Prostate brachytherapy is a very effective radiation-based treatment for localised prostate cancer. The aim is to deliver a high therapeutic dose of radiation to the prostate while minimising radiation exposure to the surrounding organs and thus limiting toxicity. Modern imaging techniques allow precise targeting of the prostate tissue and limit exposure to normal tissue. Prostate brachytherapy delivers the radiation dose directly into the target tissue without traversing skin and other structures, unlike external beam radiotherapy (EBRT). This targeted access is achieved by a template and image-guided approach delivered percutaneously through the perineum (Fig. 10.1).

There are two types of brachytherapy: low dose-rate (LDR) and high dose-rate (HDR). LDR brachytherapy (LDR-BT) involves the permanent implantation of radioactive seeds through rigid needles into the prostate. The seeds release radiation over time at a rate < 2 Gy/h¹. HDR brachytherapy (HDR-BT) delivers radiation by means of a radioactive source passing through catheters temporarily inserted into the prostate at a rate of ≥12 Gy/h [1].

Initially LDR-BT brachytherapy was delivered through an open suprapubic approach . Modern prostate brachytherapy was developed in Seattle in the 1980s when transrectal ultrasound (TRUS) probes enabled better visualisation of the prostate, improving the accuracy of the treatment and delivery of radiation by means of template-guided perineal access; the “Seattle” technique required two stages often performed under spinal or general anaesthetic [2]. The first stage involved a planning TRUS of the prostate from which the number of seeds was calculated and the seeds ordered from the manufacturer. The second stage, typically several weeks later, involved the implantation of the seeds into the prostate using the co-ordinates previously calculated. One of the limitations of this treatment was the need for two separate stages, as on occasions the prostate shape or volume could change, especially if the patient had high-risk cancer and was also being treated by hormone therapy or EBRT. The original technique did not allow for the dose to be monitored and optimised during the procedure, known as real-time planning. There have been a number of technical approaches and modifications of LDR-BT over the years seeking to improve clinical outcomes, dose delivery and distribution, convenience and optimisation of resources [3, 4]. The clinical team normally includes a radiation oncologist, a urologist and a radiation physicist.

The first remotely controlled afterloaders to deliver HDR-BT were developed in the 1960s. The use of these machines eliminated staff exposure to high activity radionuclides and made possible the use of sources such as Iridium-192 (192Ir). The radioprotection and regulatory infrastructure required for HDR-BT is considerable compared to that of LDR-BT.

LDR-BT involves permanent implantation of small titanium seeds (4.5 mm long × 0.8 mm diameter) containing the radionuclide Iodine-125 (125I), Palladium-103 (103Pd) or Cesium-131 (131Cs). The half-life of 125I, the most commonly used isotope, is approximately 60 days. Usually between 60 and 100 iodine seeds are implanted to cover the prostate with a prescription dose of 145 Gy for monotherapy and 110 Gy when combined with EBRT. The majority of the biologically effective radiation from isotope decay is released in the first 3 months, although the effect on the prostate tissue and thereby the PSA response, occurs over a number of years. Seeds for implantation are available as either loose seeds or seeds embedded in bio-absorbable stranding material. The loose seeds enable more flexible positioning, but have a higher risk of migration both within and away from the gland. Stranded seeds are prevented from migration by the stranding material for the first weeks post-implant and then by a prostate tissue capsule [5, 6]. Stranded seeds also enable extension of the dose outside the prostate capsule in order to encompass extraprostatic extension [7].

The dosimetry planning and dose delivery is evaluated according to several parameters, most importantly the V100 (percentage of the prostate volume receiving 100% of the prescribed dose) and D90 (radiation dose, in Gy, received by 90% of the prostate). The dose received by both urethra and rectum is also analysed to minimise toxicity. Post-implant dosimetry values have been correlated to long-term clinical outcomes, which is a unique feature of LDR-BT [8, 9].

The most recent technique, 4D Brachytherapy , allows the procedure to be performed in a single real-time planning procedure that lasts about 45 min. This approach requires a prior outpatient clinic-based TRUS to assess five key measurements of the prostate, which are used to calculate the number of seeds required for that specific patient using a web-based nomogram. The technique uses a combination of stranded seeds implanted around the periphery of the prostate (thus avoiding migration) followed by loose seeds implanted in the centre of the gland; as the seeds are implanted the treatment planning computer programme updates the dosimetry in real time to optimise dose coverage [10]. To evaluate the dose delivered and implant quality, patients have a post-implant CT scan immediately after the procedure. The procedure is usually performed as a day case, recovery time is short and normal activities resumed within a few days in most cases.

Post-brachytherapy follow-up involves serial PSA measurements. The downward trend of PSA values is gradual and may take between 1 and 5 years before PSA reaches its lowest level, called the PSA nadir. A biochemical recurrence of cancer is usually defined as a rise in PSA that greater than 2 ng/ml above the nadir.

After LDR-BT approximately 20% of patients experience a PSA bounce. This is a transient increase in PSA typically 1.5–2 years after the implant. The exact cause of this phenomenon is unknown, but it seems to be more common in larger glands and younger patients. Awareness of this phenomenon is important as it can be confounded with biochemical recurrence and therefore patients should be monitored closely, but mainly reassured.

Rising PSA values should trigger investigations such as template biopsy, multiparametric MRI or a PET-CT scan, to ascertain whether there is a local or distant recurrence.

In the immediate post-operative period, patients should be aware of the most common side effects of BT due to prostate oedema and subsequently, radiation effects which may develop from 2 to 6 weeks after implantation:

More rarely seeds may migrate into the bladder, which need to be removed by cystoscopy. Loose seeds can migrate into blood vessels and usually to the lung. For this reason the use of stranded seeds in the periphery of the prostate is commonly preferred [11].

EBRT is known to cause a small increase in the risk of secondary malignancies typically after 10 years of treatment. In prostate EBRT there is increased risk of bladder and rectal cancer by 1.9- and 2.2-fold, respectively, although the overall risk is still low. No consistent finding of an increased cancer risk has been identified in patients treated with LDR-BT, presumably due to better targeting of the radiation and relative sparing of the adjacent tissues [12].