Adenoid Cystic Carcinoma of the Trachea-Dosimetric comparison of different techniques of Radiotherapy

Background Adenoid cystic carcinoma is a rare malignancy, usually originating in the salivary glands of the head and neck region, but, rarely originating in the trachea. Surgical resection is the treatment of choice. Radiotherapy is reserved for microscopically positive margins, neural invasion or unresectable disease. Materials and MethodA forty seven year old lady presented with a thyroid swelling for 4 years, dyspnoea on exertion for 3 months and noisy breathing for 3 weeks. CT neck showed an asymmetric circumferential thickening of proximal trachea with luminal narrowing and a multinodular goiter. She underwent total thyroidectomy with tracheal sleeve resection and primary anastomosis. Histopathology of the tracheal region was reported as adenoid cystic carcinoma with the inferior and superior margins involved by tumor, however, with negative nodes. She was planned for radiotherapy for the positive margins.It was decided to treat the patient with Intensity Modulated Radiation Therapy (IMRT). The Clinical Target Volume (CTV) was 1.5 cm and the Planning Target Volume (PTV) of 0.5cm.The surrounding critical structures were contoured as Organs at Risk (OAR)Dosimetric study was done using various conformal plans and comparison was done with Intensity Modulated Radiation Therapy (IMRT) plan. The Dose Volume Histograms (DVH) generated were compared and the doses received by 95 dose to PTV (D95) Dose received by 98 of the PTV (D98) and dose received by 2 cc volume of PTV (D2cc) were compared.Maximum dose to spine and PRV spine were also compared.ResultsVarious plans - 3D CRT using various beam arrangements and IMRT -were created, evaluated and compared. The IMRT plan was deemed the best dosimetrically..ConclusionsAdenoid cystic carcinoma of the trachea is a rare malignancy and there are no definite guidelines to treat these tumours. IMRT may be the preferred modality of radiotherapy for these tumours due their location proximity to critical structures.