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Abstract
The three-dimensional field-in-field (3-D FIF) technique for radiotherapy is an advanced, state-of-the-art method that uses multileaf collimators to generate a homogeneous and conformal dose distribution via segmental subfields. The purpose of this study is to evaluate the dosimetric reproducibility of 3-D FIF plans using the original simulation computed tomography (iCT) scans and re-simulation CT (rCT) scans for whole breast irradiation (WBI) schedule. This study enrolled a total of 34 patients. The study population underwent iCT scans for standard WBI and took rCT scans after 45 Gy of WBI for cone down boost plans. The dosimetric parameters (V105%, V103%, V100%, V98%, V95%, V90%, V50%), plan quality indices (conformity index, homogeneity index) and clinical parameters (isocenter-breast axis, isocenter-lung axis, soft tissue volumes within radiation field, lung volumes within radiation field) were assessed. The median time interval from surgery to iCT was 33 days and from iCT to rCT was 35 days. All dosimetric parameters exhibited statistically significant differences between iCT and rCT among cohorts with a surgery-iCT interval of < 60 days. Homogeneity index showed a statistically significant increase from iCT to rCT among all cohorts. Soft tissue volumes (p = 0.001) and isocenter-breast axis (p = 0.032) exhibited statistically significant differences among cohorts with surgery-iCT interval < 60 days. Regarding the reproducibility of the 3-D FIF WBI plans, significant changes were observed in dosimetric and clinical factors, particularly in study cohorts with a surgery-simulation interval < 60 days. The main contributing factor of these transitions seemed to be the changes in volume of the soft tissue within the WBI field. Further confirmative studies are necessary to determine the most suitable timing and technique for WBI.

Affiliations

Dong Soo Lee  1 , Young Kyu Lee  2   3 , Young Nam Kang  2 , Yong Gyun Won  2   4 , Seung Hwan Park  2 , Yong Seok Kim  5 , Jeong Soo Kim  5 , Hye Sung Won  6
1 Department of Radiation Oncology, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea. dreamdoc77@catholic.ac.kr.
2 Department of Radiation Oncology, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.
3 Proton Therapy Center, Research Institute and Hospital, National Cancer Center, Goyang, Republic of Korea.
4 AbbVie Biopharmaceutical Company, Seoul, Republic of Korea.
5 Department of Surgery, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.
6 Division of Medical Oncology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.