Construction And Clinical Research Of Custom-made Bite Block Used In Radiation Therapy Of Head And Neck Cancer

Objective (1) We describe the construction of custom-made bite block to be used during external beam radiotherapy of head and neck cancer. This protects the opposing jaw and associated structures and can allow a smaller total treatment volume to be planned.(2) To investigate the influence of bite block on normal tissue dosimetry and toxicity in head and neck cancer patients treated with intensity-modulated radiation therapy (IMRT).Methods (1) The custom-made bite block is made by standard techniques and materials of tooth positioner.(2) Between March2012and November2012, patients with head and neck cancer were assigned to bite block arm and custom-made bite block was made for each patient. Patients in bite block arm were included and each had two sets of planning CT-scans:one with and one without an custom-made bite block. Target volumes and organs at risk (tongue, mandible and parotid gland) were contoured on the CT scans and IMRT plannings were performed. Paired-samples t-test was used to compare the Conformity number (CN) and Heterogeneity index (HI) of PTV. The maximum dose (Dmax) and mean dose (Dmean) of organs at risk (without or with bite block) were also analyzed, using paired t-test. Patients’s oral mucous reaction, tongue mucous reaction, taste fuction and salivary gland function before radiotherapy and every week during radiotherapy were examined. Primary end point was incidence of observer-rated mucositis of oral cavity, xerostomia, and taste disorders after treatment.Results (1) Three type of custom-made bite block were made. The custom-made bite blocks using intra-oral impressions fit more accurately and improve comfort. If the tongue is being treated, then its volume is reduced by compression, and a reproducible position during each treatment session is achieved.(2) Mean values of CN of patients with custom-made bite block and without custom-made bite block were0.80and0.79respectively (t=0.82, P=0.425). Mean values of HI of the two arms were1.12and1.13respectively (t=0.60, P=0.552). The Dmax and Dmean of tongue with bite block were1586±413cGy and173±42cGy, and those without bite block were6243±125cGy and1767±159cGy respectively (t=11.66, P=0.000; t=11.87, P=0.000). There were no significant differences in the dose to mandible, parotid gland and submandibular gland between patients with and without bite block. Another10patients without custom-made bite block were assigned to non-bite block arm. No patients in the bite block arm suffered from lower halp of buccal, taste disorder and xerostomia by the completion of radiotherapy. The occurrence rate of mucositis of the oral cavity was higher in non-bite block arm than the bite block arm (100%vs73%, x2=13.095, P=0.000). Patients in bite block arm had lower incidence of taste disorders than patients in the non-bite block arm (0vs90%;x2=21.094, P=0.000).Conclusions The design allows accurate and reproducible positioning of the perioral tissues, which aids planning of radiotherapy and treatment. The custom-made bite block significantly decrease the Dmax and Dmean of tongue for head and neck cancer patients treated with IMRT, which is useful in sparing the oral mucous membrane and preserving taste. This custom-made bite block should be provided as part of the overall management of patients with head and neck cancer.