Abstract book - ESTRO meets Asia

S73 ESTRO meets Asia 2018

Purpose or Objective To evaluate possible differences in heart dose distribution for hypo- fractionated radiation treatment (HFRT) of left breast cancer in the prone position on Elekta Synergy and Varian platforms. Material and Methods Treatment plans of 17 patients with varying breast size treated from 2013 to 2016 were included. Among them, 7 were treated on Elekta Synergy and 10 on Varian 21iX. All patients received radiation therapy to the whole left breast alone with HFRT to total dose of 4256 cGy in 16 fractions without boost. 5(29%) patients were of stage T1b and 4(24%) of each DCIS, T1a and T1c, respectively. During CT simulation all patients were scanned in prone position using CDR breast board with 5 BBs placed for leveling and definition of isocenter. The plans utilized opposed tangential fields, 6 MV alone or 6 and 10MV mixed photon beams carefully orientated to provide full target coverage while avoiding dose to left lung and heart. Supporting board for the contralateral breast was kept at least 1cm away from the ipsilateral breast. Traditional field borders were used to define the treatment volume (TV) and arrange the tangential beams. An open field plan was then generated. The 95% isodose line in the open field plan was used as a surrogate for the TV. Then, plans were optimized using a field in field forward planned technique, utilizing 6MV or 6/10MV mixed photon beams. Plans were approved if 95% of TV receiving 95% of the prescribed dose, maximal dosage to TV was kept below 108%, dose to heart and lung were minimized. The volume of TV receiving 105% was minimized, as well. DVHs for TV, left lung and heart were calculated heterogeneously (Pinnacle, Philips). The data were retrospectively collected and compared via one- sided t-test. Results The average left breast volume in this study was 1396±742cc. Three groups were segmented by PTV volume: <1000cc (n=5), 1000-1500cc (n=6) and >1500cc (n=6). Dose-distributions and dose-volume-histogram (DVH) of each plan were approved based on 95% of breast receiving 95% of the prescribed dose and uniformity (average homogeneity index (Dmax/Rx): 105.9±0.6%. ). V20, V5 and mean dose of left lung were 0.4±0.8%, 1.3±2.1% and 65.1±48.7cGy, respectively. V5 and mean dose of heart was 1.3±1.6% and 106.1±42.5cGy. No significant difference was observed for each dosimetry index between each PTV volume based group. Surprisingly, patients treated on Elekta Synergy platform had significant higher mean heart dose and heart V5 than those treated on Varian 21iX (Heart Dmean143.5±37.6cGy vs 79.9±20.3cGy, P<0.01; Heart V5 2.2±2.0% vs. 0.7±0.8%, P<0.05). Conclusion This study showed a significantly lower heart dose distribution for patients treated on Varian 21iX than on Elekta, which might be explained by the differences between 21iX tertiary MLC and Synergy backup diaphragm designs. Deeper understanding of this phenomenon will require further study. PO-181 Hypofractionated radiotherapy is feasible in patients undergoing breast conserving surgery S. Agrawal 1 1 Fortis Memorial Research Institute, Radiation Oncology, Gurgaon, India Purpose or Objective Evaluation of effect of hypofractionated radiotherapy in comparison to conventional radiotherapy in patients undergoing breast conserving surgery (BCS) Material and Methods A retrospective study of 117 adult carcinoma breast patient post BCS who underwent adjuvant radiotherapy (ART) and/or chemotherapy with confirmed

histopathology was done in our institution from Sept, 2012 to May, 2018. Results were analysed in 3 parts: ART technique, ART schedule, ART course tolerance. Results There were 67 (57%) hypofractionated (HF) and 50(43%) conventional fractionated (CF) patients. Treatment schedule for HF included whole breast radiotherapy in 15 fraction with dose of 40.05Gy followed by boost to tumor cavity in 5-7 fraction (median 5) with 10Gy- 17.5Gy (median 12.5Gy), CF consisted of 20 or 25 fraction to whole breast with dose of 45Gy or 50Gy respectively followed by boost to cavity in 4-8 fraction (median 6) with dose of 9Gy-20Gy (Median 15Gy). Where indicated ipsilateral supraclavicular fossa (SCF) was also treated to dose of 45Gy in 20 fractions concurrently. All were treated 5 days a week. Overall Radiotherapy treatment time (ORTT) ranged from 23-50 days. For HF it was 23-30 days (median 26) and for CF it was 30-50 days (median 42). Cavity boost in HF patients was done by VMAT in 38/67 patients (57%), by electron in 16/67 patients (24%) and rest by 3DCRT & IMRT technique. Cavity boost in CF was done by electron in 26/50 patients (52%) and by VMAT 17/50 patients (34%) and rest by 3DCRT and IMRT. Sixty three of the 67 HF patient were treated by partial volumetric arc therapy technique (pVMAT) to whole breast whereas in CF 34/50 patients were treated by pVMAT . Right breast vs left were 34 vs 33 in HF and 28 vs 22 in CF. Skin reaction grade I was seen in 65/67 patients (97%) in HF and 27/50 patients(54%) in CF. Rest had grade II reaction( 3% in HF and 46% in CF) . There was no grade III/IV skin reaction. There was no difference in right sided and left sided breast treatment (34 & 33 in HF and 28 & 22 in CF respectively) with respect to tolerability. There was no radiotherapy course interruption during radiotherapy treatment course. Conclusion HF schedule for BCS patient in 15 fraction to whole breast by pVMAT followed by boost to cavity in 5-6 fractions with completion of treatment within 4 weeks is a feasible option when compared to CF in terms of early completion of treatment and comparable acute side effect during treatment and better patient tolerance. Decrease of ORTT in form of HF schedule may improve radiotherapy compliance and reduce overall treatment time(OTT) . Long term data of such approaches to reduce ORTT and OTT and its effect on disease free and overall survival require future studies. PO-182 Clinical outcomes in patients with ER positive, HER2 negative locally advanced breast cancer N. Nakajima 1 , Y. Kumai 1 , I. Serizawa 1 , Y. Yoshioka 1 , M. Oguchi 1 1 Cancer Institute Hospital of JFCR, Radiation Oncology, Koutouku, Japan Purpose or Objective The aim of this study was to determine clinical outcomes and identify reliable prognostic factors in patients with locally advanced breast cancer who had estrogen receptor (ER) positive and HER2 negative subtype treated with neoadjuvant chemotherapy (NAC) followed by We retrospectively evaluated the relationship between clinicopathological factors and clinical outcomes in 216 patients with ER positive and HER2 negative, stage II or III breast cancer who underwent NAC followed by radical mastectomy and PMRT between March 2005 and December 2013. Locoregional recurrence free survival rate (LRFS), distant metastasis free survival rate (DMFS), and overall survival rate (OS) were calculated as clinical outcomes. Results The median follow-up duration was 81 months (range, 12– 156 months). Fourteen patients experienced locoregional mastectomy and PMRT. Material and Methods