The article  from: dianjin radiotherapy
Medical history

33 years old woman,  differentiated infiltrating ductal carcinoma diagnosis. Biopsy specimens cut edge negative; Lymphatic vascular invasion; Estrogenreceptor (ER) and progesterone receptor (PR) and human epidermal growthfactor2 (HER 2) are negative. Pathology staging for pT1cN0M0. Consider breat conservative , radiotherapy and auxiliary.
Using TomoHelical ™ spiral ct radiation dose to 45 gy, devide into 25 times for whole breast irradiation, then use 10 gy ,devide into 5 times to irradiative.

Plan:

Parameter:

Diagram:

Clinical difficulties and solutions:

1. To solve the problem of uniform and respiratory movement,  use the  thickness of 1 cm tissue compensator.

2. In order to reduce the dose of spiral fault radiotherapy for heart and lung, two assumptions were used to implement Directional Block and completeblock .Directional shielding is performed in the hypothetical structure of the patient's surface (FIG. 1, pink structure), avoiding  subfield from which it is assumed to be in the patient's body. The boundary of the directional block is located in the border of body contour and PM 'and PL, PM' and PL are respectively by the PM and the PL line behind 5-10 degrees of direction (figure 1), the Angle adjustment is to avoid increase endanger organ dose and increase the rate of tumor cladding for the compromise.
Son to avoid wild or ipsilateral lung back into the patient from the heart to the body, another assumption that structure design implement fully blocked, the assumption of both ends are connected to the direction of shielding assumption on both ends of the structure (figure 1, green structure), the total shielding structure to avoid the child field direction to enter or leave the patient's body. In combination with directional and complete shielding structure, the beam can only be accessed from the inside and outside of the limited Angle. The process of optimizing the volume dose of organ and lung restriction structures (FIG. 1, blue structure) was established. In the process of optimization, the reduction of the lung limit structure dose can effectively reduce the same lung and heart dose, and increase the dose of PTV.

Follow-up Result:

There is only one degree of dermatitis. No local recurrence or metastasis has been found.

The advantage of TomoTherapy system:

1. Compared with conventional tangent field radiotherapy, spiral ct radiation therapy on the left side of the early breast cancer , through the perfect design of  treatment plan 's Directional Block and completeblock , successfully reduce the radiation dose to the normal tissue.

2. The radiation dose target of spiral fault radiotherapy was excellent, and the concave dose distribution was good with the benign form of the breast tissue, resulting in a significant decrease in the dose of the cardiopulmonary radiation (figure 2).