A Comparison Of Modified Wide Tangent, Direct Internal Mammary And Intensity Modulated Radiation Therapy Plans In The Treatment Of Left-Sided Breast Cancer

Purpose/Objective: Radiation therapy for node positive breast cancer routinely will incorporate a Modified Wide Tangential (MWT) beam placement to include the clinical breast tissue as well as the ipsilateral internal mammary nodes (IMN). When dealing with left sided breast the inclusion of the IMN increases the amount of lung and heart in the treatment field. With long term survival comes concern of long term complications to these Organs at Risk (OAR) and future toxicity with radiation doses in excess of 30 Gy. To reduce the dose to OAR compromises are made to the IMN and PTV volumes whereby these structures are not covered by 95% isodose. This study investigates if multi-field, inverse-planned IMRT would improve conformity and reduce radiation dose to the OARs while achieving a 95% PTV (planning target volume) coverage. IMRT plan is compared to a MWT technique and a Direct Internal Mammary (DIM) to compare V30 and Mean Dose (MD) to OARs (heart and lung) and healthy tissue (HT).Materials/Methods: 24 left sided breast patients were contoured for ipsilateral breast, IMNs, heart, lungs, body and medial contralateral right breast. Standard MWT tangential plans were simulated for each patient without compromising IMN volume and therefore increasing heart and lung volumes. If there was greater than 3.5cm of lung at midtangent a DIM (reduced tangents with an angled electron and direct photon field covering IMN)plan was also generated. These plans were compared to an 11 field IMRT plan which was also generated. All plans were calculated based on 50 Gy in 25 fractions. Dose-volume histograms (DVHs) for each plan were generated and the three plans were compared for each patient. Conformity Index (CI: volume CTV divided by volume receiving > 95%), Homogenenity Index (HI: %CTV>95% and <105%) and doses to OAR and HT were compared between techniques.Results: Compared to standard MWT plans, the IMRT plans significantly improved CI, V30-heart and heart MD compared to other treatment techniques. HI improved marginally. HT was comparable between IMRT and MWT, however for IMRT there was less HT>45 Gy. Right contralateral breast had an increase in MD with the IMRT method. DIM plans had a greater variation in IMN doses depending on individual patient.Conclusions: IMRT plans are a viable option if the goal is to improve conformity by decreasing dose to heart and ipsilateral lung with a modest increase in mean contralateral breast dose. There is room to continue to develop improved technique and beam arrangement to further optimize the IMRT plan. There is more work required to define anatomic structures (breast PTV,IMN, heart) and treatment intent (inclusion of nodes to specific doses) to determine future benefit from the conformal advantages of multi-field IMRT. Purpose/Objective: Radiation therapy for node positive breast cancer routinely will incorporate a Modified Wide Tangential (MWT) beam placement to include the clinical breast tissue as well as the ipsilateral internal mammary nodes (IMN). When dealing with left sided breast the inclusion of the IMN increases the amount of lung and heart in the treatment field. With long term survival comes concern of long term complications to these Organs at Risk (OAR) and future toxicity with radiation doses in excess of 30 Gy. To reduce the dose to OAR compromises are made to the IMN and PTV volumes whereby these structures are not covered by 95% isodose. This study investigates if multi-field, inverse-planned IMRT would improve conformity and reduce radiation dose to the OARs while achieving a 95% PTV (planning target volume) coverage. IMRT plan is compared to a MWT technique and a Direct Internal Mammary (DIM) to compare V30 and Mean Dose (MD) to OARs (heart and lung) and healthy tissue (HT). Materials/Methods: 24 left sided breast patients were contoured for ipsilateral breast, IMNs, heart, lungs, body and medial contralateral right breast. Standard MWT tangential plans were simulated for each patient without compromising IMN volume and therefore increasing heart and lung volumes. If there was greater than 3.5cm of lung at midtangent a DIM (reduced tangents with an angled electron and direct photon field covering IMN)plan was also generated. These plans were compared to an 11 field IMRT plan which was also generated. All plans were calculated based on 50 Gy in 25 fractions. Dose-volume histograms (DVHs) for each plan were generated and the three plans were compared for each patient. Conformity Index (CI: volume CTV divided by volume receiving > 95%), Homogenenity Index (HI: %CTV>95% and <105%) and doses to OAR and HT were compared between techniques. Results: Compared to standard MWT plans, the IMRT plans significantly improved CI, V30-heart and heart MD compared to other treatment techniques. HI improved marginally. HT was comparable between IMRT and MWT, however for IMRT there was less HT>45 Gy. Right contralateral breast had an increase in MD with the IMRT method. DIM plans had a greater variation in IMN doses depending on individual patient. Conclusions: IMRT plans are a viable option if the goal is to improve conformity by decreasing dose to heart and ipsilateral lung with a modest increase in mean contralateral breast dose. There is room to continue to develop improved technique and beam arrangement to further optimize the IMRT plan. There is more work required to define anatomic structures (breast PTV,IMN, heart) and treatment intent (inclusion of nodes to specific doses) to determine future benefit from the conformal advantages of multi-field IMRT.