Abstract
Heart diseases and cardiovascular events are well-known side effects in left-sided breast irradiation. Deep inspiration breath hold (BH) combined with fast delivery techniques such as volumetric modulated arc therapy (VMAT) or tangential field-in-field (TFiF) can serve as a valuable solution to reduce the dose to the heart. This study aims to compare the impact of positioning errors in VMAT and TFiF plans for BH left-sided breast treatments. Fifteen left-sided breast patients treated in BH with TFiF technique were included in this retrospective study. For each patient, a second plan with VMAT technique was optimized. Eighteen setup variations were introduced in each of these VMAT and TFiF reference plans, shifting the isocenter along six different directions by 3, 5, and 10 mm. A total of 540 perturbed plans, 270 for each technique, were recalculated and analyzed. The dose distributions on the target and organs at risk obtained in the different perturbed scenarios were compared with the reference scenarios, using as dosimetric endpoints the dose-volume histograms (DVH). The results were compared using the Wilcoxon test. Comparable plan quality was obtained for the reference VMAT and TFiF plans, except for low doses to organs at risk for which higher values (p < 0.05) were obtained for VMAT plans. For TFiF plans, perturbations of the isocenter position of 3, 5, or 10 mm produced mean deviations of the target DVH dosimetric parameters up to −0.5, −1.0, and −5.2%, respectively; VMAT plans were more sensitive to positioning errors resulting in mean deviations up to −0.5, −4.9, and −13.9%, respectively, for the same magnitude of the above mentioned perturbations. For organs at risk, only perturbations along the left, posterior, and inferior directions resulted in dose increase with a maximum deviation of +2% in the DVH dosimetric parameters. A notable exception were low doses to the left lung and heart for 10 mm isocenter shifts for which the mean differences ranged between +2.7 and +4.1%. Objective information on how external stresses affect the dosimetry of the treatment is the first step towards personalized radiotherapy.
Highlights
Breast cancer is the most common cancer in women worldwide
Standard dose constraints were satisfied for all organs at risk (OARs); heart mean dose (Dm) resulted
The comparison of the target coverage obtained with the reference vs. the perturbed plans is shown in Table 3; the mean and range of the absolute differences of clinical target volume (CTV) dose-volume histograms (DVH) dosimetric parameters obtained are reported for different magnitudes and directions of the isocenter shifts
Summary
The standard of care includes conservative surgery or mastectomy as appropriate, followed by adjuvant radiotherapy. Radiotherapy is essential to improve local tumor control and overall survival; delivery of some dose to heart, lungs, and contralateral breast is unavoidable. Deep inspiration breath-hold (DIBH) in left-sided breast treatment increases the distance between the target and the heart as well as the part of lungs included in the treatment field. Many studies have been published on the benefits of DIBH showing how it enables minimized irradiation of nearby organs at risk while maintaining an adequate target dose coverage [5,6,7,8], and, has become the gold standard in clinical practice in many institutions [9,10,11,12]
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