The Applied Research Of Adaptive External Beam Radiotherapy In The Treatment Of Cervical Carcinoma

PurposeTo investigate the effects on the exposure doses and position changes during the off-line image-guided adaptive external beam radiotherapy of cervical carcinoma and study the benefits of this new technology’s clinical applying.Material and Methods6 patients with cervical carcinoma treated by the SIEMENS’s ARTISTE received totally 18 CT scans every 8 fractions. By using the Pinnacle39.2 plan system, 1 initial plan and 2 new off-line replannings with the treatment targets and OARs being delineated were created based on these images. Then the three groups named by IMRT, ART1 and ART2 were obtained to compare these plans’ measure indexes of dosimetry and position.Results1. As time went by, the average volumns of CTV in 3 goups were as follows:(694.73±146.48),(682.24±151.13) and(663.56±128.05) cm3, there was decreasing tendency and no significant difference(P>0.05). The impact of the regression of the primary tumor on the CTV is limited.2. The CTV’s change of dosimetry(D2, D50, D98,Dmean and HI) in three groups were similar, among them D2 and D98 increased while HI decreased gradually, and there was no significant difference(P>0.05).3. The bladder and rectum’s positions, which were described with the distances’ changes between their geometrical centers and the bony anatomical landmarks in the direction of L/R, A/P and I/S, changed a lot during the treatment,,especially in the superior and inferior directions(I/S>A/P>L/R). The shift of bladder’s geometrical center was(0.79±0.65)cm in left and right direction,(0.95±0.63)cm in anterior and posterior direction, and(1.54±0.59)cm in superior and inferior direction. The shift of rectum’s geometrical center was(0.77±0.58)cm in left and right direction,(0.88±0.49)cm in anterior and posterior direction, and(1.18±0.52)cm in superior and inferior direction.4. The doses of bladder and rectum reduced significantly(P<0.05) at three dose levels(V40, V45 and V50). The bowel’s V45 and Dmean also reduced, while V45’s reduction is not significant in a paired t-test between these groups.ConclusionsDuring the treatment, bladder and rectum’s positons would vary with the time. The off-line adaptive external beam radiotherapy for cervical carcinoma can adjust treatment planning depending on the feedback of scanning images, thus may not bring significant changes in targets, while on the other hand, still play a positive role in the protection of the organs at risk.