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Prostate bed and organ-at-risk deformation: Prospective volumetric and dosimetric data from a phase II trial of stereotactic body radiotherapy after radical prostatectomy

  • Author Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    Stephanie Yoon
    Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    Affiliations
    Department of Radiation Oncology, University of California Los Angeles, Los Angeles, United States
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  • Author Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    Minsong Cao
    Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    Affiliations
    Department of Radiation Oncology, University of California Los Angeles, Los Angeles, United States
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  • Author Footnotes
    2 Present address: Department of Radiation Medicine, Medstar Georgetown University Hospital, 3800 Reservoir Road, NW Washington DC 20007, United States.
    Nima Aghdam
    Footnotes
    2 Present address: Department of Radiation Medicine, Medstar Georgetown University Hospital, 3800 Reservoir Road, NW Washington DC 20007, United States.
    Affiliations
    Department of Radiation Medicine, Georgetown University, Washington, United States
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  • Author Footnotes
    3 Present address: David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095, United States.
    David Shabsovich
    Footnotes
    3 Present address: David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095, United States.
    Affiliations
    David Geffen School of Medicine, University of California Los Angeles, United States
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  • Author Footnotes
    3 Present address: David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095, United States.
    Sartajdeep Kahlon
    Footnotes
    3 Present address: David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095, United States.
    Affiliations
    David Geffen School of Medicine, University of California Los Angeles, United States
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  • Author Footnotes
    4 Present address: Department of Radiation Oncology, University of Southern California, 1975 Zonal Avenue, Los Angeles, CA 90033, United States.
    Leslie Ballas
    Footnotes
    4 Present address: Department of Radiation Oncology, University of Southern California, 1975 Zonal Avenue, Los Angeles, CA 90033, United States.
    Affiliations
    Department of Radiation Oncology, University of Southern California, Los Angeles, United States
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  • Author Footnotes
    2 Present address: Department of Radiation Medicine, Medstar Georgetown University Hospital, 3800 Reservoir Road, NW Washington DC 20007, United States.
    Sean Collins
    Footnotes
    2 Present address: Department of Radiation Medicine, Medstar Georgetown University Hospital, 3800 Reservoir Road, NW Washington DC 20007, United States.
    Affiliations
    Department of Radiation Medicine, Georgetown University, Washington, United States
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  • Author Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    Michael Lee Steinberg
    Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    Affiliations
    Department of Radiation Oncology, University of California Los Angeles, Los Angeles, United States
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  • Author Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    Amar U. Kishan
    Correspondence
    Corresponding author.
    Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    Affiliations
    Department of Radiation Oncology, University of California Los Angeles, Los Angeles, United States
    Search for articles by this author
  • Author Footnotes
    1 Present address: Department of Radiation Oncology, University of California Los Angeles, 200 Medical Plaza, Suite B265, Los Angeles, CA 90095, United States.
    2 Present address: Department of Radiation Medicine, Medstar Georgetown University Hospital, 3800 Reservoir Road, NW Washington DC 20007, United States.
    3 Present address: David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095, United States.
    4 Present address: Department of Radiation Oncology, University of Southern California, 1975 Zonal Avenue, Los Angeles, CA 90033, United States.

      Highlights

      • Stabilizing organ-at-risk anatomy (OAR) is essential.
      • Interfraction prostate bed volume is stable despite deformable surrounding organs.
      • Target underdosing and OAR overdosing is avoided in post-prostatectomy radiotherapy.
      • Volumetric and dosimetric changes from rotation and intrafraction motion are minor.
      • Shape of prostate bed may also influence target coverage.

      Abstract

      Purpose

      Stereotactic body radiotherapy (SBRT) in the post-prostatectomy setting is investigational. A major concern is the deformable prostate bed clinical target volume (CTV) and the closely juxtaposed organs-at-risk (OARs). We report a volumetric and dosimetric analysis of kilovoltage cone-beam CT (CBCT) data from the first 18 patients enrolled on a phase II trial of post-prostatectomy SBRT. With instructions on bladder filling and rectal preparation, we hypothesized acceptable CTV coverage while minimal overdosing to OARs could be achieved.

      Methods

      All patients received 5 fractions of 6–6.8 Gy to the prostate bed. CBCT were taken prior to and halfway through each fraction. CTV and OARs were contoured for each CBCT. Changes in inter- and intra-fraction volume and dose were calculated. Relative changes in CTV V95%, bladder V32.5 Gy, and rectal V32.5 Gy and V27.5 Gy were evaluated.

      Results

      Interfraction CTV volume remained stable, with median change +5.69% (IQR −1.73% to +9.84%). CTV V95% exhibited median change −0.74% (IQR −9.15% to −0.07%). Volumetric and dosimetric changes were minor from interfraction rotation and intrafraction motion. CTV V95% was ≥93% in 13 of 18 (72%) patients; in the remaining five, median change was −14.09% (IQR −16.64% to −13.56%). Interfraction CTV volume change was significantly larger among patients with CTV V95% <93% (+25.04% vs. +2.85%, p = 0.002).

      Conclusions

      With specific bladder and rectum filling protocols, CTV underdosing and overdosing to bladder and rectum are avoided in majority of patients. Changes in CTV shape may account for the underdosing that may be observed.

      Keywords

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