Abstract P1-15-08: Tangential fields (TgF) breast radiotherapy (RT): Prospective evaluation of the dose distribution in the sentinel lymph node area (SLNa) as determined intra operatively by clip placement
Authors: Belkacemi Yazid , Bigorie Veronique , Pan Quiong , Bosc Romain , Bouaita Ryan , Pigneur Frederic , Assaf Elias , Badaoui Hakima , Itti Emmanuel , Calitchi Elie 
Published: May 2015

Abstract
Purpose:
The coverage of axilla contents by radiation therapy (RT) is an important issue in the new era of minimal axillary surgery based on sentinel lymph node biopsy (SLNB). Data from recent trials demonstrated equivalent survival in breast cancer (BC) patients with 1-2 positive SLNs with or without axillary lymph node dissection (ALND). In a similar context, AMAROS trial showed that complete RT coverage of the axilla is a better option than ALND regarding the risk of arm lymphedema. Our recent data showed that axillary levels are underdosed when only tangential fields (TgFs) are used (Belkacemi et al, Ann Oncol 2013). We aimed to evaluate the dose distribution in the SLNa defined intra operatively by clips placement. This could be a important for patients with SLN involvement who have neither ALND nor RT to the axilla.
Materials/Methods:
Twenty-five patients have been prospectively included in this study. They had clips placement in the SLNa during the SLNB procedure. Breast dose was ranged between 40 to 50Gy in 15 to 25 fractions. Additional boost to the tumor bed of 10 or 16Gy was delivered in 21 patients. Level I-III and organs at risk were contoured using the RTOG contouring atlas. The SLNa was defined as 1.5 cm in diameter around the clips. Dose-volume-histograms were analyzed regarding the volumes receiving 95% or 50% of the prescribed dose. Percentages overlap between TgFs and SLNa volume were analyzed to define 3 groups: 100% overlap ("suitable group" with SNLa completely included in the TgF), &gt; 50% overlap ("partially suitable group" with SLNa partially included in the TgF) and 0-49% overlap or completely outside the TgFs ("unsuitable group").
Results:
The mean dose delivered to levels I, II, III and SLN area were 25, 5, 2 and 33Gy respectively. The volume covered by the 95%-isodose were respectively 2%, 0%, 0% and 4%. The average dose delivered to level I, II, III and SLN area were higher using High TgFs vs STgFs (38 vs 22Gy, p=0.004; 11 vs 3Gy, p=0.019; 5 vs 2Gy, p=0.003; 43 vs 31Gy,p=0.02), respectively. HTgFs covered better 50% of all axilla levels. Boost delivery and initial tumor site did not influence axilla coverage by the TgFs.
The SNLa was totally or partially covered in 48% and 28% of patients, respectively. The mean dose delivered to 95% of the SNLa was only 22Gy using STgFs and 33Gy with the HTgFs. Using the STgFs, the SNLa was either totally (n=8/20) or partially (n=6/20) covered by &gt; 50% of dose. Average dose was 46, 34 and 8Gy, respectively in the 3 groups. HTgFs allowed a complete coverage of the SLNa in all patients.
Conclusion:
In patients undergoing breast conservative therapy, TgFs provide a limited coverage of the SLNa. STgFs allowed total coverage of this area in less than half of the patients. Thus, SLNa should be delineated in patients who have only SLNB procedure. Some of these patients with nodal involvement without additional ALND could benefit from HTgFs irradiation or a better-personalized nodal RT using a dedicated nodal RT technique such that reported in AMAROS trial. The last allow better coverage of the axilla contents than TgFs.
Citation Format: Yazid Belkacemi, Veronique Bigorie, Quiong Pan, Romain Bosc, Ryan Bouaita, Frederic Pigneur, Elias Assaf, Hakima Badaoui, Emmanuel Itti, Elie Calitchi. Tangential fields (TgF) breast radiotherapy (RT): Prospective evaluation of the dose distribution in the sentinel lymph node area (SLNa) as determined intra operatively by clip placement [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-15-08.