Investigations of TiO2 NP as radiation dose enhancement agent: in vitro and phantom based studies

Radiotherapy is one of the basic methods for cancer treatments. This extremely valuable and effective technique deliver high therapeutic doses of ionising radiations to the malignant cells to shrink tumours and kill cancer cells in a way that is safer and more reliable. The source of this ionising radiation is typically high energy photon or electron beams, which are potentially carcinogenic and/or deadly to all cells at high dosage. Therefore, the major obstacle of planning and delivery of radiotherapy is the preservation of healthy surrounding tissues by limiting the delivered radiation dose to the tolerance levels of normal tissues while still ensuring the effective targeting of tumour volumes to eradicate it. Developments in the field of nanotechnology have potentially provided effective radiotherapy techniques through the use of high and medium atomic number (Z) nanostructure materials as radiosensitisation agents. The high Z nanoparticles (NPs) such as gold, bismuth compound, iodine and gadolinium have already been successfully utilised as radiosensitiser agents when applied to tumours for in vitro, in vivo and even in some preclinical trials. However, the high and medium Z materials are more toxic than low Z elements, therefore investigation of radiosensitasation induced by low Z elements have become more attractive. Several studies have been conducted to test the low Z nanoparticles as dose enhancing agents. Most of these studies were in the field of UV and X-rays of kilovoltage energy ranges. This thesis’ research extends thier application to include the most common form of radiotherapy i.e. using megavoltage range of X-rays. The aims of this thesis are focused on investigations of employing low Z materials and particularly anatase titanium dioxide nanoparticles (TiO2 NPs) as potential radiosensitisation agent and as imaging agent too. This research was conducted by two main ways, one by using phantoms (PRESAGE® dosimeters) and the other by in vitro using two types of cell lines, cultured human keratinocyte (HaCaT) and prostate cancer (DU145) cells, and both methods were aimed at determining the effects on NPs on the radiation dose enhancement at both low (kilovoltage) and high (megavoltage) radiotherapy X-ray beams. Furthermore, TiO2 NPs were activated via proton beam to investigate for their suitability as diagnostic agent hence this nano-compound qualifies to be true theranostic agent. Several characteristics of TiO2 NPs, which make them ideally suited for application in radiotherapy, are investigated throughout this research. Anatase TiO2 NPs were synthesised, characterised and functionalised to allow dispersion in culture medium for in vitro studies and halocarbons (PRESAGE® chemical compositions) for phantom based studies. The fabricated PRESAGE® dosimeters/phantoms were scanned to obtain the physical and radiological properties and further to determine the radiation dose enhancement induced by TiO2 NPs. Clonogenic and cell viability assays were employed to determine cells survival curves from which the dose enhancement levels “radiosensitisation” are deduced. The dose enhancement produced experimentally by 0.5, 1 and 4 mM TiO2 NPs concentrations for phantom and in vitro studies irradiated with 1-8 Gy ranges of radiation doses was quantified for kilovoltage and megavoltage energies of external X-ray radiation sources. Furthermore, the TiO2 NPs were activated via proton beam and the energy spectrums were acquired using Germanium detectors. The radiolabeled anatase TiO2 NPs were imaged using positron emission tomography (PET) scanner. One aspect of this research was to demonstrate that the TiO2 NPs were typically synthesised to achieve highly pure and uniform anatase nanocrystalline structure. This form of NPs creates more free radicals and effectively generates more reactive oxygen species (ROS) since it has larger surface to volume ratio. These features combined have a high impact in damaging DNA molecule of biological system during irradiation. In phantom studies, the radiation modifying effects of incorporating of PEG functionalised anatase TiO2 NPs in the formulation of the water equivalent 3D PRESAGE® dosimeter were explored. The dose enhancement factors (DEFs) were quantified and then the results were validated with the biological studies. The results clearly demonstrates that the sensitivity of the dosimeter increases to the radiation doses with the concentration of the TiO2 NPs incorporated in the composition of the PRESAGE® dosimeter. Furthermore, the measured DEF was significant at 80 kV compared to the negligible dose enhancement detected at 6 MV X-ray energy beams. The In vitro studies, TiO2 NPs proved to be cytocompatible to cells, even at very high concentrations. The DEFs were deduced from the data analysed in the form of cell survival curves. The result indicates that radiosensitisation induced by TiO2 NPs was significant at kilovoltage range of energy which the maximal dose enhancement was observed at 80 kV. Furthermore, significant radiosensitisation was observed for in vitro study at megavoltage energy beam. Higher radiosensitisation were obtained for low energy x-rays compared to the high energy ones. Generally, with the inclusion of TiO2 NPs in the target, same fraction of cells were destroyed with lower radiation doses compared to the case of absence of TiO2 NPs. This means if the TiO2 NPs are added to the biological target, a reduction of external dose of an order of magnitude can be achieved to deliver the same local control as without the inclusion of TiO2 NPs for treatments with kilovoltage and megavoltage X-rays beams. This reduction of delivered radiation dose to the target results in reducing the dose to the surrounding normal tissues during treatment that is the primary concern in all radiotherapy treatment procedures. Hence, TiO2 NPs are considered to be an efficient dose enhancer agent and have a great potential value for future clinical radiotherapy applications. In addition, the radiobiological effect of amino functionalised anatase TiO2 NPs on HaCaT and DU145 cell lines were investigated. The linear (α) and the quadratic (β) radiobiological-parameters were extracted from the cell survival curves in order to describe the DNA damage by radiation. The results clearly demonstrate that α value significantly increases with the inclusion of TiO2 NPs while β values do not show any predictable trend. This increase in α value indicates that the probability of double strand DNA breakage increases with the presence of NPs in the target. Accordingly, the DEF results for in vitro and phantom based studies showed good agreement with the hypothesis of α value increases as a consequence of inclusion TiO2 NPs in the target. There are measurable differences in the level of produced DEF between biological and phantom based studies at MV energy. The PRESAGE® dosimeters showed lower enhancements in radiosensitivity than cell in culture studies. This is due to PRESAGE® dosimeters is only able to detect the free electron generated as a result of photoelectric effect, Compton scatter and/or Auger effect and not being suited to detect the generated ROS (Biochemical effects) due to a lack of free water molecules in its structure, whereas cells can be affected by many other biochemical factors, such as the generated ROS which is added to the stress caused by generated electron free radicals, and this result in higher radiosensitivity. Therefore, the ROS generated from amino functionalised anatase TiO2 NPs upon exposed to radiotherapy X-ray energy beam was investigated. Aqueous solutions without and with the presence of TiO2 NPs was exposed to 6 MV beam. The result clearly shows that the level of generated ROS was proportionally dependent on the TiO2 NPs concentration. This explains that biochemical effects need to be considered as a key factor for enhancing the cellular radiosensitivity with the presence of nanoparticles, which would be an important consideration for in vitro and in vivo radiosensitivity measurements. Finally, the TiO2 NPs are proposed as a reliable potential candidate for producing nuclear medical radioisotopes via proton activation. The results demonstrate that intense peak was observed at 511 keV which correspond to the γ-ray resulted from electron-positron annihilation. This γ-ray peak is the most important radioisotope for potential nuclear medicine imaging applications using PET. Recently, several innovative for new radiopharmaceutical evolution potentially suggest β- and α emitters. Therefore, the produced 47Sc radionuclide is a promising therapeutic agent for preparing radiolabeled antibodies due to its favorable β- emission energy (162 keV) which decays to stable 47Ti (100% β- emission ), and to its moderate half-life (T1/2 = 3.35 d). To conclude, this research shows that TiO2 NPs improve the efficiency of dose delivery, which has implications for future radiotherapy treatments. The TiO2 NPs can also be used as a potential imaging agents hence with these findings renders these NPs as theranostic agents with dual effects (i.e. imaging and dose enhancer agent) simultaneously if it is in the targets

Automated 3D portal dosimetry for large-scale plan-specific QA in external beam radiotherapy

External beam radiation therapy (EBRT) delivers targeted radiation from outside the body to destroy cancer cells. Plan-specific quality assurance (PSQA) ensures accurate dose delivery for each treatment. Electronic portal imaging devices (EPIDs) are commonly used for PSQA, as they are widely available in linacs and have proven effective for dosimetric verification.This thesis aims to enhance a 3D EPID-based in vivo dosimetry (EIVD) system for large-scale EBRT dosimetric verification, focusing on automation, accuracy, error detection, and online MRI-guided adaptive workflows.Two extensions to an existing transit EIVD algorithm were developed to enable accurate 3D patient dose reconstruction for both in vivo (transit) and pre-treatment (non-transit) 3D EPID dosimetry, including treatment disease sites with significant tissue inhomogeneities.Sensitivity and specificity analyses revealed variability in performance across error types and magnitudes, indicators, and treatment sites, challenging the conventional use of universal γ-pass rate tolerance limits for error detection. Additionally, deep learning techniques were explored to distinguish between generic and plan-specific deviations during the EIVD review process.Automated EIVD was shown to be a feasible independent end-to-end check for online adaptive strategies on the Unity MR-Linac, highlighting its potential in similar solutions, such as upcoming online CBCT-guided adaptive workflows.Key barriers to clinical adoption include vendor-user gaps, non-water-equivalent EPID dose response, lack of open systems for accessing EPID data and metadata, limitations in EPID acquisition software, automation issues and workflow complexities. Overcoming these challenges is essential for broader clinical implementation of EIVD

COMPARISON OF METHODS FOR DETECTION OF ARSENIC IN SKIN USING XRF

Arsenic (As) is an element that is well known for its toxic capabilities. It is odorless and colorless and is known to contaminate the drinking water of populations in several parts of the world. Routine monitoring of arsenic exposure is usually performed with urine, hair or nail, where samples are collected for laboratory analysis. Arsenic’s strong affinity to keratin rich tissues make skin another possible measurement site, in addition to the latter two tissues mentioned above. In some cases, skin samples are extracted for analysis. This is painful and invasive and is not ideal for in vivo monitoring of arsenic. The ability to quantify elemental concentration non-destructively is the major calling card of x-ray fluorescence (XRF). To that end, work was started on development of XRF detection systems for arsenic. The technique has shown promise for other elements and dramatic improvements in As detection capabilities were previously found when going from a radioisotope-based x-ray source to an x-ray tube based approach. This thesis documents the comparison of three x-ray tube based detection systems intended for the measurement of arsenic in skin. Two benchtop systems were used, with a) extended development of the previously assembled system and b) the first use of a separate detection system. Two handheld x-ray analyzers (portable detection systems) were also investigated in stand mode, where they were attached to a purpose-built mounting stand, provided by the manufacturer, during all analysis. Polyester resin phantoms were used to model arsenic in skin and a nylon backing was used to represent as bulk tissue behind skin. During the course of the work, modifications were made to the laboratory setup associated with the benchtop approaches. A benchtop polychromatic Mo anode x-ray tube based x-ray fluorescence (XRF) detection system was the first system used in this work. Through modifications to the existing design of the system, the lowest minimum detection limit (MDL) achievable was found to be (0.611±0.001) ppm normalized to gross scatter, where ppm is ug of arsenic per gram of dry weight (resin). The measurement time was ~1800 seconds real time. The equivalent (skin) and whole body effective doses delivered were (19±3) uSv and (163±47) uSv respectively. The corresponding direct (un-normalized) MDL was (0.499±0.002) ppm, in agreement with that found previously. Modifications to the system allowed a reduction in the localized effective dose delivered, to achieve this MDL, from (0.64±0.03) uSv previously to (0.14±0.04) uSv here. Next, the current work investigated two handheld x-ray analyzers provided by InnovX. A PiN diode detector based Alpha 4000S model unit (W anode x-ray tube) and a Silicon Drift Detector (SDD) based Delta model (Au anode x-ray tube). Both units were operated in benchtop mode: they were mounted in a stand and a phantom was placed on a kapton exit window. The lowest gross-scatter normalized and direct detection limit with the Alpha 4000S unit was (1.649±0.002) ppm and (1.651±0.002) ppm respectively. The equivalent and whole body effective doses delivered were found to be (9.4±2.2) mSv and (94±22) uSv respectively. The localized effective dose was (6.4±1.5) X 10-3 uSv. By comparison, the Delta unit produced a gross-scatter and direct normalized detection limit of (0.570±0.002) ppm and (0.558±0.002) ppm respectively. The equivalent dose delivered was found to be (19.0±9.0) mSv. The corresponding localized and whole body effective doses delivered were (9.7±4.6) X 10-3 uSv and (190±90) uSv respectively. The last system used in the current research was a monochromatic Ag anode x-ray tube based XRF setup. A doubly curved crystal (DCC) was used to select the Ag K-alpha line and focused the beam to a spot size of mm2 at the focal length. The phantoms were placed at a farther distance where the beam had expanded to a larger area. The lowest Compton scatter normalized detection limit with the Si(Li) detector was found to be (0.696±0.002) ppm. After characterizing its performance in a range of energies, a silicon drift detector was also used on this system. It had the benefit of higher throughput capabilities and superior resolution. The housing of the detector was sufficiently small that it could be placed closer to the phantom surface than the Si(Li) detector. The lowest Compton-scatter normalized detection limit with the SDD was (0.441±0.003) ppm in 1800 seconds real time. The equivalent dose was found to be (11±2) mSv and the localized and whole body effective doses were found to be (3.92±0.87) X 10-3 uSv and (110±23) uSv respectively. A significantly lower system dead time was observed with the SDD. Finally, Monte Carlo simulations of the system were performed to evaluate the performance of three ratios when their phantom measurement values were compared against simulations of skin. Results were found to be in agreement to withinin vivo concentration of arsenic in skin (ICRP). Finally, EDXRF measurements were performed on bulk cores of skin, ex vivo. While it was not possible to detect arsenic in the samples, due to the samples being collected from members of the public as opposed to an exposed population, a depth profile of numerous skin samples, starting from the surface and running straight down, was obtained for calcium, iron and copper.Doctor of Philosophy (PhD

Radiobiology Textbook:Space Radiobiology

The study of the biologic effects of space radiation is considered a “hot topic,” with increased interest in the past years. In this chapter, the unique characteristics of the space radiation environment will be covered, from their history, characterization, and biological effects to the research that has been and is being conducted in the field. After a short introduction, you will learn the origin and characterization of the different types of space radiation and the use of mathematical models for the prediction of the radiation doses during different mission scenarios and estimate the biological risks due to this exposure. Following this, the acute, chronic, and late effects of radiation exposure in the human body are discussed before going into the detailed biomolecular changes affecting cells and tissues, and in which ways they differ from other types of radiation exposure. The next sections of this chapter are dedicated to the vast research that has been developed through the years concerning space radiation biology, from small animals to plant models and 3D cell cultures, the use of extremophiles in the study of radiation resistance mechanisms to the importance of ground-based irradiation facilities to simulate and study the space environment

Quantifying, Understanding and Predicting Differences Between Planned and Delivered Dose to Organs at Risk in Head & Neck Cancer Patients Undergoing Radical Radiotherapy to Promote Intelligently Targeted Adaptive Radiotherapy

Introduction: Radical radiotherapy (RT) is an effective but toxic treatment for head and neck cancer (HNC). Contemporary radiotherapy techniques sculpt dose to target disease and avoid organs at risk (OARs), but anatomical change during treatment mean that the radiation dose delivered to the patient – delivered dose (DA), is different to that anticipated at planning – planned dose (DP). Modifying the RT plan during treatment – Adaptive Radiotherapy (ART) – could mitigate these risks by reducing dose to OARs. However, clinical data to guide patient selection for, and timing of ART, are for lacking. Methods: 337 patients with HNC were recruited to the Cancer Research UK VoxTox study. Demographic, disease and treatment data were collated, and both DP and DA to organs at risk (OARs) were computed from daily megavoltage CT image guidance scans, using an open-source deformable image registration package (Elastix). Toxicity data were prospectively collected. Relationships between DP, DA and late toxicities were investigated with univariate, and logistic regression normal tissue complication probability (NTCP) modelling approaches. A sub-study of VoxTox recruited 18 patients who had MRI scans before RT fractions 1, 6, 16, and 26. Changes in salivary gland volumes and relative apparent diffusion coefficient (ADC) values were measured and related to toxicity events. Results: Spinal cord dose differences were small, and not predicted by weight loss or shape change. Mean DA to all other OARs was higher than DP; factors predicting higher DA included primary disease site, concomitant therapy, shape change and advanced neck disease. Nine patients (3.7%) saw DA>DP by 2Gy to more than half of the OARs assessed. These patients all had received bilateral neck RT for N-stage 2b oropharyngeal cancer. Strong uni- and multivariate relationships between OAR dose and toxicity were seen. Differences between DA and DP-based dose-toxicity models were minimal, and not statistically significant. On MRI, both parotid and submandibular glands shrank during treatment, whilst relative ADC rose. Relationships with toxicity were inconclusive. Conclusions: Small differences between OAR DP and DA mean that DA-based toxicity prediction models confer negligible additional benefit at the population level. Factors such as primary disease sub-site, concomitant systemic therapy, staging and shape change may help to select the patients that do develop clinically significant dose differences, and would benefit most from ART for toxicity reduction