Gerson M Struik1, Jean-Philippe Pignol2, Inger-Karine Kolkman-Deurloo3, Jeremy Godart3, Gerda M Verduijn3, Linetta B Koppert4, Erwin Birnie5, Ali Ghandi6, Taco M Klem7. 1. Department of Surgery, Franciscus Gasthuis and Vlietland, Rotterdam, The Netherlands; Department of Radiation Oncology, Erasmus MC Cancer Institute, Rotterdam, The Netherlands. Electronic address: g.struik@franciscus.nl. 2. Department of Radiation Oncology, Erasmus MC Cancer Institute, Rotterdam, The Netherlands; Department of Radiation Oncology, Dalhousie University, Halifax, Nova Scotia, Canada. 3. Department of Radiation Oncology, Erasmus MC Cancer Institute, Rotterdam, The Netherlands. 4. Department of Surgery, Erasmus MC Cancer Institute, Rotterdam, The Netherlands. 5. Department of Statistics and Education, Franciscus Gasthuis and Vlietland, Rotterdam, The Netherlands; Division of Woman and Baby, Department of Obstetrics and Gynecology, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands. 6. Department of Radiology, Franciscus Gasthuis and Vlietland, Rotterdam, The Netherlands. 7. Department of Surgery, Franciscus Gasthuis and Vlietland, Rotterdam, The Netherlands.
Abstract
PURPOSE: Accelerated partial breast irradiation is a treatment option for selected patients with early-stage breast cancer. Some accelerated partial breast irradiation techniques lead to skin toxicity with the skin dose as a main risk factor. Biodegradable spacers are effective and safe in prostate brachytherapy to protect the rectum. We hypothesize that a subcutaneous spacer injection reduces the skin dose in breast brachytherapy. METHODS AND MATERIALS: Ultrasound-guided spacer injections, either hyaluronic acid (HA) or iodined polyethylene glycol (PEG), were performed on fresh mastectomy specimens. Success was defined as a spacer thickness of ≥5 mm in the high-dose skin area. Usability was scored using the system usability scale. Pre and postinjection CT scans were used to generate low-dose-rate seed brachytherapy treatment plans after defining a clinical target volume. Maximum dose to small skin volumes (D0.2cc) and existence of hotspots (isodose ≥90% on 1 cm2 of skin) were calculated as skin toxicity indicators. RESULTS: We collected 22 mastectomy specimens; half had HA and half had PEG injection. Intervention success was 100% for HA and 90.9% for PEG (p = NS). Hydrodissection was feasible in 81.8% with HA and 63.6% with PEG. Median system usability scale score was 97.5 for HA and 82.5 for PEG (p < 0.001). Mean D0.2cc was 80.8 Gy without spacer and 53.7 Gy with spacer (p < 0.001). Skin hotspots were present in 40.9% without spacer but none with spacer (p < 0.001). CONCLUSIONS: A spacer injection in mastectomy specimens is feasible. An extra 5 mm space is always achieved, thereby potentially reducing the skin dose dramatically in low-dose-rate seed breast brachytherapy.
PURPOSE: Accelerated partial breast irradiation is a treatment option for selected patients with early-stage breast cancer. Some accelerated partial breast irradiation techniques lead to skin toxicity with the skin dose as a main risk factor. Biodegradable spacers are effective and safe in prostate brachytherapy to protect the rectum. We hypothesize that a subcutaneous spacer injection reduces the skin dose in breast brachytherapy. METHODS AND MATERIALS: Ultrasound-guided spacer injections, either hyaluronic acid (HA) or iodined polyethylene glycol (PEG), were performed on fresh mastectomy specimens. Success was defined as a spacer thickness of ≥5 mm in the high-dose skin area. Usability was scored using the system usability scale. Pre and postinjection CT scans were used to generate low-dose-rate seed brachytherapy treatment plans after defining a clinical target volume. Maximum dose to small skin volumes (D0.2cc) and existence of hotspots (isodose ≥90% on 1 cm2 of skin) were calculated as skin toxicity indicators. RESULTS: We collected 22 mastectomy specimens; half had HA and half had PEG injection. Intervention success was 100% for HA and 90.9% for PEG (p = NS). Hydrodissection was feasible in 81.8% with HA and 63.6% with PEG. Median system usability scale score was 97.5 for HA and 82.5 for PEG (p < 0.001). Mean D0.2cc was 80.8 Gy without spacer and 53.7 Gy with spacer (p < 0.001). Skin hotspots were present in 40.9% without spacer but none with spacer (p < 0.001). CONCLUSIONS: A spacer injection in mastectomy specimens is feasible. An extra 5 mm space is always achieved, thereby potentially reducing the skin dose dramatically in low-dose-rate seed breast brachytherapy.