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Dosimetric Studies Affecting the Quality of Delivered Radiation Plan with and Without Rotational Setup Corrections for Treating Prostate Cancer

R Gupta*, R Lalonde, M Huq, UPMC Hillman Cancer Center and University of Pittsburgh School of Medicine, Pittsburgh, PA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: aim of this study was to explore if the limitation of couch rotation on the Varian Halcyon (3D couch translations only) affects the quality of delivered treatment plans for prostate cases by resampling the simulation CT images (CT Sim) in to the geometry of the daily cone-beam CT (CBCT) images; performing automated 6D (Auto6D) and 3D corrections (Auto3D); then recalculating dose distribution on the rotated images and comparing dose statistics.

Methods: prostate hypofractionated VMAT-plans, planned in Varian Eclipse and delivered on Halcyon, were evaluated in this study. For each case, original CTSim was resampled in Velocity into the geometry of a representative sample of five daily CBCT images (selected throughout the treatment course). Prostate, PTV, Bladder and Rectum were contoured on each of these reformatted CBCT images. The CT Sim images were matched in Eclipse Image registration software with each reformatted CBCT scan with Auto3D match with rotations turned off and Auto 6D match with rotations turned on. For each image set, the dose distribution was then recalculated on the registered CT images derived from Auto3D match and Auto6D match. Dose statistics were compared.

Results: with Auto3D corrected plans, Auto6D corrected plans resulted in improved planning target volume (PTV) coverage D95% (45.69 ± 0.51Gy vs 42.33 ±6.90Gy). No significant reduction was observed in Bladder D25, D35, D50, V50 and Rectum V25, D35 and D50. However, Auto6D plans reduced rectum D25 significantly, 28.34 ± 0.76Gy as compared to Auto3D plans 31.76± 4.5Gy.

Conclusion: deliver the hypofractionated radiotherapy in prostate cancer, Auto6D plans increased PTV D95% dose and decreased rectum dose significantly as compared to Auto3D plans. Improved daily online image-guidance and better management of bladder and rectum could make a more precise treatment delivery.


Not Applicable / None Entered.


TH- External Beam- Photons: Dose reconstruction over deforming anatomies

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