br Practical Radiation Oncology May

Practical Radiation Oncology: May-June 2019 Cardiac segment radiation doses breast cancer 161
A Midline photon tangents B Wide photon tangents
C Direct 172922-91-7 IMC D Oblique electron chest wall
Direct electron chest wall, lateral thorax photons
Oblique cobalt IMC,
oblique cobalt chest wall
G Direct cobalt bilateral IMC H Direct cobalt IMC, oblique electron chest wall
Table 1 Mean radiation therapy doses to myocardial structures from left-sided breast cancer radiation therapy regimens used in Sweden (1958-2001) or Denmark (1978-2000)
Radiation therapy regimen*
Mean cardiac doses (Gy)y
Country Median Medial Field arrangementz,x Usual Dose
Whole
Ventricles
Left ventricular myocardial segments
Year Border r> Heart Left Right
Apex Lateral Inferior Septal Anterior
energy Gy
Tangential
contra
contra
contra
contra
Anterior electron or orthovoltage
contra
contra
contra
contra
contra
Anterior megavoltage
contra
contra
Practical Radiation Oncology: May-June 2019
Practical Radiation Oncology: May-June 2019
supraclavicular fossa
orthovoltage tangents
Z
for
60ZZZZZZZcobalt60;contracontralateral;IMCinternalmammarychain;kVkilovoltage;latlateral;MeVmegaelectron-volts;MVmegavoltage;SCF electronororthovoltageregimensareobliqueelectronelds,othersincludedirectelds.fifi
Meancardiacdosesestimatedusingmanualplanning(ie,orthovoltageandcobaltchain)aregiventothenearestGy. RegimensathroughpareillustratedinFigures1andE1(availableonlineathttps://doi.org/10.1016/j.prro.2019.01.004). Regimens1through7werereconstructedon10scanstostudytheeffectofpatientanatomyonsegmentdoses(Figs.3-5). except
Cardiacdosesarethesameforleft-andright-sidedbreastcancersbecausethesameeldwasusedforboth.fi 23
Co
Usualtotaldose(100%)tothetargettissues.Fordirectregimens,thiswastheD
wall,
breast/chest
the
center of
the
to
dose delivered
regimens the
, and for tangential
Bold tangential regimens are wide tangents, others are midline tangents. Bold anterior
max
Abbreviations:Co * For further details on the radiation therapy regimens, see Table E1.y z x where the total dose was the skin dose at the surface of the breast.k ** For a description of cobalt chain, see Taylor (2009).
Cardiac segment radiation doses breast cancer 163
because interpatient variability in cardiac dose is usually lower from right radiation therapy.22
For each regimen, interpatient variability in mean doses was calculated as the difference between the highest and lowest mean doses recorded for each cardiac segment. Interpatient variability in hotspot doses was calculated as the difference between the highest and lowest hotspot doses recorded for each cardiac segment. The hotspot doses recorded included D2cc (minimum dose covering the hottest 2.0 cc) of the ventricular myocardium (right ventricle [RV] and LV combined) and D0.5cc (minimum dose covering the hottest 0.5 cc) of the main coronary arteries (left main coronary artery, left-anterior descending coronary artery [LADCA], right coronary artery [RCA], and circumflex coronary artery [Cx] combined).
Correlations
Correlation analyses between cardiac segment and whole heart doses, and between coronary artery segment and LV segment doses, were performed using STATA, version 13.2 (StataCorp, College Station, TX).
Results
A total of 41 regimens were identified from 470 ra-diation therapy charts, including 20 regimens for left breast cancer, 20 for right cancer, and 1 that was the same for left and right cancers (Fig. 1, Fig. E1, Table E1).
Tangential regimens
For left megavoltage tangential radiation therapy, cardiac doses were determined mainly by the position of the medial border and divergence of the posterior border (Tables 1, 2, E3, and E4 [available online https://doi. org/10.1016/j.prro.2019.01.004], Fig. 2). For left midline megavoltage tangents, the mean doses were 6.0 Gy to 7.6 Gy for LV and 3.0 Gy to 4.7 Gy for RV (Table 1, Fig. 2A). For left wide megavoltage tangents with a divergent posterior field border, both ventricles received 12.5 Gy, but for the partially wide tangents, both ventricles received <6.1 Gy (Table 1, Fig. 2B). For the left megavoltage tangents, the mean individual LV segment doses varied substantially (range, 0.6-38.8 Gy). The LV apex received the highest doses of 22.5 Gy. The anterior LV segment received 11.7 Gy from the wide divergent and partially wide megavoltage tangents but 9.2 Gy from the midline megavoltage tangents. The LV septal segment received 12.8 Gy from the wide divergent megavoltage tangents but 5.3 Gy from partially wide and midline megavoltage tangents. The lateral and inferior segments were further from the fields and received 6.4 Gy from all left megavoltage tangents.