Previous section | Next section

Evidence‐based approaches

Methods of application

Intracavity applicators and interstitial implants

The application of sources varies according to the source and delivery method. Small sealed sources inserted into the body may take the form of:
  • intracavity applicators, where sources are placed in natural cavities and usually held in place by packing
  • interstitial implants, where sources are inserted directly into the tumour‐bearing tissue (Hoskin and Coyle [28]).
Intracavity applicators and interstitial implants can be used in three forms.
  1. The source is preloaded in the applicator before it is placed in the patient for a fixed length of time, for example caesium‐137 needles and iridium‐192 hair pins.
  2. Permanent insertion in the case of iodine‐125 seeds which, once inserted, would be difficult to remove. The available data show that, except in the case where the patient's partner is pregnant at the time of implantation, no restrictions are required once the patient is discharged home. Written information must be given to the patient on discharge which must include the following.
    • Possibility of triggering certain types of security radiation monitors.
    • Altered fertility, which is dependent on diagnosis, previous treatment, age, and type of brachytherapy offered.
    • The implant should be discussed if surgery is a possibility in the future.
    • Specific instruction should be available if the patient dies and cremation is required (ICRP [33]).
    • During hospital stay, all urine must be checked to ensure no seed has become dislodged; if this occurs, the loose seed should be placed in a lead pot with long‐handled forceps. Any seed in a catheter bag should also be saved and placed into a lead pot and collected by the Hospital Radiation Protection Service, which is generally the medical physics department.
  3. Afterloading systems. The applicator is placed in position and the radioactive source is inserted when the position of the applicator and the condition of the patient are satisfactory. Insertion of the sealed source can be undertaken manually in the case of iridium‐192 wires or by remote control in the case of the low dose‐rate ‘Selectron’ and high dose‐rate ‘micro‐Selectron’ machines, which are mainly used in the gynaecological setting. The proportions of radioisotope, initially radium and latterly caesium‐137, within the intrauterine tube and the vaginal ovoids (oval intracavity applicators inserted into the vagina) are calculated to give a constant dose rate to a geometrical point A when using different lengths of intrauterine tube and different sizes of vaginal ovoids.

Types of gynaecological brachytherapy applicators

Manchester applicator

Manchester applicators (Figure 24.6a) in their original form were live sources enclosed in intrauterine tubes of varying lengths and vaginal applicators (ovoids) of varying sizes. The applicators were inserted under general anaesthetic and held in place by a gauze pack and were modified for either manual or remote afterloading for low or high dose rates with the principle of the three‐applicator system remaining. Removal of the applicators and live sources is carried out on the ward.
image
Expand Download
Figure 24.6  Gynaecological caesium applicators. Arrangement of brachytherapy sources in the uterus and vagina for treatment of cervical carcinoma. Sources may be active or, more usually these days, afterloaded into applicators along catheters protruding from the vagina. (a) Manchester applicator. (b) Modified Stockholm applicator. (c) Fletcher applicator. (d) Dobbie applicator. Source: Dougherty and Lister ([16]).

Stockholm applicator

This is used for carcinoma of the uterine body or cervix. Usually a uterine tube and two vaginal packets are inserted. Occasionally, if the vaginal vault is small, one packet is omitted or replaced by a vaginal tube. The radioactive material is held in place with a proflavine‐soaked gauze pack left in situ for approximately 22 hours. Tubes and packets have strings attached for removal and colour‐coded beads indicate which should be removed first (Bomford [8]).

Modified Stockholm applicator

This is used for carcinoma of the uterine body and cervix; it consists of a uterine tube and a square box which connect together by a point and a hole. The vagina is then packed with proflavine‐soaked gauze pack and the applicator is left in situ for approximately 20 hours; the box is removed first (Bomford [8]). See Figure 24.6b.

Fletcher applicator

This is used for carcinoma of the corpus or cervix, with the patient needing to have a fairly capacious vaginal vault. Hollow applicators, a uterine tube and two vaginal ovoids are inserted in theatre and afterloaded with the radioactive sources on the ward by the radiotherapist. The apparatus is held in place with a proflavine pack; long ends project through the vulva so that afterloading can be carried out. No strings are needed for this procedure, with insertions usually left in place for 60–72 hours (Bomford [8]). See Figure 24.6c.

Dobbie applicator

This is used for irradiation of the whole vagina. It is a Perspex cylindrical applicator with radioactive sources in the centre and is inserted into the vagina and sutured in place to the vulva. It can be used with low or high dose rate sources with strings attached to the applicator for removal (Bomford [8]). See Figure 24.6d.

Manual afterloading systems for treatment of gynaecological malignancies

The basis of ‘afterloading brachytherapy’ is that the applicators are placed within the cervix and vaginal fornices and the sources may then be inserted manually or by remote control. The radiation source is only introduced when the applicator's position has been checked as correct by specific imaging techniques and the patient is comfortable and is in a designated protected environment (Hoskin and Coyle [28]).
These rules ensure that the correct source has been inserted into the correct applicator for the programmed length of time. They also allow the dose rate of brachytherapy to be increased. Classically, the dose rate with the ‘Manchester system’ was approximately 50 cGy per hour to point A. With modern engineering methods, caesium‐137 pellets can be produced which will allow a dose rate of between 150 and 200 cGy per hour to point A. Many systems now use sources that allow a higher than standard dose rate to be delivered, with the added advantage of reducing treatment time for the patient (Kuipers et al. [40]).
Manual afterloading systems are now largely being replaced by remote systems, but are still used in a few hospitals where services are still developing. The plastic applicator tubes follow the pattern of the ‘Manchester system’ with an intrauterine tube and two vaginal ovoids. The plastic tubes are designed to be disposed of after a single use. The tubes are inserted under general anaesthetic. X‐rays are taken to confirm that the ‘inactive’ sources are in the correct position.
As with the classic ‘Manchester system’, there are varying lengths of intrauterine tube and sizes of ovoids. With X‐ray confirmation and dosimetry calculated, the radioactive caesium‐137 sources are introduced using long‐handled forceps; once in place, a silver metal cap is screwed over the end of the plastic tube to hold the sources securely. Manual afterloading does not permit the use of high‐activity sources for reasons of staff safety and treatment may last many hours or even several days. When treatment is complete, the caps are removed from the tubes and the sources are withdrawn and placed immediately in a lead storage vessel. The plastic applicator tubes are then removed.
It is particularly important to observe for displacement or extrusion of the applicator tubes over the long treatment times. It is customary to mark the thigh level with the end of the applicator tubes and to compare this alignment at regular intervals as the treatment progresses. The silver metal caps must be monitored regularly to assess for loosening or displacement (Bomford [8]).

Remote afterloading

Remote systems have the advantage of complete protection of staff but the disadvantage of high cost and the need for interlocking mechanisms (Bomford [8]).
Remote‐controlled afterloading machines transfer active sources from a radiation‐proof ‘safe’ to the patient only when all safety checks are completed (Hoskin and Coyle [28]). There are two types of delivery machine: one with a low dose rate (LDR), termed a Selectron, and a high dose rate (HDR) machine termed a micro‐Selectron. Both machines are used generally in the treatment of gynaecological cancers and in some cases may also be useful in the treatment of bronchial, oesophageal and other intraluminal carcinomas (Tessa et al. [68], Ung et al. [71]).

Low dose rate (LDR) Selectron unit

The Selectron unit comprises a lead‐shielded safe, containing caesium‐137 sources in the form of small spherical pellets, and a microprocessor, keyboard, display unit and printer (see Figure 24.7). Leading from the unit are either three or six flexible plastic transfer tubes corresponding to numbered treatment channels; each tube ends in a fragile plastic catheter which is inserted into the appropriately numbered applicator and secured by a coupling device. The unit has a supply of compressed air and it is air pressure that the system uses to transfer the sources from the safe within the unit to the applicators along the connecting tubes.
image
Expand Download
Figure 24.7  Selectron unit. Source: Dougherty and Lister ([16]).
Operation of the unit is initiated from a remote‐control unit situated outside the protected treatment area (Hoskin and Coyle [28]). The Selectron provides an accurate and safe method of radiotherapy treatment for cancers of the cervix, uterus and upper part of the vagina.
The advantages of the LDR Selectron system are as follows:
  • Remote afterloading eliminates contact with radioactive material and protects personnel. The unit is switched off each time someone enters the patient's room, and only once all staff leave the room will the unit be switched back on. The unit will automatically return the radioactive pellets into the applicators, and the treatment that was temporarily discontinued will be recommenced (Hart [25]).
  • It allows highly accurate dosimetry.
  • The activity of the caesium‐137 sources is such (up to 1.5 GBq) that treatment times for patients are considerably shorter than with conventional techniques.
Patients have hollow, lightweight stainless steel applicators positioned in the operating theatre under a general anaesthetic. These are usually modified Manchester or Fletcher type applicators consisting of a uterine tube and two vaginal ovoids held in place with proflavine‐soaked vaginal packing. A urinary catheter is inserted in theatre at the same time to reduce urinary retention and the risk of the sources becoming dislodged by the patient when micturating. Accurate positioning of the applicators is confirmed by taking X‐rays with dummy sources in situ and the optimum source configuration is selected, taking account of individual anatomical variations.
The Selectron unit is then programmed by the physicist. For each treatment channel being used, active source pellets are interspersed with inactive stainless steel spacer pellets to achieve the desired dose distribution (Hoskin and Coyle [28]). The treatment time required to reach the prescribed dose is also entered; with a six‐channel Selectron, it is possible to treat two patients with three applicators each simultaneously. The radiotherapist/clinical oncologist is responsible for connecting the transfer tubes to the applicators. The transfer tubes are led over a bed bracket which supports the weight of the tubes and prevents traction being applied to the applicators inside the patient. If the wrong catheter is connected to the applicator, the system will fail to operate.

Operating the Selectron

Treatment is commenced by activation of the remote‐control unit when all staff have left the treatment area. While treatment is in progress, it can be interrupted and restarted from the remote‐control unit by pressing the stop and start buttons. The display panel indicates which channels are being used for treatment and which are unused, with red and green lights respectively. The time of the longest treatment is displayed on the panel and a telephone intercom system allows for communication with the patient without the need to interrupt treatment (Hoskin and Coyle [28]).
Interrupting the treatment is done by pressing the green stop button, which results in the radioactive sources being withdrawn into the Selectron unit and stops the treatment timer. This then allows nursing staff to enter the treatment area in safety and give care to the patient. Pressing the red start button transfers the sources back into the applicators and restarts the treatment timer; the red lights demonstrate that the channels are operating again satisfactorily. The system has built‐in safety features so that in the event of a failure in the system, treatment stops automatically and an audible and visual alarm at the remote‐control unit is instigated. This alerts staff to a problem, indicating whether this is a fault related to the air or power supply, the sources or the timer.
In some hospitals, an optional nurse station display unit is installed with similar alarm indicators which emit audible signals when treatment has been interrupted. This helps to prevent treatment being inadvertently interrupted for long periods. The Selectron records all breaks in treatment and these are shown on the print‐out from the unit itself together with any programming or system fault. These appear as an error code and can be identified by reference to the Selectron user's manual.
At the end of the treatment time, all sources will be withdrawn automatically from the applicators back into the Selectron unit. If two patients are being treated simultaneously, termination of the treatment of one patient may be some time before that of the other. This means the timer will register the longer treatment time, but the indicator lights for the channels used for the first patient will have changed from red to green.
Additional safety features include a door switch facility to retract sources immediately if the door to the treatment area is opened when treatment is in progress, and/or Geiger dose meters visible when entering the treatment area and approaching the patient, which indicate when there are radioactive sources either in the patient or in the connecting tubes.

High dose rate (HDR) micro‐Selectron unit

The operating principles of the HDR micro‐Selectron are similar to those of the LDR Selectron. LDR Selectron applicators are afterloaded with active sources interspersed with inactive spacers to produce the correct isodose pattern. HDR micro‐Selectron machines, on the other hand, achieve the desired isodose pattern with a single iridium‐192 source that moves within the applicators and stops at preset positions for pre‐determined dwell times.
The HDR micro‐Selectron delivers radiation at approximately 100 times the rate of the LDR Selectron and treatment times are therefore much shorter, with the added advantage of applicators with a smaller diameter which can be put in place under local anaesthetic in the outpatient department. This is a suitable alternative for patients who may not be able to tolerate the demands of LDR (Hoskin and Coyle [28]).
Once in position, the micro‐Selectron intracavity applicators are fixed to the treatment couch by means of an adjustable clamp; movement of the applicators is minimal and dosimetry calculations accurately represent actual treatment. In addition, more constant and reproducible geometry of source positioning is possible (Jones et al. [37]). Treatment protocols generally consist of two treatments but can involve as many as five. Following explanation and support for the patient, the procedure is carried out under local anaesthetic (Faithfull and Wells [17]); for the first treatment, a urinary catheter is passed and the balloon is inflated with dilute contrast medium. A check X‐ray is taken once the applicator tubes are in place to collect information which is fed into the Selectron planning computer to calculate the treatment time (Hoskin and Coyle [28]).
The HDR micro‐Selectron follows the same principles for programming and treatment as the LDR Selectron; when treatment is complete, the applicators and catheter are removed and the patient is free to go home after they have passed urine. A case report on patients undergoing treatment with the HDR micro‐Selectron for gynaecological cancer suggested that they found the experience to be acceptable (Tan et al. [66]).
Adequate preparation and information sharing about this treatment is essential, as time spent preparing the patient for brachytherapy treatment makes them better equipped to make informed decisions related to their care (Faithfull and Wells [17], Wallace et al. [75]). Poorly prepared patients are more anxious and less able to follow instructions and can be less tolerant of the implant procedure (Montgomery et al. [47]). An assessment of patients’ physical and emotional needs must be made prior to each treatment to identify whether any aspect of the treatment is problematic (Faithfull and Wells [17]).
The advantages of HDR micro‐Selectron brachytherapy are as follows.
  • Shorter treatment time reduces variations in the patient's position and allows more accurate dosimetry (Jones et al. [37]).
  • Treatment lasts only minutes, minimizing the need for immobilization; this reduces discomfort and the risk of complications associated with bedrest.
  • Treatment can be offered on an outpatient basis with a consequent reduction in cost.
  • It is an alternative to the LDR Selectron and may be more suitable for some patients.
  • Complication rates are comparable with low‐dose brachytherapy (Wong et al. [79]).
Previous section | Next section