Abstract Book

S702

ESTRO 37

The FIF technique was useful in HTRT and improved homogeneity in the target. EP-1275 Displacement of surgical clips and volume change of MegaDerm during whole-breast irradiation W. Jung 1 , J. Lee 1 , S. Jeong 1 , J. Kim 1 , K. Kim 1 1 Ewha Womans University Medical Center, Radiation Oncology, Yangcheon-gu, Korea Republic of Purpose or Objective The purpose of this study was to investigate the displacement of surgical clips and the volume change of human acellular dermal matrix (MegaDerm) during whole- breast irradiation (50.4 Gy in 28 fractions) following breast-conserving surgery. Material and Methods From February 2016 to May 2017, 53 breast cancer patients who underwent breast-conserving surgery with the placement of surgical clips in the excision cavity were included in this study. All patients took second planning computed tomography (CT) scan before boost irradiation. Patients were divided into two groups according to breast volume replacement. Group A consisted of 26 patients with breast volume replacement using MegaDerm insertion in the excision cavity, and group B consisted of 27 patients without breast volume replacement. Results Forty-six out of 53 patients (86.8%) had five clips (superior, inferior, medial, lateral and deep) in the tumor bed. The means and 1 standard deviations (SD) of the three-dimensional (3D) displacement for superior, inferior, medial, lateral and deep clips were 5.5 ± 2.9 mm, 6.9 ± 4.3 mm, 6.9 ± 6.9 mm, 7.1 ± 4.6 mm and 6.9 ± 7.7 mm in group A; 4.4 ± 2.3 mm, 4.3 ± 2.0 mm, 4.6 ± 2.3 mm, 4.3 ± 2.1 mm and 3.9 ± 2.3 mm in group B, respectively. The 3D displacements of group A were longer than those of group B in inferior and lateral clips (p = 0.01 and 0.008, respectively). The volume of MegaDerm was decreased in 23 of 26 patients (88.5%) in group A and the mean volume reduction was 9.68% (p < 0.001). The relative reduction of MegaDerm volume during radiotherapy was inversely proportional to the time elapsed since surgical excision (R = -0.532, p = 0.009). Conclusion This study demonstrates significant displacement of surgical clips and volume reduction of MegaDerm during whole-breast irradiation in patients with MegaDerm insertion. For patients who had breast volume replacement using MegaDerm, CT simulation at boost planning is needed. EP-1276 Risk factors for treatment failure in cT1-2N0- 1 breast cancer treated with neoadjuvant chemotherapy X. Wang 1 , L. Xu 2 , L. Zhao 2 , P. Wang 2 1 Tianjin Medical University Cancer Hospital & Institute, Department of Radiation Oncology, Tianjin, China 2 Tianjin Medical University Cancer Hospital, Department of Radiation Oncology, Tianjin, China Purpose or Objective In order to identify risk factors associated with locoregional failure in early breast cancer (BC) managed with neoadjuvant chemotherapy (NAC) and mastectomy and assess the role of post-mastectomy radiotherapy, a retrospective analysis of BC diagnosed with clinical staged T1-2N0-1 were conducted. Material and Methods 222 patients were included in this analysis. The median age was 50 years old (24-72 years old). The clinical stage distributions were cT1 in 16 cases, cT2 in 206, cN0 in 53 and cN1 in 169 patients. All patients were treated with NAC and mastectomy, and 129 patients also received

and knowledge. We anticipate that the QI skills gained will enable the residents to elevate the quality of their practice throughout their subsequent careers. EP-1274 Does field-in-field technique improve homogeneity in high tangent radiotherapy for breast cancer H. Tanaka 1 , M. Ito 1 , T. Yamaguchi 1 , K. Esaki 1 , M. Futamura 2 , F. Hyodo 1 , M. Matsuo 1 1 Gifu University, Radiology, Gifu, Japan 2 Gifu University, Surgical Oncology, Gifu, Japan Purpose or Objective Patients with positive axillary sentinel lymph node biopsy specimen (SLNB) often undergo axillary lymph node dissection (ALND). In recent days, attempts have been made to omit axillary lymph node dissection even for sentinel lymph node biopsy-positive patients if certain conditions are met. As a replacement to this procedure, high tangent radiation therapy (HTRT) that intentionally irradiates the axillary lymph node region was examined. We evaluated whether the field-in-field (FIF) technique improves the homogeneity of the target in HTRT. Material and Methods This study included 30 patients. A 6-MV energy photon beam was used. The prescribed dose was 50 Gy in 25 fractions. The radiotherapy plan was generated as follow: two opposed tangential fields were created, and the gantry angles and beam weight were optimized (Conv-p). The method used to create the FIF plan (FIF-p) has been reported previously [13]. The medial fields were copied as the first subfield. Using multileaf collimators (MLCs) for blocking, the dose to the first subfield was 1-3% lower than the maximum dose on the beam’s eye view. After dose calculation, the beam weight was shifted away from the original field to the first subfield until the dose cloud disappeared. The lateral field was copied as the second subfield. Again using MLCs for blocking, the dose to the second subfield was 2-4% lower than the dose blocked in the first subfield, and the beam weight was shifted as described above. If the maximum dose was over 107% of the prescribed dose, the medial field was copied again as the third subfield (FIF-p). Finally, the plan with lung block subfields (FIF-LB-p) was created. Another main field was copied again, and the MLCs were set to block the ipsilateral lung area. The beam weight of the lung- blocked subfield was set at approximately one-tenth of the main field. The doses administered to 95% (D95%) and 90% (D90%), as well as the mean dose (Dmean) of the axilla levels I and II were calculated. The maximum dose (Dmax) to the breast or planning target volume (PTV) and the volumes of the breast or the PTV receiving 95% and 90% of the prescribed dose (V95% and V90%, respectively) were also calculated. The homogeneity index (HI) was calculated. Results Although the investigated methods were statistically significant, they showed very small differences in the D95%, D90%, and Dmean of the axilla levels I and II. The Dmax of the breast and PTV were significantly lower for FIF-p and FIF-LB-p than for Conv-p. HI of PTV was also significantly lower for FIF-p and FIF-LB-p than for Conv-p. HI of the breast or PTV were significantly better for FIF-p than for FIF-LB-p. V95% and V90% of the breast and PTV were also significantly better for FIF-p, indicating the advantages of FIF-p. The average of Dmax and HI of PTV Conv-p FIF-p FIF-LB-p Dmax 56.1 ± 1 53.1 ± 1 53.1 ± 1

023 ± 0.03

0.19 ± 0.03

0.21 ± 0.03

HI

Conclusion