Target definition for internal mammary lymph node irradiation based on distribution of internal mammary sentinel lymph node developed on SPECT/CT fusion imaging / 中华放射医学与防护杂志

ABSTRACT

Objective To explore the target definition for internal mammary lymph nodes ( IMLNs) irradiation based on the distribution of internal mammary sentinel lymph nodes ( IM-SLNs ) developing on SPECT/CT fusion imaging. Methods A total of 709 breast cancer patients who underwent preoperative SPECT/CT fusion imaging examination in IM-SLN from 2014 to 2018 were selected. All of the selected patients were first diagnosed and did not receive neoadjuvant treatment before SPECT/CT examination. Finally, totally 97 patients with 136 positive imaging IM-SLNs were included in this study. The clinical target volumes ( CTVs) were delineated according to the consensus guidelines from RTOG and DBCG and defined as CTVRTOG and CTVDBCG , respectively. The positional relationship of CTVRTOG , CTVDBCG and IM-SLNs were determined. Results The number of IM-SLNs from the first to fifth intercostal spaces were 55, 40, 33, 6 and 1, respectively. And the number of IM-SLNs in the first three intercostal spaces accounted for 94. 85％ of the total. The average distance from the edge of CTVRTOG to the centre points and the edges of IM-SLNs were 4. 10 mm ( 95％CI 3. 54-4. 65 mm) and 6. 40 mm ( 95％CI 5. 81-6. 98 mm), respectively (t=-30. 486,P<0. 05). For the CTVDBCG, the average distance was 1. 60 mm ( 95％CI 1. 16-2. 05 mm) and 3. 34 mm ( 95％CI 2. 78-3. 89 mm) , respectively ( t=-16. 364,P<0. 05) . The average distances from the edge of CTV to the centre points and the edge of IM-SLNs for CTVRTOG were all significantly greater than those for CTVDBCG(t=16. 640, 19. 815, P<0. 05). The rate of covering IM-SLN center points for CTVRTOG and CTVDBCG were 18. 4％ and 60. 3％, respectively. In order to cover 90％or 100％ of the IM-SLN center points, the edge of CTVRTOG should be expanded by 8 or 15 mm, respectively, and the edge of CTVDBCG should be expanded by 5 or 13 mm, respectively. If the diameter of IM-SLN was assumed as 5 mm, the edge of CTVRTOG needed an expansion of 11 or 17 mm to contain 90％or 100％ of IM-SLNs, respectively, while the edge of CTVDBCG needed 7 or 16 mm to cover 90％ or 100％of IM-SLNs, respectively. Conclusions It is reasonable to include the first three intercostal spaces IMLNs for prophylactic irradiation based on the distribution of IM-SLNs. However, CTVs based on the two guidelines are both insufficient to cover 90％ of IM-SLNs.