The treatment of patients using superficial and orthovoltage radiotherapy is quite different to that of megavoltage or isocentric treatment techniques. For superficial and orthovoltage treatments the emphasis is on making the patient as comfortable as possible, ensuring their stability, if this means the patient has to be treated sitting rather than lying on the treatment couch this can be easily achieved.

Superficial and orthovoltage equipment are specifically designed to allow a full range of movement over several different planes making it ideally suited to the variety of tehniques used to treat benign and malignant conditions [1].  Compared with an  isocentric  treatment there are no predefined gantry or collimator angles, treatment accuracy  is purely down to the expertise and skill of the radiographer to accurately fit the machine to the patient, as is demonstrated in the Gulmay Treatment Video.

Due to the nature of the treatment techniques, immobilisation for superficial and orthovoltage therapy differs somewhat from that used with isocentric equipment treatments. The treatment couch is an independent couch, fully moveable with an adjustable height and backrest, allowing the patient to comfortably sit up. It has a soft top to further aid patient comfort and can have the addition of cot sides if required.

Patients are treated in whatever position they find most comfortable, utelising pillows and additional supports and if necessary can be treated in their own wheelchair or on a trolley. For treatments of facial lesions either a vacubag or sandbags can be used to support the patients head and ensure immobility. For all treatments further pillows and foam wedges are commonly used whenever needed to allow the patient to maintain a comfortable position [2].

The beam arrangement employed for the treatment of patients using superficial and orthovoltage therapy is known as skin apposition; where the end of the applicator is angled so that it is parallel to the surface of the treatment volume.  Contact should be established between the entire periphery of the applicator and the surface of the patient, therefore accurately establishing the required Focal Skin Distance (FSD).

Due to the short FSD's used for superficial and orthovoltage treatments, even small variations in distance between the end of the applicator and the patient’s skin will have an important effect on the dose delivered to the patient.  It should be noted that:

• Where the surface of the treatment volume is convex, the surface of the target volume may protrude into the lumen of the applicator:  this phenomenon is known as ‘stand-in’.
• Where the surface of the treatment volume is concave, the surface of the target volume may be at some distance from the face of the applicator:  this phenomenon is known as ‘stand-off’.

In both cases, it is necessary to apply a factor to the standard dose charts to take into account the effect of the inverse-square-law on the dose rate, as follows: 

Stand-in will act to increase the dose rate at the surface of the treatment volume [3]:

Stand-off will act to decrease the dose rate at the surface of the treatment volume:

Beam definition on superficial and orthovoltage machines is achieved using solid walled applicators, these are available in a range of square, rectangular and circular sizes and FSD's, allowing the flexibility to treat a wide range of conditions. However, on occasion it may be necessary to further define the treatment field from the size of the applicator chosen. Such incidences may include situations where a field size is required within the predefined applicator size, or the shape of the field is irregular, in such cases a lead cut out is used [2].

A sheet of lead of varying millimetre thickness, depending on the energy range, is used to define the shape and size of the field. The lead cut out is placed on the patient’s skin (secured with medical tape) and the treatment is set up as normal using an applicator to achieve apposition with the cut out.

Lead cut outs are used not only to define the shape of the beam but also to protect the surrounding normal tissue from exposure to X-rays.

Depending on the treatment area further shielding to protect normal tissues may be required. For treatment in close proximity to the eye an external eye shield may be required. This is an oval shaped piece of lead which is placed over the patients closed eye to protect the lens from unecessary irradiation.

If the eyelid itself is being treated it is necessary to use an internal or contact eye shield to protect the eye. This is an oval shaped, concaved gold eye shield with a protective lead lining. The eye shield is placed in the patients eye, like a contact lens, between the cornea and the eyelid. The procedure is carried out following the use of local anaesthetic to the eye, which stops the blink reflex, allowing insertion of the eye shield. It is important that patients are cared for properly following this procedure and a protective eye patch is used until the blink reflex returns [1].     

In situations where treatment overlies a mucous membrane i.e. the nose or mouth, a lead shield is used to protect the membrane, as the mucosa are very sensitive to radiation and treatment reactions can be severe and painful. For treatment overlying the nostrils a small piece of lead should be inserted into the nostril to protect the mucosa and nasal septum within the treatment area [4]. Towards the end of treatment the inside of the nose will become very sore so care should be taken when inserting and removing the lead shield, if necessary lubricants can be used to assist this proceedure. Similarly, when treating areas near the lips, it is advisable to insert a lead shield into the patient’s mouth between the lips and teeth to protect the teeth and gums. 

In cases where the patient is young a lead apron should be used to cover their torso to protect them from any scattered radiation arising from the exposure.

In some cases the tumour will form a thick scab. In these cases it is important to debulk the tumour and remove the scab as this acts as a layer of build up, absorbing the photons and therefore preventing the higher energy X-rays from reaching the tumour [1].  It is important however that the patient is advised not to interfere with the lesion and any debulking is done by the radiographer. This should be done carefully using aseptic techniques i.e. by thoroughly cleaning the area first and using gloves and sterile tweezers to gently pry away pieces of the scab. It is quite common during this debulking that the lesion will bleed; following treatment it can be dressed and cared for according to the advice in the patient care section. 

Throughout treatment patients are monitored via closed circuit television. It is important to observe the patient closely as any movement may compromise the treatment. Generally a CCTV system is employed using two independent cameras. One is focused on the patient whilst the other is focused on the end of the applicator. Due to the nature of low energy X-rays and their short penetrative distance it is essential that the end of the applicator is kept in contact with the patient. If there is any movement, or the patient pulls away from the applicator it is necessary to interrupt the treatment and re-enter the room to reposition the patient.

The control panel of the machine allows the operator to select all relevant treatment parameters such as the correct filter and applicator and the required beam on time or monitor units as in dose based systems. During treatment the unit control panel will display:

• The actual tube voltage and current                       
• Treatment Exposures: 
  • The set and administered values are displayed either in time or dose (monitor units) dependent on the system
  • Backup timer  
• Designated Field size
  • Applicator selection interlock (where specified)
• Filter selection interlock
  • This defines the filter and exposure parameters such as the tube kV, mA and the HVL

Gulmay Medical Control Screen

It is also possible to attach a record and verify system to the unit which allows a patient prescription to be input and all associated treatment parameters for each delivered exposure to be recorded. It also acts as a verification system providing interlocks between the system and the selected filters and applicators, preventing the X-rays being switched on until all recorded parameters are correct.

Gulmay Medical Record and Verify Screen