Photomedicine

 

Photomedicine uses special optical radiation sources for therapeutic, diagnostic, endoscopic, illumination and dental curing purposes. Gigahertz-Optik GmbH produces a wide range of measuring instruments that measure the intensity and efficacy of these sources. There follows some example applications using Gigahertz-Optik GmbH products.

Our sales team will be pleased to support you regarding your particular application requirements. Please contact us via +49 (0) 8193 93700-0 or info@gigahertz-optik.de. 

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Measurement of effective irradiance in bilirubin phototherapy

Blue light phototherapy is widely used for the treatment for neonatal hyperbilirubinaemia, a condition in which there is too much bilirubin in the blood. This causes a yellowing of the infant’s skin, known as jaundice. Effective phototherapy requires sufficiently high irradiance with appropriate wavelengths, generally accepted as ‘blue light’ over a large effective treatment area. 

Neonatal phototherapy has been widely used for more than 50 years employing many lighting technologies including various fluorescent tube types, tungsten halogen and metal halide lamps as well as LED based units which are becoming increasingly commonplace. This diverse range of treatment lamps produces widely differing spectral outputs. Unfortunately, there is no universally accepted ‘action spectra’ or agreement on the most effective wavelengths which has resulted in rather poor quality dosimetry and radiometry in this field over the years.

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The standard IEC EN 60601-2-50:2009+A1:2016 [1] defines total irradiance for bilirubin, Ebi where:

Ebi = integrated irradiance 400 to 550nm, generally reported in mW/cm2

No wavelength preference is given thereby accommodating many different lamp types. The standard also defines that the minimum integrated irradiance, Ebi MIN, needs to be greater than 40% of the maximum, Ebi MAX, value over the effective treatment area. Manufacturers are also required to ensure UV and IR emissions are within strict limits (see Hazard Applications).

However, the most recent guidelines issued by the American Academy of Pediatrics [2] in 2011 recommend ‘intensive phototherapy’ resulting from average spectral irradiance levels over the 460 to 490nm spectral range exceeding 30 µW/cm2/nm. Previously, the AAP guidelines had referenced the same irradiance level but over a wider wavelength band of 430 to 490nm. Intensities above 65 µW/cm2/nm may be considered potentially harmful however.

Manufacturers have also chosen to select their own wavelength range over which to specify the average spectral irradiance of their products, with 425 to 475nm being widely used for example. In practice, radiometers do not have perfectly flat spectral responses over their desired wavelength band and also suffer from out of band responsivity. Therefore, radiometers can only measure with good accuracy if used to measure a phototherapy treatment lamp with spectral distribution closely matching that for which it was calibrated [3].

Consequently, optimising treatment dosimetry and agreement on best practises as well as medical research have all been hindered by the large variability of measurement data produced by the many proprietary broadband radiometers employed, each with its specific spectral response and typically tailored to specific lamp or LED types. The MSC15 spectral light meter conveniently and effectively eliminates these issues. It measures the actual spectral irradiance produced by the lamp and provides display modes in accordance with the latest standards and guidance, irrespective of the lamp type or manufacturer. It directly displays total irradiance for bilirubin, Ebi (mW/cm2) in accordance with IEC 60601-2-50:2009+A1:2016 as well as average spectral irradiance (µW/cm2/nm) in accordance with the latest AAP recommendations. Full spectral data is also available enabling matching to any proprietary wavelength band specified by a manufacturer.


References

[1] IEC 60601-2-50:2009+A1:2016  Medical electrical equipment - Part 2-50: Particular requirements for the basic safety and essential performance of infant phototherapy equipment.

[2] Phototherapy to Prevent Severe Neonatal Hyperbilirubinemia in the Newborn Infant 35 or More Weeks of Gestation 

[3] Neonatal phototherapy radiometers: Current performance characteristics and future requirements

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UV phototherapy dosimetry

Phototherapy refers to the use of optical radiation (ultraviolet, visible and infrared light) to treat medical conditions. In particular, UV radiation is widely used to treat a range of skin conditions such as psoriasis, parapsoriasis, vitiligo, atopic dermatitis (eczema), and mycosis fungoide.

There are three principal forms of UV phototherapy:

  • Broadband UVB (BB-UVB) in which the skin condition is treated with the full spectrum of UVB radiation, 280-315nm. BB-UVB lamps are typified by the Philips TL12 range;
  • Narrowband UVB (NB-UVB) in which just a narrow wavelength range within the UVB spectrum is used for treatment. Typically, lamps emitting 311nm such as Philips TL01 lamps are employed. Excimer lamps and pulsed lasers (308nm) are also used.
  • PUVA (Psoralen + UVA) in which broadband UVA radiation (315-400nm) is used in conjunction with a psoralen, (a compound that increases the effect of UVA radiation on the skin). PUVA is also sometimes referred to as photochemotherapy.
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UVB is most routinely used to treat common skin conditions. NB-UVB has largely replaced BB-UVB as it eliminates the short wavelengths found in BB-UVB which are more likely to cause erythema and hence carries greater long-term cancer risks. PUVA is often preferred for conditions such as mycosis fungoides, hand and foot eczema, and pustular psoriasis as well as for conditions that have not been responsive to UVB.

Accurate patient dosimetry is important in UV phototherapy. It not only ensures that patients can be treated consistently irrespective of the clinic attended, but is also necessary to ensure that a patient’s absolute cumulative dose of UV radiation can be accurately recorded so that the long-term skin cancer risks can be best managed.

For clinical phototherapy purposes UV radiation dose is determined by the irradiance measured at the skin surface multiplied by the length of exposure. The irradiance is measured in units of power per unit area, typically in mW/cm2. Therefore, for an exposure time in seconds, the dose is expressed in units of energy per unit area, typically J/cm2. However, large discrepancies in dosimetry between treatment centres have been reported [1]. The main sources of error have been attributed to a number of factors including poor cosine response, poor spectral matching of UVA and UVB bands, as well as inappropriate and non-traceable calibration of the radiometers used. Where CCD-based spectroradiometers are used for UV dosimetry, their poor scattered light rejection is often an additional significant source of error.  

Gigahertz-Optik GmbH manufactures cosine corrected radiometric sensors with dual detectors, XD-9503 and XD-9501, designed specifically to measure the UVA and UVB irradiance of phototherapy lamps. The X1 Optometer provides direct display in dose or irradiance units for these detectors.

Consideration should also be given to the protection of clinical staff from UV radiation scattered from walls and ceilings for example. The European Directive 2006/25/EC[2] sets minimum health and safety of workers requirements from the risks related to UV optical radiation. Gigahertz-Optik GmbH manufactures detectors and personal dosimeters specifically for this purpose (See Light hazard applications). 


References

[1] Guidelines on the measurement of ultraviolet radiation levels in ultraviolet phototherapy (2015), British Journal of Dermatology

[2] Directive 2006/25/EC - artificial optical radiation

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Pulsed excimer laser phototherapy dosimetry

Phototherapy with narrowband UVB (NB-UVB) radiation is the preferred treatment method for many skin conditions, such as psoriasis, vitiligo, and atopic dermatitis. Low-pressure fluorescent lamps with emission at 311nm are commonly used. However, excimer lamps and lasers offer a high intensity alternative with emission at 308nm. In particular, pulsed excimer lasers enable targeted therapy with higher doses of UVB light resulting in fewer treatment sessions. The ability to target specific areas enables high doses of therapeutically effective monochromatic UVB light while leaving healthy skin unexposed and protected, thereby lowering the risk of premature skin aging and carcinogenesis. 

NB-UVB phototherapy is now considered the premier treatment for localised vitiligo. NB-UVB light can help stimulate the melanocytes (pigment making cells) in less time than it takes the UV radiation to burn the skin. Psoriasis plaques can withstand higher doses of UV radiation than normal skin Therefore, the targeted delivery possible with excimer lasers permits higher doses and can result in reduced treatment time.

Accurate dosimetry is crucial with high intensity excimer laser sources. 

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Gigahertz-Optik GmbH manufactures and calibrates the UV-3711-308 detector which is specifically designed for the measurement of irradiance resulting from excimer laser and lamp illumination. The calibration of its irradiance responsivity is performed at 308 nm. This detector benefits from a flat spectral responsivity around 308 nm which reduces the measurement uncertainty resulting from any wavelength shift by the excimer laser. Together with the P-9710-2 Optometer, the pulse energy (dose) of individual pulses or pulse chains can be precisely determined within defined temporal measurement windows. The P-9710-2 Optometer has a pulse energy measuring mode based on the principle of pulse-stretching. This technique employs a meter with a fixed time constant for all gain ranges that is much longer than the short pulses, typically a few ns, produced by the excimer source. High speed sampling, relative to the time constant, enables the pulse energy to be determined by measuring the integral of the resulting ‘pulse-stretched’ signal. See also Laser application example.

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Compact integrating sphere for total flux of radial emitting fibres used for photodynamic therapy

Photodynamic therapy (PDT) can be used to treat certain types of cancer as well as some skin and eye conditions. In PDT abnormal cells are destroyed by the use of light-sensitive medication, known as photosensitizers, in conjunction with a suitable light source. Typically, the activation spectrum of the photosensitizer falls within the 630nm to 850nm wavelength range. Individually, the photosensitizer medication and light source are harmless, but when the medication is exposed to the light in the presence of tissue oxygen, it activates and causes a reaction that damages the nearby cells.

Delivering sufficient optical power to the target tissue area has been a topic of much research and development over the years. Any normal tissue covering the target tissue will be highly scattering. Consequently, only limited penetration of the visible/near-IR light occurs. Therefore, PDT techniques rely heavily on fibre optic technology to provide suitable light delivery solutions. Laser diodes offering power levels in the 1W to 10W range are now typically coupled to fibre-optic light guides for PDT. Radial emitting fibres are used for the endoscopic delivery of PDT light within hollow organs.

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Such side emitting fibres produce a radial light pattern at the end of the fibre, ideally with a high uniformity. The length of the light emitting portion of the fibre is determined by the treatment area required and is typically less than 80mm in length. Integrating sphere based laser power meters are most commonly used for the measurement of total flux from radially emitting sources. To precisely measure the radiation output from the side emitting section of the fibre, a conventional integrating sphere would need to be around 200mm (8 inches) in diameter and would require a very specific design of internal baffling. Whilst such a sphere may be acceptable within a laboratory, it is too large to integrate into the laser source equipment used for PDT. For this purpose Gigahertz-Optik GmbH has designed elongated integrated spheres that have a small diameter of only 30mm. Model UPK-30S60-L accommodates fibres with light emitting length of up to 60mm and the model UPK-30S105-L is suitable for up to 80mm length fibres. The UPK-30S60 is also supplied with a removable protective quartz insert to prevent the fibre from touching the sphere’s coating. A stretched integrating sphere does not offer the same uniformity of light distribution than spherical integrating spheres. Therefore, particular attention has to be given to ensuring appropriate calibration procedures are used. This is best achieved using radial emitting fibres as the reference source.