Dose-time relationships for post-irradiation cutaneous telangiectasia

Initiation of non-neoplastic late effects: the role of endothelium and connective tissue

While early radiation lesions might be a direct consequence of parenchymal cell loss, late-radiation injury most probably develops as a consequence of functional perturbations that may involve both parenchymal and nonparenchymal elements. Damage to blood vessels and consequent perturbations in blood flow and endothelial physiology play an important role in the development of late effects. The development of late-radiation damage has been studied in three different tissue systems: the skin, kidney and central nervous system. The results suggested that damage to vascular tissue played a major role in the development of radiation-induced late effects.

Studies of dose-fractionation on early and late responses in pig skin: a reappraisal of the importance of the overall treatment time and its effects on radiosensitization and incomplete repair

Studies in pig skin have examined the effects of dose fractionation on the acute radiation response. The variation in ED50 values for moist desquamation for doses given as 1-48 fractions over less than or equal to 16 days were best fitted by a log-log plot of iso-effect dose against the number of fractions; the slope of this plot indicated a fraction number exponent (N) of 0.42 +/- 0.007. Based on the assumptions made in applying the linear-quadratic (LQ) model, the alpha/beta ratio was found to decrease with decreasing per fraction: for doses given as 6-27 Gy per fractions the alpha/beta ratio was 8.74 +/- 0.48 Gy, whereas for doses of 2.55-6 Gy per fraction it was only 0.85 +/- 0.29 Gy. A simple approach to a time factor could not be used to calculate iso-effect doses for acute reactions in pig skin when treatment time was increased from less than or equal to 16 days to 28-39 days. This was due to the opposing effects of radiosensitization and repopulation when the cell cycle time of epidermal basal cells was shortened. For late dermal necrosis in pig skin, repair of sublethal damage was not completed in 24 hr. This finding has a significant effect on the interpretation of the results of fractionation studies using this late endpoint. Expressed in terms of a simple power-law function, there was a significant change in the fraction number exponent "N" from 0.43 +/- 0.007 to 0.37 +/- 0.006 for the complete and incomplete repair data, respectively. Many of the fractionation effects reported for acute and late damage to pig skin would appear to be in excellent agreement with those for human skin.

Relationship between early and late normal-tissue injury after postmastectomy radiotherapy

Factors of importance in the development of telangiectasia were investigated in a series of 229 patients who, between 1978 and 1982, received postmastectomy radiotherapy with two different fractionation schedules. Patients who developed moist desquamation had a statistically significantly increased risk of developing telangiectasia after a specific course of radiotherapy. As an example the estimated incidence of severe telangiectasia after 44 Gy in 22 fractions increases from 27% to 49% in patients who developed grade greater than or equal to 2 moist desquamation as an early radiation reaction. A reanalysis of the Aarhus data with telangiectasia as the endpoint gave an alpha/beta ratio at 2.8 Gy (95% c.l. (-0.1, 8.1) Gy) and a relative biological effectiveness (RBE) of high energy electrons relative to 8 MV photons at 0.89 (95% c.l. (0.85, 0.93)). Patients age or the occurrence of severe erythema did not predispose to telangiectasia. A similar predisposition after moist desquamation was not seen for subcutaneous fibrosis. The RBE of high energy electrons relative to 8 MV photons for this endpoint was estimated at 0.88 (95% c.l. (0.86, 0.91].

Fractionation sensitivity of a functional endpoint: impaired shoulder movement after post-mastectomy radiotherapy

A clinical radiobiological study of the fractionation sensitivity of impaired shoulder movement after postmastectomy radiotherapy is presented. From 1978 to 1980, 163 breast cancer patients received postmastectomy irradiation delivered in 12 fractions, 2 fractions per week, over a period of 37 to 46 days. The total dose was specified either as a maximum absorbed dose of 51.36 Gy, or as a minimum target dose of 36.6 Gy specified at the level of midaxilla. From 1981 to 1982, 66 patients received a minimum target dose of 40.92 Gy in 22 fractions with 5 fractions per week over a period of 29 to 35 days. The treatment technique remained essentially unchanged during the whole period of 1978 to 1982. Maximal flexion and abduction of the arm were measured with unfixed scapula. A relative score, indicating the grade of impaired shoulder movement on a nominal scale from 0-3, was established by comparison with the mobility of the contralateral arm. In addition, working ability and pain at movement and at rest were evaluated. These performance parameters significantly correlated with the grade of impaired shoulder movement. The occurrence of moderately or severely impaired shoulder movement was analyzed using a mixture model incorporating dose-fractionation, latency, and predisposing clinical factors. The risk of shoulder problems was significantly higher among patients above 60 years of age. The analysis pointed to subcutaneous fibrosis as a disposing factor and indicates that postoperative physical exercise programs are beneficial. Arm edema had no statistically significant influence on shoulder performance. The alpha/beta ratio was estimated at 3.5 Gy with 95% confidence limits (c.l.) [0.7, 6.2] Gy. The length of time to expression of 90% of the ultimate frequency of moderate and severe shoulder impairment was estimated at 3.9 years with 95% confidence limits [3.1, 4.6] years. The nominal standard dose (NSD) formalism failed to produce isoeffective total doses with respect to impaired shoulder movement in the two fractionation schedules. Although the deleterious effects of larger-than-conventional dose fractions have been documented in a number of clinical series, this study represents the first quantitation of the fractionation sensitivity of a functional clinical endpoint.

Analysis of late effects data using dose-response models: application to human skin telangiectasia data

The clinical data for skin telangiectasia from previous prospective studies at the Radiotherapy Department in Gothenborg are reanalyzed using two dose-response models - the general formulations of the well known linear-quadratic (LQ) and NSD isoeffect models. Assuming that essentially no repopulation appears in the vessel endothelium for overall treatment times up to 68 days, the alpha/beta-value of 2.75 Gy is obtained for the LQ-model. The time factor is found not to be significant by the NSD-model for the treatment times used (less than or equal to 68 days) at the 95% level of confidence. The estimated value of the exponent of the number of fractions, A, is 0.321. The obtained values of the alpha/beta-ratio and of A show high sensitivity of the vessel endothelium to changes in the dose per fraction. Our results show that within the interval of the number of fractions used, 10-35 fractions, the NSD-model gives predictions comparable to those of the LQ-model. For number of fractions smaller than 5, a high discrepancy occurs between the two models, the NSD-model predicting higher values of the isoeffective total dose. The maximal deviation between the models appears for N = 1; 25% and 27% at the 5 and 50% level of effect, respectively. For large N and especially at low effect probabilities the NSD-model again predicts higher isoeffective doses: the dose predicted by the NSD-model for a regimen with 40 fractions and for 5% probability of telangiectasia is 7.5%, higher than that predicted by the LQ-model. Based on the estimated dose-response curves, considering the telangiectasia as the decisive late tissue effect, the requirement for the combined uncertainty in the dose delivery is estimated between 3 and 4.5%.

Some methodological problems in estimating radiobiological parameters from clinical data. Alpha/beta ratios and electron RBE for cutaneous reactions in patients treated with postmastectomy radiotherapy

A number of biological, dosimetric, and statistical problems encountered in the determination of alpha/beta ratios and the relative biological efficiency (RBE) of high energy electrons are discussed. The analysis is based on isoeffect dose determination from logit analysis of dose-response data. Monte Carlo simulations of the logit analysis show that the estimated isoeffect dose may be treated as a normally distributed random variable. Under this assumption, formulae for the standard error of the derived radiobiological parameters are presented. The importance of specifying not only parameter estimates but also their confidence limits is emphasized. As a practical example, the dose-response relationships for severe erythema and subcutaneous fibrosis are discussed in two series of patients treated with postmastectomy irradiation with electrons and photons in two fractionation schedules. Because of a different dose per fraction in the electron and photon fields, a determination of RBE requires a fraction size correction. This is performed using the alpha/beta formalism. The present analysis suggests a high energy electron RBE for severe erythema of 0.93 (95% confidence limits 0.89 and 0.96) and for subcutaneous fibrosis of 0.84 (95% confidence limits 0.77 and 0.92).

The value of the NSD formula in equation of acute and late radiation complications in normal tissue following 2 and 5 fractions per week in breast cancer patients treated with postmastectomy irradiation

In 1978-1980, inclusive, all breast cancer patients referred for postmastectomy irradiation were treated by 2 fractions per week (73 patients) but due to a high incidence of late complications this fractionation schedule was changed from early 1981 to 5 fractions per week (66 patients) with dose adjustment according to the nominal standard dose (NSD) concept. The dose aim in both regimens was 1345 ret minimum target dose. This allowed a comparison of acute and late complications in the two patient groups treated to the same NSD value, but with different fractionation. The patients have been analysed with respect to acute and late reaction in the skin, subcutaneous tissue, lung and bone, as well as related complications, such as arm oedema and impairment of shoulder movement. Except for the acute skin reactions, all other endpoints could not be adequately predicted by the NSD formula. Thus, telangiectasia greater than or equal to grade 1 and skin fibrosis greater than or equal to grade 2 were found to be 75% and 67% in patients treated with the 2-fraction scheme versus 39% and 5% in patients treated with the 5-fraction scheme. In the 2-fraction regimen, a higher frequency of impairment of shoulder movement and arm oedema was found compared to the 5-fraction regimen, 38% versus 11% and 44% versus 33%, respectively. The acute lung reaction as well as late lung reaction were significantly more pronounced in the 2-fraction regimen than in the 5-fraction regimen (pneumonitis greater than or equal to grade 2, 43% versus 23%, and lung fibrosis greater than or equal to grade 2, 32% versus 17%, in the photon fields, respectively). Further, radiation-induced osteonecrosis in the ribs was significantly more frequent in patients treated with large dose per fraction (19% versus 2%). The data clearly demonstrates the danger by using the NSD formula in equation of two different fractionation schedules. This formula as well as other mathematical models can only be used with caution within the limitations defined by the underlying clinical and experimental data on which they have been derived.

Treatment of post-radiotherapy telangiectasia by injection sclerotherapy

A new treatment for post-radiotherapy telangiectasia is reported. Five patients were successfully treated by injection of a dilute solution of sodium tetradecyl sulphate. Several (4-7) half hour sessions of injection sclerotherapy at 5-weekly intervals were necessary.

Chronic radiation damage in the rectum of the rat after protracted fractionated irradiation

In this experiment, a protracted fractionation regime (18 fractions/170 days, dose/fraction: 6,7,8 Gy) caused late rectal obstruction in rats independently of any clinically detectable acute damage. Rectal obstruction was due to an ulcer which developed secondary to an atrophic mucosa and capillary damage. In agreement with our earlier protracted fractionation schedules, the results were not fitted well by the linear-quadratic model. However, there are indications of relatively low alpha/beta values. Hydronephroses and hydroureters were the only competing risks to rectal obstruction and they occurred independently of it.

Iso-effect tables and therapeutic ratios for epidermoid cancer and normal tissue stroma

Available literature on radiation injury to normal tissue stroma and ablation of epidermoid carcinoma was surveyed. Computer programs (RAD3 and RAD1) were then used to derive cell kinetic parameters and generate iso-effect tables for the relevant tissues. The two tables provide a set of limiting doses for tolerance of normal connective tissue (16% risk of injury) and for ablation of epidermoid cancer (16% risk of recurrence) covering a wide range of treatment schedules. Calculating the ratios of normal tissue tolerance to tumor control doses for each treatment scheme provides an array of therapeutic ratios, from which appropriate treatment schemes can be selected.