Automated thermoluminescence reader. II. Experiments and theory

Characteristics of dose-response relationships for late radiation effects: an analysis of skin telangiectasia and of head and neck morbidity

The dose-response characteristics were analysed for late skin telangiectasia in patients for 1, 2 and 5 fractions per week and 3 to 4 dose levels per schedule. Altogether 286 fields were used. Skin telangiectasia was scored on an arbitrary scale and dose-response analysis was performed at 10 year's follow-up for various degrees of telangiectasia, score greater than or equal to 1 to greater than or equal to 4. The following parameters were determined for each schedule and the equivalent single dose-response curves for each endpoint using probit analysis: the ED50, the absolute steepness, measured as the probit width, K, the relative steepness, K/ED50, and the normalised effect gradient, gamma 50. The inverse radiosensitivity, Doeff or Do, was estimated using the Poisson and LQ-models for tissue response. The alpha/beta value was found to be independent of the degree of telangiectasia used as endpoint. The absolute steepness of the dose-incidence curve increased with increasing dose per fraction and was correlated to the degree of damage. The relative steepness was independent of the dose per fraction when the dose-response curve was generated by a fixed dose per fraction, and was less than if generated by a fixed number of fractions. The relative steepness increased with higher degree of damage. Doeff decreased with increasing dose per fraction, and also with higher degree of telangiectasia. The highest steepness determined for telangiectasia score greater than or equal to 4 (partially confluent or more) at 10 years corresponded to K = 0.8 Gy, K/ED50 = 5%, gamma 50 = 7 and Do = 0.7 Gy. The dose-response characteristics found for late skin telangiectasia score greater than or equal to 2 to greater than or equal to 4 were consistent with those determined for necrosis and fatal complications 5 years after radiotherapy to head and neck tumours in our department.

Repair capacity and kinetics of human skin during fractionated radiotherapy: erythema, desquamation, and telangiectasia after 3 and 5 year's follow-up

Prospective clinical fractionation studies on acute and late reactions in skin have been going on since 1972 at the Radiotherapy Department in Gothenburg. The clinical assay consisted of breast cancer patients irradiated postoperatively to the internal mammary nodes from unilateral or bilateral fields exposed to various dose schedules. 750 fields in 450 patients have been analysed. Schedules with 1, 2 or 5 fractions per week and 2 or 3 fractions per day were evaluated with erythema, desquamation and telangiectasia as endpoints. For some schedules a dose-response relationship was established in a limited dose range, but often there was only one dose group per schedule. These data are suited to analysis by the method of direct analysis of quantal response. This was used in the present analysis, along with the linear quadratic (LQ) model and its generalization, the incomplete repair (IR) model. The repair capacity was similar for erythema and desquamation, with alpha/beta ratios between 7.5 and 11.2 Gy. Unexpectedly, there was more significant time factor during radiotherapy courses up to 6 weeks for erythema and desquamation, but the repair capacity was changed after 4 weeks for both endpoints, and alpha/beta increased to between 18.3 and 34.5 Gy. The repair capacity for late telangiectasia differed significantly from that for erythema and desquamation, with alpha/beta values between 2.8 and 4.3 Gy. There was a significant time factor for telangiectasia with characteristic doubling time of about 16 days, when an exponential function for time was used. Concerning the repair kinetics in skin, there were insufficient data to obtain precise estimates, but there was a suggestion of two components of repair. This was inferred from higher-than-predicted recovery with 15-min intervals, when the data were fitted with the monoexponential model. The monoexponential fit gave t1/2 between 1.1 and 1.3 h for acute effects and 3.5 h for late effects. Recovery after 15-min fractionation intervals, if it resulted from a fast repair component, would be consistent with a half-time of 0.3-0.4 h. The time factor and the relative long half-time for repair for late effects have important implications for multiple-fraction-per-day treatment, and imply that interfraction intervals of 4 h or less, as commonly used, will be insufficient. Instead, intervals of 6 h or longer are recommended. Using accelerated fractionation with a significant reduction in overall treatment time a dose reduction is still necessary to take into account the time factor for late effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Quality assurance control in the EORTC cooperative group of radiotherapy. 3. Intercomparison in an anatomical phantom

Two papers concerning the quality control study organised by the EORTC (European Organisation for Research on Treatment of Cancer) Cooperative Group on Radiotherapy have been published. The medical profile (part 1) and the dosimetric intercomparison (part 2) of the participating institutions were presented. This part (paper 3) presents an integrated clinical and dosimetric investigation in an anatomical phantom. A tonsillar tumour and a homolateral subdigastric node were marked in an anatomical phantom. The institutions were asked to treat the phantom once like an ordinary patient. The phantom was loaded with dosimeters and irradiated. From the results obtained, it can be concluded that we did not find any major dosimetric problem related to absorbed dose calibration or calculation in the phantom. However, several major problems were related to non-optimal planning, treatment technique and dose distribution. The investigation shows the importance of a quality assurance programme for cooperative groups.

The predictive value of skin telangiectasia for late radiation effects in different normal tissues

Alterations in the microcirculation and parenchymal cell loss are common phenomena after irradiation of different organs. Whether parenchymal cell loss is a process well dissociated from vasculoconnective damage, or a consequence of this, is much debated. However, comprehensive radiopathological studies have shown that vasculoconnective tissue is an important common target for late effects in various organs. Scoring of skin telangiectasia was used by us as a clinical assay of late tissue effects after different dose schedules. All studies were done prospectively with standardized skin area, field size and radiation quality. The patients were scored regularly up to 10 years. The number of patients at risk for a prescribed score versus time was calculated with the life-table method. The late effects after 5 X 2.0 Gy/wk, in the dose range 40 to 70 Gy and after 2 X 4.0 Gy/wk, in the dose range 40 to 56 Gy have been established. The skin dose is 90% of the referred dose. Dose-response curves, relating the proportion of patients with a certain score at a fixed time and radiation dose and dose-latency curves, relating the latent period for a fixed proportion of patients with a certain score and radiation dose, were constructed. The analysis shows that: ED10/5 yr and ED50/5 yr for 5 X 2.0 Gy/wk is 50 Gy and 65 Gy, respectively, for distinct telangiectasia; The latent period, concerning both a certain frequency and degree of reaction, varies exponentially with dose level; The latent period for 50% of the patients, to obtain a certain score, LP50, is correlated to that for 10%, LP10, with LP50/LP10 = 2.2 +/- 0.2 (S.D.). This correlation is independent of score, total dose, and fractionation; Isoeffective doses for 5 X 2.0 Gy/wk and 2 X 4.0 Gy/wk, determined from the dose-response curves, resulted in the repair exp N between 0.31 and 0.32 and alpha/beta ratio between 2.9 and 3.1 Gy and determined from the dose-latency curves in exp N between 0.30 and 0.32 and alpha/beta ratio between 3.4 and 2.9 Gy. In conclusion, frequent and careful follow-up with registration of normal tissue reactions, until at least 10% of the patients have obtained the prescribed effect, is predictive for the further progression of the late effects. The fractionation characteristics for telangiectasia agree well with those for animal experimental morphological and functional endpoints for late effects in different organs and support the relevance of telangiectasia as a model for predicting late effects.

The influence of the overall treatment time in radiotherapy on the acute reaction: comparison of the effects of daily and twice-a-week fractionation on human skin

A comparison of the acute skin erythema and pigmentation after daily fractions of 2 Gy and twice-a-week fractions of 4 Gy was performed on post-operatively irradiated parasternal fields in patients with breast cancer. The radiation quality used was electron beams with an energy of about 12 MeV. The overall treatment time varied between 4 and 6 weeks. The two schedules were also compared for an overall treatment time of 10 weeks, with a rest period of 3 weeks after 4 weeks of irradiation, followed by another 3 weeks of treatment. With 5 to 6 weeks irradiation, daily fractions resulted in a significantly more pronounced skin erythema (p less than 0.05) than twice-a-week fractions, corresponding to about 10% in terms of absorbed dose. With 4 weeks irradiation and split-course therapy, the acute reactions were identical with both schedules. We interpret these findings as indicating a radiation-induced accelerated repopulation of the basal cells in the epidermis, with a fairly abrupt onset after 4 weeks. The higher effect after more frequent fractions of smaller size would be expected from a sensitizing effect of redistribution. In conclusion, the overall treatment time is of importance for establishment of iso-effect relationships for acutely responding tissues. The implication is that different fractionation parameters used in models to predict equivalent radiation effects of different fractionation schedules also vary significantly with the overall treatment time.

Design of flattening filters based on intracavitary absorbed dose measurements in external radiation therapy

A method has been developed for the design of flattening filters on the basis of in-vivo oesophagus measurements of absorbed dose distribution in patients given external radiation therapy. The measurements were made by means of LiF-Teflon thermoluminescent dosimeters, read out by an automatic TL-system. A single filter was designed from the resultant dose distribution of parallel opposing fields. The method was checked clinically and was found to be convenient and reliable. The filters reduced the dose variation along the midline of the patients undergoing upper mantle treatments from about +/- 20% to about +/- 5%. The same limits of variation are believed to exist through the entire mid-plane of the body, though it was not possible to prove this by direct measurements.

Skin reactions after different fractionation schedules giving the same cumulative radiation effect

The CRE formula was used for calculation of biologically equivalent radiation doses with different fractionation schedules. The early radiation effects, skin erythema and pigmentation were measured with a reflectance spectrophotometer at wavelengths 578 and 660 nm. The course and maximum for both erythema and pigmentation agreed well with the two types of fractionation. The results seem to justify further use of this simple formula.