doi:10.1016/j.meddos.2009.10.006 CONFORMAL LOCOREGIONAL BREAST IRRADIATION WITH AN OBLIQUE PARASTERNAL PHOTON FIELD TECHNIQUE KATRIEN ERVEN, M.D., SASKIA PETILLION, M.SC., CAROLINE WELTENS, M.D., PH.D., FRANK VAN DEN HEUVEL,PH.D., GILLES DEFRAENE, M.ENG., ERIK VAN LIMBERGEN, M.D., PH.D., and WALTER VAN DEN BOGAERT, M.D., PH.D. Department of Radiation Oncology, University Hospital Gasthuisberg, Leuven, Belgium (Received 10 April 2009; accepted 26 October 2009) Abstract—We evaluated an isocentric technique for conformal irradiation of the breast, internal mammary, and medial supra-clavicular lymph nodes (IM-MS LN) using the oblique parasternal photon (OPP) technique. For 20 breast cancer patients, the OPP technique was compared with a conventional mixed-beam technique (2D) and a conformal partly wide tangential (PWT) technique, using dose-volume histogram analysis and normal tissue complication probabilities (NTCPs). The 3D techniques resulted in a better target coverage and homogeneity than did the 2D technique. The homogeneity index for the IM-MS PTV increased from 0.57 for 2D to 0.90 for PWT and 0.91 for OPP (both p < 0.001). The OPP technique was able to reduce the volume of heart receiving more than 30 Gy (V 30 ), the cardiac NTCP, and the volume of contralateral breast receiving 5 Gy (V 5 ) compared with the PWT plans (all p < 0.05). There is no significant difference in mean lung dose or lung NTCP between both 3D techniques. Compared with the PWT technique, the volume of lung receiving more than 20 Gy (V 20 ) was increased with the OPP technique, whereas the volume of lung receiving more than 40 Gy (V 40 ) was decreased (both p < 0.05). Compared with the PWT technique, the OPP technique can reduce doses to the contralateral breast and heart at the expense of an increased lung V 20 . © 2011 American Association of Medical Dosim- etrists. Key Words: Breast cancer, Internal mammary nodes, Radiotherapy, Treatment technique. INTRODUCTION Postoperative locoregional radiotherapy improves local control and overall survival in node-positive breast can- cer patients. 1 The complex target volume in locoregional irradiation for breast cancer, in close proximity to the heart and the lungs, renders treatment planning difficult, because different fields have to be aligned to cover the whole target. The dose distribution near the junction area is often inhomogeneous, both at the skin surface and in depth, which can lead to recurrences or complications. A variety of treatment techniques for breast and internal mammary and medial supraclavicular lymph node (IM-MS LN) radiotherapy has been proposed, indicating the absence of a generally accepted technique. 2 A widely used technique for irradiation of the breast and the IM-MS LN, in the era before computed tomo- graphy (CT)-based treatment planning, combines the tangential breast fields with an anterior mixed photon and electron beam, covering the IM-MS LN. The posi- tion of the fields is mostly based on surface anatomy and the dose is prescribed to a point. 3 It has been shown that the whole target volume is not always covered with this technique. 4 This is partly due to the lack of consensus regarding the target volume definition in lo- coregional breast cancer, and partly because of large interpatient variability in position of the different target volumes. Currently, guidelines for target volume delin- eation are available and several studies support the use of CT-based treatment planning in locoregional breast irra- diation. 4–7 When a mixed photon and electron beam technique is planned, based on full CT data, matchline problems are highlighted. Adjacent fields can be de- signed to overlap, to abut, or to allow a small gap to optimise the target coverage. However, even with ade- quate patient immobilization, there is no guarantee that the overlap or gap can be reproduced consistently. The subclavicular matchline problems can be solved readily by using half beams for the tangential fields and the supraclavicular field. Modern linear accelerators enable this with asymmetric collimation. 8 The alignment between the tangential fields and the parasternal field is a bigger challenge. In the partly wide tangential (PWT) technique, the use of a parasternal match- line is avoided by including the IM LN in the tangential fields. 9 This technique was advocated in several compara- tive planning studies as the most appropriate solution for conformal irradiation of the breast and IM LN. 5,10 –12 A disadvantage to this technique is the contralateral breast dose. To minimize matchline problems and avoid irradi- ating the contralateral breast, the oblique parasternal photon (OPP) technique is developed. This mono-isocentric Reprint requests to: Katrien Erven, M.D., Department of Radia- tion Oncology, University Hospital Gasthuisberg, Herestraat 49, 3000 Leuven, Belgium. E-mail: Katrien.Erven@uzleuven.be Medical Dosimetry, Vol. 36, No. 1, pp. 28-34, 2011 Copyright © 2011 American Association of Medical Dosimetrists Printed in the USA. All rights reserved 0958-3947/11/$–see front matter 28