Prediction of normal tissue response and individualization of doses in radiotherapy

In Silico Ventilation Within the Dose-Volume is Predictive of Lung Function Post-radiation Therapy in Patients with Lung Cancer

Lung cancer is a leading cause of death worldwide. Radiation therapy (RT) is one method to treat this disease. A common side effect of RT for lung cancer is radiation-induced lung damage (RILD) which leads to loss of lung function. RILD often compounds pre-existing smoking-related regional lung function impairment. It is difficult to predict patient outcomes due to large variability in individual response to RT. In this study, the capability of image-based modelling of regional ventilation in lung cancer patients to predict lung function post-RT was investigated. Twenty-five patient-based models were created using CT images to define the airway geometry, size and location of tumour, and distribution of emphysema. Simulated ventilation within the 20 Gy isodose volume showed a statistically significant negative correlation with the change in forced expiratory volume in 1 s 12-months post-RT (p = 0.001, R = - 0.61). Patients with higher simulated ventilation within the 20 Gy isodose volume had a greater loss in lung function post-RT and vice versa. This relationship was only evident with the combined impact of tumour and emphysema, with the location of the emphysema relative to the dose-volume being important. Our results suggest that model-based ventilation measures can be used in the prediction of patient lung function post-RT.

Human mesenchymal stem cells enhance the systemic effects of radiotherapy

The outcome of radiotherapy treatment might be further improved by a better understanding of individual variations in tumor radiosensitivity and normal tissue reactions, including the bystander effect. For many tumors, however, a definitive cure cannot be achieved, despite the availablity of more and more effective cancer treatments. Therefore, any improvement in the efficacy of radiotherapy will undoubtedly benefit a significant number of patients. Many experimental studies measure a bystander component of tumor cell death after radiotherapy, which highlights the importance of confirming these observations in a preclinical situation. Mesenchymal stem cells (MSCs) have been investigated for use in the treatment of cancers as they are able to both preferentially home onto tumors and become incorporated into their stroma. This process increases after radiation therapy. In our study we show that in vitro MSCs, when activated with a low dose of radiation, are a source of anti-tumor cytokines that decrease the proliferative activity of tumor cells, producing a potent cytotoxic synergistic effect on tumor cells. In vivo administration of unirradiated mesenchymal cells together with radiation leads to an increased efficacy of radiotherapy, thus leading to an enhancement of short and long range bystander effects on primary-irradiated tumors and distant-non-irradiated tumors. Our experiments indicate an increased cell loss rate and the decrease in the tumor cell proliferation activity as the major mechanisms underlying the delayed tumor growth and are a strong indicator of the synergistic effect between RT and MSC when they are applied together for tumor treatment in this model.

Among 45 variants in 11 genes, HDM2 promoter polymorphisms emerge as new candidate biomarker associated with radiation toxicity

Due to individual variations in radiosensitivity, biomarkers are needed to tailor radiation treatment to cancer patients. Since single nucleotide polymorphisms (SNPs) are frequent in human, we hypothesized that SNPs in genes that mitigate the radiation response are associated with radiotoxicity, in particular late complications to radiotherapy and could be used as genetic biomarkers for radiation sensitivity. A total of 155 patients with nasopharyngeal cancer were included in the study. Normal tissue fibrosis was scored using RTOG/EORTC grading system. Eleven candidate genes (ATM, XRCC1, XRCC3, XRCC4, XRCC5, PRKDC, LIG4, TP53, HDM2, CDKN1A, TGFB1) were selected for their presumed influence on radiosensitivity. Forty-five SNPs (12 primary and 33 neighboring) were genotyped by direct sequencing of genomic DNA. Patients with severe fibrosis (cases, G3–4, n = 48) were compared to controls (G0–2, n = 107). Results showed statistically significant (P < 0.05) association with radiation complications for six SNPs (ATM G/A rs1801516, HDM2 promoter T/G rs2279744 and T/A rs1196333, XRCC1 G/A rs25487, XRCC5 T/C rs1051677 and TGFB1 C/T rs1800469). We conclude that these six SNPs are candidate genetic biomarkers for radiosensitivity in our patients that have cumulative effects as patients with severe fibrosis harbored significantly higher number of risk alleles than the controls (P < 0.001). Larger cohort, independent replication of these findings and genome-wide association studies are required to confirm these results in order for SNPs to be used as biomarkers to individualize radiotherapy on genetic basis.

Direct and bystander radiation effects: a biophysical model and clinical perspectives

In planning treatment for each new patient, radiation oncologists pay attention to the aspects that they control. Thus their attention is usually focused on volume and dose. The dilemma for the physician is how to protract the treatment in a way that maximizes control of the tumor and minimizes normal tissue injury. The initial radiation-induced damage to DNA may be a biological indicator of the quantity of energy transferred to the DNA. However, until now the biophysical models proposed cannot explain either the early or the late adverse effects of radiation, and a more general theory appears to be required. The bystander component of tumor cell death after radiotherapy measured in many experimental works highlights the importance of confirming these observations in a clinical situation.

Low-dose radiation hyper-radiosensitivity in multicellular tumour spheroids

OBJECTIVE

We propose and study a new model aimed at describing the low-dose hyper-radiosensitivity phenomenon appearing in the survival curves of different cell lines.

METHODS

The model uses the induced repair assumption, considering that the critical dose at which this mechanism begins to act varies from cell to cell in a given population. The model proposed is compared with the linear-quadratic model and the modified linear-quadratic model, which is commonly used in literature and in which the induced repair is taken into account in a heuristic way. The survival curve for the MCF-7 line of human breast cancer is measured at low absorbed doses and the uncertainties in these doses are estimated using thermoluminiscent dosemeters.

RESULTS

It is shown that these multicellular spheroids present low-dose hyper-radiosensitivity. The new model permits an accurate description of the data of two human cell lines (previously published) and of the multicellular spheroids of the MCF-7 line here measured.

CONCLUSION

The model shows enough flexibility to account for data with very different characteristics and considers in a faithful way the hypothesis of the repair induction.

Monte Carlo role in radiobiological modelling of radiotherapy outcomes

Radiobiological models are essential components of modern radiotherapy. They are increasingly applied to optimize and evaluate the quality of different treatment planning modalities. They are frequently used in designing new radiotherapy clinical trials by estimating the expected therapeutic ratio of new protocols. In radiobiology, the therapeutic ratio is estimated from the expected gain in tumour control probability (TCP) to the risk of normal tissue complication probability (NTCP). However, estimates of TCP/NTCP are currently based on the deterministic and simplistic linear-quadratic formalism with limited prediction power when applied prospectively. Given the complex and stochastic nature of the physical, chemical and biological interactions associated with spatial and temporal radiation induced effects in living tissues, it is conjectured that methods based on Monte Carlo (MC) analysis may provide better estimates of TCP/NTCP for radiotherapy treatment planning and trial design. Indeed, over the past few decades, methods based on MC have demonstrated superior performance for accurate simulation of radiation transport, tumour growth and particle track structures; however, successful application of modelling radiobiological response and outcomes in radiotherapy is still hampered with several challenges. In this review, we provide an overview of some of the main techniques used in radiobiological modelling for radiotherapy, with focus on the MC role as a promising computational vehicle. We highlight the current challenges, issues and future potentials of the MC approach towards a comprehensive systems-based framework in radiobiological modelling for radiotherapy.

The importance of bystander effects in radiation therapy in melanoma skin-cancer cells and umbilical-cord stromal stem cells

PURPOSE

To examine direct and bystander radiation-induced effects in normal umbilical-cord stromal stem cell (HCSSC) lines and in human cancer cells.

MATERIALS AND METHODS

The UCSSC lines used in this study were obtained in our laboratory. Two cell lines (UCSSC 35 and UCSSC 37) and two human melanoma skin-cancer cells (A375 and G361) were exposed to ionizing radiation to measure acute radiation-dosage cell-survival curves and radiation-induced bystander cell-death response. Normal cells, although extremely sensitive to ionizing radiation, were resistant to the bystander effect whilst tumor cells were sensitive to irradiated cell-conditioned media, showing a dose-response relationship that became saturated at relatively low doses. We applied a biophysical model to describe bystander cell-death through the binding of a ligand to the cells. This model allowed us to calculate the maximum cell death (χ(max)) produced by the bystander effect together with its association constant (K(By)) in terms of dose equivalence (Gy). The values obtained for K(By) in A375 and G361 cells were 0.23 and 0.29 Gy, respectively.

CONCLUSION

Our findings help to understand how anticancer therapy could have an additional decisive effect in that the response of sub-lethally hit tumor cells to damage might be required for therapy to be successful because the survival of cells communicating with irradiated cells is reduced.

The influence of gender- and age-related differences in the radiosensitivity of hematopoietic progenitor cells detected in steady-state human peripheral blood

To investigate the importance of gender and aging on the individual radiosensitivity of lineage-committed myeloid hematopoietic stem/progenitor cells (HSPCs) detected in mononuclear cells (MNCs) of steady-state human peripheral blood (PB), the clonogenic survival of HPCs, including colony-forming unit-granulocyte macrophage; burst-forming unit-erythroid; colony-forming unit-granulocyte-erythroid-macrophage-megakaryocyte cells derived from MNCs exposed to 0.5 Gy and 2 Gy X-irradiation were estimated. MNCs were prepared from the buffy-coats of 59 healthy individual blood donors. The results showed that large individual differences exist in the number of HSPCs, as well as in the surviving fraction of cells. Furthermore, the number of progenitor cells strongly correlated with their surviving fraction, suggesting that the radiosensitivity of hematopoietic progenitor cells decreases with the number of cells in the 10(5) cells population. A statistically significant negative correlation was observed between the surviving fraction observed at a dose of 0.5 Gy and the age of an individual, however, none of these correlations were observed after 2 Gy irradiation. No statistically significant difference was observed in individual radiosensitivity between males and females at either radiation dose. The present results indicated a correlation between the individual responsiveness of HSPCs to ionizing irradiation, especially to low dose irradiation, and aging.

Radiation induced apoptosis and initial DNA damage are inversely related in locally advanced breast cancer patients

Background

DNA-damage assays, quantifying the initial number of DNA double-strand breaks induced by radiation, have been proposed as a predictive test for radiation-induced toxicity. Determination of radiation-induced apoptosis in peripheral blood lymphocytes by flow cytometry analysis has also been proposed as an approach for predicting normal tissue responses following radiotherapy. The aim of the present study was to explore the association between initial DNA damage, estimated by the number of double-strand breaks induced by a given radiation dose, and the radio-induced apoptosis rates observed.

Methods

Peripheral blood lymphocytes were taken from 26 consecutive patients with locally advanced breast carcinoma. Radiosensitivity of lymphocytes was quantified as the initial number of DNA double-strand breaks induced per Gy and per DNA unit (200 Mbp). Radio-induced apoptosis at 1, 2 and 8 Gy was measured by flow cytometry using annexin V/propidium iodide.

Results

Radiation-induced apoptosis increased in order to radiation dose and data fitted to a semi logarithmic mathematical model. A positive correlation was found among radio-induced apoptosis values at different radiation doses: 1, 2 and 8 Gy (p < 0.0001 in all cases). Mean DSB/Gy/DNA unit obtained was 1.70 ± 0.83 (range 0.63-4.08; median, 1.46). A statistically significant inverse correlation was found between initial damage to DNA and radio-induced apoptosis at 1 Gy (p = 0.034). A trend toward 2 Gy (p = 0.057) and 8 Gy (p = 0.067) was observed after 24 hours of incubation.

Conclusions

An inverse association was observed for the first time between these variables, both considered as predictive factors to radiation toxicity.

Association between normal tissue complications after radiotherapy and polymorphic variations in TGFB1 and XRCC1 genes

Genetic predictive biomarkers of radiosensitivity are being sought to individualize radiation treatment of cancer patients. In this pilot case-control study, we tested the association between TGFB1 T869C codon 10 Leu/Pro (rs1982073), XRCC1 G28152A codon 399 Arg/Gln (rs25487), and XRCC3 C18067T codon 241 Thr/Met (rs861539) single-nucleotide polymorphisms (SNPs) and late reaction to radiotherapy in 60 nasopharyngeal cancer patients. Subcutaneous and deep tissue fibrosis was scored using the RTOG/EORTC grading system. Patients with moderate to severe fibrosis (radiosensitive cases, G2-3, n = 30) were matched and compared to those with little or no reaction (controls, G0-1, n = 30). The three nonsynonymous SNPs were genotyped by direct DNA sequencing. Significant association was observed for TGFB1 T869C and XRCC1 G28152A genotypes (P < or = 0.05). Both variant alleles, TGFB1 869C and XRCC1 28152A, were associated with a lower grade of fibrosis (odds ratios were 0.41, 95% CI: 0.20-0.86, P = 0.02 and 0.30, 95% CI: 0.10-0.89, P = 0.02, respectively), and therefore the wild-types were the risk alleles. Interestingly, there was a significant difference in the median number of risk alleles between the radiosensitive and the control groups (P = 0.006). We conclude that radiotherapy complications are associated with genetic variations in our nasopharynx cancer patients. Our findings support the assumption of the combined effects of multiple SNPs. Large-scale studies are required to confirm these findings before polymorphisms can be used as predictive markers to individualize radiation therapy on genetic bases.

Bystander effects and their implications for clinical radiotherapy

Radiation-induced bystander effects are defined as those biological effects expressed, after irradiation, by cells whose nuclei have not been directly irradiated. Radiation oncologists are only gradually beginning to appreciate the clinical relevance of radiation-induced bystander effects and associated phenomena: adaptive responses, genomic instability and abscopal effects. Incorporating bystander effects into the science underpinning clinical radiotherapy will involve moving beyond simple mechanistic models and towards a more systems-based approach. It is, given the protean nature of bystander effects, difficult to devise a coherent research strategy to investigate the clinical impact and relevance of bystander phenomena. Epidemiological approaches will be required, the traditional research models based on randomised controlled trials are unlikely to be adequate for the task. Any consideration of bystander effects challenges not only clinicians' preconceptions concerning the effects of radiation on tumours and normal tissues but also their ingenuity. This review covers, from a clinical perspective, the issues and problems associated with radiation-induced bystander effects.

Individual differences in the radiosensitivity of hematopoietic progenitor cells detected in steady-state human peripheral blood

The aim of this study is to evaluate the individual differences in radiosensitivity of lineage-committed myeloid hematopoietic progenitors, colony-forming cells (CFC), detected in steady-state human peripheral blood (PB). Mononuclear cells were prepared from the buffy-coat of 30 individuals PB, and were assayed for CFC by semi-solid culture supplemented with cytokines. X irradiation was performed in the range of 0.5-4 Gy at a dose rate of about 80 cGy/min. The mean number of hematopoietic progenitor cells is 5866 alpha 3408 in 1 ml of buffy-coat, suggesting that the erythroid progenitor cells are the major population. The total CFC radiosensitivity parameter D(0) and n value are 1.18 alpha 0.24 and 1.89 alpha 0.98, respectively. Using a linear regression analysis, a statistically significant correlation is observed between the D(0) value and the surviving fraction at 4 Gy (r = 0.611 p < 0.001). Furthermore, we evaluate the relationship between individual radiosensitivity and the level of antioxidants, plasma uric acid, plasma bilirubin, and intracellular glutathione. No statistically significant correlations are observed, however, between the D(0) parameter and the level of antioxidants, plasma uric acid, plasma bilirubin, and intracellular glutathione. The present study demonstrates that there are large individual differences in the radiosensitivity of hematopoietic progenitor cells as detected in steady-state human PB. These differences demonstrate almost no correlation with plasma or intracellular antioxidants. The prediction of individual differences in radiosensitivity of CFC can only be measured by 4 Gy irradiation.

Radiation-induced DNA damage as a predictor of long-term toxicity in locally advanced breast cancer patients treated with high-dose hyperfractionated radical radiotherapy

This 14-year-long study makes a novel contribution to the debate on the relationship between the in vitro radiosensitivity of peripheral blood lymphocytes and normal tissue reactions after radiation therapy. The aims were (1) to prospectively assess the degree and time of onset of skin side effects in 40 prospectively recruited consecutive patients with locally advanced breast cancer treated with a hyperfractionated dose-escalation radiotherapy schedule and (2) to assess whether initial radiation-induced DNA damage in peripheral blood lymphocytes of these patients could be used to determine their likelihood of suffering severe late damage to normal tissue. Initial radiation-induced DNA double-strand breaks (DSBs) were assessed in peripheral blood lymphocytes of these patients by pulsed-field electrophoresis. Acute and late cutaneous and subcutaneous toxicity was evaluated using the Radiation Therapy Oncology Group morbidity score. A wide interindividual variation was observed in toxicity grades and in radiation-induced DNA DSBs in peripheral blood lymphocytes (mean 1.61 +/- 0.76 DSBs/Gy per 200 MBp, range 0.63- 4.08), which were not correlated. Multivariate analysis showed a correlation (P < 0.008) between late toxicity and higher prescribed protocol dose (81.6 Gy). Analysis of the 29 patients referred to 81.6 Gy revealed significantly (P < 0.031) more frequent late subcutaneous toxicity in those with intrinsic sensitivity to radiation-induced DNA DSBs of >1.69 DSBs/Gy per DNA unit. Our demonstration of a relationship between the sensitivity of in vitro-irradiated peripheral blood lymphocytes and the risk of developing late toxic effects opens up the possibility of predicting normal tissue response to radiation in individual patients, at least in high-dose non-conventional radiation therapy regimens.

Early and late skin reactions to radiotherapy for breast cancer and their correlation with radiation-induced DNA damage in lymphocytes

Introduction

Radiotherapy outcomes might be further improved by a greater understanding of the individual variations in normal tissue reactions that determine tolerance. Most published studies on radiation toxicity have been performed retrospectively. Our prospective study was launched in 1996 to measure the in vitro radiosensitivity of peripheral blood lymphocytes before treatment with radical radiotherapy in patients with breast cancer, and to assess the early and the late radiation skin side effects in the same group of patients. We prospectively recruited consecutive breast cancer patients receiving radiation therapy after breast surgery. To evaluate whether early and late side effects of radiotherapy can be predicted by the assay, a study was conducted of the association between the results of in vitro radiosensitivity tests and acute and late adverse radiation effects.

Methods

Intrinsic molecular radiosensitivity was measured by using an initial radiation-induced DNA damage assay on lymphocytes obtained from breast cancer patients before radiotherapy. Acute reactions were assessed in 108 of these patients on the last treatment day. Late morbidity was assessed after 7 years of follow-up in some of these patients. The Radiation Therapy Oncology Group (RTOG) morbidity score system was used for both assessments.

Results

Radiosensitivity values obtained using the in vitro test showed no relation with the acute or late adverse skin reactions observed. There was no evidence of a relation between acute and late normal tissue reactions assessed in the same patients. A positive relation was found between the treatment volume and both early and late side effects.

Conclusion

After radiation treatment, a number of cells containing major changes can have a long survival and disappear very slowly, becoming a chronic focus of immunological system stimulation. This stimulation can produce, in a stochastic manner, late radiation-related adverse effects of varying severity. Further research is warranted to identify the major determinants of normal tissue radiation response to make it possible to individualize treatments and improve the outcome of radiotherapy in cancer patients.