Seeds of iodine‐125 have replaced those of gold‐198, the half‐life of iodine‐125 being approximately 60 days. Some therapists believe that there is a radio‐biological advantage to this long half‐life in treating slow‐growing tumours such as carcinoma of the prostate (Blank et al. [6]). The iodine‐125 seeds are inserted into the tissue that is to be irradiated, for example the prostate gland, utilizing ultrasound guidance or an image intensifier control. The procedure requires the patient to have a general anaesthetic for the seeds to be inserted.

As the energy of the gamma‐ray emission from iodine‐125 is very low compared with that of gold‐198, large numbers of seeds are required. This means that more precautions must be taken in order to achieve a regular geometrical arrangement to ensure satisfactory distribution of the dose (Stock et al. [63]). Implantation of iodine‐125 is now a well‐established procedure and an increasing number of patients throughout the world are treated in this manner (Anglesio et al. [2], NICE [50]).

There are known complications from this form of treatment including incontinence, obstructive urinary symptoms, rectal symptoms and sexual dysfunction. The impotence rate has been reported at between 10% and 15%, much lower when compared with 45% of those patients undergoing radical prostatectomy (NICE [50]).

Zelefsky's ([81]) study found that quality of life was initially worse during the first 4 weeks following iodine‐125 treatment but returned to baseline values 1 year after the implants were inserted. It is therefore of great importance that the patient understands the uncertainties of iodine‐125 seed therapy and the possible alternative treatment options. The consent process should ensure that the patient is fully informed of:

It is also important that the patient understands that it is unclear how the procedure affects general health or the chance of the cancer returning in the long term (Wust et al. [80]). The patient should be followed up and monitored as per local clinical guidance (NICE [50]).

Iridium‐192 is a radioisotope which is used in the form of pins or wires in interstitial therapy (Fung [21]). The half‐life is 74.2 days and iridium is used because of the low energy of its gamma emission compared with caesium. This simplifies radiation protection issues. Iridium‐192 is available in the form of a platinum–iridium alloy thin flexible wire. The active platinum–iridium alloy core of the wire is encased in a sheath of platinum 10 µm thick, which screens out the beta radiation from the iridium‐192.

This high‐activity source of iridium is used in a high dose‐rate remote afterloading system, reducing the amount of radiation to which staff are exposed. Iridium‐192 is used under the following circumstances:

Iridium‐192 hair pin and single pin types of implants (see Figure 24.2) are usually used intraorally and are slotted into tissue using steel guides to obtain accurate alignment. Radiological examination is used to check the position of the guides before the iridium is inserted and the pins are held in place by sutures. Physicists are normally responsible for calculating how long a radioactive implant is to stay in place, usually about 6 days depending on the size of the tumour. Removal is carried out in theatre by appropriately trained clinical staff. Iridium‐192 wires are usually used for head and neck, breast, vulval or perineal lesions (see Figure 24.3). Polythene or metal cannulas are inserted under a general anaesthetic, and in the case of breast lesions, both ends of each tube protrude through the skin. Correct alignment is established often with the aid of a Perspex template which fits over the breast and holds the metal cannulas in the correct alignment or, in the case of vulval or perineal insertions, one end of the tube protrudes. For alignment of the sources to be achieved, a Perspex template and vaginal obturator are used.

Iridium‐192 interstitial brachytherapy can be used to treat locally advanced or recurrent tumours. Interstitial brachytherapy is a suitable alternative to standard intracavity brachytherapy where the treatment may be considered unsuitable because the dose distribution may be suboptimal (Agrawal et al. [1]).

The device itself consists of two acrylic cylinders and an acrylic template with an array of holes that serve as guides for trocars and a cover plate (Figure 24.4). The cylinders are usually placed in the vagina but can also be used in the rectum for rectal tumours. They are then fastened to the template, so that a fixed geometric relationship between the tumour volume and normal structures, that is bladder and rectum, is produced. This ensures that the source placement is preserved throughout the course of the implantation. The iridium wire is then manually afterloaded and held in place with a crimped washer to prevent movement of the source during treatment (see Figure 24.3).

The tiny size of the high‐activity iridium‐192 source in high dose‐rate machines may allow some interstitial brachytherapy to be given as a few treatments of several minutes each, in contrast to the single treatment of many hours’ duration that is necessary with low‐activity iridium wire (Hart [25]).

Clinical oncologists are responsible for calculating how long a radioactive implant should stay in place, usually 3–6 days depending on the size of the tumour. Removal of these implants is usually carried out in the ward area. The procedures deliver a dose that is higher than can be achieved by external beam radiation alone, improving organ preservation rates and reducing acute and late side‐effects (Karakoyun‐Celik et al. [38]).

In a study by Budrukkar et al. ([10]) evaluating the long‐term efficacy and safety of transperineal interstitial implants for advanced pelvic malignancy, it was found that treatment offered a 5‐ and 10‐year disease‐free survival of 48% for patients aged 45 years and less, and an 80% disease‐free survival in patients aged over 45 years.

Nursing care is similar to the care that patients receive for intracavity brachytherapy, with side‐effects similar to those seen in ‘afterloading’ techniques. According to Syed et al. ([64]) these side‐effects are considered to be acceptable. Late effects of this type of treatment, specifically fistula formation and bowel complications that may require surgery, have been documented (Nag et al. [49]).

Caesium‐137 is a radioisotope that can be used in the form of interstitial implants or in intracavity applicators, allowing a highly conformal dose of radioactivity to be delivered directly to the site of the cancer (Karakoyun‐Celik et al. [38]). The most common malignancies treated by the use of radioactive applicators are tumours of the female genital tract (Kucera et al. [39]). Intracavity applicators are used to deliver a high dose to the region of the cervix, the paracervical tissue, the upper part of the vagina and the uterine body. Caesium has a half‐life of 30 years and has largely replaced radium as a source for various brachytherapy treatments.

Oral implants of caesium‐137 are ‘needle‐like’ implants that are inserted directly into the tissue surrounding the tumour. They are a fairly common treatment for early lesions of the cheek, lip and anterior two‐thirds of the tongue (Leborgne et al. [45], Nutting et al. [53]). Oral implants have the advantage of allowing preservation of the structure and function of the tongue whilst avoiding the toxicity of external beam radiotherapy to the oral mucosa (Wadsley et al. [74]). If there is known or suspected bone involvement, in the mandible for example, the alternative external beam treatment will be given.

Caesium‐137 sources (see Figure 24.5) are inserted in theatre under a general anaesthetic and placed individually in a predetermined pattern so that the implant covers the whole growth with a safety margin of at least 1 cm. Each individual needle is positioned by pushers so that its eye, through which silk is threaded, is just visible beneath the mucosal surface. Each silk is then stitched to the tongue with a single suture, and when all the needles have been inserted the silks are counted and gathered together. They are then threaded through a piece of rubber to prevent friction and trauma to the mouth. The silks are then strapped to the cheek to prevent any needle being swallowed should it work loose. Small beads are attached to the ends of the threads to facilitate counting the needles. X‐rays are always taken to check the positions of the needles and to enable estimation of the dose distribution (Takacsi‐Nagy et al. [65]).