Genitourinary Cancer

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SU_26_2269 - Who Benefits From a Prostate Rectal Spacer? : Secondary Analysis of Dosimetry and Bowel Quality of Life from a Phase III Trial

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Who Benefits From a Prostate Rectal Spacer? : Secondary Analysis of Dosimetry and Bowel Quality of Life from a Phase III Trial
D. A. Hamstra1, S. Daignault-Newton2, W. R. Bosch3, N. F. Mariados Jr4, J. E. Sylvester5, E. T. Gross6, D. K. Shah7, S. M. Kurtzman8, J. A. Bogart9, R. A. Hsi10, M. Kos11, R. J. Ellis III12, M. D. Logsdon13, S. H. Zimberg14, K. Forsythe15, H. Zhang16, E. M. Soffen17, P. M. Francke18, H. A. Gay19, and J. M. Michalski20; 1Oakland University William Beaumont School of Medicine, Department of Radiation Oncology, Dearborn, MI, 2The University of Michigan Health System, Ann Arbor, MI, 3Department of Radiation Oncology, Washington University, St. Louis, MO, 4Associated Medical Professionals of NY PLLC, Syracuse, NY, 521st Century Oncology, Sarasota, FL, 6The Urology Center of Colorado, Denver, CO, 7Cancer Care of Western New York, Cheektowaga, NY, 8Urological Surgeons of Northern California, Inc., Campbell, CA, 9SUNY Upstate Medical University, Syracuse, NY, 10Peninsula Cancer Center, Poulsbo, WA, 11Urology Nevada, Reno, NV, 12Radiation Oncology, University Hospitals Seidman Cancer Center, Case Comprehensive Cancer Center, Cleveland, OH, 13Sutter Institute for Medical Research, Sacramento, CA, 14Advanced Radiation Centers of New York, Lake Success, NY, 15Oregon Urology Institute, Springfield, OR, 16Wilmot Cancer Institute, University of Rochester, Rochester, NY, 17Princeton Radiation Oncology, Jamesburg, NJ, 1821st Century Oncology, Fort Myers, FL, 19Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 20Washington University School of Medicine, St. Louis, MO

Purpose/Objective(s): A phase III rectal spacer (Sp) trial of prostate RT found a clinically significant 5.8 pt difference in bowel quality of life (QOL) by EPIC and a 27% absolute lower rate of minimally important decline (MID). We performed a secondary analysis to identify men less likely to benefit from Sp.

Materials/Methods: The volume of rectum treated to 70 Gy (V70) as well as the QUANTEC rectal dose goals were utilized as surrogates for plan quality and clinical benefit. The likelihood of 1x (5 pt) or 2x (10 pt) MID changes were assessed as a function of clinical variables with odds ratios reported from logistic models.

Results: There was no correlation between prostate volume and rectal V70 (R2=0.006) or V70 reduction with Sp placement (p>0.5). Rectal V70 pre and post Sp was 13/3% for the smallest prostates (<40 cc) and 12/2% for the largest (>80 cc). The relative reduction in rectal V70 of 78% did not vary by pre Sp V70, but the absolute reduction was greater for higher V70 (18.3% reduction if rectal V70>20% vs. 3.4% for rectal V70≤5%). All Sp plans met the 5 QUANTEC rectal dose constraints while 92% of Cntrl plans met all 5 constraints. Declines in bowel QOL were directly correlated with rectal dosimetry from V50 through V70 (all p<0.05). Those not meeting all QUANTEC goals had -15.0 pt (stdev 15.1) decline, Cntrl pts meeting QUANTEC goals had -4.0 (9.5) pt decline and Sp had +0.5 (7.6) (p<0.01). Previous abdominal/pelvic surgery did not change baseline QOL (p>0.1) while at 3 mo there was a small and clinically insignificant greater decline in bowel QOL in those with prior surgery (-6.4 pt (no surgery) vs. -8.1 pt (surgery), p>0.1) with this small difference persistent over time. Across prognostic groups including: age, body mass index, previous surgery, target volume, or quality of radiation plans there was no statistically significant heterogeneity in the relative benefit of Sp in decreasing the risk of 1x or 2xMID declines (Table). Conclusion: There was little heterogeneity in the likelihood of Sp reducing the risk of declines in bowel QOL across clinical and dosimetric variables. Even for the >95% of plans meeting QUANTEC rectal criteria Sp provided meaningful benefit. Further analysis into biologic differences that predict changes in bowel QOL after RT are needed.
Impact of Spacer on Likelihood of Bowel MID at 3-years
Variable Number 1x MID Odds Ratio (95%CI) Ctrl % Sp % 2x MID Odds Ratio (95%CI) Ctrl % Sp %
Overall 137 0.23 (0.1-0.5) 41 14 0.22 (0.07-0.7) 21 5
Age<67 68 0.20 (0.06-0.7) 44 14 0.08 (0.01-0.5) 33 4
Age>67 69 0.26 (0.08-0.8) 39 14 0.57 (0.11-3.1) 12 7
BMI<28 66 0.33(0.11-1.01) 42 19 0.32 (0.08-1.3) 25 10
BMI>28 71 0.16(0.05-0.6) 40 10 0.11 (0.01-1.2) 15 2
No Previous Surgery 59 0.13(0.04-0.4) 46 10 0.07 (0.01-0.6) 23 2
Previous Surgery 63 0.42(0.12-1.3) 36 20 0.49 (0.11-2.2) 18 10
Prostate 66 0.30 (0.08-1.2) 28 10 0.22 (0.03-1.4) 17 4
Prostate + SV 71 0.22 (0.07-0.6) 50 18 0.24 (0.05-1.1) 23 7
Plan didn’t meet all 5 QUANTEC rectal goals 5 - 80 - - 60 -
Plan met all 5 QUANTEC rectal goals 132 0.29 (0.12-0.7) 36 14 0.31 (0.09-1.1) 15 5

Author Disclosure: D.A. Hamstra: Research Grant; Augmenix. Honoraria; Augmenix. Consultant; Augmenix. Advisory Board; Genome DX. S. Daignault-Newton: Consultant; Augmenix. W.R. Bosch: Research Grant; National Cancer Institute. Honoraria; Augmenix, Inc. Travel Expenses; AAPM. N.F. Mariados: Stock Options; Augmenix. J.E. Sylvester: Honoraria; Augmenix. Stock Options; Augmeinx. E.T. Gross: None. D.K. Shah: Stock Options; Augmenix. S.M. Kurtzman: None. J.A. Bogart: Partner; Upstate University Radiation Oncology. Travel Expenses; Alliance Clinical Trials. Chair, Radiation Oncology Committee; Alliance. R.A. Hsi: None. M. Kos: None. M.D. Logsdon: None. K. Forsythe: None. J.M. Michalski: Independent Contractor; Sheila Michalski and Associates. Research Grant; NCI.; Veteran's Administration. Consultant; Veteran's Administration. Stock; ViewRay Inc. Chair Radiation Oncology Committee; NRG Oncology. Radiation Oncology Practice Assessment; Veterans Affairs. Co-chair GU Steering Committee; NCI.

Daniel Hamstra, MD, PhD

William Beaumont Hospital (Dearborn, MI)

Texas Oncology: Staff Physician: Employee

Augmenix: Consultant, Honoraria, Research Grants

Daniel A. Hamstra, MD, PhD
Professor of Radiation Oncology and Clinical Director
William Beaumont Oakland University School of Medicine
Beaumont Health (Dearborn)

Dr. Hamstra currently is an attending physician at William Beaumont Oakland University School of Medicine (’17-present) after previously being on the faculty of the University of Michigan (Ann Arbor, MI, ’06-’15) and employed by Texas Oncology at the Texas Center for Proton Therapy (Irving, TX, ’15-‘17).
He has been an active member of the RTOG (now NRG) GU steering committee (where he serves as the principle radiation oncologist on RTOG 1115) and on the Patient Centered Outcomes Committee as well as on the Radiation Oncology and Neuroblastoma committees for the Children’s Oncology Group (COG). His research focus has been on integrating advanced radiation techniques including MRI, SBRT, and rectal spacers into GU care with a particular emphasis on patient reported health related quality of life.
When not working Dr. Hamstra enjoys cooking (and eating), scuba diving, skiing, as well as spending time with his wife of more than 25-years and 4 children (aged 10-30).


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SU_26_2269 - Who Benefits From a Prostate Rectal Spacer? : Secondary Analysis of Dosimetry and Bowel Quality of Life from a Phase III Trial

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