Genitourinary Cancer

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SU_29_2296 - Changes Over Time in MRI Findings in the Rectum Following External Beam Radiation Therapy for Prostate Cancer

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

Changes Over Time in MRI Findings in the Rectum Following External Beam Radiation Therapy for Prostate Cancer
H. Maemoto, S. Iraha, and F. Ganaha; Okinawa Prefectural Nanbu Medical Center and Children's Medical Center, Okinawa, Japan

Purpose/Objective(s): The aim of this study was to investigate the changes over time in magnetic resonance imaging (MRI) findings in the rectum following external beam radiation therapy (EBRT) for prostate cancer, and to analyze whether subsequent rectal hemorrhage after EBRT might be predictable from the severity of radiation changes in magnetic resonance (MR) images of the rectum.

Materials/Methods: We retrospectively reviewed 44 consecutive patients who underwent definitive EBRT for prostate cancer at our institution between 2007 and 2008. Seven, four, and two patients were excluded from this study because of <2 years of follow-up, no MRI images, and development of rectal cancer, respectively. A total of 227 MRI scans from the remaining 31 patients were classified into 7 groups depending on the time obtained from the last day of EBRT: prior to RT, <10, 10–25, 26–50, 51–75, 76–100, and 101–150 weeks. MR images were evaluated according to the MRI grading system as follows: grade 0, wall thickness <6 mm, and signal intensity (SI) of outer muscle layer low on T2-weighted image (T2WI); grade 1, wall thickness ≥6 mm, SI of outer muscle layer remains low on T2WI, and muscle layer can be separated from the submucosa; grade 2, wall thickness >6 mm, SI of outer muscle layer high on T2WI, and outer muscle layer is indistinguishable from the submucosa. Whether there was a difference in the severity of MRI grade between the groups with and without rectal bleeding was analyzed.

Results: The median total dose applied was 74 Gy (range, 66.6–76 Gy) in 1.8 or 2.0 Gy per fraction. Five patients were treated with 3-dimensional conformal radiation therapy (RT), while 26 patients were treated with intensity-modulated RT. The median follow-up time for patients was 85 months (range, 25–111 months). Two patients had RTOG/EORTC grade 1, and 7 patients had grade 2 radiation proctitis. The first instance of rectal hemorrhage occurred a median of 18 months after RT (range, 10–25 months). The results of the evaluation of MRI are shown in Table 1. MRI grade 2 was the most common in the 26–50 weeks group. There was no significant difference in the severity of MRI grade at each timing in the group with and without rectal hemorrhage. Table 1. MRI grade of the rectum
Rectal hemorrhage (-) Rectal hemorrhage (+)
Weeks from RT Grade 0 Grade 1 Grade 2 Grade 0 Grade 1 Grade 2
Prior to RT 9 11 2 2 6 1
<10 1 13 7 0 6 1
10–25 1 12 9 0 5 4
26–50 0 10 24 0 5 9
51–75 1 6 13 0 4 4
76–100 0 9 7 0 3 2
101–150 1 15 11 0 8 5

Conclusion: The severity of radiation changes in MR images in the rectum are strongest at 26–50 weeks after EBRT. Estimation of future rectal bleeding after EBRT for prostate cancer from MRI findings in the rectum may be difficult.

Author Disclosure: H. Maemoto: None. S. Iraha: None. F. Ganaha: None.

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