8.3.1 After Breast-conserving Surgery
At present，total breast irradiation has rarely been done in two-dimensional plans，and CT positioning is generally used to develop a three-dimensional radiotherapy plan（Fig.8-0-7）.When the CT simulator is positioned，the patient lies on the breast frame，the upper limbs are abducted，and the phantom is not fixed，and the marking line is directly drawn on the patient's skin.On the one hand，the fixation of the phantom increases the dose of the breast skin，and on the other hand，it easily causes the displacement of the breast，which in turn affects the accuracy of the treatment placement.In order to reduce the secondary error caused by the illumination field center position，the center of the whole breast irradiation is found at the time of positioning，generally placed in the nipple layer，and the marking line is drawn on the patient's skin（the marking line in the direction of the head and foot is as long as possible，beyond Breast range）.Because it is difficult to accurately distinguish the breast tissue range on the CT image，it is recommended to mark the anatomical boundary of the breast with the lead wire before the CT scan，and mark the surgical scar at the breast tumor bed with the lead wire，and then scans with 5mm layer.
Fig.8-07 Position and body surface markers of the patient during total breast radiotherapy.Positioning of the mammary gland outline and tumor bed scar before the CT scan
Target area of total breast radiotherapy：CTV：affected side of the breast，pectoralis major fascia.Excludes skin（received subcutaneous 0.5 cm），chest size muscles，ribs，and intercostal muscles（unless these sites are infested）.PTV：CTV is placed 0.5～1.0cm，and the skin direction is not released（limited to 0.5cm under the skin）（Fig.8-08）.Normal organs need to delineate the lungs，the healthy breast，the left anterior descending coronary artery and the left anterior descending coronary artery（left breast cancer patient）.The left anterior descending coronary artery（LAD）is emitted from the left main trunk of the coronary artery and travels in the interventricular sulcus.When CT scans，some can show，and some can not be displayed.When it cannot be displayed，it is drawn according to the position of the inter-chamber groove（Fig.8-09）.
Fig.8-08 Whole breast target area，blue：CTV，green：PTV(https://www.daowen.com)
Fig.8-09 Left anterior descending coronary artery（red）
After the target area is drawn，the prescription dose and normal tissue limit requirements are submitted，and the physicist develops a radiotherapy plan.In order to protect the heart and lungs，the tangential field-based three-dimensional conformal plan（3DCRT）or the wild-field wild-strong plan（IMRT）is most commonly used.The 3D-CRT technique uses two tangential field illuminations with wedge plates.Different from the two-dimensional technique，the 3D-CRT has a three-dimensional dose distribution of the whole breast，a wedge plate according to the actual tissue density（lung correction），and conformal protection of the lung.Multi-sub-field IMRT technology is the wild-field radiation technique，also known as simplified intensity-modulated radiotherapy：on the basis of the conformal tangent field，6 to 8 subfields are added in the direction of the incision and the excision field to regulate the reduction of the high dose area inside.breast target area.80%of the total dose is still given by the two most basic conformal tangent fields.As with the two-dimensional radiotherapy technique，the two basic tangent fields are open 1 to 2 cm outward in the direction of the breast skin to ensure that during the irradiation.The entire breast is always in the field.The remaining 20%of the dose was administered by the subfield to reduce the volume of the high dose area and to evenly distribute the dose within the target area（Figure 8-10）.
Fig.8-10 Dose distribution map and DNH of total breast radiotherapy