Preliminary exploration of 3D printed individualized applicator for 3D-image-guided intracavitary HDR-brachytherapy for nasopharyngeal carcinoma

Objective To explore the feasibility of 3D printed individualized applicator for the intracavitary HDR-brachytherapy for nasopharyngeal carcinoma. Methods CT scan was performed in 1 case of recurrent rT1 nasopharyngeal carcinoma and 1 case of T2 residual nasopharyngeal carcinoma and the obtained images were transmitted to 3D image processing software. The geometric contour parameters of the nasopharyngeal cavity were obtained and a pipeline was designed to make it close to the recurrent gross tumor volume (rGTV). Individualized cavity applicators were created by using 3D printer. The applicator was inserted into the patient′s nasopharyngeal cavity through oral cavity. The source tube and false source were inserted into the preset pipe of the applicator. CT scan was performed again and the images were transmitted to the 3D brachytherapy planning system. After delineating the target volume and organ at risk, treatment plan was optimized. After completing the first treatment, the applicator was removed. Before second treatment in a few days, CT scan was reviewed to confirm whether the position was correct. Results When the applicator was inserted into the nasopharyngeal cavity, it could be fully aligned with the nasopharyngeal wall and self-fixed without additional fixation measures. Comparing the location of false source in multiple reviews of CT scan, the error was ≤1 mm. No significant discomfort was reported throughout the treatment. In optimized three-dimensional treatment, 100% prescription dose curve included the full rGTV, maximum dose of the brain stem and spinal cord was<30% prescription dose. Recurrent patients were given with a prescription dose of DT 40Gy/8 fractions/4 weeks and patients with residual tumors were given with 12Gy/2 fractions/1 week. No tumor recurrence was observed at postoperative 3 months in two cases. Conclusions The 3D printed individualized nasopharyngeal intracavitary applicator has the advantages of self-fixation, accurate location, good repeatability and good patient tolerance. The short-term outcome is effective, whereas its long-term clinical effect and adverse reactions need to be further observed. Key words: 3D printed; Individualized applicator; Nasopharyngeal neoplasm/intracavitary radiotherapy