Cone-beam computed tomography dose monitoring during intensity-modulated radiotherapy in head and neck cancer: parotid glands

To evaluate the dosimetric changes of parotid glands (PG) during a course of intensity-modulated radiotherapy (IMRT) in head and neck (H&N) cancer patients. METHODS: Ten patients with H&N cancer treated by IMRT were analyzed. The original treatment plan (CT(plan)) was transferred to cone-beam computed tomography (CBCT) acquired at the 15th and 20th treatment day (CBCT(plan) I and II, respectively). The PG mean dose (D(mean)), the dose to 50 % of the volume, and the percent of volume receiving 30 and 50 Gy were measured by the dose volume histogram. RESULTS: 30 IMRT plans were evaluated (3 plans/patient). All dosimetric end points increased significantly for both PG only when CT(plan) was compared to CBCT(plan) I. The D(mean) increased significantly only for ipsilateral PG (p = 0.02) at week 3. CONCLUSION: During a course of IMRT, CBCT is a feasible method to check the PG dosimetric variations. Perhaps, the 3rd week of radiotherapy could be considered as the time-check-point.