MV X-ray Research Articles

Kilovoltage radiotherapy for companion animals: dosimetric comparison of 300 kV, 450 kV, and 6 MV X-ray beams.

Radiotherapy for the treatment of cancer in companion animals is currently administered by using megavoltage X-ray machines. Because these machines are expensive, most animal hospitals do not perform radiotherapy. This study evaluated the ability of relatively inexpensive kilovoltage X-ray machines to treat companion animals. A simulation study based on a commercial treatment-planning system was performed for tumors of the brain (non-infectious meningoencephalitis), nasal cavity (malignant nasal tumors), forefoot (malignant muscular tumors), and abdomen (malignant intestinal tumors). The results of kilovoltage (300 kV and 450 kV) and megavoltage (6 MV) X-ray beams were compared. Whereas the 300 kV and 6 MV X-ray beams provided optimal radiation dose homogeneity and conformity, respectively, for brain tumors, the 6 MV X-rays provided optimal homogeneity and radiation conformity for nasal cavity, forefoot, and abdominal tumors. Although megavoltage X-ray beams provided better radiation dose distribution in most treated animals, the differences between megavoltage and kilovoltage X-ray beams were relatively small. The similar therapeutic effects of the kilovoltage and 6 MV X-ray beams suggest that kilovoltage X-ray beams may be effective alternatives to megavoltage X-ray beams in treating cancers in companion animals.

Transplantation of Bone Marrow Mesenchymal Stem Cells Prevents Radiation-Induced Artery Injury by Suppressing Oxidative Stress and Inflammation.

The present study aims to explore the protective effect of human bone marrow mesenchymal stem cells (hBMSCs) on radiation-induced aortic injury (RIAI). hBMSCs were isolated and cultured from human bone marrow. Male C57/BL mice were irradiated with a dose of 18-Gy 6MV X-ray and randomly treated with either vehicle or hBMSCs through tail vein injection with a dose of 103 or 104 cells/g of body weight (low or high dose of hBMSCs) within 24 h. Aortic inflammation, oxidative stress, and vascular remodeling were assessed by immunohistochemical staining at 3, 7, 14, 28, and 84 days after irradiation. The results revealed irradiation caused aortic cell apoptosis and fibrotic remodeling indicated by aortic thickening, collagen accumulation, and increased expression of profibrotic cytokines (CTGF and TGF-β). Further investigation showed that irradiation resulted in elevated expression of inflammation-related molecules (TNF-α and ICAM-1) and oxidative stress indicators (4-HNE and 3-NT). Both of the low and high doses of hBMSCs alleviated the above irradiation-induced pathological changes and elevated the antioxidant enzyme expression of HO-1 and catalase in the aorta. The high dose even showed a better protective effect. In conclusion, hBMSCs provide significant protection against RIAI possibly through inhibition of aortic oxidative stress and inflammation. Therefore, hBMSCs can be used as a potential therapy to treat RIAI.

Investigation of Temperature Dependence of Polymer Gels for Use with Scanning Magnetic Resonance Imaging

Polymer gels are three-dimensional dosimetric tools. The purpose of the present study was to investigate the temperature dependence of polymer gels during scanning Magnetic Resonance Imaging. Prepared gels were irradiated with a 6MV X-ray beam at intensities ranging from 0 to 20 Gy in order to investigate their dose-R2 and dose-R1 responses. Irradiated gels were evaluated from 1.5-T magnetic resonance R2 and R1 images for each 5°C change in temperature from 5°C to 41°C, and then the four-field box technique irradiation plan was used to deliver a total dose of 4 Gy using the same beam weight in each direction to the prepared gels. The profile of the dose map generated from the four-field irradiated gel data at 20°C was then compared with the planned data. The dose-R2 response curve was linear up to 20 Gy at 20°C, with a slope of 1.17 Gy-1˙s-1. The slopes of the fitted curves of the dose-R2 decreased as gel temperature increased. The slopes of the dose-R1 curves were more parallel than the slopes of the dose-R2 curves between 5 and 41°C. The difference in the full width of half maximum of the gel profile data obtained using the four-field box technique at 20°C and the planned data were below 5% on average. The dose map from the irradiated gels obtained using the dose-R2 curve was the same as that from the planned data under the same temperature conditions. Measurement of difference between various temperatures is significant with dose accuracy. It is suitable to evaluate the gel dosimeter under the thermal equilibrium condition, MRI room temperature from the point of view of the stability of the irradiated gels.

Radiotherapy Enhancement with Electroporation in Human Intestinal Colon Cancer HT-29 Cells

Background:The efficiency of radiotherapy for tumors can be enhanced with different radiosensitizers. Previous studies have shown that electroporation (EP) can sensitize some cancer cell lines to ionizing radiation (IR). HT-29 is a radiation resistant colorectal cancer cell line, representative of a cancer type which is the second cause of cancer mortalities in developed countries. The present study aimed to evaluate radiosensitizing effects of EP on HT-29 cells in vitro exposed to 6 MV X-ray photon beams.Methods:HT-29 cells were exposed to a 6 MV X-ray photon beam as the control or to a combination of electroporation and irradiation. The response of cells was evaluated by colony formation assay and survival curves.Results:The survival fraction of the HT-29 cells was significantly decreased by electroporation prior to radiotherapy. A single electric pulse increased colorectal HT-29 cancer cell sensitivity to mega-voltage radiation by a factor of 1.36.Conclusion:Our findings showed that EP before radiotherapy can significantly enhance tumor cell sensitivity. This combined treatment modality should be assessed for its applicability in clinic settings for employment against radioresistant cancers. However, to facilitate achieving this goal, many different tumors with a broad range of radiosensitivities should be evaluated.

Dose rate and energy dependence study of methacrylic acid gelatin tetrakis (hydroxymethyl) phosphonium chloride gel with flattened and unflattened photon beams.

The aim of this study is to evaluate the dose rate and energy dependency of methacrylic acid gelatin tetrakis (hydroxymethyl) phosphonium chloride (MAGAT) gel in unflattened photon beam using X-ray computed tomography (CT) and ultraviolet (UV)-visible spectroscopy. MAGAT gel was prepared and it was exposed to 6 MV flattened and unflattened beams. The dose selected for irradiation was ranging from 3 to 15 Gy with an increment of 3 Gy. The dose rate dependency of the gel was investigated by exposing the gel to three different dose rates of 250, 500, and 1500 cGy/min for flattening filter free (FFF). To verify the energy dependency of the gel, it was exposed by both FFF and flattening filter (FF) for constant dose rate (250 cGy/min) and different energy (6 and 10 MV X-ray photons). The exposed gels were scanned by X-ray CT and UV-visible spectrophotometer. The change in dose sensitivity observed over the dose rate from 250 cGy/min to 1500 cGy/min was 58.00% and 57.89% using a UV-visible spectrophotometer and X-ray CT analysis method. Energy dependency was evaluated with respect to dose sensitivity and the variation between 6 MV FF and FFF photon beams was found to be 2.20% and 2.21% using UV-visible spectrophotometer analysis and X-ray CT, respectively. Similarly, the variation noticed with 10 MV FF and FFF was 2.30% using UV-visible spectrophotometer analysis and 2.22% using X-ray CT analysis. The results clearly show that the MAGAT gel was highly dose rate-dependent and less dependent on energy. The beam quality variation between FF and FFF was less. The similar results obtained using X-ray CT scanner and UV-visible spectrophotometer indicate that this study can be recommended for polymer gel scanning procedure.

Détermination expérimentale des facteurs de correction de quatre détecteurs actifs utilisés pour la dosimétrie des minifaisceaux utilisés en radiothérapie

PurposeThe aim of this work is to determine experimentally the correction factors kQclinQmsrfclinfmsr for four active commercial dosimeters: two microchambers and two diode detectors based on the output factor measured with radiochromic film for a radiotherapy linear accelerator equipped with circular cones. Materials and methodsInitially, a radiochromic film dosimetry measurement protocol with an accuracy of 2% was developed to approach the “reference output factor”. Afterwards, the corrective factors of four detectors were determined for two ionization chambers (PinPoint PTW 31016 3D, Micropoint Extradin A16) and two diodes (PTW T60017 Diode, PTW-60019 Micro-Diamond). These measurements were carried out under conical BrainLAB® collimators defining circular fields with diameters equal to 7.5mm, 10mm, 12.5mm, 15mm, 17.5mm, 20mm, 25mm, 30mm, 35mm and 45mm of a 6MV X-ray beam generated by the ClinaciX linear accelerator (Varian®). These factors are weakly dependent on the type of accelerator, whether the model and the collimation type. This allowed their comparisons with those published for the same type of detector and for an accelerator with the same index of beam quality. ResultsThe correction factors obtained experimentally were comparable in maximum deviation of 1.9% with published ones of the works using the same type of detector (mark and model) and an accelerator delivering the same beam quality for the same field size at the measurement point. ConclusionThe measurement protocol using the EBT3 film, which was used as a passive dosimeter to determine the “reference output factor”, was validated by comparing measured and published data of active detector correction factors.

Radioluminescence of Ge-doped silica optical fibre and Al2O3:C dosimeters

Using an electron accelerator producing a 6 MV X-ray photon beam several experimentally observed excitation phenomena that are associated with radioluminescence (RL) have been investigated, the signal originating from a Ge-doped silica optical fibre and commercial nanoDot Al2O3:C dosimeters. Using PMMA optical communication fibres the RL signals have been guided from the beam-delivery room out to the readout instrumentation that has been located beyond the concrete maze providing effective radiation shield. Ge-doped silica fibre memory effects and afterglow (phosphorescence) were compared with that of the commercial Al2O3:C dosimeter. Immediately following RL, observation was made of the decay curves of the afterglow signal of Al2O3:C. Conversely, there was little practically observable afterglow for the Ge-doped fibre used for the majority of present investigations (the dopant concentration of this being 3.6 wt %). Among three different concentration of Ge-doped fibres that were subsequently investigated in a follow-up study, the intensity of afterglow was found to be greatest for the more highly doped concentration (7.0 wt % Ge), with progressive reduction of the effect for the Ge 4.7 wt % and Ge 3.6 wt % fibres. These observations can be compared against the much more marked RL memory effect observed using the Al2O3:C chips. Current results point to the Ge-doped silica optical fibre being a highly promising candidate for real-time RL dosimetry and sensing.

Evaluation of the combined effect of NIR laser and ionizing radiation on cellular damages induced by IUdR-loaded PLGA-coated Nano-graphene oxide.

Glioma is one of the most common malignant cancers of the central nervous system (CNS). Radiatherapy and chemotherapy may be used to slow the growth of tumors that cannot be removed with surgery. The current study developed a combination therapy tool using Nanographene oxide (NGO) functionalized with poly lactic-co-glycolic acid (PLGA) as a carrier of 5-iodo-2-deoxyuridine (IUdR) for glioma cancer treatment. U87MG cells were treated in different groups with IUdR, PLGA-coated Nanographene oxide (PLGA-NGO), IUdR-loaded PLGA-coated Nanographene oxide (IUdR-PLGA-NGO), 2Gy 6MV X-ray radiation, and near-infrared region (NIR) laser radiation. PLGA-NGO showed excellent biocompatibility, high storage capacity for IUdR and high photothermal conversion efficiency. It was effectively employed to create cell damage in the U87MG cell line in the presence of X-ray (6 MV) and NIR laser. Moreover, IUdR-PLGA-NGO+X-ray+NIR laser significantly reduced the plating efficiency of the cells in comparison with IUdR-PLGA-NGO+X-ray and IUdR-PLGA-NGO+NIR laser. Furthermore, Prussian blue staining showed that IUdR-PLGA-NGO-SPIONs were delivered into glioblastoma cells. The PLGA-NGO loaded with IUdR under NIR and X-ray radiation exhibited the highest cytotoxicity toward U87MG cells when compared with other treatment methods, indicating efficient radio-photothermal targeted therapy.

Effect of E1A gene on radiosensitivity of human nasopharyngeal carcinoma cells and its possible mechanism

Objective To investigate the effect of E1A gene on the radiosensitivity of human nasopharyngeal carcinoma cells and its possible mechanism. Methods The E1A gene was transfected into nasopharyngeal carcinoma CNE-2R cells by adenovirus vector. The expression of E1A gene was detected by RT-PCR. Untransfected CNE-2R cells (PBS group) and CNE-2R cells transfected with empty vector Ad-β-gal (Ad-β-gal group) and E1A (Ad-E1A group) were given 0 Gy, 2 Gy, 4 Gy, 6 Gy, 8 Gy 6 MV X-ray irradiation. The changes in radiosensitivity of CNE-2R cells were determined by colony-forming assay. Flow cytometry was used to analyze cell apoptosis in each group. The expression of NF-κB, CK2α, Bcl-2, and cleaved caspase-3 was measured by Western blot. Results RT-PCR confirmed that the E1A gene was transfected into CNE-2R cells and stably expressed. The Ad-E1A group had a significantly lower plating efficiency than the PBS group and the Ad-β-gal group (P<0.05). The Ad-E1A group had significantly lower cell survival rate at 2 Gy irradiation than the PBS group and the Ad-β-gal group (0.217 vs. 0.602, P<0.05; 0.217 vs. 0.585, P<0.05). The Ad-E1A group had a significantly higher α/β value than the PBS group and the Ad-β-gal group (24.680 vs. 5.268, P<0.05; 24.680 vs. 5.132, P<0.05). Flow cytometry results showed that irradiation alone could promote the apoptosis of CNE-2R cells, when combined with E1A gene, the apoptosis rate was significantly increased (P<0.05). Western blot results showed that E1A gene down-regulated the expression of NF-κB/p65, CK2α, and Bcl-2 and up-regulated the expression of cleaved caspase-3. Conclusions E1A gene can enhance the radiosensitivity of nasopharyngeal carcinoma cells by inhibiting the expression of CK2 to block the NF-κB signaling pathway and promoting cell apoptosis. Key words: E1A gene; NF-κB; Casein Kinase 2; Nasopharyngeal Carcinoma Cell; Radiosensitivity; Apoptosis

Thermal limits on MV x-ray production by bremsstrahlung targets in the context of novel linear accelerators.

To study the impact of target geometrical and linac operational parameters, such as target material and thickness, electron beam size, repetition rate, and mean current on the ability of the radiotherapy treatment head to deliver high-dose-rate x-ray irradiation in the context of novel linear accelerators capable of higher repetition rates/duty cycle than conventional clinical linacs. The depth dose in a water phantom without a flattening filter and heat deposition in an x-ray target by 10 MeV pulsed electron beams were calculated using the Monte-Carlo code MCNPX, and the transient temperature behavior of the target was simulated by ANSYS. Several parameters that affect both the dose distribution and temperature behavior were investigated. The target was tungsten with a thickness ranging from 0 to 3 mm and a copper heat remover layer. An electron beam with full width at half maximum (FWHM) between 0 and3 mm and mean current of 0.05-2 mA was used as the primary beam at repetition rates of 100, 200, 400, and 800 Hz. For a 10 MeV electron beam with FWHM of 1 mm, pulse length of 5 μs, by using a thin tungsten target with thickness of 0.2 mm instead of 1 mm, and by employing a high repetition rate of 800 Hz instead of 100 Hz, the maximum dose rate delivered can increase two times from 0.57 to 1.16 Gy/s. In this simple model, the limiting factor on dose rate is the copper heat remover's softening temperature, which was considered to be 500°C in our study. A high dose rate can be obtained by employing thin targets together with high repetition rate electron beams enabled by novel linac designs, whereas the benefit of thin targets is marginal at conventional repetition rates. Next generation linacs used to increase dose rate need different target designs compared to conventional linacs.

Effect of Ku80 on the radiosensitization of cisplatin in the cervical carcinoma cell line HeLa.

Cisplatin chemotherapy in combination with radiotherapy is the primary therapeutic strategy for the treatment of cervical cancer; however, the underlying molecular mechanism for cisplatin radiosensitization remains unknown. The aim of the present study was to investigate the effect of Ku80, a DNA double-strand break (DSB) repair protein, on cisplatin radiosensitization in cervical cancer. The pre-established Ku80 suppression cervical cancer cell line HeLa/Ku80-siRNA and the normal HeLa cell line underwent 6 MV X-ray irradiation (6 Gy) individually or in combination with 5 µg/ml cisplatin treatment. Alterations in apoptosis, the cell cycle and γH2AX expression were detected. Following irradiation individually and combined with cisplatin, compared with normal HeLa cells, HeLa/Ku80-siRNAexhibited an increased rate of apoptosis (P<0.05). It was identified that the earlier cisplatin was administered following irradiation, the higher the rate of apoptosis. Cell cycle analysis indicated that, following irradiation combined with cisplatin, the cells were arrested in G1 and S phase rather than in G2/M phase following irradiation alone. Microscopic imaging of immunofluorescence staining and western blotting identified that HeLa/Ku80-siRNA cells exhibited more γH2AX foci remaining following treatment with irradiation and cisplatin, particularly in the group treated with 6 Gy irradiation for 1 h together with 23 h of exposure to cisplatin. Irradiation in combination with cisplatin promoted the apoptosis of HeLa cells in association with the inhibition of Ku80, and it was identified that the earlier cisplatin was administered following irradiation, the more apoptosis was induced. This maybe because irradiation combined with cisplatin is able to arrest cells in G1 and S phase to rapidly repair damaged DNA, and the lack of Ku80 induces the inability to repair DSB, resulting in increased apoptosis. The results of the present study suggest that Ku80 may be a potent molecular target in cisplatin radiosensitization.

Portal MV imaging with thin-film high-energy current X-ray detectors: A Monte Carlo study.

We investigate the potential of the recently introduced high-energy current (HEC) thin-film detector as an alternative design to existing electronic portal imaging devices (EPID). The HEC radiation detectors employ multiple nano-/micrometer layers made of disparate atomic number (Z) conductors separated by solid or gaseous (e.g., air) dielectrics. The HEC detector may be designed as an external structure or an auxiliary device integrated into the existing EPID. Using Geant4 Monte Carlo simulations, we compare the image contrast of a HEC detector to that of a commercial EPID device (AS500) for a 2.5MV X-ray beam. The detector response was modeled using a series of monoenergetic incident photons with detector signal scored as the energy deposition in the air gaps (HEC) and in the phosphor layer (EPID). Las Vegas (LV) phantom was employed to test the spatial resolution and contrast of the single- and multielement HEC detector. The HEC detector pixel size was the same as for AS500 (0.78 mm×0.78mm). In addition, image contrast of a water/bone phantom using both the multielement HEC and EPID detectors was simulated and compared. The HEC detector has higher relative response to low-energy photons compared to EPID. The multielement HEC has 32.3 times greater response at 100keV than at 500keV, while the EPID without copper plate shows a factor of 6.8 between the same energies. LV phantom images indicate that the image contrast is approximately the same for single- and multielement HEC detectors, but the latter has lower noise. Both single- and multielement HEC could resolve a 2mm diameter hole with an image magnification factor of 1.2. In the present design, the HEC detector has much less material (9.66mg/cm2 gold) compared to EPID (133mg/cm2 Gd2 O2 S) to interact with incident photons. For imaging bony structures, the HEC detector needs about nine times greater photon flux as the EPID to acquire data at same uncertainty level. Despite this, the HEC sensor requires less than 1cGy dose to obtain images with statistical uncertainty better than 2.5%. In the case when the field diameter is 10cm, the multielement HEC image contrast is 14.3% higher than that of EPID with copper removed. When the field diameter is decreased to 5cm, HEC contrast is 27.1% better than the EPID contrast. It is demonstrated that the image contrast of HEC detectors are comparable and in some cases better than that of the standard EPID design. This opens a potential for complementary HEC and EPID designs that may better utilize the kV portion of the spectrum.

The Anti-apoptotic Mechanism of Metformin Against Apoptosis Induced by Ionizing Radiation in Human Peripheral Blood Mononuclear Cells.

In a previous article, we showed that metformin (MET) can reduce ionizing radiation (IR) induced apoptosis in human peripheral blood mononuclear cells. However, the anti-apoptotic mechanism of MET against IR remains unclear. The present study attempts to investigate the mechanism of action of MET in limiting X-ray induced apoptosis in human peripheral blood mononuclear cells. Mononuclear cells were treated with MET for 2 hours and irradiated with 6 MV X-rays. The gene expression levels of BAX, CASP3 and BCL2 were determined 24 hours post irradiation using real time quantitative polymerase chain reaction (qPCR) technique. Furthermore, the protein levels of BAX, CASP3 and BCL2 were analyzed by Western blotting assay. Radiation exposure increased the expressions of BAX and CASP3 genes, and decreased the expression of BCL2 gene in mononuclear cells. Conversely, an increase in BCL2 gene expression along with a decrease in BAX and CASP3 genes expression was observed in MET plus irradiated mononuclear cells. It was found that radiation increased BAX/BCL2 ratio, while MET pretreatment reduced these ratios. Also, treatment with MET without irradiation did not change the expressions of BAX, CASP3 and BCL2 genes. On the other hand, downregulated expression of BCL2 protein and upregulated expressions of BAX and CASP3 proteins were found in 2 Gy irradiated mononuclear cells, while pretreatment with MET significantly reversed this tendency. These results suggest that MET can protect mononuclear cells against apoptosis induced by IR through induction of cellular anti-apoptotic signaling.Key words: ionizing radiation - metformin - apoptosis - genes - proteins - blood cells.

Treatment Outcomes of Radiation Therapy Combined with Superselective Intra-arterial Infusion Therapy for Maxillary Sinus Cancer

The purpose of this retrospective study is to evaluate the efficacy of radiotherapy combined with superselective intra-arterial infusion therapy of cisplatin for locally advanced maxillary sinus cancer at single institution. We have evaluated 38 patients with locally advanced maxillary sinus cancer, who were treated with curative intent radiotherapy combined with superselective intra-arterial infusion therapy of cisplatin from 2002 to 2016. There were 31 males and 7 females. The median age was 67.5 years (range 47 to 87 years). Stage distribution was T2 in 1 case, T3 in 5 cases, T4a in 23 cases, and T4b in 9 cases. All patients have no nodal involvement. There were 36 patients who had squamous cell carcinomas, and 2 with undifferentiated carcinomas. Thirty-five patients received three-dimensional conventional radiotherapy, and the 3 most recent patients received intensity-modulated radiation therapy. We used 4 MV and/or 10 MV X-ray with or without electron beams. Median prescribed dose was 66 Gy (range 50 to 70 Gy) in 2 Gy/fraction. All patients did not receive either prophylactic neck irradiation or volume reduction surgery before radiotherapy. Superselective intra-arterial infusions of high-dose cisplatin was performed in 36 patients with simultaneous intra-venous infusions of thiosulfate to neutralize cisplatin toxicity, and 2 patients received selective intra-arterial infusion chemotherapy without sodium thiosulfate neutralization. All patients were treated with median 6 cycles (range 2 to 10 cycles) of intra-arterial infusion chemotherapy per week during radiotherapy. Systemic chemotherapy was also combined in 2 patients after the completion of radiotherapy. The median follow-up period was 38.9 months (range 3.6 to 178.3 months). The 5-year overall survival rate, disease-free survival rate, and local progression-free survival rate were 78.3% (T2-3/T4:100%/70.4%), 44.5% (T2-3/T4:83.3%/36.0%) and 58.3% (T2-3/T4:83.3%/53.7%), respectively. Although 13 patients had persistence of disease, delayed local failure occurred only in 2, regional recurrence in 3, and distant metastasis in 4. As salvage treatment, 9 patients underwent salvage surgery, and 2 patients underwent stereotactic radiotherapy. Although acute Grade 3 mucositis developed in 10 patients, no renal dysfunction occurred during the treatment. There were 9 late complications, including osteonecrosis (2 patients), carotid cavernous sinus fistula (1 patient), cateract (2 patients), blindness (4 patients) as late adverse reactions. Radiotherapy combined with superselective intra-arterial infusion therapy of cisplatin for maxillary sinus cancer appears to be efficient. However, further work is needed to decrease late complications.

Temporally separating Cherenkov radiation in a scintillator probe exposed to a pulsed X-ray beam

Cherenkov radiation is generated in optical systems exposed to ionising radiation. In water or plastic devices, if the incident radiation has components with high enough energy (for example, electrons or positrons with energy greater than 175keV), Cherenkov radiation will be generated. A scintillator dosimeter that collects optical light, guided by optical fibre, will have Cherenkov radiation generated throughout the length of fibre exposed to the radiation field and compromise the signal. We present a novel algorithm to separate Cherenkov radiation signal that requires only a single probe, provided the radiation source is pulsed, such as a linear accelerator in external beam radiation therapy. We use a slow scintillator (BC-444) that, in a constant beam of radiation, reaches peak light output after 1 microsecond, while the Cherenkov signal is detected nearly instantly. This allows our algorithm to separate the scintillator signal from the Cherenkov signal. The relative beam profile and depth dose of a linear accelerator 6MV X-ray field were reconstructed using the algorithm. The optimisation method improved the fit to the ionisation chamber data and improved the reliability of the measurements. The algorithm was able to remove 74% of the Cherenkov light, at the expense of only 1.5% scintillation light. Further characterisation of the Cherenkov radiation signal has the potential to improve the results and allow this method to be used as a simpler optical fibre dosimeter for quality assurance in external beam therapy.

Dosimetric Analysis of Radiation Therapy Plans With or Without Flattening Filter in Superficial Tumors of Head and Neck

The definite indication of flattening filter free Rapid-ARC is still unclear yet. Our study compared the dose distribution of target volumes, dose fall, protection of normal organs at risk (OAR) and monitor unit (MU) of 3 radiotherapy techniques (Rapid-ARC FFF, IMRT FF and Rapid-ARC FF) in superficial tumors of head and neck. Nine patients were enrolled. The three RT plans mentioned above were designed for each patient with 6MV X-ray. The prescribed dose was 54Gy/30f/1.8Gy to PTV concurrent with 64.2Gy/30f/2.14Gy to PGTV. The target volume coverage indicators included conformity and homogeneity index (CI, HI). The dose fall indicators included V40 and V20 (the covered volume by 40Gy and 20Gy, respectively). OARs included the brainstem and spinal cord. All the optimized parameters and target values for plans were consistent. Rapid-ARC FFF provided significantly improved conformity (0.762±0.013) and homogeneity (1.073±0.022) of PGTV than IMRT FF (CI= 0.677±0.076, p<0.01; HI= 1.116±0.048, p<0.05), and Rapid-ARC FF (CI= 0.717±0.077, HI= 1.080±0.018, p<0.05). Rapid-ARC FFF has a better CI (0.800±0.049) of PTV compared with IMRT FF (0.754±0.071, p<0.05) and Rapid-ARC FF (0.768±0.074, p<0.05) respectively.Furthermore, RapidArc FFF had a rapider dose fall. RapidArc FFF remarkably reduced V40 (445.85±213.60cm3) and V20(972.42±428.70cm3) compared with IMRT FF (V40= 472.62±219.63cm3, V20= 1000.18±445.74cm3, p<0.01) and Rapid-ARC FF (V40= 454.51±221.50cm3, V20= 1018.17±475.67cm3, p<0.01). However, the dose of brain stem was increased in RapidArc FFF (D1cc=2669.46±927.05cGy) but kept in the nomal threshold compared with IMRT FF (2593.97±872.12cGy, p<0.05) and Rapid-ARC FF (2656.97±909.73cGy,p<0.05). Similarly, the dose of cord was increased in RapidArc FFF (D1cc=3031.25±438.77cGy) but kept in the nomal threshold compared with IMRT FF (3027.76±426.03cGy,p<0.05) and Rapid-ARC FF (3025.33±487.39cGy,p<0.05). RapidArc FFF greatly reduced MU (344.00±40.62) compared with IMRT FF (613.50±100.06, p<0.01) but slightly increased MU compared with RapidArc FF (325.75±31.15,p<0.05). Rapid-ARC FFF is superior to IMRT FF or RapidArc FF in superficial tumors of head and neck for better target coverage and rapider dose fall. Rapid-ARC FFF can be the first option for superficial tumors of head and neck.

The Imaging Dose to Patients From a 2.5 MV Imaging Beam

A 2.5 MV imaging beam has become available in the TrueBeam linear accelerator. The aim of this work is to simulate this new beam and to evaluate its image dose to patients. The Monte Carlo technique has been used to simulate the 2.5 MV imaging beam. From the simulated beam the beam characteristics have been analyzed including the energy spectra and the fluence distributions as a function of position away from the beam central axis. The accuracy of a simulated beam was validated by the agreement between the Monte Carlo calculated and measured dose distributions in a water phantom. The simulated 2.5 MV beam was also used to obtain the water-to-air stopping power ratios for reference beam absorbed dose calibration. The simulated beams were then used to evaluate the image dose to patients compared with that from a conventional therapeutic 6 MV x-ray beam. The mean energies of photons and electrons are 0.48 MeV and 0.37 MeV respectively. The dose decrease at 20 cm away from the central axis is less than 30% for a 40×40 cm2 field. The values of percentage depth-dose curves are 53% and 63% for 10×10 cm2 and 40×40 cm2 fields respectively. Portal image doses (D50 of the DVHs) to the eyes, heart and bladder from representative pairs of 2.5 MV (or 6 MV) setup images are 1.8 cGy (3.5 cGy), 1.1 cGy (2.5 cGy) and 1.0 cGy (2.4 cGy) for head, thorax and pelvis image acquisitions respectively. The dosimetric data of the 2.5 MV imaging beam have been generated. The study shows that the image dose when using the 2.5 MV beam is about 50% of that when using a 6 MV beam.

Dosimetric Evaluation of a Gamma Ray System for Advanced Radiation Therapy Treatments

Gamma ray systems have exhibited superior dosimetric advantages for stereotactic radiosurgery/radiotherapy (SRS/SRT) of intracranial tumors due to the use of non-coplanar multiple sources and the rapid dose fall-off outside the treatment target as a result of lower secondary electron energies. In this work we performed a dosimetric planning comparison study on a novel Gamma ray system to evaluate its potential clinical benefits for SRS of intracranial tumors and stereotactic body radiotherapy (SBRT) of other body sites. The new Gamma ray system (CybeRT, OUR United RT Group, China) consists of a ring gantry with two treatment heads: a focusing head with 16 cobalt-60 sources and an adjustable (1-2cm) cobalt-60 source equipped with a multileaf collimator (MLC). The MLC has 60 paired leaves, and the maximum field size is 40cmx40cm (40 pairs of 0.5cm central leaves, 20 pairs of 1cm outer leaves). The treatment heads can provide a total of 35° non-coplanar beam incidence. The treatment couch provides 6-degrees-of-freedom motion compensation and the kV cone-beam CT system has a spatial resolution of 0.4mm. Monte Carlo simulations were performed to obtain dose distributions and compare with measurements. A retrospective study of 27 previously treated patients was performed using the Prowess RT Pro (a prototype version), Accuray MultiPlan and Varian Eclipse TPS to compare cobalt plans with 6 MV x-ray plans on the CybeRT, CyberKnife and linac systems. Monte Carlo results confirmed the new Gamma ray system design parameters including output factors and 3D dose distributions. Its beam penumbra/dose gradient was similar to or better than that of 6MV photon beams with adjustable source sizes that also resulted in variable dose rates required for treatment optimization and VMAT delivery. CybeRT had a 0.3mm isocenter accuracy. The low-dose acquisition mode of the CBCT system provided fluoroscopy and 3D imaging at a dose level 3 times less than conventional CBCT systems. Since cobalt beams produced lower-energy secondary electrons the new Gamma ray system exhibited better dose properties in low-density lung tissues. Because of their rapid depth dose falloff, cobalt beams were favorable for peripheral lung tumors with partial-arc deliveries to spare the opposite lung and critical structures. The skin dose with CybeRT for head and neck treatments was similar to that with CyberKnife and conventional linacs and only 2-3% higher for abdominal and pelvic treatments. Superior treatment plans were obtained using the focusing Gamma treatment head for small (up to 50cc) tumor volumes and using the Gamma MLC treatment head for large (> 30cc) tumor volumes for intracranial, head and neck, breast, lung, liver and prostate patients investigated in this study. The unique dosimetric properties of cobalt beams and the accurate stereotaxy/dose delivery techniques make the new Gamma ray system an ideal RT system for advanced SRS/SBRT as well as conventional radiation therapy.

Effects of NF-κB inhibitor on nuclear factor-κB and intercellular adhesion moceule-1 in lung injury associated with radiation of rats

Objective: To investigate the mechanism of lung injury caused by radiation-induced lung injury by observing the change of nuclear factor (NF-κB) and intercellular adhesion moceule-1 (ICAM-1) in rats and the effects of pyrrolidine dithiocarbamate (PDTC) . Methods: 80 SD female rats were randomly classified into 4 groups: control group, radiation group, PDTC treatment group and PDTC group.The radiation induced pulmonary injury model was preformed by using 6 MV X-rays to deliver 8 Gy per day for 5 consecutive days with 40 Gy in total to the thorax of each animal.PDTC was given from 3 d before radiation to 30 d after the first radiation. Rats in control group and PDTC group received the same dose of saline. Animals were sacrificed at 8 week and 24 week after radiation, respectively. The lungs were removed and processed for HE and Masson staining, hydroxyproline content measurement, and real-time quantitative reverse transcription-polymerase chain (RT-PCR) ICAM-1mRNA and NF-κB p65mRNA were detected, Statistical analysis were carried out. Results: Compared with radiation group, there was an obvious amelioration in pathological injury of lung tissue in PDTC treatment group. The lung coefficient and the content of Hyp in PDTC treatment group were significantly lower than those in radiation group (t=3.651, 5.293, 2.348 and 4.126, respectively, allP<0.05) , while slightly higher than those in control group. The levels of ICAM-1mRNA and NF-κB p65mRNA were significantly higher in radiation group than that in PDTC treatment group (allP<0.05) , There were no significant differences in these indicators between control group and PDTC group (P>0.05) . Conclusion: The expression of ICAM-1mRNA and NF-κB p65mRNA is increased in rats with radiation-induced lung injury. Suggest that ICAM-1 and NF-κB are a key factor lead to radiation-induced lung injury. PDTC may inhibits NF-κB activity and further significantly deceases expression of ICAM-1, leading to significantly attenuated pulmonary inflammation and fibrosis, which provides a new therapeutic target for the prevention and treatment of radiation-induced lung injury.

EVALUATION OF TUMOR CONTROL AND NORMAL TISSUE COMPLICATION PROBABILITY IN HEAD AND NECK CANCERS WITH DIFFERENT SOURCES OF RADIATION: A COMPARATIVE STUDY

Introduction: The ultimate goal of radiation treatment planning is to yield a high tumor control probability (TCP) with a low normal tissue complication probability (NTCP). Historically dose volume histogram (DVH) with only volumetric dose distribution was utilized as a popular tool for plan evaluation hence present study aimed to compare the radiobiological effectiveness of the cobalt-60 (Co-60) gamma photon and 6MV X-rays of linear accelerators (Linac) in the radiotherapy of head and neck tumors. Materials and Methods: TCP and NTCP were calculated using DVH through the BIOPLAN software developed by Sanchez-Nieto and Nahum . The treatment planning was performed for all the patients using both treatment modalities (i.e., Co-60 and 6 MV Linac). The TCP was also manually calculated using a mathematical formula proposed by Brenner’s et al. Results: The average TCP calculated by the BIOPLAN for Co-60 and 6 MV X-rays were 44.6% and 60.8%, respectively. Furthermore, the average NTCPs obtained for the organ at risk, namely optic nerve, for Co-60 and 6 MV X-ray were 0.24 % and 0.03 %, respectively. Regarding the spinal cord, the average NTCPs for Co-60 gamma photon and 6 MV X-ray of Linac were 0.05 % and 0.002%, respectively. Conclusion: As the findings of the present study indicated, Co-60 unit could provide comparable TCP along with minimal NTCP, compared to the high-cost technologies of Linac. The design of treatment plans based on the radiobiological parameters facilitated the judicious choice of physical parameters for the achievement of high TCP and low NTCP.