Tangential Fields (Tgfs) Breast Radiation Therapy (Rt): Prospective Evaluation Of The Dose Distribution In The Axilla And The Sentinel Lymph Node Area (Slna) Determined Intraoperatively By Clip Placement

Purpose/Objective(s)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. Our recent data showed that axillary level I-II are underdosed when only tangential fields (TgFs) are used. We aimed to evaluate the dose distribution in the SLN area defined intra operatively by clips placement. This could be a crucial point for patients with SLN involvement who have neither ALND nor RT to the axilla.Materials/MethodsTwenty-five patients have been prospectively selected for this study. They had clips placement in the SLN area during the SLNB procedure. Breast dose was ranged between 40 to 50 Gy (in 15 to 25 fractions; n = 4). Additional boost to the tumor bed (10 or 16 Gy) was delivered in 21. Level I-III and organs at risk were contoured using the RTOG contouring atlas. The SLN area was defined as 1.5cm in diameter around the clips. Dose-volume histograms (DVH) were analyzed regarding the volumes receiving 95% (V95) or 50% (V50) of the prescribed dose. Overlap between TgFs and SLNa volume was analyzed as percentage.ResultsThe mean dose delivered to levels I, II, III and SLN area were 25, 5, 2, and 33 Gy respectively. The volume covered by the 95%-isodose in these 4 levels were respectively 2%, 0%, 0% and 4%; while the 50%-isodose covered 47%, 4%, 1% and 65%, respectively. The mean dose delivered to level I, II, III and SLN area were higher using High TgFs vs STgFs (38 vs 22 Gy, p = 0.004; 11 vs 3 Gy, p = 0.019; 5 vs 2 Gy, p = 0.003; 43 vs 31 Gy, p = 0.02), respectively. In addition, HTgFs covered better 50% of all axilla levels. Boost delivery and initial tumor site did not influence axilla coverage by the TgFs. The SNL area was totally or partially covered in 48% and 28% of patients, respectively. The mean dose delivered to 95% of the SNL area was only 22 Gy using STgFs and 33 Gy with the HTgFs. Using the STgFs, the SNL area was either totally (n = 8/20) or partially (n = 6/20) covered by > 50% of dose. In 6 cases the SLN area dose was < 50%. HTgFs allowed a complete coverage of the SLN area in all patients.ConclusionsIn patients undergoing breast conservative therapy, TgFs provide a limited coverage of the SLN area. STgFs allowed total coverage of this area in less than half of the patients. Thus, SLNB area 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 and a better-personalized nodal RT. Purpose/Objective(s)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. Our recent data showed that axillary level I-II are underdosed when only tangential fields (TgFs) are used. We aimed to evaluate the dose distribution in the SLN area defined intra operatively by clips placement. This could be a crucial point for patients with SLN involvement who have neither ALND nor RT to the axilla. 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. Our recent data showed that axillary level I-II are underdosed when only tangential fields (TgFs) are used. We aimed to evaluate the dose distribution in the SLN area defined intra operatively by clips placement. This could be a crucial point for patients with SLN involvement who have neither ALND nor RT to the axilla. Materials/MethodsTwenty-five patients have been prospectively selected for this study. They had clips placement in the SLN area during the SLNB procedure. Breast dose was ranged between 40 to 50 Gy (in 15 to 25 fractions; n = 4). Additional boost to the tumor bed (10 or 16 Gy) was delivered in 21. Level I-III and organs at risk were contoured using the RTOG contouring atlas. The SLN area was defined as 1.5cm in diameter around the clips. Dose-volume histograms (DVH) were analyzed regarding the volumes receiving 95% (V95) or 50% (V50) of the prescribed dose. Overlap between TgFs and SLNa volume was analyzed as percentage. Twenty-five patients have been prospectively selected for this study. They had clips placement in the SLN area during the SLNB procedure. Breast dose was ranged between 40 to 50 Gy (in 15 to 25 fractions; n = 4). Additional boost to the tumor bed (10 or 16 Gy) was delivered in 21. Level I-III and organs at risk were contoured using the RTOG contouring atlas. The SLN area was defined as 1.5cm in diameter around the clips. Dose-volume histograms (DVH) were analyzed regarding the volumes receiving 95% (V95) or 50% (V50) of the prescribed dose. Overlap between TgFs and SLNa volume was analyzed as percentage. ResultsThe mean dose delivered to levels I, II, III and SLN area were 25, 5, 2, and 33 Gy respectively. The volume covered by the 95%-isodose in these 4 levels were respectively 2%, 0%, 0% and 4%; while the 50%-isodose covered 47%, 4%, 1% and 65%, respectively. The mean dose delivered to level I, II, III and SLN area were higher using High TgFs vs STgFs (38 vs 22 Gy, p = 0.004; 11 vs 3 Gy, p = 0.019; 5 vs 2 Gy, p = 0.003; 43 vs 31 Gy, p = 0.02), respectively. In addition, HTgFs covered better 50% of all axilla levels. Boost delivery and initial tumor site did not influence axilla coverage by the TgFs. The SNL area was totally or partially covered in 48% and 28% of patients, respectively. The mean dose delivered to 95% of the SNL area was only 22 Gy using STgFs and 33 Gy with the HTgFs. Using the STgFs, the SNL area was either totally (n = 8/20) or partially (n = 6/20) covered by > 50% of dose. In 6 cases the SLN area dose was < 50%. HTgFs allowed a complete coverage of the SLN area in all patients. The mean dose delivered to levels I, II, III and SLN area were 25, 5, 2, and 33 Gy respectively. The volume covered by the 95%-isodose in these 4 levels were respectively 2%, 0%, 0% and 4%; while the 50%-isodose covered 47%, 4%, 1% and 65%, respectively. The mean dose delivered to level I, II, III and SLN area were higher using High TgFs vs STgFs (38 vs 22 Gy, p = 0.004; 11 vs 3 Gy, p = 0.019; 5 vs 2 Gy, p = 0.003; 43 vs 31 Gy, p = 0.02), respectively. In addition, HTgFs covered better 50% of all axilla levels. Boost delivery and initial tumor site did not influence axilla coverage by the TgFs. The SNL area was totally or partially covered in 48% and 28% of patients, respectively. The mean dose delivered to 95% of the SNL area was only 22 Gy using STgFs and 33 Gy with the HTgFs. Using the STgFs, the SNL area was either totally (n = 8/20) or partially (n = 6/20) covered by > 50% of dose. In 6 cases the SLN area dose was < 50%. HTgFs allowed a complete coverage of the SLN area in all patients. ConclusionsIn patients undergoing breast conservative therapy, TgFs provide a limited coverage of the SLN area. STgFs allowed total coverage of this area in less than half of the patients. Thus, SLNB area 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 and a better-personalized nodal RT. In patients undergoing breast conservative therapy, TgFs provide a limited coverage of the SLN area. STgFs allowed total coverage of this area in less than half of the patients. Thus, SLNB area 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 and a better-personalized nodal RT.