Cancer caused by x-rays--a random event?

Peripheral Doses Beyond Electron Applicators in Conventional C-Arm Linear Accelerators: A Systematic Literature Review

Background: This review investigates peripheral dose levels in electron beam treatments, comparing different manufacturers including Varian, Elekta, and Siemens. Accurate measurement of peripheral dose is vital for patient safety and precise radiation delivery in radiation therapy. Methods: This review followed PRISMA standards, conducting a comprehensive literature search from 1978 to July 2023. Emphasis was on identifying studies analyzing peripheral doses related to various electron beam energies, beam angle, field sizes, cutouts, and applicator combinations. Three major databases including PubMed, Web of Science, and Scopus were searched. Results: A total of 7 articles were included in this review. Strategies such as bolus materials, personalized cutouts, and optimal treatment procedures have all been developed to reduce peripheral radiation exposure and enhance patient safety. Ongoing research in this field is focused on further minimizing the risks associated with out-of-field radiation by improving dose delivery systems. Conclusion: The literature emphasizes importance of precision in electron beam radiation therapy, highlighting the critical need for managing peripheral doses and optimizing hardware to ensure patient safety. It advocates for the use of advanced tools and protocols to maintain a balance between effective treatment while protecting healthy tissues. Continuous research, careful treatment planning, and effective management of peripheral doses are essential.

Dual anticancer activity of Aspergillus nidulans pigment and Ionizing γ-Radiation on human larynx carcinoma cell line

BACKGROUND

Fungi are a readily available source of naturally generated colored compounds. These compounds might be used as radiosensitizers for treating cancer cells.

METHODS

Aspergillus nidulans was examined for its color-producing ability in Potato dextrose agar (PDA) broth medium. The pigment was characterized by Ultraviolet (UV) spectrophotometer and Gas Chromatography Mass Spectrometry (GC/MS). Pigment extracts from A. nidulans were studied for their cytotoxic effects on the growth of human larynx carcinoma cell line (HEp-2) with or without exposure to γ-radiation at three different doses (5, 10, and 15 Gy). A. nidulans pigment cytotoxic activity was tested against normal Vero cells. Cell apoptosis was studied using flow cytometry. Gene expression of P53, Caspase 3 and Bcl-2 were quantified.

RESULTS

Ultraviolet spectrum and GC/MS revealed the ability of Aspergillus nidulans to produce Rhodopin pigment. HEp-2 cells treated with A. nidulans pigment only give IC50 about 208 µg/ml. In contrast, when treated with the pigment +10 Gy γ-radiation, it give about 115 µg/ml. However, for normal cells, lower cytotoxic activity was detected. Treatment with pigment (208 g/mL) caused about 50% ± 1.0 total apoptosis level and gene expression of P53: 2.3 fold and Caspase 3: 1.84 fold in respect to untreated HEp-2), while Bcl-2 was decreased (Bcl-2: 0.63 fold in respect to untreated HEp-2). Furthermore, treated with pigment (115 µg/mL) + 10Gy caused about 47.41% ± 1.7 total apoptosis level and P53: 2.53 fold and Caspase 3: 2.0 fold in respect to untreated HEp-2, while Bcl-2 was downregulated (Bcl-2: 0.61 fold in respect to untreated HEp-2).

CONCLUSION

This study concluded that the anti-cancer activity of Aspergillus nidulans pigment was enhanced by ionizing radiation at 10 Gy, as well as its low cytotoxic activity against normal Vero cells.

Monocyte programming by cancer therapy

Monocytes in peripheral blood circulation are the precursor of essential cells that control tumor progression, that include tumor-associated macrophages (TAMs), dendritic cells (DCs) and myeloid-derive suppressor cells (MDSC). Monocytes-derived cells orchestrate immune reactions in tumor microenvironment that control disease outcome and efficiency of cancer therapy. Four major types of anti-cancer therapy, surgery, radiotherapy, chemotherapy, and most recent immunotherapy, affect tumor-associated macrophage (TAM) polarization and functions. TAMs can also decrease the efficiency of therapy in a tumor-specific way. Monocytes is a major source of TAMs, and are recruited to tumor mass from the blood circulation. However, the mechanisms of monocyte programming in circulation by different therapeutic onsets are only emerging. In our review, we present the state-of-the art about the effects of anti-cancer therapy on monocyte progenitors and their dedifferentiation, on the content of monocyte subpopulations and their transcriptional programs in the circulation, on their recruitment into tumor mass and their potential to give origin for TAMs in tumor-specific microenvironment. We have also summarized very limited available knowledge about genetics that can affect monocyte interaction with cancer therapy, and highlighted the perspectives for the therapeutic targeting of circulating monocytes in cancer patients. We summarized the knowledge about the mediators that affect monocytes fate in all four types of therapies, and we highlighted the perspectives for targeting monocytes to develop combined and minimally invasive anti-cancer therapeutic approaches.

Carcinogenesis induced by space radiation: A systematic review

The carcinogenic risk from space radiation has always been a health risk issue of great concern during space exploration. In recent years, a large number of cellular and animal experiments have demonstrated that space radiation, composed of high-energy protons and heavy ions, has shown obvious carcinogenicity. However, different from radiation on Earth, space radiation has the characteristics of high energy and low dose rate. It is rich in high-atom-number and high-energy particles and, as it is combined with other space environmental factors such as microgravity and a weak magnetic field, the study of its carcinogenic effects and mechanisms of action is difficult, which leads to great uncertainty in its carcinogenic risk assessment. Here, we review the latest progress in understanding the effects and mechanisms of action related to cell transformation and carcinogenesis induced by space radiation in recent years and summarize the prediction models of cancer risk caused by space radiation and the methods to reduce the uncertainty of prediction to provide reference for the research and risk assessment of space radiation.

Targeted Osmotic Lysis: A Novel Approach to Targeted Cancer Therapies

The conventional treatment of cancer has been based on the delivery of non-selective toxins and/or ionizing energy that affect both the cancer and normal tissues in the hope of destroying the offending disease before killing the patient. Unfortunately, resistance often develops to these treatments and patients experience severe, dose-limiting adverse effects that reduce treatment efficacy and compromise quality of life. Recent advances in our knowledge of the biology of tumor cells and their microenvironment, the recognition of surface proteins that are unique to specific cancers and essential to cell growth and survival and signaling pathways associate with invasion and metastasis have led to the development of targeted therapies that are able to identify specific cellular markers and more selectively deliver lethal treatment to the invading cancer thus improving efficacy and limiting adverse effects. In the context of targeted approaches to cancer therapy, we present targeted osmotic lysis as a novel and fundamentally different approach for treating advanced-stage carcinoma that exploits the conserved relationship between voltage-gated sodium channels and Na⁺, K⁺-ATPase and has the potential to increase survival without compromising quality of life in a broad spectrum of highly malignant forms of cancer.

Radiation-induced tumors and secondary malignancies following radiotherapy

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Molecular Mechanism and Prevention Strategy of Chemotherapy- and Radiotherapy-Induced Ovarian Damage

Fertility preservation is an emerging discipline, which is of substantial clinical value in the care of young patients with cancer. Chemotherapy and radiation may induce ovarian damage in prepubertal girls and young women. Although many studies have explored the mechanisms implicated in ovarian toxicity during cancer treatment, its molecular pathophysiology is not fully understood. Chemotherapy may accelerate follicular apoptosis and follicle reservoir utilization and damage the ovarian stroma via multiple molecular reactions. Oxidative stress and the radiosensitivity of oocytes are the main causes of gonadal damage after radiation treatment. Fertility preservation options can be differentiated by patient age, desire for conception, treatment regimen, socioeconomic status, and treatment duration. This review will help highlight the importance of multidisciplinary oncofertility strategies for providing high-quality care to young female cancer patients.

Physicochemical damage and early-stage biological response to X-ray radiation studied in prostate cancer cells by Raman spectroscopy

Exposure to ionizing radiation significantly affects biochemistry of cancer cells. The effect of irradiation can be divided into two stages, that is, the physicochemical stage and the biological response. Both effects induce different biochemical changes in the cells and should be analyzed as two separate phenomena. Thus, in the current study, Raman spectroscopy of prostate cancer cells fixed before (the physicochemical damage model) and just after (the biological response model) irradiation was undertaken to compare biochemical composition of irradiated cancer cells at both stages. Spectroscopic analysis of the cells was performed separately for cytoplasmic and nuclear regions. Biochemical changes of irradiated cells were analyzed using partial least squares regression (PLSR) method on the basis of the collected Raman spectra. Regression coefficients were therefore used to describe differences and similarities between biochemical composition of cancer cells undergoing the physicochemical stage and biological response. Additionally, PLSR models of both phenomena were compared for linear dose-dependence and a cross prediction.

New quercetin-coated titanate nanotubes and their radiosensitization effect on human bladder cancer

Interest in nanostructures such as titanate nanotubes (TNT) has grown notably in recent years due to their biocompatibility and economic viability, making them promising for application in the biomedical field. Quercetin (Qc) has shown great potential as a chemopreventive agent and has been widely studied for the treatment of diseases such as bladder cancer. Motivated by the possibilities of developing a new hybrid nanostructure with potential in biomedical applications, this study aimed to investigate the incorporation of quercetin in sodium (NaTNT) and zinc (ZnTNT) titanate nanotubes, and characterize the nanostructures formed. Qc release testing was also performed and cytotoxicity in Vero and T24 cell lines evaluated by the MTT assay. The effect of TNTs on T24 bladder cancer cell radiosensitivity was also assessed, using cell proliferation and a clonogenic assay. The TNT nanostructures were synthesized and characterized by FESEM, EDS, TEM, FTIR, XRD and TGA. The results showed that the nanostructures have a tubular structure and that the exchange of Na⁺ ions for Zn²⁺ and incorporation of quercetin did not alter this morphology. In addition, interaction between Zn and Qc increased the thermal stability of the nanostructures. The release test showed that maximum Qc delivery occurred after 24 h and the presence of Zn controlled its release. Biological assays indicated that the NaTNTQc and ZnTNTQc nanostructures decreased the viability of T24 cells after 48 h at high concentrations. Furthermore, the clonogenic assay showed that NaTNT, NaTNTQc, ZnTNT and ZnTNTQc combined with 5 Gy reduced the formation of polyclonal colonies of T24 cells after 48 h. The results suggest that the nanostructures synthesized in this study interfere in cell proliferation and can therefore be a powerful tool in the treatment of bladder cancer.

Exploring subcellular responses of prostate cancer cells to X-ray exposure by Raman mapping

Understanding the response of cancer cells to ionising radiation is a crucial step in modern radiotherapy. Raman microspectroscopy, together with Partial Least Squares Regression (PLSR) analysis has been shown to be a powerful tool for monitoring biochemical changes of irradiated cells on the subcellular level. However, to date, the majority of Raman studies have been performed using a single spectrum per cell, giving a limited view of the total biochemical response of the cell. In the current study, Raman mapping of the whole cell area was undertaken to ensure a more comprehensive understanding of the changes induced by X-ray radiation. On the basis of the collected Raman spectral maps, PLSR models were constructed to elucidate the time-dependent evolution of chemical changes induced in cells by irradiation, and the performance of PLSR models based on whole cell averages as compared to those based on average Raman spectra of cytoplasm and nuclear region. On the other hand, prediction of X-ray doses for individual cellular components showed that cytoplasmic and nuclear regions should be analysed separately. Finally, the advantage of the mapping technique over single point measurements was verified by a comparison of the corresponding PLSR models.

Basal cell carcinoma induced by therapeutic radiation for tinea capitis-clinicopathological study

AIMS

An increased prevalence of aggressive histological subtypes, such as micronodular and morpheaform, has been seen, irrespective of the clinical course, in basal cell carcinoma (BCC) following irradiation for tinea capitis. The aim of this study was to assess the histopathological features of BCCs among patients irradiated for tinea capitis and correlate them with the clinical course.

METHODS AND RESULTS

The medical records and BCC biopsy specimens of individuals who were previously irradiated for tinea capitis were reviewed. Demographic data and clinical characteristics were retrieved. Biopsy specimens were evaluated for histological subtype classification and additional histopathological features. A telephone survey was conducted to assess the clinical behaviour of the tumours. Thirty-one patients (17 male; 14 female) were included. The average age at time of first biopsy was 56 years. The total number of lesions was 185, with 80% of subjects showing multiple lesions. The nodular subtype was the most prevalent, followed by superficial, micronodular and mixed tumours. One-third of the BCCs could be classified as aggressive histologically. Stromal fibroplasia and melanin deposits were common. There was no mortality related to BCC. None of the 17 patients who completed the survey had evidence of local invasiveness or metastases.

CONCLUSIONS

BCCs following radiation therapy for tinea capitis show unique histological characteristics related to aggressive behaviour. These aggressive features did not reflect the clinical behaviour in the current cohort.

Molecular Pathogenesis of Radiation-Induced Cell Toxicity in Stem Cells

Radiation therapy is an effective cancer therapy, but damage to normal tissues surrounding the tumor due to radiotherapy causes severe complications. The importance of the therapeutic area between tumor suppression and normal tissue injury has long been highlighted in radiation therapy. Recent advances in stem cell biology have shown that stem cell (SC) responses to genotoxic stresses of ionizing radiation can improve the therapeutic effect of radiation by repairing damaged cells. In contrast, cancer stem cells (CSCs), a small subpopulation of cells within tumors, are generally resistant to chemotherapy and radiotherapy and cause tumor recurrence. Although the underlying mechanisms are not clearly understood in detail, efforts are still underway to identify SC treatment or CSC resistant pathogenesis of DNA damage agents such as radiation therapy. In response to radiation, CSCs differ from normal SCs in their biological properties due to severe deregulation of the self-renewal ability in CSCs. Differences of cleavage mode, cell cycle characteristics, replication potential, and activation/inactivation of DNA damage treatment and cancer-specific molecular pathways between normal SCs and CSCs confer a malignant phenotype upon CSCs. However, further studies are needed to identify normal SC and CSC-specific targets. In this review, we summarize the current advances in research regarding how normal SCs and CSCs respond to ionizing radiation, with a special emphasis on cell toxicity, radiosensitivity, signaling networks, DNA damage response (DDR) and DNA repair. In addition, we discuss strategies to develop new diagnostic and therapeutic techniques for predicting responses to cancer treatment and overcoming radiation-related toxicity.

Palliative effects of lutein intervention in gamma-radiation-induced cellular damages in Swiss albino mice

Objectives:

Radiation-induced hematological, biochemical, and cytogenetic damages to the normal cells are major concerns in the field of radiotherapy. The carotenoids and their derivatives have been the source of antioxidants with wide range of medicinal applications. The objective is to evaluate the protective effects of lutein, a carotenoid, against radiation-induced cellular and tissue damages.

Methods:

Swiss albino mice were grouped into 5, 50, 250, and 500 mg/kg b.wt. of lutein treatment groups, a sham and vehicle control group. The groups were irradiated with a lethal dose of 10 Gy y'-radiation. The mortality was recorded for 30 days to optimize the protective dose against radiation. The mice were administered with the compound orally for 15 consecutive days and irradiated with a sublethal dose of 6Gy. The hematological changes in blood and antioxidant parameters were determined in liver, kidney homogenates, and hemolysate/serum. The hematological parameters were recorded using an automated cell counter. The antioxidants such as malondialdehyde (MDA), glutathione (GSH), superoxide dismutase, catalase, glutathione peroxidase and glutathione-S-transferase were spectrophotometrically determined.

Results:

The red blood cell, white blood cell count, lymphocyte count, hemoglobin, platelet levels, and hematocrit value were found to be decreased in the irradiated groups. Lutein pretreatment maintains near-normal levels of these parameters indicating resistance/recovery from the radiation-induced damages. The antioxidant levels were found to be reduced in all the irradiated groups. However, lutein pretreatment (50 mg/kg b.wt.) has increased the catalase activity of hemolysate. Lutein pretreatment has reduced the MDA levels in hemolysate, when administered at doses of 5, 250, and 500 mg/kg b.wt. in comparison to its control.

Conclusion:

The study demonstrates the radioprotective potential of lutein by maintaining the hematological and antioxidant homeostasis.

Role of Natural Radiosensitizers and Cancer Cell Radioresistance: An Update

Cancer originates from genetic mutations accumulation. Cancer stem cells have been depicted as tumorigenic cells that can differentiate and self-renew. Cancer stem cells are thought to be resistant to conventional therapy like chemotherapy and radiation therapy. Radiation therapy and chemotherapy damage carcinomic DNA cells. Because of the ability of cancer stem cells to self-renew and reproduce malignant tumors, they are the subject of intensive research. In this review, CSCs radioresistant mechanisms which include DNA damage response and natural radiosensitizers have been summed up. Reactive oxygen species play an important role in different physiological processes. ROS scavenging is responsible for regulation of reactive oxygen species generation. A researcher has proved that microRNAs regulate tumor radiation resistance. Ionizing radiation does not kill the cancer cells; rather, IR just slows down the signs and symptoms. Ionizing radiation damages DNA directly/indirectly. IR is given mostly in combination with other chemo/radiotherapies. We briefly described here the behavior of cancer stem cells and radioresistance therapies in cancer treatment. To overcome radioresistance in treatment of cancer, strategies like fractionation modification, treatment in combination, inflammation modification, and overcoming hypoxic tumor have been practiced. Natural radiosensitizers, for example, curcumin, genistein, and quercetin, are more beneficial than synthetic compounds.

Therapeutic Implications for Overcoming Radiation Resistance in Cancer Therapy

Ionizing radiation (IR), such as X-rays and gamma (γ)-rays, mediates various forms of cancer cell death such as apoptosis, necrosis, autophagy, mitotic catastrophe, and senescence. Among them, apoptosis and mitotic catastrophe are the main mechanisms of IR action. DNA damage and genomic instability contribute to IR-induced cancer cell death. Although IR therapy may be curative in a number of cancer types, the resistance of cancer cells to radiation remains a major therapeutic problem. In this review, we describe the morphological and molecular aspects of various IR-induced types of cell death. We also discuss cytogenetic variations representative of IR-induced DNA damage and genomic instability. Most importantly, we focus on several pathways and their associated marker proteins responsible for cancer resistance and its therapeutic implications in terms of cancer cell death of various types and characteristics. Finally, we propose radiation-sensitization strategies, such as the modification of fractionation, inflammation, and hypoxia and the combined treatment, that can counteract the resistance of tumors to IR.

Quiescence does not affect p53 and stress response by irradiation in human lung fibroblasts

Cells in many organs exist in both proliferating and quiescent states. Proliferating cells are more radio-sensitive, DNA damage pathways including p53 pathway are activated to undergo either G1/S or G2/M arrest to avoid entering S and M phase with DNA damage. On the other hand, quiescent cells are already arrested in G0, therefore there may be fundamental difference of irradiation response between proliferating and quiescent cells, and this difference may affect their radiosensitivity. To understand these differences, proliferating and quiescent human normal lung fibroblasts were exposed to 0.10-1 Gy of γ-radiation. The response of key proteins involved in the cell cycle, cell death, and metabolism as well as histone H2AX phosphorylation were examined. Interestingly, p53 and p53 phosphorylation (Ser-15), as well as the cyclin-dependent kinase inhibitors p21 and p27, were induced similarly in both proliferating and quiescent cells after irradiation. Furthermore, the p53 protein half-life, and expression of cyclin A, cyclin E, proliferating cell nuclear antigen (PCNA), Bax, or cytochrome c expression as well as histone H2AX phosphorylation were comparable after irradiation in both phases of cells. The effect of radioprotection by a glycogen synthase kinase 3β inhibitor on p53 pathway was also similar between proliferating and quiescent cells. Our results showed that quiescence does not affect irradiation response of key proteins involved in stress and DNA damage at least in normal fibroblasts, providing a better understanding of the radiation response in quiescent cells, which is crucial for tissue repair and regeneration.

Biological response of cancer cells to radiation treatment

Cancer is a class of diseases characterized by uncontrolled cell growth and has the ability to spread or metastasize throughout the body. In recent years, remarkable progress has been made toward the understanding of proposed hallmarks of cancer development, care, and treatment modalities. Radiation therapy or radiotherapy is an important and integral component of cancer management, mostly conferring a survival benefit. Radiation therapy destroys cancer by depositing high-energy radiation on the cancer tissues. Over the years, radiation therapy has been driven by constant technological advances and approximately 50% of all patients with localized malignant tumors are treated with radiation at some point in the course of their disease. In radiation oncology, research and development in the last three decades has led to considerable improvement in our understanding of the differential responses of normal and cancer cells. The biological effectiveness of radiation depends on the linear energy transfer (LET), total dose, number of fractions and radiosensitivity of the targeted cells or tissues. Radiation can either directly or indirectly (by producing free radicals) damages the genome of the cell. This has been challenged in recent years by a newly identified phenomenon known as radiation induced bystander effect (RIBE). In RIBE, the non-irradiated cells adjacent to or located far from the irradiated cells/tissues demonstrate similar responses to that of the directly irradiated cells. Understanding the cancer cell responses during the fractions or after the course of irradiation will lead to improvements in therapeutic efficacy and potentially, benefitting a significant proportion of cancer patients. In this review, the clinical implications of radiation induced direct and bystander effects on the cancer cell are discussed.

New challenges in high-energy particle radiobiology

Densely ionizing radiation has always been a main topic in radiobiology. In fact, α-particles and neutrons are sources of radiation exposure for the general population and workers in nuclear power plants. More recently, high-energy protons and heavy ions attracted a large interest for two applications: hadrontherapy in oncology and space radiation protection in manned space missions. For many years, studies concentrated on measurements of the relative biological effectiveness (RBE) of the energetic particles for different end points, especially cell killing (for radiotherapy) and carcinogenesis (for late effects). Although more recently, it has been shown that densely ionizing radiation elicits signalling pathways quite distinct from those involved in the cell and tissue response to photons. The response of the microenvironment to charged particles is therefore under scrutiny, and both the damage in the target and non-target tissues are relevant. The role of individual susceptibility in therapy and risk is obviously a major topic in radiation research in general, and for ion radiobiology as well. Particle radiobiology is therefore now entering into a new phase, where beyond RBE, the tissue response is considered. These results may open new applications for both cancer therapy and protection in deep space.

Cancer and radiation therapy: current advances and future directions

In recent years remarkable progress has been made towards the understanding of proposed hallmarks of cancer development and treatment. However with its increasing incidence, the clinical management of cancer continues to be a challenge for the 21st century. Treatment modalities comprise of radiation therapy, surgery, chemotherapy, immunotherapy and hormonal therapy. Radiation therapy remains an important component of cancer treatment with approximately 50% of all cancer patients receiving radiation therapy during their course of illness; it contributes towards 40% of curative treatment for cancer. The main goal of radiation therapy is to deprive cancer cells of their multiplication (cell division) potential. Celebrating a century of advances since Marie Curie won her second Nobel Prize for her research into radium, 2011 has been designated the Year of Radiation therapy in the UK. Over the last 100 years, ongoing advances in the techniques of radiation treatment and progress made in understanding the biology of cancer cell responses to radiation will endeavor to increase the survival and reduce treatment side effects for cancer patients. In this review, principles, application and advances in radiation therapy with their biological end points are discussed.

Emerging role of radiation induced bystander effects: Cell communications and carcinogenesis

Ionizing radiation is an invaluable diagnostic and treatment tool used in various clinical applications. On the other hand, radiation is a known cytotoxic with a potential DNA damaging and carcinogenic effects. However, the biological effects of low and high linear energy transfer (LET) radiations are considerably more complex than previously thought. In the past decade, evidence has mounted for a novel biological phenomenon termed as "bystander effect" (BE), wherein directly irradiated cells transmit damaging signals to non-irradiated cells thereby inducing a response similar to that of irradiated cells. BE can also be induced in various cells irrespective of the type of radiation, and the BE may be more damaging in the longer term than direct radiation exposure. BE is mediated either through gap-junctions or via soluble factors released by irradiated cells. DNA damage response mechanisms represent a vital line of defense against exogenous and endogenous damage caused by radiation and promote two distinct outcomes: survival and the maintenance of genomic stability. The latter is critical for cancer avoidance. Therefore, efforts to understand and modulate the bystander responses will provide new approaches to cancer therapy and prevention. This review overviews the emerging role of BE of low and high LET radiations on the genomic instability of bystander cells and its possible implications for carcinogenesis.

Heavy ion carcinogenesis and human space exploration

Before the human exploration of Mars or long-duration missions on the Earth's moon, the risk of cancer and other diseases from space radiation must be accurately estimated and mitigated. Space radiation, comprised of energetic protons and heavy nuclei, has been shown to produce distinct biological damage compared with radiation on Earth, leading to large uncertainties in the projection of cancer and other health risks, and obscuring evaluation of the effectiveness of possible countermeasures. Here, we describe how research in cancer radiobiology can support human missions to Mars and other planets.

Beam path toxicities to non-target structures during intensity-modulated radiation therapy for head and neck cancer

BACKGROUND

Intensity-modulated radiation therapy (IMRT) beams traverse nontarget normal structures not irradiated during three-dimensional conformal RT (3D-CRT) for head and neck cancer (HNC). This study estimates the doses and toxicities to nontarget structures during IMRT.

MATERIALS AND METHODS

Oropharyngeal cancer IMRT and 3D-CRT cases were reviewed. Dose-volume histograms (DVH) were used to evaluate radiation dose to the lip, cochlea, brainstem, occipital scalp, and segments of the mandible. Toxicity rates were compared for 3D-CRT, IMRT alone, or IMRT with concurrent cisplatin. Descriptive statistics and exploratory recursive partitioning analysis were used to estimate dose "breakpoints" associated with observed toxicities.

RESULTS

A total of 160 patients were evaluated for toxicity; 60 had detailed DVH evaluation and 15 had 3D-CRT plan comparison. Comparing IMRT with 3D-CRT, there was significant (p </= 0.002) nonparametric differential dose to all clinically significant structures of interest. Thirty percent of IMRT patients had headaches and 40% had occipital scalp alopecia. A total of 76% and 38% of patients treated with IMRT alone had nausea and vomiting, compared with 99% and 68%, respectively, of those with concurrent cisplatin. IMRT had a markedly distinct toxicity profile than 3D-CRT. In recursive partitioning analysis, National Cancer Institute's Common Toxicity Criteria adverse effects 3.0 nausea and vomiting, scalp alopecia and anterior mucositis were associated with reconstructed mean brainstem dose >36 Gy, occipital scalp dose >30 Gy, and anterior mandible dose >34 Gy, respectively.

CONCLUSIONS

Dose reduction to specified structures during IMRT implies an increased beam path dose to alternate nontarget structures that may result in clinical toxicities that were uncommon with previous, less conformal approaches. These findings have implications for IMRT treatment planning and research, toxicity assessment, and multidisciplinary patient management.