• Radiation therapy treatment schedules

    Between 1930 and 1945 the general approach was to use multiple courses of low-dose radiation, repeated at intervals of 4 to 8 weeks. In general, a total of 3 to 5 courses were applied, guided by patient’s visual response. Daily doses of 200 rads were used to a total dose ranging from 2450 to 3000 rads per course.
    Between 1945 and 1955, this policy changed into multiple courses of medium dose radiation (i.e. total dose of 30-40% more per course) and repeated with shorter intervals.
    From 1955 the multiple course approach was abandoned because it was more dele-terious for the normal tissues, due to the total accumulated dose of the different courses in a shorter overall treatment time. Since then, single-course high dose radiation therapy has generally been applied, intended to deliver a radiation dose sufficiently high to achieve permanent tumour control. The total dose increased in time from 2000 to 3000 rads in 2-3 weeks, to 3500 to 4500 rads in 4 to 5 weeks. Occasionally, the total dose exceeded 5000 rads in 5-6 weeks, based on higher success rates (i.e. improved vision) with a higher dose.
    In 1953 the International Commission on Radiological Units and Measurements introduced the concept of absorbed dose and defined its unit, the rad. The rad was in use until the introduction after 1960 by Le Systeme Internationale (SI) of the SI unit for absorbed dose, called “Gray”, defined as J/kg. 100 rad is 1 J/kg is 1 Gray.
    In the sixties an initial slow build-up treatment with a small daily increment of 25 to 50 cGray for the first three to four days was applied in order to minimize any radiation-induced edema in the optic chiasm. Nowadays, we have abandoned the incremental dose in the first treatment week and the most frequently used schedules are 23 to 25 fractions with a total dose of 45 to 50 Gray. Higher doses do not improve local control43.
    Besides fractionation, the radiation source used also changed in time, based on technical improvements. In the period 1930 to 1940 200 kV photons were used, followed by 250 kV photons in the period 1940 to 1960. In 1955 the 25 MeV betatron came into use, followed in 1962 by the cobalt 60 machine. In 1966 the introduction of the linear accele-rator was started, generating 6MV photons, still in use nowadays.
    The irradiation techniques evolved in time as well; the older two lateral opposed field technique irradiated a large volume normal brain with an equivalent or even higher dose of what was applied to the tumour with reports of brain necrosis as a result of that. This technique was replaced by at least a three-field technique, consisting of 2 lateral fields and one vertex field, or a plan with multiple fields with wedges, following a bicoronal 1100 arc, better targeting the high dose to the tumour and reducing the high dose volume in the normal brain. Both coplanar techniques are still in use today44.
    Since the availability of 3D radiation treatment planning systems in the nineties of the previous century, non-coplanar radiation techniques became possible. It became clear that for stereotactically guided conformal radiation therapy to volumes above 13 ml, four to six non-coplanar fixed fields are clearly superior to coplanar field arrangements, whereas even techniques approaching dynamic conformal radiation therapy such as a 30-field approach reveal no further sparing of normal brain tissue45. This technique has been introduced in the Radiation Oncology Department of the University Medical Center Groningen in 2001.

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