Corrigendum: Stylopine: a potential natural metabolite to block vascular endothelial growth factor receptor 2 (VEGFR2) in osteosarcoma therapy

[This corrects the article DOI: 10.3389/fphar.2023.1150270.].

Stylopine: A potential natural metabolite to block vascular endothelial growth factor receptor 2 (VEGFR2) in osteosarcoma therapy

Vascular endothelial growth factor (VEGF) signals cell survival, cell migration, osteogenesis, cell proliferation, angiogenesis, and vascular permeability by binding to VEGF receptor 2 (VEGFR-2). Osteosarcoma is the most common primary bone cancer, majorly affects young adults. Activation of VEGFR-2 signaling is a therapeutic target for osteosarcoma. The present study aimed to evaluate the potency of stylopine in regulation of the VEGFR-2 signaling pathway and its anti-tumour effect human MG-63 osteosarcoma cells. The in silico study on benzylisoquinoline alkaloids was carried out for analyzing and shortlisting of compounds using a virtual screening, Lipinski's rule, bioavailability graphical RADAR plot, pharmacokinetics, toxicity, and molecular docking studies. Among the benzylisoquinoline alkaloids, stylopine was selected and subjected to in-vitro studies against human MG-63 osteosarcoma cells. Various experiments such as MTT assay, EtBr/AO staining, mitochondrial membrane potential assessment, transwell migration assay, gene expression analysis by a quantitative real time polymerase chain reaction (qRT-PCR) method, SDS-PAGE followed by immunoblotting were performed to evaluate its anti-tumour effect as compared to standard axitinib. The MTT assay indicates that stylopine inhibits cell proliferation in MG-63 cells. Similarly, as confirmed by the EtBr/Ao staining method, the MMP assay indicates that stylopine induces mitochondrial membrane damage and apoptosis as compared to axitinib. Moreover, stylopine inhibits the VEGF-165 induced MG-63 cell migration by a trans-well migration assay. The immunoblotting and qRT-PCR analysis showed that stylopine inhibits the VEGF-165 induced VEGFR2 expression in MG-63 cells. It is concluded that stylopine has potential to regulate VEGFR2 and can inhibit osteosarcoma cells to offer a new drug candidate for the treatment of bone cancer in future.

Enhancement of the production of L-glutaminase, an anticancer enzyme, from Aeromonas veronii by adaptive and induced mutation techniques

Microbial anti-cancer enzymes have been proven to be effective and economical agents for cancer treatment. Aeromonas veronii has been identified as a microorganism with the potential to produce _L-glutaminase, an anticancer agent effective against acute lymphocytic leukaemia. In this study, a selective medium of Aeromonas veronii was used to culture the microorganism. Strain improvement was done by adaptive and induced mutational techniques. A selective minimal agar media was incorporated for the growth of the strain which further supports adaptive mutation. Strains were also UV-irradiated and successively treated with N-methyl-N'-nitro-N-nitrosoguanidine to find a resilient strain capable of producing _L-glutaminase efficiently. The Plackett-Burman design and central composite designs were used to screen and optimize additional carbon and nitrogen sources. Adaptive mutation resulted in promising yield improvements compared to native strain (P<0.001). The mean yield of 30 treated colonies from the induced mutation was significantly increased compared to the non-induced strain (P< 0.001). The economically feasible statistical designs were found to reinforce each other in order to maximize the yield of the enzyme. The interactions of nutrient factors were understood from the 3D response surface plots. The model was found to be a perfect fit in terms of maximizing enzyme yield, with the productivity improving at every stage to a fourfold output of enzyme (591.11 ±7.97 IU/mL) compared to the native strain (135±3.51 IU/mL).

Analysis of small field percent depth dose and profiles: Comparison of measurements with various detectors and effects of detector orientation with different jaw settings

The advent of modern technologies in radiotherapy poses an increased challenge in the determination of dosimetric parameters of small fields that exhibit a high degree of uncertainty. Percent depth dose and beam profiles were acquired using different detectors in two different orientations. The parameters such as relative surface dose (D_S), depth of dose maximum (D_max), percentage dose at 10 cm (D₁₀), penumbral width, flatness, and symmetry were evaluated with different detectors. The dosimetric data were acquired for fields defined by jaws alone, multileaf collimator (MLC) alone, and by MLC while the jaws were positioned at 0, 0.25, 0.5, and 1.0 cm away from MLC leaf-end using a Varian linear accelerator with 6 MV photon beam. The accuracy in the measurement of dosimetric parameters with various detectors for three different field definitions was evaluated. The relative D_S(38.1%) with photon field diode in parallel orientation was higher than electron field diode (EFD) (27.9%) values for 1 cm ×1 cm field. An overestimation of 5.7% and 8.6% in D₁₀ depth were observed for 1 cm ×1 cm field with RK ion chamber in parallel and perpendicular orientation, respectively, for the fields defined by MLC while jaw positioned at the edge of the field when compared to EFD values in parallel orientation. For this field definition, the in-plane penumbral widths obtained with ion chamber in parallel and perpendicular orientation were 3.9 mm, 5.6 mm for 1 cm ×1 cm field, respectively. Among all detectors used in the study, the unshielded diodes were found to be an appropriate choice of detector for the measurement of beam parameters in small fields.

Design and Testing of Indigenous Cost Effective Three Dimensional Radiation Field Analyser (3D RFA)

The aim of the study is to design and validate an indigenous three dimensional Radiation Field Analyser (3D RFA). The feed system made for X, Y and Z axis movements is of lead screw with deep ball bearing mechanism made up of stain less steel driven by stepper motors with accuracy less than 0.5 mm. The telescopic column lifting unit was designed using linear actuation technology for lifting the water phantom. The acrylic phantom with dimensions of 800 × 750 × 570 mm was made with thickness of 15 mm. The software was developed in visual basic programming language, classified into two types, viz. beam analyzer software and beam acquisition software. The premeasurement checks were performed as per TG 106 recommendations. The physical parameters of photon PDDs such as Dmax, D10, D20and Quality Index (QI), and the electron PDDs such as R50, Rp, E0, Epoand X-ray contamination values can be obtained instantaneously by using the developed RFA system. Also the results for profile data such as field size, central axis deviation, penumbra, flatness and symmetry calculated according to various protocols can be obtained for both photon and electron beams. The result of PDDs for photon beams were compared with BJR25 supplement values and the profile data were compared with TG 40 recommendation. The results were in agreement with standard protocols.

Cytokine profile and induction of T helper type 17 and regulatory T cells by human peripheral mononuclear cells after microbial exposure

The immunomodulatory effects of probiotics were assessed following exposure of normal peripheral blood mononuclear cells (PBMC), cord blood cells and the spleen-derived monocyte/macrophage cell line CRL-9850 to Lactobacillus acidophilus LAVRI-A1, Lb. rhamnosus GG, exopolysaccharides (EPS)-producing Streptococcus thermophilus St1275, Bifidobacteriun longum BL536, B. lactis B94 and Escherichia coli TG1 strains. The production of a panel of pro- and anti-inflammatory cytokines by PBMC following bacterial stimulation was measured, using live, heat-killed or mock gastrointestinal tract (GIT)-exposed bacteria, and results show that (i) all bacterial strains investigated induced significant secretion of pro- and anti-inflammatory cytokines from PBMC-derived monocytes/macrophages; and (ii) cytokine levels increased relative to the expansion of bacterial cell numbers over time for cells exposed to live cultures. Bifidobacteria and S. thermophilus stimulated significant concentrations of transforming growth factor (TGF)-β, an interleukin necessary for the differentiation of regulatory T cells (T(reg) )/T helper type 17 (Th17) cells and, as such, the study further examined the induction of Th17 and T(reg) cells after PBMC exposure to selected bacteria for 96 h. Data show a significant increase in the numbers of both cell types in the exposed populations, measured by cell surface marker expression and by cytokine production. Probiotics have been shown to induce cytokines from a range of immune cells following ingestion of these organisms. These studies suggest that probiotics' interaction with immune-competent cells produces a cytokine milieu, exerting immunomodulatory effects on local effector cells, as well as potently inducing differentiation of Th17 and T(reg) cells.

Impact of cutout off axis on electron beam dosimetric parameters

Dosimetric changes caused by the positional uncertainty of centering a small electron cutout to the machine central axis (CAX) of the linear accelerator (linac) were investigated. Six circular cutouts with 4 cm diameter were made with their centres shifted off by 0, 2, 4, 6, 8 and 10 mm from the machine CAX. The 6 x 6 cm(2) electron applicator was used for the measurement. The percentage depth doses (PDDs) were measured at the Machine CAX and also with respect to cutout centre for 6, 9, 12, 16 and 20 MeV electron beams. The in-line and cross-line profiles were measured at the depth of maximum dose (R100). The relative output factor (ROF) was measured at the reference depth. All the measurements were made at nominal source to surface distance (100 cm SSD) as well as at extended SSDs (100, 102, 106 and 110 cm). When the cutout centre was shifted away from the machine CAX for low energy beams the depth of 100% dose (R(100)), the depth of 90% dose (R(90)) and the depth of 80% dose (R(80)) had no significant change. For higher energies (>9 MeV) there was a reduction in these dosimetric parameters. The isodose coverage of the in-line and cross-line profile was reduced when the cutout centre was shifted away from the machine CAX. At extended SSDs the dosimetric changes are only because of geometric divergence of the beam and not by the positional uncertainty of the cutout. It is important for the radiation oncologist, dosimetrist, therapist and physicist to note such dosimetric changes while using the electron beam to the patients.

Implementation and validation of a commercial portal dosimetry software for intensity-modulated radiation therapy pre-treatment verification

Electronic portal imaging devices (EPIDs) are extensively used for obtaining dosimetric information of pre-treatment field verification and in-vivo dosimetry for intensity-modulated radiotherapy (IMRT). In the present study, we have implemented the newly developed portal dosimetry software using independent dose prediction algorithm EPIDose^™ and evaluated this new tool for the pre-treatment IMRT plan quality assurance of Whole Pelvis with Simultaneous Integrated Boost (WP-SIB-IMRT) of prostate cases by comparing with routine two-dimensional (2D) array detector system (MapCHECK^™). We have investigated 104 split fields using γ -distributions in terms of predefined γ frequency parameters. The mean γ values are found to be 0.42 (SD: 0.06) and 0.44 (SD: 0.06) for the EPIDose and MapCHECK^™, respectively. The average γ∆ for EPIDose and MapCHECK^™ are found as 0.51 (SD: 0.06) and 0.53 (SD: 0.07), respectively. Furthermore, the percentage of points with γ < 1, γ < 1.5, and γ > 2 are 97.4%, 99.3%, and 0.56%, respectively for EPIDose and 96.4%, 99.0% and 0.62% for MapCHECK^™. Based on our results obtained with EPIDose and strong agreement with MapCHECK^™, we may conclude that the EPIDose portal dosimetry system has been successfully implemented and validated with our routine 2D array detector

Dosimetric comparison of high dose rate brachytherapy and intensity-modulated radiation therapy for cervical carcinoma

Intracavitary brachytherapy is an integral part of radiotherapy for locally advanced gynecologic malignancies. A dosimetric intercomparison of high dose rate intracavitary brachytherapy (HDR_BT) and intensity-modulated radiotherapy in cervical carcinoma has been made in the present study. CT scan images of 10 patients treated with HDR_BT were used for this study. A sliding-window IMRT (IMRT_SW) and step-and-shoot IMRT plans were generated using 6-MV X-rays. The cumulative dose volume histograms of target, bladder, rectum and normal tissue were analyzed for both techniques and dose distributions were compared. It was seen that the pear-shaped dose distribution characteristic of intracavitary brachytherapy with sharp dose fall-off outside the target could be achieved with IMRT. The integral dose to planning target volume was significantly higher with HDR_BT in comparison with IMRT. Significant differences between the two techniques were seen for doses to 1 cc and 2 cc of rectum, while the differences in 1 cc and 2 cc doses to bladder were not significant. The integral doses to the nontarget critical and normal structures were smaller with HDR_BT and with IMRT. It is concluded that IMRT can be the choice of treatment in case of non-availability of HDR brachytherapy facilities or when noninvasive treatments are preferred

Comparison of IMRT and Rapidarc treatment plans using AAPM task group test suites

The purpose of this study is to examine the plan quality and monitor unit with sliding window IMRT and RapidArc (RA) treatment plans using American Association Physicists in Medicine TG119 test suite DICOM-RT images and structure sets. The structure set includes multi-target (superior, central, inferior), prostate, head and neck and C-shape. Plans were performed with Eclipse planning system using AAA algorithm with the plan goals specified in TG119. The plan results for multitarget shows that the D99 is greater than the plan goal for all the targets. The D10 is less than the plan goal for superior and inferior targets in both IMRT and RA plans. The D10 is 5% more with IMRT plan and 7% more with RA plan for central target in comparison with plan goal. The plan results for prostate shows that D95 is greater than the plan goal for both IMRT and RA plans. The D5 is less than the plan goal for IMRT plan and almost equal to plan goal for RA plan. The D30 is less than the plan goal for bladder and rectum in both the plans. The D10 is higher than the plan goal by 1.9% and 2.5% in IMRT and RA plan for rectum. The plan results for head and neck shows that the D99 and D90 were greater than the plan goal for PTV. The spinal cord and parotid doses were less than the plan goal in both the plans. The plan results for C-shape shows that the D95 was greater than the plan goal and D10 was less than the plan goal for PTV. The dose to central core was less than the plan goal in both IMRT and RA plans. Both the IMRT and RapidArc plans have met the plan goal for all the target and normal structures. RapidArc optimization and treatment planning requires more time than the IMRT plan. The monitor unit calculated by the RapidArc plan is less compared to IMRT plan, which reduces the treatment error caused by patient motion during treatment and integral dose.

Peripheral dose from a dual energy linear accelerator equipped with tertiary multileaf collimators and enhanced dynamic wedge

Peripheral dose (PD) or the dose outside the geometrical boundaries of the radiation field is of clinical importance when anatomical structures with low dose tolerances might be involved(1). It is the aim of this study is to estimate the PD on linear accelerators on different wedge systems without multileaf collimator (MLC). Measurements were performed on a dual energy linear accelerator equipped with tertiary MLC and enhanced dynamic wedge (EDW). Measurements were made using an ionization chamber embedded in a Radiation Field Analyser (RFA-300) with the secondary collimator and MLC setting of 5x5, 10x10, 15x15, and 20x20 cm2, and with the MLC fully retracted. The effects of SSD on PD were measured at three SSDs of 90, 100, and 110 cm for the irradiation fields of 5x5, 10x10, 15x15, and 20x20 cm2 and the effects of the three different wedges (Upper wedge, Lower Wedge and Enhanced Dynamic Wedge) on PD were measured for 45° wedges with field size of 15x15 cm2. Data were taken from 3 cm to 24 cm away from the field edge. Results show that due to tertiary MLC, PD can be reduced by means of a factor of two to three at certain distance from the edge of the field compared with TG-36 data. In between the wedges, the PD was less for the EDW when compared with the upper and lower physical wedges. We conclude that the reduction in PD is significant in reducing or eliminating the need for external peripheral shielding to reduce the dose on affected critical organs.

Variation of beam characteristics between three different wedges from a dual-energy accelerator

The use of megavoltage X-ray sources of radiation, with their skin-sparing qualities in radiation therapy, has been proved useful in relieving patient discomfort and allowing higher tumor doses to be given with fewer restrictions due to radiation effects in the skin. The purpose of this study was to compare the dosimetric characteristics of a physical and enhanced dynamic wedge from a dual-energy (6 and 18 MV) linear accelerator such as surfaces doses with different source to surface distances (SSD), half value layer (HVL) in water and peripheral doses for both available energies. At short SSD such as 85 cm, higher surface doses are produced by the lower wedges by the short wedge-to-skin distance. For physical wedged field, at heel edge side HVL value was high (17 cm) compared with the measured that of EDW (15.1 cm). It was noticed that, the HVL variation across the beam was significantly higher for 6 MV X-rays than for 18 MV X-rays. The lower wedge has the maximum variation of peripheral dose compared to other wedges. The three wedge systems discussed in this work possess vastly different dosimetric characteristics. These differences will have a direct impact on the choice of the wedge system to be used for a particular treatment. Complete knowledge of the dosimetric characterisitics, including the surface and peripheral doses, is crucial in proper choice of particular wedge systems in clinical use.

Electron beam characteristics at extended source-to-surface distances for irregular cut-outs

Electron beam therapy is widely used in the management of cancers. The rapid dose fall-off and the short range of an electron beam enable the treatment of lesions close to the surface, while sparing the underlying tissues. In an extended source-to-surface (SSD) treatment with irregular field sizes defined by cerrobend cutouts, underdosage of the lateral tissue may occur due to reduced beam flatness and uniformity. To study the changes in the beam characteristics, the depth dose, beam profile, and isodose distributions were measured at different SSDs for regular 10 × 10 cm² and 15 × 15 cm² cone, and for irregular cutouts of field size 6.5 × 9 cm² and 11.5 × 15 cm² for beam energies ranging from 6 to 20 MeV. The PDD, beam flatness, symmetry and uniformity index were compared. For lower energy (6 MeV), there was no change in the depth of maximum dose (R100) as SSD increased, but for higher energy (20 MeV), the R₁₀₀ depth increased from 2 cm to 3 cm as SSD increased. This shows that as SSD increases there is an increase in the depth of the maximum dose for higher energy beams. There is a +7 mm shift in the R₁₀₀ depth when compared with regular and irregular field sizes. The symmetry was found to be within limits for all the field sizes as the treatment distance extended as per International Electro technical Commision (IEC) protocol. There was a loss of beam flatness for irregular fields and it was more pronounced for lower energies as compared with higher energies, so that the clinically useful isodose level (80% and 90%) width decreases with increase in SSD. This suggests that target coverage at extended SSD with irregular cut-outs may be inadequate unless relatively large fields are used.

IMRT implementation and patient specific dose verification with film and ion chamber array detectors

Implementation of Intensity Modulation Radiotherapy (IMRT) and patient dose verification was carried out with film and I'mariXX using linear accelerator with 120-leaf Millennium dynamic multileaf collimator (dMLC). The basic mechanical and electrical commissioning and quality assurance tests of linear accelerator were carried out. The leaf position accuracy and leaf position repeatability checks were performed for static MLC positions. Picket fence test and garden fence test were performed to check the stability of the dMLC and the reproducibility of the gap between leaves. The radiation checks were performed to verify the position accuracy of MLCs in the collimator system. The dMLC dosimetric checks like output stability, average leaf transmission and dosimetric leaf separation were also investigated. The variation of output with gravitation at different gantry angles was found to be within 0.9 %. The measured average leaf transmission for 6 MV was 1.6 % and 1.8% for 18 MV beam. The dosimetric leaf separation was found to be 2.2 mm and 2.3 mm for 6 MV and 18 MV beams. In order to check the consistency of the stability and the precision of the dMLC, it is necessary to carryout regular weekly and monthly checks. The dynalog files analysis for Garden fence, leaf gap width and step wedge test patterns carried out weekly were in good agreement. Pretreatment verification was performed for 50 patients with ion chamber and I'mariXX device. The variations of calculated absolute dose for all treatment fields with the ion chamber measurement were within the acceptable criterion. Treatment Planning System (TPS) calculated dose distribution pattern was comparable with the I'mariXX measured dose distribution pattern. Out of 50 patients for which the comparison was made, 36 patients were agreed with the gamma pixel match of >95% and 14 patients were with the gamma pixel match of 90-95% with the criteria of 3% delta dose (DD) and 3 mm distance-to-agreement (DTA). Commissioning and quality assurance of dMLC for IMRT application requires considerable time and effort. Many dosimetric characteristics need to be assessed carefully failing which the delivered dose will be significantly different from the planned dose. In addition to the issues discussed above we feel that individual MU check is necessary before the treatment is delivered.

Optimized dose distribution of Gammamed plus vaginal cylinders

Endometrial carcinoma is the most common malignancy arising in the female genital tract. Intracavitary vaginal cuff irradiation may be given alone or with external beam irradiation in patients determined to be at risk for locoregional recurrence. Vaginal cylinders are often used to deliver a brachytherapy dose to the vaginal apex and upper vagina or the entire vaginal surface in the management of postoperative endometrial cancer or cervical cancer. The dose distributions of HDR vaginal cylinders must be evaluated carefully, so that clinical experiences with LDR techniques can be used in guiding optimal use of HDR techniques. The aim of this study was to optimize dose distribution for Gammamed plus vaginal cylinders. Placement of dose optimization points was evaluated for its effect on optimized dose distributions. Two different dose optimization point models were used in this study, namely non-apex (dose optimization points only on periphery of cylinder) and apex (dose optimization points on periphery and along the curvature including the apex points). Thirteen dwell positions were used for the HDR dosimetry to obtain a 6-cm active length. Thus 13 optimization points were available at the periphery of the cylinder. The coordinates of the points along the curvature depended on the cylinder diameters and were chosen for each cylinder so that four points were distributed evenly in the curvature portion of the cylinder. Diameter of vaginal cylinders varied from 2.0 to 4.0 cm. Iterative optimization routine was utilized for all optimizations. The effects of various optimization routines (iterative, geometric, equal times) was studied for the 3.0-cm diameter vaginal cylinder. The effect of source travel step size on the optimized dose distributions for vaginal cylinders was also evaluated. All optimizations in this study were carried for dose of 6 Gy at dose optimization points. For both non-apex and apex models of vaginal cylinders, doses for apex point and three dome points were higher for the apex model compared with the non-apex model. Mean doses to the optimization points for both the cylinder models and all the cylinder diameters were 6 Gy, matching with the prescription dose of 6 Gy. Iterative optimization routine resulted in the highest dose to apex point and dome points. The mean dose for optimization point was 6.01 Gy for iterative optimization and was much higher than 5.74 Gy for geometric and equal times routines. Step size of 1 cm gave the highest dose to the apex point. This step size was superior in terms of mean dose to optimization points. Selection of dose optimization points for the derivation of optimized dose distributions for vaginal cylinders affects the dose distributions.

Long-term results of radiofrequency ablation of slow pathway in patients with atrioventricular nodal reentrant tachycardia: single-center experience

BACKGROUND

This study sought to evaluate the long-term recurrence rate of atrioventricular nodal reentrant tachycardia (AVNRT) after radiofrequency catheter ablation. The clinical and electrophysiological features of patients with AVNRT and their immediate outcomes after undergoing slow pathway ablation/modification were also studied.

METHODS AND RESULTS

The study included 264 consecutive patients with AVNRT (mean age 46 -/+ 15 years, 143 women, 121 men) who underwent slow pathway ablation/modification using a combined electrophysiological and anatomical approach. The primary endpoint of ablation procedure was non- inducibility of the arrhythmia. The primary endpoint of the study was the recurrence of AVNRT on follow-up. Acute success was achieved in 262 (99.6%) patients. Complication rate of the ablation procedure was 2.6% and the average fluoroscopy time was 18.3 -/+ 11 minutes. The patients were followed up for a mean duration of 20 -/+ 9 months during which there was only one case of recurrence.

CONCLUSION

Radiofrequency ablation or modification of slow pathway is highly effective in the treatment of AVNRT. The technique has a high initial success rate and a low complication rate. The recurrence rates are extremely low (0.3%) on long-term follow-up.

Electrospray ionisation mass spectral studies on hydrolysed products of sulfur mustards

Off-site detection of the hydrolysed products of sulfur mustards in aqueous samples is an important task in the verification of Chemical Weapons Convention (CWC)-related chemicals. The hydrolysed products of sulfur mustards are studied under positive and negative electrospray ionisation (ESI) conditions using an additive with a view to detecting them at trace levels. In the presence of cations (Li(+), Na(+), K(+) and NH(4) (+)), the positive ion ESI mass spectra of all the compounds include the corresponding cationised species; however, only the [M+NH(4)](+) ions form [M+H](+) ions upon decomposition. The tandem mass (MS/MS) spectra of [M+H](+) ions from all the hydrolysed products of the sulfur mustard homologues were distinct and allowed these compounds to be characterised unambiguously. Similarly, the negative ion ESI mass spectra of all the compounds show prominent adducts with added anions (F(-), Cl(-), Br(-), and I(-)), but the [M-H](-) ion can only be generated by decomposition of an [M+F](-) ion. The MS/MS spectra of the [M-H](-) ions from all the compounds result in a common product ion at m/z 77. A precursor ion scan of m/z 77 is shown to be useful in the rapid screening of these compounds in aqueous samples at trace levels, even in the presence of complex masking agents, without the use of time-consuming sample preparation and chromatography steps. An MS/MS method developed to measure the detection limits of the hydrolysed products of sulfur mustards found these to be in the range of 10-500 ppb.

Successful radiofrequency ablation of atypical left ventricular outflow tachycardia guided by epicardial activation signals

A 12-year-old girl, with incessant atypical idiopathic left ventricular tachycardia, underwent successful radiofrequency ablation of ventricular tachycardia focus originating from a subepicardial site adjacent to the left coronary cusp. Ventricular tachycardia was successfully eliminated by targeting an endocardial site concordant to the epicardial site of early activation. Epicardial mapping was useful in locating an effective ablation site, and aortic root angiography was used to avoid potential injury to important structures, such as the left main coronary artery and left coronary cusp.

Transcatheter closure of post-myocardial infarction ventricular septal defect with Amplatzer septal occluder

Rupture of the interventricular septum is an uncommon but often fatal complication of acute myocardial infarction. Transcatheter closure is an established method of treating selected congenital defects but clinical experience on transcatheter closure of postinfarction ventricular septal defects (VSDs) is minimal. We report a case of successful transcatheter closure of postinfarction VSD using the Amplatzer septal occluder.

Measurement of backscattered radiation from secondary collimator jaws into the beam monitor chamber from a dual energy linear accelerator

AIM

The photons and electrons backscattered from the upper and lower secondary collimator jaws give rise to a significant increase in the ion charge measured by the monitor chamber, and this increase varies between different accelerators. We have studied the effect of backscatter into the monitor chamber at 6 MV and 18 MV photon energies for the linear accelerator Clinac-1800.

MATERIALS AND METHODS

The variation of the output factor was first studied for variable asymmetric fields of fixed field size defined by variable right upper collimator jaw together with a variable Cerrobend block low melting point alloy, with constant lower jaw position. Output measurements were carried out at Dmax in a polystyrene phantom at the geometric center of the asymmetric field. The backscatter radiation effect was also analyzed applying a pair of 20 x 20 x 7.5 cm Cerrobend alloy blocks with 6.0 mm diameter pin-holes in the center aligned telescopically with the field defining light beam. The ion chamber with build-up cap was placed at 25 cm behind the second pin-hole. The in air measurements were made varying upper and lower collimators individually and together. For comparison, a similar study was conducted in a Theratron-780C cobalt-60 beam.

RESULTS

In the asymmetric field experiment it was noticed that till the collimator jaw crosses the midline, the output factor is almost constant for 6 and 18 MV photon beams. For extreme field asymmetry, the decreases in output factor were 3.2% and 4.3% for 6 and 18 MV, respectively. The telescopic experiment demonstrated 4.0% and 3.9% reduction in output factor for 6 and 18 MV beams when only the upper jaws were varied. Field definition by the lower jaws only reduced the output factor by 3.3% and 3% for 6 and 18 MV photon beams. For square fields achieved by both the jaws, the output factor variation was similar to that achieved with the upper collimator for both energies. Cobalt-60 measurements with the telescopic arrangement did not show significant dependency of output with field variation, provided that the field-dependent scatter from source capsule and collimator jaws is excluded.

CONCLUSION

From this study a maximum reduction of 4% and 4.3% in dose delivery was observed for 6 MV and 18 MV photon beams due to backscattered radiation originating mainly from upper collimator reaching the beam monitor chamber. For asymmetric fields it is felt that direct output measurement is more reliable in order to avoid errors in output factor due to radiation backscattered from the collimator jaws into beam monitor chamber.

Forward scatter dose effect at metallic interfaces irradiated by X and gamma ray therapy beams

AIM

In this study forward scattering effects near different metallic interfaces are measured for Co-60 gamma and 6 and 18 MV photon beams. The studied effects are the transport of secondary electrons across the metallic interface and the scattering of photons by the metallic inhomogeneity.

MATERIALS AND METHODS

All measurements were carried out with a PTW thin-window, parallel plate ionisation chamber (B 23344-036) and an RDM-1F electrometer with digital readout. Thin sheets of aluminium, mild steel, copper, cadmium and lead were used as inhomogeneities. The inhomogeneities were placed between the polystyrene phantom and the front window of the chamber which was maintained at 100 cm SSD.

RESULTS

It was noticed that for a high energy photon beam (18 MV) the forward scatter dose factor (FSDF) increases rapidly as the thickness of the metallic inhomogeneity increases. For low energy photons, there is a sharp initial decrease of the FSDF until a minimum value is reached followed by a slow increase with increasing thickness of the inhomogeneity. It was also noted that the FSDF variation at off-axis distances has slightly more slope compared with the ionization ratio (IR) curves for both 6 MV and 18 MV photons. However, the variation in slope is prominent for 18 MV compared with 6 MV photon beam.

CONCLUSION

The sharp dose decrease observed downstream of a metallic inhomogeneity at relatively low photon energies (Co-60, 6 MV) is attributed to the internal scattering of secondary electrons within the metal. The dose enhancement observed for high energy photon beams is attributed to the domination of the pair production process, increasing with atomic number. Since FSDF is dependent on the photon beam spectra, it can be used as a measure of beam quality across the beam.

Dose measurements in the build-up region for the photon beams from Clinac-1800 dual energy medical linear accelerator

AIM

Since the skin dose becomes the limiting factor while deciding the tumorcidal dose, the detailed analysis of dose distribution in the build-up region is necessary for high-energy photon beams. In this study the beam characteristics affecting the build-up and skin dose for 6- and 18-MV photons are analyzed.

MATERIALS AND METHODS

Measurements were made with 6- and 18-MV photons using a PTW parallel-plate ionization chamber (B 23344-036) and a RDM-1F electrometer. Build-up ionization measurements were made with the chamber fitted into a 25 x 25 x 25 cm polystyrene phantom with a fixed SSD of 100 cm. The entrance and build-up dose measurements were made with a polycarbonate and a mesh type metallic shielding tray and a 45 degrees wedge. Exit dose measurements were carried out for the graphite patient supporting assembly table top, 1.0 cm thick piece of wood and the 1.0 cm thick patient supporting perspex base frame for head and neck treatments.

RESULTS

It was observed that the dmax decreased slightly with field size as with other accelerators. For both photon energies the surface dose was observed to increase with increase in field size. It was also noticed that the dose in the build-up region increases slightly when the polycarbonate secondary blocking tray is introduced with the increase in surface dose. The data show that the tray perturbation factor (TPF) at surface decreases steadily with tray-surface distance for both photon beams for all field sizes. It was noted that the TPF was more when the polycarbonate tray was introduced at shorter tray-surface distances for both energies. At tray-surface distances above 60 cm the TPF almost remained close to unity for 6-MV photons for all field sizes, whereas the continuous decrease in TPF could be noted for 18-MV photon beams even after the TPF reached unity.

CONCLUSION

The increase in surface dose with field size for both photon energies is due to the electron scattering from the intervening materials. The use of wedge filters absorbs low-energy scattered electrons significantly and hence, the relative surface dose (RSD) is always less than unity. The increase in dose enhancement percentage with graphite compared to perspex supporting assembly indicates that the electron backscatter is proportional to the atomic number of the medium.