PURPOSE: In prostate proton radiotherapy, three fiducial markers are used for @entity1 daily alignment. However fiducial alignment can change beamline heterogeneity in proton therapy. The purpose of this study is to determine the difference in fiducial and boney anatomy alignment for @entity1 treatment. METHODS AND MATERIALS: @entity263 @entity1 who received proton treatment were included in this study. 3 fiducial markers were implanted before the initial CT. All the @entity1 were re-CT'd every 2 weeks to check the fiducial marker position reproducibility as well as dosimetric consistence of target coverage. In geometry study, re-CT were fused to the initial CT base on the boney anatomy and the average fiducial marker displacement was measured the centers of the fiducials. Dosimetrically, the initial plan was recalculated directly to re-CT image set based on the boney alignment and fiducial alignment to determine the difference from daily treatment. Prostate coverage and hotspots were evaluated using the dose to 98% of the CTV (D98) and dose to 2% (D2), respectively. RESULTS: The shift from the initial 6 @entity1 CT image sets resulted in an average change in the fiducial location of 5.70 +/- 3 mm. Dosimetric comparison from a single @entity1 revealed that differences from the planned dose resulted from both boney and fiducial alignment. Planned clinical treatment volume coverage resulted in a D98 of 70.44Gy and D2 of 70.84Gy compared to a D98 of 70.13Gy and D2 70.94Gy for boney alignment and a D98 of 70.08Gy and D2 71.18Gy for fiducial alignment respectively. CONCLUSION: This study demonstrates that with boney anatomy alignment there is little change to CTV coverage and only slightly worse CTV coverage and hotspot production with fiducial alignment. An increase @entity1 cohort and further investigation is necessary to determine the whether boney alignment can help better control dose heterogeneity.

SU-E-T-27: A Dosimetric Evaluation of Boney Anatomy Versus Fiducial Marker Alignment for the Treatment of XXXX Using Scanned Beam Proton Therapy.

@entity1 :: ('9606', 'Species') :: ['patients', 'patient'] @entity263 :: ('MESH:D011471', 'Disease') :: ['Prostate cancer']
@entity263 :: (MESH:D011471,Disease) :: ['Prostate Cancer']
