Migration of intraprostatic fiducial markers and its influence on the matching quality in external beam radiation therapy for prostate cancer

doi:10.1016/j.radonc.2010.03.017

Radiotherapy and Oncology

Volume 96, Issue 1, July 2010, Pages 43-47

https://doi.org/10.1016/j.radonc.2010.03.017 Get rights and content

Abstract

Purpose

To assess the influence of fiducial marker (FM) migration on the matching quality in external beam radiation therapy (EBRT) for prostate cancer.

Materials and methods

The position of FMs were identified using on-board kV imaging (OBI) and their 3-D position established using an in-house reconstruction algorithm for 31 patients with prostate adenocarcinoma. To carry out the match, the positions were overlaid on the digitally reconstructed radiographs (DRR) generated from the planning CT. The distance between each FM was calculated for seven treatments throughout the EBRT course. Four radiotherapy technologists were asked to independently perform and rate the match from OBI to DRR which was then correlated to the extent of FM migration.

Results

All the matches were rated by at least three radiotherapy technologists as “very easy” (“easy” subgroup) for 24 patients (77%), while the other seven patients had their match rated less than “very easy” and considered the “not easy” subgroup. The average daily FM migration was 0.93 ± 0.34 mm for the “easy” subgroup vs. 1.82 ± 0.75 mm for the latter. An average migration >2 mm was seen in five/seven patients in the “not easy” subgroup as compared to none in the “easy” subgroup. There was a trend towards less FM migration and better matching if the planning CT was done later than the day of the FM implant (p = 0.093).

Conclusions

FM migration >2 mm predicts for a more difficult matching process; PTV margins might have to be adjusted or the planning CT repeated.

Section snippets

Patient cohort

We analyzed 31 randomly chosen men treated for T1–3 clinically localized adenocarcinoma of the prostate who underwent image-guided three-dimensional conformal radiotherapy at our institution between December 2006 and October 2007. Each patient had prophylactic antibiotic coverage before and after the implant. Intrarectal anesthesia was administered. Twenty-six patients (84%) had four cylindrical gold FM measuring 4 mm in length inserted into the prostate transrectally under ultrasound guidance.

Patient cohort

Table 1 describes the pre-treatment patient characteristics. Forty-eight percent of patients had low risk prostate cancer and 52% of patients had intermediate or high risk prostate cancer. None of the patients had prior hormonal therapy.

Assessment of FM position during treatment

The quantitative assessment of the relative FM migration was performed. The distance between the FM position during the specific evaluated treatment and its reference position on the DRR as generated from the planning CT was calculated, this distance is referred

Discussion

The use of FM is not a perfect solution. FM are only surrogates for the prostate gland position and do not account for prostate distortion or volume change during a course of EBRT [10].

Intraprostatic FM displacement (FM migration) is a well-known phenomenon in prostate brachytherapy and seems to be a surprisingly minor problem when intraprostatic seeds are used as fiducial markers for EBRT. In this study, we present the analysis on FM migration in a cohort consisting of 31 patients.

To measure

Conclusion

For several years already, there has been a widespread use of FM in prostate EBRT. However, little research has been done regarding its daily use and its associated shortfalls. We found that only 77% of patients had an easy match of FM. We believe that a FM migration of >2 mm between the DRR generated from the planning CT and the OBI images obtained on the first day of EBRT treatment might influence treatment accuracy and therefore PTV margins might have to be adjusted or the planning CT

Conflict of interest notification

None of the authors have any conflict of interest related to this work.

Acknowledgments

The authors wish to thank the following radiotherapy technologists for their work in this study: Mr. Isaac Laplante, Ms. Lauréanne St-Pierre, Ms. Emilie Beauchemin and Ms. Louise Petit.

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The area between the centre of the three markers was also assessed within each group in absence of an updated prostate contour. This methodology combines the practices of earlier studies that relied on 2D measurements from planar films [7,22,23] with more recent publications that utilise 3D datasets to assess volumetric information [5,6,8]. All clinical data were retrospectively collected from hospital databases.
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The health service saved an average of AU$ 361 (CI $311 – $412) per patient after the practice change. There was no significant difference in fiducial marker position pre- and post- implementation (p < 0.05).
The practice change to perform insertion and radiotherapy simulation on the same day resulted in substantial savings to the health system, without compromising clinical outcomes. The decrease in number of required patient attendances is of real consequence to rural and remote populations. The practice change increases both the value and accessibility of best-practice health care to those most at risk of missing out.
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This is of course expected and shows consistency of the fiducial-based and seed-based registrations in our Python script. Several groups (34–36) have studied intraprostatic fiducial displacements in relation to position verification during external beam radiation therapy. The reported displacements were in general smaller than 2–3 mm.
To accurately quantify local seed displacement from Day 0 to Day 30 for our brachytherapy procedure. To quantify seed loss/migration and to identify the locations from where seeds are missing.
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Local seed displacements are smaller than 5 mm for 76.3% of the seeds; 2.3% show displacements larger than 10 mm. The largest seed displacements are seen along the inferior-superior axis: on average 1.0 ± 3.2 mm in superior direction with respect to the intraprostatic fiducials. Largest displacements are seen at the inferior-lateral sides of the prostate. On average, the inferior seeds move 1.0 ± 2.8 mm in anterior and 1.8 ± 3.3 mm in superior direction. The percentage of missing seeds is 0.2% (8 out of 3893 seeds for 5 patients). Most of the missing seeds were also originally implanted at the inferior-lateral sides of the prostate.
Local seed displacements and number of missing seeds are small, and predominantly occur around the apex.
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Catheter insertion is less invasive than inserting fiducial markers. Moreover, fiducial markers can migrate, which can greatly reduce the accuracy of image guidance [29]. The NZCC also allows computerized couch control to fuse the automatically segmented urethra before treatment with the planning CT scan.
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While there are many papers describing intrafractional fiducial marker movement in the treatment of prostate cancer(10–17), only a few have described the movement of fiducial markers in gynecological cancers (18–20). Various surrogates for fiducial marker position have been described including center of mass (19–21) and intermarker distance (10,22). A comprehensive review of prostate marker migration studies found that nearly all analyses considered planar intermarker distances as the metric for marker migration and the most common source of migration was post-implant edema (23).
Implanted fiducial markers are a commonly used tool in delineating the CTV in high-dose-rate interstitial brachytherapy (HDR-ISBT) for gynecologic malignancy, but their reliability in gynacological sites is not well understood. These markers and interstitial applicators can experience interfractional motion due to organ swelling or other anatomical changes. The purpose of this study was to evaluate the spatial variation of these features.
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Prostate radiotherapyMigration of intraprostatic fiducial markers and its influence on the matching quality in external beam radiation therapy for prostate cancer

Abstract

Purpose

Materials and methods

Results

Conclusions

Section snippets

Patient cohort

Patient cohort

Assessment of FM position during treatment

Discussion

Conclusion

Conflict of interest notification

Acknowledgments

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Radiother Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Radiother Oncol

Int J Radiat Oncol Biol Phys

Urology

Prostate radiotherapy
Migration of intraprostatic fiducial markers and its influence on the matching quality in external beam radiation therapy for prostate cancer