UNASSIGNED: 35 Background: To characterize the effect of a prostate-rectum spacer on dose to rectum during external beam radiotherapy for @entity263 , and to assess for factors correlated with rectal dose reduction. METHODS: Fifty-two @entity1 at 4 institutions were enrolled onto a prospective pilot clinical trial. @entity1 underwent baseline scans, then were injected with perirectal spacing hydrogel and re-scanned. IMRT plans were created on both scans for comparison. Objectives were to establish rates of creation of >= 7.5mm of prostate-rectal separation, and decrease in rectal V70 of >= 25%. Multiple regression analysis was performed to evaluate associations between pre- vs. post-injection changes in rectal V70 and changes in plan conformity, rectal volume, bladder volume, bladder V70, @entity343 volume, as well as post-injection mid-gland separation, gel volume, gel thickness, length of @entity343 /gel contact, or gel left-to-right symmetry. RESULTS: Hydrogel resulted in > 7.5mm prostate-rectal separation in 95.8% of @entity1 ; 95.7% had decreased rectal V70 of > 25%, with mean reduction of 8.0 Gy. There were no significant differences in pre- and post-injection prostate, @entity343 , rectal, and bladder volumes. Plan conformities were significantly different pre- vs. post-injection (P = 0.02). In multiple regression analysis, change in plan conformity was negatively associated with reduction in V70 (P=0.01); plans with worse conformity indexes post-injection compared to pre-injection (n=13) still had improvements in rectal V70. Reductions in V70 did not significantly vary by institution, despite significant inter-institutional variations in plan conformity. There were no significant relationships between reduction in V70 and the other characteristics analyzed. CONCLUSIONS: Injection of hydrogel into prostate-rectal interface resulted in dose reductions to rectum for > 90% of @entity1 treated. Rectal sparing was statistically significant across a range of 10-75 Gy, and was demonstrated within the presence of significant inter-institutional variability in plan conformity, target definitions, and injection results.

A multi-institutional clinical trial of rectal dose reduction via injected polyethylene-glycol hydrogel during IMRT for XXXX : Analysis of dosimetric outcomes.

@entity1 :: ('9606', 'Species') :: ['patients', 'Patients'] @entity263 :: ('MESH:D011471', 'Disease') :: ['prostate cancer'] @entity343 :: ('187978', 'Species') :: ['PTV']
@entity263 :: (MESH:D011471,Disease) :: ['prostate cancer']
