Abstract
Cardiac irradiation increases the risk of coronary artery disease in patients with left‐sided breast cancer. Techniques exist to reduce cardiac irradiation, but the optimum technique depends on individual patient anatomy and physiology. We investigated the correlation of delta heart volume in field (dHVIF) and sternal excursion with dose sparing in heart and left anterior descending artery (LAD) to develop quantitative predictive models for expected dose to heart and LAD. A treatment planning study was performed on 97 left‐breast cancer patients who underwent whole breast radiotherapy (prescription dose = 50 Gy) under deep inspiratory breath hold (DIBH). Two CT datasets, free breathing (FB) and DIBH, were utilized for treatment planning and for determination of the internal anatomy‐based DIBH amplitude. The mean heart and LAD dose were compared between FB and DIBH plans and dose to the heart and LAD as a function of dHVIF and sternal excursion were determined. The [Average (STD); Range] mean heart doses from free breathing and DIBH are [120.5(65.2); 28.9 ~ 393.8] cGy and [67.5(25.1); 19.7 ~ 145.6] cGy, respectively. The mean LAD doses from free breathing and DIBH are [571.0(582.2); 42.2 ~ 2332.2] cGy and [185.9(127.0); 41.2 ~ 898.4] cGy, respectively. The mean dose reductions with DIBH are [53.1(50.6); ‐15.4 ~ 295.1] cGy for the heart and [385.1(513.4); ‐0.6 ~ 2105.8] cGy for LAD. Percent mean dose reductions to the heart and LAD with DIBH are 44% (p < 0.0001) and 67% (p < 0.0001), respectively, compared to FB. The dHVIF mean dose reduction correlation is 8.1 cGy/cc for the heart and 81.6 cGy/cc for LAD (with linear trend and y intercept: 26.0 cGy for the heart, 109.1 cGy for LAD). DIBH amplitude using sternal position was [1.3(4.8); .38 ~2.5] cm. The DIBH amplitude mean dose reduction correlation is 14 cGy/cm for the heart and 212 cGy/cm for LAD (with linear trend with y intercept: 35.6 cGy for the heart, 102.4 cGy for LAD). The strong correlation of dose sparing to the heart and LAD with dHVIF and sternal excursion suggests that mean dose sparing to heart and LAD can be predicted with either dHVIF or sternal excursion equally well. The metrics proposed could be utilized to allow providers to determine the relative dosimetric benefits of different heart‐sparing techniques as early as time of consultation.PACS number(s): 87.53.Tf
Highlights
A number of previous studies reported the significant reduction of cardiac doses with deep inspiration breath-hold (DIBH).[9,11,12] For example, the comparison study with 17 breast cancer patients by Korreman et al[13] showed that the median heart volume receiving more than 50% of the prescription dose was reduced from 19.2% with free breathing (FB) to 1.9% with DIBH when the mean chest wall position with DIBH was 12.6 mm higher from that of FB
We investigated for the first time the functional form of dose sparing to the heart and left anterior descending artery (LAD) with delta heart volume in field (HVIF) and sternal excursion as predictors, and provide a predictive model for the expected dose sparing of heart and LAD from delta heart volume in field (dHVIF) and sternal displacement
We investigated the dose sparing to the heart and LAD with 3D conformal treatment plans using DIBH with dHVIF as a direct predictor and sternal displacement as an indirect predictor
Summary
There is level one evidence from multiple phase III clinical trials that adjuvant whole-breast radiotherapy can reduce recurrence and breast cancer death.[1,2,3] long-term follow-up studies indicate that incidental irradiation of the heart during external beam radiotherapy can increase the risk of cardiovascular damage, potentially limiting the long-term survival benefit of adjuvant radiotherapy.[2,4,5] Recently, a population-based analysis of radiation-induced cardiac toxicity following treatment of left-sided breast cancer suggested a 7.4% relative increase in major coronary events per 1 Gy increase in mean heart dose.[6]There are a variety of techniques available to reduce irradiation of the heart and left anterior descending artery (LAD) from the tangential left breast fields, including voluntary deep inspiration breath-hold (DIBH),(7) active breathing control (ABC),(8) and prone positioning.[9]with audio and/or visual coaching, patients can be trained to take a deeper breathhold.[10]. A number of previous studies reported the significant reduction of cardiac doses with DIBH.[9,11,12] For example, the comparison study with 17 breast cancer patients by Korreman et al[13] showed that the median heart volume receiving more than 50% of the prescription dose was reduced from 19.2% with free breathing (FB) to 1.9% with DIBH when the mean chest wall position with DIBH was 12.6 mm higher from that of FB. A parameteric model for cardiac dosimetric sparing with DIBH has not been fully established in routine clinical practice.[12,15] For example, Nissen and Appelt[12] reported the lack of correlation between age/breath-hold volume and the heart dose from 319 breast cancer patients. Its main limitation is that the dosimetric results are unknown until after radiotherapy planning when changing the technique may require repeat simulation and delay of treatment
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