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Multicenter Study
. 2022 Jun;49(6):3529-3537.
doi: 10.1002/mp.15658. Epub 2022 Apr 19.

HDR prostate brachytherapy plan robustness and its effect on in-vivo source tracking error thresholds: A multi-institutional study

Joel Poder  1   2 , Dylan Koprivec  2 , Yashiv Dookie  2 , Andrew Howie  1 , Dean Cutajar  1   2 , Antonio L Damato  3 , Nicolas Côté  3 , Marco Petasecca  2 , Joseph Bucci  1 , Anatoly Rosenfeld  2
Affiliations
Multicenter Study

HDR prostate brachytherapy plan robustness and its effect on in-vivo source tracking error thresholds: A multi-institutional study

Joel Poder et al. Med Phys. 2022 Jun.

Abstract

Purpose: The purpose of this study was to examine the effect of departmental planning techniques on appropriate in-vivo source tracking error thresholds for high dose rate (HDR) prostate brachytherapy (BT) treatments, and to determine if a single in-vivo source tracking error threshold would be appropriate for the same patient anatomy.

Methods: The prostate, rectum, and urethra were contoured on a single patient transrectal ultrasound (TRUS) dataset. Anonymized DICOM files were disseminated to 16 departments who created an HDR prostate BT treatment plan on the dataset with a prescription dose of 15 Gy in a single fraction. Departments were asked to follow their own local treatment planning guidelines. Source positioning errors were then simulated in the 16 treatment plans and the effect on dose-volume histogram (DVH) indices calculated. Change in DVH indices were used to determine appropriate in-vivo source tracking error thresholds. Plans were considered to require intervention if the following DVH conditions occurred: prostate V100% < 90%, urethra D0.1cc > 118%, and rectumtt Dmax > 80%.

Results: There was wide variation in appropriate in-vivo source tracking error thresholds among the 16 participating departments, ranging from 1 to 6 mm. Appropriate in-vivo source tracking error thresholds were also found to depend on the direction of the source positioning error and the endpoint. A robustness parameter was derived, and found to correlate with the sensitivity of plans to source positioning errors.

Conclusions: A single HDR prostate BT in-vivo source tracking error threshold cannot be applied across multiple departments, even for the same patient anatomy. The burden on in-vivo source tracking devices may be eased through improving HDR prostate BT plan robustness during the plan optimisation phase.

Keywords: HDR; brachytherapy; in-vivo; prostate; robustness; source tracking.

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Conflict of interest statement

The authors have no conflict of interest or funding sources to report.

Figures

FIGURE 1
FIGURE 1
Axial TRUS slice of the patient anatomy, the prostate, urethra, and rectum contours are shown in red, yellow, and blue, respectively. The frequency of location of the three most heavily weighted catheters across all the plans is shown using the colour scale
FIGURE 2
FIGURE 2
(A) Change in prostate V100% DVH metric as a function of source positioning error in the caudal (negative) and cranial (positive) direction, (B) the medial (negative) and lateral (positive) direction, and, (C) the posterior (negative) and anterior (positive) direction. Red lines within the boxes represent the median across all 16 departments, the boxes represent the interquartile range, whiskers represent the minimum and maximum, red crosses represent the outliers. The thick solid red line represents the tolerance of 90% coverage for the prostate V100% used to determine the source tracking error threshold
FIGURE 3
FIGURE 3
(A) Change in rectum D max DVH metric as a function of source positioning error in the caudal (negative) and cranial (positive) direction, (B) The medial (negative) and lateral (positive) direction, and (C) the posterior (negative) and anterior (positive) direction. Red lines within the boxes represent the median across all 16 departments, the boxes represent the interquartile range, whiskers represent the minimum and maximum, red crosses represent the outliers. The thick solid red line represents the tolerance of 80% for the rectum D max used to determine the source tracking error threshold
FIGURE 4
FIGURE 4
(A) Change in urethra D0.1cc DVH metric as a function of source positioning error in the caudal (negative) and cranial (positive) direction, (B) the medial (negative) and lateral (positive) direction, and (C) the posterior (negative) and anterior (positive) direction. Red lines within the boxes represent the median across all 16 departments, the boxes represent the interquartile range, whiskers represent the minimum and maximum, red crosses represent the outliers. The thick solid red line represents the tolerance of 118% for the urethra D0.1cc used to determine the source tracking error threshold
FIGURE 5
FIGURE 5
(A) Prostate robustness parameter for each of the 16 departments, (B) rectum robustness parameter, (C) urethra robustness parameter. Red dashed lines represent ±1 standard deviation from the mean of the 16 departments
See this image and copyright information in PMC

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