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  • br Hotspot doses were located in the LV apex

    2020-08-28


    Hotspot doses were located in the LV apex, LV ante-rior, and LADCA segments for most left regimens, and in the RV, RCA proximal, and RCA mid segments for most right regimens (Figs. 4 and 5). The order of the segments according to higher-versus-lower doses was the same as in the typical CT scan for 91% of LV segment and regimen combinations, 91% of whole coronary artery and regimen combinations, and 81% of coronary artery segment and regimen combinations (Tables E5 and E6; available online at https://doi.org/10.1016/j.prro.2019.01.004).
    Correlations between cardiac segments
    The doses to all LV and LADCA segments were highly correlated with doses to the whole heart (range of correlation coefficients, 0.7-0.9; all P < .0001; Fig. 6).
    LMCA
    LADCA prox
    LADCA mid LADCA dist RCA prox RCA mid RCA dist RCA pd Cx
    Left sided regimen
    Right sided regimen
    LMCA
    LADCA prox
    LADCA mid LADCA dist RCA prox RCA mid RCA dist RCA pd Cx 
    Wide tangents, divergent (41 Gy/22f)* (2) Direct electron internal mammary chain (40 Gy/10f) (5) LMCA LADCA prox LADCA mid LADCA dist
    RCA prox
    RCA mid
    RCA dist RCA pd Cx
    LADCA prox
    LADCA prox
    LADCA mid
    LADCA mid
    LADCA dist
    LADCA dist
    RCA prox
    RCA prox
    RCA mid
    RCA mid
    RCA dist
    RCA dist
    RCA pd
    RCA pd
    Cx
    Cx
    LMCA Partially wide tangents, block posteriorly (48 Gy/24f) (4)
    LADCA prox
    LADCA prox
    LADCA mid
    LADCA mid
    LADCA dist
    LADCA dist
    RCA prox
    RCA prox
    RCA mid
    RCA mid
    RCA dist
    RCA dist
    RCA pd
    RCA pd
    Cx
    Cx
    D0.5cc main coronary ZD 1839 (%)
    y Block tapered inferiorly around breast. z Block tapered inferiorly below the fifth rib, medial border: 3 cm contralateral x Doses are shown in percent rather than Gy to enable a comparison based on patient anatomy rather than differing target dose. The spatial location of the D0.5cc main coronary arteries hotspot was identified for each regimen and computed tomography combination using the dose range selection tool on the treatment planning system to highlight the voxels within the volume receiving this dose. Some hotspot volumes spanned >1 structure and were not always contiguous. Abbreviations: LMCA Z left main coronary artery; LADCA Z left anterior descending coronary artery; RCA Z right coronary artery; Cx Z circumflex coronary artery; f Z fractions; IMC Z internal mammary chain; prox Z proximal; dist Z distal; pd Z posterior descending.
    Correlations between the RCA segments and whole heart were much lower (range of correlation coefficients, 0.1-0.3; P Z .008- .25). LADCA mid and distal segment doses were highly correlated with doses to the LV seg-ments usually supplied by the LADCA: LV apex, and anterior and septal segments (range of correlation co-efficients, 0.7-0.9; all P < .0001), but the RCA segment doses showed little correlation with doses to the LV segments usually supplied by the RCA: LV inferior, and septal segments (range of correlation coefficients, -0.1 to 0.2; P Z .04 to .5).
    Discussion
    Cardiac segment radiation doses from 41 breast cancer regimens, estimated retrospectively using information from radiation therapy charts, varied substantially. For most regimens, certain segments received >20 Gy, but others received <1 Gy. Different segments received high doses from different regimens. Such variability provides 
    potential opportunities for the assessment of the effects of different doses to individual segments.
    Many years hence, cardiac doses based on patient-specific CT-planning scans may be available to study long-term adverse effects. At the present time, however, most patients who developed clinical heart disease after radiation therapy were irradiated before the 2000s and did not receive CT-based dosimetry planning. Therefore, estimating cardiac doses using a typical CT scan is necessary. This method previously enabled the derivation of a linear dose-response relationship for radiation-related IHD (expressed as percentage increase in IHD rate per Gy mean whole heart dose). This dose response relationship has been validated in 2 independent studies.24,25
    When using the typical CT-scan method, cardiac doses actually received by individual patients vary on the estimated dose, principally owing to interpatient differ-ences in anatomy. In our study, the effect of interpatient differences in anatomy varied by regimen and segment and was the greatest for segments that were near the field edges, and thus close to the high-dose gradient at the anterior aspect of the heart. This type of error is known as
    Practical Radiation Oncology: May-June 2019 Cardiac segment radiation doses breast cancer 169