Radiation therapy in prostate cancer – techniques and ‘spacers’

This content is part of a paid partnership with GenesisCare.

By age 85, one in six men will have developed prostate cancer. Techniques in radiation therapy have significantly advanced in recent years and, ideally as part of a multidisciplinary decision, provide a treatment option in a variety of settings:

Adjuvant radiation therapy (ART) is given following radical prostatectomy to patients with high risk features such as positive surgical margins, seminal vesicle invasion, extraprostatic extension and higher Gleason scores. A 2019 Finnish trial concluded that adjuvant radiotherapy following radical prostatectomy is generally well-tolerated and prolongs biochemical recurrence-free survival compared with radical prostatectomy alone in patients with positive margins or extracapsular extension.

Salvage radiation therapy (SRT) is the administration of RT in a patient with PSA recurrence (detectable PSA level ≥ 0.2 ng/mL with a second confirmatory level ≥ 0.2 ng/mL) after surgery but no evidence of metastatic disease.  A predictive model in a large patient cohort showed that progression-free survival is best when SRT is administered at the earliest sign of recurrence (PSA <0.50 ng/mL).

Stereotactic body radiation therapy (SBRT) is an extremely precise and advanced radiation technique that can be used to treat both primary tumours or metastatic disease, particularly in the lung, bone, or liver.  This technique, now available in Perth, delivers high doses of radiation to the cancer in an ablative fashion over typically one to five treatments. In addition to SBRT being non-invasive, time efficient and cost-effective, there is a strong radiobiological rationale to support its use. Results from the available data indicate low rates of late adverse effects and excellent biochemical relapse-free survival outcomes.  It is expected that the use of SBRT in prostate cancer will increase.

Reducing treatment side effects with spacers: While the delivery of radiation therapy now has submillimetre accuracy, radiation oncologists are highly conscious of the need to avoid radiation exposure to healthy organs. In prostate cancer, the primary ‘organ at risk’ is the rectum. The seminal vesicles are also an area of concern. Radiation exposure to these organs can now be mitigated with the use of ‘prostate spacers’ which are inserted between the rectum and the prostate to create a stable space.  Insertion takes places under general anaesthesia, typically at the same time as the placement of fiducial markers used to ensure reproducible and accurate patient positioning.

First-generation prostate spacers use fast-polymerising polyethylene glycol which can harden in the syringe or needle if injected too slowly. While still very effective, the final shape and symmetry may be less predictable.  A second-generation spacer, Barrigel®, uses non-animal stabilised hyaluronic acid – the same product used as a cosmetic dermal filler.  The non-polymerising attribute provides the clinician with time to optimally sculpt the spacer to the patient’s anatomy. The product is also easily viewed on trans-rectal ultrasound due to its highly hypoechoic characteristics.

Urologists working in the field of prostate cancer are experienced in the placement of these relatively new spacing products which are helping radiation oncologists to reduce radiation exposure to otherwise healthy organs. 

Dr Sia is a radiation oncologist with GenesisCare.

– References are available upon request.

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