Estimation of the risk of secondary cancer in the thyroid gland and the breast outside the treated volume in patients undergoing brain, mediastinum and breast radiotherapy

Abstract

The purpose of this study was to measure the peripheral dose which is the absorbed dose in organs located outside the treatment volume such as the thyroid gland and the breast in patients undergoing radiotherapy, utilising the MOSFET dosemeters, as well as to estimate the probability of secondary cancer. The thyroid gland doses, expressed as a percentage of the prescribed dose (%TD), were measured to be 2.0±0.3 %, in whole brain irradiation, 10.0±8.0 % in mediastinum treatment and 8.0±2.0 and 2.0±0.8 % in breast treatment, with and without the supraclavicular irradiation, respectively, with a corresponding risk of 0.2, 2.0, 1.0 and 0.3 %. The dose to the breast was 7.0±2.0 %, in the mediastinum treatment, and 4.0±1.0 and 2.0±0.8 %, in the breast treatment, with and without supraclavicular irradiation, respectively, with a corresponding risk of 4.0, 2.0 and 1.0 %. Although the results indicate that the risk is not negligible, its significance should be considered in conjunction with the existing pathology and age of the patients.

Estimation of the thyroid secondary cancer risk on the patient of standard breast external beam radiotherapy

“…The relevant risk of secondary thyroid cancer of obtained thyroid dose is calculated using the ICRP 103 risk model 1% and 0.3%, respectively. [13] Farhood et al . reported SED 7% of the prescribed dose in one fraction in patients undergoing breast treating with Tan and SC plans using TLD.…”

“…finding. [13] The proximity of the thyroid to the SC fields and high dependency of PD to distance from field edge could be the cause of this difference. Comparison of the average thyroid dose in patients undergoing breast-saving and mastectomy surgery against who had treated with the same Tan + SCL plan, does not show any significant difference ( P = 0.667).…”

“…[8] Several studies have shown that women with breast cancer have an additional risk for other cancers such as thyroid cancer. [121314] Many studies evaluated the risk of secondary cancer in radiotherapy of breast cancer patients and also a great variety can be seen in their methodology (measurement[15] or calculation[16]), dosimetry mediums (phantom[1718] or patient[19]), dosimeters (thermoluminescent dosimeter [TLD], metal-oxide-semiconductor field-effect transistor or other types),[131720] treatment techniques (standard or complex),[1718] type of treatment machines, reported quantity (medium dose, equivalent dose, and skin dose),[202122] and the risk models (International Radiation Protection Commission [ICRP] or biological effects of ionizing radiation [BEIR]). [1823]…”

“…The results of an in vivo study on 23 patients, who underwent breast radiotherapy using tangential and supraclavicular (SC) fields, shown the thyroid dose were 2 and 8% of the prescribed dose, respectively. [13] In another study, the skin entrance dose (SED) of thyroid following breast radiotherapy was 7% of the prescribed dose for SC field, which was more than thyroid's tolerance. [17] In another study on 69 patients, the mean reported thyroid doses were 3.7% of the delivered dose measured by the TLD.…”

Assessment of leakage dose in vivo in patients undergoing radiotherapy for breast cancer

“…The improving survival of patients with early breast cancer underpins this concern, and adds emphasis to the need to accurately quantify radiation doses to untargeted healthy tissues during treatment for a more accurate estimation of the risk of radiation-related second malignancy. In addition, the out-of-field radiation received by surrounding healthy tissues during breast irradiation is associated with toxicities of the heart, lung and thyroid [8][9][10].…”