'Field in field' for the treatment of breast cancer with lymph nodes: A comparative study with conventional radiotherapy using wedge filters

Introduction Treatment of breast cancer with lymph nodes (internal mammary and clavicular nodes) is achieved in most of the centers using a conventional radiotherapy based on electron-photon beams with junctions and wedge filters. Wedge filters correct for surface obliquities but do not provide optimal dose homogeneity within the breast volume. This study aims at comparing treatment plans using the ‘‘field in field” technique, equivalent to a ‘‘simplified” intensity modulation with treatment plans using wedge filters. Material and methods This study focused on eight patients (for half of the patients, the internal mammary nodes were included in the breast fields) treated for breast cancer with lymph nodes using wedge filters. For these patients a ‘‘field in field” plan was prepared retrospectively. Patients were positioned supine with ipsilateral arm above the head and head turned to the opposite treatment side. The prescribed dose was 50 Gy to the PTV breast and 46–50 Gy for the lymph nodes. For both technics, after treatment plan optimization, doses delivered to targets, heart and ipsilateral lung are reported. Results For the 8 patients and for the same coverage of breast and lymph nodes PTV, the volume of 105% (52.5 Gy) of the dose remaining in the breast volume was 2.65–24.29 cc (mean 13.9 cc) with the ‘‘field in field” technic and 9.49–231.63 cc (mean 98.5 cc) with wedge filters technic. For ipsilateral lung, the mean dose, V20 and V30 were respectively 15.1–16.6 Gy (average 15.8 Gy), 25.4–27.1 Gy (average 26.1 Gy), and 17.3–19 Gy (mean 17.9 Gy) for both technics. Conclusion For 8 patients, ‘‘field in field” treatment plans showed that remaining volume of 105% of the dose was up to 10 times smaller than using wedge filters treatment plans. This technics allowed reducing significantly overdosage areas and therefore having a better dose homogeneity in the breast.