Dosimetric comparison between three- and four-dimensional computerised tomography radiotherapy for breast cancer

At present, methods of radiotherapy simulation for breast cancer based on four-dimensional computerised tomography (4D-CT) or three-dimensional CT (3D-CT) simulation remain controversial. In the present study, 7 patients with residual breast tissue received whole breast radiotherapy based on 3D-CT and 4D-CT simulation. For the 4D-CT plan, four types of CT images were produced, including images of the end of inspiration and the end of expiration, and images acquired by the maximal intensity projection (MIP) and average intensity projection (AIP). In the 3D-CT plan, the clinical target volume (CTV) and plan target volume (PTV) were marginally higher compared with the 4D-CT plan. In addition, the minimum point dose of the target volume (D _min), the maximum point dose of the target volume (D _max) and the mean point dose of the target volume (D _mean) of the CTV and PTV in the MIP and AIP plans were marginally higher compared with the 3D-CT plan. For the contralateral breast (C-B), volumes of the 4D-CT plan were markedly lower compared with the 3D-CT plan. Furthermore, D _min, D _max and D _mean of the 3D-CT plan were higher compared with the AIP and MIP plans. For the ipsilateral lungs (I-L), volumes of the 3D-CT and AIP plans were higher compared with the MIP plan. Furthermore, when breast lesions were on the left side, for the heart, the volume receiving no less than 40% of the prescription dose (V ₄₀) and the volume receiving no less than 30% of the prescription dose (V ₃₀) of the MIP and AIP plans were slightly lower compared with those of the 3D plan. In conclusion, 4D-CT radiotherapy based on the MIP and AIP plans provides a slightly smaller radiation area and slightly higher radiotherapy dosage of the CTV and PTV compared with 3D-CT radiotherapy for breast radiotherapy. Therefore, the MIP and AIP plans prevent C-B radiation exposure and improve sparing of the heart and I-L.