Initial Experience of Adaptive Radiation Therapy for Patients with Early Stage Prostate Cancer Treated on the Ethos Unit

Committee/Faculty

Presenting Author(s)

JW

James A. Wheeler, MD, PhD

MD, PhD
Goshen Center for Cancer Care
Goshen, Indiana, United States

Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.

Co-Author(s)

JL

John Lowden, MS, DABR

MS, DABR
Goshen Center for Cancer Care
Goshen, Indiana, United States

Disclosure: Disclosure information not submitted.
FL

Fang Liu, PhD

PhD
University of Notre Dame
Notre Dame, Indiana, United States

Disclosure: Disclosure information not submitted.
SK

Samantha Korda, MS

MS
Goshen Center for Cancer Care
Goshen, Indiana, United States

Disclosure: Disclosure information not submitted.
BY

Brayton Yoder, n/a

Undergraduate Student
Goshen Center for Cancer Care
Nappanee, Indiana, United States

Disclosure: Disclosure information not submitted.
HV

Houman Vaghefi, MD, PhD

MD, PhD
Goshen Center for Cancer Care
Goshen, Indiana, United States

Disclosure: Disclosure information not submitted.
IS

Irina Sparks, MD

MD
Goshen Center for Cancer Care
Goshen, Indiana, United States

Disclosure: Disclosure information not submitted.
AM

Adam Moore, RTT, CMD

RTT, CMD
Goshen Center for Cancer Care
Goshen, Indiana, United States

Disclosure: Disclosure information not submitted.

Purpose: The volume and configuration of the bladder and rectum change daily, and the dose-volume histogram analysis of the treatment plan obtained from the planning CT data set may not accurately reflect the actual doses received throughout the course of treatment.

The Ethos unit allows cone beam CT imaging to be acquired and a new treatment plan generated daily for that day’s treatment session. This study compares target coverage and normal tissue doses for the initial cohort of patients treated with this new technology.

Methodology: Nineteen patients with early stage prostate cancer were given between 15 and 29 fractions of external beam radiation therapy. The prostate, seminal vesicles, bladder, rectum, and other structures were auto-contoured daily and adjusted by the physician prior to planning and treatment. A “standard plan” incorporated the changes in organ contours but did not change the beam fluence derived from the treatment plan of the original CT simulation dataset. An “adaptive plan” then optimized the beam fluence according to the newly contoured structures.

Results: Substantial differences were seen not only in the bladder and rectal volumes, but also in the contoured volumes of the prostate, seminal vesicles, and resultant PTV (planning target volume). The average absolute value of the difference between the prostate volume on the planning CT compared to the daily treatment was 19.7%. For the seminal vesicles it was 21.8%; for the PTV 10.8%; bladder 27.7%, and rectum 20.3%.

The Wilcox signed rank test for the adaptive versus scheduled treatments favored adaptive planning in terms of coverage to the prostate (Holm-adjusted p-value 0.0229), seminal vesicles (Holm-adjusted p-value 0.0010) and PTV (Holm-adjusted p-value <0.00005). The adaptive plan was favored versus the scheduled plan for bladderV70 per the raw p-value from the Wilcox signed rank test (p-value 0.0401) and rectumV40 (p-value 0.0181), but the statistically significant differences no longer exist with the Holm multiplicity adjustment (p-value 0.2809 for bladderV70 and p-value 0.1447 for rectumV40).

Conclusions: Adaptive planning provided significantly better coverage of the prostate, seminal vesicles, and PTV compared to the scheduled plan. Contouring variability of the targets was significant, and its impact on the evaluation of plan quality is under investigation. There was no significant difference between the adaptive plan and the original plan in terms of target coverage or normal organ sparing.

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