Investigation of AAA dose calculation algorithm accuracy in surface and buildup region for 6MV photon beam using markus parallel-plate ion chamber.

In radiotherapy, dose distributions are obtained by using dose calculation algorithms that are implanted in treatment planning systems (TPS). This study aims to compare the surface doses of separate field sizes calculated by different version of The Analytical Anisotropic Algorithm (AAA) and measured by the parallel-plate ion chamber that is admitted as the most reliable dosimetry system for the surface region dose measurements. In order to measure the near surface dose, water equivalent solid phantom was used and measurements were made for 6MV photon beam at 100 cm source-detector distance for 5×5, 10×10, and 20×20 cm2 field sizes. AAA 8.9 and AAA 15.1 versions of the Varian Eclipse TPS were used for surface dose calculations by generating beams with separate field sizes. The doses were read by considering the effective buildup thickness of Markus parallel-plate ion chamber. The surface doses using 6 MV photon beams for 10×10 cm2 field size at 0.07 mm were found to be 11.04%, 26.25%, and 19.69% for AAA v8.9, AAA v15.1 and Markus chamber, respectively. It was seen that for both of the AAA versions and Markus parallel-plate ion chamber, increasing field sizes also increase surface dose. For all field sizes, surface dose was lowest by using AAA v8.9 at 0.07 mm. The different versions of the same TPS algorithms may calculate the surface doses distinctively. After upgrading of TPS algorithms, surface doses should be calculated and compared by measurements with different dosimetry systems to better understand their calculation behaviors in the near surface region.

Patient-specific quality assurance for intracranial cases in robotic radiosurgery system.

PURPOSE: The purpose of this study was to perform pretreatment patient-specific quality assurance (QA) for intracranial irradiation using CyberKnife with an ion chamber. METHODS: Twenty-five intracranial plans created using the ray-tracing algorithm were used for this study. Computed tomography (CT) images of the water-equivalent RW3 slab phantom with PinPoint ionization chamber were acquired with 1-mm slice thickness and transferred to the MultiPlan treatment planning system (TPS). Four gold fiducial markers embedded into two different plates were used to tracking during the irradiation. Intracranial plans were transferred to CT images of the RW3 phantom. The isodose curves and sensitive volume of ion chamber were overlapped. Point dose measurements were performed three times and the mean point doses were calculated for each plan. The mean doses measured by the PinPoint ion chamber were compared with those of the calculated by MultiPlan TPS in the sensitive volume of PinPoint. RESULTS: The mean percentage difference (MPD) in point dose measurements was -2.44±1.97 for 25 plans. The maximum and minimum percentage differences between the measured and calculated absolute point doses were -7.14 and 0.23, respectively. The MPD was -1.70±1.90 for 12 plans using a fixed collimator and -3.11±1.86 for 13 plans using an IRIS cone. CONCLUSIONS: Point dose measurement is a reliable and functional method for pre-treatment patient-specific QA in intracranial CyberKnife plans. Point dose verification should be performed to correct any possible errors prior to patient treatment. It is recommended for use in patient-specific QA process in the CyberKnife plans.

Investigation of approaches for internal target volume definition using 4-dimensional computed tomography in stereotactic body radiotherapy of lung cancer.

The present study was undertaken to investigate the suitability of alternative internal target volume (ITV) delineation strategies based on maximum intensity projection (MIP), average intensity projection (AIP), 2 extreme phases and 4 phases images relative to the ITV10phase in stereotactic body radiation therapy (SBRT) for lung cancer. The 4-dimensional computed tomography (4DCT) data of 15 lung cancer patients treated with SBRT in our clinic were used. Five different ITVs were generated as follows: merging GTVs from 10 phases (ITV10Phase); merging GTVs from 2 extreme phases (0%, 50%) (ITV2Phase); merging GTVs from 4 phases (0%, 20%, 50%, and 70%) (ITV4Phase); delineating GTV on MIP (ITVMIP), and delineating GTV on AIP (ITVAIP). PTV10Phase, PTV2Phase, PTV4Phase, PTVMIP, and PTVAIP were generated by adding a 5-mm margin around the related ITV. Volumetric analyses were performed for 4 ITVs and PTVs relative to ITV10phase and PTV10phase. SBRT plans made for all PTVs were evaluated for dosimetric effect of alternative ITV delineation strategies. The mean percentage overlap volume (POV) for PTV2phase, PTV4phase, PTVMIP, and PTVAIP relative to PTV10phase were 84.2 ± 5.4%, 92.0 ± 2.9%, 82.2 ± 5.7%, and 73.8 ± 9.3%, for lower-lobe tumors, respectively. The mean POV for PTV2phase, PTV4phase, PTVMIP, and PTVAIP relative to PTV10phase were 93.2 ± 2.5%, 95.9 ± 1.0%, 87.5 ± 6.7%, and 83.3 ± 6.8% for upper-lobe, respectively. For lower-lobe tumors the mean differences in V20 and MLD for plans based on PTV2phase and PTV4phase were <0.5% and <10 cGy, compared with a plan based on PTV10phase. The use of PTV based on 4 respiratory phases and a 5-mm margin is a safe approach to reduce the workload of target delineation for tumors located in both lower and upper lobes.

Surface dose measurements with GafChromic EBT film for 6 and 18MV photon beams.

The aim of this study was to determine the surface doses using GafChromic EBT films and compare them with plane-parallel ionization chamber measurements for 6 and 18 MV high energy photon beams. The measurements were made in a water equivalent solid phantom in the build-up region of the 6 and 18MV photon beams at 100 cm SSD for various field sizes. Markus type plane-parallel ion chamber with fixed-separation between collecting electrodes was used to measure the percent depth doses. GafChromic EBT film measurements were performed both on the phantom surface and maximum dose depth at the same geometry with ion chamber measurements. The surface doses found using GafChromic EBT film were 15%, 20%, 29%and 39%+/-2% (1SD) for 6 MV photons, 6%, 11%, 23% and 32%+/-2% (1SD) for 18 MV photons at 5, 10, 20 and 30 cm(2) field sizes, respectively. GafChromic EBT film provides precise measurements for surface dose in the high energy photons. Agreement between film and plane-parallel chamber measurements was found to be within +/-3% for 18 MV photon beams. There was 5% overestimate on the surface doses when compared with the plane-parallel chamber measurements for all field sizes in the 6 MV photon beams.

Nasopharyngeal carcinoma radiotherapy with hybrid technique.

The aim of the study was to investigate the effect of the Hybrid technique which was created by combining of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for the treatment of nasopharyngeal cancer (NPC) patients. 7 to 9 field IMRT, triple arc VMAT, and Hybrid plans were generated for 10 advanced stage NPC patients. The homogeneity index (HI) and the conformity index (CI) of planning target volumes (PTVs) were calculated for each technique to evaluate the plan quality. The techniques were compared in terms of plan quality, sparing of organs at risk (OARs), monitor units (MUs), and delivery time. Hybrid technique significantly improved the target dose homogeneity and the conformity for PTV70 and PTV60 compared to IMRT and VMAT. Hybrid plans significantly reduced the maximum dose of the brainstem sparing compared to the VMAT plans and also improved the sparing of spinal cord compared to IMRT and VMAT. The MUs and the delivery time of Hybrid plans were found to be between values for IMRT and VMAT plans. Hybrid technique can be useful when IMRT and VMAT techniques are not adequate alone in the treatment of NPC patients.

A column generation heuristic for VMAT planning with adaptive CVaR constraints.

In this study we develop an efficient computational procedure that generates medically acceptable treatment plans for volumetric modulated arc therapy with constant gantry speed. Our proposed method is a column generation heuristic based on a mixed integer linear programming model, where the objective function contains minimization of total monitor unit of the treatment plan and dose-volume requirements are included as conditional value-at-risk constraints. Our heuristic generates a full treatment arc for the restricted master problem and calibrates the right hand side parameters of the conditional value-at-risk constraints in the first phase. In the second phase, this initial solution is improved by performing column generation. This is a fully automated procedure and produces treatment plans in a single call without any human intervention. We evaluate its performance on real prostate cancer data by comparing the quality of the generated plans with those obtained by a widely used commercial treatment planning system. Our analysis shows that the results are promising, and the generated plans satisfy the prescription restrictions and require [Formula: see text] fewer monitor units on average compared to the ones obtained using Eclipse.

Gamma Knife 3-D dose distribution near the area of tissue inhomogeneities by normoxic gel dosimetry.

The accuracy of the Leksell GammaPlan, the dose planning system of the Gamma Knife Model-B, was evaluated near tissue inhomogeneities, using the gel dosimetry method. The lack of electronic equilibrium around the small-diameter gamma beams can cause dose calculation errors in the neighborhood of an air-tissue interface. An experiment was designed to investigate the effects of inhomogeneity near the paranosal sinuses cavities. The homogeneous phantom was a spherical glass balloon of 16 cm diameter, filled with MAGIC gel; i.e., the normoxic polymer gel. Two hollow PVC balls of 2 cm radius, filled with N2 gas, represented the air cavities inside the inhomogeneous phantom. For dose calibration purposes, 100 ml gel-containing vials were irradiated at predefined doses, and then scanned in a MR unit. Linearity was observed between the delivered dose and the reciprocal of the T2 relaxation time constant of the gel. Dose distributions are the results of a single shot of irradiation, obtained by collimating all 201 cobalt sources to a known target in the phantom. Both phantoms were irradiated at the same dose level at the same coordinates. Stereotactic frames and fiducial markers were attached to the phantoms prior to MR scanning. The dose distribution predicted by the Gamma Knife planning system was compared with that of the gel dosimetry. As expected, for the homogeneous phantom the isodose diameters measured by the gel dosimetry and the GammaPlan differed by 5% at most. However, with the inhomogeneous phantom, the dose maps in the axial, coronal and sagittal planes were spatially different. The diameters of the 50% isodose curves differed 43% in the X axis and 32% in the Y axis for the Z =90 mm axial plane; by 44% in the X axis and 24% in the Z axis for the Y=90 mm coronal plane; and by 32% in the Z axis and 42% in the Y axis for the X=92 mm sagittal plane. The lack of ability of the GammaPlan to predict the rapid dose fall off, due to the air cavities behind or near the lesion led to an overestimation of the dose that was actually delivered. Clinically, this can result in underdosing of lesions near tissue inhomogeneities in patients under treatment.

A Phantom Study on Fetal Dose Reducing Factors in Pregnant Patients with Breast Cancer during Radiotherapy Treatment.

PURPOSE: This study aims to investigate the factors that reduce fetal dose in pregnant patients with breast cancer throughout their radiation treatment. Two main factors in a standard radiation oncology center are considered as the treatment planning systems (TPSs) and simple shielding for intensity modulated radiation therapy technique. MATERIALS AND METHODS: TPS factor was evaluated with two different planning algorithms: Anisotropic analytical algorithm and Acuros XB (external beam). To evaluate the shielding factor, a standard radiological purpose lead apron was chosen. For both studies, thermoluminescence dosimeters were used to measure the point dose, and an Alderson RANDO-phantom was used to simulate a female pregnant patient in this study. Thirteen measurement points were chosen in the 32nd slice of the phantom to cover all possible locations of a fetus up to 8th week of gestation. RESULTS: The results show that both of the TPS algorithms are incapable of calculating the fetal doses, therefore, unable to reduce them at the planning stage. Shielding with a standard lead apron, however, showed a slight radiation protection (about 4.7%) to the fetus decreasing the mean fetal dose from 84.8 mGy to 80.8 mGy, which cannot be disregarded in case of fetal irradiation. CONCLUSIONS: Using a lead apron for shielding the abdominal region of a pregnant patient during breast irradiation showed a minor advantage; however, its possible side effects (i.e., increased scattered radiation and skin dose) should also be investigated further to solidify its benefits.

Histopathological comparison of topical therapy modalities for acute radiation proctitis in an experimental rat model.

AIM: To evaluate the prevalent topical therapeutic modalities available for the treatment of acute radiation proctitis compared to formalin. METHODS: A total of 120 rats were used. Four groups (n = 30) were analyzed with one group for each of the following applied therapy modalities: control, mesalazine, formalin, betamethasone, and misoprostol. A single fraction of 17.5 Gy was delivered to each rat. The rats in control group rats were given saline, and the rats in the other three groups received appropriate enemas twice a day beginning on the first day after the irradiation until the day of euthanasia. On d 5, 10, and 15, ten rats from each group were euthanized and a pathologist who was unaware of treatment assignment examined the rectums using a scoring system. RESULTS: The histopathologic scores for surface epithelium, glands (crypts) and lamina propria stroma of the rectums reached their maximum level on d 10. The control and formalin groups had the highest and mesalazine had the lowest, respectively on d 10. On the 15th d, mesalazine, betamethasone, and misoprostol had the lowest scores of betamethasone. CONCLUSION: Mesalazine, betamethasone, and misoprostol are the best topical agents for radiation proctitis and formalin has an inflammatory effect and should not be used.

Investigation of conformal and intensity-modulated radiation therapy techniques to determine the absorbed fetal dose in pregnant patients with breast cancer.

The aim of this research was to investigate the fetal doses of pregnant patients undergoing conformal radiotherapy or intensity-modulated radiation therapy (IMRT) for breast cancers. An Alderson Rando phantom was chosen to simulate a pregnant patient with breast cancer who is receiving radiation therapy. This phantom was irradiated using the Varian Clinac DBX 600 system (Varian Medical System, Palo Alto, CA) linear accelerator, according to the standard treatment plans of both three-dimensional conformal radiation therapy (3-D CRT) and IMRT techniques. Thermoluminescent dosimeters were used to measure the irradiated phantom׳s virtually designated uterus area. Thermoluminescent dosimeter measurements (in the phantom) revealed that the mean cumulative fetal dose for 3-D CRT is 1.39cGy and for IMRT it is 8.48cGy, for a pregnant breast cancer woman who received radiation treatment of 50Gy. The fetal dose was confirmed to increase by 70% for 3-D CRT and 40% for IMRT, if it is closer to the irradiated field by 5cm. The mean fetal dose from 3-D CRT is 1.39cGy and IMRT is 8.48cGy, consistent with theoretic calculations. The IMRT technique causes the fetal dose to be 5 times more than that of 3-D CRT. Theoretic knowledge concerning the increase in the peripheral doses as the measurements approached the beam was also practically proven.

An investigation of the dose distribution effect related with collimator angle in volumetric arc therapy of prostate cancer.

To investigate the dose-volume variations of planning target volume (PTV) and organ at risks (OARs) in eleven prostate cancer patients planned with single and double arc volumetric modulated arc therapy (VMAT) when varying collimator angle. Single and double arc VMAT treatment plans were created using Monaco5.0(®) with collimator angle set to 0°. All plans were normalized 7600 cGy dose to the 95% of clinical target volume (CTV) volume. The single arc VMAT plans were reoptimized with different collimator angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°), and for double arc VMAT plans (0-0°, 15°-345, 30-330°, 45-315°, 60-300°, 75-285°, 90-270°) using the same optimization parameters. For the comparison the parameters of heterogeneity index (HI), dose-volume histogram and minimum dose to the 95% of PTV volume (D95 PTV) calculated and analyzed. The best plans were verified using 2 dimensional ion chamber array IBA Matrixx(®) and three-dimensional IBA Compass(®) program. The comparison between calculation and measurement were made by the γ-index (3%/3 mm) analysis. A higher D95 (PTV) were found for single arc VMAT with 15° collimator angle. For double arc, VMAT with 60-300° and 75-285° collimator angles. However, lower rectum doses obtained for 75-285° collimator angles. There was no significant dose difference, based on other OARs which are bladder and femur head. When we compared single and double arc VMAT's D95 (PTV), we determined 2.44% high coverage and lower HI with double arc VMAT. All plans passed the γ-index (3%/3 mm) analysis with more than 97% of the points and we had an average γ-index for CTV 0.36, for PTV 0.32 with double arc VMAT. These results were significant by Wilcoxon signed rank test statistically. The results show that dose coverage of target and OAR's doses also depend significantly on the collimator angles due to the geometry of target and OARs. Based on the results we have decided to plan prostate cancer patients in our clinic with double arc VMAT and 75°-285° collimator angles.

The effect of glutamine on radiation-induced organ damage.

Radiation enteritis is a significant clinical problem in patients receiving ionizing radiation directed to the abdomen or pelvis. Although radiation is aimed to be directed against the malignant tissue, adjacent healthy tissues are also affected. The small intestine is the most sensitive organ to radiation. The present study was undertaken to investigate the possible protective effect of glutamine against radiation-induced intestinal, hepatic and pancreatic toxicity. Rats received 1 g/kg/day glutamine for seven days before irradiation and continued for three days after irradiation until sacrifice. Then intestinal, pancreatic and hepatic myeloperoxidase (MPO) activities, malondialdehyde (MDA) levels and caspase-3 activities of the sacrificed rats were measured. Irradiation significantly increased the intestinal and pancreatic MPO and caspase-3 activities and MDA levels in comparison to sham group. Glutamine treatment significantly decreased this elevation. Histopathological examination revealed that the intestinal mucosal structure was preserved and pancreatic inflammation decreased in the glutamine treated group. In irradiation group, NF-kappaB over expression was detected. There was no significant difference in histopathological and biochemical examinations of the liver between the groups. In conclusion, glutamine has beneficial effects on intestinal and pancreatic damage in abdominal irradiation through the inflammatory process and apoptosis.

A comparison of TPS and different measurement techniques in small-field electron beams.

In recent years, small-field electron beams have been used for the treatment of superficial lesions, which requires small circular fields. However, when using very small electron fields, some significant dosimetric problems may occur. In this study, dose distributions and outputs of circular fields with dimensions of 5cm and smaller, for nominal energies of 6, 9, and 15MeV from the Siemens ONCOR Linac, were measured and compared with data from a treatment planning system using the pencil-beam algorithm in electron beam calculations. All dose distribution measurements were performed using the Gafchromic EBT film; these measurements were compared with data that were obtained from the Computerized Medical Systems (CMS) XiO treatment planning system (TPS), using the gamma-index method in the PTW VeriSoft software program. Output measurements were performed using the Gafchromic EBT film, an Advanced Markus ion chamber, and thermoluminescent dosimetry (TLD). Although the pencil-beam algorithm is used to model electron beams in many clinics, there is no substantial amount of detailed information in the literature about its use. As the field size decreased, the point of maximum dose moved closer to the surface. Output factors were consistent; differences from the values obtained from the TPS were, at maximum, 42% for 6 and 15MeV and 32% for 9MeV. When the dose distributions from the TPS were compared with the measurements from the Gafchromic EBT films, it was observed that the results were consistent for 2-cm diameter and larger fields, but the outputs for fields of 1-cm diameter and smaller were not consistent. In CMS XiO TPS, calculated using the pencil-beam algorithm, the dose distributions of electron treatment fields that were created with circular cutout of a 1-cm diameter were not appropriate for patient treatment and the pencil-beam algorithm is not convenient for monitor unit (MU) calculations in electron dosimetry.

Protective effect of mesalamine against oxidativeinjury in a rat model of radiation rectitis.

BACKGROUND: Radiation rectitis is a major problem associated with high-doseirradiation used for pelvic malignancies. OBJECTIVE: The aim of this study was to investigate the possible protectiveeffect of mesalamine against irradiation-induced oxidative tissue damage in an experimental model. METHODS: THREE GROUPS OF FEMALE SPRAGUE DAWLEY RATS WERE ASSIGNED TO RECEIVE TREATMENT AS FOLLOWS: mesalamine enema (60 mg/mL) BID + irradiation (IR) was given to the mesalamine + IR group, and isotonic saline enema BID + irradiation to the control group. Treatments were given from the day before irradiation until euthanization (72 hours after the irradiation). Sham control rats received isotonic saline enema BID but no irradiation. On the third day of treatment, all animals were euthanized, and reduced glutathione (GSH) level, malondialdehyde (MDA) level, and myeloperoxidase (MPO) activity were measured in the rectal, intestinal, and hepatic tissue of the rats. RESULTS: The sham group comprised 7 rats; the control and mesalamine + IRgroups, 16 rats each. The median GSH levels of rectal and intestinal specimens were lower in the control group compared with the sham group. The rectal and intestinal MDA levels were higher in the control group compared with the sham group. The rectal and intestinal MPO activities were higher in the control group compared with the sham group. All of these differences were statistically significant (P < 0.001) and indicated oxidative stress. With the topical application of mesalamine, the GSH and MDA levels and MPO activities were similar to those of the sham group. CONCLUSION: The pelvic irradiation of rats caused oxidative rectal, intestinal,and hepatic tissue damage, which was ameliorated with the use of mesalamine.

The peripheral dose outside the applicator in electron beams of Oncor linear accelerator.

In this study, the peripheral dose outside the applicator was measured using electron beams produced by an Oncor linear accelerator and compared with the data of the treatment planning system (TPS). The dose profiles have been measured, by using a water-equivalent slab phantom and a parallel plate ionisation chamber, at 6, 9 and 15 MeV energy levels in 5×5, 10×10, 15×15, 20×20 and 25×25 cm(2) applicators and at 0, 10 and 20° gantry angles; and at the surface, 0.2, 0.5, 1 cm and d(max) depth for each electron energy level. The peripheral dose has been determined with these profiles by normalisation at the field central beam axis (CAX). It has been noticed that, using a 10×10 cm(2) applicator, there is a 1.4 % dose peak on the surface 6 cm away from the field edge where the field CAX is at 100 %, at a gantry angle of 0° with 6 and 9 MeV electron beams; also for the 15 MeV electron beam there is a 2.3 % dose peak. It has been discovered that the peak dose approaches a minimum depending on the increase in depth and reaches 2.5-4 % depending on the growth of the field dimension. At gantry angles of 10 and 20°, 6 and 9 MeV electron beams created small peaks and a maximum dose could be reached at 0.2 and 1 cm depth. Electron beam of 15 MeV did not peak at depths of 0.2 and 1 cm at gantry angles of 10 and 20°. The measured peripheral dose outside the applicators has been compared with the data from a TPS's computer using the Pencil Beam algorithm; it has been stated that dose calculations can be made as far as 3 cm outside the field. In conclusion, the TPS is not sufficient to measure the peripheral dose outside the applicators, and this dose can only be determined by direct measurement.

Surface dose and build-up region measurements with wedge filters for 6 and 18 MV photon beams.

PURPOSE: High-energy photons are most commonly used in radiotherapy to treat cancer. Wedge filters are required to obtain homogeneous dose distribution in the patient. Different wedge filter types create different surface doses. In this study, the effect of the virtual and physical wedge filters on the surface and build-up region doses was examined for 6- and 18-MV high-energy photon beams. MATERIALS AND METHODS: The measurements were made in a water equivalent phantom in the build-up region at a 100-cm source-to-surface distance for various field sizes using virtual and physical wedge filters having different angles. A parallel-plate ion chamber was used to measure the percent depth doses. RESULTS: The percentage dose at the surface increased as the field size increased for open, virtual, and physical wedged beams. For open, physical, and virtual wedged beams, the surface doses were found to be 15.4%, 9.9%, and 15.9% with 6-MV photons and 10.6%, 8.8%, 11.9% with 18-MV photons, respectively, at 10 x 10 cm(2) field size. CONCLUSION: Build-up doses of virtual wedged beams were similar to those of open beams. Surface and buildup doses of physical wedged beams were lower than those of open and virtual wedged beams.

The effect of oblique electron beams to the surface dose under the bolus.

The aim of this study is to determine the effect of bolus to the surface dose in oblique electron incidences. Irradiations with 4.5, 6, 7.5, 9, and 12-MeV electron beams were made for the incidence angles of 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees and using 3 different bolus setups: (1) unbolused (no bolus), (2) 5-mm bolus, and (3) 10-mm bolus. A set of EBT gafchromic film pieces placed on the phantom surface was irradiated with a 400-cGy dose at D(max) for each setup. Whereas surface dose increased with increasing incidence degrees in the absence of a bolus, it was seen that there was a large surface dose decreasing in the presence of a bolus with increasing incidence angles. For 60 degrees incidence angle, the relative surface doses with unbolused setup were: 88.10%, 90.06%, 89.35%, 90.25%, and 97.10%; with 5-mm bolus: 66.45%, 81.20%, 99.78%, 124.43%, and 116.07%; and with 10-mm bolus: 22.65%, 45.20%, 55.20%, 65.82%, and 90.27% for 4.5, 6, 7.5, 9, and 12 MeV, respectively. The use of bolus in the treatment of highly oblique surfaces with low-energy electron beams significantly decreases the surface dose.

The efficacy of octreotide in pancreatic and intestinal changes: radiation-induced enteritis in animals.

Radiation enteritis occurs during the radiotherapy of many intraabdominal malignancies. Radiation induces cellular injury directly and through the generation of free radicals. In the present study we aimed to investigate the effect of octreotide (OCT) pretreatment in irradiation-induced enteritis. For this aim, rats were injected with 50 microg/kg OCT 4 days before irradiation and continued for 3 more days, until sacrifice. Then intestinal and pancreatic myeloperoxidase (MPO) activities and intestinal malondialdehyde (MDA) levels of the rats were measured. Irradiation significantly increased intestinal and pancreatic MPO activities and MDA levels of intestinal tissues in comparison to those of the sham group. OCT treatment improved this elevation. The histopathologic evaluation of the mucosal structure was also preserved in the OCT-treated group. Inflammation of pancreatic tissue was also confirmed with histopathological examinations. In the irradiation group, NFkappa-B overexpression was detected. OCT treatment decreased the end organ damage and inflammation of the small intestine. In conclusion, OCT appears to have beneficial effects on intestinal and pancreatic damage in abdominal irradiation through the inflammatory process.

Relative dose distribution in gamma knife treatment near tissue inhomogeneties.

The primary goal in this study was to investigate 3-D dose distribution, near the areas of tissue inhomogeneities, in Gamma Knife Radiosurgery with the gel dosimetry. The spherical glass balloon of a diameter of 16 cm filled with the gel forms the homogeneous phantom; and an identical balloon with two corks placed on each side to represent the air cavities forms the inhomogeneous phantom. Dose calibration is performed by irradiating vials at known doses and then utilizing the R2- dose calibration curve. Stereotactic frames and fudicial markers were attached to the phantoms for MR scanning and image processing. Dose distributions from a single shot, using all 201 Cobalt sources, delivered to a known point with identical coordinates, are calculated both in homogeneous and inhomogeneous gel phantoms. In the aspect of dosimetrical quality control, the Gamma Knife planning system predicted dose distribution is compared with the experimental results. In the homogeneous phantom, the gel dosimetry calculated dose distribution is in good agreement with the GammaPlan predicted dose distribution. However, with the inhomogeneous phantom, the dose distribution is spatially different and significant differences in dose levels are observed.

Bone healing regulated by nitric oxide: an experimental study in rats.

Nitric oxide has many functions in wound healing and metabolism of bone. In the current study the role of nitric oxide on bone healing was investigated. Thirty-six young adult male Sprague-Dawley rats were divided into three groups: control, nitroso-bovine serum albumin, and aminoguanidine. Five millimeter segmental defects were created in the middle of the right femora. A polyethylene plate and screw posts were used for rigid fixation. Demineralized bone matrix served as the graft material in all groups. Nitroso-bovine serum albumin (an active nitric oxide congener) carried by demineralized bone matrix was applied locally at the defect in the nitroso-bovine serum albumin group. Aminoguanidine (an inducible nitric oxide synthase inhibitor) group received oral aminoguanidine treatment. Formation and healing of bone were determined by radiographic and histologic analyses. In comparison to the control group the healing rate was faster in both experimental groups as indicated by radiographic and histologic data. If accompanied by bone graft with a suitable delivery system, nitric oxide may be useful as a therapeutic adjuvant in clinical situations when local formation of bone is needed. Moreover, when combined appropriately, treatment with orthotopic nitric oxide supplementation and systemic inducible nitric oxide synthase inhibition may enhance bone healing.