ESTRO consensus guidelines ESTRO consensus guideline on target volume delineation for elective radiation therapy of early stage breast cancer

Background and purpose: Delineation of clinical target volumes (CTVs) is a weak link in radiation therapy (RT), and large inter-observer variation is seen in breast cancer patients. Several guidelines have been proposed, but most result in larger CTVs than based on conventional simulator-based RT. The aim was to develop a delineation guideline obtained by consensus between a broad European group of radiation oncologists. Material and methods: During ESTRO teaching courses on breast cancer, teachers sought consensus on delineation of CTV through dialogue based on cases. One teacher delineated CTV on CT scans of 2 patients, followed by discussion and adaptation of the delineation. The consensus established between teachers was sent to other teams working in the same field, both locally and on a national level, for their input. This was followed by developing a broad consensus based on discussions. Results: Borders of the CTV encompassing a 5 mm margin around the large veins, running through the regional lymph node levels were agreed, and for the breast/thoracic wall other vessels were pointed out to guide delineation, with comments on margins for patients with advanced breast cancer. Conclusion: The ESTRO consensus on CTV for elective RT of breast cancer, endorsed by a broad base of the radiation oncology community, is presented to improve consistency. 2014 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 114 (2015) 3–10 Elective radiation therapy (RT) of early stage breast cancer has proven to be very effective in lowering the risk of recurrences and improving overall survival [1], and it is therefore offered to many patients in the postoperative setting. However, there is also treatment-related morbidity, some relatively frequent and related to breast and shoulder [2,3], and others more seldom but potentially serious such as heart disease and secondary cancer development [4,5]. The risk of local recurrence has progressively decreased over the last decades [6], while overall survival of breast cancer patients improved considerably [7]. It is therefore increasingly important to provide optimal RT to the patients to obtain a maximal effect at the lowest risk of late morbidity. During the last decade a transition from 2D to 3D RT planning in early stage breast cancer has taken place in most European countries. In the 2D era bony landmarks were used to design RT fields, and it was difficult to individualise the field planning with respect to e.g. the heart because soft tissues were poorly visualised and displayed in a planar simulator-based projection only. Since then, the complexity of RT has increased gradually from just a few large fields to forward-planned field-in-field and even fully computerised intensity 4 ESTRO consensus on RT volumes in breast cancer modulated radiotherapy (IMRT). With these approaches now used in most European clinics, it is possible to shape the fields closely around the target volumes with steep dose gradients between the CTV and the organs at risk (OAR) and to deliver a homogeneous dose distribution, reducing side effects and improving cosmetic outcome and the quality of life of patients [8]. In general, multiple equi-spaced axial fields are not recommended for breast RT, because this technique results in a low dose to a large volume of the body including the OAR [6]. Other advanced techniques are also being introduced quite rapidly, for example the simultaneous integrated boost to the primary tumour bed [9], and respiratory controlled techniques in left-sided patients [10]. Moreover, highly individualised treatment techniques can be required for individual patients based on anatomical variations that lead to a suboptimal dose distribution with standard treatment planning. This increasing complexity in the field of breast cancer RT emphasises the need for optimising the consistency and reproducibility in treatment planning, also to ensure comparability of treatment outcome among departments. Currently, target volume delineation can be considered as the weakest part of the quality chain in RT. A large inter-observer variation is seen in delineation of regional lymph nodes, breast and thoracic wall. To minimise this, several guidelines for target volume delineation in early breast cancer [11–18] have been published. Atlases for delineating the heart have also been proposed [19,20], and recently software has been developed for autosegmentation of target volumes to support RT planning [21,22]. However, most of these guidelines, if applied as described, result in larger treated volumes than treated with conventional simulator-based RT. This can be explained in part by the use of the same fixed bony landmarks as used for simulator-based treatment set-up, followed by the addition of margins from CTV to PTV and to the field borders. An increase in treated volume should be avoided as no clinical reason for this exists and as this might lead to an increase in the dose to OAR [23]. Furthermore the use of systemic treatment has increased considerably over the last decade, and this may also have implications for the risk of radiation-related morbidity [3]. Since the first ESTRO teaching course on multidisciplinary management of breast cancer in 2009, target volume delineation has been practised and discussed in hands-on workshops, and during the five consecutive live courses as well as contouring exercises at congresses and online, the teachers from four countries (DK, ESP, F and NL) continued to work towards a European consensus on delineation guidelines for the clinical target volumes (CTVs) for elective lymph node areas, the breast and the thoracic wall in early stage breast cancer. The consensus has been sent to several colleagues active in treating early breast cancer, both in Europe and abroad, for further discussion, fine tuning and agreement. We now present hereby the final consensus guideline including the outcome of discussions held with radiation oncology specialists dedicated to the care of breast cancer patients from all over the world. Materials and methods One of the teachers of the ESTRO course (PP) started with delineating relevant CTV on non-contrast-enhanced computer tomography (CT) scans of two typical patients treated with breast conserving surgery and mastectomy for early breast cancer and scanned in supine treatment position, i.e. the patients were positioned on a breast-board inclined at 12.5–15 with both arms abducted around 120 . The head was positioned straight with the chin slightly upwards, avoiding skin folds at the level of the lower neck. This guideline does not describe the special issues regarding patients treated in prone position, because the anatomy is significantly different in that position. Before CT scanning two circles of radio-opaque wires were placed around the breast representing the palpable/visible CTV breast (inner circle) and the provisional field borders (outer circle) to aid in target volume delineation. The scans were made under free breathing and with 2.5 mm thick sections. It was decided to use nomenclature according to Santanam et al. [24], thus the suffix n indicates nodal areas and p indicates (post-operative) primary tumour volumes. The three other teachers commented, and specific borders were discussed during ESTRO courses and at telephone conferences, also using ESTRO’s FALCON platform for volume delineation. Based on this, PP and BVO adapted the delineations. Most of the discussions among teachers were devoted to finding a compromise between real anatomical borders and practical clinical borders to prevent an increase in size of the RT fields compared to conventional RT fields. For example, although the anatomical medial border of the supraclavicular region was considered to be 5 mm around the veins, the carotid artery was excluded and no margin around the jugular vein was added, since a Danish analysis has shown a very limited number of regional recurrences, and those that appeared were within the high dose zone [23]. In addition, the guidelines were discussed with the Belgium group [25], and further adaptations were made with more attention paid to the vessels and less to bony structures. A suggestion for an anatomical overview of vessels is to look at http://www.ikonet. com/en/health/virtualhuman-body/virtualhumanbody.php.