Isoray - Innovative Brachytherapy
Cesium-131 - Proven, Personalized, Precise

Isoray’s proprietary isotope, Cesium-131, has over 10 years of proven patient outcomes for the treatment of prostate cancer. Cesium-131 offers patients a combination of quality of life preservation and the rapid resolution of side effects.

Learn how one little seed is redefining modern brachytherapy.


Cancer Treatment with Cesium-131 Brachytherapy Seeds by Isoray

Not all seed brachytherapy radioisotopes are the same. You and your doctor should choose the best isotope for your cancer treatment. Patients should ask their doctor about Cesium-131 by Isoray.

Higher Energy

Isoray’s proprietary isotope, Cesium-131, has a higher energy allowing for a more uniform dose distribution with less overdosing than other permanent isotopes. (1)

Shorter Half-Life

Isoray’s proprietary isotope, Cesium-131, has a shorter half-life than other commonly used isotopes for the treatment of cancer throughout the body, resulting in a shorter duration of radiation which contributes to a rapid resolution of patient side effects. (2)

Improved Coverage of the Prostate

Isoray’s Cesium-131 proprietary permanent prostate cancer brachytherapy seeds allow for better dose homogeneity and the sparing of the urethra and rectum while providing comparable prostate coverage compared to other seeds with comparable or fewer seeds and needles. (3, 4, 5, 6)

Rapid Resolution of Side effects

With higher energy and a shorter half-life than competitors, Cesium-131 is proven to be a highly customized and effective treatment for the rapid recovery of patients in the fight against prostate cancer. (7, 8, 9, 10)

Higher Biologically Effective Dose

Isoray’s Cesium-131 also delivers a higher “biological effective dose” or BED compared to I-125 or Pd-103 across a wide range of tumor types. (11)

PSA Control

Isoray along with investigators tracking PSA in both single arm and randomized prostate cancer treatment trials have concluded that Cesium-131’s PSA response rates have similar early tumor control to I-125, which was previously considered the gold standard in permanent seed brachytherapy. (8, 12, 13)

Your Isotope Choice Makes a Difference


Introduced in 1986
  • 17 Day Half Life (18)

  • 20.8 Kev

  • 58 Days for 90% Dose

  • Detectable in the body for 170 Days


Introduced in 1965
  • 60 Day Half Life (18)

  • 28.5 Kev

  • 204 Days for 90% Dose

  • Detectable in the body for 600 Days


Patients & Families

Find a Doctor Near You

A diagnosis is just the first step toward treating your cancer. We are here to help you make an informed treatment decision with your doctor so you can begin living your life again. 


1. Prestidge B.R., Bice W.S., Jurkovic I., et al. Cesium-131 Permanent Prostate Brachytherapy: An Initial Report. Int. J. Radiation Oncology Biol. Phys. 2005: 63 (1) 5336-5337.

2. Neill B, et al. The Nature and Extent of Urinary Morbidity in Relation to Prostate Brachytherapy Urethral Dosimetry. Brachytherapy 2007:6(3)173-9.

3. Musmacher JS, et al. Dosimetric Comparison of Cesium-131 and Palladium-103 for Permanent Prostate Brachytherapy. Int. J. Radiation Oncology Biol. Phys. 2007:69(3)S730-1.

4. Yaparpalvi R, et al. Is Cs-131 or I-125 or Pd-103 the “Ideal” Isotope for Prostate Boost Brachytherapy? A Dosimetric View Point. Int. J. Radiation Oncology Biol. Phys. 2007:69(3)S677-8.

5. Sutlief S, et al. Cs-131 Prostate Brachytherapy and Treatment Plan Parameters. Medical Physics 2007:34(6)2431.

6. Yang R, et al. Dosimetric Comparison of Permanent Prostate Brachytherapy Plans Utilizing Cs-131, I-125 and Pd-103 Seeds. Medical Physics 2008:35(6)2734.

7. Prestidge B, et. al. Clinical Outcomes of a Phase-II, Multi-institutional Cesium-131 Permanent Prostate Brachytherapy Trial. Brachytherapy. 2007: 6 (2)78.

8. Moran B, et al. Cesium-131 Prostate Brachytherapy: An Early Experience. Brachytherapy 2007:6(2)80.

9. Jones A, et al. IPSS Trends for Cs-131 Permanent Prostate Brachytherapy. Brachytherapy 2008:7(2)194.

10. DeFoe SG, et al. Is There Decreased Duration of Acute Urinary and Bowel Symptoms after Prostate Brachytherapy with Cesium 131 Radioisotope? Int. J. Radiation Oncology Biol. Phys. 2008:72(S1)S317.

11. Armpilia CI, Dale RG, Coles IP et al. The Determination of Radiobiologically Optimized Half-lives for Radionuclides Used in Permanent Brachytherapy Implants. Int. J. Radiation Oncology Biol. Phys. 2003; 55 (2): 378-385.

12. Bice W, et. al. Recommendations for permanent prostate brachytherapy with 131Cs: a consensus report from the Cesium Advisory Group. Brachytherapy 2008:7(4)290-296.

13. Platta CS, et al. Early Outcomes of Prostate Seed Implants with 131Cs: Toxicity and Initial PSA Dynamics from a Single Institution. Int. J. Radiation Oncology Biol. Phys. 2008:72(S1)S323-4.

14. Tomaszewski JJ, et al. Cesium 131 versus iodine 125 implants for prostate cancer: evaluation of early PSA response. The Canadian Journal of Urology. 2010;17(5): 5360-5364.

15. R.M. Benoit, R.P. Smith, S. Beriwal. Five Year Prostate-specific Antigen Outcomes after Caesium Prostate Brachytherapy. Clinical Oncology. 26 (2014) 776 780.

16. Brian J. Moran, MD, Michelle H. Braccioforte, MPH. Prostate Cancer Foundation of Chicago, Westmont, IL. PSA Outcomes in a Single Institution, Prospective Randomized 131Cs/125I Permanent Prostate Brachytherapy Trial Abstracts / Brachytherapy. 13 (2014) S15eS126.

17. Amit B. Shah, MD, Arnav A. Shah, Gregory A. Fortier, MD. Radiation Oncology, York Cancer Center, Wellspan Health, York, PA. A Comparison of AUA Symptom Scores following Permanent Low-Dose-Rate Prostate Brachytherapy with Iodine-125 and Cesium-131, Abstracts / Brachytherapy 12 (2013) S11eS77.

18. Herstein A, Wallner K, Merrick G, Mitsuyama H, Armstrong J, True L, Cavanagh W, Butler W. I-125 versus Pd-103 for low-risk prostate cancer: long-term morbidity outcomes from a prospective randomized multicenter controlled trial. Cancer J. 2005 Sep-Oct;11(5):385-9.