ESTRO 36 Abstract Book

S629 ESTRO 36 _______________________________________________________________________________________________

4 National Cancer Center, Study Coordination Section, Chuo, Japan 5 National Cancer Center Hospital, Radiation Oncology, Chuo, Japan 6 Kindai University Faculty of Medicine, Radiation Oncology, Osakasayama, Japan 7 Osaka Medical Center for Cancer and Cardiovascular Diseases, Radiation Oncology, Osaka, Japan 8 Saitama Cancer Center, Radiation Oncology, Kitaadachi, Japan 9 Hiroshima University Graduate School of Biomedical Science, Radiation Oncology, Hiroshima, Japan 10 Niigata Cancer Center Hospital, Radiation Oncology, Niigata, Japan 11 National Cancer Center Hospital East, Radiation Oncology and Particle Therapy, Kashiwa, Japan 12 Shizuoka Cancer Center, Radiation and Proton Therapy Center, Sunto, Japan 13 Graduate School of Medicine- Chiba University, Diagnostic Radiology and Radiation Oncology, Chiba, Japan 14 Hyogo Cancer Center, Radiation Oncology, Akashi, Japan 15 Shikoku Cancer Center Hospital, Radiotherapy, Matsuyama, Japan 16 Aichi Cancer Center Hospital, Radiation Oncology, Nagoya, Japan 17 The University of Tokyo Hospital, Radiology, Bunkyo, Japan 18 Tochigi Cancer Center, Radiotherapy, Utsunomiya, Japan 19 Osaka University Graduate School of Medicine, Radiation Oncology, Suita, Japan 20 Graduate School of Medicine- Kyoto University, Radiation Oncology and Image-applied Therapy, Kyoto, Japan 21 Tokyo Metropolitan Cancer and Infectious diseases Center- Komagome Hospital, Radiology, Bunkyo, Japan 22 Tokyo Women’s Medical University, Radiation Oncology, Shinjuku, Japan 23 University of Tsukuba, Radiation Oncology, Tsukiba, Japan Purpose or Objective To evaluate the safety and efficacy of short-course hypofractionated whole-breast irradiation (HWBI) on Japanese women after breast-conserving surgery (BCS), a prospective single-arm confirmatory trial (JCOG0906, UMIN000003200) has been conducted in 25 hospitals. Material and Methods Japanese women who had invasive breast cancer with clinical tumor size of 3 cm or less, no or one to three pathologically positive lymph nodes and pathologically negative inked margin were prospectively registered after BCS with or without adjuvant chemotherapy. The HWBI of 42.56Gy/16fr was delivered to the whole-breast without regional nodal irradiation, and a boost irradiation (BI) of 10.64Gy/4fr to the original tumor bed was added when the surgical margin was 5 mm or less. The recommended treatment period was within 29 days for HWBI and 33 days for HWBI and BI. The primary endpoint was the proportion of pre-specified eight items of grade 2 or higher late adverse reactions (ARs) including telangiectasia, ulceration, fibrosis-deep connective tissue, fracture, pneumonitis, cardiac ischemia/infarction, pericardial effusion and pain-breast occurring between 91 days and three years from the start of HWBI. The sample size was set as 310 patients with one-side alpha of 5%, power of 90%, threshold value of 8%, and expected value of 4%, estimated from the proportion of the late ARs on the historical control including 703 patients followed up for three years or more after conventional fractionated whole-breast irradiation (CWBI) in our pilot survey prior to

the present trial. Secondary endpoints included the proportion of treatment completion within the recommended period, early adverse events (AEs) occurring during 90 days from the start of HWBI, overall survival (OS), disease-free survival (DFS), ipsilateral- breast relapse-free survival (IB-RFS), and the proportion of breast cosmetic change. Early AEs and late ARs were evaluated using CTCAE ver3.0. Survival time was estimated by the Kaplan-Meier methods. Results Between 2010 and 2012, 312 women were registered. 306 patients received HWBI and 66 patients received HWBI with BI, but six chose CWBI prior to the start of irradiation. 301 patients (96.5%; 95%CI: 93.8-98.2) were treated within the recommended period. Evaluation of early AEs found that 38 patients (12.4%) had grade 2, including 25 patients (8.2%) with radiation dermatitis, and no patients had grade 3/4. On 306 patients receiving HWBI, 3-years OS, DFS and IB-RFS were 99.7% (95%CI: 97.7-100), 95.7% (95%CI: 92.7-97.5) and 99.0% (95%CI: 97.0-99.7). Among 303 (97%) patients, evaluation of late ARs found that 13 patients (4.3%; 90%CI: 2.6-6.7) had grade 2/3, including one of grade 3 pneumonitis. None had grade 4 or treatment-related death. Conclusion Short-course HWBI is considered as one of the standard treatments for Japanese women with margin-negative invasive breast cancer after BCS. Further follow-up is continued and cosmetic outcome will be analyzed. EP-1157 Serial changes of post-lumpectomy seroma during MRI-guided partial breast irradiation S.H. Jeon 1 , K.H. Shin 1 , S.Y. Park 1 , J.M. Park 1 1 Seoul National University Hospital, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective After breast conserving surgery, the volume of post- lumpectomy seroma changes by time. We analyzed serial changes of seroma volume (SV) using magnetic resonance image (MRI) to investigate the possible benefit of adaptive radiation therapy during partial breast irradiation (PBI). Material and Methods From October 2015 to July 2016, 37 patients were prospectively included in the study. A total dose of 38.5 Gy in 3.85 Gy fractions once daily was prescribed to the planning target volume (PTV). The PTV was defined as unequal margins of 1-1.5cm added according to the directional safety margin status of each seroma. Treatment was done using MRI-guided radiation therapy (ViewRay system). During the 10 fractions of treatment, MRI scans were acquired at the time of simulation, 1st, 6th and 10th fractions. Results The average time intervals of surgery-simulation, simulation-1st, 1st-6th, and 6th-10th fractions were 23.1, 8.5, 7.2, and 5.9 days, respectively. SV was smaller during treatment than at simulation in 34 patients. Mean SV decreased from 100% at simulation to 65%, 55%, and 47% at each MRI scan. Age, body mass index, tumor size, seroma location, SV and delivery of radiotherapy did not showed association with SV change (p>0.05, student’s t- test). In 34 patients with decreased SV, mean PTVs were 84.7 cm 3 and 56.9 cm 3 at simulation and 6th fraction, respectively, and their difference was proportional to SV at simulation (r=0.832, p<0.001, pearson’s correlation test). Conclusion During PBI, rate of SV change is associated with time elapsed from surgery. Frequent monitoring of seroma change with MRI seems helpful for all patients receiving PBI.