may affect cardiovascular mortality. Also, patients receiving whole breast radiation therapy are at an increased risk for development of secondary lung malignancies. Recent studies have demonstrated a significant reduction in dose to the heart and lungs when treated in the face-down position. Similarly, correcting for the movement of breathing (respiratory gating) in the face-up position has also become an available option for reducing unwanted dose to the heart and lungs, particularly in left sided breast cancers. No study to date has compared these newer organ-sparing techniques head-to-head for early stage breast cancer.

It is institutional policy to perform CT simulation in left-sided breast cancer patients with and without the respiratory gating (this is one CT scan), in the face-up position. It is also standard of care to perform the face-down CT simulation in large breasted women. Both of these simulations are meant to reduce the exposure of the heart and lungs to radiation.

In this study, all left-sided breast cancer patients that consent will receive face-up CT simulation with and without gating AND face-down CT simulation, regardless of breast size; thus, each patient is their own control.

The treating physician will determine which of the two simulations, if any, offers better protection to each patients' heart and lungs. Two dosimetrists will be required to independently verify planned dosimetry with all treatment setups. Treatment will be planned in standard fashion using the best of the two plans.

Radiation therapy to the breast has remained a standard practice for breast conserving therapy. Because of the location of the heart and lungs when patients are positioned face-up, whole breast radiation therapy has been reported to increase the risk of damage to the heart a few years after treatment until at least 20 years after exposure, and may affect cardiovascular mortality. Also, patients receiving whole breast radiation therapy are at an increased risk for development of secondary lung malignancies. Recent studies have demonstrated a significant reduction in dose to the heart and lungs when treated in the face-down position. Similarly, correcting for the movement of breathing (respiratory gating) in the face-up position has also become an available option for reducing unwanted dose to the heart and lungs, particularly in left sided breast cancers. No study to date has compared these newer organ-sparing techniques head-to-head for early stage breast cancer.

It is institutional policy to perform CT simulation in left-sided breast cancer patients with and without the respiratory gating (this is one CT scan), in the face-up position. It is also standard of care to perform the face-down CT simulation in large breasted women. Both of these simulations are meant to reduce the exposure of the heart and lungs to radiation. In this study, all left-sided breast cancer patients that consent will receive face-up CT simulation with and without gating AND face-down CT simulation, regardless of breast size; thus, each patient is their own control.

The treating physician will determine which of the two simulations, if any, offers better protection to each patients' heart and lungs. Two dosimetrists will be required to independently verify planned dosimetry with all treatment setups. Treatment will be planned in standard fashion using the best of the two plans.

Inclusion Criteria:

• Stage 0-IIA left, breast cancer,
• After lumpectomy or segmental mastectomy,
• With negative surgical margins

Exclusion Criteria:

• Right breast cancer
• Positive surgical margins
• Stage 2B or higher