Interobserver Variability and Dosimetric Impact in Structure Delineation of Organs at Risk on Cone Beam CT

Abstract Background Evaluation of delivered dose to the dominant intraprostatic lesion (DIL) for moderately hypofractionated radiotherapy of prostate cancer by cone beam computed tomography (CBCT)-based dose accumulation and target coverage analysis. Methods Twenty-three patients with localized prostate cancer treated with moderately hypofractionated prostate radiotherapy with simultaneous integrated boost (SIB) between December 2016 and February 2020 were retrospectively analyzed. Included patients were required to have an identifiable DIL on bi-parametric planning magnetic resonance imaging (MRI). After import into the RayStation treatment planning system and application of a step-wise density override, the fractional doses were computed on each CBCT and were consecutively mapped onto the planning CT via a deformation vector field derived from deformable image registration. Fractional doses were accumulated for all CBCTs and interpolated for missing CBCTs, resulting in the delivered dose for PTVDIL, PTVBoost, PTV, and the organs at risk. The location of the index lesions was recorded according to the sector map of the Prostate Imaging Reporting and Data System (PIRADS) Version 2.1. Target coverage of the index lesions was evaluated and stratified for location. Results In total, 338 CBCTs were available for analysis. Dose accumulation target coverage of PTVDIL, PTVBoost, and PTV was excellent and no cases of underdosage in DMean, D95%, D02%, and D98% could be detected. Delivered rectum DMean did not significantly differ from the planned dose. Bladder mean DMean was higher than planned with 19.4 ± 7.4 Gy versus 18.8 ± 7.5 Gy, p < 0.001. The penile bulb showed a decreased delivered mean DMean with 29.1 ± 14.0 Gy versus 29.8 ± 14.4 Gy, p < 0.001. Dorsal DILs, defined as DILs in the posterior medial peripheral zone of the prostate, showed a significantly lower delivered dose with a mean DMean difference of 2.2 Gy (95% CI 1.3–3.1 Gy, p < 0.001) compared to ventral lesions. Conclusions CBCT-based dose accumulation showed an adequate delivered dose to the dominant intraprostatic lesion and organs at risk within planning limits. Cautious evaluation of the target coverage for index lesions adjacent to the rectum is warranted to avoid underdosage.

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Quantification of interobserver variability in image registration using cone beam CT for partial bladder radiotherapy—a comparison between lipiodol and bladder wall surface

British Journal of Radiology ◽

10.1259/bjr.20180413 ◽

2019 ◽

Vol 92 (1094) ◽

pp. 20180413

Author(s):

Vickie Kong ◽

Maisie Kwan ◽

Susan Chen ◽

Peter Chung ◽

Tim Craig ◽

...

Keyword(s):

Image Registration ◽

Interobserver Variability ◽

Cone Beam Ct ◽

Bladder Wall ◽

Cone Beam ◽

Wall Surface

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MO-E-330A-06: Cone Beam CT (CBCT) Image Fusion for Prostate Localization: Interobserver Variability Study Using Manual and Automatic Registration

Medical Physics ◽

10.1118/1.2241454 ◽

2006 ◽

Vol 33 (6Part15) ◽

pp. 2171-2171

Author(s):

R Hammoud ◽

J Kim ◽

S Li ◽

B Lord ◽

S Patel ◽

...

Keyword(s):

Image Fusion ◽

Interobserver Variability ◽

Cone Beam Ct ◽

Cone Beam ◽

Automatic Registration ◽

Cbct Image ◽

Variability Study

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Computer-aided segmentation on MRI for prostate radiotherapy, part I: Quantifying human interobserver variability of the prostate and organs at risk and its impact on radiation dosimetry

Radiotherapy and Oncology ◽

10.1016/j.radonc.2021.12.011 ◽

2021 ◽

Author(s):

Jeremiah W. Sanders ◽

Henry Mok ◽

Alexander N. Hanania ◽

Aradhana M. Venkatesan ◽

Chad Tang ◽

...

Keyword(s):

At Risk ◽

Radiation Dosimetry ◽

Interobserver Variability ◽

Organs At Risk ◽

Prostate Radiotherapy ◽

Computer Aided

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Dosimetric impact of organ at risk daily variation during prostate stereotactic ablative radiotherapy

British Journal of Radiology ◽

10.1259/bjr.20190789 ◽

2020 ◽

Vol 93 (1108) ◽

pp. 20190789 ◽

Cited By ~ 1

Author(s):

Lynsey Devlin ◽

David Dodds ◽

Azmat Sadozye ◽

Philip McLoone ◽

Nicholas MacLeod ◽

...

Keyword(s):

At Risk ◽

Organs At Risk ◽

Cone Beam Ct ◽

Volumetric Modulated Arc Therapy ◽

Interquartile Range ◽

Stereotactic Ablative Radiotherapy ◽

Geometric Uncertainties ◽

Rectal Volume ◽

Significant Difference ◽

Dosimetric Analysis

Objective: Prostate stereotactic ablative radiotherapy (SABR) delivers large doses using a fast dose rate. This amplifies the effect geometric uncertainties have on normal tissue dose. The aim of this study was to determine whether the treatment dose–volume histogram (DVH) agrees with the planned dose to organs at risk (OAR). Methods: 41 low–intermediate risk prostate cancer patients were treated with SABR using a linac based technique. Dose prescribed was 35 Gy in five fractions delivered on alternate days, planned using volumetric modulated arc therapy (VMAT) with 10X flattening filter free (FFF). On treatment, prostate was matched to fiducial markers on cone beam CT (CBCT). OAR were retrospectively delineated on 205 pre-treatment CBCT images. Daily CBCT contours were overlaid on the planning CT for dosimetric analysis. Verification plan used to evaluate the daily DVH for each structure. The daily doses received by OAR were recorded using the D%. Results: The median rectum and bladder volumes at planning were 67.1 cm3 (interquartile range 56.4–78.2) and 164.4 cm3 (interquartile range 120.3–213.4) respectively. There was no statistically significant difference in median rectal volume at each of the five treatment scans compared to the planning scan (p = 0.99). This was also the case for median bladder volume (p = 0.79). The median dose received by rectum and bladder at each fraction was higher than planned, at the majority of dose levels. For rectum the increase ranged from 0.78–1.64Gy and for bladder 0.14–1.07Gy. The percentage of patients failing for rectum D35% < 18 Gy (p = 0.016), D10% < 28 Gy (p = 0.004), D5% < 32 Gy (p = 0.0001), D1% < 35 Gy (p = 0.0001) and bladder D1% < 35 Gy (p = 0.001) at treatment were all statistically significant. Conclusion: In this cohort of prostate SABR patients, we estimate the OAR treatment DVH was higher than planned. This was due to rectal and bladder organ variation. Advances in knowledge: OAR variation in prostate SABR using a FFF technique, may cause the treatment DVH to be higher than planned.

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