MV X-ray Research Articles

Radiation Therapy for Sebaceous Carcinoma of the Eyelid: Tumor Control and Preservation of Visual Function

Sebaceous carcinoma of the eyelid is rare and considered radioresistant; thus, surgical excision is currently the standard and most reliable curative treatment. However, surgery is sometimes not possible because many patients are elderly, and it frequently causes functional and cosmetic impairment of the eyelid. We therefore investigated the outcomes of radiation therapy for sebaceous carcinoma of the eyelid, particularly its efficacy and preservation of visual function. Twenty-four patients with sebaceous carcinoma of the eyelid received radiation therapy with curative intent. Of these 24 patients, eight were men and 16 were women; their ages at irradiation ranged from 50 to 88 years (median, 77 years). Maximum diameters of primary tumors were 4–30 mm (median, 12 mm). Five patients had T1 disease, five T2a, 10 T2b, Three T3a, and one T3b. Only one patient had cervical lymph node metastasis and none had distant metastasis. A total dose of 50–66.6 Gy (median, 60 Gy) was delivered to tumor sites in 22–37 fractions (median, 30 fractions) using 5–11 MeV electrons in 23 patients and 6 MV X-rays in one. A tungsten eye shield was used to protect the eye in 10 patients. Of the 24 patients, 22 had survived at a median follow-up period of 56 months after radiation therapy. The remaining two patients died of old age and gastric cancer at 19 and 25 months after radiation therapy, respectively. The overall and cause-specific survival rates were 87% and 100% at 2 years, and 80% and 100% at 5 years, respectively. All patients had objective responses to radiation therapy. However, two patients had recurrences; one primary progression within the radiation field at 15 months after irradiation, and one cervical lymph node metastasis outside the radiation field at 22 months after irradiation. These two patients were managed by tumorectomy and neck dissection, respectively. The 5-year primary progression-free and disease-free rates were 93% and 80%, respectively. Although radiation-induced cataracts developed in three patients who had been treated without an eye shield, at 23–35 months after irradiation, no patients had abnormalities in the ocular fundus, such as retinopathy. Corrected visual acuity of the irradiated eyes was 0.2–1.2 (median, 0.8) before irradiation and 30 cm/n.d.–1.2 (median, 0.5) at the last follow up, involving a visual acuity test using a Landolt ring chart. Seven patients showed deterioration in visual acuity, and it was considered to be caused mainly by cataracts because of radiation or aging. There were no other therapy-related toxicities of Grade 3 or greater. Radiation therapy is effective and safe for patients with sebaceous carcinoma of the eyelid. It appears to be a curative treatment option and facilitates functional and cosmetic preservation of the eyelid. Visual acuity of patients without cataracts is fairly well preserved and an eye shield is useful for preventing cataracts.

P53-Suppression by Overexpression of the HPV16 E6 Gene in Lymphoblastoid TK6 Cells Causes a Change in Cell-Death Mode but not Radiosensitivity

The human lymphoblastoid cell line TK6E6 with suppressed expression of tumor suppressor protein p53 shows similar high radiosensitivity as p53-wildtype TK6 cells with a linear survival curve but reduced/delayed apoptosis compared with TK6. By contrast, the related cell line WTK1 expresses high levels of mutated p53, is radioresistant with a shouldered survival curve and shows little apoptosis. The purpose was to test if the differences in radiosensitivity might be related to differences in cell-cycle progression and cell-death mode. The related human lymphoblastoid cell lines TK6 (p53-wildtype), TK6E6 (overexpressing the E6 gene of human papilloma virus 16), and WTK1 (p53-mutant) were irradiated with 6 MV X-rays. Cell survival was determined by the colony formation assay and apoptosis quantified by the sub-G1 fraction using flow cytometry. Cell-cycle analysis was performed by flow cytometry on BrdU pulse-labeled cells. The ratio of p-PLK1 to p-CHK1, which controls the release from the G2 phase into mitosis, was quantified by Western blotting using phospho-specific antibodies. After irradiation (IR) with a dose of 3 Gy, progression of BrdU-negative cells from G1 into S was arrested in TK6 showing an intact G1/S checkpoint which was absent in TK6E6 and WTK1. Normal cell-cycle progression was slower in TK6E6 and WTK1 (cell doubling time: 11.6h) than in TK6 (10.3h). However, progression of BrdU-positive cells from S into G2 showed a larger delay relative to unirradiated controls in TK6E6 (4h) compared with TK6 and WTK1 (2h). Notably, following irradiation of cultures enriched in S-phase, only 50% (1 Gy) to 30% (3 Gy) of the BrdU-labelled TK6E6 cells leaving G2 after release of the G2/M block entered G1 compared with 100% and 60% for TK6 cells. Together with the reduced levels of apoptosis in TK6E6 this strongly suggests a shift in cell death mode from apoptotic towards mitotic death. All three cell lines showed an intact G2/M checkpoint (blockage). A 15-25% decrease in the ratio p-PLK1p-CHK1 was seen after irradiation of TK6 and TK6E6 cells, respectively, which were restored to the original levels 7h and 12h after irradiation. By contrast, p-PLK1/p-CHK1 in unirradiated, normally cycling cells was 45% higher in WTK1 cells than in TK6 but continued to decrease up to 24h after irradiation although by this time WTK1 cells had started to progress through M into G1. Suppression of p53 had little influence on survival rates but caused a shift from apoptotic to mitotic cell death. The radioresistance of p53-mutated WTK1 cells was not associated with an inefficient G2/M block or premature release into mitosis but the cells progressed through G1 and S at the same rate as unirradiated cells. Since WTK1 are known to show genomic instability, their radioresistance might be due to tolerance to some type(s) damage that inactivate p53-wildtype cells, possibly mediated by a gain-of-function mutation in p53 or by a change in a different gene.

Quality Assurance of Small Animal Irradiation: Validation of a 3D-Printed Phantom for “Quasi In-Vivo” Dosimetry

New therapeutic options in radiation oncology are often explored in preclinical in vivo studies using small animals. In this study we report on the use of a 3D-printed rat phantom for radiotherapy dosimetric “quasi-in vivo”quality assurance. In the context of a research project, we aimed to irradiate with a dose of 2Gy per fraction the half-brain of a rat model as homogeneously as possible and with maximal sparing of the contralateral half-brain. The dose was delivered by a 4 MV X-ray beam using a direct anterior-posterior, hemi-field beam, with a size of 3cm x 4cm. A 2cm thick 3D-printed bolus made of poly lactic acid (PLA) was used to avoid the build-up region of the beam in the target volume. Target alignment within the planned position was performed using online kilo-voltage on-board imaging. To verify proper dose delivery, considering the small size of the animal and the region to treat, a 3D 1:1 scale printed copy of the rat body was produced from the CT dataset of the rat to be used as a phantom for dose measurements. A plane section of the phantom perpendicular to the beam axis was created to insert thermoluminescent dosimeters (TLDs) and accommodate a radiochromic film. TLD measurements were made in field and out of field in the brain region, and just beneath the bolus, and were repeated 3 times per position. Kilo-voltage doses as well as linac daily output dose fluctuations were taken into account for dose corrections. The radiochromic film measurements were performed to analyse the dose profiles within the brain, from the cold to the hot region. Radiochromic film dosimetry showed a good concordance between the planned dose distribution and the measured dose, with the steep dose gradient at the edge of the hemi-field properly aligned to spare the contralateral half-brain. Mean TLDs percentage dose differences, (measurements minus planned/ planned), were 1.3% in-field and 0.9% beneath bolus. Out of field, dose measurements gave a mean of 0.05Gy for an expected dose of 0.04Gy. A 3D-printed 1:1 scale rat phantom is an effective and reliable tool for “quasi in-vivo” dosimetric quality assurance in the setting of small animal radiotherapy research.

Modulation of cancer cells' radiation response in the presence of folate conjugated Au@Fe2O3 nanocomplex as a targeted radiosensitizer.

To investigate the effects of Au@Fe2O3 core-shell nanoparticle (NP), with and without conjugation to folic acid (FA) as a targeting ligand, on radiosensitization of both cancer and healthy cells. Au@Fe2O3 NPs were first synthesized, then modified with FA, and finally characterized. Radiation dose enhancement studies were performed on KB cancer cells and L929 healthy cells. NPs at the concentration of 20µg/ml were first incubated with both cell lines and then different doses of 6 MV X-ray radiation were examined. The end effects were evaluated via MTT assay and flow cytometry using AnnexinV/PI kit. It was indicated that viability of KB cells has a much lower rate than L929 cells when the cells were treated by {(FA-Au@Fe2O3) + (X-ray)} regimen. Cell viability was even decreased significantly when X-ray dose increased. Moreover, flow cytometry studies revealed that FA-targeted NPs induced higher level of apoptosis for KB cancer cells than L929 healthy cells. Our findings provide a new perspective on high ability of the synthesized FA-targeted Au@Fe2O3 NPs which may be considered as an efficient radiosensitizer in the process of targeted radiation therapy of cancer.

Effect of Gold Nanoparticles on Dose Enhancement of 6 MV X-ray in MAGIC_f Polymer Gel Dosimeter

Background:Currently, the potential application of gold nanoparticles (AuNPs) to increase the efficiency of radiation therapy has been widely investigated. However, lack of an appropriate method to estimate the dose distribution in a nanoparticle-laden tissue limits the applicability of nanoparticles in radiotherapy clinics. Polymer gel dosimetry provides an accurate and precise system that facilitates the measurement of dose distribution in full three dimensions.Objective: In this study, the effect of radiation dose enhancement of AuNPs was assessed through gel dosimetry analysis.Material and Methods: For this purpose, AuNPs were integrated in MAGIC_f polymer gel dosimeter and irradiated by 6 Mv X-ray beam. The irradiated gel was then evaluated through two modalities of magnetic resonance imaging (MRI) and optical computed tomography (OCT).Result: MRI and OCT scanning of MAGIC_f gels containing 0.1 mM AuNPs demonstrated dose enhancements of 7.8% and 6.8%, respectively.Conclusion: Polymer gel dosimetry has the potential to provide a new platform for the investigation and optimization of the applicability of nanoparticles in radiation therapy.

Single Intense Microsecond Electric Pulse Induces Radiosensitization to Ionizing Radiation: Effects of Time Intervals Between Electric Pulse and Ionizing Irradiation.

Background and Objective: Recent studies have shown the potential of electroporation (EP) as a physical radiosensitizer for ionizing radiation (IR). The amount of sensitizing effect depends on some factors the most important of them is the time interval between the EP and IR. This experimental in vitro study aims to investigate the radiosensitizing effect of EP exposure prior to IR and also evaluate the effects of EP-IR time intervals on the amount of radiosensitizing effects.Methods: Chinese hamster ovary (CHO) cell lines were cultured in vitro. The cells were divided into 10 groups including one untreated or control group, IR, and EP treatment alone groups, and seven combined EP-IR groups with 10, 20, 30, 40, 50, 60, and 70 min intervals. The dose enhancement factors (DEFs) for 6 MV X-rays IR were comparatively investigated between the groups using MTT assay.Results: The EP significantly induced radiosensitizing effect and its amount depends on the time intervals. The viability rate of the cells in the combined EP-IR treatment groups for intervals of 10, 20, 30, 40, and 50 min was significantly lower than the IR alone group. The highest DEF (1.18) was observed 10 min time interval between EP and IR.Conclusion: The radiosensitizing effects of EP persist long enough, 10–50 min, which allows safe application of EP as a radiosensitizer before IR in clinical setting.

Relation between DNA double-strand breaks and energy spectra of secondary electrons produced by different X-ray energies

Purpose: In a radiological examination, low-energy X-radiation is used (<100 keV). For other radiological procedures, the energy used is several MeV. ICRP in publication 103 has currently considered that photons irrespective of their energy have the same radiation weighting factor. Nevertheless, there are topological differences at the nanoscale of X-ray energy deposition as a function of its energy spectrum, meaning that the different interactions with living matter could vary in biological efficacy.Materials and methods: To study these differences, we characterized our irradiation conditions in terms of initial photon energies, but especially in terms of energy spectra of secondary electrons at the cell nucleus level, using Monte Carlo simulations. We evaluated signaling of DNA damage by monitoring a large number of γH2A.X foci after exposure of G0/G1-phase synchronized human primary endothelial cells from 0.25 to 5 Gy at 40 kV, 220 kV and 4 MV X-rays. Number and spatial distribution of γH2A.X foci were explored. In parallel, we investigated cell behavior through cell death and ability of a mother cell to produce two daughter cells. We also studied the missegregation rate after cell division.Results: We report a higher number of DNA double-strand breaks signaled by γH2A.X for 40 kVp and/or 220 kVp compared to 4 MVp for the highest tested doses of 2 and 5 Gy. We observed no difference between the biological endpoint studies with 40 kVp and 220 kVp X-ray spectra. This lack of difference could be explained by the relative similarity of the calculated energy spectra of secondary electrons at the cell monolayer.Conclusion: The energy spectrum of secondary electrons seems to be more closely related to the level of DNA damage measured by γH2A.X than the initial spectrum of photon energy or voltage settings. Our results indicate that as the energy spectrum of secondary electrons increases, the DNA damage signaled by γH2A.X decreases and this effect is observable beyond 220 kVp.

Quantitative comparison of volumetric-modulated arc therapy plans for liver cancer using flattening filter-free and flattening filter modes based on plan quality metric (PQM)

Objective To quantitatively assess the plan quality of conventional fractionated volumetric modulated arc therapy (VMAT) plans for liver cancer treatments using flattening filter-free (FFF) and flattening filter (FF) modes based on plan quality metric (PQM). Methods A total of ten patients with liver tumor were selected. The patients were planned in FF and FFF mode of 6 MV X-ray respectively. The dose distribution of the planning target volume (PTV) and the organ at risk (OAR) were evaluated, and the monitor units (MUs) and the beam on time (BoT) were compared. According to the clinical requirements, a PQM with 16 submetrics was defined to evaluate the plan quality of the two modes. Results The maximal dose of FFF plan was less than that of FF plan (t=3.828, P<0.05). The normalized volume of 5 Gy (V5) and mean dose (Dmean) of the normal liver of FFF plan were lower than those of the FF plan (t=2.716, 3.007, P<0.05). The average MU of FFF plan [(574±130) MU] was higher than that of FF plan [(518±81) MU](t=-2.782, P<0.05), while the average BoT of FFF plan [(108±36)s] was significantly lower than that of FF plan [(160±29) s](t=6.767, P<0.05). The score of FFF plan was higher than that of FF plan (t=-2.746, P<0.05). Conclusions FFF mode can better protect the OAR at low dose levels. The MU of FFF mode plan were higher, but the beam on time was significantly lower than FF mode plan. With reference to the PQM evaluation criteria, the overall plan quality of the FFF mode was slightly higher. Key words: Plan quality metric; Flattening filter-free; Liver cancer; Volumetric modulated arc therapy; Dosimetry

Effect of metal-containing topical agents on surface doses received during external irradiation.

The ability of topical metal-containing agents (MCAs) to enhance radiation dermatitis remains controversial. In the present study, we evaluated increases in surface doses associated with topical agents at different application thicknesses and with MCAs versus non-metal containing agents (NMCAs). We assessed two clinically available MCAs, zinc oxide ointment (ZOO) and silver sulfadiazine cream (SSDC), and eight NMCAs. Surface doses were measured using a Markus chamber placed on a polystyrene phantom. To evaluate the role of application thickness, each agent was applied to the chamber in oil-slick (<0.1-mm), 1-mm and 5-mm layers prior to irradiation of a 10 × 10 cm field with 4-, 6- and 10-MV X-ray beams. The surface dose enhancement ratio (SDER) was calculated as the ratio of the surface dose with an agent to the dose without an agent. The SDER values for the eight NMCAs, ZOO and SSDC at an oil-slick thickness were 101.6–104.6% (mean: 103.3%), 104.5% and 105.0%, respectively, using a 6-MV X-ray beam. The corresponding values at a 1-mm thickness were 196.8–237.8% (mean: 215.7%), 229.3% and 201.4%, respectively, and those at a 5-mm thickness were 342.2–382.4% (mean: 357.9%), 357.1% and 352.6%, respectively. A similar tendency was found using 4- and 10-MV X-ray beams. The lack of a significant difference in surface dose enhancement between MCAs and NMCAs, particularly when applied in oil-slick layers, suggests that MCAs do not need to be avoided or applied in a restricted manner during radiotherapy for dosimetric reasons.

Gold-coated iron oxide nanoparticles trigger apoptosis in the process of thermo-radiotherapy of U87-MG human glioma cells.

Recently, gold-coated iron oxide nanoparticles (Au@IONPs) have received a great deal of attention in cancer therapy. In this in vitro study we aimed to investigate the anti-cancer effects of Au@IONPs core-shell nanoparticles when applied in thermo-radiotherapy. Moreover, we investigated the level of apoptosis induced in U87-MG human glioma cells after receiving a combinatorial treatment regimen (Au@IONPs + hyperthermia + radiotherapy). Firstly, the Au@IONPs nanocomplex was prepared and characterized. Cytotoxicity of the nanoparticles (various concentrations; 4h incubation time) was investigated on U87-MG cells and finally the concentrations of 10 and 15µg/mL were selected for further studies. After incubation of the cells with nanoparticles, they received hyperthermia (43°C; 1h) and then were immediately exposed to 6 MV X-ray (2 and 4Gy). Following the treatments, MTT assay was used to analyze cell viability and flow cytometry was used to determine the level of apoptosis in each treatment group. The results revealed that nanoparticles have no significant cytotoxicity at concentrations lower than 10µg/mL. Also, we observed that nanoparticles are able to enhance the cytotoxic effect of hyperthermia and radiation. The major mode of cell death was apoptosis when nanoparticles, hyperthermia and radiation were concomitantly applied to cancer cells. In conclusion, Au@IONP nanoparticle can be considered as a good thermo-radio-sensitizer which triggers significant levels of apoptosis in cancer therapy. In this in vitro study, we report the anti-cancer effects of gold-coated iron oxide nanoparticles (Au@IONPs) when applied in thermo-radiotherapy.

Patient-specific quality control for intensity-modulated radiation therapy and volumetric-modulated arc therapy using electronic portal imaging device and two-dimensional ion chamber array

AbstractAimThe purpose of this study was to develop the patient-specific quality control (QC) process by most commonly used dosimeters in Bangladesh and recommend a suitable passing rate for QC, irrespective of the dosimetric tools used.Materials and methodsIntensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans of five head-and-neck (HN) and five prostate patients were selected for the patient-specific QC. These plans were generated using the Eclipse TPS v11·0 (Varian Medical Systems, Inc., Palo Alto, CA, USA) 6 MV X-ray from a Varian TrueBeam linear accelerator (Varian Medical Systems, Inc.) for each case. Each IMRT and VMAT plans were measured by two-dimensional (2D) ion chamber arrays (I’matriXX) and electronic portal imaging devices (EPID), respectively. The passing rates of the dosimetric tools were calculated using criteria of 3%/3 mm.ResultsThe average passing rates (±SD) of I’matriXX for prostate and HN were 97·9±0·76 and 98·88±0·24, respectively. For VMAT verification, the average passing rates of EPID for prostate for arc1 and arc2 were 96·15±0·49 and 97·8±0·70, respectively; similarly, for HN the rates were 97·85±0·63 and 97·2±0·56, respectively.ConclusionThe results showed that both the dosimeters can be used in patient-specific QC, although the EPID-based IMRT and VMAT QC is more advantageous in terms of time-saving and ease of use. Hence, for patient-specific QC, one can use the ion chamber arrays (I’matriXX) or EPID in hospital, but the systems need to be cross-checked.

A key-point based real-time tracking of lung tumor in x-ray image sequence by using difference of Gaussians filtering and optical flow

In radiation therapy, for accurate radiation dose delivery to a target tumor and reduction of the extra exposure of normal tissues, real-time tumor tracking is typically an important technique in lung cancer treatment since lung tumors move with patients’ respiration. To observe a tumor motion in real time, x-ray fluoroscopic devices can be employed, and various tracking techniques have been proposed to track tumors. However, development of a fast and accurate tracking method for clinical use is still a challenging task since the obscured image of the tumor can cause decreased tracking accuracy and can result in additional processing time for remedying the accuracy. In this study, a new key-point-based tumor tracking method, which is sufficiently fast and accurate, is presented. Given an x-ray image sequence, the proposed method employs a difference-of-Gaussians filtering technique to detect key points in the tumor region of the first frame which are robust against noise and outliers in the subsequent frames. In the subsequent frames, these key points are tracked using a fast optical flow technique, and tumor motion is estimated via their movement. To evaluate the performance, the proposed method has been tested on several clinical kV and MV x-ray image sequences. The experimental results showed that the average of the root mean square errors of tracking were and for kV and MV x-ray image sequences, respectively. This tracking performance was more accurate than previous tracking methods. In addition, the average processing times for each frame were and for kV and MV image sequences, respectively, and the proposed method was faster than previous methods as well as shorter than frame acquisition interval. Therefore, the proposed method has the potential for both highly accurate and fast tumor tracking in clinical applications.

Effect of radiation-induction on cell cycle and apoptosis in breast cancer cell lines MDA-MB-231 and MCF-7

Objective To investigate the properties of radiation-induced changes of cell cycle and apoptosis in breast cancer cell lines MDA-MB-231 and MCF-7, and to further explore its relationship with radiosensitivity. Methods The two cell lines MCF-7 and MDA-MB-231 were irradiated with 6 MV X-rays. The cell survival curves were fitted by clonogenic formation assay, then according to the radiosensitivity parameters average lethal dose (D0), quasi-threshold dose (Dq) and survival fraction after 2 Gy irradiation (SF2), the radiosensitivity of the two cell lines was compared. The apoptosis rate and cell cycle distribution of the two cell lines were detected by Hoechst 33342 and PI staining. Results The survival curve of MDA-MB-231 cell line shifted to the right compared with that of MCF-7 cell line. The values of D0, Dq and SF2 of MDA-MB-231 cell line were higher than those of MCF-7 cell line (1.603±0.023 vs. 1.233±0.027, 1.76±0.04 vs. 1.03±0.10, 0.639 3±0.008 2 vs. 0.398 1±0.018 5, t values were -17.981, -11.745, -20.596, P values were 0.000, 0.003, 0.000). The apoptosis rate of MCF-7 cell line was significantly higher than that of MDA-MB-231 cell line at the doses of 2, 4, 8 Gy irradiated 24 h and at the 12, 48 h after 6 Gy X-irradiation (t values were 4.441, 7.299, 10.499, 6.375, 7.743, P values were 0.011, 0.002, 0.000, 0.003, 0.001). Compared with the non-irradiated group, G2 phase arrest appeared in both cell lines after irradiation. The percentage of the G2/M phase in MDA-MB-231 cell line increased as the time or dosage accumulated. Furthmore, the percentage didn't go down even after 48 hours later. However, the blockage began to gradually release in MCF-7 cell line at the dose of 8 Gy irradiated 24 h and the 48 h after 6 Gy X-irradiation. Followed with that, it turned out the percentage of the G0/G1 phase increased [(65.80±0.56)%, (62.53±0.67)%]. Conclusions 6 MV X-irradiation with the doses of 2-8 Gy can induce the cell cycle arrest at G1 and G2 phase in MCF-7 cell line, G2 phase in MDA-MB-231 cell line. Thus more apoptosis appears in MCF-7 cell line, which may cause the difference in radiosensitivity between the two cell lines. Key words: Breast neoplasms; Radiosensitivity; MCF-7 cell line; MDA-MB-231 cell line; Apoptosis; Cell cycle

Disulfiram, a Re-positioned Aldehyde Dehydrogenase Inhibitor, Enhances Radiosensitivity of Human Glioblastoma Cells In Vitro

PurposeGlioblastoma, the most common brain tumor in adults, has poor prognosis. The purpose of this study was to determine the effect of disulfiram (DSF), an aldehyde dehydrogenase inhibitor, on in vitro radiosensitivity of glioblastoma cells with different methylation status of O6-methylguanine-DNA methyltransferase (MGMT) promoter and the underlying mechanism of such effect.Materials and MethodsFive human glioblastoma cells (U138MG, T98G, U251MG, U87MG, and U373MG) and one normal human astrocyte (NHA) cell were cultured and treated with DSF or 6MV X-rays (0, 2, 4, 6, and 8 Gy). For combined treatment, cells were treated with DSF before irradiation. Surviving fractions fit from cell survival based on colony forming ability. Apoptosis, DNA damage repair, and cell cycle distributionwere assayed bywestern blot for cleaved caspase-3, γH2AX staining, and flow cytometry, respectively.ResultsDSF induced radiosensitization in most of the glioblastoma cells, especially, in the cells with radioresistance as wildtype unmethylated promoter (MGMT-wt), but did not in normal NHA cell. DSF augmented or induced cleavage of caspase-3 in all cells after irradiation. DSF inhibited repair of radiation-induced DNA damage in MGMT-wt cells, but not in cells with methylated MGMT promoter. DSF abrogated radiation-induced G2/M arrest in T98G and U251MG cells.ConclusionRadiosensitivity of glioblastoma cells were preferentially enhanced by pre-irradiation DSF treatment compared to normal cell, especially radioresistant cells such as MGMT-wt cells. Induction of apoptosis or inhibition of DNA damage repair may underlie DSF-induced radiosensitization. Clinical benefit of combining DSF with radiotherapy should be investigated in the future.

Multimodal cancer cell therapy using Au@Fe2O3 core-shell nanoparticles in combination with photo-thermo-radiotherapy.

In this study, gold coated iron oxide nanoparticle (Au@Fe2O3 NP) was synthesized in a core-shell structure. Photothermal and radiosensitization effects of Au@Fe2O3 NPs were investigated on KB human mouth epidermal carcinoma cell line. Cell death and apoptosis were measured to study the effects of nanoparticles in combination with both radiotherapy (RT) and photothermal therapy (PTT). The KB cells were treated with Au@Fe2O3 NPs (20 μg/ml; 4 h) and then received different treatment regimens of PTT and/or RT using laser (808 nm, 6 W/cm2, 10 min) and/or 6 MV X-ray (single dose of 2 Gy). Following the various treatments, MTT assay was performed to evaluate the cell survival rate. Also, the mode of cell death was determined by flow cytometry using an annexinV-fluorescein isothiocyanate/propidium iodide apoptosis detection kit. No significant cell death was observed due to laser irradiation. The viability of the cells firstly incubated with NPs and then exposed to the laser was significantly decreased. Additionally, our results demonstrated that Au@Fe2O3 NP is a good radiosensitizer at megavoltage energies of X-ray. When nanoparticles loaded KB cells were received both laser and X-ray, the cell viability substantially decreased. Following such a combinatorial treatment, flow cytometry determined that the majority of cell death relates to apoptosis. In conclusion, Au@Fe2O3 NP has a great potential to be applied as a photo-thermo-radiotherapy sensitizer for treatment of head and neck tumors.

P258] Optical absorbance properties of PVA-GTA Fricke gel dosimeters irradiated with 6 MV and 15 MV X-rays

Purpose Quality assurance procedures required in the modern radiotherapy would greatly benefit by the development of tissue equivalent dosimeters able of rendering 3D dose profiles with high spatial resolution. In this scenario, Fricke gel (FG), consisting in gel matrices infused with Fricke ferrous sulphate solution combined with xylenol orange, could be good candidates, but some limits have prevented their introduction in clinical practice. Recently, new FG formulations based on gel matrices of poly-vinyl alcohol (PVA) cross-linked with glutaraldehyde (GTA) have shown important decrease of the limitations affecting FGs obtained with gelatin or agarose. Purpose of this study is the characterization of the optical absorbance (OA) and dosimetric properties of PVA-GTA FG dosimeters. Methods PVA-GTA FG dosimeters were prepared using 9.1 w/w of Mowiol®-PVA and 26.4 mM of GTA. The dosimeters, placed in spectrophotometry cuvettes (10 mm optical path), were uniformly irradiated using 6 and 15 MV X-rays generated by a Varian Clinac-2100. OA spectra were measured by means of an Agilent Cary-100 spectrophotometer. Dosimetric properties of PVA-GTA-FG dosimeters, such as reproducibility, dose–response, sensitivity, dose-rate dependence and energy dependence, were studied. Furthermore, FG in form of layers (3 mm optical path) were irradiated producing steep dose gradients and used to investigate ferric ions diffusion phenomena by means of sequential light transmittance images. Results The analysis of the OA spectra of the PVA-GTA-FG dosimeters in the wavelength interval of interest for dosimetry purposes (around 550–600 nm) revealed an intra-batch reproducibility of the order of 1.5%. The OA proved to increase linearly with increasing dose, in the investigated interval 0–15 Gy, if the wavelength used for the analysis is properly chosen. The optical response of the PVA-GT-FG dosimeters was independent of both energy and dose-rate. Furthermore, PVA-GTA matrix enables to achieve ferric ions diffusion rates approximatively 3 times lower than those observed in natural gel matrices. Conclusions This study confirmed the interesting properties of PVA-GTA FG dosimeters and indicated the best parameters for their optical analysis. Currently, studies are in progress in order to optimize Magnetic Resonance Imaging procedures for the assessment of 3D dose distributions in PVA-GTA FG phantoms.

Investigation of Combination Effect Between 6 MV X-Ray Radiation and Polyglycerol Coated Superparamagnetic Iron Oxide Nanoparticles on U87-MG Cancer Cells.

Background: Radiosensitization using nanoparticles is proposed as a novel strategy for treatment of different cancers. Superparamagnetic iron oxide nanoparticles (SPIONs) have been reported to enhance effects of radiotherapy in several researches.Objective: The objective of this research is to investigate the radiosensitization properties of polyglycerol coated SPIONs (PG-SPIONs) on U87-MG cancer cells.Material and Methods: In this experimental study, polyglycerol coated SPIONs were synthesized by thermal decomposition method and characterized by FTIR, TEM and VSM analysis. Cellular uptake of nanoparticles by cells was examined via AAS. Cytotoxicity and radiosensitization of nanoparticles in combination with radiation were evaluated by MTT and colony assay, respectively.Results: Mean size of nanoparticles was 17.9±2.85 nm. FTIR verified SPIONs coating by Polyglycerol and VSM showed that they have superparamagnetic behaviour. Viability significantly (P < 0.001) decreased at concentrations above 100µg/ml for SPIONs but not for PG-SPIONs (P > 0.05). Dose verification results by TLD for doses of 2 and 4 Gy were 2±0.19 and 4±0.12 Gy respectively. The combination index for all situations was less than 1 and the effect is antagonism.Conclusion: However, PG-SPIONs combination with 6 MV X-ray reduced survival of U87-MG cells compared to radiation alone but the effect is antagonism.

Assessment of in vitro radiosensitivity parameters of breast cancer cells following exposure to radiotherapy hospital-based facilities

Introduction: The aim of the present study was to assess the radiosensitivity parameters for SK-BR-3 (SKBR3) breast cancer cells that could be implemented in the cutting-edge treatment planning systems (TPS) for accelerated partial-breast irradiation (APBI). Materials and Methods: The cell survival fraction and its relevant radiosensitivity coefficients, namely α and β, in linear-quadratic (LQ) formalism were evaluated for 6 MV X-rays and 60Co γ-rays using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. During the irradiation time, the medium temperature was kept at 4°C to prevent the repair of sublethal radiation damages over the exposure time and keep the survival fractions independent of the dose rate. Results: Fitting the LQ model to experimental data, α, β, and α/β radiosensitivity parameters were obtained as 0.156±0.027 Gy-1, 0.026±0.007 Gy-2,and 6.0 Gy for 6 MV X-rays and 0.162±0.028 Gy-1, 0.028±0.007 Gy-2, and 5.8 Gy for 60Co gamma radiation, respectively. The average relative biological effectiveness (RBE) values were 0.91 and 0.96 for 6 MV X-rays and 60Co γ-rays, respectively. The derived LQ parameters were also compared with those previously obtained from in vitro studies for different breast cancer cell lines using various regimes, such as radiotherapy modality with different dose rates and delivered doses. Conclusion: The results of this study provided essential constant values for α and β parameters. The data could be useful for the improvement of TPS to include the effect of different biological responses to radiation in APBI treatment plans.

Abstract 1376: Effect of gold nanoparticle on radiation induced DNA damage in MCF7 breast cancer cells

Abstract Nanoparticles (NPs) are 1-100 nm constructs explored for their application in cancer diagnosis and treatment. Exposure of cells to ionizing irradiation leads to DNA damage, with DNA double strand breaks (DSBs) being the most toxic that can lead to apoptosis. The presence of gold in NPs enhances radiation damage and DSBs, the latter measured by the levels of phosphorylated DNA histone protein H2AX (γH2AX). The goal of this study was to decipher biological mechanisms of NP radio-sensitization. We analyzed the effects of two different sizes of gold nanoparticles (AuNP) on DSBs in MCF-7 breast cancer cells by assessing H2AX phosphorylation at three photon energies. Cells were incubated with either 4 nm or 14 nm AuNP and irradiated with 2, 4 or 8 Gy using 2.5 FFF MV (60 MU/min), 6 MV (600 MU/min) or 10 FFF MV (2400 MU/min) X-rays. Percent of cells positive for γH2AX was determined by flow cytometry. Live cells (100000) were gated using forward (FSC; cell size) versus side scatter (SSC; complexity) characteristics (gate P1). Cells positive for γH2AX were further gated to identify subpopulations exhibiting brighter (gate P2) or dimmer (gate P3) fluorescence intensity. Treatment with 4 nm AuNP resulted in significantly more γH2AX positive cells after irradiation at all three energies, compared to their respective controls. When treated at 6 MV energy, increases in the percentage of cells positive for H2AX phosphorylation was detected at all three doses (2, 4 and 8 Gy). Increased phosphorylation was accompanied by an increase of cells in the P2 gate accompanied by an increase in their FCS and SSC characteristics, consistent with activation. In cells treated with 10 MV the effect was most pronounced at 4Gy dose, while 2 and 8 Gy resulted in a slight increase in the percentage of γH2AX positive cells. Nevertheless, these cells still exhibited prominent increases within the P2 gate and FCS vs SSC characteristics, compared to their irradiated controls. In cells treated with 2.5 MV energy similar results were observed using 4 and 8 Gy, while no effect was detected with 2 Gy. Data from the experiments using 14 nm size AuNP were less clear and require further investigation. The difference may be due to the localization of the smaller NPs within the nucleus and therefore cause more DNA damage thereby greater H2AX phosphorylation. We hypothesize that the NP radio-sensitization mechanism involves directing cells towards apoptosis by enhancing DNA damage and interfering with DNA repair. Hence, γH2AX positive cells exhibiting bright fluorescence (P2) and an increase in FCS and SSC identified even in the conditions without significant increase in the percent of total γH2AX positive cells, may reflect cells primed for apoptosis. Future studies are planned to elucidate the exact intracellular mechanisms of NP biological radio-sensitization effect. Citation Format: Branislava Janic, Fangchao Liu, Kevin Bobbitt, Stephen Brown, Guangzhao Mao, Indrin J. Chetty, Benjamin Movsas, Ning Winston Wen. Effect of gold nanoparticle on radiation induced DNA damage in MCF7 breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1376.

Construction of dose response curves up to 6 Gy for Micronucleus and Dicentric Chromosome Aberration Assay with 6 MV X-ray Beam

In-vitro dose response curves were built with 6 MV X-ray for a dose range of 0.1–6 Gy, at a dose rate of 300 cGy/min, using Linear Accelerator (LINAC, SIMENS PRIMUS) for Cytokinesis-Block Micronucleus (CBMN) and Dicentric Chromosome Aberration assay (DCA). The dose response curves constructed up to 6 Gy and also up to 4 Gy using the manual method were compared to those curves obtained with the software program such as CABAS (V.2) and Dose Estimate software (V.5.2). The alpha and beta coefficients for MN and CA obtained for the curves constructed up to 6 Gy showed variation compared to those obtained in dose response curve constructed up to 4 Gy. However, the doses estimated based on these coefficients did not show much variation. The results are discussed in this paper.