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

Exploiting biological and physical determinants of radiotherapy toxicity to individualize treatment

The recent advances in radiation delivery can improve tumour control probability (TCP) and reduce treatment-related toxicity. The use of intensity-modulated radiotherapy (IMRT) in particular can reduce normal tissue toxicity, an objective in its own right, and can allow safe dose escalation in selected cases. Ideally, IMRT should be combined with image guidance to verify the position of the target, since patients, target and organs at risk can move day to day. Daily image guidance scans can be used to identify the position of normal tissue structures and potentially to compute the daily delivered dose. Fundamentally, it is still the tolerance of the normal tissues that limits radiotherapy (RT) dose and therefore tumour control. However, the dose-response relationships for both tumour and normal tissues are relatively steep, meaning that small dose differences can translate into clinically relevant improvements. Differences exist between individuals in the severity of toxicity experienced for a given dose of RT. Some of this difference may be the result of differences between the planned dose and the accumulated dose (DA). However, some may be owing to intrinsic differences in radiosensitivity of the normal tissues between individuals. This field has been developing rapidly, with the demonstration of definite associations between genetic polymorphisms and variation in toxicity recently described. It might be possible to identify more resistant patients who would be suitable for dose escalation, as well as more sensitive patients for whom toxicity could be reduced or avoided. Daily differences in delivered dose have been investigated within the VoxTox research programme, using the rectum as an example organ at risk. In patients with prostate cancer receiving curative RT, considerable daily variation in rectal position and dose can be demonstrated, although the median position matches the planning scan well. Overall, in 10 patients, the mean difference between planned and accumulated rectal equivalent uniform doses was -2.7 Gy (5%), and a dose reduction was seen in 7 of the 10 cases. If dose escalation was performed to take rectal dose back to the planned level, this should increase the mean TCP (as biochemical progression-free survival) by 5%. Combining radiogenomics with individual estimates of DA might identify almost half of patients undergoing radical RT who might benefit from either dose escalation, suggesting improved tumour cure or reduced toxicity or both.

[Evaluation and management of acute radiation dermatitis]

Acute radiation dermatitis remains one of the most commonly observed side effect during radiation therapy leading to complication such as superinfection or treatment disruption. Its management is characterized by a great heterogeneity. Few strategies have demonstrated a benefit in preventing radiation dermatitis, which relies mostly on decreasing dose delivered to the skin and skin care practices. Simple emollients and use of topical steroids can be useful in early stages. The singularity of the skin toxicity seen with cetuximab and radiotherapy warrants a specific grading system and distinctive clinical treatment with use of antibiotics.

Objective measurements of radiotherapy-induced erythema

BACKGROUND/AIMS

The development of acute radiation erythema is a common phenomenon among patients under-going radiotherapy treatment. Because of the absence of reliable objective classification methods, the degree of skin reaction can at present mainly be judged subjectively in the clinic. This has motivated the present preliminary study,concerning the first steps in the development of an objective method for skin reaction classification.

METHODS

Three non-invasive techniques were used:near-infrared (NIR) spectroscopy, laser Doppler perfusion imaging and digital photography. The NIR spectra were analysed with principal component analysis (PCA), and the results from the other two with traditional univariate methods. Measurements were made on breast cancer patients who had been exposed to different irradiation doses. A total of 28 breast cancer patients participated one to three times each; 12 were treated with photons at 4 or 6MeV and 16 were treated with high-energy electrons between 10 and 20 MeV to a maximum dose of 50 Gy.

RESULTS

PCA of NIR spectra shows that information on radiation dose lies mainly in the first principal component. It is observed that the higher the dose the higher the score value. The results from the laser Doppler measurements show that in 79% of the cases the perfusion increases significantly with radiation dose. Analysis of the digital photography shows that a proposed skin redness index(SRI), increases with a higher radiation dose. However,the increase in most cases is not significant. By combining all data, correlation to radiation doses was seen for 74% of the patients who participated more than once.

CONCLUSION

All three non-invasive methods correlate with the radiation dose but to various degrees. NIR spectroscopy, laser Doppler and a combination of the three techniques are the most promising methods for characterising erythema.

Potent corticosteroid cream (mometasone furoate) significantly reduces acute radiation dermatitis: results from a double-blind, randomized study

PURPOSE

Radiation-induced dermatitis is a very common side effect of radiation therapy, and may necessitate interruption of the therapy. There is a substantial lack of evidence-based treatments for this condition. The aim of this study was to investigate the effect of mometasone furoate cream (MMF) on radiation dermatitis in a prospective, double-blind, randomized study.

MATERIAL AND METHODS

The study comprised 49 patients with node-negative breast cancer. They were operated on with sector resection and scheduled for postoperative radiotherapy using photons with identical radiation qualities and dosage to the breast parenchyma. The patients were randomized to receive either MMF or emollient cream. The cream was applied on the irradiated skin twice a week from the start of radiotherapy until the 12th fraction (24 Gy) and thereafter once daily until 3 weeks after completion of radiation. Both groups additionally received non-blinded emollient cream daily. The intensity of the acute radiation dermatitis was evaluated on a weekly basis regarding erythema and pigmentation, using a reflectance spectrophotometer together with visual scoring of the skin reactions.

RESULTS

MMF in combination with emollient cream treatment significantly decreased acute radiation dermatitis (P=0.0033) compared with emollient cream alone. There was no significant difference in pigmentation between the two groups.

CONCLUSIONS

Adding MMF, a potent topical corticosteroid, to an emollient cream is statistically significantly more effective than emollient cream alone in reducing acute radiation dermatitis.

Single dose irradiation response of pig skin: a comparison of brachytherapy using a single, high dose rate iridium-192 stepping source with 200 kV X-rays

An experimental brachytherapy model has been developed to study acute and late normal tissue reactions as a tool to examine the effects of clinically relevant multifractionation schedules. Pig skin was used as a model since its morphology, structure, cell kinetics and radiation-induced responses are similar to human skin. Brachytherapy was performed using a microSelectron high dose rate (HDR) afterloading machine with a single stepping source and a custom-made template. In this study the acute epidermal reactions of erythema and moist desquamation and the late dermal reactions of dusky mauve erythema and necrosis were evaluated after single doses of irradiation over a follow-up period of 16 weeks. The major aims of this work were: (a) to compare the effects of iridium-192 (192Ir) irradiation with effects after X-irradiation; (b) to compare the skin reactions in Yorkshire and Large White pigs; and (c) to standardize the methodology. For 192Ir irradiation with 100% isodose at the skin surface, the 95% isodose was estimated at the basal membrane, while the 80% isodose covered the dermal fat layers. After HDR 192Ir irradiation of Yorkshire pig skin the ED50 values (95% isodose) for moderate/severe erythema and moist desquamation were 24.8 Gy and 31.9 Gy, respectively. The associated mean latent period (+/- SD) was 39 +/- 7 days for both skin reactions. Late skin responses of dusky mauve erythema and dermal necrosis were characterized by ED50 values (80% isodose) of 16.3 Gy and 19.5 Gy, with latent periods of 58 +/- 7 days and 76 +/- 12 days, respectively. After X-irradiation, the incidence of the various skin reactions and their latent periods were similar. Acute and late reactions were well separated in time. The occurrence of skin reactions and the incidence of effects were comparable in Yorkshire and Large White pigs for both X-irradiation and HDR 192Ir brachytherapy. This pig skin model is feasible for future studies on clinically relevant multifractionation schedules in a brachytherapy setting.

Describing patients' normal tissue reactions: concerning the possibility of individualising radiotherapy dose prescriptions based on potential predictive assays of normal tissue radiosensitivity. Steering Committee of the BioMed2 European Union Concerted Action Programme on the Development of Predictive Tests of Normal Tissue Response to Radiation Therapy

Clinical radiotherapeutic doses are limited by the tolerance of normal tissues. Patients given a standard treatment exhibit a range of normal tissue reactions, and a better understanding of this individual variation might allow for individualisation of radiotherapeutic prescriptions, with consequent improvement in the therapeutic ratio. At present, there is no simple way to describe normal tissue reactions, which hampers communication between clinic and laboratory and between groups from different centres. There is also no method for comparing the severity of reactions in different normal tissues. This arises largely because there is no definition of a "normal" reaction, an "extreme" reaction or the particular term "over-reactor" (OR). This report proposes definitions for these terms, as well as a simple terminology for describing normal tissue reactions in patients having radiotherapy. The "normal" range represents the individual variation in normal tissue reactions amongst large numbers of patients treated in the same way which is within clinically acceptable limits. The term "OR" is applied to an individual whose reaction is more severe than the normal range but also implies that this forced a major change in the radiotherapeutic prescription or that the reactions were very severe or fatal. A "severe OR" would develop serious problems with a typical radical dose, while an "extreme OR" would have such difficulties at a much lower dose. To describe the normal range, a numerical scale is suggested, from 1 to 5, resistant to sensitive. The term "highly radiosensitive" (HR) is suggested for category 5. An "informal" relative scale, as suggested here, is quick and simple. It should allow comparison between different hospitals, compensate for differences in radiotherapeutic dose and technique and allow comparison of reactions between different anatomical sites. It should be adequate for discriminating patients at the extremes of the normal range from those at the centre. It is hoped that the definitions and terminology proposed here will aid communication in the field of predictive testing of normal tissue radiosensitivity.

A dielectric method for measuring early and late reactions in irradiated human skin

BACKGROUND AND PURPOSE

To measure the dielectric constant of irradiated human skin in order to test the feasibility of the dielectric measurements in the quantitation of acute and late radiation reactions.

MATERIALS AND METHODS

The dielectric constant of irradiated breast skin was measured at an electromagnetic frequency of 300 MHz in 21 patients during postmastectomy radiotherapy. The measurements were performed with an open-ended coaxial line reflection method. The irradiation technique consisted of an anterior photon field to the lymph nodes and a matched electron field to the chest wall using conventional fractionation of five fractions/week to 50 Gy. Fourteen out of the 21 patients were remeasured 2 years later and the skin was palpated for subcutaneous fibrosis.

RESULTS

At 5 weeks the dielectric constant had decreased by 31 and 39% for the investigated skin sites of the photon and electron fields, respectively. There was a statistically significant inverse correlation between the mean dielectric constant and the clinical score of erythema. An unexpected finding was a decrease of the dielectric constant of the contralateral healthy skin during radiotherapy. Two years later a statistically significant positive correlation was found between the dielectric constant at the irradiated skin sites and the clinical score of subcutaneous fibrosis.

CONCLUSIONS

Dielectric measurements non-invasively yield quantitative information concerning radiation-induced skin reactions.

Tumor response, mucosal reactions and late effects after conventional and hyperfractionated radiotherapy

BACKGROUND

Relationships between normal tissue reactions and tumor response to radiotherapy have generally been investigated in retrospective studies, with the attendant difficulties such as different times of treatment and lack of standard scales for scoring of normal tissue reactions. This study analyses the correlation between normal tissue reactions and tumor response in a randomized trial of hyperfractionation versus conventional radiotherapy.

MATERIALS AND METHODS

EORTC trial 22791, which accrued 325 T2-3, N0-1 and M0 oropharynx squamous cell carcinomas, compared conventional radiotherapy (70 Gy in 7 weeks) to a hyperfractionated regime (two daily irradiations of 1.15 Gy up to 80.5 Gy in 7 weeks). Acute and late toxicities were assessed according to the RTOG/EORTC scales. The variables were tumor regression at treatment completion, tumor control for unlimited follow-up, severity of acute mucosal reactions (grade of the peak reaction, time to onset of grade 2 mucositis, or duration of acute reactions of grade 3) and severity of late effects in normal tissues (late ulceration, cervical edema secondary to lymphatic drainage damage, late muscular fibrosis, or late mucosal necrosis as consequential damage). Kendall's rank correlation was used to assess the levels of significance of the correlation. The 95% confidence interval (95% CI) was calculated for each correlation tau-b coefficient.

RESULTS

Irradiation doses and overall treatment times were consistent between the treatment arms. The time to onset of patchy mucosal reactions was inversely correlated to tumor regression at treatment completion in the hyperfractionated arm (arm 2) but not in the conventional fractionation arm (arm 1). The other significant correlations were restricted to the following pairs of end-points and patient subgroups: acute mucositis of grade 3 versus tumor regression at the end of treatment in arm 2 for T2 tumors, late ulceration versus tumor control in arm 2 and acute mucosal reactions versus late effects in normal tissues in arm 2 for T3 tumors. By and large, the 95% CIs for Kendall's tau-b included zero and did not include 0.5, an indication that the comparison had sufficient power to detect a difference, if indeed one existed.

CONCLUSIONS

These results do not represent clinical evidence strong enough to demonstrate that individual differences in sensitivity influence the response of tumors to radiation.

Radiation therapy tolerance limits. For one or for all?--Janeway Lecture

BACKGROUND

The optimal use of radiation therapy for cancer treatment is hampered by the application of tolerance limits of normal tissues derived empirically from population averages. Such limits do not reflect the considerable differences from patient to patient in susceptibility to late radiation sequelae. Assays that accurately predict normal tissue tolerance in individual patients would permit real application of the concept of treatment to tolerance thereby increasing the probability of an uncomplicated cure for the population as a whole.

METHODS

A summary of laboratory research is presented to test the hypothesis that the cellular radiosensitivity of normal skin fibroblasts can predict the severity of late connective tissue damage that develops following radiotherapy. The pathogenesis of radiation reactions and the possible role of radiation induced cellular senescence in the development of clinical late effects are briefly reviewed.

RESULTS

Although the pathogenesis of radiation injury is highly complex, several clinical studies have demonstrated a significant correlation between fibroblast radiosensitivity and the severity of late sequelae from treatment. However, the precision and reproducibility of fibroblast cell survival assays are inadequate for routine clinical use. Newer assays incorporating insights into the effects of radiation on cellular senescence and cytokine production are being developed. Such assays may, in the future, be complemented or replaced by molecular and/or cytogenetic probes to derive robust estimates of individual tolerance.

CONCLUSIONS

The principle of prediction of tolerance to radiotherapy has been established. Although current assays lack the precision required for clinical use, the goal of individualized treatment to tolerance ultimately should be achieved.

Skin treatment with bepanthen cream versus no cream during radiotherapy--a randomized controlled trial

In several radiotherapy departments, dexpanthenol cream (Bepanthen 'Roche') has been used extensively to ameliorate acute radiotherapy skin reactions. The evidence base for this practice is obscure as no randomized trials have been performed. In the present clinical prospective study of 86 patients we have compared Bepanthen cream with no topical ointment at all. The cream was applied on randomly selected parts of treatment fields in laryngeal and breast cancer patients, and so each patient acted as his own control. Seven patients were withdrawn from analysis. Scoring of skin reactions in 16 laryngeal and 63 breast cancer patients was performed without knowledge of which area that had been given cream or not. Endpoints were a modified skin reaction grading according to EORTC/RTOG, and itching/pain in treated fields. The study did not indicate any clinically important benefits of using Bepanthen cream for ameliorating radiogenic skin reactions under the conditions applied.

A 100-year Nordic perspective on the dose-time problem in radiobiology

The therapeutic use of x-rays began almost immediately after their discovery by Röntgen, and within a few years two Swedish physicians could report the first successful treatment of human skin cancer by radiotherapy. Almost from the start it was clear that the biological effect of ionizing radiation depended critically on the exact distribution of the dose in time. The present paper reviews the historical development of dose-time concepts in radiotherapy as seen from a Nordic perspective. Among the topics reviewed are the discussion of single versus fractionated doses, Strandqvist's thesis and the development of power-law biological dose formulas, the effect of dose per fraction and of overall treatment time. It is only within the last 10-15 years that biologically and clinically important dissociation between the radiobiology of early- and late-responding human normal tissues has been appreciated. Biological developments have led to the proposal of altered fractionation schedules, hyperfractionation and accelerated fractionation, that are currently undergoing clinical trial.

The relationship between cellular radiation sensitivity and tissue response may provide the basis for individualising radiotherapy schedules

There is a wide variation in normal tissue reactions to radiotherapy and in many situations the severity of these reactions limits radiotherapy dose. Clinical fractionation studies carried out in Gothenburg have demonstrated that a large part of the spectrum of normal tissue reactions is due to differences in individual normal tissue sensitivity. If this variation in normal tissue reactions is due to differences in intrinsic cellular radiosensitivity, it should be possible to predict tissue response based on measurement of cellular sensitivity. Here we report the initial results of a study aimed at establishing whether a direct relationship exists between cellular radiosensitivity and tissue response. Ten fibroblasts strains, including four duplicates, were established from a group of patients in the Gothenburg fractionation trials who had received radiotherapy following mastectomy. Skin doses were measured and both acute and late skin changes were observed following radiotherapy. Right and left parasternal areas were treated with different dose fractionation schedules. Clonogenic assays were used to assess intrinsic cellular radiosensitivity, and all experiments were carried out without prior knowledge of the clinical response, or which strains were duplicates. Irradiation was carried out using 60Co gamma-rays at high dose-rate (HDR) of 1-2 Gy/min and low dose-rate (LDR) of 1 cGy/min. A spectrum of sensitivity was seen, with SF2 values of 0.17-0.28 at HDR and 0.25-0.34 at LDR, and values of D0.01 of 5.07-6.38 Gy at HDR and 6.43-8.12 Gy at LDR. Comparison of the in vitro results with the clinical normal tissue effects shows a correlation between cellular sensitivity and late tissue reactions, which is highly significant with p = 0.02. A correlation between cellular sensitivity and acute effects was noted in the left-sided parasternal fields, but not the right. This is thought to be coincidental, and without biological significance. Our results suggest that cellular sensitivity might form the basis for the development of an assay system capable of predicting late normal tissue effects to curative radiotherapy, which might allow dose escalation in some patients. Increased local control and cure, with unchanged or improved normal tissue complications, could result from such individualised radiotherapy prescriptions.

Quantification of patient to patient variation of skin erythema developing as a response to radiotherapy

A method is described to determine accurately skin redness during a course of radiotherapy using reflectance spectroscopy utilizing information from across the visible spectrum according to the L*a*b* color coordinate system. The method was used to quantify the development of skin erythema during and after electron beam irradiation of the chest wall following mastectomy. A number of factors were identified which could influence the wide variation in response seen between patients. These were: intra- and inter-observer variation; intra- and inter-patient variation and variation in the actual dose delivered. Statistical analysis, including an analysis of variance of inter- and intra-patient variation, revealed that the major factor that accounts for the observed difference between patients is a true inter-patient variation, with a coefficient of variation, corrected for intra-patient variation, of 43%. Within the narrow dose range administered in this study, there was no demonstrable dose-effect relationship, raising questions about the role of cell death in the basal layer of the epidermis in the pathogenesis of radiation induced erythema.

Evidence for individual differences in the radiosensitivity of human skin

Previously published clinical data have been re-analysed to investigate individual differences in the radiosensitivity of human skin. In the clinical studies, acute and late skin reactions were recorded for 254 breast cancer patients receiving radiotherapy to the internal mammary nodes following simple or modified radical mastectomy. Each patient was treated bilaterally with different fractionation schedules to the right and left fields. Patients were assigned prospectively to 10 different treatment groups of 11-35 patients each, with all patients in a group receiving the same pair of fractionation schedules to the right and left fields. In the present study, correlations between the skin reactions in the two treatment fields per patient were investigated. For each of three different endpoints--peak reflectance measure of erythema, peak acute skin reaction score, and a ranking measure of the progression rate of telangiectasia--significant correlations were found between the levels of skin injury to the right and left treatment fields of the patients in most treatment groups. Although there were correlations between the absorbed doses in the right and left fields, statistical analyses indicated that dose effects were not sufficient to explain fully the patient-to-patient differences in skin response. Thus, these data provide evidence for the existence of individual differences in the radiation response of human skin, both for early and late effects. Whether these differences are dominated by heterogeneity in intrinsic cell radiosensitivity or by other factors has yet to be determined. However, there was no clear evidence of a correlation between the acute and late endpoints, suggesting that the individual differences in radiosensitivity are not dominated by a common genetic component expressed equally in all cells.

Individual variation and dose dependency in the progression rate of skin telangiectasia

The progression rate of late skin telangiectasia after radiotherapy has been studied prospectively in patients for various fractionation schedules and dose levels. The degree of telangiectasia was scored on an arbitrary scale ranging from no detectable to totally confluent telangiectasia. Skin telangiectasia showed a progressive development at least up to 10 years. The rate of progression was strongly dose dependent. This finding has two important implications: the dose-latency relationship is steep, and the steepness of the dose-response relationship increases with the follow-up time. The most striking finding in this study was that the individual variation in progression rate was very large for the same treatment with a documented small variation in dose. For example, the latency for telangiectasia score 2 ranged between 17 and 90 months after 35 fractions of 1.8 Gy. The reasons for the large individual variation in progression rate are unclear and will be investigated further.

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)

Skin response to cobalt 60 irradiation and the consequences for matching the color of facial prostheses

A radiotherapy treatment (60Co) of cancer in the head and neck region causes side effects in the skin that postpone the facial prosthetic treatment. The increasing and fading erythema and pigmentation of the skin was investigated with the use of a subtractive colorimeter. This method was verified with photographs scored according to the Oxford scoring system. Fourteen patients were investigated during a period of 24 weeks. The mean colorimetric skin response showed a peak 6 weeks after the onset of irradiation. Six to 7 weeks later, there was no significant difference between the skin color before and after irradiation. At this time the dry desquamation of the skin is healed. From this viewpoint, the color matching procedure for a facial prosthesis may start not earlier than 15 weeks from the onset of irradiation. If a nonirradiated control field in the facial region is present, a color match for the facial prosthesis can be started just after the irradiation period.

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.

The influence of fraction size in radiotherapy on the late normal tissue reaction--II: Comparison of the effects of daily and twice-a-week fractionation on human skin

A comparison of the normal tissue reactions to daily and twice-a-week fractionation over 4 to 6 weeks was performed on postoperatively irradiated parasternal fields in patients with breast cancer. The radiation used was electron beams at 12-13 MeV. We have previously reported that the overall treatment time was of importance for establishment of iso-effect relationships for the acute skin erythema. In this paper we present the degree of telangiectasia after 5 years. Generally, a more pronounced late reaction was found after twice-a-week fractionation than was predicted from the acute reactions. The findings imply that the cumulative radiation effect (CRE) formula has to be modified for both acute and late reactions in certain clinical situations. The main conclusion is that the iso-effect relationship varies significantly over the dose range used in clinical radiotherapy. In the dose range of 30 fractions between 1.6 and 2.1 Gy in 6 weeks, the slope of the curve for iso-effect dose versus number of fractions varies between 0.26 and 0.35, the beta/alpha-ratios between 0.22 and 0.37 Gy-1 and the RBE 2 Fractions/week/5 Fractions/week between 1.97 and 1.82.

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.

Effect of different radiation fractionation schedules on metastases from an oesophageal carcinoma

Subcutaneous metastases from an oesophageal carcinoma were irradiated using different schedules. The results have to be evaluated with greatest caution but indicate that with the same CRE value, few fractions caused less skin reactions than several, and the size of the shoulder of the cell survival curve was of the order of 0.7 Gy.