This study examined the concentrations of brain metabolites visible to in-vivo ¹ H-Magnetic Resonance Spectroscopy ( ¹ H-MRS) at 1.5 T in a sample of 28 normal subjects. Quantitation was attempted for inositol compounds, choline units, total creatine and N-acetyl moieties, using open-source software. Six brain regions were considered: frontal and parietal white matter, medial temporal lobe, thalamus, pons and cerebellum. Absolute concentrations were derived using tissue water as an internal reference and using an external reference; metabolite signal intensity ratios with respect to creatine were also calculated. The inter-individual variability was smaller for absolute concentrations (internal reference) as compared to that for signal intensity ratios. Significant regional variability in concentration was found for all metabolites, indicating that separate normative values are needed for different brain regions. The values obtained in this study can be used as reference in future studies, provided the same methodology is followed; it is confirmed that despite unsuccessful attempts in the past, smaller coefficients of variation can indeed be obtained through absolute quantification.

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Accelerated partial breast irradiation (APBI) with high dose rate (HDR) brachytherapy offers an excellent compact course of radiation due to its limited number of fractions for early-stage carcinoma of breast. One of the recent devices is SAVI (strut-adjusted volume implant), which has 6, 8 or 10 peripheral source channels with one center channel. Each channel can be differentially loaded. This paper focuses on the treatment planning, dosimetry and quality assurance aspects of HDR brachytherapy implant with GammaMed Plus HDR afterloader unit. The accelerated PBI balloon devices normally inflate above 35 cc range, and hence these balloon type devices cannot be accommodated in small lumpectomy cavity sizes. CT images were obtained and 3-D dosimetric plans were done with Brachyvision planning system. The 3-D treatment planning and dosimetric data were evaluated with planning target volume (PTV)_eval V90, V95, V150, V200 skin dose and minimum distance to skin. With the use of the SAVI 6-1 mini device, we were able to accomplish an excellent coverage - V90, V95, V150 and V200 to 98%, 95%, 37 cc (<50 cc volume) and 16 cc (<20 cc volume), respectively. Maximum skin dose was between 73% and 90%, much below the prescribed dose of 34 Gy. The minimum skin distance achieved was 5 to 11 mm. The volume that received 50% of the prescribed radiation dose was found to be lower with SAVI. The multi-channel SAVI-based implants reduced the maximum skin dose to markedly lower levels as compared to other modalities, simultaneously achieving best dose coverage to target volume. Differential-source dwell-loading allows modulation of the radiation dose distribution in symmetric or asymmetric opening of the catheter shapes and is also advantageous in cavities close to chest wall.

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The comparative dosimetry of GammaMed (GM) Plus high-dose rate brachytherapy source was performed by an experiment using 0.1-cc thimble ionization chamber and simulation-based study using EGSnrc code. In-water dose measurements were performed with 0.1-cc chamber to derive the radial dose function (r = 0.8 to 20.0 cm) and anisotropy function (r = 5.0 cm with polar angle from 10° to 170°). The nonuniformity correction factor for 0.1-cc chamber was applied for in-water measurements at shorter distances from the source. The EGSnrc code was used to derive the dose rate constant (L), radial dose function g _L (r) and anisotropy function F(r, q) of GM Plus source. The dosimetric data derived using EGSnrc code in our study were in very good agreement relative to published data for GM Plus source. The radial dose function up to 12 cm derived from measured dose using 0.1-cc chamber was in agreement within ±3% of data derived by the simulation study.

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This study aims at evaluating the impact of tissue heterogeneity corrections on dosimetry of stereotactic body radiation therapy treatment plans. Four-dimensional computed tomography data from 15 low stage non-small cell lung cancer patients was used. Treatment planning and dose calculations were done using pencil beam convolution algorithm of Varian Eclipse system with Modified Batho Power Law for tissue heterogeneity. Patient plans were generated with 6 MV co-planar non-opposing four to six field beams optimized with tissue heterogeneity corrections to deliver a prescribed dose of 60 Gy in three fractions to at least 95% of the planning target volume, keeping spinal cord dose <10 Gy. The same plans were then regenerated without heterogeneity correction by recalculating previously optimized treatment plans keeping identical beam arrangements, field fluences and monitor units. Compared with heterogeneity corrected plans, the non-corrected plans had lower average minimum, mean, and maximum tumor doses by 13%, 8%, and 6% respectively. The results indicate that tissue heterogeneity is an important determinant of dosimetric optimization of SBRT plans.

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The study was aimed to compare accuracy of monitor unit verification in intensity modulated radiation therapy (IMRT) using 6 MV photons by three different methodologies with different detector phantom combinations. Sixty patients were randomly chosen. Zero degree couch and gantry angle plans were generated in a plastic universal IMRT verification phantom and 30Χ30Χ30 cc water phantom and measured using 0.125 cc and 0.6 cc chambers, respectively. Actual gantry and couch angle plans were also measured in water phantom using 0.6 cc chamber. A suitable point of measurement was chosen from the beam profile for each field. When the zero-degree gantry, couch angle plans and actual gantry, couch angle plans were measured by 0.6 cc chamber in water phantom, the percentage mean difference (MD) was 1.35%, 2.94 % and Standard Deviation (SD) was 2.99%, 5.22%, respectively. The plastic phantom measurements with 0.125 cc chamber Semiflex ionisation chamber (SIC) showed an MD=4.21% and SD=2.73 %, but when corrected for chamber-medium response, they showed an improvement, with MD=3.38 % and SD=2.59 %. It was found that measurements with water phantom and 0.6cc chamber at gantry angle zero degree showed better conformity than other measurements of medium-detector combinations. Correction in plastic phantom measurement improved the result only marginally, and actual gantry angle measurement in a flat- water phantom showed higher deviation.

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This study aims to determine the precision (reproducibility) of volume assessment in routine clinical computed tomography (CT) using adrenal glands as surrogate tumors. Seven patients at our institution were identified retrospectively as having received numerous abdominal CT scans (average 13.1, range 5 to 20). The adrenal glands were used as surrogate tumors, assuming no actual volume change. Left and right adrenal gland volumes were assessed by hand segmentation for each patient scan. Over 1240 regions of interest were outlined in total. The reproducibility, expressed as the coefficient of variation (COV), was used to characterize measurement precision. The average volumes were 5.9 and 4.5 cm ³ for the left and right adrenal gland, respectively, with COVs of 17.8% and 18.9%, respectively. Using one patient's data (20 scans) as an example surrogate for a spherical tumor, it was calculated that a 13% change in volume (4.2% change in diameter) could be determined with statistical significance at P=0.05. For this case, cursor positioning error in linear measurement of object size, by even 1 pixel on the CT image, corresponded to a significant change in volume (P=0.05). The precision of volume determination was dependent on total volume. Precision improved with increasing object size (r ² =0.367). Given the small dimensions of the adrenal glands, the ~18% COV is likely to be a high estimate compared to larger tumors. Modern CT scanners working with thinner sections (i.e. <1 mm) are likely to produce better measurement precision. The use of volume measurement to quantify changing tumor size is supported as a more precise metric than linear measurement.

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Dosimetric properties of virtual wedge (VW) and physical wedge (PW) in 6- and 10-MV photon beams from a Siemens ONCOR linear accelerator, including wedge factors, depth doses, dose profiles, peripheral doses, are compared. While there is a great difference in absolute values of wedge factors, VW factors (VWFs) and PW factors (PWFs) have a similar trend as a function of field size. PWFs have stronger depth dependence than VWF due to beam hardening in PW fields. VW dose profiles in the wedge direction, in general, match very well with those of PW, except in the toe area of large wedge angles with large field sizes. Dose profiles in the nonwedge direction show a significant reduction in PW fields due to off-axis beam softening and oblique filtration. PW fields have significantly higher peripheral doses than open and VW fields. VW fields have similar surface doses as the open fields, while PW fields have lower surface doses. Surface doses for both VW and PW increase with field size and slightly with wedge angle. For VW fields with wedge angles 45° and less, the initial gap up to 3 cm is dosimetrically acceptable when compared to dose profiles of PW. VW fields in general use less monitor units than PW fields.

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In biology, materials science, radiography quality control or film dosimetry in radiotherapy, a transmission densitometer is useful for measurements of optical density. The design proposed here is oriented to quality control in radiographic films. The instrument described here utilizes low-cost solid-state devices and is easy to construct. The use of 1-watt white light-emitting diode in this densitometer enables low power consumption and a cold light source. Moreover, the instrument does not need a reference light, which results in decreasing the number of parts and reducing the overall size of the apparatus.

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