Feasibility study of defining planning target volume using surgical margins in permanent breast seed implant brachytherapy.

PURPOSE:This study investigates the feasibility and potential impacts of utilizing a Groupe Européen de Curiethérapie-European Society for Therapeutic Radiation and Oncology (GEC ESTRO) recommended surgical margin-based planning margin in permanent breast seed implant (PBSI) brachytherapy. METHODS AND MATERIALS:Seventy-nine patients were included in this retrospective study. Three margin selections were used for PTV construction: (1) 1.25 or 1.5 cm isotropic margin (PTVPBSI), (2) 2 cm minus surgical margin in each direction as recommended by GEC ESTRO (PTVaniso), and (3) 2 cm minus minimum surgical margin isotropically (PTViso). PTV volume and dose coverage using clinical PBSI plans were compared across three groups. New PBSI plans were constructed on PTVaniso for 20 patients and planning parameters were compared to original plans constructed on PTVPBSI. RESULTS:Twenty patients had surgical margins in six directions reported, with a median value of 8 mm anteriorly, and 10 mm in all other directions. PTVaniso (36.3 ± 15.0 cc) was overall smaller than PTVPBSI (55.6 ± 14.3 cc), p value < 0.05. PBSI clinical plans showed satisfactory coverage on PTVaniso, with a median (range) V100 of 97.9% (85.8%-100.0%). Comparing to original treatment plans, new plans constructed on PTVaniso reduced the number of implant seeds and skin dose. CONCLUSIONS:Clinical PBSI plans provide satisfactory coverage of GEC ESTRO recommended PTVs. In this patient cohort, GEC ESTRO planning margin resulted in smaller target volumes, and therefore, new plans constructed on PTVaniso required fewer implanted seeds and lower skin doses were achieved. However, given PBSI delivery uncertainties, further investigations are required to determine if the GEC ESTRO planning margin will be sufficiently robust.