| Sumario: | Purpose To examine scatter contribution to the thyroid during breast irradiation for the treatment of breast cancer. The thyroid gland is a radiosensitive structure; therefore, exploring its exposure to radiation during supine breast cancer treatment techniques is warranted. Methods A left-breast setup was simulated using an adult anthropomorphic phantom. Thermoluminescent dosimeters (TLDs) were placed in the thyroid location of the phantom. Using 6 different techniques, researchers irradiated the phantom with a 6 MV beam and recorded the TLD readings. Results Analysis of the intact breast-only TLD readings show the field-in-field technique consistently had lower average scatter readings than the half-beam blocked isocentric tangent and the unblocked, or "pin-and-shift," plans. Among the plans that included treatment of the supraclavicular nodes, the half-beam blocked 3-field plan demonstrated the lowest average scatter readings, while the pin-and-shift 3-field technique had the highest scatter reading in the thyroid area. Discussion One might consider the effect of isocenter placement and beam divergence on the reported results. The fieldin- field isocenter placement is inferior relative to the position of the thyroid, which might account for the low scatter dose readings observed using this breast treatment technique. Furthermore, the field-in-field technique uses additional segments to smooth the dose distribution and reduce hot spots; 3 segments were used in this study. This research confirms that some dose is reaching the thyroid in all breast cancer treatment techniques explored. Conclusion Thyroid dysfunction resulting from radiation exposure can be lessened by incorporating thyroid contouring and tracking dose when it is in the primary beam, selecting a breast treatment technique that lessens the dose that might risk thyroid exposure, and considering pretreatment thyroid function analysis. Ongoing surveillance should be considered as part of the patient's post-treatment survivorship plan.
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