Analysis of parotid gland and target volume variations during the head neck cancer intensity modulated radiation therapy

Objective: To study the changes in gross tumor volume (GTV) and parotid gland volume dur- ing intensity modulated radiation therapy (IMRT) for head and neck cancer. Methods: Five patients with head and neck squamous carcinoma were treated by IMRT. Cone beam CT was done every week during the whole course of radiotherapy. All images were fused with cone beam CT pictures and the initial CT pictures. The contouring was on normal parotid gland and gas cavity in each slide of cone beam CT. The changes of parotid gland and gas volume in GTV were calculated. Results: The parotid gland volume decreased, and gas volume in the GTV increased throughout the course of IMRT. At the end of radiotherapy, the parotid gland volume decreased to 90.1%- 52.3% compared with the volume before IMRT, gas cavity volume increased and took up to 3.7%-16.8% of GTV at the beginning of radiotherapy. Conclusion: Normal parotid gland volume and GTV is changed during IMRT in head and neck cancer. Cone beam CT can be used to find these changes which are helpful in carrying out the second IMRT plan. (authors)