Normal tissue development, homeostasis, senescence, and the sensitivity to radiation injury across the age spectrum

A comprehensive review of 30 years of pediatric clinical trial radiotherapy dose constraints

BACKGROUND

Radiation therapy normal tissue dose constraints are critical when treating pediatric patients. However, there is limited evidence supporting proposed constraints, which has led to variations in constraints over the years. In this study, we identify these variations in dose constraints within pediatric trials both in the United States and in Europe used in the past 30 years.

PROCEDURE

All pediatric trials from the Children's Oncology Group website were queried from inception until January 2022 and a sampling of European studies was included. Dose constraints were identified and built into an organ-based interactive web application with filters to display data by organs at risk (OAR), protocol, start date, dose, volume, and fractionation scheme. Dose constraints were evaluated for consistency over time and compared between pediatric US and European trials RESULTS: One hundred five closed trials were included-93 US trials and 12 European trials. Thirty-eight separate OAR were found with high-dose constraint variability. Across all trials, nine organs had greater than 10 different constraints (median 16, range 11-26), including serial organs. When comparing US versus European dose tolerances, the United States constraints were higher for seven OAR, lower for one, and identical for five. No OAR had constraints change systematically over the last 30 years.

CONCLUSION

Review of pediatric dose-volume constraints in clinical trials showed substantial variability for all OAR. Continued efforts focused on standardization of OAR dose constraints and risk profiles are essential to increase consistency of protocol outcomes and ultimately to reduce radiation toxicities in the pediatric population.

Second allogeneic hematopoietic stem cell transplantation in patients with inborn errors of immunity

Graft failure (GF) remains a serious issue of hematopoietic stem cell transplantation (HSCT) in inborn errors of immunity (IEI). Second HSCT is the only salvage therapy for GF. There are no uniform strategies for the second HSCTs and limited data are available on the second HSCT outcomes. 48 patients with various IEI received second allogeneic HSCT from 2013 to 2020. Different conditioning regimens were used, divided into two main groups: containing myeloablative doses of busulfan/treosulfan (n = 19) and lymphoid irradiation 2-6 Gy (n = 22). Irradiation-containing conditioning was predominantly used in suspected immune-mediated rejection of the first graft. Matched unrelated donor was used in 28 patients, mismatched related in 18, and matched related in 1. 35 patients received TCRαβ/CD19 graft depletion. The median follow-up time was 2.4 years post-HSCT. One patient died at conditioning. The OS was 0.63 (95% CI: 0.41-0.85) after busulfan/treosulfan and 0.68 (95% CI: 0.48-0.88) after irradiation-based conditioning, p = 0.66. Active infection at HSCT significantly influenced OS: 0.43 (95% CI: 0.17-0.69) versus 0.73 (95% CI: 0.58-0.88) without infection, p = 0.004. The cumulative incidence of GF was 0.15 (95% CI: 0.08-0.29). To conclude, an individualized approach is required for the second HSCT in IEI. Low-dose lymphoid irradiation in suspected immune-mediated GF may be a feasible option.

The Normal, the Radiosensitive, and the Ataxic in the Era of Precision Radiotherapy: A Narrative Review

(1) Background: radiotherapy is a cornerstone of cancer treatment. When delivering a tumoricidal dose, the risk of severe late toxicities is usually kept below 5% using dose-volume constraints. However, individual radiation sensitivity (iRS) is responsible (with other technical factors) for unexpected toxicities after exposure to a dose that induces no toxicity in the general population. Diagnosing iRS before radiotherapy could avoid unnecessary toxicities in patients with a grossly normal phenotype. Thus, we reviewed iRS diagnostic data and their impact on decision-making processes and the RT workflow; (2) Methods: following a description of radiation toxicities, we conducted a critical review of the current state of the knowledge on individual determinants of cellular/tissue radiation; (3) Results: tremendous advances in technology now allow minimally-invasive genomic, epigenetic and functional testing and a better understanding of iRS. Ongoing large translational studies implement various tests and enriched NTCP models designed to improve the prediction of toxicities. iRS testing could better support informed radiotherapy decisions for individuals with a normal phenotype who experience unusual toxicities. Ethics of medical decisions with an accurate prediction of personalized radiotherapy's risk/benefits and its health economics impact are at stake; (4) Conclusions: iRS testing represents a critical unmet need to design personalized radiotherapy protocols relying on extended NTCP models integrating iRS.

Heightened apoptotic priming of vascular cells across tissues and life span predisposes them to cancer therapy-induced toxicities

Although major organ toxicities frequently arise in patients treated with cytotoxic or targeted cancer therapies, the mechanisms that drive them are poorly understood. Here, we report that vascular endothelial cells (ECs) are more highly primed for apoptosis than parenchymal cells across many adult tissues. Consequently, ECs readily undergo apoptosis in response to many commonly used anticancer agents including cytotoxic and targeted drugs and are more sensitive to ionizing radiation and BH3 mimetics than parenchymal cells in vivo. Further, using differentiated isogenic human induced pluripotent stem cell models of ECs and vascular smooth muscle cells (VSMCs), we find that these vascular cells exhibit distinct drug toxicity patterns, which are linked to divergent therapy-induced vascular toxicities in patients. Collectively, our results demonstrate that vascular cells are highly sensitive to apoptosis-inducing stress across life span and may represent a "weakest link" vulnerability in multiple tissues for development of toxicities.

Muscle-specific functional deficits and lifelong fibrosis in response to paediatric radiotherapy and tumour elimination

BACKGROUND

As paediatric cancer survivors are living into adulthood, they suffer from the age-related, accelerated decline of functional skeletal muscle tissue, termed sarcopenia. With ionizing radiation (radiotherapy) at the core of paediatric cancer therapies, its direct and indirect effects can have lifelong negative impacts on paediatric growth and maintenance of skeletal muscle. Utilizing our recently developed preclinical rhabdomyosarcoma mouse model, we investigated the late effects of paediatric radiation treatment on skeletal muscles from late adolescent (8 weeks old) and middle-aged (16 months old) mice.

METHODS

Paediatric C57BL/6J male mice (3 weeks old) were injected with rhabdomyosarcoma cells into their right hindlimbs, and then fractionated irradiation (3 × 8.2 Gy) was administered to those limbs at 4 weeks old to eliminate the tumours. Radiation-alone and tumour-irradiated mice were assessed at either 8 weeks (3 weeks post-irradiation) or 16 months (14 months post-irradiation) of age for muscle physiology, myofibre characteristics, cell loss, histopathology, fibrosis, inflammatory gene expression, and fibrotic gene expression.

RESULTS

Mice that received only paediatric radiation demonstrated reduced muscle mass (-17%, P < 0.001), muscle physiological function (-25%, P < 0.01), muscle contractile kinetics (-25%, P < 0.05), satellite cell number (-45%, P < 0.05), myofibre cross-sectional area (-30%, P < 0.0001), and myonuclear number (-17%, P < 0.001). Paediatric radiation increased inflammatory gene expression, increased fibrotic gene expression, and induced extracellular matrix protein deposition (fibrosis) with tumour elimination exacerbating some phenotypes. Paediatric tumour-eliminated mice demonstrated exacerbated deficits to function (-20%, P < 0.05) and myofibre size (-17%, P < 0.001) in some muscles as well as further increases to inflammatory and fibrotic gene expression. Examining the age-related effects of paediatric radiotherapy in middle-aged mice, we found persistent myofibre atrophy (-20%, P < 0.01), myonuclear loss (-18%, P < 0.001), up-regulated inflammatory and fibrotic signalling, and lifelong fibrosis.

CONCLUSIONS

The results from this paediatric radiotherapy model are consistent and recapitulate the clinical and molecular features of accelerated sarcopenia, musculoskeletal frailty, and radiation-induced fibrosis experienced by paediatric cancer survivors. We believe that this preclinical mouse model is well poised for future mechanistic insights and therapeutic interventions that improve the quality of life for paediatric cancer survivors.

Atlas construction and spatial normalisation to facilitate radiation-induced late effects research in childhood cancer

Reducing radiation-induced side effects is one of the most important challenges in paediatric cancer treatment. Recently, there has been growing interest in using spatial normalisation to enable voxel-based analysis of radiation-induced toxicities in a variety of patient groups. The need to consider three-dimensional distribution of doses, rather than dose-volume histograms, is desirable but not yet explored in paediatric populations. In this paper, we investigate the feasibility of atlas construction and spatial normalisation in paediatric radiotherapy. We used planning computed tomography (CT) scans from twenty paediatric patients historically treated with craniospinal irradiation to generate a template CT that is suitable for spatial normalisation. This childhood cancer population representative template was constructed using groupwise image registration. An independent set of 53 subjects from a variety of childhood malignancies was then used to assess the quality of the propagation of new subjects to this common reference space using deformable image registration (i.e. spatial normalisation). The method was evaluated in terms of overall image similarity metrics, contour similarity and preservation of dose-volume properties. After spatial normalisation, we report a dice similarity coefficient of 0.95 ± 0.05, 0.85 ± 0.04, 0.96 ± 0.01, 0.91 ± 0.03, 0.83 ± 0.06 and 0.65 ± 0.16 for brain and spinal canal, ocular globes, lungs, liver, kidneys and bladder. We then demonstrated the potential advantages of an atlas-based approach to study the risk of second malignant neoplasms after radiotherapy. Our findings indicate satisfactory mapping between a heterogeneous group of patients and the template CT. The poorest performance was for organs in the abdominal and pelvic region, likely due to respiratory and physiological motion and to the highly deformable nature of abdominal organs. More specialised algorithms should be explored in the future to improve mapping in these regions. This study is the first step toward voxel-based analysis in radiation-induced toxicities following paediatric radiotherapy.

Late effects of radiation therapy in pediatric patients and survivorship

Advances in multimodality therapy have led to childhood cancer cure rates over 80%. However, surgery, chemotherapy, and radiotherapy may lead to debilitating or even fatal long-term effects among childhood survivors beyond those inflicted by the primary disease process. It is critical to understand, mitigate, and prevent these late effects of cancer therapy to improve the quality of life of childhood cancer survivors. This review summarizes the various late effects of radiotherapy and acknowledges the Pediatric Normal Tissue Effects in the Clinic (PENTEC), an international collaboration that is systematically analyzing the association between radiation treatment dose/volume and consequential organ toxicities, in developing children as a basis to formulate recommendations for clinical practice of pediatric radiation oncology. We also summarize initiatives for survivorship and surveillance of late normal tissue effects related to radiation therapy among long-term survivors of childhood cancer treated in the past.

Analysis of Radiation Dose/Volume Effect Relationship for Anorectal Morbidity in Children Treated for Pelvic Malignancies

PURPOSE

To examine dose-volume effect relationships for anorectal morbidity in children treated with image-guided brachytherapy for pelvic tumors.

METHODS AND MATERIALS

Medical records of all consecutive children with pelvic tumors treated in our center and receiving image-guided pulsed-dose-rate brachytherapy with or without external beam radiation therapy (EBRT) between 2005 and 2019 were reviewed. The effect of the minimal doses to the most exposed 0.5 cm³, 1 cm³, and 2 cm³ of the anorectum (respectively: D_0.5cm³, D_1cm³, and D_2cm³), total reference air kerma (TRAK), and volume of 100% isodose was examined for anorectal toxicities.

RESULTS

Seventy-eight consecutive children were included. Median age was 2.9 years (range, 0.8-14.9 years). Most of the tumors were bladder or prostate (67%) or vaginal (22%) rhabdomyosarcoma. Six patients received EBRT in addition to brachytherapy. Median follow-up was 21.3 months. At last follow-up, 30 children (38%) had experienced Common Terminology Criteria for Adverse Events version 5 grade ≥1 acute or late anorectal events: 24% had grade 1 events, 7.7% had grade 2 events, and 6.4% had grade 3 events. No toxicity greater than grade 3 was observed (eg, fistula or stricture). In univariate analysis, the D_0.5cm³ and D_1cm³ were significant for probability of grade 1 to 3 (P = .009 and P = .017, respectively) and grade 2 to 3 anorectal morbidity (P = .007 and P = .049, respectively). There was no significant correlation for D_2cm³ (P = .057 for grade 1-3; P = .407 for grade 2-3). A 10% probability (95% confidence interval, 4%-20%) for anorectal toxicity of grade 2 or greater was reached for a D_0.5cm³ = 52 Gy. The age, EBRT use, TRAK, and treated volume values were not significant.

CONCLUSIONS

To our knowledge, this study is the first to show a significant dose-volume effect relationships for anorectal morbidity in children undergoing treatment with brachytherapy. Integrating these data into brachytherapy treatment planning could help to optimize the therapeutic index in these young patients.

Radiotherapy and Late Effects

Advances in multimodality care for patients with pediatric cancer continues to improve long-term survival. The use of surgery, chemotherapy, and radiotherapy may lead to debilitating late effects in childhood cancer survivors. It is critically important to understand, mitigate, and screen for late effects to improve the quality of life in childhood cancer survivors. This review summarizes the use of radiotherapy in children, radiobiology of tissue injury, impact of age on late effects, important organ systems affected by radiotherapy during survivorship, and screening for radiotherapy late effects.

Therapy-Related Cardiac Risk in Childhood Cancer Survivors: An Analysis of the Childhood Cancer Survivor Study

PURPOSE

The impacts of radiotherapy dose and exposed cardiac volume, select chemotherapeutic agents, and age at exposure on risk for late-onset cardiac disease in survivors of childhood cancer remain unresolved.

PATIENTS AND METHODS

We determined the rates of severe to fatal cardiac disease in 24,214 5-year survivors in the Childhood Cancer Survivor Study diagnosed between 1970 and 1999 at a median age of 7.0 years (range, 0 to 20.9 years), with a median attained age of 27.5 years (range, 5.6 to 58.9 years). Using piecewise exponential models, we evaluated the association between cardiac disease rates and demographic and treatment characteristics.

RESULTS

The cumulative incidence of cardiac disease 30 years from diagnosis was 4.8% (95% CI, 4.3 to 5.2). Low to moderate radiotherapy doses (5.0 to 19.9 Gy) to large cardiac volumes (≥ 50% of heart) were associated with an increased rate of cardiac disease (relative rate, 1.6; 95% CI, 1.1 to 2.3) compared with survivors without cardiac radiotherapy exposure. Similarly, high doses (≥ 20 Gy) to small cardiac volumes (0.1% to 29.9%) were associated with an elevated rate (relative rate, 2.4; 95% CI, 1.4 to 4.2). A dose-response relationship was observed between anthracycline chemotherapy and heart failure with younger children (age ≤ 13 years) at the greatest risk for heart failure after comparable dosing.

CONCLUSION

These observations support advances in radiation field design and delivery technology to reduce cardiac dose/volume and should guide future treatment protocols. They also inform clinical practice guidelines for post-therapy surveillance and risk-reducing strategies.

Regulation of apoptosis in health and disease: the balancing act of BCL-2 family proteins

The loss of vital cells within healthy tissues contributes to the development, progression and treatment outcomes of many human disorders, including neurological and infectious diseases as well as environmental and medical toxicities. Conversely, the abnormal survival and accumulation of damaged or superfluous cells drive prominent human pathologies such as cancers and autoimmune diseases. Apoptosis is an evolutionarily conserved cell death pathway that is responsible for the programmed culling of cells during normal eukaryotic development and maintenance of organismal homeostasis. This pathway is controlled by the BCL-2 family of proteins, which contains both pro-apoptotic and pro-survival members that balance the decision between cellular life and death. Recent insights into the dynamic interactions between BCL-2 family proteins and how they control apoptotic cell death in healthy and diseased cells have uncovered novel opportunities for therapeutic intervention. Importantly, the development of both positive and negative small-molecule modulators of apoptosis is now enabling researchers to translate the discoveries that have been made in the laboratory into clinical practice to positively impact human health.

Pediatric Normal Tissue Effects in the Clinic (PENTEC): An International Collaboration to Analyse Normal Tissue Radiation Dose-Volume Response Relationships for Paediatric Cancer Patients

With advances in multimodality therapy, childhood cancer cure rates approach 80%. However, both radiotherapy and chemotherapy can cause debilitating or even fatal late adverse events that are critical to understand, mitigate or prevent. QUANTEC (Quantitative Analysis of Normal Tissue Effects in the Clinic) identified radiation dose constraints for normal tissues in adults and pointed out the uncertainties in those constraints. The range of adverse events seen in children is different from that in adults, in part due to the vulnerability/characteristics of radiation damage to developing tissues, and in part due to the typical body sites affected by childhood cancer that lead to collateral irradiation of somewhat different normal tissues and organs compared with adults. Many childhood cancer survivors have a long life expectancy and may develop treatment-induced secondary cancers and severe organ/tissue injury 10, 20 or more years after treatment. Collaborative long-term observational studies and clinical research programmes for survivors of paediatric and adolescent cancer provide adverse event data for follow-up periods exceeding 40 years. Data analysis is challenging due to the interaction between therapeutic and developmental variables, the lack of radiation dose-volume data and the fact that most childhood malignancies are managed with combined modality therapy. PENTEC (Pediatric Normal Tissue Effects in the Clinic) is a volunteer research collaboration of more than 150 physicians, medical physicists, mathematical modellers and epidemiologists organised into 18 organ-specific working groups conducting a critical review and synthesis of quantitative data from existing studies aiming to: (1) establish quantitative, evidence-based dose/volume/risk guidelines to inform radiation treatment planning and, in turn, improve outcomes after radiation therapy for childhood cancers; (2) explore the most relevant risk factors for toxicity, including developmental status; (3) describe specific physics and dosimetric issues relevant to paediatric radiotherapy; and (4) propose dose-volume outcome reporting standards for publications on childhood cancer therapy outcomes. The impact of other critical modifiers of normal tissue radiation damage, including chemotherapy, surgery, stem cell transplantation and underlying genetic predispositions are also considered. The aims of the PENTEC reports are to provide clinicians with an analysis of the best available data to make informed decisions regarding radiation therapy normal organ dose constraints for planning childhood cancer treatment, and to define future research priorities.

Inhibition of Radiation-Induced Ccl2 Signaling Protects Lungs from Vascular Dysfunction and Endothelial Cell Loss

Aims: Radiation-induced normal tissue toxicity often precludes the application of curative radiation doses. Here we investigated the therapeutic potential of chemokine C-C motif ligand 2 (Ccl2) signaling inhibition to protect normal lung tissue from radiotherapy (RT)-induced injury. Results: RT-induced vascular dysfunction and associated adverse effects can be efficiently antagonized by inhibition of Ccl2 signaling using either the selective Ccl2 inhibitor bindarit (BIN) or mice deficient for the main Ccl2 receptor CCR2 (KO). BIN-treatment efficiently counteracted the RT-induced expression of Ccl2, normalized endothelial cell (EC) morphology and vascular function, and limited lung inflammation and metastasis early after irradiation (acute effects). A similar protection of the vascular compartment was detected by loss of Ccl2 signaling in lungs of CCR2-KO mice. Long-term Ccl2 signaling inhibition also significantly limited EC loss and accompanied fibrosis progression as adverse late effect. With respect to the human situation, we further confirmed that Ccl2 secreted by RT-induced senescent epithelial cells resulted in the activation of normally quiescent but DNA-damaged EC finally leading to EC loss in ex vivo cultured human normal lung tissue. Innovation: Abrogation of certain aspects of the secretome of irradiated resident lung cells, in particular signaling inhibition of the senescence-associated secretory phenotype-factor Ccl2 secreted predominantly by RT-induced senescent epithelial cells, resulted in protection of the endothelial compartment. Conclusions: Radioprotection of the normal tissue via Ccl2 signaling inhibition without simultaneous protection or preferable radiosensitization of tumor tissue might improve local tumor control and survival, because higher doses of radiation could be used.

Practice Patterns of Stereotactic Radiotherapy in Pediatrics: Results From an International Pediatric Research Consortium

PURPOSE/OBJECTIVES

There is little consensus regarding the application of stereotactic radiotherapy (SRT) in pediatrics. We evaluated patterns of pediatric SRT practice through an international research consortium.

MATERIALS AND METHODS

Eight international institutions with pediatric expertise completed a 124-item survey evaluating patterns of SRT use for patients 21 years old and younger. Frequencies of SRT use and median margins applied with and without SRT were evaluated.

RESULTS

Across institutions, 75% reported utilizing SRT in pediatrics. SRT was used in 22% of brain, 18% of spine, 16% of other bone, 16% of head and neck, and <1% of abdomen/pelvis, lung, and liver cases across sites. Of the hypofractionated SRT cases, 42% were delivered with definitive intent. Median gross tumor volume to planning target volume margins for SRT versus non-SRT plans were 0.2 versus 1.4 cm for brain, 0.3 versus 1.5 cm for spine/other bone, 0.3 versus 2.0 cm for abdomen/pelvis, 0.7 versus 1.5 cm for head and neck, 0.5 versus 1.7 cm for lung, and 0.5 versus 2.0 cm for liver sites.

CONCLUSIONS

SRT is commonly utilized in pediatrics across a range of treatment sites. Margins used for SRT were substantially smaller than for non-SRT planning, highlighting the utility of this approach in reducing treatment volumes.

New Agents, Emerging Late Effects, and the Development of Precision Survivorship

Incremental improvements in the treatment of children and adolescents with cancer have led to 5-year survival rates reaching nearly 85%. In the past decade, impressive progress has been made in understanding the biology of many pediatric cancers. With that understanding, multiple new agents have become available that offer the promise of more-effective and less-toxic treatment. These include agents that target various cell surface antigens and engage the adaptive immune system, as well as those that interfere with key signaling pathways involved in tumor development and growth. For local control, surgery and radiation techniques also have evolved, becoming less invasive or featuring new techniques and particles that more precisely target the tumor and limit the dose to normal tissue. Nevertheless, targeted agents, like conventional chemotherapy, radiotherapy, and surgery, may have off-target effects and deserve long-term follow-up of their safety and efficacy. These include injury to the endocrine, cardiovascular, and immunologic systems. New radiation and surgical techniques that theoretically reduce morbidity and improve long-term quality of life must also be validated with actual patient outcomes. Finally, with advances in genomics, information on host susceptibility to late effects is beginning to emerge. Such knowledge, coupled with improved metrics that better describe the spectrum of potential late effects across the entire lifespan, can lead to the development of decision models that project the potential long-term health outcomes associated with various treatment and follow-up strategies. These developments will help extend the current focus on precision medicine to precision survivorship, where clinicians, patients, and families will have a better grasp of the potential risks, benefits, and tradeoffs associated with the growing number of cancer treatment options.

Response of rats to dose rates of ionizing radiation evaluated by dielectric properties of bone marrow

The response of adult Wistar albino female rats toward two dose rates of gamma radiation delivered as acute dose of 7 Gy is investigated using classical methodologies as chemical, hematological and histological parameters in comparison with newly introduced dielectric parameters. Two groups of rats were exposed to γ ray with dose rates 533.35 mGy/min and 325.89 mGy/min. Then the irradiated groups were followed up for two weeks after irradiation. In case of higher dose rate, high percentage of animals was lost and there were substantial alterations in the dielectric parameters in addition to massive damage in liver and bone marrow cells. On the other hand, a reduction of death rate of rats, different behavior in the dielectric parameters of bone marrow and lesser injury of liver tissue were well noticeable in case of lower dose rate. Moreover, the sensitivity of dielectric parameters toward the two different dose rates was well pronounced during the 1st and 2nd weeks after irradiation more than other parameters.

Multidisciplinary European Low Dose Initiative (MELODI): strategic research agenda for low dose radiation risk research

MELODI (Multidisciplinary European Low Dose Initiative) is a European radiation protection research platform with focus on research on health risks after exposure to low-dose ionising radiation. It was founded in 2010 and currently includes 44 members from 18 countries. A major activity of MELODI is the continuous development of a long-term European Strategic Research Agenda (SRA) on low-dose risk for radiation protection. The SRA is intended to identify priorities for national and European radiation protection research programs as a basis for the preparation of competitive calls at the European level. Among those key priorities is the improvement of health risk estimates for exposures close to the dose limits for workers and to reference levels for the population in emergency situations. Another activity of MELODI is to ensure the availability of European key infrastructures for research activities, and the long-term maintenance of competences in radiation research via an integrated European approach for training and education. The MELODI SRA identifies three key research topics in low dose or low dose-rate radiation risk research: (1) dose and dose rate dependence of cancer risk, (2) radiation-induced non-cancer effects and (3) individual radiation sensitivity. The research required to improve the evidence base for each of the three key topics relates to three research lines: (1) research to improve understanding of the mechanisms contributing to radiogenic diseases, (2) epidemiological research to improve health risk evaluation of radiation exposure and (3) research to address the effects and risks associated with internal exposures, differing radiation qualities and inhomogeneous exposures. The full SRA and associated documents can be downloaded from the MELODI website ( http://www.melodi-online.eu/sra.html ).

Long term effects of radiation exposure on telomere lengths of leukocytes and its associated biomarkers among atomic-bomb survivors

Ionizing radiation (IR) is a major source of cellular damage and the immediate cellular response to IR has been well characterized. But the long-term impact of IR on cell function and its relationship with aging are not known. Here, we examined the IR effects on telomere length and other biomarkers 50 to 68 years post-exposure (two time points per person) in survivors of the atomic bombing at Hiroshima during WWII. We found that telomere length of leukocytes was inversely correlated with the dose of IR (p=0.008), and this effect was primarily found in survivors who were exposed at younger ages; specifically those <12 years old (p=0.0004). Although a dose-related retardation of telomere shortening with age was observed in the cross-sectional data, longitudinal follow-up after 11 years did not show IR exposure-related alteration of the rate of telomere shortening with age. In addition, IR diminished the associations between telomere length and selected aging biomarkers that were observed in survivors with no dose. These included uric acid metabolism, cytokines, and blood T cell counts. These findings showed long-lasting detrimental effects of IR on telomere length of leukocytes in both dose- and age-at-exposure dependent manner, and on alterations of biomarkers with aging.

Comparison of height and weight after 12 vs. 18 Gy cranial radiation therapy in pediatric acute lymphoblastic leukemia (ALL) patients

Purpose

To compare the effect of 12 versus 18 Gy cranial radiation therapy (RT) on height and weight indices among pediatric patients with acute lymphoblastic leukemia (ALL).

Methods and materials

Records of children with ALL who were 2 to 14 years old at the time of RT and were treated at a single institution between 2000 and 2011 were reviewed. Patients' height, weight, and body mass index were converted into z-scores using the Centers for Disease Control growth charts to normalize the values to number of standard deviations from the mean. These values were measured at the pre-RT clinic visit and subsequent yearly intervals. The z-scores of the growth indices were fitted into a generalizing estimating equations model and analyzed by various clinical factors.

Results

A total of 48 patients met the study criteria, including 32 boys and 16 girls. The median age at the time of RT was 7 years (range, 2-14 years). Patients were separated into 2 dose groups: 12 Gy (n = 30) and 18 Gy (n = 18). Median follow-up was 4.9 years (range, 3.0-11.8 years) and 6.0 years (range, 3.1-10.5 years) and the median pre-RT height z-scores were −0.55 (range, −2.2 to 1.4) and −0.85 (range, −3.1 to 0.8) for the 2 groups, respectively (P = .65). Patients who received 18 Gy had a significant difference in change in height compared with those who received 12 Gy, who were able to maintain normal growth during the first 3 years of follow-up. This did not appear to be sex-specific, and there was no difference in change in weight or body mass index.

Conclusions

Compared with 18 Gy, patients with ALL who received 12 Gy of cranial RT had less height impairment in the first 3 years post-RT, but further prospective studies are needed.

Outcomes for pediatric patients with central nervous system germ cell tumors treated with proton therapy

Purpose

We assessed outcomes after proton therapy (PT) for central nervous system germinomas or non-germinomatous germ cell tumors (NGGCTs) in children.

Patients and methods

We identified children with germ cell tumors of the central nervous system who received proton therapy in 2006–2009 and extracted information on tumor response, treatment failures, and toxicity.

Results

Of the 20 identified patients (median age 12 years [range 3–16]), 9 had germinoma and 11 NGGCTs; 19 patients received three-dimensional conformal PT and 1 scanning-beam PT. Fourteen patients had craniospinal irradiation (CSI), 4 had ventricular irradiation that excluded the 4th ventricle, and 2 had whole-ventricle irradiation. All received involved-field boosts. At a median follow-up interval of 5.6 years (range, 0.3–8.2 years), 1 patient with germinoma had an out-of-field failure in the 4th ventricle and 2 with NGGCT died from disease progression after CSI. Rates of local control, progression-free survival, and overall survival at 5 years were 89%, 89%, and 100% for patients with germinoma; corresponding rates for NGGCTs were 82%, 82%, and 82%. The most common late toxicity (9 patients [45%]) was endocrinopathy.

Conclusions

PT for CNS germ cell tumors is associated with acceptable disease control rates and toxicity profiles.

The concept of radiation-enhanced stem cell differentiation

BACKGROUND

Efficient stem cell differentiation is considered to be the holy grail of regenerative medicine. Pursuing the most productive method of directed differentiation has been the subject of numerous studies, resulting in the development of many effective protocols. However, the necessity for further improvement in differentiation efficiency remains. This review contains a description of molecular processes underlying the response of stem cells to ionizing radiation, indicating its potential application in differentiation procedures. In the first part, the radiation-induced damage response in various types of stem cells is described. Second, the role of the p53 protein in embryonic and adult stem cells is highlighted. Last, the hypothesis on the mitochondrial involvement in stem cell development including its response to ionizing radiation is presented.

CONCLUSIONS

In summary, despite the many threats of ionizing radiation concerning genomic instability, subjecting cells to the appropriate dosage of ionizing radiation may become a useful method for enhancing directed differentiation in certain stem cell types.

Type 2 Diabetes is a Delayed Late Effect of Whole-Body Irradiation in Nonhuman Primates

One newly recognized consequence of radiation exposure may be the delayed development of diabetes and metabolic disease. We document the development of type 2 diabetes in a unique nonhuman primate cohort of monkeys that were whole-body irradiated with high doses (6.5-8.4 Gy) 5-9 years earlier. We report here a higher prevalence of type 2 diabetes in irradiated monkeys compared to age-matched nonirradiated monkeys. These irradiated diabetic primates demonstrate insulin resistance and hypertriglyceridemia, however, they lack the typical obese presentation of primate midlife diabetogenesis. Surprisingly, body composition analyses by computed tomography indicated that prior irradiation led to a specific loss of visceral fat mass. Prior irradiation led to reductions in insulin signaling effectiveness in skeletal muscle and higher monocyte chemoattractant protein 1 levels, indicative of increased inflammation. However, there was an absence of large defects in pancreatic function with radiation exposure, which has been documented previously in animal and human studies. Monkeys that remained healthy and did not become diabetic in the years after irradiation were significantly leaner and smaller, and were generally smaller and younger at the time of exposure. Irradiation also resulted in smaller stature in both diabetic and nondiabetic monkeys, compared to nonirradiated age-matched controls. Our study demonstrates that diabetogenesis postirradiation is not a consequence of disrupted adipose accumulation (generalized or in ectopic depots), nor generalized pancreatic failure, but suggests that peripheral tissues such as the musculature are impaired in their response to insulin exposure. Ongoing inflammation in these animals appears to be a consequence of radiation exposure and can interfere with insulin signaling. The reasons that some animals remain protected from diabetes as a late effect of irradiation are not clear, but may be related to body size. The translational relevance for these results suggest that muscle may be an important and underappreciated target organ for the delayed late effect of whole-body irradiation, leading to increased risk of insulin resistance and diabetes development.

Long-term disease control and toxicity outcomes following surgery and intensity modulated radiation therapy (IMRT) in pediatric craniopharyngioma

PURPOSE

To report long-term progression-free survival (PFS) and late-toxicity outcomes in pediatric craniopharyngioma patients treated with IMRT.

PATIENTS AND METHODS

Twenty-four children were treated with IMRT to a median dose of 50.4Gy (range, 49.8-54Gy). The clinical target volume (CTV) was the gross tumor volume (GTV) with a 1cm margin. The planning target volume (PTV) was the CTV with a 3-5mm margin. Median follow-up was 107.3months.

RESULTS

The 5- and 10-year PFS rates were 65.8% and 60.7%. The 5- and 10-year cystic PFS rates were 70.2% and 65.2% while the 5- and 10-year solid PFS were the same at 90.7%. Endocrinopathy was seen in 42% at initial diagnosis and in 74% after surgical intervention, prior to IMRT. Hypothalamic dysfunction and visual deficits were associated with increasing PTV and number of surgical interventions.

CONCLUSIONS

IMRT is a viable treatment option for pediatric craniopharyngioma. Despite the use of IMRT, majority of the craniopharyngioma patients experienced long-term toxicity, many of which present prior to radiotherapy. Limitations of retrospective analyses on small patient cohort elicit the need for a prospective multi-institutional study to determine the absolute benefit of IMRT in pediatric craniopharyngioma.

Regulation of tumor growth and metastasis: the role of tumor microenvironment

The presence of abnormal cells with malignant potential or neoplastic characteristics is a relatively common phenomenon. The interaction of these abnormal cells with their microenvironment is essential for tumor development, protection from the body's immune or defence mechanisms, later progression and the development of life-threatening or metastatic disease. The tumor microenvironment is a collective term that includes the tumor's surrounding and supportive stroma, the different effectors of the immune system, blood platelets, hormones and other humoral factors. A better understanding of the interplay between the tumor cells and its microenvironment can provide efficient tools for cancer management, as well as better prevention, screening and risk assessment protocols.

Ninth Annual Warren K. Sinclair Keynote Address: effects of childhood radiation exposure: an issue from computed tomography scans to Fukushima

The acute and chronic effects of radiation on children have been and will continue to be of great social, public health, scientific, and clinical importance. The focus of interest on ionizing radiation and children has been clear for over half a century and ranges from the effects of fallout from nuclear weapons testing to exposures from accidents, natural radiation, and medical procedures. There is a loosely stated notion that "children are three to five times more sensitive to radiation than adults." Is this really true? In fact, children are at greater risk for some health effects, but not all. For a few sequelae, children may be more resistant than adults. Which are those effects? How and why do they occur? While there are clear instances of increased risk of some radiation-induced tumors in children compared to adults, there are other tumor types in which there appears to be little or no difference in risk by age at exposure and some in which published models that assume the same relative increase in risks for child compared to adult exposures apply to nearly all tumor types are not supported by the scientific data. The United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR) has a task group producing a comprehensive report on the subject. The factors to be considered include relevant radiation sources; developmental anatomy and physiology; dosimetry; and stochastic, deterministic, and hereditary effects.

Critical windows for nutritional interventions against stunting

An analysis of early growth patterns in children from 54 resource-poor countries in Africa and Southeast Asia shows a rapid falloff in the height-for-age z score during the first 2 y of life and no recovery until ≥5 y of age. This finding has focused attention on the period -9 to 24 mo as a window of opportunity for interventions against stunting and has garnered considerable political backing for investment targeted at the first 1000 d. These important initiatives should not be undermined, but the objective of this study was to counteract the growing impression that interventions outside of this period cannot be effective. We illustrate our arguments using longitudinal data from the Consortium of Health Oriented Research in Transitioning collaboration (Brazil, Guatemala, India, Philippines, and South Africa) and our own cross-sectional and longitudinal growth data from rural Gambia. We show that substantial height catch-up occurs between 24 mo and midchildhood and again between midchildhood and adulthood, even in the absence of any interventions. Longitudinal growth data from rural Gambia also illustrate that an extended pubertal growth phase allows very considerable height recovery, especially in girls during adolescence. In light of the critical importance of maternal stature to her children's health, our arguments are a reminder of the importance of the more comprehensive UNICEF/Sub-Committee on Nutrition Through the Life-Cycle approach. In particular, we argue that adolescence represents an additional window of opportunity during which substantial life cycle and intergenerational effects can be accrued. The regulation of such growth is complex and may be affected by nutritional interventions imposed many years previously.

X-ray irradiation selectively kills thymocytes of different stages and impairs the maturation of donor-derived CD4(+)CD8(+) thymocytes in recipient thymus

The aim of the present study was to determine whether the sensitivity of thymocytes to X-ray radiation depends on their proliferative states and whether radiation impairs the maturation of donor-derived thymocytes in recipient thymus. We assigned 8-week-old C57BL/6J mice into three treatment groups: 1) untreated; 2) X-ray radiation; 3) X-ray radiation plus bone marrow transplantation with donor bone marrow cells from transgenic mice expressing enhanced green fluorescent protein (GFP) on a universal promoter. After 4 weeks, the size of the thymus, the number and proliferation of thymocytes and ratios of different stage thymocytes were analyzed by immunohistochemistry and flow cytometry. The results showed that: 1) CD4⁺CD8⁺ thymocytes were more sensitive to X-ray radiation-induced cell death than other thymocytes; 2) the proliferative capacity of CD4⁺CD8⁺ thymocytes was higher than that of other thymocytes; 3) the size of the thymus, the number of thymocytes and ratios of thymocytes of different stages in irradiated mice recovered to the normal level of untreated mice by bone marrow transplantation; 4) the ratio of GFP-positive CD4⁺CD8⁺ thymocytes increased significantly, whereas the ratio of GFP-positive CD4⁺ or CD8⁺ thymocytes decreased significantly. These results indicate that the degree of sensitivity of thymocytes to X-ray radiation depends on their proliferative states and radiation impairs the maturation of donor-derived CD4⁺CD8⁺ thymocytes in recipient thymus.

Comparison of different adjuvant radiotherapy approaches in childhood bladder/prostate rhabdomyosarcoma treated with conservative surgery

BACKGROUND AND PURPOSE

Multimodality treatment approaches provide high local control and satisfying overall survival (OS) for children with localized bladder and/or prostate rhabdomyosarcoma (BP-RMS). However, current strategies including surgery and conventional radiotherapy are compromised by high rates of long-term genitourinary adverse effects. Therefore, a planning study combining organ preserving surgery with three different innovative adjuvant radiotherapy approaches was performed.

PATIENTS AND METHODS

A case of a 21-month-old boy with BP-RMS treated with polychemotherapy according to the CWS 2002-P protocol, prostatectomy, partial cystectomy, and adjuvant high dose rate brachytherapy (HDR-BT) was used to perform a planning study comparing HDR-BT with intensity-modulated radiotherapy (IMRT) and intensity-modulated proton therapy (IMPT) planning.

RESULTS

All modalities provide good coverage of the target volume and spare critical normal tissues. Rectum doses could be reduced by 2/3 using IMPT and by 1/3 using BT compared to IMRT. In terms of sparing the pelvis growth plates, BT and IMPT are also superior to IMRT.

CONCLUSION

All modalities provide good sparing of normal tissue. BT and IMPT are superior to IMRT with regard to doses on rectum and growth plates. BT is equivalent to IMPT in adequately selected tumors.