Abstract
PurposeThe current study aimed to compare contouring of glandular tissue only (gCTV) with the clinical target volume (CTV) as defined according to European Society for Radiotherapy and Oncology (ESTRO) guidelines (eCTV) and historically treated volumes (marked by wire and determined by palpation and anatomic landmarks) in breast cancer radiotherapy.MethodsA total of 56 consecutive breast cancer patients underwent treatment planning based solely on anatomic landmarks/wire markings (“wire based”). From these treatment plans, the 50% and 95% isodoses were transferred as structures and compared to the following CT-based volumes: eCTV; a Hounsfield unit (HU)-based automatic contouring of the gCTV; and standardized planning target volumes (PTVs) generated with 1‑cm safety margins (resulting in the ePTVs and gPTVs, respectively).ResultsThe 95% isodose volume of the wire-based plan was larger than the eCTV by 352.39 ± 176.06 cm3 but smaller than the ePTV by 157.58 ± 189.32 cm3. The 95% isodose was larger than the gCTV by 921.20 ± 419.78 cm3 and larger than the gPTV by 190.91 ± 233.49 cm3. Patients with larger breasts had significantly less glandular tissue than those with small breasts. There was a trend toward a lower percentage of glandular tissue in older patients.ConclusionHistorical wire and anatomic landmarks-based treatment planning sufficiently covers the glandular tissue and the theoretical gPTV generated for the glandular tissue. Modern CT-based CTV and PTV definition according to ESTRO results in a larger treated volume than the historical wire-based techniques. HU-standardized glandular tissue contouring results in a significantly smaller CTV and might be an option for reducing the treatment volume and improving reproducibility of contouring between institutions.
Highlights
Breast cancer is the most frequent cancer in women worldwide
There was no statistical difference between the ipsilateral ESTRO CTV (eCTV) and the contralateral eCTV
The current study was able to demonstrate that wire-based treatment planning sufficiently covered the European Society for Radiotherapy and Oncology (ESTRO) clinical target volume (CTV), the glandular tissue, and the theoretical planning target volumes (PTVs) generated for the glandular tissue
Summary
All patients diagnosed with breast cancer between 2014 and 2018 were retrospectively screened for this study. The field edge was marked with wire (by palpating the breast tissue) before the planning CT and treatment plans were calculated by experienced physicists without planning target volumes (PTVs), taking exclusively this information into account. All patients underwent “2D-analogous planning” based on wire markings/anatomic landmarks (such as the humeral head). A typical plan consisted of up to six photon fields with mixed accelerating voltages (6 and 15 megavolts, MV) for the two main tangential irradiation angles. These tangent fields were shaped on the basis of wire markings/anatomic landmarks and were counterbalanced (medial vs lateral and 6 MV vs 15 MV) so that the buildup regions as well as the inner-lying tissues were covered with the desired homogeneous amount of dose.
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