Essential Radiotherapy Techniques – Superficial and Orthovoltage
What are superficial and orthovoltage treatments?
Superficial (SXT) and Orthovoltage (DXT) radiotherapy utilise low energy ionizing radiation to treat cancer and other conditions that occur either on or close to the skin surface. SXT utilises x-ray energies of between 50 and 200 kV, having a treatment range of up to 5mm, and DXT utilises 200 to 500 kV x-rays penetrating to a useful depth of 4 – 6cm.
The shallow penetrating power of both SXT and DXT means that they are often superior to megavoltage external beam radiation for the treatment of superficial lesions. Orthovoltage and superficial treatment machines are becoming less common, with much of the treatment that was previously delivered with them now being delivered using linear accelerators.
Conditions treated with superficial and orthovoltage radiotherapy
Superficial and orthovoltage radiotherapy are used for the treatment of skin lesions such as melanoma, squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) as well as non-malignant skin conditions such as keloids. Relatively high absorption of these low energy x-rays in bone also means that orthovoltage treatment is well suited to the palliative treatment of painful bony metastases in shallow regions such as the ribs and sternum.
These above mentioned conditions are those commonly treated with these techniques but do not constitute an exhaustive list.
Superficial and orthovoltage services across Australia 14
Superficial and orthovoltage radiotherapy are offered in 28 centres (55%) nationally. 86% of the relevant equipment is located in the public sector, while the remaining 14% is located at privately owned facilities. Northern Territory is the only jurisdiction which does not offer Superficial and orthovoltage radiotherapy.
SXT and DXT equipment distribution
| State | Percentage of total machines |
|---|---|
| ACT | 4% |
| NSW | 46% |
| QLD | 14% |
| SA | 7% |
| TAS | 4% |
| VIC | 21% |
| WA | 4% |
| NT | 0% |
Trends and issues arising
Superficial and orthovoltage radiotherapy will remain a useful technique for treating skin cancer and a number of other conditions. It is likely that the caseload for these treatments will increase due to the ageing population and the consequent rise in the incidence of cancer. However, this trend may be offset by:
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Impact of the prevention campaigns (such as ‘sun-smart’ strategies);
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Better management prior to the condition turning into a malignancy;
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More effective management of early skin cancer;
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Use of alternative methods of treatment (such as Moh’s surgery and laser surgery or ablation).
Equipment availability
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It is anticipated that superficial treatments will move solely to the domain of radiotherapy departments as anecdotal evidence suggests this equipment is being phased out in the private dermatology practices.
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Some radiotherapy departments and centres will choose not to install superficial and orthovoltage machine units. This is because most of the applications can also be delivered by appropriately configured linear accelerators.
There still are some specific clinical situations where the unique characteristics and physical properties of superficial radiotherapy remain compelling, one example being treatments around the eye, such as skin cancers on the eye.