ESTRO 38 Abstract book

S578 ESTRO 38

1 Inselspital- Bern University Hospital- University of Bern, Department of Radiation Oncology, Bern, Switzerland Purpose or Objective To evaluate the efficacy, toxicity profile and dosimetric parameters of accelerated partial breast irradiation (APBI) delivered with interstitial multicatheter HDR brachytherapy (HDR-BT) after breast-conserving surgery (BCS). Material and Methods We analyzed a series of patients (pts) treated from 2005 to 2017 with HDR-BT APBI using multicatheter interstitial brachytherapy after BCS. HDR-BT APBI was offered to pts fulfilling the ESTRO criteria for APBI and to selected pts with high-risk features but with metastatic disease and/or significant comorbidities and a limited life expectancy. In total 419 pts were treated. 279 (66.6%) pts fulfilled the ESTRO criteria for APBI and 140 (33.4%) pts did not. Catheters were implanted during or 4 - 8 weeks after BCS. Dose-volume parameters and quality indices were reported according to the ICRU 58 recommendations. We assessed the locoregional control and survival. Toxicity profiles were evaluated according to CTCAE v4.0. Results The median age at time of therapy was 68 years (range: 31 - 93 years). A total dose of 32 Gy was delivered in 8 fractions of 4 Gy twice daily. 289 (69%) pts received hormonal therapy, 99 (24%) pts did not, for 31 (7%) unknown. Chemotherapy was administered in 45 (11%), omitted in 343 (82%) and unknown in 31 (7%) pts. HER2 oriented therapy was given in 6 (1%) pts. Median follow- up time was 25 months (range 3 – 131 months). 29 (6.9%) pts developed disease relapse. Seven (1.7%) pts developed in-breast tumor relapse, 10 (2.4%) relapsed in the regional nodal area and 22 (5.3%) developed systemic metastases. We did not record any relapse within the planning target volume. During follow-up 50 (11.9%) pts died. 384 (91.6%) pts did not experience any acute toxicities, 32 (7.6%) developed Gr. I toxicity, 1 (0.2%) Gr. II and 2 (0.5%) Gr. III toxicity. Late toxicity was not recorded in 263 (62.8%) pts, 145 (34.6%) pts presented Gr. I toxicity, 9 (2.1%) Gr. II and 2 (0.5%) pts developed late Gr. III toxicity. There were no cases of acute or late Gr. IV or higher toxicity. The mean volumetric doses were: MCD 5.3 (range 3.2 to 6.1), V PTV (ccm): 62.6 (8.7 - 332.6), V100 (ccm): 72.7 (range 13.1 – 960.2), V100(%) = CI – 91.0 (47.4 – 99.0), V150 (lmp ccm): 19.9 (5.4 – 90.9) V150 (%): 27.1 (range 15.1 – 51.1). The mean DNR was 0.3 (range 0.2 – 0.5), while the DHI was 0.7 (0.3 – 0.8). The mean COIN was 0.7 (0.4 – 0.8). Conclusion HDR-BT APBI achieves excellent local control with a favorable toxicity profile. In selected pts with high-risk features, HDR-BT APBI provides a viable alternative to conventional radiotherapy. PO-1041 Benefit of interstitial needles supplementing the ring applicator in cervical cancer brachytherapy J. Ståhl Kornerup 1 , E. Thorstensen Andersen 2 , S. Danielsen 1 , A. Dybdahl Wanderås 1 , M. Sundset 3 , K. Fjellanger 2 , M. Eidem 1 , A.B. Langeland Marthinsen 1 1 St Olav’s University Hospital, Department of Radiotherapy- the Cancer Clinic, Trondheim, Norway ; 2 Norwegian University of Science and Technology, Department of Physics, Trondheim, Norway ; 3 St Olav’s University Hospital, Department of Gynaecological Oncology, Trondheim, Norway Purpose or Objective How well can dose prescription for target coverage and dose limits for organs at risk (OARs) be fulfilled in Poster: Brachytherapy: Gynaecology

We investigate how much additional modulation is provided by the proximal MLC between SX2 and SX1 by analyzing the amount of leaf shaping for leading and trailing leaves. In Halcyon 2.0, the proximal MLC was found to shape the field on average by 29.5±6.2%. Despite the increase in modulation from SX1 to SX2, the MCS for the Millennium MLC is lower for all cases compared to SX2 plans. For delivery accuracy measurement, all TrueBeam plans were adjusted to be 1400 MU/min as compared to 800 MU/min available in the Halcyon platform to optimize delivery characteristics. The 2%/2mm gamma index passing rates for SX1 and SX2 are 98.8±0.2% and 96.9±2.0%, respectively. The delivery time for SX2 plans are 4:19.0±25 sec compared to 3:59.46±24 sec for the Millennium MLC.

Conclusion Halcyon SBRT plans are shown to have similar plan quality to plans generated with the Millennium MLC but inferior to HD MLC. Despite the increase in modulation between SX1 to SX2 and the theoretical modulation resolution of 0.5cm in the latter, the lower MCS implies SX2 is generating plans with less modulation than the 120- Millennium MLC with 0.5cm physical width. SX2 plans are superior in terms of heterogeneity and conformity than SX1.

Posters Brachytherapy

Poster: Brachytherapy: Breast

PO-1040 Partial breast irradiation with interstitial multicatheter HDR BT for breast cancer. N. Cihoric 1 , A. Tsikkinis 1 , D. Terribilini 1 , D. M. Aebersold 1 , K. Lössl 1