Dosage calculation

The most important parameter is the dose which is the same as the energy density. Low-level laser doses are indicated in joules (J) per cm² or sometimes, for small areas, joule per “point”. Mathematically this is calculated as laser output in milliwatts multiplied by the number of seconds of irradiation per square cm. For example, 100 mW x 10 seconds produces a dose of 1000 millijoules, or 1 J, and, if this energy is distributed equally over 1 cm², we have given the dose 1 J/cm². Suitable therapeutic doses range from 1 to 10 J/cm² for superificial conditions. If we are treating a small area, this can be regarded as a “point” even though this is not correct mathematically. A “point” is usually an area with a diameter of 5 mm or less. A suitable dose for a “point” is 0.2 to 2 joules for superficial conditions. At this level, there generally is no heat sensation involved with the therapy.

Another important parameter is the power density (the light intensity in the treated area), which is measured in watts per cm².

If treatment is performed in contact mode and the probe is not moved, the area being treated is the area of the laser probe opening. If this area is 2 mm² , (equals 0.02 cm²) the dose (energy density) created by a 100 mW laser during 10 seconds is 100 mW x 10 sec / 0.02 cm²  = 50000 mJ/cm² = 50 J/cm² . The power density in this little area is 100 mW / 0.02 cm²  = 5000 mW/cm²  = 5 W/cm².  These values are rather high, but they are only high in the directly illuminated surface of 2 mm²  – a few mm away they are much lower. If the target area is an open wound e.g. an aphte, it may be too high for the cells in the surface, but if the problem is situated deeper (like an apex) and the tissue inbetween is healthy, the dose is correct. One always has to consider the location of the problem and the tissue condition in the surrounding area. Another way to avoid very high dose peaks is to move the probe during treatment, or to – in some situations – spread out the light.

If irradiation instead is performed from a distance with a divergent beam, and the laser beam is spread out over an area of 1 cm², then the calculation becomes (same laser power):  100 mW x 10 s / 1 cm² =1000 mJ/cm² = 1 J/cm²