Basal cell density in human skin for various fractionation schedules in radiotherapy

Epidermal Keratinocyte Depletion during Five Weeks of Radiotherapy is Associated with DNA Double-Strand Break Foci, Cell Growth Arrest and Apoptosis: Evidence of Increasing Radioresponsiveness and Lack of Repopulation; the Number of Melanocytes Remains Unchanged

During fractionated radiotherapy, epithelial cell populations are thought to decrease initially, followed by accelerated repopulation to compensate cell loss. However, previous findings in skin with daily 1.1 Gy dose fractions indicate continued and increasing cell depletion. Here we investigated epidermal keratinocyte response with daily 2 Gy fractions as well as accelerated and hypofractionation. Epidermal interfollicular melanocytes were also assessed. Skin-punch biopsies were collected from breast cancer patients before, during and after mastectomy radiotherapy to the thoracic wall with daily 2 Gy fractions for 5 weeks. In addition, 2.4 Gy radiotherapy four times per week and 4 Gy fractions twice per week for 5 weeks, and two times 2 Gy daily for 2.5 weeks, were used. Basal keratinocyte density of the interfollicular epidermis was determined and immunostainings of keratinocytes for DNA double-strand break (DSB) foci, growth arrest, apoptosis and mitosis were quantified. In addition, interfollicular melanocytes were counted. Initially minimal keratinocyte loss was observed followed by pronounced depletion during the second half of treatment and full recovery at 2 weeks post treatment. DSB foci per cell peaked towards the end of treatment. p21-stained cell counts increased during radiotherapy, especially the second half. Apoptotic frequency was low throughout radiotherapy but increased at treatment end. Mitotic cell count was significantly suppressed throughout radiotherapy and did not recover during weekend treatment gaps, but increased more than threefold compared to unexposed skin 2 weeks post-radiotherapy. The number of melanocytes remained constant over the study period. Germinal keratinocyte loss rate increased gradually during daily 2 Gy fractions for 5 weeks, and similarly for hypofractionation. DSB foci number after 2 Gy irradiation revealed an initial radioresistance followed by increasing radiosensitivity. Growth arrest mediated by p21 strongly suggests that cells within or recruited into the cell cycle during treatment are at high risk of loss and do not contribute significantly to repopulation. It is possible that quiescent (G₀) cells at treatment completion accounted for the accelerated post-treatment repopulation. Recent knowledge of epidermal tissue regeneration and cell cycle progression during genotoxic and mitogen stress allows for a credible explanation of the current finding. Melanocytes were radioresistant regarding cell depletion.

A Retrospective Analysis of Toxicity and Efficacy for 2 Hypofractionated Irradiation Schedules Versus a Conventional One for Post-Mastectomy Adjuvant Radiotherapy in Breast Cancer

INTRODUCTION

The aim of this analysis was a retrospective evaluation of the efficacy and toxicity of 2 hypofractionated irradiation schedules compared to conventional therapy in post-mastectomy patients.

METHODS

3 irradiation schedules were analyzed: 48.30 Gy in 21 fractions (group A, n = 60), 42.56 Gy in 16 fractions (group B, n = 27) and 50 Gy in 25 fractions (group C, n = 30) of the front chest wall. All groups were also treated with a supraclavicular field, with 39.10 Gy in 17 fractions (group A), 37.24 Gy in 14 fractions (group B) or 45 Gy in 25 fractions (group C).

RESULTS

No local recurrences were noted in any group during 36 months of follow-up. Acute skin toxicity presented in all groups, with 58.3%, 70.4% and 60% of grade I; 35%, 25.9% and 40% of grade II; 6.7%, 3.7% and 0% of grade III being seen in groups A, B and C, respectively. Late skin toxicity was noted only as grade I in 16.7%, 25.9% and 26.7% of groups A, B and C, respectively. No significant difference was noted among all groups for either acute or late skin toxicity, or for radio-pneumonitis (chi² test, p > 0.05).

CONCLUSION

All schedules were equally effective with equivalent toxicity. A prospective randomized study is needed to confirm our results.

Where Do We Look for Markers of Radiotherapy Fraction Size Sensitivity?

The response of human normal tissues to radiotherapy fraction size is often described in terms of cellular recovery, but the causal links between cellular and tissue responses to ionising radiation are not necessarily straightforward. This article reviews the evidence for a cellular basis to clinical fractionation sensitivity in normal tissues and discusses the significance of a long-established inverse association between fractionation sensitivity and proliferative indices. Molecular mechanisms of fractionation sensitivity involving DNA damage repair and cell cycle control are proposed that will probably require modification before being applicable to human cancer. The article concludes by discussing the kind of correlative research needed to test for and validate predictive biomarkers of tumour fractionation sensitivity.

Cancer etiology. Variation in cancer risk among tissues can be explained by the number of stem cell divisions

Some tissue types give rise to human cancers millions of times more often than other tissue types. Although this has been recognized for more than a century, it has never been explained. Here, we show that the lifetime risk of cancers of many different types is strongly correlated (0.81) with the total number of divisions of the normal self-renewing cells maintaining that tissue's homeostasis. These results suggest that only a third of the variation in cancer risk among tissues is attributable to environmental factors or inherited predispositions. The majority is due to "bad luck," that is, random mutations arising during DNA replication in normal, noncancerous stem cells. This is important not only for understanding the disease but also for designing strategies to limit the mortality it causes.

Fraction size in radiation treatment for breast conservation in early breast cancer

BACKGROUND

Shortening the duration of radiation therapy would benefit women with early breast cancer treated with breast conserving surgery. It may also improve access to radiation therapy by improving efficiency in radiation oncology departments globally. This can only happen if the shorter treatment is as effective and safe as conventional radiation therapy. This is an updated version of the original Cochrane Review published in Issue 3, 2008.

OBJECTIVES

To determine the effect of altered radiation fraction size on outcomes for women with early breast cancer who have undergone breast conserving surgery.

SEARCH STRATEGY

We searched the Cochrane Breast Cancer Group Specialised Register, MEDLINE, EMBASE and the WHO ICTRP search portal to June 2009, reference lists of articles and relevant conference proceedings. We applied no language constraints.

SELECTION CRITERIA

Randomised controlled trials of unconventional versus conventional fractionation in women with early breast cancer who had undergone breast conserving surgery.

DATA COLLECTION AND ANALYSIS

The authors performed data extraction independently, with disagreements resolved by discussion. We sought missing data from trial authors.

MAIN RESULTS

Four trials reported on 7095 women. The women were highly selected: tumours were node negative and 89.8% were smaller than 3 cm. Where the breast size was known, 87% had small or medium breasts. The studies were of low to medium quality. Unconventional fractionation (delivering radiation therapy in larger amounts each day but over fewer days than with conventional fractionation) did not affect: (1) local recurrence risk ratio (RR) 0.97 (95% CI 0.76 to 1.22, P = 0.78), (2) breast appearance RR 1.17 (95% CI 0.98 to 1.39, P = 0.09), (3) survival at five years RR 0.89 (95% CI 0.77 to 1.04, P = 0.16). Acute skin toxicity was decreased with unconventional fractionation: RR 0.21 (95% CI 0.07 to 0.64, P = 0.007).

AUTHORS' CONCLUSIONS

Two new studies have been published since the last version of the review, altering our conclusions. We have evidence from four low to medium quality randomised trials that using unconventional fractionation regimens (greater than 2 Gy per fraction) does not affect local recurrence, is associated with decreased acute toxicity and does not seem to affect breast appearance or late toxicity for selected women treated with breast conserving therapy. These are mostly women with node negative tumours smaller than 3 cm and negative pathological margins. Long-term follow up (> 5 years) is available for a small proportion of the patients randomised. Longer follow up is required for a more complete assessment of the effect of altered fractionation.

Fraction size in radiation treatment for breast conservation in early breast cancer

BACKGROUND

Shortening the duration of radiation therapy would benefit women with early breast cancer treated with breast conservation. It may also improve access to radiation therapy by improving efficiency in radiation oncology departments globally. This can only happen if the shorter treatment is as effective and safe as conventional radiation therapy.

OBJECTIVES

To assess the effects of altered fraction size on women with early breast cancer who have undergone breast conserving surgery.

SEARCH STRATEGY

We searched the Cochrane Breast Cancer Group Specialised Register (June 2006), MEDLINE (November 2006), EMBASE (November 2006), reference lists for articles, and relevant conference proceedings. No language constraints were applied.

SELECTION CRITERIA

Randomised controlled trials of unconventional versus conventional fractionation in women with early breast cancer who had undergone breast conserving surgery.

DATA COLLECTION AND ANALYSIS

Data extraction was performed independently by the authors with disagreements resolved by discussion. Missing data was sought by contacting the authors concerned.

MAIN RESULTS

Two trials were included and reported on 2644 women. The women were highly selected with node negative tumours smaller than 5 cm and negative pathological margins; 46% of the women had a cup separation size of less than 25 cm. The studies were of high quality. Data for local recurrence and breast appearance were not available in a form which could be combined. Unconventional fractionation (delivering radiation therapy in larger amounts each day but over fewer days than with conventional fractionation) did not appear to affect: (1) local-recurrence free survival (absolute difference 0.4%, 95% CI -1.5% to 2.4%), (2) breast appearance (risk ratio (RR) 1.01, 95% CI 0.88 to 1.17; P = 0.86), (3) survival at five years (RR 0.97, 95% CI 0.78 to 1.19; P = 0.75), (4) late skin toxicity at five years (RR 0.99, 95% CI 0.44 to 2.22; P = 0.98, or (5) late radiation toxicity in sub-cutaneous tissue (RR 1.0, 95% CI 0.78 to 1.28; P = 0.99).

AUTHORS' CONCLUSIONS

We have evidence from two high quality randomised trials that the use of unconventional fractionation regimes (greater than 2 Gy per fraction) does not affect breast appearance or toxicity and does not seem to affect local recurrence for selected women treated with breast conserving therapy. These are women with node negative tumours smaller than 5 cm and negative pathological margins. Two new trials have been published in March 2008. Their results are consistent with our findings. The results of these trials will be incorporated in the next update of this review.

The preventive effect of vitamin D3 on radiation-induced hair toxicity in a rat model

Our aim is to investigate the protective effect of vitamin D3 especially from radiation-induced hair toxicity. A model of skin radiation injury was developed and a single fraction of 20 Gy Gamma irradiation was applied to the right dorsal skin of fourteen rats. All animals were randomly divided into 2 groups: Group I: irradiation alone (n = 7) and Group II: irradiation and 0.2 microg vitamin D3 given IM (n = 7). Fifty days after post-irradiation rats were sacrificed. The outcomes were evaluated on the basis of histopathological findings and immunohistochemical staining for Vitamin D receptor (VDR) in skin and hair follicles. The number of hair follicles in the radiation field for the group of animals irradiated without pretreatment was significantly lower than outside of the irradiated area (p = 0.016) as it is expected. Contrarily the number of hair follicles did not show significant difference in the pretreated group between the irradiated field and outside of the fields (p = 0,14). Skin of the vitamin D3 pretreated group demonstrated stronger immunoreactivity for VDR compared to irradiation alone group. These results indicate that administration of vitamin D3 may protect hair follicles from radiation toxicity. Further clinical trials should be conducted to prove the preventive effect of vitamin D3 as well as dosing and timing of the agent on radiation-induced alopecia.

The evaluation of low dose hyper-radiosensitivity in normal human skin

BACKGROUND AND PURPOSE

The laboratory phenomenon of low dose hyper-radiosensitivity (LDHRS) describes an excess of cell kill at doses below 1Gy relative to that predicted by the linear quadratic model. These data have stimulated clinical investigation into LDHRS in vivo.

PATIENTS AND METHODS

Skin was used as a model of normal human tissue. Two studies were initiated investigating the response to low doses of radiation. Study 1 compared once daily skin doses of approximately 0.5 and >1.0Gy in 24 patients receiving pelvic radiotherapy. Skin biopsies before and during radiotherapy were analysed histologically to assess the basal cell density (BCD). Study 2 compared two regimens of equal dose/time intensity--an ultrafractionated regimen (0.5Gy TDS x 12 days) with a conventional regimen (1.5Gy OD x 12 days). Skin biopsies taken during treatment assessed BCD and proliferative index. In both studies the changes in BCD were compared using non-linear regression analysis.

RESULTS

Study 1. The results show a significantly greater reduction in BCD in the low dose group when BCD is plotted against dose. This effect is lost when BCD is plotted against time Study 2. The results demonstrate a significantly greater reduction in BCD in the higher dose/fraction arm. The proliferative response was similar in both treatment groups.

CONCLUSIONS

These data suggest that LDHRS does not occur in skin following doses of approximately 0.5Gy/fraction when regimens of equal dose/time intensity are compared. As only small volumes of normal tissue were irradiated it is difficult to predict the biological relevance of this with respect to larger field low dose per fraction irradiation regimens or risk of cancer induction. Equally we cannot extrapolate to effects resulting from exposure to doses <0.5Gy or to the effects of low doses on other endpoints.

Time factor for acute tissue reactions following fractionated irradiation: a balance between repopulation and enhanced radiosensitivity

Experimental data for acute radiation-induced skin reactions are reviewed. These show that for dose fractionation schedules with gaps, repopulation is initiated after a lag period. After this lag period, the isoeffective dose for a given level of skin reaction first increases rapidly, but then slows. The timing of the lag period is related to the total turnover time of the tissue under investigation and, for example, is shorter in rodent skin than in pig or human skin. At the point when accelerated repopulation is initiated, there is a major shortening of the turnover time of the target cell population. At this time, there is evidence, for a short period, for an increase in radiosensitivity of the surviving stem cells in a number of acutely responding normal tissues. This effect is clearly illustrated by the results of experiments using sequential dose fractionation schedules. Prolongation of the schedule from 'short' to schedules that include irradiation over the period when the cell turnover is accelerated is associated with a marked increase in tissue radiosensitivity. Clinically, this is best illustrated by a comparison of the effects of accelerated fractionation schedules, involving multiple fractions/day, with daily fractionation schedules. The increase in radiosensitivity produced by the prolongation of the treatment from 2 to 4-5 weeks was equivalent to > or =1 Gy day(-1). Comparable findings were obtained from animal studies. In the oral mucosa of mice, the initiation of accelerated cell proliferation in surviving cells is associated with the loss of dose sparing by subsequent dose fractionation due to the loss of the capacity to repair sublethal damage. Studies in pig and human skin have indicated that increased radiosensitivity is associated with a loss of cells in the G1 phase of the cell cycle. A collation of these two sets of findings suggests that the repair of sublethal damage takes place over this phase of the cell cycle. One clinical implication of these findings is that the alpha/beta ratio for acute skin reaction changes with the length of the overall treatment time; it is approximately 4.0 Gy for 'short' fractionation schedules that avoid any shortening of the cell cycle time. This increases to 11.2-13.3 Gy for schedules given in 3-4 weeks and to approximately 35 Gy for schedules given in 5-6 weeks. Results for pig skin were in total agreement with those for human skin.

Induction of p53 expression in skin by radiotherapy and UV radiation: a randomized study

BACKGROUND

p53 protein plays an important role in the response to DNA damage, and radiotherapy can cause radiation dermatitis. p53 and p21 levels increase in vitro when DNA is damaged by UVA, UVB, or gamma-radiation. To determine whether this response occurs in human skin and predicts the level of radiation dermatitis, we investigated levels of p53 and p21 in skin exposed to different types of radiation as part of a randomized study of women with breast cancer to evaluate topical steroid or emollient cream treatments for radiation dermatitis of their irradiated breast.

METHODS

After surgery but before receiving tangential 5-mV photo-beam radiotherapy (2 Gy and 54 Gy) to the affected breast parenchyma, multiple areas on the backs of 50 women were irradiated with UVA and other areas were irradiated with UVB. Skin biopsy samples were taken from areas of normal unirradiated skin and all irradiated areas, and p53 and p21 were detected immunohistochemically. All statistical tests are two-sided.

RESULTS

In skin irradiated with UVA or UVB, medians of 4.4% (range = 0%-40.5%) or 45.5% (range = 5.3%-74.6%) p53-positive keratinocytes, respectively, were observed. Radiotherapy produced medians of 31.0% (range = 0%-79.3%) p53-immunoreactive cells after 2 Gy of radiation and 83.2% (range = 37.6%-95.2%) after 54 Gy of radiation. Despite large interindividual differences in p53 response, comparable increases in epidermal p53 response were independent of the type of radiation. A correlation between p53 and p21 was also evident (r(s) =.78). In breast skin, there was no association between the p53 response and the degree of erythema (a measure of radiation dermatitis) and no statistically significant difference between treatment arms and p21/p53 responses.

CONCLUSIONS

Individual responses to radiation-induced DNA damage varied widely and may be independent of the type of radiation. The epidermal p53 response does not predict the degree of radiation dermatitis.

Repair, repopulation and cell cycle redistribution in rat foot skin

The influence of the phenomena of the repair of sublethal damage, repopulation and the role of the reassortment of surviving clonogenic target cells within the cell cycle have been examined in the foot skin of rats using a series of split dose experiments. The dose-related incidence of moist desquamation was used as an end-point. Initially the iso-effect dose for moist desquamation (ED50) increased with an increasing time interval (1-22 h) between two equal fractions. This effect was attributed to the well established phenomenon of the repair of sublethal damage. This appeared to be maximal with a 22 h gap between fractions. A further increase in the time interval, from 2-7 days, between two equal fractions resulted in a decrease in the ED50 value for moist desquamation. The phenomenon is most likely to be explained by a shortening of the cell cycle time in surviving epithelial target cells as repopulation first initiated. With intervals between two fractions of greater than 10 days the ED50 for moist desquamation again increased. This is likely to represent an increase in the number of epidermal target cells (repopulation). Further evidence for the effect of a reassortment of cells in the cell cycle has come from another study in which a half-tolerance priming dose of 16.8 Gy was followed by three daily fractions starting 48 or 125 h after the priming dose. The ED50 for moist desquamation based on the total fractionated dose (three fractions) was significantly lower (P < 0.05) after the longer time interval, i.e. fractions given on days 5, 6 and 7 after the primary dose. These findings were supported by the results of a cell proliferation kinetic study and jointly question the validity of a frequently made assumption of equal biological effect per fraction in a prolonged fractionated irradiation schedule.

Response of human hair cortical cells to fractionated radiotherapy

Hair cortical cell counting (HCCC) represents a non-invasive, in-vivo measure of cell kill in the human integument. Sixty-six patients undergoing conventionally fractionated, external beam radiotherapy for early stage carcinoma of the prostate had groin hair samples counted. This technique is a sensitive and reproducible measure of radiation effect and may have applicability as an in-vivo prediction tool or in the field of biological dosimetry. A repopulative follicular response occurring at 3-4 weeks may explain flattening of the dose response curve.

Review article: effects of radiation on the cell proliferation kinetics of epithelial tissues--therapeutic implications

The cell kinetic responses of the epithelia of the skin, oral mucosa and intestine to photon irradiation are reviewed. One of the fundamental assumptions made in the development of mathematical models, used to predict the acute response of normal tissues to changes in fractionation protocols, is "equal effect per fraction". There is now accumulating cell kinetic data to indicate that this assumption is unlikely to be valid. The implications of these findings are discussed.

Factors influencing the degree of erythematous skin reactions in humans

Dose-response relationships have been studied using an ordinal visual scale and reflectance spectrophotometry data from 123 treatment sites on 110 patients treated with 10 dose fractions over 12-14 days. Dose rates varied between 3 and 240 Gy/h and total doses of between 25 and 41 Gy were given using teletherapy apparatus. We found qualitative scoring of erythematous skin reactions to be subject to considerable inter- and intra-observer variation. Reflectance spectrophotometry provided more reproducible information, some of which was undetectable by naked eye. Baseline erythema readings were significantly higher in male patients and at anatomical sites of previous heavy UV exposure. In addition, a pronounced decline in erythema readings during the second week of therapy and 'reciprocal vicinity' (abscopal) effects adjacent to the field, undetected by the eye, were observed in a subset of patients. Meaningful dose-response relationships could be derived only from reflectance data with peak change from the pretreatment baseline measure providing the best discrimination. Peak erythema measures following treatment were found to depend on the age and gender of the patient as well as the treatment site and its baseline erythema measurement. This was independent of the total dose administered or the instantaneous dose rate at which it was delivered. The rate of erythema development was also dose rate dependent but only weakly dependent on the biological dose intensity (Gy equiv./day) of the treatment course. The data raise the question of whether irradiation-induced erythema is exclusively a secondary phenomenon occurring as a result of basal cell killing. The short repair half time value of 0.06 h obtained by direct analysis is perplexing and may reflect a dose rate-dependent physiological vasodilatory response to irradiation and/or a multi-component cellular repair process.

Does the interval between fractions matter in the range of 4-8 h in radiotherapy? A study of acute and late human skin reactions

Accelerated radiotherapy has the potential to increase local control of rapidly growing tumours. To determine the necessary time interval for complete repair of sublethal damage in normal tissue in a clinical situation, we have compared the acute and late skin reactions with 8 and 24 h between fractions, using the same dose per fraction and total dose. Forty-nine breast cancer patients participated in this study, and received bilateral parasternal irradiation to 50 Gy with 2 Gy per fraction as part of their adjuvant postoperative radiotherapy. The time interval between daily fractions was always 8 h on the left field and 24 h on the right, and the total treatment time was 2.5 and 5 weeks, respectively. The acute endpoint was erythema, measured by reflectance spectrophotometry and an acute reaction score for erythema and desquamation. The late endpoint was telangiectasia, scored on an arbitrary scale. The results have also been compared with those in a previously treated group of patients with 4 and 24 h between fractions. The degree of acute reactions was decreased with an 8-h interval compared with 24 h between fractions with the peak acute score as endpoint; no difference was seen with the peak reflectance measurements. The maximal expression occurs approximately 1 week earlier with the accelerated schedule, possibly as a consequence of the reduction of the treatment time. The pattern of the acute reaction for 8 h between fractions is similar to that for 4 h.(ABSTRACT TRUNCATED AT 250 WORDS)