First cases of use of implanted fiducial markers for imaging in performing definitive radiotherapy of prostate carcinoma with volume modulated rotation therapy in University Hospital 'Dr. Georgi Stranski' - Pleven

Definitive Radiation is an effective alternative to radical prostatectomy in selected prostate cancer patients. Due to the high focal dose, the proximity of radiosensitive organs and their periodic physiological variations, the daily accurate image verification of both the target volumes and the position of the critical structures is essential for the precise execution of the radiotherapy plan. The use of cone-beam CT for visualizing the tissues and organs of interest and the registration of the acquired CT imaging data from the radiotherapy plan is a modern standard for Image-guided radiation therapy (IGRT), but the method is often not sensitive enough for small soft tissue structures such as the prostate gland. Our goal is to present the use of implanted X-ray positive fiduciary markers as a method for a more precise day-to-day visual verification of the intended volume position in hypofractionated radiotherapy of prostate carcinoma. Under ultrasound, a fiducial marker with a diameter of 5 mm and a length of 10 mm was implanted in the two prostate gland sections. We retrospectively analyzed the data from the daily controlled CT with a conical beam made during the radiotherapy of the patient. We compared the results of applying different registration methods - automatically and manually, respectively, on bones and fiduciary markers. We analyzed the differences in resultant displacements of the isocentre of the planned volume from both methods and the reasons for the obtained results. As a result of changes in the volumes of critical organs (rectum, bladder), the target volume changes its position, and this displacement can be estimated more accurately by tracking the location of the fiducial markers. The security at the location of the clinical target volumes during irradiation allows for the application of narrower additional security zones in determining the intended target volume and dose reduction in critical organs and tissues, and the method is accessible and safe for the patient.