PURPOSE: Our previous study showed that weekly dose monitoring using cone-beam CT (CBCT) images can guide the timing and need for adaptive re-planning during the treatment of @entity135 . Here we aim to confirm the dosimetric improvement of adaptive radiotherapy (ART) using weekly CBCTs. METHODS: We randomly selected seven @entity135 @entity1 treated with ART due to noticeable anatomic changes. Twenty weekly images acquired during the second treatment course were included. These CBCTs were aligned with both the initial and re-planning simulation CTs according to the clinical shifts. Daily doses were re-calculated for both the initial and adaptive plans. Contours of the @entity5 and organs-at-risk (OARs) were manually delineated by a physician on the re-planning CT and then were transferred to the CBCTs for plan evaluation. Contour modifications were made based on the daily anatomic changes observed on CBCTs. All @entity1 were treated with 70Gy to the @entity5 and 56Gy to the elective lymph nodes. RESULTS: Volumetric changes of the @entity5 (range - 43.9%   +15.9%) were observed. The average D99 to the @entity5 was (70.1  2.0)Gy (range 62.2   72.5Gy) for the adaptive plan and (66.0  5.5)Gy (range 50.9   70.7Gy) for the initial plan(p<0.01). The average D99 to the elective neck was (56.3  1.3)Gy (range 52.8   59.2Gy) for the adaptive plan and (52.4  7.0)Gy (range 37.7   58.6Gy) for the initial plan(p=0.01). The parotid decreased in volume during the treatment course (range 7.3%   42.2%). The average D_mean to the spared parotid decreased by 15.3% (p=0.002) for the adaptive plan when compared to the original. With ART, 4 out of 7 @entity1 experienced better sparing of the spinal cord (D_max reduced by 2.5%   10.2%) and the oral cavity (D_mean reduced by 3.5%   20.1%). CONCLUSION: Weekly CBCT dosimetry confirms that ART is an effective method to accommodate on-treatment anatomic changes. In select @entity1 , @entity5 coverage and OAR sparing may be improved with ART. Research is funded by Siemens.

SU-E-J-74: Dosimetric Advantages of Adaptive Radiotherapy for XXXX Are Confirmed with Weekly CBCT Images.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity135 :: ('MESH:D006258', 'Disease') :: ['head and neck (HN) cancer', 'HN'] @entity5 :: ('MESH:D009369', 'Disease') :: ['tumor', 'primary tumor']
@entity135 :: (MESH:D006258,Disease) :: ['Head and Neck Cancer']
