The evaluation of 3DRT and IMRT techniques in postoperative radiotherapy for thyroid medullary carcinoma

Abstract

Summary Background Radical surgical excision is the treatment of choice in all medullary thyroid carcinomas. External beam radiotherapy for medullary thyroid carcinoma is necessary in advanced cases. Unfortunately, a large volume of the head and neck region which has to be irradiated is close to critical structures such as the spinal cord, larynx, and parotid glands, which creates a challenge during radiotherapy planning. Aim The aim of the study is to compare IMRT and 3D plans of patients diagnosed with medullary thyroid carcinoma in terms of CTV coverage and normal tissue sparing. Materials and Methods A 46-year-old woman with medullary thyroid carcinoma, stage pT4a N1b M0, underwent radical resection, followed by adjuvant radiotherapy to a total dose 60 Gy to the clinical target volume (CTV). Three plans were generated to irradiate the thyroid bed and regional lymph nodes. Two intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3DRT) plans were compared in terms of CTV coverage and organ at risk sparing. Results Using the IMRT plans we achieved more homogeneous dose distribution with higher minimal dose and lower maximal dose in the target volume compared to 3DRT technique. Furthermore, mean and maximal dose to critical structures were lower when IMRT was applied compared to 3DRT. Conclusions IMRT results in improved dose distribution within CTV compared to 3DRT. With the IMRT plan it is also possible to reduce the dose to the organ at risk, especially the larynx, salivary glands and spinal cord.