1. By: Matthew Kosch
Advantages and Recent Implementation of Fiducials in Image-Guided Radiation Therapy

2. Background
Fiducials are small metallic objects used in Image Guided Radiation Therapy (IGRT)
Often used for matching instead of bone or soft tissue
No standard for their use

3. Objective
Update radiation therapists through a literature review on the benefits of fiducial use, comparisons between different types, and contraindications (or lack thereof)

4. Soft Tissue vs. Fiducials3,4
One study showed radiation therapists could much more accurately and reproducibly align to fiducials compared to soft tissue for prostate patients
Half of the patients had fiducials, half were matched to soft tissue
Statistical analysis showed the fiducial group daily matches were almost all within 2mm of the average
The soft tissue group showed many matches more than 3mm different from the average matching location

5. Stability of Fiducials in Soft Tissue5
Much debate about the reliability of fiducials to remain in place
This study looked at 100 prostate patients receiving fiducials
CT scan was done on the day they were implanted
Another scan was done 7 days later
About the time the dosimetrists would start planning
Over 2/3 of them had their fiducials move less than 1mm
Under ¼ had theirs move 1-2mm
Concluded dosimetrists could be confident the movement was negligible and the prescribed treatment would accurately treat the PTV

6. Fiducial Comparisons6-8
Fiducials vs. surgical clips
Retrospective analysis showed fiducial patient matches were within 0.8mm of the mean on average
Over 2mm for surgical clip matching
Gold seeds, gold coils, and polymer comparison
Tested all of them on multiple imaging techniques (US, CBCT, MV)
Determined small gold seeds, coils, and polymers were ideal if primarily using kV energy modalities
Large gold seeds necessary if primarily using MV
caused artifacts on kV modalities
No “perfect fiducial”
Carbon fiber fiducials

7. Fiducials in Proton Therapy9
Big concern with fiducials causing dose perturbations
Change in dose deposition
Gold and high-z fiducials caused up to an 18 percent or more dose perturbation
Polymer or carbon fiber fiducials much more ideal

8. Infection Risk after Placement10-11
Big reason why many facilities don’t bother with fiducials
“unnecessary risk”
UTI, pain with urination, fever
Prophylactic antibiotics

9. Conclusion
Fiducials allow for more consistent and reproducible matching
Research shows they do not migrate very much on average
Type of fiducial should depend on imaging modality rather than actual treatment
Can even be implemented in proton therapy
Infection risk

10. References
1De Los Santos J, Popple R, Agazaryan N, et al. Image guided radiation therapy (IGRT) technologies for radiation therapy localization and delivery. International Journal of Radiation Oncology*Biology*Physics ;87(1): doi: /j.ijrobp
2. Singh J, Greer P, White M, et al. Treatment-related morbidity in prostate cancer: A comparison of 3-dimensional conformal radiation therapy with and without image guidance using implanted fiducial markers. International Journal of Radiation Oncology*Biology*Physics ;85(4): doi: /j.ijrobp
3. Deegan T, Owen R, Holt T, et al. Assessment of cone beam CT registration for prostate radiation therapy: Fiducial marker and soft tissue methods. Journal of Medical Imaging and Radiation Oncology ;59(1): doi: /
4. Harris D, McDonald A, and Fiveash J. Comparing CBCT alignment to fiducial alignment in terms of necessity and organ at risk dosimetry in prostate radiation therapy. International Journal of Radiation Oncology*Biology*Physics ;93(3):E240. doi: /j.ijrobp
5. Kumar K, Wu T, Tonlaar N, et al. Image-guided radiation therapy for prostate cancer: A computed tomography–based assessment of fiducial marker migration between placement and 7 days. Practical Radiation Oncology ;5(4):
doi: /j.prro
6. Fortin I, Carrier JF, Beauchemin MC, et al. Using fiducial markers in the prostate bed in postprostatectomy external beam radiation therapy improves accuracy over surgical clips. Strahlentherapie und Onkologie ;190(5): doi: /s
7. Chan M, Cohen G, and Deasy J. Qualitative evaluation of fiducial markers for radiotherapy imaging. Technology in Cancer Research and Treatment ;15(3): doi: /
8. HaberMehl D, Henkner K, Ecker S, et al. Evaluation of different fiducial markers for image-guided radiotherapy and particle therapy. Journal of Radiation Research ;54(1):i61-i68. doi: /jrr/rrt071.
9. Cheung J, Kudchadker R, Zhu X R, and Lee A. Dose perturbations and image artifacts caused by carbon-coated ceramic and stainless steel fiducials used in proton therapy for prostate cancer. Physics in Medicine and Biology ;55(23): doi: / /55/23/S13.
10. Loh J, Baker K, Sridharan S, et al. Infections after fiducial marker implantation for prostate radiotherapy: Are we underestimating the risks? Radiation Oncology ;10(38):1-5. doi: /s
11. Clavel S, Gauthier-Pare AS, Duplan D, et al. Infections after fiducial markers implantation for prostate radiation therapy: Optimizing the antimicrobial prophylaxis. International Journal of Radiation Oncology*Biology*Physics ;96(2):E272. doi: /j.ijrobp