Vector analysis of bladder cancer patient setup utilizing a magnetic resonance image-guided radiation therapy (MR-IGRT) system.

Authors

null

Benjamin Walker Fischer-Valuck

Washington University in St. Louis, Department of Radiation Oncology, St. Louis, MO

Benjamin Walker Fischer-Valuck , Olga L Green , Hiram Alberto Gay , Sasa Mutic , Jeff M. Michalski

Organizations

Washington University in St. Louis, Department of Radiation Oncology, St. Louis, MO, Washington University School of Medicine in St. Louis, St. Louis, MO

Research Funding

No funding sources reported

Background: Inter and intra-fraction anatomy changes in patients undergoing radiation therapy (RT) for bladder cancer (BC) are common but have thus far been studied with implanted fiducial markers, limited quality 2-D orthogonal films and computed tomography (CT). The adverse impact of daily set-up variation could be more significant than appreciated. Our goal was to employ the soft tissue imaging capabilities of an integrated magnetic resonance image-guided RT (MR-IGRT) system to analyze daily positioning. Methods: Fourteen patients with BC were treated on a MR-IGRT system. Patient setup was performed via volumetric MR imaging with a resolution of 0.15 x 0.15 cm. Alignment was performed according to skin marks then shifts assessed by comparing the treatment volume from the planning CT to the daily MR image. 240 pretreatment MR images were analyzed and 3 shifts were recorded for each image. A vector shift was calculated by combining the square root of the combined sum of the shifts squared. Number of times that the vector of combined shifts would have exceeded the planning tumor volume (PTV) was recorded. Results: Daily volumetric MR imaging allowed for accurate alignment and daily monitoring of bladder volume and normal tissue anatomy. Recorded shifts of the treated volume were 0.9±0.5 cm in the right/left direction, 0.7±0.3 cm in the anterior/posterior direction, and 0.7±0.4 cm in the cranio-caudal direction. In 66 (28%) of cases the vector shift was initially greater than the PTV margin. For 2 patients, pre-treatment MR imaging revealed the tumor reduced in size and dose to the bowel would have exceeded constraints, and treatment adaptation was performed to reduce normal tissue toxicity. Using CTCAE criteria, no grade 3 or higher toxicities have been reported. Conclusions: Accurate and reproducible treatment delivery is required to avoid marginal misses to the target volume as well as excess dose to normal tissue. MR-IGRT allows for excellent soft tissue visualization which enables for the avoidance of potential setups errors by allowing daily alignment changes to ensure the target is included in the PTV. It also allows the ability to make treatment changes based on anatomy variations.

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Abstract Details

Meeting

2016 Genitourinary Cancers Symposium

Session Type

Poster Session

Session Title

Poster Session B: Prostate Cancer; Urothelial Carcinoma; Penile, Urethral, and Testicular Cancers

Track

Urothelial Carcinoma,Prostate Cancer,Penile, Urethral, and Testicular Cancers

Sub Track

Urothelial Carcinoma

Citation

J Clin Oncol 34, 2016 (suppl 2S; abstr 412)

DOI

10.1200/jco.2016.34.2_suppl.412

Abstract #

412

Poster Bd #

H5

Abstract Disclosures

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