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Abstract
Background: A relationship between the axillary-lateral thoracic vessel juncture (ALTJ) dose and lymphedema rate has been reported in patients with breast cancer. The purpose of this study was to validate this relationship and explore whether incorporation of the ALTJ dose-distribution parameters improves the prediction model's accuracy.

Methods: A total of 1,449 women with breast cancer who were treated with multimodal therapies from two institutions were analyzed. We categorized regional nodal irradiation (RNI) as limited RNI, which excluded level I/II, vs extensive RNI, which included level I/II. The ALTJ was delineated retrospectively, and dosimetric and clinical parameters were analyzed to determine the accuracy of predicting the development of lymphedema. Decision tree and random forest algorithms were used to construct the prediction models of the obtained dataset. We used Harrell's C-index to assess discrimination.

Results: The median follow-up time was 77.3 months, and the 5-year lymphedema rate was 6.8 %. According to the decision tree analysis, the lowest lymphedema rate (5-year, 1.2 %) was observed in patients with ≤ six removed lymph nodes and ≤ 66 % ALTJ V35Gy. The highest lymphedema rate was observed in patients with > 15 removed lymph nodes and an ALTJ maximum dose (Dmax) of > 53 Gy (5-year, 71.4 %). Patients with > 15 removed lymph nodes and an ALTJ Dmax ≤ 53 Gy had the second highest rate (5-year, 21.5 %). All other patients had relatively minor differences, with a rate of 9.5 % at 5 years. Random forest analysis revealed that the model's C-index increased from 0.84 to 0.90 if dosimetric parameters were included instead of RNI (P <.001).

Conclusion: The prognostic value of ALTJ for lymphedema was externally validated. The estimation of lymphedema risk based on individual dose-distribution parameters of the ALTJ seemed more reliable than that based on the conventional RNI field design.

그림. ALTJ is the anatomical junction where the lateral thoracic vein and the subscapular vein join the axillary vein.

그림. Prediction model and a regression tree for predicting 5-year lymphedema risk.

Affiliations

Jee Suk Chang 1, Heejoo Ko 2, Sang Hee Im 3, Jin Sung Kim 1, Hwa Kyung Byun 1, Yong Bae Kim 1, Wonguen Jung 4, Goeun Park 5, Hye Sun Lee 5, Wonmo Sung 6, Robert Olson 7, Chae-Seon Hong 1, Kyubo Kim 4
1Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Republic of Korea.
2College of Medicine, The Catholic University of Korea, Republic of Korea.
3Department and Research Institute of Rehabilitation Medicine, Severance Hospital, Yonsei University College of Medicine, Republic of Korea.
4Department of Radiation Oncology, Ewha Womans University College of Medicine, Republic of Korea.
5Biostatistics Collaboration Unit, Yonsei University College of Medicine, Republic of Korea.
6Department of Biomedical Engineering and of Biomedicine & Health Sciences, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.
7British Columbia Cancer Agency - Centre for the North, Prince George, BC, Canada.