Abstract
BackgroundBefore generating radiotherapy plans for breast cancer patients, the choice of plan techniques (three-dimensional conformal radiation therapy (3D-CRT) and volumetric modulated arc therapy (VMAT)) should be made. This study investigated the performance of two geometric indices in aiding the choice of 3D-CRT and VMAT plans in women undergoing left-sided whole breast radiotherapy.Materials and methods119 patients, previously treated with left-sided breast radiotherapy (61 3D-CRT treatments and 58 VMAT treatments) from a single institution, were retrospectively studied. Two geometric indices, which were cardiac junction (CJ) index and pulmonary junction (PJ) index, were defined and the relationship between these indices and dose of organs at risk (OARs) were evaluated. Two-tailed Student’s t-test was performed to compare patient characteristics between 3D-CRT and VMAT. Linear regressions were calculated to investigate the association between geometric indices and absorbed dose of heart and left lung, including mean dose of heart (MHD), V5, V30 of heart, and mean dose of left lung (MLLD), V5, V10, V20, V30, V40 of left lung.ResultsThe CJ index was strongly correlated with the MHD in 3D-CRT group and VMAT group. The linear regression formulas were MHD = 4826.59 ×CJ Index+310.48 (R = 0.857, F = 163.77, P = 0.000) in 3D-CRT plans and MHD = 1789.29×CJ Index+437.50 (R = 0.45, F = 14.23, P = 0.000) in VMAT plans. The intersection of the two formulas was CJ index = 4.2% and MHD = 512.33 cGy. The PJ index demonstrated a strongly positive correlation with MLLD in 3D-CRT group and VMAT group as well. The linear regression formulas were MLLD = 2879.54×PJ Index+999.79 (R = 0.697, F = 55.86, P = 0.000) in 3D-CRT plans and MLLD = 1411.79×PJ Index+1091.88 (R = 0.676, F = 47.11, P = 0.000) in VMAT plans, the intersection of the two formulas was PJ index = 6.3% and MLLD = 1180.46 cGy.ConclusionsCJ index and PJ index could be used as a practical tool to select 3D-CRT or VMAT before generating plans. We recommend that VMAT plan is preferable when CJ index is greater than 4.2% and/or PJ index is greater than 14.6%, while 3D-CRT plan is the first choice in the opposite.
Highlights
Post mastectomy radiation therapy (PMRT), which significantly improves local tumor control and increases 5-year overall survival for breast cancer patients, is an effective and well-established adjuvant treatment for breast cancer patients with modified radical mastectomy [1–5].the heart and lungs are routinely exposed to incidental ionizing radiation during adjuvant radiotherapy of breast cancer
cardiac junction (CJ) index and pulmonary junction (PJ) index could be used as a practical tool to select 3D-CRT or VMAT before generating plans
We recommend that VMAT plan is preferable when CJ index is greater than 4.2% and/or PJ index is greater than 14.6%, while 3D-CRT plan is the first choice in the opposite
Summary
The heart and lungs are routinely exposed to incidental ionizing radiation during adjuvant radiotherapy of breast cancer. It can result in increasing cardio-toxicity and cardiovascular mortality especially in left sided breast cancer patients [6]. Except for cardio-toxicity, radiation related lung toxicity is a concern in left-sided breast radiotherapy. Grantzau et al conducted a research indicated that the risk of second non-breast cancer after radiotherapy of the breast cancer patients, including the lung, esophagus, thyroid and connective tissues progressively increased over time, peaking at 10–15 years following breast cancer diagnosis [12]. Before generating radiotherapy plans for breast cancer patients, the choice of plan techniques (three-dimensional conformal radiation therapy (3D-CRT) and volumetric modulated arc therapy (VMAT)) should be made. This study investigated the performance of two geometric indices in aiding the choice of 3D-CRT and VMAT plans in women undergoing leftsided whole breast radiotherapy
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