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Aim:Purpose of study is to validate COMPASS 3D patient specific quality-assurance software with Monaco treatment planning system (TPS) for routine quality assurance. Materials & methods:Purpose is to test the MLC modelling in COMPASS software, using Elekta Express QA package contains eight QA fields as follows (i) 10x10 (ii) 20x20 (iii) 3ABUT (iv) DMLC1 (v) HIMRT (vi) HDMLC(vii) 7SegA (viii) Four L were measured with COMPASS and compared with Monaco TPS. For clinical validation of COMPASS, VMAT plans were created for downloadable contoured structure set of AAPM TG119 cases for energy 6MV using Monaco (5.11) TPS for Versa-HD linear-accelerator and verified by COMPASS (calculated and measured). Results:For express QA check, all beams showed gamma pass-rate above 95% except for FourL field. FourL field Monaco versus COMPASS reconstructed gamma pass-rate was 98.4% but Monaco versus COMPASS computed gamma pass rate was 93.4%. COMPASS computed and measured, TG119 test cases showed good agreement with Monaco TPS, except some higher variation in low dose region. Conclusion:COMPASS measured (reconstructed) and computed results are in good agreement with Monaco TPS, therefore can be used for routine patient-specific quality-assurance. Special consideration has to be taken for superficially located targets.

Narrow band ultraviolet B (NB UVB) radiation doses are administered during phototherapy for various dermatological ailments. Precise quantification of these doses is vital because the absorbed irradiation can cause adverse photochemical reactions which can lead to potential phototherapeutic side effects. The paper presents development of diacetylene based dosimeter for the determination of therapeutic NB UVB doses during phototherapy. The amide terminated diacetylene analogues have been synthesized by tailoring them with different functional groups. The synthesized diacetylene monomers have been introduced in a polyvinyl alcohol binder solution to obtain a film dosimeter. The influence of different headgroups on the colorimetric response to UV radiation has been studied. Among all the synthesized diacetylene analogues, the naphthylamine substituted diacetylene exhibited excellent color transition from white to blue color at 100 mJ cm−2 NB UVB radiation dose. The developed amide films can be easily pasted on multiple sites of the patient’s skin to monitor doses during phototherapy simultaneously at different anatomical regions. The digital image processing of the scanned images of the irradiated films facilitates rapid dose measurement which enables facile implementation of the developed film dosimeters and promising application in routine clinical dosimetry.

Purpose: To investigate the feasibility of three-dimensional (3D) dose measurements near thin high-Z materials placed in a water-like medium by using a polymer gel dosimeter (PGD) when the medium was irradiated with high energy photon beams. Methods: PGD is potentially a useful tool for this application because it can record the dose around a small object made of a high-Z material in a continuous 3D medium. In this study, the authors manufactured a methacrylic acid–based normoxic PGD, nMAG. Two 0.5 mm thick lead foils (1 × 1 cm) were placed in foil supports with 0.7 cm separation in a 1000 ml polystyrene container filled with nMAG. The authors used two foil configurations, i.e., orthogonal and parallel. In the orthogonal configuration, two foils were placed in the direction orthogonal to the beam axis. The parallel configuration had two foils arranged in parallel to the beam axis. The phantom was irradiated with an 18 MV photon beam of 5 × 5 cm field size. It was imaged with a three-Tesla (3 T) magnetic resonance imaging (MRI) scanned using the Car-Purcell-Meiboom-Gill pulse sequence. The spin–spin relaxation time (R2) to-dose calibration data were obtained by using small vials filled with nMAG and exposing to known doses. The DOSXYZnrc Monte Carlo (MC) code was used to get the expected dose distributions. More than 35 × 106 of histories were simulated so that the average error was less than 1%. An in-house matlab-based software was used to obtain the dose distributions from the measured R2 data as well as to compare the measurements and the MC predictions. The dose change due to the presence of the foils was studied by comparing the dose distributions with and without foils (or the reference). Results: For the orthogonal configuration, the measured dose along the beam axis showed an increase in the upstream side of the first foil, between the foils, and on the downstream side of the second foil. The range of increased dose area was 1.1 cm in the upstream of the first foil. However, in the downstream of the second foil, it was 0.2 cm, beyond which the dose fell below the reference dose by 10%. The dose profile between the foils showed a well-like shape with the minimum dose still larger than the reference dose by 1.8%. The minimum dose point was closer to the first foil than to the second foil. For the parallel configuration, the dose between foils was the largest at the center. The increased dose area opposite to the gap between foils extended outward to 1 cm. The spatial dose distributions of PGD and MC showed the same geometrical patterns except for the points inside the foils for both orthogonal and parallel foil arrangements. Conclusions: The authors demonstrated that the nMAG PGD with MRI could be used to measure the 3D dosimetric structures at the mm-scale in the vicinity of the foil. The current study provided more accurate 3D spatial dose distribution than the previous studies. Furthermore, the measurements were validated by the MC simulation.

In this work urethane substituted diacetylene compound was synthesized to prepare its radiochromic films which can be sensitive to therapeutic radiation doses. The developed radiochromic films showed significant color change from white to blue in 0–16 Gy dose range. The colorimetric spectral response of the developed films was studied and a maximum absorption at 624 nm was observed which increased with the radiation doses. The change in the morphology of the films pre and post irradiation was analyzed by acquiring their SEM images. The radiation induced color changes were studied quantitatively in terms of optical density by using high resolution Epson scanner along with MATLAB software. The dose response of the developed films was compared with the commercially available Gafchromic EBT3 films. Both the films showed similar dose response with an uncertainty of less than 2%. The post irradiation stability and environmental stability of the films were also analyzed. The films were found to be highly stable under normal environmental conditions with only 1.67% and 1.19% variation in optical density due to the change in temperature and light intensity, respectively. The developed radiochromic films were tissue equivalent and possessed promising characteristics for a potential film dosimeter for medical applications.

Purpose: The photoneutron contamination problem was encountered due to laminated barrier wall and short maze. The purpose of this study was to report our experience in evaluating the photoneutron contamination during radiation safety survey and solution. Methods: The photoneutron contamination measurement was carried out in Elekta Synergy‐S high‐energylinear accelerator for 15MV beam. A NE Neutron survey meter and for photon, Victoreen and RADOS survey meters were used. The laminated barrier wall composed of 37cm steel with 30cm concrete both side and short maze length of 5 meter. During safety survey, higher photoneutron levels for 15MV X‐rays at treatment room door found. The effect of photoneutron contamination as function of neutron shielding materials of wood, polyethylene and boron and thickness, distance, locations and directions to the control console at distance upto 7 meter were investigated for 4 gantry angles at locations of treatment room entry doors namely door1(A), door2(B), console(C), conduit (D) and above‐ceiling(G) for 15MV. Results: The initial safety survey showed that neutron level of 47mR/h and photon leakage of 3.2mR/hr at the treatment entry room door1. The neutron values could bring down to the level of acceptance at the treatment entry door2, but the photon values are not acceptable. Therefore, 30cm concrete wall block was made at the location of door2 and another bend was taken. Finally, treatment entrance room door was made using 3cm polyethylene neutron shielding materials in order to achieve the both neutron contamination and photon leakage within the acceptable levels. Conclusions: The neutron sliding‐door is operated manually in finger‐push by technologist for day‐to‐day usage. This simple solution is cost effective and increases the patient throughput. This study underlines that one needs to take appropriate safety measures prior to facility design whenever the space constraints situations arises for high energy linear accelerator.

To investigate the feasibility of three-dimensional (3D) dose measurements near thin high-Z materials placed in a water-like medium by using a polymer gel dosimeter (PGD) when the medium was irradiated with high energy photon beams.PGD is potentially a useful tool for this application because it can record the dose around a small object made of a high-Z material in a continuous 3D medium. In this study, the authors manufactured a methacrylic acid-based normoxic PGD, nMAG. Two 0.5 mm thick lead foils (1 × 1 cm) were placed in foil supports with 0.7 cm separation in a 1000 ml polystyrene container filled with nMAG. The authors used two foil configurations, i.e., orthogonal and parallel. In the orthogonal configuration, two foils were placed in the direction orthogonal to the beam axis. The parallel configuration had two foils arranged in parallel to the beam axis. The phantom was irradiated with an 18 MV photon beam of 5 × 5 cm field size. It was imaged with a three-Tesla (3 T) magnetic resonance imaging (MRI) scanned using the Car-Purcell-Meiboom-Gill pulse sequence. The spin-spin relaxation time (R2) to-dose calibration data were obtained by using small vials filled with nMAG and exposing to known doses. The DOSXYZnrc Monte Carlo (MC) code was used to get the expected dose distributions. More than 35 × 10For the orthogonal configuration, the measured dose along the beam axis showed an increase in the upstream side of the first foil, between the foils, and on the downstream side of the second foil. The range of increased dose area was 1.1 cm in the upstream of the first foil. However, in the downstream of the second foil, it was 0.2 cm, beyond which the dose fell below the reference dose by 10%. The dose profile between the foils showed a well-like shape with the minimum dose still larger than the reference dose by 1.8%. The minimum dose point was closer to the first foil than to the second foil. For the parallel configuration, the dose between foils was the largest at the center. The increased dose area opposite to the gap between foils extended outward to 1 cm. The spatial dose distributions of PGD and MC showed the same geometrical patterns except for the points inside the foils for both orthogonal and parallel foil arrangements.The authors demonstrated that the nMAG PGD with MRI could be used to measure the 3D dosimetric structures at the mm-scale in the vicinity of the foil. The current study provided more accurate 3D spatial dose distribution than the previous studies. Furthermore, the measurements were validated by the MC simulation.

The purpose of this study was to validate the newly designed acrylic phantom for routine dosimetric purpose in radiotherapy. The phantom can be used to evaluate and compare the calculated dose and measured dose using film and gel dosimetric methods. In this study, a doughnut‐shaped planning target volume (8.54 cm3) and inner organ at risk (0.353 cm3) were delineated for an IMRT test plan using the X‐ray CT image of the phantom. The phantom consists of acrylic slabs which are integrated to form a human head with a hole in the middle where several dosimetric inserts can be positioned for measurement. An inverse planning with nine coplanar intensity‐modulated fields was created using Pinnacle TPS. For the film analysis, EBT2 film, flatbed scanner, in‐house developed MATLAB codes and ImageJ software were used. The 3D dose distribution recorded in the MAGAT gel dosimeter was read using a 1.5 T MRI scanner. Scanning parameters were CPMG pulse sequence with 8 equidistant echoes, TR=5600, echo step=22 ms, pixel size=0.5 times 0.5, slice thickness=2 mm. Using a calibration relationship between absorbed dose and spin‐spin relaxation rate (R2), R2 images were converted to dose images. The dose comparison was accomplished using in‐house MATLAB‐based graphical user interface named “IMRT3DCMP”. For gel measurement dose grid from the TPS was extracted and compared with the measured dose grid of the gel. Gamma index analysis of film measurement for the tolerance criteria of 2%/2 mm, 1%/1 mm showed more than 90% voxels pass rate. Gamma index analysis of 3D gel measurement data showed more than 90% voxels pass rate for different tolerance criteria of 2%/2 mm and 1%/1 mm. Overall both 2D and 3D measurement were in close agreement with the Pinnacle TPS calculated dose. The phantom designed is cost‐effective and the results are promising, but further investigation is required to validate the phantom with other 3D conformal techniques for dosimetric purpose. PACS numbers: 87.53.Kn, 87.55.km, 87.56.N‐

Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients by using modern and sophisticated radiation therapy techniques. However, the adequate tools which enable us to directly measure the dose distributions in three-dimensional (3D) space are not commonly available. One such 3D dose measurement device is the polymer-based dosimeter, which changes the material property in response to radiation. These are available in the gel form as polymer gel dosimeter (PGD) and ferrous gel dosimeter (FGD) and in the solid form as solid plastic dosimeter (SPD). Those are made of a continuous uniform medium which polymerizes upon irradiation. Hence, the intrinsic spatial resolution of those dosimeters is very high, and it is only limited by the method by which one converts the dose information recorded by the medium to the absorbed dose. The current standard methods of the dose quantification are magnetic resonance imaging, optical computed tomography, and X-ray computed tomography. In particular, magnetic resonance imaging is well established as a method for obtaining clinically relevant dosimetric data by PGD and FGD. Despite the likely possibility of doing 3D dosimetry by PGD, FGD or SPD, the tools are still lacking wider usages for clinical applications. In this review article, we summarize the current status of PGD, FGD, and SPD and discuss the issue faced by these for wider acceptance in radiation oncology clinic and propose some directions for future development.

One of treatment planning techniques with Leksell GammaPlan (LGP) for Gamma Knife stereotactic radiosurgery (GKSRS) uses multiple matrices with multiple dose prescriptions. Computational complexity increases when shots are placed in multiple matrices with different grid sizes. Hence, the experimental validation of LGP calculated dose distributions is needed for those cases. For the current study, we used BANG3 polymer gel contained in a head‐sized glass bottle to simulate the entire treatment process of GKSRS. A treatment plan with three 18 mm shots and one 8 mm shot in separate matrices was created with LGP. The prescribed maximum dose was 8 Gy to three shots and 16 Gy to one of the 18 mm shots. The 3D dose distribution recorded in the gel dosimeter was read using a Siemens 3T MRI scanner. The scanning parameters of a CPMG pulse sequence with 32 equidistant echoes were as follows: TR=7s, echo step = 13.6 ms, field‐of‐view = 256 mm× 256 mm, and pixel size=1 mm×1 mm. Interleaved acquisition mode was used to obtain 15 to 45 2‐mm‐thick slices. Using a calibration relationship between absorbed dose and the spin‐spin relaxation rate (R2), we converted R2 images to dose images. MATLAB‐based in‐house programs were used for R2 estimation and dose comparison. Gamma‐index analysis for the 3D data showed gamma values less than unity for 86% of the voxels. Through this study we accomplished the first application of polymer gel dosimetry for a true comparison between measured 3D dose distributions and LGP calculations for plans using multiple matrices for multiple targets. PACS number: 87.53.Ly, 87.55‐x, 87.56 ‐g

Verification of the dose calculation model and the software used for treatment planning is an important step for accurate radiation delivery in radiation therapy. Using BANG3 polymer gel dosimeter with a 3 Tesla magnetic resonance imaging (MRI) scanner, we examined the accuracy of TomoTherapy treatment planning and radiation delivery. We evaluated one prostate treatment case and found the calculated three‐dimensional (3D) dose distributions agree with the measured 3D dose distributions with an exception in the regions where the dose was much smaller (25% or less) than the maximum dose (2.5 Gy). The analysis using the gamma‐index (3% dose difference and 3 mm distance‐to‐agreement) for a volume of 12 cm×11 cm×9 cm containing the planning target volume showed that the gamma values were smaller than unity for 53% of the voxels. Our measurement protocol and analysis tools can be easily applied to the evaluation of other newer complex radiation delivery techniques, such as intensity‐modulated arc therapy, with a reasonably low financial investment. PACS numbers: 87.53Bn, 87.56Fc

A commercial metal oxide silicon field effect transistor (MOSFET) dosimeter of model TN502-RD has been characterized for its linearity, reproducibility, field size dependency, dose rate dependency, and angular dependency for Cobalt-60 (60Co), 6-MV, and 15-MV beam energies. The performance of the MOSFET clearly shows that it is highly reproducible, independent of field size and dose rate. Furthermore, MOSFET has a very high degree of linearity, with r-value>0.9 for all 3 energies. The calibration factor for 2 similar MOSFET detectors of model TN502-RD were also estimated and compared for all 3 energies. The calibration factor between the 2 similar MOSFET detectors shows a variation of about 1.8% for 60Co and 15 MV, and for 6 MV it shows variation of about 2.5%, indicating that calibration should be done whenever a new MOSFET is used. However, the detector shows considerable angular dependency of about 8.8% variation. This may be due to the variation in radiation sensitivity between flat and bubble sides of the MOSFET, and indicates that positional care must be taken while using MOSFET for stereotactic radiosurgery and stereotactic radiotherapy dosimetric applications.

Gel dosimetry is a promising technique for the implementation of 3D dose verification within the radiation therapy clinic, since it is the only methodology which provides comprehensive 3D dose measurement of conformal treatments such as Intensity Modulated Radiation Therapy (IMRT), Stereotactic radiosurgery (SRS) and Stereotactic Radiotherapy (SRT), and volumetric arc therapies (VMAT). In polymer gel dosimetry, monomer molecules polymerize and are fixed in the gel matrix when exposed to radiation. The spatial dose information thus can be obtained by gel imaging. Gel imaging methods which are currently under investigation are MRI, optical computed tomography and x-ray computed tomography. While promising, x-ray CT images of irradiated polymer gel exhibit low contrast due to small change in density that occurs during polymerization. The response of CT contrast to dose is weak and noise reduction is critical in order to achieve adequate dose resolution in gel dosimetry using x-ray computed tomography. Ideally, image noise is minimized using high tube current, long scan times and high number of image averages [Hilts et al 2005]. Digital image filtering is an effective method in reducing image noise while maintaining accurate spatial dose information. Generally it is performed in either frequency domain or spatial domain. In a previous work, several spatial filters were applied to Stereotactic Radiosurgery (SRS) irradiated polymer gel image [Hilts and Duzenli 2004]. In their study it was found that the two highest performing filters were the adaptive mean (Wiener) and smallest univalue segment assimilating nucleus (SUSAN). In another study a new method of signal to noise ratio (SNR) enhancement by 2D two-point maximum entropy regularization method (TPMEM) was investigated [Jirasek 2006]. However, a comprehensive examination of the best performing filters from these two studies has not been undertaken. Here, we test the Weiner and TPMEM digital filters on X-ray CT image of the irradiated PAGAT gel in order to reduce noise and improve dose resolution. This work builds off of previous studies and evaluates and compares the highest-performing filters from past individual works [Hilts and Duzenli 2004, Jirasek et al 2006].

Purpose: Aim of the study is to evaluate mechanical and radiological accuracy of multi-fraction regimen and validate Gamma knife based fractionation using newly developed patient simulating multipurpose phantom. Methods: A patient simulating phantom was designed to verify fractionated treatments with extend system (ES) of Gamma Knife however it could be used to validate other radiotherapy procedures as well. The phantom has options to insert various density material plugs and mini CT/MR distortion phantoms to analyze the quality of stereotactic imaging. An additional thorax part designed to predict surface doses at various organ sites. The phantom was positioned using vacuum head cushion and patient control unit for imaging and treatment. The repositioning check tool (RCT) was used to predict phantom positioning under ES assembly. The phantom with special inserts for film in axial, coronal and sagittal plane were scanned with X-Ray CT and the acquired images were transferred to treatment planning system (LGP 10.1). The focal precession test was performed with 4mm collimator and an experimental plan of four 16mm collimator shots was prepared for treatment verification of multi-fraction regimen. The prescription dose of 5Gy per fraction was delivered in four fractions. Each fraction was analyzed using EBT3 films scanned with EPSON 10000XL Scanner. Results: The measurement of 38 RCT points showed an overall positional accuracy of 0.28mm. The mean deviation of 0.28% and 0.31 % were calculated as CT and MR image distortion respectively. The radiological focus accuracy test showed its deviation from mechanical center point of 0.22mm. The profile measurement showed close agreement between TPS planned and film measured dose. At tolerance criteria of 1%/1mm gamma index analysis showed a pass rate of > 95%. Conclusion: Our results show that the newly developed multipurpose patient simulating phantom is highly suitable for the verification of fractionated stereotactic radiosurgery using ES of Gamma knife. The study is a part of intramural research project of Research Section, All India Institute of Medical Sciences New Delhi India (A 247).

Purpose: To evaluate forward and inverse planning methods for acoustic neuroma cases treated in Gamma Knife Perfexion. Methods: Five patients with acoustic neuroma tumour abutting brainstem were planned twice in LGP TPS (Version 10.1) using TMR10 algorithm. First plan was entirely based on forward planning (FP) in which each shot was chosen manually. Second plan was generated using inverse planning (IP) for which planning parameters like coverage, selectivity, gradient index (GI) and beam-on time threshold were set. Number of shots in IP was automatically selected by objective function using iterative process. In both planning methods MRI MPRAGE sequence images were used for tumour localization and planning. A planning dose of 12Gy at 50% isodose level was chosen. Results and Discussion: Number of shots used in FP was greater than IP and beam-on time in FP was in average 1.4 times more than IP. One advantage of FP was that the brainstem volume subjected to 6Gy dose (25% isodose) was less in FP than IP. Our results showed use of more number of shots as in FP results in GI less than or equal to 2.55 which is close to its lower limit. Dose homogeneity index (DHI) analysis of FP and IP showed average values of 0.59 and 0.67 respectively. General trend in GK for planning in acoustic neuroma cases is to use small collimator shots to avoid dose to adjacent critical structures. More number of shots and prolonged treatment time causes inconvenience to the patients. Similarly overuse of automatic shot shaping as in IP results in increased scatter dose. A compromise is required in shot selection for these cases. Conclusion: IP method could be used in acoustic neuroma cases to decrease treatment time provided the source sector openings near brainstem are shielded or adjusted appropriately to reduce brainstem dose.

Purpose: To evaluate a calibration method using the depth-dose data of an electron beam for MRI-based polymer gel dosimetry. Methods: MAGAT was manufactured in-house to fill two 400mL-cylindrical phantoms and nine 22mL-glass vials. Phantom-A was irradiated along the cylinder axis with a 9MeV electron beam of 6 cm x 6 cm field size (FS). Phantom-B was irradiated with a 6MV photon beam of 3 cm x 3 cm FS by a 360-degree arc technique. Eight vials were irradiated in a water-bath to various doses with a 20 cm x 20 cm FS 6MV photon beam. All irradiated phantoms and one un-irradiated vial were scanned with a 3T MRI scanner to obtain the spin-spin relaxation rate (R2) distributions. By comparing the measured R2-to-depth data with the known depth-dose data for Phantom-A, R2-to-dose calibration data were obtained (e-beam method). Another calibration data were obtained from the 9 vials data (9-vial method). We tested two regression equations, i.e., third-order polynomial and tangent functions, and two dose normalization methods, i.e., one-point and two-point methods. Then, these two calibration methods were used to obtain the 3D dose distribution of Phantom-B and evaluated by comparing the measured data with the dose distribution from a treatment planning system. The comparison was made with gamma passing rate (2%/2mm criteria). Results: We did not observe a clear advantage of the e-beam method over the 9-vial method for the 3D dose comparison with the test case. Nevertheless, we found that the e-beam method required a smaller dose scaling for the dose comparison. Furthermore, the tangent function showed better data fitting than the polynomial function with smaller uncertainty of the estimated coefficients. Conclusions: Considering the overall superior performance, we recommend the e-beam method with the tangent function as the regression equation and one-point dose normalization for the MRI-based polymer gel dosimetry.

Purpose: Gamma Knife perfexion (GKPFX) with extend system is being used for multi-fraction or fractionated stereotactic radiosurgery (fGKSRS). Patient surveillance Unit (PSU) is used to attain a non invasive immobilization for fractionation. Calibrated digital probe is used to measure encoded mechanical positions on repositioning check tool (RCT). The objective of this study is to check consistency and statistical position variation during multi-fraction stereotactic radiosurgery using GKPFX extend system. Methods: 31 fractions through 7 patients being delivered to check the positional variation during patient setup. Variation is calculated after sampling the collected data at same point measurement for all the patients. Average value of three stage measurements or the reference values are compiled with the sample data using SPSS (statistical software). Measurement of encoded points has been taken and various statistical parameters are observed. Reproducibility is checked, comparing the reference to measured values through encoded points before treatment. Intra-fraction variation is measured on compiling pre and post treatment RCT measurements while inter-fractionation variation compiled along with fractions before treatment. Results: Pre-treatment radial setup difference auto calculated by the system varies from 0.5mm to 0.8 mm with mean variation of 0.7 mm. Positional variation was observed for post-treatment and was found that it varies from 0.9 mm - 1.0 mm. Paired sample test results the paired difference mean from the reference (for pre and post measurements) was 0.26 mm (0.1775 mm- 0.3475 mm) with only 25% of error significance. The distribution of the random component of observer uncertainty was 0.06mm. Conclusion: Post treatment positional variation is 20%-30% of pre treatment measurements, i.e. about treatment measurements, i.e. about 0.2 mm. Explaining complete procedure to patient, limiting head rotation/lift and preventing other movements, may maximize positional accuracy during fractionations. Contending positional accuracy, supports the extend system for fractionated stereotactic radiosurgery among other multisession radiosurgery techniques.

Purpose: To perform dosimetric evaluation of convolution algorithm in Gamma Knife (Perfexion Model) using solid acrylic anthropomorphic phantom. Methods: An in-house developed acrylic phantom with ion chamber insert was used for this purpose. The middle insert was designed to fit ion chamber from top(head) as well as from bottom(neck) of the phantom, henceforth measurement done at two different positions simultaneously. Leksell frame fixed to phantom simulated patient treatment. Prior to dosimetric study, hounsfield units and electron density of acrylic material were incorporated into the calibration curve in the TPS for convolution algorithm calculation. A CT scan of phantom with ion chamber (PTW Freiberg, 0.125cc) was obtained with following scanning parameters: Tube voltage-110kV, Slice thickness-1mm and FOV-240mm. Three separate single shot plans were generated in LGP TPS (Version 10.1.) with collimators 16mm, 8mm and 4mm respectively for both ion chamber positions. Both TMR10 and Convolution algorithm based planning (CABP) were used for dose calculation. A dose of 6Gy at 100% isodose was prescribed at centre of ion chamber visible in the CT scan. The phantom with ion chamber was positioned in the treatment couch for dose delivery. Results: The ion chamber measured dose was 5.98Gy for 16mm collimator shot plan with less than 1% deviation for convolution algorithm whereas with TMR10 measured dose was 5.6Gy. For 8mm and 4mm collimator plan merely a dose of 3.86Gy and 2.18Gy respectively were delivered at TPS calculated time for CABP. Conclusion: CABP is expected to perform accurate prediction of time for dose delivery for all collimators, but significant variation in measured dose was observed for 8mm and 4mm collimator which may be due collimator size effect. Effect of metal artifacts caused by pins and frame on the CT scan also may have role in misinterpreting CABP. The study carried out requires further investigation.

Purpose: To validate the three‐dimensional (3D) dose distributions calculated by Leksell Gamma Plan (LGP) for Gamma Knife stereotactic radiosurgery. (GKSRS) cases with multiple matrices using MRI‐based polymergeldosimetry.Method and Materials: BANG3 polymergel contained in a head size glass bottle simulated the entire treatment process of GKSRS. All phantoms were fixed in the Leksell stereotactic frame. For the first study one phantom was used for calibration and the second was irradiated with five 18‐mm shots in five dose matrices. For the second study the calibration was performed with 8‐mm shots and a treatment plan was generated with three 18‐mm shots and one 8‐mm shot. The 3D‐dose distribution recorded in the gel dosimeter was read using a 3T MRI scanner (Siemens Magnetom Trio). Scanning parameters were CPMG pulse sequence with 32 equidistant echoes, TR = 7 s, echo step = 13.6 ms, pixel size = 1mm × 1mm. Interleaved acquisition mode was used to obtain 15 to 45 2mm‐thick slices. Using a calibration relationship between absorbed dose and spin‐spin relaxation rate (R2), we converted R2 images to dose images. The dose comparison was accomplished using an in‐house MATLAB‐based program. Results:Calibrations indicate the dose response of the current polymergel was non‐linear for doses higher than 10 Gy. The artifacts mainly caused by the metallic pins used to immobilize the phantom distorted the measured dose distributions. Away from the pin positions, however, we could compare the LGP dose distributions with measured dose distributions. Preliminary analyses indicated some spatial position discrepancies in addition to the dose differences. Conclusion: Through this study we could perform a true comparison between 3D dose distributions measured with a polymergel dosimeter and LGP calculations for plans using multiple matrices/targets.

Materials/Methods: Using current imaging technologies (e.g. cone beam CT, portal imaging), an image of the tumor target is easily obtained before and/or during each fraction of radiation. This allows the shape of the target, as seen in the beam’s-eye view, to be defined on sequential patient images. A rigid-body transformation is then applied to remove possible translation and rotation differences between the target shapes. Corresponding landmarks on each processed target shape are automatically identified using the MDL principle. Next, ASM, a statistical description of the target shape, is constructed based on the landmarks. In ASM the shape variability is learned through observation. Finally, a Monte Carlo method is used to generate synthetic target shapes based on ASM, as follows. Points will be sampled in the beam’s-eye view plane, and each point will be assigned a score based on the computed statistical probability that it is inside the target. The iso-score lines form level sets, with each level set corresponding to target shape and size for a given probability. These level sets reflect clinical information learned from the available images will be good candidates for radiotherapy field shapes with non-uniform margins.

Purpose:Doses to rectum, bladder and Point‐A in patients who received intracavitary HDR brachytherapy treatment were calculated by both orthogonal radiographsreconstruction method and by image based reconstruction method and were compared. Method and Materials: Twenty‐five patients of carcinoma cervix who received intracavitary brachytherapy treatment by micro‐Selectron HDR unit were included in this study. For these patients, in Plato treatment planning system, reconstruction of sources, applicator, organs at risk and Point‐A were done using conventional orthogonal radiographs and by using 1 mm thick CT scanimages. Bladder was identified on radiographs through a Foley's catheter inserted into it filled with 7 cc of radio‐opaque fluid and the rectum through a rectal marker. Doses were calculated at 5 points each on bladder and rectum, for the treatment dose of 7 Gy to Point‐A (right & left). On CTimages, these organs were delineated with the radiologists help and from dose‐volume‐histograms,doses to 1, 2 and 5 cc of these organs were calculated besides dose to Point‐A (right & left). Results: The critical organdoses estimated by the CT method were consistently higher when compared to those by the radiographs method. When compared to the radiographicdose maximum for bladder, doses to 1, 2 and 5 cc of bladder were higher by 89%, 69.7% and 41.6% on an average respectively. For rectum, the corresponding values were 36.6%, 21.7% and 0.4%. However dose to Point‐A did not differ by more than 3% between the two methods. Conclusion: The conventional orthogonal radiography based reconstruction method consistently underestimates the doses to critical organs while the doses to reference points are comparable in these two methods. Long‐term follow‐up in such patients can identify the threshold volumes for these critical organs beyond which complication rates are bound to rise.

Purpose: To present EBT2 film verification of treatment planning with the eXtend System, a relocatable frame system for multiple‐fraction or serial multiple‐session radiosurgery.Methods: A human head shaped phantom simulated the verification process for fractionated Gamma Knife (GK) treatment. Phantom preparation for eXtend Frame based treatment planning involved creating a dental impression, fitting the phantom to the frame system, acquiring a stereotactic computed tomography(CT) scan. A CT scan (Siemens, Emotion6) of the phantom was obtained with following parameters: Tube Voltage ‐ 110 kV, Tube Current ‐ 280 mA, pixel size ‐ 0.5 mm × 0.5 mm and 1 mm slice thickness. A treatment plan with two 8 mm collimator shots and three sector blocking in each shot was made. Dose prescription of 4.0 Gy at 100% was delivered for the first fraction out of the two fractions planned. Gafchromic EBT2 film (ISP Wayne, NJ) was used as 2D verification dosimeter in this process. Films were cut and placed inside the film insert of the phantom for treatment dose delivery. Meanwhile a set of films from the same batch were exposed from 0 Gy to 12 Gy doses for calibration purpose. EPSON (Expression 10000XL) scanner was used for scanning the exposed films in transparency mode. Scanned films were analyzed with in‐house made Matlab codes. Results: Gamma index analysis of film measurement in comparison with TPS calculated dose resulted in high pass rates >90% for different tolerance criteria of 2%/2mm, 1%/1mm, and 0.5%/0.5mm. The isodose overlay and linear dose profiles of film measured and computed dose distribution on sagittal and coronal plane was in close agreement. Conclusions: Through this study we propose a treatment verification QA method for eXtend frame based fractionated Gamma Knife radiosurgery using EBT2 film. Acknowledgement: Authors acknowledge the help of Andre Micke, ISP for sharing his expertise on EBT2 film.

Purpose of this work is to present the role of in-house manufactured MAGAT gel for treatment verification in small field dosimetric techniques such as Gammaknife (GK) and intensity-modulated radiation therapy (IMRT). Magnetic resonance imaging (MRI) is one of the most extensively used imaging technique for polymer gel dosimetry hence we used this method for gel evaluation. Different MR scanners and MRI sequences were used in this study for obtaining calibration plot between R2 and absorbed dose. An experimental plan was created for Gammaknife and IMRT. The prepared gel was filled in spherical glass phantom and in-house designed human head shape phantom for verification purpose. We used 8 TE values for all the imaging sequences for two reasons. Firstly it is sufficient enough to give good signal to noise ratio. Second considering the enormous scanning time involved in multiple spin echo sequence. MATLAB based in-house programs were used for R2 estimation and dose comparison. The isodose comparison with MAGAT gel showed reasonable agreement for both Gammaknife and IMRT techniques.

Purpose: To evaluate the penumbral characteristics as function of collimation systems, conventional detector, depth, energy and MLC travel orientations using diode detectors.Methods and Materials: The experiment was carried out in a Clinac 2300C/D linear accelerator for 6 and 15 MV. For penumbral width determination, cross‐beam profiles were measured using Blue phantom radiation field analyzer, 0.13cm3 ionchamber and diode detectors, CU‐500E dual‐channel electrometer and OmniPro beam‐data acquisition system. The penumbra was measured for both Jaw and MLC‐defined field sizes of 4×4 to 30×30cm2 depths at dmax, 5, 10, 15 and 20cm and also for cross‐plane and in‐plane MLC travel orientations at 100cm SSD. The penumbra width was calculated as the distance between 80%–20% intensity in the profiles. Results: The MLC penumbra was in the range of 3.6mm to 4mm for 6MV and 5.4mm to 7.1mm for 15MV at dmax depth for field sizes of 4×4 to 30×30cm2 as measured by diode detector. The mean differences between Jaw and MLC‐defined field's penumbra were 0.8mm ± 0.2, and 1mm ± 0.2 for 6MV and 1.2mm ±0.2 and 1.8mm ±0.5 for 15MV at dmax and 10cm depths. The maximum difference of 1.9mm ±0.3 for 6MV and 2.2mm ±0.2 for 15MV between diode and 0.13cm3detectors were found. Use of diode detectors, maximum differences of 3.4mm ±3 at 20cm depths between energies and the differences of 3.3mm ± 2.2 for 6 MV and 1.2mm ± 0.3 for 15MV between cross‐plane and in‐plane MLC penumbra were found. Conclusions: The rounded‐end MLC penumbra was larger as compared to Jaw penumbra. The penumbra measured by diode was increasing with energy upto a certain depths and field sizes and then it increases more with low‐energy at larger depths and field sizes as compared to high‐energy. The adequate accounting of penumbra is important in intensity modulated beam dose calculation.

Purpose: To evaluate the volume effect of detector's in multiple points dose in small and large field IMRT verification and to compare the planar dose distribution between fixed‐fields coronal‐plane and multifield axial‐plane verification methods. Method and Materials: Patient‐specific dosimetric verification was conducted for 20 patients of nasopharynx's small‐field, SIB‐IMRT large‐field and prostate tumors. Eclipse‐Helios system, Clinac‐2300C/D linear accelerator, Med‐Tec IMRT phantom and ionchambers of 0.6, 0.13 and 0.015cm3 and MOSFET detectors were used. For each patient, 15 IMRT plans were generated. The multiple points doses were measured at multifield and fixed‐fields on‐axis, 4‐offsets and inhomogeneous points. The agreements between calculated and measured doses were found for small and large field IMRT verification. For relative dosimetry, EDR2 films, Virtual Water phantom for fixed‐fields coronal‐plane and IMRT Body phantom for multifield axial‐plane verifications RITsystem and Vidar scanner were used. The agreements between calculated and measured dose distributions between two methods were compared using various gamma criteria. Results: The agreements between measured and calculated doses using 0.6 and 0.13cm3 chambers at multifield and fixed‐fields on‐axis points were within 4.7% ±2.3. The dose differences of 6% ±1.7, 19.7% ±5.5, and 12.1% ±3.2 at offset1 to 3 points were found. The 0.015cm3 chamber and MOSFET detectors were showed the dose differences of upto 8.4% in large field verification. The mean differences in percentage of pixels passing the gamma criteria of 3mm/5% were 98.2% ±0.9 and 90% ±5.4 for fixed‐fields coronal‐plane and multifield axial‐plane verifications. Conclusions: This study is useful in evaluating the detector's response at high and low dose, outside the fields and inhomogeneous points dose verification. In offset points, 0.6cm3 is more accurate than 0.13cm3 chamber in both small and large field verification. The fixed‐fields coronal‐plane verification is more accurate, however, the multifield axial‐plane is clinically realistic method of verification and to be adopted.