The Use of 18F–FDG PET-CT Imaging to Determine Internal Mammary Lymph Node Location for Radiation Therapy Treatment Planning in Breast Cancer Patients

Publication date: Available online 5 November 2016
Source:Practical Radiation Oncology
Author(s): Tima Davidson, Merav Ben-David, Shira Galper, Tess Haskin, Megan Howes, Roland Scaife, Nayroz Kanana, Uri Amit, Noam Weizman, Boris Chikman, Elinor Goshen, Simona Ben-Haim, Zvi Symon, Jeffrey Goldstein
IntroductionAdjuvant Internal mammary lymph node (IMN) radiation is often delivered using 2D techniques that use anatomical landmarks and predetermined depths for field placement and dose specification. In contrast, 3D planning uses the internal mammary vessels (IMV) to localize the IMN for planning. We evaluated if localization of involved-IMN (i-IMN) by ¹⁸F–FDG PET-CT offers opportunities to improve treatment.MethodsBreast cancer patients (n=80) who had i-IMN (n=112) on PET-CT for initial staging (n=40) or recurrence (n=40) were studied. Size, intercostal space (IC), distance from skin, sternum and IMV were recorded. Effects on 2D and 3D planning were evaluated.ResultsMost i-IMN were in the1st-3rd (94.6%) IC. Few were in the 4th (4.5%) or 5th (0.9%) IC. Mean i-IMN depth was 3.4cm (range: 1.1cm–7.3cm). Prescriptive depths of 4cm, 5cm and 6cm would result in under-treatment of 25%, 10.7%, and 5.3% of IMN respectively. Most IMN (86.6%) were lateral or adjacent to the sternal edge. Only13.4% were posterior to the sternum. Use of the ipsilateral or contralateral sternal edge for field placement increases risk of geographic miss or excess normal tissue exposure. Most i-IMN were adjacent to (83%), or ≤0.5cm (14%) from the IMV edge. Three (3%) were >0.5cm beyond the IMV edge. The clinical target volume (CTV) defined by the 1st – 3rd IC encompassed 78% of i-IMN. IMN-CTV coverage of i-IMN increased with inclusion of the 4th IC (82%), 0.5cm medial and lateral margin expansion (93%) or both (96.5%).Conclusion2D treatment techniques risk geographic miss of IMN and exposure of excess normal tissue to radiation. An IMN-CTV defined by the IMV from the 1st-3rd IC with 0.5cm medial and lateral margin expansion encompasses almost all i-IMN identified on PET-CT imaging. Inclusion of the 4th IC offers modest coverage improvement and its inclusion should be weighed against potential increase in cardiac exposure.SummaryThe use of 2D treatment techniques for adjuvant IMN radiation may cause geographic miss of tumor and expose normal tissue to radiation injury. Conformal 3D planning improves coverage and reduces risk of normal tissue damage by using the IMV to define an IMN-CTV. Contouring the IMN-CTV from the 1st -3rd IC space with a 0.5cm expansion medially and laterally encompasses most IMN. PET-CT may have a role in radiation planning by identifying involved-IMN for dose escalation.



from Cancer via ola Kala on Inoreader http://ift.tt/2f5wWpT
via IFTTT