100 years orthovoltage radiotherapy, a historical overview of X-ray machines.


29 October 2012, the radiation oncologists specialized in skin tumours pose with the new orthovoltage machine. From left to right: Olga Hamming-Vrieze, Arash Navran and Rick Haas. (Photograph: Patricia Fewer) 

The new X-ray unit is an Xstrahl, type 300, the tube voltage can be set between 40 kV and 300 kV. The unit is manufactured by Xstrahl from Camberley, UK.   

Superficial tumours and skin tumours can be treated with X-rays and electron beams. For electron beam treatment a large linear accelerator is needed with an accelerating potential of at least 6 million Volts . The Netherlands Cancer Institute (NKI) chooses to use a simple orthovoltage machine with a tube voltage between 40 and 300 thousand Volts. In 2012 the Radiotherapy Department commissions a new orthovoltage machine after the old one broke down a year before. After a year of absence the NKI has again its own X-ray machine available that can be used to irradiate thin superficial skin tumours, but also larger and thicker abnormalities, effectively. This orthovoltage machine is very patient friendly.

"That is because of its flexible construction which allows the patient to be irradiated lying in bed or even sitting in a wheel chair" the radiation oncologist Rick Haas tells us. "We have deliberately chosen to purchase various beam energies. So we can adequately treat various skin tumours such as basal cell carcinoma, squamous cell carcinoma, Karposi sarcoma and melanocytic defects such as Dubreuilh disease.  Now, after a year of referral, the NKI can again offer this treatment …." 

Overview of orthovoltage equipment in the NKI since 1915

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1915. The first X-ray machine in the NKI at Keizersgracht 706 in central Amsterdam. The manufacturer is Reiniger, Gebbert & Schall. The tube voltage is between 80 and 100 kV, at a tube current of 3 mA.

When the NKI started in 1915, modern radiotherapy consisted of radium applications and X-ray irradiation with a tube voltage between 80 and 100 kV. The relatively shallow penetration of this radiation makes it less suitable for treating deeper seated tumours, but the available technology was limited to these sources of radiation. With beam hardening filters, intraoperative irradiation and crossfire irradiation (irradiation aimed from different angles at the same area), the radiologist tried to make radiotherapy of deeper seated tumours somewhat effective. 

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1929. Three X-ray machines, each with a tube voltage up to about 200 kV in the treatment room of the NKI-AVL in the Sarphatistraat

Around 1920 a tube voltage of 200 kV becomes possible. By the end of the 1920s the Philips-Müller company introduces a ceiling suspension for X-ray tubes which is installed here for the middle machine.

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1940, a modern Philips orthovoltage machine has been installed. It is equipped with safe shielded high-voltage cables.  Dr. Daniel den Hoed performs an irradiation in the head and neck region.

The name Orthovoltage explained: The term orthovoltage is still used for X-ray machines with hard radiation at voltages from about 200 to 300 kV maximum. These higher voltages became available in about 1920 and this improved the possibilities of irradiating deeper seated tumours. This was the highest available energy for some time, and the X-ray equipment with voltages up to about 300 kV were named orthovoltage equipment (ortho in ancient Greek means straight or correct).   Even higher voltages were reached at the end of the 1930s with technically experimental machines. Examples are the 1 MV cascade generator that was installed in the NKI in 1939 and the resonance transformer. Soon after the Second World War these early high energy machines were made redundant by the introduction of linear electron accelerators with a megavoltage accelerating potential.  

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1954. The new orthovoltage X-ray machine in the NKI-AVL. The manufacturer is Philips, the X-ray tube operates at a maximum tube voltage of 250 kV and a tube current of about 20 mA.




Besides the big 250 kV machine, two smaller ones are taken into use. A Contact Therapy machine (tube voltage 50 kV) and a "Surface Therapy" machine (tube voltages 80 to 150 kV) 

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Around 1955. The head radiotherapist, Nel de Haan, gives a guided tour to a group of Italian physicians and representatives of industry.

On the left in the photograph is the machine for "Contact Therapy" at 50 kV, and on the right the machine for "Surface Therapy" at approx. 80 kV, in Dutch "Oppervlakte Therapie" (the "OT").  In another room the large orthovoltage machine with 250 kV tube voltage, also called "Deep Therapy" machine, (the "DT") is situated. 

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1975ca röntgen contactbestraling.jpg

Left: the new "DT" orthovoltage machine (250 kV) in 1973 in a treatment room of the new NKI in Amsterdam Slotervaart. Right: performing an irradiation with the "CT" machine (50 kV). The radiotherapist is Nannette van Drevelt. For many years she was the therapist who performed the orthovoltage irradiations.

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1995. The new orthovoltage machine is delivered by the Pantak Company. The tube voltage is 300 kV at maximum with a current of 20 mA. The machine is used at 250 kV. For very superficial treatments a smaller machine, with a tube voltage of up to 150 kV, is bought from the same company. This unit can be seen on the left in the photograph.

For fixation of the head and neck region a vacuum cushion is available on the table. This cushion is filled with plastic granules and takes the shape of the body. Using the vacuum pump on the little cart on the right, the cushion is extracted. The surrounding air compresses the cushion and the granules lock together to form a rigid mould in which the head is kept in a fixed position.  

The era of orthovoltage has now ended for the big manufacturers. In radiotherapy, the orthovoltage treatment has largely been replaced by megavolt photon and electron treatments with linear accelerators or by advanced applications of brachytherapy. Only some large radiotherapy departments, with a tradition in orthovoltage, maintain this form of therapy. The manufacturers Philips and Siemens terminate the production of orthovoltage machines. Some small companies, such as Pantak and more recently Xstrahl in the UK, develop machines with modern technology and computer control for the remaining users. The therapeutic options basically remain the same as those of the old machines.


The new orthovoltage machine in 2012 is an Xstrahl 300 type

In the NKI-AVL the orthovoltage machine from 1995 breaks down after 16 years. In 2012 it is decided to replace two old X-ray machines by one single machine. This will be used for all X-ray irradiations in the range of 50 to 300 kV, at a maximum current of 10 mA for the highest voltage. This machine is described at the top of this article. On this occasion the treatment room is renovated and a new ceiling support is installed.