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Grenz ray therapy

Author: Vanessa Ngan, Staff Writer, 2005.

Table of contents

What are grenz rays?

Grenz rays are a form of radiation, similar to ultraviolet radiation, x-rays and gamma rays. The difference is that grenz rays are produced at low kilovoltages giving them a very low penetration power. Ninety per cent of the rays are absorbed within the first 5 mm of skin (and 50% in the first mm), which means they do not penetrate beneath the dermis of the skin. Grenz rays appear to reduce Langerhans cell numbers, hence producing an anti-inflammatory effect. It is said to “calm down” inflammation of the skin.

Grenz rays are also referred to as “border” rays and Bucky rays. They are classified as 'ultrasoft' or 'soft' radiation. They are difficult to calibrate.  They should not be confused with superficial radiation therapy which is used in the treatment of malignant skin cancers.

What is grenz ray therapy used for?

Grenz ray therapy is seldom used nowadays as more recent medical advances in the treatment of skin diseases have made radiation treatments less necessary. However, grenz ray therapy is occasionally very helpful for refractory conditions that fail to respond to the usual therapeutic modalities.

Grenz rays can be used in combination with other therapies in the treatment of many skin conditions including:

What does the grenz ray procedure involve?

Grenz ray therapy usually consists of 200 Roentgens, given weekly or twice weekly for a total of 800–1000 Roentgens (ie, over 3 or 4 sessions). If necessary, further treatment with grenz rays can be repeated at 4 to 6-month intervals.

The radiation dose is delivered from the tube of a grenz machine at a target skin distance of 10–15 cm. The dose depends on the treatment site.

What are the side effects and complications of grenz ray therapy?

Very few side effects are associated with grenz ray therapy. Doses over 200 Roentgens cause a mild sunburn reaction at the site. A persistent dark tan may linger for several months afterwards.

It is essential that proper radiation safety measures are followed when using grenz ray therapy. It has been found that grenz rays, given alone, are capable of causing nonmelanoma skin cancers in patients that are abnormally sensitive to radiation exposure.

  • A few cases of basal cell carcinoma (BCC) and squamous cell carcinomaS (SCCs) have been described in association with grenz rays.
  • The risk of squamous cell carcinoma is estimated at 0.2 per 10,000 gr.



  • Grenz Rays — Dermatologic Disease Database, American Osteopathic College of Dermatology
  • Frentz G. Grenz ray-induced nonmelanoma skin cancer. J AM Acad Dermatol. 1989 Sep; 21 (3 Pt 1): 457–8. PubMed

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