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Radiation therapy of prostate cancer

Prostate cancer is not especially sensitive to radiation. It is therefore problematic to obtain an optimal radiation dose due to side effects. Modern radiation therapy has, however, made it possible to drastically increase the radiation dose toward the prostate itself.

Radiation therapy with a curative goal can be given as:

  • Radical conformal external radiation therapy
  • Brachytherapy
  • Brachytherapy combined with conformal external radiation therapy

Radiation therapy can be an appropriate alternative to surgery in localised disease (T ≤ 2). Radiation therapy with a curative aim can also be appropriate, possibly combined with hormone treatment, in T3-disease.

External radiation therapy

External radiation therapy with a curative goal is given over 5-9 weeks, with 5 treatments a week. The treatment can  be given in a true out-patient setting, or with hotel accommodations, depending on travel time and the patients general condition/wishes.

It can also be appropriate to give external radiation therapy after a radical prostatectomy (adjuvant), for local relapse after radical prostatectomy or cryotherapy (salvage), and to reduce pain and tumor size (palliative).

Procedures

  • Primary external radiation therapy
  • Adjuvant external radiation therapy
  • Palliative external radiation therapy

Brachytherapy

For brachytherapy the radiation source is implanted within the target organ/tumor and delivers radiation of  a high dose, but short penetration. This permits a high radiation dose to the tumor and limits radiation damage to neighboring organs.

Brachytherapy in prostate cancer can be given in two ways. Both ways the radiation source is inserted into the gland transperineally, guided by transrectal ultrasound (TRUS).

In the first method, radioactive “seeds” are implanted permanently into the prostate. These radioactive sources provide a low radiation dose over a prolonged period of time (“low dose-rate”). The other method, the so-called “after loading-technique” is used in which the radiation dose is inserted in the prostate by means of hollow needles. The radiation is completed after a few minutes and the radiation source is removed (“high dose-rate”). 

Twenty years ago, at RR HF, a study was completed with “seed” implantation. The hospital now has a treatment option with “after loading” brachytherapy combined with external radiation therapy. This is performed with a curative aim on patients with high risk disease.

Radiation therapy combined with hormone treatment

Hormone treatment is often completed 3-6 months before radiation therapy to reduce the tumor size. A smaller target volume provides less toxicity and a possibility for dose-escalation. Studies also show that hormone treatment before and after radiation therapy increases the cancer cells’ radiation sensitivity and shows improved survival for some groups of patients.

Possible treatment of relapse after radical prostatectomy

For PSA-increase after radical prostatectomy (PSA measured in serum), local relapse or metastasis should be assessed. If no metastases are proven and with unfavorable histology (pT3 or non-free surgical margins) external salvage radiation treatment toward the “prostate bed” may be considered. The treatment is not more mutilating to the patient than primary radiation therapy. It can be discussed whether histological verification of recurrence is necessary, but the effect seems to be stronger when radiation treatment is given at a low PSA-level. It appears also to be a connection between dose and response, but it has not been shown that a total dose above 70 Gy provides additional response. When there is clinical suspicion of local recurrence (palpable at ultrasound or MRI) this should be verified by biopsy.

Local relapse after primary radiation treatment

In patients who have undergone curative radiation therapy, PSA-serum will fall to nadir value during the course of 6 to 12 months. Nadir value should fall < 1 ng/ml. If there is a rise in serum PSA of over 2ng/ml above the lowest PSA level, the disease is perceived as active (PSA-relapse). When cancer can still be proven by biopsy of the local tumor, surgery with curative intent may be concidered. With current techniques one can not repeat radiation therapy with curative intent.

The treatment methods under discussion are:

  • Salvage radical prostatectomy. This can be completed but the side effect rate is clearly higher than after primary radical prostatectomy. The curation rate is unknown.
  • Salvage cryoablation. Can be completed but the side effect rate is clearly higher than for primary cryoablation. The curation rate is unknown.

Curative treatment options in patients with local recurrance after primary radiation therapy are so uncertain, and the side effects are so serious, that treatment should only be performed in a protocol setting.

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