Measurement of backscattered dose at metallic interfaces using high energy electron beams

BackgroundThe amount of backscattered electrons depends on the thickness of the backscattering metal. The electron backscatter increases with the increase in thickness of the metal until a saturation level is reached and thereafter no change in scatter enhancement is noticed.AimElectron backscatter effects at metallic interfaces were analysed in this study. High energy electron beams ranging from 6 to 20 MeV were used.Materials/MethodsMeasurements were carried out with a PTW thin-window parallel plate ionization chamber and an RDM-1F electrometer. Thin sheets of aluminium, copper and lead were used as inhomogeneities. The chamber was positioned below the inhomogeneities with the gantry maintained under the couch.ResultsThe electron backscatter factor (EBSF) increases with increase in energy for aluminium, copper and lead. With low atomic number materials EBSF increases with increase in scatterer thickness and for lead it attains saturation within a few millimetres.ConclusionsThe information from this study could be useful in predicting the increase in dose at the metal-tissue interface due to electron backscatter

Preliminary study on CT imaging of polymer gel radiation dosimetry

BackgroundNew radiotherapy techniques such as stereotactic radiotherapy (SRT) stereotactic radiosurgery (SRS), three dimensional conformal radiotherapy (3DCRT) and intensity modulated radiation therapy (IMRT) aim to deliver a high dose to the tumour while sparing the surrounding normal healthy tissues. As a result of these complicated treatment techniques there is a need for a 3-dimensional (3D) dose verification system. However, currently available dosimeters such as ion chambers, diodes, thermoluminescent dosimeters and films are limited to point (or) planar measurement. Multiple measurements are required to obtain the 3-dimensional dose distribution using the above dosimeters. Hence volumetric measurements are not feasible without multiple detectors (or) multiple measurements. Gel dosimetry attempts to meet the requirements of 3D radiation dose distribution. Gel dosimetry is tissue equivalent [1] and it acts as a phantom as well as dosimeter so there is no need for dose perturbation correction.AimRadiation-induced polymerization in polymer gel dosimeters gives rise to a change in CT number which can be measured with X-ray computed tomography (CT). The aim of this study is to assess the feasibility of using the X-ray CT scanner for the evaluation of dose distribution in polymer gel dosimetry.Materials/MethodsPolymer gel called PAGAT (Polyacrylamide Gelatin and Tetrakis hydroxymethyl phosphonium) consisting of 3.5% (w/w) BIS, 3.5% (w/w) acrylamide, 5% (w/w) gelatin, 10 mM Tetrakis hydroxymethyl phosphonium (THP) and 88% (w/w) water was manufactured in normal atmospheric conditions. The gel was irradiated using a Siemens Primus linear accelerator. The radiation-induced change in CT number was evaluated using a Siemens Somatom Emotion CT scanner. The percentage depth doses and profiles were deduced. The same study was carried out using radiation field analyzer RFA-200 with RK-ion chamber and film and compared with polymer gel measurements.ResultsPolymer gel dosimetry measurement was in agreement with ion chamber and film measurements except for a slight deviation in the build-up region. Discrepancies found were due to analysis of image without image averaging and background subtraction.ConclusionsThis preliminary study was conducted to evaluate the feasibility of using X-ray CT-based polymer gel dosimetry for clinical use. The results of this study encourage further use of X-ray CT in conjunction with polymer gel for 3D radiation dose measurements

Validity of bioeffect dose response models for normal tissue early and late complications of the skin

SummaryBackgroundThe bioeffect of a physical dose depends on the nature of the tissue, fractionation scheme, dose rate and treatment time. Certainly, experienced radiotherapists are convinced of the existence of patient-to-patient variability in normal tissue response to radiotherapy for malignant tumours. The absorbed dose needs to be translated into a bioeffect dose, which takes into account treatment variables and the radiobiological characteristics of the relevant tissue. Various bioeffect models such as NSD, CRE, TDF and BED have been proposed to predict the biological effect of radiotherapy treatments.AimThis study was aimed at deriving tolerance bioeffect dose values for normal tissue complication rate.Materials/MethodsCompiled clinical data of time dose fractionation schedules and incidence of erythema, desquamation and telangiectasia were used for the present analysis.ResultsFor erythema and desquamation the radiation dose varied from 23.9 to 55.1Gy in 04 to 50 fractions (dose per fraction 1.1 to 7.3Gy) in 11 to 40 days. For telangiectasia (score ≥1 at 3 years) the radiation dose varied from 25.8 to 55.1Gy in 04 to 50 fractions (dose per fraction 1.1 to 7.3Gy) in 11 to 40 days. For telangiectasia (score ≥2 at 5 years) the radiation dose varied from 25.8 to 63.0Gy in 04 to 50 fractions (dose per fraction 1.1 to 7.3Gy) in 11 to 68 days. For telangiectasia (score ≥1, ≥2, ≥3, ≥4 at 10 years) the radiation dose varied from 25.8 to 63.0Gy in 04 to 35 fractions (dose per fraction 1.7 to 7.3Gy) in 22 to 68 days. TDF and LQF values for erythema, desquamation and telangiectasia were evaluated with α/β values of 7.5Gy, 11.2Gy and 2.8Gy respectively. TDF and LQF had a statistically significant correlation with probability of erythema, desquamation and telangiectasia (p<0.001).ConclusionsTDF and LQF values should be limited to 60 and 86Gy in order to limit the probability of telangiectasia

Gastroretentive drug delivery system of captopril and hydrochlorothiazide bilayer tablet: formulation, optimization and in vivo evaluation

The purpose of the present study was to develop and optimize floating-bioadhesive bilayer gastroretentive drug delivery system (GRDDS) exhibiting a unique combination of floatation and bioadhesion to prolong residence in the stomach using captopril (CP) and hydrochlorothiazide (HCTZ) as a model drug. Captopril being unstable in intestinal pH and HCTZ has specific absorption from duodenum and the first part of the jejunum and to a small extent in the stomach are suitable candidate for GRDDS. 32 factorial design was employed in formulating and optimizing the GRDDS for bilayer tablet of CP and HCTZ matrix tablet. The main effect and interaction terms were quantitatively evaluated using a mathematical model. The gastroretentive ability of the tablets was evaluated by X-radiographic studies in healthy human volunteer. The tablet releases CP and HCTZ for extended period up to 24 h in controlled manner. The predicted values agreed well with the experimental values and the results demonstrate the feasibility of the optimization methodology in the development of GRDDS. The tablet was buoyant for up to 16 h in human stomach. Development of once a day gastroretentive formulation of CP and HCTZ improves the patience compliance and bioavailability of drugs.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Gastroretentive drug delivery system of captopril and hydrochlorothiazide bilayer tablet: formulation, optimization and in vivo evaluation

The purpose of the present study was to develop and optimize floating-bioadhesive bilayer gastroretentive drug delivery system (GRDDS) exhibiting a unique combination of floatation and bioadhesion to prolong residence in the stomach using captopril (CP) and hydrochlorothiazide (HCTZ) as a model drug. Captopril being unstable in intestinal pH and HCTZ has specific absorption from duodenum and the first part of the jejunum and to a small extent in the stomach are suitable candidate for GRDDS. 32 factorial design was employed in formulating and optimizing the GRDDS for bilayer tablet of CP and HCTZ matrix tablet. The main effect and interaction terms were quantitatively evaluated using a mathematical model. The gastroretentive ability of the tablets was evaluated by X-radiographic studies in healthy human volunteer. The tablet releases CP and HCTZ for extended period up to 24 h in controlled manner. The predicted values agreed well with the experimental values and the results demonstrate the feasibility of the optimization methodology in the development of GRDDS. The tablet was buoyant for up to 16 h in human stomach. Development of once a day gastroretentive formulation of CP and HCTZ improves the patience compliance and bioavailability of drugs.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Measurements of peripheral dose for multileaf collimator based linear accelerator

BackgroundIn radiation therapy, peripheral dose (PD), or the dose outside the geometrical boundaries of the radiation field, is of clinical importance when anatomical structures such as foetus in pregnant women, gonads, and lenses of the eye, with low dose tolerances are involved. Even a small percentage of the total treatment dose might cause injury in such cases. The sources of peripheral dose are leakage from the treatment unit, scatter from the secondary collimators and beam modifiers such as wedges and blocks, and internal scatter originating in the patient.AimTo determine the peripheral dose (PD) for multileaf collimator (MLC) based linear accelerator in water equivalent slab phantom for open and wedged fields.Materials/MethodsPD measurements were carried out for 6 and 15 MV photons using a 0.4cc parallel plate chamber in the slab phantom. Measurements were performed for different field sizes at different depths (Dmax, 5 cm and 10 cm) and up to a maximum distance of 30 cm beyond the field edges. PD was measured using wedge filters also. PD was further computed using a three-dimensional treatment planning system (3D TPS).ResultsFor 6 MV photon beams, the maximum PD for open beams at 5 cm distance from the field edge was 3.42% and the minimum PD at 20 cm distance was 0.11%. For 15 MV, the maximum PD for open beam at 5 cm distance was 3.07% and the minimum PD was 0.14%. For wedge filters, the maximum PD measured at 5 cm distance for 6 and 15 MV photons were 5.56% (60° Wedge) and 5.03% (45° wedge). The TPS PD values showed minimal variation from the measured values.ConclusionsThe PD due to MLC and beam modifiers would definitely be helpful to assess the doses received by the relevant critical structures outside the treatment field

Influence of photon beam energy on IMRT plan quality for radiotherapy of prostate cancer

BackgroundIntensity-modulated radiation therapy (IMRT) has been widely used for prostate cancer treatments. 6MV photon beams were found to be an effective energy choice for most IMRT cases. The use of high-energy photons raise concerns about increased leakage and secondary neutron dose for the patients.AimIn this work, the effect of beam energy on the quality of IMRT plans for prostate radiotherapy was systematically studied for competing IMRT plans optimized for delivery with either 6 or 10MV beams.Materials and MethodsA cohort of 20 prostate cases was selected for this study. All patients received full-course IMRT treatments to a dose of 79.2Gy to PTV in 44 fractions. For all of the cases we developed treatment plans using 6 MV and 10MV intensity-modulated beams with identical dose volume constraints.ResultsPercentage of doses received by the percentage volume of PTV was higher for 6MV photons compared to 10MV photons for 12 patients, less than or equal to 1% for 6 patients and 2.6%, 3.6% for the remaining 2 patients irrespective of the PTV volume. Percentage doses received by 15% of bladder volume were higher for 10 MV photons. Percentage doses received by 15% of rectum volume were also higher for 10 MV photons.ConclusionsSince there is no greater advantage from 10MV photons as compared with 6MV photons in large volume pelvic IMRT dosimetry and also 10MV photons lie on the threshold energy border for the induction of photo neutrons from the accelerator components, we recommend the use of 6MV photons for IMRT of prostate cancer to achieve better results in tumour control and acceptable probability of complication rate

Validity of bioeffect dose response models for normal tissue early and late complications of the skin

BackgroundThe bioeffect of a physical dose depends on the nature of the tissue, fractionation scheme, dose rate and treatment time. Certainly, experienced radiotherapists are convinced of the existence of patient-to-patient variability in normal tissue response to radiotherapy for malignant tumours. The absorbed dose needs to be translated into a bioeffect dose, which takes into account treatment variables and the radiobiological characteristics of the relevant tissue. Various bioeffect models such as NSD, CRE, TDF and BED have been proposed to predict the biological effect of radiotherapy treatments.AimThis study was aimed at deriving tolerance bioeffect dose values for normal tissue complication rate.Materials/MethodsCompiled clinical data of time dose fractionation schedules and incidence of erythema, desquamation and telangiectasia were used for the present analysis.ResultsFor erythema and desquamation the radiation dose varied from 23.9 to 55.1Gy in 04 to 50 fractions (dose per fraction 1.1 to 7.3Gy) in 11 to 40 days. For telangiectasia (score ≥1 at 3 years) the radiation dose varied from 25.8 to 55.1Gy in 04 to 50 fractions (dose per fraction 1.1 to 7.3Gy) in 11 to 40 days. For telangiectasia (score ≥2 at 5 years) the radiation dose varied from 25.8 to 63.0Gy in 04 to 50 fractions (dose per fraction 1.1 to 7.3Gy) in 11 to 68 days. For telangiectasia (score ≥1, ≥2, ≥3, ≥4 at 10 years) the radiation dose varied from 25.8 to 63.0Gy in 04 to 35 fractions (dose per fraction 1.7 to 7.3Gy) in 22 to 68 days. TDF and LQF values for erythema, desquamation and telangiectasia were evaluated with α/β values of 7.5Gy, 11.2Gy and 2.8Gy respectively. TDF and LQF had a statistically significant correlation with probability of erythema, desquamation and telangiectasia (

Dosimetric verification of brain and head and neck intensity-modulated radiation therapy treatment using EDR2 films and 2D ion chamber array matrix

Background: The evaluation of the agreement between measured and calculated dose plays an essential role in the quality assurance (QA) procedures of intensity-modulated radiation therapy (IMRT). Aim: The purpose of this study is to compare performances of the two dosimetric systems (EDR2 and I\u2032matriXX) in the verification of the dose distributions calculated by the TPS for brain and head and neck dynamic IMRT cases. Materials and Methods: The comparison of cumulative fluence by using Kodak extended dose rate (EDR2) and I\u2032matriXX detectors has been done for the evaluation of 10 brain, 10 head and neck IMRT cases treated with 6 MV beams. The parameter used to assess the quality of dose calculation is the gamma-index (g -index) method. The acceptance limits for g calculation we have used are 3% and 3 mm respectively for dose agreement and distance to agreement parameters. Statistical analyses were performed by using the paired, two-tailed Student t-test, and P&lt; 0.01 is kept as a threshold for the significance level. Results: The qualitative dose distribution comparison was performed using composite dose distribution in the measurement plane and profiles along various axes for TPS vs. EDR2 film and TPS Vs I\u2032matriXX. The quantitative analysis between the calculated and measured dose distribution was evaluated using DTA and g-index. The percentage of pixels matching with the set DTA and g values are comparable for both with EDR2 film and I\u2032matriXX array detectors. Statistically there was no significant variation observed between EDR2 film and I\u2032matriXX in terms of the mean percentage of pixel passing g for brain cases (98.77 \ub1 1.03 vs 97.62 \ub1 1.66, P = 0.0218) and for head and neck cases (97.39 \ub1 2.13 vs 97.17 \ub1 1.52%, P = 0.7404). Conclusion: Due to simplicity and fast evaluation process of array detectors, it can be routinely used in busy departments without compromising the measurement accuracy

Gastroretentive drug delivery system of captopril and hydrochlorothiazide bilayer tablet: formulation, optimization and in vivo evaluation

The purpose of the present study was to develop and optimize floating-bioadhesive bilayer gastroretentive drug delivery system (GRDDS) exhibiting a unique combination of floatation and bioadhesion to prolong residence in the stomach using captopril (CP) and hydrochlorothiazide (HCTZ) as a model drug. Captopril being unstable in intestinal pH and HCTZ has specific absorption from duodenum and the first part of the jejunum and to a small extent in the stomach are suitable candidate for GRDDS. 32 factorial design was employed in formulating and optimizing the GRDDS for bilayer tablet of CP and HCTZ matrix tablet. The main effect and interaction terms were quantitatively evaluated using a mathematical model. The gastroretentive ability of the tablets was evaluated by X-radiographic studies in healthy human volunteer. The tablet releases CP and HCTZ for extended period up to 24 h in controlled manner. The predicted values agreed well with the experimental values and the results demonstrate the feasibility of the optimization methodology in the development of GRDDS. The tablet was buoyant for up to 16 h in human stomach. Development of once a day gastroretentive formulation of CP and HCTZ improves the patience compliance and bioavailability of drugs.Colegio de Farmacéuticos de la Provincia de Buenos Aire