The influence of irradiation time per treatment session on acute and late skin reactions: a study on human skin

A comparison of the radiation effect of altering the treatment time per session in fractionated radiotherapy was performed on human skin with 12 MeV electrons. Four fractions of 7.2 Gy were given within 22 days, once a week. The dose per fraction was administered in 4 min and 32 min, respectively. The dose rate was about 2 Gy/min and the prolonged treatment time was achieved by dividing each dose fraction into three equal subfractions with intervals of 14-15 min. Prolongation of the treatment time resulted in a significant reduction of the skin erythema (p less than 0.001), pigmentation (p less than 0.05) and the degree of telangiectasia at 5 years (p less than 0.001). The relative biological effectiveness (RBE) for the prolonged (32 min), in relation to that of the short (4 min) treatment time, RBE4 min/32 min, was 1.09-1.10 for erythema and 1.07-1.12 for telangiectasia. These findings indicate that prolongation of the treatment time per session has to be adjusted for in clinical radiation oncology.

Dosimetric intercomparison at the Scandinavian radiation therapy centres. I. Absorbed dose intercomparison

A dosimetric intercomparison was carried out at all the centres in Denmark, Norway and Sweden. All the beam qualities (except conventional roentgen rays) used in radiation therapy were investigated. The ratio of the absorbed dose measured by us to that stated by the centre was determined. The mean ratio and standard deviation with the reference field-size were for 60Co gamma beams 1.001 +/- 0.014, for roentgen ray beams (4-45 MV) 1.017 +/- 0.023, electron beams with energy E0 less than 10 MeV 0.989 +/- 0.027, and electron beams with energy E0 greater than or equal to 10 MeV 0.996 +/- 0.034. The difference between the highest and lowest ratios was 17.8 per cent. A systematic difference due to the application of different protocols (NACP 1972 and 1980) was found.

Ferrous sulphate dosimeter for control of ionization chamber dosimetry of electron and 60Co gamma beams

A check of the dosimetry using ionization chambers and applying the procedures described in the Nordic dosimetry protocols (NACP 1980, 1981) was carried out using the ferrous sulphate dosimeter as reference. Measurements have been carried out in electron beams in the energy range 2.8 to 27.5 MeV and in 60Co gamma beams. Consistent results were obtained with the two systems within about one per cent. Larger differences were only observed in electron beams containing a large proportion of scattered low energy electrons and contaminating roentgen rays which were not corrected for in the ionization chamber method.

Liquid ionization chamber for absorbed dose determinations in photon and electron beams

The use of a liquid ionization chamber for measurements in electron and photon beams with energies above 1 MeV has been investigated. The liquid in the chamber is 2,2,4-trimethylpentane. Fundamental properties such as the reproducibility of the measured charge per absorbed dose, the temperature dependence, and the angular dependence have been experimentally analysed. The general recombination losses in pulsed beams are shown to be dependent on the transport time of the ions in the liquid. For a longer transport time than the time between two consecutive pulses the losses depend on the mean dose rate and for a shorter transport time the losses depend on the absorbed dose per pulse. The Jaffe method is used for determination of the initial recombination losses, and compared with results from other authors. The chamber is particularly useful for absorbed dose determination in electron beams since the relation between measured charge and absorbed dose to water is almost energy independent. In photon beams the relation is somewhat quality dependent particularly at qualities below 10 MV. The change of the free ion yield caused by the small change of mean LET with the quality of the photon beam is probably the reason. Procedures for the calibration of the liquid chamber and the absorbed dose determination in electron and photon beams are described.

Calibration and use of plane-parallel ionization chambers for the determination of absorbed dose in electron beams

The dosimetry procedures to be used at electron energies, E0, below 15 MeV in order to determine absorbed dose to water with an ionization chamber have been investigated. The performance of different types of plane parallel ionization chambers was tested. A chamber suitable for use in accordance with the Nordic dosimetry recommendations was designed. Correction factors to be applied in order to use solid phantom materials instead of water were determined.

Postal intercomparison of absorbed dose for high energy x rays with thermoluminescence dosimeters

This study concerns the accuracy and precision of the IAEA/WHO LiF TLD system used in intercomparison by mail of absorbed doses from 60Co gamma-radiation and 4-25 MV x rays. The system employs 160 mg LiF powder in polystyrene capsules, which are placed at 5 or 7 cm depth in water and irradiated to doses close to 200 rad (2.00 Gy). The dosimeters are mailed to the IAEA Dosimetry Laboratory and read out under conditions to minimize variatons in instrument sensitivity. The precision of the readout technique, using 3 capsules per irradiation and the readout of 5 aliquots per capsule, is characterized by 0.2% standard deviation of the resulting mean. Since random errors during the irradiation are added, the detectable systematic descrepancy in dose delivery, at the 95% confidence level, is +/- 2% for 60Co gamma and +/- 3% for high-energy x rays.