ESTRO 38 Abstract book

S703 ESTRO 38

EP-1283 Three-dimensional versus four-dimensional dose calculation for breast IMRT J. Chung 1 , M. Chun 1 , J.M. Park 1 , J. Kim 1 , K. Shin 1 1 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea Republic of Purpose or Objective This study was performed to analyze the effect of intra- fractional motion caused by free-breathing during breast IMRT by using newly generated “four-dimensional (4D) calculated plan”. Material and Methods From 2017 to 2018, twenty patients diagnosed with left breast cancer from Seoul National University Hospital (SNUH) were enrolled. Every patient was eligible for regional lymph node irradiation including internal mammary node (IMN). After the 3D-CT for the initial plan was taken, 4D-CT comprised of 0% to 90% respiratory phases was taken for every patient. Target contouring was performed on 3D-CT and on all ten respiratory phases of 4D-CT. After IMRT planning on 3D-CT, the plan parameters were copied to all ten respiratory phases of 4D-CT sets. One-tenth of the total dose (43.2 Gy / 16 fx) was applied to each phase, and the dose distribution was re- calculated. Ten re-calculated doses were then summated into one to generate “4D-calculated plan” which was compared with “3D-original plan”. Results Mean PTV volume was 1253.8 ± 575.6 ml. Mean IMN volume was 76.5 ± 16.6 ml. There were no significant differences in conformity and heterogeneity index between the 3D- original plan and the 4D-calculated plan. Mean heart dose was significantly lower in the 4D-calculated plan by 1.7 ± 0.8 Gy (p=0.041), whereas a mean dose of ipsilateral lung did not differ between two plans. When PTV was subdivided into the breast, supraclavicular lymph node (SCL), and IMN, both breast and SCL had no significant differences in mean dose between two plans. However, the mean IMN dose was significantly higher by 2.2 ± 1.8 Gy (p=0.023) in the 4D-calculated plan, compared to the 3D- original plan. Conclusion The interplay effect between the free-breathing motion and the multi-leaf collimator modulation may have caused a discrepancy in dose distribution, especially in heart and IMN. Therefore heart and IMN doses should be optimized when calculating the delivery dose for the free-breathing left breast IMRT. EP-1284 Older age and comorbidity in breast cancer: is radiotherapy alone the new therapeutic frontier? E. La Rocca 1,2 , M. Dispinzieri 1,2 , E. Meneghini 3 , A. Fiorentino 4 , F. Bonfantini 5 , S. Di Cosimo 6 , M. Gennaro 7 , V. Cosentino 5 , M. Sant 3 , E. Pignoli 5 , R. Valdagni 1,8 , L. Lozza 2 , M.C. De Santis 2 1 University of Milan, Department of Oncology and Hemato-Oncology, Milan, Italy ; 2 Fondazione IRCCS Istituto Nazionale dei Tumori, Radiotherapy Unit 1, Milan, Italy ; 3 Fondazione IRCCS Istituto Nazionale dei Tumori, Analytical Epidemiology and Health Impact Unit, Milan, Italy ; 4 Regional General Hospital “F Miulli”, Department of Radiation Oncology, Acquaviva delle Fonti Ba, Italy ; 5 Fondazione IRCCS Istituto Nazionale dei Tumori, Medical Physics Unit, Milan, Italy ; 6 Fondazione IRCCS Istituto Nazionale dei Tumori, Department of Applied Research and Technological Development DRAST, Milan, Italy ; 7 Fondazione IRCCS Istituto Nazionale dei Tumori, Breast Surgery Unit, Milan, Italy ; 8 Fondazione IRCCS Istituto Nazionale dei Tumori, Director- Radiation Oncology 1 and Prostate Cancer Program, Milan, Italy Purpose or Objective To assess the impact of age, comorbidities and hormonotherapy (HT) use in

patient group with multicentric tumors the five year OS was significantly worse than in the 397 for patients with unicentric tumors. P=0,01, HR 3,34. The RFS and DFS were also significantly worse (p=0.000, p=0.012) Conclusion In our cohort OS, RFS and DFS were statistically significant better in patients with unifocal breast cancer than in multicentric breast cancer. The only significant parameter in the multivariate analysis was the ER-Status. Regardings this, more aggressive treatment (chemotherapy, targeted therapy and radiotherapy) may be necessary. EP-1282 Postmastectomy radiation therapy using VMAT for breast cancer patients with expander reconstructions F. De Rose 1 , A. Fogliata 1 , D. Franceschini 1 , C. Iftode 1 , S. Cozzi 1 , A. Stravato 1 , G. Masci 2 , R. Torrisi 2 , A. Testori 3 , C. Tinterri 3 , A.V.E. Lisa 4 , A. Veronesi 4 , S. Giannasi 4 , M. Klinger 4 , M. Scorsetti 1 1 Humanitas Research Hospital, Radiotherapy and Radiosurgery, Rozzano Milan, Italy ; 2 Humanitas Research Hospital, Medical Oncology, Rozzano Milan, Italy ; 3 Humanitas Research Hospital, Breast Surgery, Rozzano Milan, Italy ; 4 Humanitas Research Hospital, Plastic Surgery, Rozzano Milan, Italy Purpose or Objective The use of post-mastectomy radiotherapy (PMRT) following immediate breast reconstruction has increased over the past decade, and this integration is becoming crucial in the management of breast cancer patients. We aimed to retrospectively evaluate the complication rates of PMRT to immediate tissue-expander-based reconstructions and the improvement of radiation delivery We retrospectively reviewed clinical data of patients who underwent immediate expander breast reconstruction and received PMRT. All patients underwent VMAT technique to irradiate the reconstructed breast and supraclavicular region. The total dose was 50 Gy delivered in 25 fractions over 5 weeks. Neoadjuvant or adjuvant systemic therapy was administered in all patients. Protective lipofilling was routinely performed at the time of second-stage reconstruction. Results Between December 2014 and June 2017, PMRT was delivered to 46 consecutive patients with expander reconstruction. Median age was 49 years (range 36-73). Median follow-up was 27.7 months (range 10.8–42.6 months). Only two patients (4.6%) experienced reconstruction failure, in one case due to expander rupture and in the other one due to infection, following the first and the second-stage reconstruction, respectively. In most cases expanders were completely inflated before PMRT (79%). Median expander volume before PMRT was 450 cm3 (range 140-690 cm3). The amount of expander inflation did not significantly affect dosimetry, except for skin dose, with a surface receiving more than 30 Gy of 36.6±0.9 cm2 and 47.0±2.5 cm2 for a volume expander below or above the median volume of 450 cm3, respectively. However, this variable was not a predictor for complications. Disease progression (local or distant) was recorded in 10.8% of patients. Conclusion Postmastectomy radiation therapy using VMAT technique for breast cancer patients with expander reconstructions is associated with a very low complication rate after both first and second-stage reconstruction. The expander volume before PMRT does not significantly compromise target coverage or increase dose to organs at risk. using VMAT technique. Material and Methods