ESTRO 36 Abstract Book

S506 ESTRO 36 2017 _______________________________________________________________________________________________

technique (orthogonal vs. CBCT and high vs. low quality) on the doses to normal tissue was evaluated using Eclipse, where the imaging doses were used as based plans in the treatment planning process. For breast plans, doses to the heart and lung were evaluated. For head/neck plans, doses to all the normal tissues were compared.

Image-guided radiation therapy using MV imaging can be incorporated into the treatment plan to give clinically acceptable dose distributions. Dose to normal tissues is increased, however, and depends on the imaging technique, it is important to select the technique which minimizes normal tissue dose while providing sufficient image quality for patient setup.

Poster: Brachytherapy: Breast

PO-0922 Late toxicity and cosmetic outcome following APBI using interstitial multicatheter HDR brachytherapy T. Soror 1,2 , G. Kovács 2 , N. Seibold 2 , C. Melchert 2 , K. Baumann 3 , E. Wenzel 4 , S. Stojanovic-Rundic 5 1 National Cancer Institute, Radiation Oncology Department, Cairo, Egypt 2 Interdisciplinary Brachytherapy Unit, University of Luebeck/UKSH-CL- Germany, Lübeck, Germany 3 Clinic for Gynecology and Obstetrics, University of Luebeck/UKSH-CL- Germany, Lübeck, Germany 4 Clinic for Plastic Surgery, University of Luebeck/UKSH- CL- Germany, Lübeck, Germany 5 5Institute for Oncology and Radiology IORS, Radiation Oncology Department, Belgrad, Serbia Purpose or Objective Accelerated partial breast irradiation (APBI) has became a valid option in treating patients with early stage breast cancer following breast conservation surgery (BCS). This work reports on the late toxicity and the cosmetic outcome following APBI using interstitial multicatheter HDR intensity modulated brachytherapy (HDR-IMBT). Material and Methods Between 2006 and 2014, 114 patients received adjuvant APBI using interstitial multicatheter HDR-IMBT. Late toxicities were reported according to both the RTOG/EORTC score and the LENT/SOMA score. Cosmetic changes were documented by taking digital photographs before the APBI and during each follow-up visit. For each patient, we assessed two photographs, the first was taken after surgery and before APBI (baseline image), and the second at the last available follow-up visit. The cosmesis was assessed through a multidisciplinary team using the Harvard breast cosmesis scale. The clinical and the dosimetric parameters were investigated for any potential correlations with the cosmetic results.

Figure 1. Anthropomorphic phantom (CIRS) with dose measurement points identified. Results Average imaging dose was measured as 1.3, 2.5, 3.7, and 7.6cGy for daily low dose MV pairs, high quality MV pairs, low dose CBCT and high quality CBCT, respectively. Over a 30 fraction treatment with daily IGRT, this equates to 38 - 227cGy. The average agreement between measured and calculated tissue doses due to imaging was 0.4±0.4cGy. The largest difference was 1.3cGy, found in the lung for high quality CBCT imaging (~39cGy over a 30 fraction treatment). With imaging dose incorporated into the treatment planning process, it was possible to create clinically acceptable treatment plans for a range of treatment sites, including breast, head and neck and prostate. The imaging technique did, however, increase the heart and lung dose for breast plans. For an example left breast treatment, the mean heart dose in our original, clinically delivered plan was 60cGy. With daily MV imaging included, this increased to 140, 150, 190 and 260cGy for daily low dose MV pairs, high quality MV pairs, low dose CBCT and high quality CBCT, respectively. The corresponding values for mean lung dose were 360cGy (original clinical) and 470, 490, 510 and 570cGy.

Results The median follow-up period was 3.5 years (range 0.6 – 8.5). Late skin/soft tissue toxicities at the last follow-up visit are listed in Table1. Ten patients had grade-3 toxicity (8.8%) and no patients showed grade-4 toxicity. The most common toxicities were fibrosis (56.2% by LENT/SOMA score, and 47.4% by RTOG/EORTC score) followed by pain (42.1%). The final cosmetic scores were 81.5% excellent/good and 18.5% fair/poor. Comparing both the baseline and the last follow-up cosmetic scores, 59.6% of the patients had the

Table 1: Tissue doses(cGy/fraction) at different points in the anthropomorphic phantom. M: Measured. C:

Calculated Conclusion