Hypothesis of a decision-making algorithm for adjuvant radiotherapy in left-sided breast cancer patients

In a recent issue of this journal Ferdinand et al. reported interesting data about deep inspiratory breath-hold (DIBH) technique in the treatment of left breast cancer patients []. This paper has been published almost simultaneously to our work focused on the same issue []. Since cardiac structures are intended to be spared from undesirable radiation exposure in order to prevent heart injuries, in recent years various radiotherapy techniques and technical ploys were tested, likewise to what was done for other clinical scenarios [, ], to averting such a concern in radiotherapy departments []. Among these solutions, radiation delivery with a respiratory gating system emerges as the most promising, although not the easiest to apply and the least cumbersome one from a treatment planning point of view []. Furthermore, this treatment option is not always feasible and equally advantageous for all patients, some of them requiring a long training or even the recourse to more compliant radiotherapy techniques (i.e. IMRT or VMAT in free-breathing), as those effectively used for other curative settings []. Hence, the need for in advance selection of eligible patients for DIBH technique is evident, also to streamline the workload of high capacity centers []. The attempt to identify some immediately recognizable anatomical predictors for such an aim was quite ineffectual []. This finding was likely due to a not adequately large sample size or to an inappropriate searching. The anatomical and dosimetric parameters to evaluate for assessing and preventing cardiac risk are those proposed by Register et al. []. Accordingly, Ferdinand et al. [] found a significant correlation between reduction in heart volume in field (HVIF) and maximum heart depth (MHD) with reduction in mean heart dose. However, these parameters are not a priori foreseeable. Interestingly, none of the two Δ correlated with left anterior descending coronary artery (LAD) maximum dose, but only with its mean dose (exclusively ΔHVIF), thereby remarking the substantially borderline and high risk location of this serial organ at risk, hardly displaceable and extremely close to the edge of dangerous isodose lines in tangent fields pattern (i.e. V19Gy for hypofractionated schedule and V20Gy for normofractionated one). This condition questions the actual reliability of DIBH technique in preventing cardiac risk. To address this issue, an in vivo dosimetry or an indirect assessment of cardiac absorbed dose by means of specific tests, such as blood levels of myocardial enzymes (i.e. troponin isoforms), electrocardiogram, radionuclide cardiac imaging, are required: the latter approach is the only viable. Indeed, all DIBH reports are dosimetric and have never been clinically confirmed. So, we believe that DIBH technique advantage over other equally promising approaches (i.e. IMRT) is to be detected in specific clinical trials. While waiting for it, we feel confident enough to propose our findings, relative to breast size and chest wall separation (namely the tangent fields distance in our article), to better predict the main beneficiaries of DIBH technique, as we are aware of the lack of a standard therapeutic proposal and of the need for a personalized approach, as for other treatment body sites []. We recommend to pay particular attention when treating left breast, a site that, as well known, may keep trace of a previous radiation treatment []. Lastly, we propose the following algorithm to determine the better therapeutic choice for left-sided breast cancer patients (Fig. 1). We think it is important for the authors to comment on these issues and reply in the context of this journal.