Optimizing of the tangential technique and supraclavicular fields in 3 Dimensional conformal radiation therapy for breast cancer

Abstract

Radiotherapy plays an essential role in the management of breast cancer. Three-dimensional conformal radiation therapy (3D-CRT) is applied based on 3D image information of anatomy of patients. In three-dimensional conformal radiation therapy (3D-CRT) for breast cancer one of the common techniques is tangential technique. In this project, various parameters of tangential and supraclavicular fields are optimized.

This project has been done on CT images of 100 patients in Isfahan Milad Hospital. All patients have been simulated and all the important organs have been contoured by radiation oncologist. Two techniques in supraclavicular region are evaluated including: 1- A single field (AP Anterior Posterior) with a dose of 200cGy per fraction with 6MV energy. This is a common technique. 2- Two parallel opposed fields (Anterior Posterior-Posterior Anterior).  The dose of AP was 150cGy with 6MV energy and PA 50cGy with 18MV. In the second part of the project, the tangential fields has been optimized with change of normalization point in five points: 1- Iso center (Confluence of rotation gantry axis and collimator axis) 2- Middle of thickest part of breast or middle of inter field distance (IFD) 3- Border between lung and chest wall 4- Physician’s choice 5- Between IFD and isocenter.

Dose distributions have been compared for all patients in different methods of   supraclavicular and tangential field. In parallel opposed fields average lung dose was 4% more than single field and the maximum received heart dose was 21.5% less than single field.

The average dose of PTV (Planning Tumor Volume) in method 2 is 2 % more than method 1.  In general AP-PA method because of a better coverage of PTV is suggested.

In optimization of the tangential field all methods have similar coverage of PTV. Each method has spatial advantages and disadvantages. If it is important for the physician to reduce the dose received by the lung and heart, fifth  method is suggested since in this method average and maximum received dose to heart and lung  have been reduced few percent in comparison to other methods. If a better coverage of PTV is important for the physician second method can be an optimized method. In this method average and maximum received dose to PTV have been increased few percent in comparisons of physician’s choice method and three other methods.

In optimizing of supraclavicular field AP-PA method due to better coverage of PTV is suggested. In optimizing of tangential all methods are similar. Each method has special advantages and disadvantages. The physicians can change the depth of the normalization point in the breast to get the desired average dose.