MV X-ray Research Articles

Measurements of doses from photon beam irradiation and scattered neutrons in an anthropomorphic phantom model of prostate cancer: a comparison between 3DCRT, IMRT and tomotherapy

Abstract Introduction. The rapid development of new radiotherapy technologies, such as intensity modulated radiotherapy (IMRT) or tomotherapy, has resulted in the capacity to deliver a more homogenous dose in the target. However, the higher doses associated with these techniques are a reason for concern because they may increase the dose outside the target. In the present study, we compared 3DCRT, IMRT and tomotherapy to assess the doses to organs at risk (OARs) resulting from photon beam irradiation and scattered neutrons. Material and methods. The doses to OARs outside the target were measured in an anthropomorphic Alderson phantom using thermoluminescence detectors (TLD 100) 6Li (7.5%) and 7Li (92.5%). The neutron fluence rate [cm−2·s−1] at chosen points inside the phantom was measured with gold foils (0.5 cm diameter, mean surface density of 0.108 g/cm3). Results. The doses [Gy] delivered to the OARs for 3DCRT, IMRT and tomotherapy respectively, were as follows: thyroid gland (0.62 ± 0.001 vs. 2.88 ± 0.004 vs. 0.58 ± 0.003); lung (0.99 ± 0.003 vs. 4.78 ± 0.006 vs. 0.67 ± 0.003); bladder (80.61 ± 0.054 vs. 53.75 ± 0.070 vs. 34.71 ± 0.059); and testes (4.38 ± 0.017 vs. 6.48 ± 0.013 vs. 4.39 ± 0.020). The neutron dose from 20 MV X-ray beam accounted for 0.5% of the therapeutic dose prescribed in the PTV. The further from the field edge the higher the contribution of this secondary radiation dose (from 8% to ~45%). Conclusion. For tomotherapy, all OARs outside the therapeutic field are well-spared. In contrast, IMRT achieved better sparing than 3DCRT only in the bladder. The photoneutron dose from the use of high-energy X-ray beam constituted a notable portion (0.5%) of the therapeutic dose prescribed to the PTV.

Analysis of spatial diffusion of ferric ions in PVA-GTA gel dosimeters through magnetic resonance imaging

This work focused on the analysis of the temporal diffusion of ferric ions through PVA-GTA gel dosimeters. PVA-GTA gel samples, partly exposed with 6MV X-rays in order to create an initial steep gradient, were mapped using magnetic resonance imaging on a 7T MRI scanner for small animals. Multiple images of the gels were acquired over several hours after irradiation and were analyzed to quantitatively extract the signal profile. The spatial resolution achieved is 200μm and this makes this technique particularly suitable for the analysis of steep gradients of ferric ion concentration. The results obtained with PVA-GTA gels were compared with those achieved with agarose gels, which is a standard dosimetric gel formulation. The analysis showed that the diffusion process is much slower (more than five times) for PVA-GTA gels than for agarose ones. Furthermore, it is noteworthy that the diffusion coefficient value obtained through MRI analysis is significantly consistent with that obtained in separate study Marini et al. (Submitted for publication) using a totally independent method such as spectrophotometry. This is a valuable result highlighting that the good dosimetric features of this gel matrix not only can be reproduced but also can be measured through independent experimental techniques based on different physical principles.

Practical time considerations for optically stimulated luminescent dosimetry (OSLD) in total body irradiation.

Total body irradiation (TBI) treatments are used to treat the whole body in preparation for hematopoietic stem cell (or bone marrow) transplantation. Our standard clinical regimen is a 12Gy in 6 fraction, bi-daily technique using 6 MV X-rays at an extended Source-to-Surface distance (SSD) of 300cm. Utilizing these characteristics, the beam dose rate is reduced below 7cGy/min as is standard for TBI treatment. Dose received by the patient is monitored using optically stimulated luminescent dosimetry (OSLD). This work presents some practical calibration corrections based on time-dependant factors for OSLD calibration related to TBI procedure. Results have shown that a negligible difference is seen in OSL sensitivity for 6MV X-rays irradiated in standard SSD (100cm) and high dose rate (600cGy/min) conditions compared to extended SSD (300cm) and low TBI dose rate (6cGy/min) conditions. Results have also shown that whilst short term signal fading occurs in the OSL after irradiation at a high dose rate (37% reduction in signal in the first 15min), thereafter, negligible differences are seen in the OSL signal between 600 and 7cGy/min irradiations. Thus a direct comparison can be made between calibration OSLs and clinical TBI OSLs between 15min and 2h. Finally a table is presented to provide corrections between calibration OSL readout and clinical TBI dose readout for a period up to 7 days. Combining these three results allows users to pre-irradiate their calibration OSLs at standard dose rate and SSD, up to 1 week prior to clinical treatment, and still provide accurate in-vivo dosimetry. This can help with time saving and work efficiency in the clinic.

Comparison of dosimeter response of TLD-100 and ionization chamber for high energy photon beams at KIRAN Karachi in Pakistan

This study was conducted by measuring point dose at different depths of water phantom by using two types of dosimeters (PTW N30013 ionization chamber and TLD-100 chips) at Karachi institute of radiotherapy and nuclear medicine (KIRAN), Pakistan. Two different TLD chips were used (circular pallets and square chips). The main aim of this study was to compare the responses of two different types of dosimeter irradiated with 6MV X-rays using same parameters. Both types of dosimeter were irradiated with different dose value ranging from 25cGy to 500cGy. The deviation between different shapes of TLD and ionization chamber remained within 5% limit. Maximum deviations of circular pallets reading from that of ion chamber are 3.56% at 1.5cm depth and 4.91% at 5cm depth. For square chips maximum deviation happened to be 4.38% at 1.5cm depth and 4.23% at 5cm depth. This measurement shows that TLDs are reliable tool for dosimetry regardless of their shape or manufacturer and they can be used as re-validation tool for ion chamber dosimetry.

Outcomes of Spatially Fractionated Radiotherapy (GRID) for Bulky Soft Tissue Sarcomas in a Large Animal Model.

GRID directs alternating regions of high- and low-dose radiation at tumors. A large animal model mimicking the geometries of human treatments is needed to complement existing rodent systems (eg, microbeam) and clarify the physical and biological attributes of GRID. A pilot study was undertaken in pet dogs with spontaneous soft tissue sarcomas to characterize responses to GRID. Subjects were treated with either 20 Gy (3 dogs) or 25 Gy (3 dogs), delivered using 6 MV X-rays and a commercial GRID collimator. Acute toxicity and tumor responses were assessed 2, 4, and 6 weeks later. Acute Radiation Therapy Oncology Group grade I skin toxicity was observed in 3 of the 6 dogs; none experienced a measurable response, per Response Evaluation Criteria in Solid Tumors. Serum vascular endothelial growth factor, tumor necrosis factor α, and secretory sphingomyelinase were assayed at baseline, 1, 4, 24, and 48 hours after treatment. There was a trend toward platelet-corrected serum vascular endothelial growth factor concentration being lower 1 and 48 hours after GRID than at baseline. There was a significant decrease in secretory sphingomyelinase activity 48 hours after 25 Gy GRID (P = .03). Serum tumor necrosis factor α was quantified measurable at baseline in 4 of the 6 dogs and decreased in each of those subjects at all post-GRID time points. The new information generated by this study includes the observation that high-dose, single fraction application of GRID does not induce measurable reduction in volume of canine soft tissue sarcomas. In contrast to previously published data, these data suggest that GRID may be associated with at least short-term reduction in serum concentration of vascular endothelial growth factor and serum activity of secretory sphingomyelinase. Because GRID can be applied safely, and these tumors can be subsequently surgically resected as part of routine veterinary care, pet dogs with sarcomas are an appealing model for studying the radiobiologic responses to spatially fractionated radiotherapy.

The effects of gold nanoparticles concentrations and beam quality/LET on dose enhancement when irradiated with X-rays and protons using alanine/EPR dosimetry

This research investigates the effects on dose enhancement (DE) caused by secondary electrons when varying concentrations of gold nanoparticles (AuNPs) are irradiated with different quality beams (proton, kV and MV X-rays) over clinical doses ranges (2–20 Gy). Spherical gold-nanoparticles (5 nm) were added to l-alanine, producing composites of 3, 2 and 1% (w/w) AuNPs, dispersed uniformly within wax pellets of dimensions 10 × 5 × 5 mm. The pellets were irradiated within a phantom alongside control pellets (l-alanine) and the yield of alanine radicals quantified by Electron Paramagnetic Resonance (EPR) spectroscopy. Comparison of the EPR signal produced by the AuNP/alanine composites to that of the control l-alanine pellets is reported as the DE. For X-rays (kV and MV) the DE increased with increasing AuNP concentration, with kV X-rays (80 kV) having the highest levels of DE; 55% for the 3% AuNP/alanine composites, which reduced to 15% for the 1 %-composites. Whilst 6 MV X-rays showed a DE of 17% for the 3 %-composites, which was reduced to 2% DE for the 1 %-composites. Irradiations with protons (150 MeV, SOBP) showed no such dependence on the AuNP concentration and consistently yielded DE levels of ≤5% for all AuNP concentrations investigated. These results agree with recent Monte Carlo simulations reporting little to no secondary electron production when AuNPs are irradiated with protons, and supports studies that the higher DE seen in cell and animal studies (ca.15–20%) for AuNPs irradiated with protons is due to other processes, such as the production of reactive oxygen species (ROS) generated from the aqueous media in cells, which are not measured in this experiment.

Dedicated high dose rate 192Ir brachytherapy radiation fields for in vitro cell exposures at variable source-target cell distances: killing of mammalian cells depends on temporal dose rate fluctuation

Afterloading brachytherapy is conducted by the stepwise movement of a radioactive source through surgically implanted applicator tubes where at predefined dwell positions calculated dwell times optimize spatial dose delivery with respect to a planned dose level. The temporal exposure pattern exhibits drastic fluctuations in dose rate at a given coordinate and within a single treatment session because of the discontinuous and repeated source movement into the target volume. This could potentially affect biological response. Therefore, mammalian cells were exposed as monolayers to a high dose rate 192Ir source by utilizing a dedicated irradiation device where the distance between a planar array of radioactive source positions and the plane of the cell monolayer could be varied from 2.5 mm to 40 mm, thus varying dose rate pattern for any chosen total dose.The Gammamed IIi afterloading system equipped with a nominal 370 GBq (10 Ci) 192-Ir source was used to irradiate V79 Chinese hamster lung fibroblasts from both confluent and from exponential growth phase with dose up to 12 Gy (at room temperature, total exposure not exceeding 1 h). For comparison, V79 cells were also exposed to 6 MV x-rays from a clinical linear accelerator (dose rate of 2.5 Gy min−1). As biological endpoint, cell survival was determined by standard colony forming assay. Dose measurements were conducted with a diamond detector (sensitive area 7.3 mm2), calibrated by means of 60Co radiation. Additionally, dose delivery was simulated by Monte Carlo calculations using the EGSnrc code system. The calculated secondary electron fluence spectra at the cell location did not indicate a significant change of radiation quality (i.e. higher linear energy transfer) at the lower distances.Clonogenic cell survival curves obtained after brachytherapy exhibited an altered biological response compared to x-rays which was characterized by a significant reduction of the survival curve shoulder when dose rate fluctuations were high. Therefore, also for the time scale of the present investigation, cellular effects of radiation are not invariant to the temporal pattern in dose rate. We propose that with high dose rate variation the cells activate less efficiently their DNA damage response than after continuous irradiation.

Nanostructures, concentrations and energies: an ideal equation to extend therapeutic efficiency on radioresistant 9L tumor cells using ceramic nanostructured particles

This work presents an in-depth analysis into the dependencies of radiosensitisation on x-ray beam energy, particle morphology and particle concentration for nanostructured particles (NSPs). A maximum sensitisation enhancement ratio of 1.46 was attained with irradiation of a 10 MV x-ray photon beam on 9L cells exposed to the less aggregated form of NSPs at 500 μg ml−1. A significant increase in sensitisation of 30% was noted at 150 kVp for irradiation of the less aggregated form of tantalum pentoxide NSPs compared to its more agglomerated counterpart. Interestingly, no differences in sensitisation were observed between 50 and 500 μg ml−1 for all beam energies and NSPs tested. This is explained by a physical ‘shell effect’, where by the NSPs form layers around the cells (observed using confocal microscopy), with the inner layers contributing to enhancement, while the outer layers shield the cell from damage.

Applicability of two-dimensional thermoluminescence slab dosimeter based on Al2O3:Cr for the quality assurance of robotic radiosurgery

Two-dimensional (2-D) thermoluminescence (TL) slab dosimeters based on Al2O3:Cr have been recently developed. They have high solidity, spatial resolution, repeatability and linearity, and they can be immersed in water. In the present work, their clinical applicability for quality assurance (QA) testing of the CyberKnife® robotic radiosurgery system was investigated. Those TL slabs were irradiated with 6 MV X-rays and were read out using a 2-D TL reader equipped with a large hot plate and a complementary metal-oxide-semiconductor (CMOS) camera. A comparison was made with the results obtained using radiochromic films (RCFs), which are typically used as 2-D dosimeters. It was found that those TL slabs provided sufficient precision for geometric QA tests and dose-distribution verification. Although the energy dependence for Al2O3:Cr TL slabs was larger than that for tissue-equivalent thermoluminescence dosimeters (TLDs), this had little effect in robotic radiosurgery. Thus, the results demonstrated that those TL slabs can act as replacements for RCFs for QA of robotic radiosurgery.

Increased radiotoxicity in two cancerous cell lines irradiated by low and high energy photons in the presence of thio-glucose bound gold nanoparticles

Purpose: Gold nanoparticles modified by thio-glucose are believed to increase the toxicity of radiotherapy in human malignant cells. We report the effect of thio-glucose bound gold nanoparticles (Glu-G nanoparticles), 16 nm in size, on two human lung (QU-DB) and breast (MCF7) cancer cell lines combined with kilo and megavoltage X-rays.Materials and methods: The shape and surface characteristics, the size distribution and light absorption spectrum of the prepared nanoparticles were measured by transmission electron microscopy, dynamic light scattering, and ultraviolet-visible spectrophotometry, respectively. The cell uptake was assayed using the atomic absorption spectrometry. Mitochondrial activity, colony formation, and comet assays were applied to assess and compare the enhanced radiotoxicity of 100 KV and 6 MV X-rays, when combined with Glu-G nanoparticles.Results: Glu-G nanoparticles had no significant toxicity for MCF7 and QU-DB cells up to 100 micromolar concentration. Compared to radiation alone, the intracellular uptake of Glu-G nanoparticles resulted in increased inhibition of cell proliferation by 64.1% and 38.7% for MCF7 cells, and 64.4% and 32.4% for QU-DB cells by 100 kVp and 6 MV X-rays, respectively. Comet assay confirmed an increase of DNA damage as a result of combination of 6 MV photons with Glu-G nanoparticles.Conclusion: Glu-G nanoparticles have remarkable potential for enhancing radiotoxicity of both low and high energy photons in MCF7 and QU-DB cells.

Enhanced DNA Damages of Human Prostate Cancer Cells Induced by Radiofrequency Capacitive Hyperthermia Pre- and Post X-rays: 6 MV versus 15 MV.

Objective This study aimed to determine the effect of 13.56 MHz radiofrequency (RF) capacitive hyperthermia (HT) on radiosensivity of human prostate cancer cells pre and post X-ray radiation treatment (RT). Materials and Methods In this experimental study, the human prostate cancer cell line DU145 was cultured as 300 µm diameter spheroids. We divided the spheroids into group I: control, group II: HT at 43˚C for 30 minutes (HT), group III: 4 Gy irradiation with 6 MV X-ray [RT (6 MV)], group IV: 4 Gy irradiation with 15 MV X-ray [RT (15 MV)], group V: HT+RT (6 MV), group VI: HT+RT (15 MV), group VII: RT (6 MV)+HT, and group VIII: RT (15 MV)+HT. The alkaline comet assay was used to assess DNA damages in terms of tail moment (TM). Thermal enhancement factor (TEF) was obtained for the different treatment combinations. Results Mean TM increased with increasing photon energy. Group II had significantly greater TM compared to group I. Groups III and IV also had significantly higher TM compared to group I. Significant differences in TM existed between groups V, VII, and III (P<0.05). We observed significant differences in TM between groups VI, VIII, and IV. TEF values demonstrated that enhanced response to radiation was more pronounced in group V compared to the other combined treatments. ConclusionOur results suggest that HT applied before RT leads to higher radiosensivity compared to after RT. HT at 43˚C for 30 minutes added to 6 MV X-ray causes higher enhancement of radiation compared to 15 MV X-ray.

P1.05-031 Primary Results of Dose Escalated Stereotactic Body Radiotherapy for Stage IA Non-Small Cell Lung Cancer

JCOG 0403 showed excellent overall survival in stereotactic body radiotherapy (SBRT) for stage IA non-small cell lung cancer (NSCLC). In Japan, 48Gy/4Fr for isocenter have been the standard dose fractionation of SBRT for stage IA NSCLC. JCOG0702 showed that dose escalation of 55Gy for PTVD95% was feasible in SBRT for peripheral small (PTV volume 100cc or less) NSCLC. Intensification of local treatment with dose escalation is considered to be one of the measures for improvement of overall survival. In 2011, we adopted dose escalated regimen (50Gy/4Fr for PTVD95%) for SBRT for stage IA NSCLC, expected improvement of local control and overall survival. The purpose of this study was to review and report the primary results of dose escalated SBRT for stage IA NSCLC. From August 2011 to April 2015, 31 patients with stage IA NSCLC were treated with dose escalated SBRT at the University of Yamanashi. The patients' ages ranged from 61 to 86 (median 79) years. Twenty two patients were male, 9 were female. Performance status was 0 in 26, 1 in 5 patients. Tumor histology was squamous cell carcinoma in 6 and adenocarcinoma in 23, other NSCLC in 2 patients. Clinical stage was T1a in 19, T2b in 12 patients. A multiple static ports radiation planned by a radiation treatment planning system (Pinnacle3 Version 9.2-9.8) was performed with linac using 6MV x-ray beams. The Breath hold technique and CT image guided set-up were used in all cases. A total dose of 50Gy was delivered in 4 fractions over 4-5days. Radiation doses were prescribed to the 95% of planning target volume (PTVD95%). A superposition algorithm with heterogeneity correction was used for dose calculations. The follow-up period for all patients was 3.3-43.1 (median 23.7) months. The overall survival rate at one year and two years were 87.1%, 79.3%, respectively. The local control rate at one year and two years were both 96.4%. Local recurrence, regional lymph node metastases, and distant metastases were observed in 1, 4 and 3 patients, respectively. Regarding to the toxicities, grade 3 radiation pneumonitis were observed in 3 patients. Grade 2 rib fractures were observed in 3 patients. There were no Grade 4 or greater adverse events in the follow-up period. The toxicity was considered to be acceptable. The local control effect was considered to be sufficient. Longer follow- up durations are needed to validate the clinical benefits of dose escalated SBRT for stage IA NSCLC.

Radioprotective effects of lentil sprouts against X-ray radiation.

The present study investigated the radioprotective efficacy of lentil (Lens culinaris) sprouts against X-ray radiation-induced cellular damage. Lentil seeds were dark germinated at low temperature and the sprout extract was prepared in PBS. Free radical scavenging of extract was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and then the radioprotective potency of extract (0 to 1000 μg/mL) on the lymphocyte cells was determined by lactate dehydrogenases assay. Moreover, micronuclei assay was assessed using the cytokinesis-block technique. The irradiations were performed using 6 MV X-ray beam. The value of IC50 for DPPH assay was 250 μg/mL. The median lethal dose for radiation was determinate at 5.37 Gy. Pretreatment with lentil sprout extract at 1000 μg/mL reduced cytotoxicity at 6 Gy total concentration from 70% to 50%. The results of micronuclei assay indicated that cells were resistant to radiation at concentrations of 500–1000 μg/mL of exogenous lentil sprout extract. The value of median effective concentration for micronuclei assay was 500 μg/mL. The results indicated that lentil sprout extract showed actually somewhat radioprotective effect on lymphocyte cell. In addition, the obtained results suggest that extract of total lentil sprout have more antioxidant activity than radicle part.

The Impact of Small Field’s Off-Set on Output Factor in Intensity Modulated Radiation Treatment

In intensity modulated radiation treatment (IMRT) planning, the use of asymmetrically collimated fields that are placed on central axis or its off-set is mostly required. Output is the main topic discussed today for extremely small and/or severe irregularly shaped fields. The air scatter data are involved directly or indirectly in obtaining the output. Despite the fact that extensive data have been published in many studies to provide a guide on the magnitude of output factor for clinical accelerators, there are very few data reviewed about output factor in-air or phantom for off-set fields. This study was aimed to investigate the impact of these conditions for small fields. This study was conducted in Elekta Synergy linear accelerator which produces 6 MV X-ray energy. The in-air output factor (Sc) has been measured by CC04 ion chamber with brass-alloy “build-up” cap and Dose-1 electrometer, and the total output (Scp) measurements were carried on at dose maximum depth in phantom by the same chamber and Thermoluminescence dosimeter (TLD) for 1 - 10 cm2 fields. The all measurements at center of isocenter and off-set fields at three directions (X2, Y1, Diagonal) were done. By decreasing field size from 10 to 2 cm2 at isocenter, the Sc value using CC04 was decreased to 5.4% and Scp using CC04 and TLD to 14.5% and 11% respectively. By increasing off-set value, the Sc and Scp values were increased in all directions comparing to central fields. The maximum increase was obtained in Y1 direction for Sc and Scp. TLD results for Scp is slightly higher than CC04. The dosimetric properties of small fields and their off-set should be evaluated and modelled appropriately in the treatment planning system to ensure accurate dose calculation in Intensity Modulated Radiation Treatment.

Outcome and long-term efficacy of four facio-cervical fields conformal radiotherapy for nasopharyngeal carcinoma.

PurposeTo evaluate the outcomes of 255 patients with nasopharyngeal carcinoma (NPC) treated with four facio-cervical fields conformal radiotherapy (4F-CRT).ResultsIn one patient's 3 different RT treatment modalities, the 4F-CRT techniques resulted in sharper of the dose-volume histograms (DVHs) for primary gross tumor volume (PGTVnx) and planning target volume (PTVnx), similar to the intensity modulated radiation therapy (IMRT). The median follow-up duration was 43 months. Locoregional relapse and distant metastases as the first treatment failure events occurred in 32 (32/255, 12.5%) and 20 (30/255, 11.8%) patients, respectively. The 3-year and 5-year local control, disease-free survival, and overall survival rates were 83.3%, 82%, 83.8%, and 76.1%, 73.2%, 76.3% respectively. Univariate analysis displayed that clinical stage, T-stage, N-stage, and tumor response were related to prognosis. Multivariate analysis indicated that age, T-stage, N-stage, and combined chemotherapy were independent prognosticators. The incidence of grade 1–2 acute mucositis and leukocytopenia were 93.7% and 91.0%, respectively, with no cases of grade 4 toxicity detected.Materials and MethodsFrom November 2007 to December 2011, 255 patients with histologically diagnosed, non-metastatic NPC were enrolled into this study and received 4F-CRT. Magnetic resonance imaging scans of the nasopharynx were performed on every patient. All patients received definitive radiotherapy with 6 MV X-rays using conventional fractions at 2 Gy daily, 5 fractions per week, and 231 patients with stage IIb-IV received concurrent chemotherapy and cisplatin-based adjuvant chemotherapy. The accumulated survival was calculated according to the Kaplan-Meier method; the log-rank test was used to compare survival differences. Multivariate analysis was performed using Cox's proportional hazard model.ConclusionsCompared with the conventional treatment plans, the 4F-CRT plan delivered more dose to cover the tumor volume and reduces the doses of the normal tissues including the parotid gland, TMJs and so on. The long-term efficacy of 4F-CRT is satisfactory and its toxicities are tolerable.

6 MV X-선 빔의 등가에너지 결정

본 연구의 목적은 실험으로 6 MV X-선 빔의 등가에너지를 결정하는 데 있다. 6 MV X-선 빔에 대한 납의 반가층은 전리함을 사용하여 측정하였다. 선감쇠계수는 측정된 반가층을 사용하여 계산하였다. 그리고 질량감쇠계수는 납의 밀도로 선감쇠계수를 나누어 얻었다. 얻어진 질량감쇠계수의 등가에너지는 미국표준기술연구소에서 주어진 납의 광자에너지 대 질량감쇠계수 자료를 사용하여 결정하였다. 그 결과로서, 6 MV X-선 빔에 대한 등가에너지는 1.61 MeV로 결정되었다. 이 등가에너지는 Reft가 보고한 것 보다 약 30% 낮게 결정되었다. 그 원인은 납 감쇠기 사이의 공기공동의 존재에 기인한 것으로 추정된다. The purpose of this study is to determine the equivalent energy of a 6MV X-ray beam in the experiment. The half-value layer (HVL) of lead for the 6 MV X-ray beam was measured using an ionization chamber. The linear attenuation coefficients were calculated with HVL. And, the mass attenuation coefficient was obtained by dividing the linear attenuation coefficient by the density of lead. The equivalent energy of mass attenuation coefficient was determined using the photon energy versus mass attenuation coefficient data of lead given by National Institute of Standards and Technology (NIST). In conclusion, the equivalent energy of the 6 MV X-ray beam was determined to be 1.61 MeV. This equivalent energy was determined to be about 30% lower than reported by Reft. The reason is presumed to be due to the presence of an air cavity between the lead attenuators.

Gold nanoparticles in combination with megavoltage radiation energy increased radiosensitization and apoptosis in colon cancer HT-29 cells

Purpose: Gold nanoparticles (GNP) act as a radiosensitizer in radiation therapy. However, recent studies have shown contradictory evidence in terms of radiosensitization in the presence of GNP combined with X-ray megavoltage energy (MV) on different cell types. In this study, the effect of GNP on radiosensitization enhancement of HT-29 human colorectal cancer cells at MV X-ray energy was evaluated.Materials and methods: The cytotoxicity and radiosensitization of GNP were evaluated in HT-29 human colorectal cancer cells by MTS-assay and multiple MTS-assay, respectively. Cellular uptake was assayed using graphite furnace atomic absorption spectrometry (GFAAS). Apoptosis and cell cycle progression were determined by an Annexin V-FITC/propidium iodide (PI) kit and PI/RNase solution with flow cytometry, respectively.Results: Results showed that the cell viability of the HT-29 cells was not influenced by exposure to different concentrations of GNP (10–100 μM). GNP alone did not affect the cell cycle progression and apoptosis. In contrast, GNP, in combination with radiation (9 MV), induced more apoptosis. The interaction of GNP with MV energy resulted in a significant radiosensitization enhancement compared with irradiation alone.Conclusion: It was concluded that GNP may work as bio-inert material on HT-29 cancer cells and their enhancement of radiosensitization may be due to increase in the absorbed irradiation dose.

OPTIMUM TREATMENT MODE APPLIED TO POST-OPERATIVE CERVICAL CANCER FOR 5F-IMRT PLAN BASED ON FOUR VARIABLES IN VARIAN ECLIPSE TPS

Purpose: This study aimed to determine the dosimetric effect on the target volume, organs at risk (OARs) and normal tissues based on the different choice for four types of mechanical variables, i.e., treatment position, dose calculation algorithm, mulitleaf collimator (MLC) motion mode and X-ray energy; and to investigate the optimum treatment mode applied to post-operative cervical cancer for 5-field intensity-modulated radiation therapy (5F-IMRT) technique. Methods: The dosimetric difference on the target volume and OARs under the influence of four types of variables were initially compared by changing one variable at a time. Then, based on the above compared results, we compared the dosimetric difference on planning target volume (PTV) and OARs between group A composed of the superior four variables and group B composed of the relatively inferior four variables. The dosimetric parameters included dose distribution of the target volume, OARs and normal tissues, conformal index (CI), homogeneity index (HI), monitor units (MU) and beam-on time ([Formula: see text]. The independent and paired t-tests were used for statistical analysis, and the threshold for statistical significance was [Formula: see text]. Results: Compared with the supine position, the maximum dose of PTV ([Formula: see text]), the maximum dose of small intestine ([Formula: see text]) and [Formula: see text] of bladder ([Formula: see text] were all lower in prone position. In contrast with the pencil beam convolution (PBC), CI of PTV (CI[Formula: see text]) was larger while HI of PTV (HI[Formula: see text]) was lower, both [Formula: see text] and the maximum dose of rectum ([Formula: see text]) were lower using anisotropic analytical algorithm (AAA). Moreover, the same results were obtained using sliding window (SW) compared with multiple static segments (MSS). The mean dose of PTV ([Formula: see text] and CI[Formula: see text] was larger while the maximum dose of the spinal cord ([Formula: see text]), [Formula: see text] and the maximum dose of femoral heads were lower with 15 MV X-rays compared with 6 MV X-rays. In comparison with group B comprising the supine position, PBC, MSS and 6 MV X-rays, [Formula: see text] and HI[Formula: see text] decreased 1.4% and 53.4% respectively, CI[Formula: see text] increased 5.8% medially, while [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] all decreased in group A comprising of prone position, AAA, SW and 15 MV X-rays. Conclusion: The treatment mode composed of prone position, AAA algorithm, SW and 15 MV X-rays is chosen for the post-operative cervical cancer of 5F-IMRT technique, which is more capable of meeting the target volume constraints and maximal protection of OARs.

Development of a combined radiation and full thickness burn injury minipig model to study the effects of uncultured adipose-derived regenerative cell therapy in wound healing

Purpose: To develop an approach that models the cutaneous healing that occurs in a patient with full thickness thermal burn injury complicated by total body radiation exposure sufficient to induce sub-lethal prodromal symptoms. An assessment of the effects of an autologous cell therapy on wound healing on thermal burn injury with concomitant radiation exposure was used to validate the utility of the model.Methods: Göttingen minipigs were subjected to a 1.2 Gy total body irradiation by exposure to a 6 MV X-ray linear accelerator followed by ∼10 cm2 full thickness burns (pre-heated brass block with calibrated spring). Three days after injury, wounds were excised to the underlying fascia and each animal was randomized to receive treatment with autologous adipose-derived regenerative cells (ADRC) delivered by local or intravenous injection, or vehicle control. Blood counts were used to assess radiation-induced marrow suppression. All animals were followed using digital imaging to assess wound healing. Full-thickness biopsies were obtained at 7, 14, 21 and 30 days’ post-treatment.Results: Compared to animals receiving burn injury alone, significant transient neutropenia and thrombocytopenia were observed in irradiated subjects with average neutrophil nadir of 0.79 × 103/μl (day 15) and platelet nadir of 60 × 103/μl (day 12). Wound closure through a combination of contraction and epithelialization from the wound edges occurred over a period of approximately 28 days’ post excision and treatment. Re-epithelialization was accelerated in wounds treated with ADRC (mean 3.5-fold increase at 2 weeks post-treatment relative to control). This acceleration was accompanied by an average 67% increase in blood vessel density and 30% increase in matrix (collagen) deposition. Similar results were observed when ADRC were injected either directly into the wound or by intravenous administration.Conclusions: Although preliminary, this study provides a reproducible minipig model of thermal burn injury complicated by myelosuppressive total body irradiation that utilizes standardized procedures to evaluate novel countermeasures for potential use following attack by an improvised nuclear device.

Comparison of DSB effects of the beta particles of iodine-131 and 6 MV X-ray at a dose of 2 Gy in the presence of 2-Methoxyestradiol, IUdR, and TPT in glioblastoma spheroids

Glioblastoma is one of the lethal brain tumors and one of the resistant tumors against radiotherapy. Multiple treatment methods and different types of radiation and Radiosensitizers drugs have been combined to optimize the efficacy of radiotherapy. Radiosensitizers are employed to reinforce tumor cell killing and have much fewer effects on the normal tissue. Inducing DNA double strand break in tumoral cells is a major goal of radiation sensitivity. In this study, the level of DNA double strand break in glioblastoma spheroids irradiated by 2Gy beta particles of iodine-131 and 6MV X-rays in the presence of 2-Methoxyestradiol (2ME2), iodo-deoxy-uridine (IUdR) and Topotecan (TPT) was measured using the PicoGreen method.Spheroids of the U87MG cell line were cultured to reach a 300µm diameter. In the phase one of the study, the spheroids were treated in four groups individually, including 2Gy of iodine-131, TPT+iodine-131, IUdR+iodine-131, IUdR+2ME2+iodine-131. In the next phase, the cells were treated with 2Gy of 6MV X-ray, TPT+6MV X-ray, IUdR+6MV X-ray, TPT+IUdR+6MV X-ray. DSB lesions were measured by the Pico Green assay. The amount of DSB lesions in groups irradiated with iodine-131 individually was greater than the group irradiated with 6MV X-ray (p<0.05). DNA double strand breaks became more significant in combination with TPT. However, the amount of DSBs in the two independent groups of TPT+IUdR+2ME2+iodine-131 and TPT+IUdR+2ME2+6MV X-ray was approximately in the same range (P>0.05). The level of DNA double strand breaks in cells irradiated with Iodine-131 was higher than cells irradiated with 6MV X-ray at the same dose and Topotecan had a positive effect on inducing the damage. The role of 2ME2+IUdR in increasing the damage caused by beta particles of iodine-131 was not significant. Iodine-131 could lead to major DSB damage than 6MV X-ray at the same dose due to its cross fire effect and spatial distribution of energy in different angels. This study showed that a combination of chemotherapy and iodine-131 had better efficacy than radiotherapy with 6MV X-ray in the treatment of glioblastoma.