Study On Thyroid Radiation Protection In Radiotherapy After Breast Conserving Surgery

The research backgroundThe long-term local control rate and survival rate of breast conserving surgery combined with radiotherapy have been comparable to that of radical mastectomy[1].Breast conserving surgery meets people’s aesthetic requirements for breast appearance.Therefore,breast conserving surgery combined with postoperative radiotherapy has become the preferred treatment for early breast cancer.During radiotherapy,normal tissues and organs in the field in the target area,such as thyroid,will inevitably be exposed to high-energy ray scattering radiation,which will induce hypothyroidism,thyroiditis and other related diseases[2-3].Basic Standard for Protection against Ionizing Radiation and Safety of Radiation Sources GB18871-2002 clearly states that any radiation practice should follow the principle of optimization of protection,and non-irradiated sensitive parts should be protected to avoid unnecessary exposure[4].Research purpose1.To investigate the protective effect of different types of lead collar on thyroid gland in radiotherapy after breast conserving surgery.2.To analyze the attenuation law of radiation dose of patients irradiated field important organ thyroid gland with the distance from the edge of radiation field during breast conserving surgery.The research methods1.First,the ART model was placed on the treatment bed,and the TLD dose tablets were placed in the thyroid section holes corresponding to the model,and irradiated with the tangent field plan of 6MV,8MV and 10MV.Secondly,40 breast cancer patients with radiotherapy after breast-conserving surgery were randomly divided into 4 groups,10 patients in each group,and 8MV X-ray tangent field plan was formulated for treatment.Among them,both the model and patients were treated with 0mmPb group(control group),0.5mmPb group,2mmPb group,and 2mmPb new material group for thyroid protection.The protective effect of different types of lead collar on thyroid gland was analyzed by monitoring the dose value in and on the neck.Through the questionnaire survey to obtain the patient’s acceptability of the lead collar and other related results.2.Based on 40 cases of breast cancer,postoperative radiotherapy in patients with treatment based on the thyroid gland and beam edge distance,divided the patients into 4 groups(thyroid gland from radiation field edge distance is 3 cm,3.5 cm,4 cm and 4.5 cm group),record the biggest scattering dose treatment planning of thyroid,minimum average scattering dose and dose scattering,The attenuation law of radiation dose with distance is discussed.The results of the studyI.In the ART model,the attenuation rate of the thyroid radiation dose of the four kinds of lead collars varied from 2.96%to 25.48%when the radiation was 6MV.Under 8MV radiation,the attenuation rates of the four kinds of lead collars ranged from 3.34%to 31.22%.The attenuation rates of the four lead collars ranged from 3.73%to 32.16%when exposed to 10MV radiation.2.In clinical samples,there was no significant difference in the average amount of lead collars scattered from inside and outside the neck of the control group(P>0.05),there were significant differences in other groups(P<0.05),and the average attenuation rate of scattering from inside and outside the lead collar of 2mmPb new material group is 33.64%.3.The results of the questionnaire showed that after radiotherapy,the skin color and appearance of patients wearing lead collar in the 4 groups did not change significantly;In terms of acceptability,2mmPb new material group lead collar has the highest acceptability;The first re-examination of thyroid B ultrasound,examination results were normal.4.There were significant differences in the maximum,minimum and average scattered doses of thyroid among groups with different distances from the edge of irradiation field(P<0.05),and the thyroid dose decreased gradually with the increase of the distance from the edge of the radiation field.The research conclusion1.Except for the control group,all kinds of lead collar in the study have certain protective effect on thyroid gland,but the new lead collar material has the best protective effect and is highly accepted by patients,which can be popularized in clinical use.2.The radiation dose of thyroid in the field decreases gradually with the increase of the distance from the edge of the irradiation field,and the scattered dose of thyroid can be reduced by planning optimization.