[Volumetric and geometric changes of parotids occurring during IMRT for XXXX ( @entity189 ) using daily CBCT].

@entity1 @entity5 @entity189
OBJECTIVE: To study the volumetric and geometric changes of parotids occurring during IMRT treatment for @entity189 . METHODS: The pre-treatment CBCT images of 10 @entity1 were obtained using kV-CBCT and transmitted back to TPS. The gross @entity5 volumes (GTVs) and volumes of parotids were manually drawn slice by slice on the CBCT images by the same @entity1 using image analysis software system Tomcon 3.0. For position changes, the center-of-mass (COM) were calculated using Pinnacle 8.0 software. Then the distance from the parotid to the atlas was assessed. RESULTS: The volumetric changes of GTVs and parotids were correlated with the days of treatment. The volumes of GTVs decreased with a mean total loss of 9.85 cm3 (5.10-21.40 cm3) and a median change rate of 0.20 cm3/d (0.10-0.46 cm3/d). The volumes of left parotids decreased with a median total loss of 5.70 cm3 (3.20-12.00 cm3) and a median change rate of 0.13 cm3/d (0.07-0.27 cm3/d). The volumes of right parotids decreased with a median total loss of 8.05 cm3 (3.00-13.40 cm3) and a median change rate of 0.18 cm3/d (0.06-0.29 cm3/d). The distance between the left parotid and the atlas decreased with a median total loss of 3.45 mm (0.70-7.60 mm) and a median change rate of 0.07 mm/d (0.01-0.11 mm/d). The distance between the right parotids and the atlas decreased with a median total loss of 2.60 mm (1.50-4.40 mm) and a median change rate of 0.05 mm/d (0.03-0.12 mm/d). CONCLUSION: Significant reductions of GTVs occur after the third or forth week of IMRT treatment for @entity189 , which indicates that a second plan of CT scanning or treatment replanning might be necessary after 3-4 weeks of treatment to minimize radiations to vital organs.
