In which position is breast external beam irradiation not typically delivered?

Breast external beam irradiation is most commonly delivered to ensure optimal dosimetry and patient comfort while minimizing potential movements during treatment. The supine position is frequently used because it allows for better access to the treatment area and can facilitate uniform distribution of radiation across the breast tissue. The prone position is also utilized in certain cases, particularly when targeting the breast while sparing the heart and lungs, as it can provide a more favorable geometry for radiation delivery.

Sitting and standing positions are generally less practical for this type of radiation therapy. The standing position can make it challenging to maintain stability and alignment over the treatment area, while the sitting position may not provide the necessary anatomical positioning for effective delivery of radiation to the breast tissue. Thus, these two positions are not typically used for breast external beam irradiation, with standing being particularly impractical for ensuring consistent and accurate targeting.