Collimator Opening Research Articles

The Impact of Dose Calibration Point Differences Between the Treatment Plan and Patient-specific Quality Assurance in Passive Scattering Proton Beam Therapy.

Passive scattering proton beam therapy (PSPT) is performed by taking actual measurements of all pre-designated fields in a treatment plan followed by appropriate adjustments to the prescribed dose. For this reason, it is necessary to ensure precision management of the measurements (patient-specific calibration) in the administration of a planned dose. Therefore, this study investigated the impact on dose distribution in treatment planning when the patient calibration point differs from the normalized point in a treatment plan. A total of 16 cases were selected, where the patient calibration point and normalized point did not match, and the normalized point used in the treatment plan was changed to the patient calibration point using a treatment planning system (VQA ver. 2.01, HITACHI). At this point, the displacement of the relative dose at the isocenter was estimated as an error owing to the difference compared to the patient calibration point. Overall, the error was within the range of ±1.5%, with the exception of orbit cases. Calibrated points also tended to be lower than the normalized points in the treatment plan. In terms of treatment sites, a greater deviation was observed for head cases. Cases with a large deviation in sites other than the head were attributed to poor flatness within the radiation field owing to a narrower opening of the patient collimator. Dose measurement errors in PSPT due to differing calibration points were generally within ±1.5%, with higher deviations observed in head treatments because of complex structures and narrow collimator openings. A γ analysis for significant deviations showed a 98.7% passing rate, suggesting limited overall impact. It is important to select stable calibration points in dosimetry to ensure high precision in dose administration, particularly in complex treatment areas.

Development of a novel delivery quality assurance system based on simultaneous verification of dose distribution and binary multi-leaf collimator opening in helical tomotherapy

BackgroundIntensity-modulated radiation therapy (IMRT) requires delivery quality assurance (DQA) to ensure treatment accuracy and safety. Irradiation techniques such as helical tomotherapy (HT) have become increasingly complex, rendering conventional verification methods insufficient. This study aims to develop a novel DQA system to simultaneously verify dose distribution and multi-leaf collimator (MLC) opening during HT.MethodsWe developed a prototype detector consisting of a cylindrical plastic scintillator (PS) and a cooled charge-coupled device (CCD) camera. Scintillation light was recorded using a CCD camera. A TomoHDA (Accuray Inc.) was used as the irradiation device. The characteristics of the developed system were evaluated based on the light intensity. The IMRT plan was irradiated onto the PS to record a moving image of the scintillation light. MLC opening and light distribution were obtained from the recorded images. To detect MLC opening, we placed a region of interest (ROI) on the image, corresponding to the leaf position, and analyzed the temporal change in the light intensity within each ROI. Corrections were made for light changes due to differences in the PS shape and irradiation position. The corrected light intensity was converted into the leaf opening time (LOT), and an MLC sinogram was constructed. The reconstructed MLC sinogram was compared with that calculated using the treatment planning system (TPS). Light distribution was obtained by integrating all frames obtained during IMRT irradiation. The light distribution was compared with the dose distribution calculated using the TPS.ResultsThe LOT and the light intensity followed a linear relationship. Owing to MLC movements, the sensitivity and specificity of the reconstructed sinogram exceeded 97%, with an LOT error of − 3.9 ± 7.8%. The light distribution pattern closely resembled that of the dose distribution. The average dose difference and the pass rate of gamma analysis with 3%/3 mm were 1.4 ± 0.2% and 99%, respectively.ConclusionWe developed a DQA system for simultaneous and accurate verification of both dose distribution and MLC opening during HT.

Experimental Investigation of X-Ray Radiation Shielding and Radiological Properties for Various Natural Composites.

Shielding from radiation and plan dose verification is vital during the potential applications in industrial and medical applications. A number of natural composites have been investigated for protecting against high-energy X-ray shielding. The aim is to learn about how natural composites behave under various X-ray energies at STP. The radiological parameters of wood samples were determined using computed tomography imaging, specifically relative electron density (RED), Hounsfield units (HUs), and mass density (MD). Percentage attenuation was measured using a semiflux ionization chamber incorporated with a brass build-up cap and an ionization chamber placed at the beam Isocenter for a different type of natural composite. Measurements are being carried out on a Linear accelerator at an SSD of 110 cm with different collimator sizes. Measured values of HUs, RED, and MD were -232 ± 40, 0.738 ± 0.039, 0.768 ± 0.024 g/cc,-368 ± 41, 0.662 ± 0.047, 0.632 ± 0.024 g/cc, -334 ± 44, 0.639 ± 0.042, 0.666 ± 0.026 g/cc, -370±61, 0.604±0.059, 0.63± 0.036 g/cc, -433±39, 0.543±0.038, 0.608 ± 0.035 g/cc, -382±54, 0.5±0.052, 0.618 ± 0.0316 g/cc, -292±68, 0.680±0.066, 0.708 ± 0.039 g/cc, -298±27, 0.680±0.0229, 0.702± 0.131 g/cc, for Acacia Nilotica, Mangifera Indica, Azadirachta Indica, Tectona Grandis L, Ficus Religiosa, Tecomella Undulata, Sesamum Indicum, Pinus respectively. Measurements show that attenuation is affected by the energy of incident photons, collimator opening, and the type of density of the wood. Various radiological parameters were determined for wood samples that can be utilized to create inhomogeneous phantoms in dosimetry. The largest attenuation is found in Acacia Nilotica and Sesamum Indicum, while the lowest attenuation is found in Ficus religiosa.

Study on the sensitivity of a volumetric modulated arc therapy plan verification equipment on multi-leaf collimator opening and closing errors and its gamma pass rate limit

To investigate the γ pass rate limit of plan verification equipment for volumetric modulated arc therapy (VMAT) plan verification and its sensitivity on the opening and closing errors of multi-leaf collimator (MLC), 50 cases of nasopharyngeal carcinoma VMAT plan with clockwise and counterclockwise full arcs were randomly selected. Eight kinds of MLC opening and closing errors were introduced in 10 cases of them, and 80 plans with errors were generated. Firstly, the plan verification was conducted in the form of field-by-field measurement and true composite measurement. The γ analysis with the criteria of 3% dose difference, distance to agreement of 2 mm, 10% dose threshold, and absolute dose global normalized conditions were performed for these fields. Then gradient analysis was used to investigate the sensitivity of field-by-field measurement and true composite measurement on MLC opening and closing errors, and the receiver operating characteristic curve (ROC) was used to investigate the optimal threshold of γ pass rate for identifying errors. Tolerance limits and action limits for γ pass rates were calculated using statistical process control (SPC) method for another 40 cases. The error identification ability using the tolerance limit calculated by SPC method and the universal tolerance limit (95%) were compared with using the optimal threshold of ROC. The results show that for the true composite measurement, the clockwise arc and the counterclockwise arc, the descent gradients of the γ passing rate with per millimeter MLC opening error are 10.61%, 7.62% and 6.66%, respectively, and the descent gradients with per millimeter MLC closing error are 9.75%, 7.36% and 6.37%, respectively. The optimal thresholds obtained by the ROC method are 99.35%, 97.95% and 98.25%, respectively, and the tolerance limits obtained by the SPC method are 98.98%, 97.74% and 98.62%, respectively. The tolerance limit calculated by SPC method is close to the optimal threshold of ROC, both of which could identify all errors of ±2 mm, while the universal tolerance limit can only partially identify them, indicating that the universal tolerance limit is not sensitive on some large errors. Therefore, considering the factors such as ease of use and accuracy, it is suggested to use the true composite measurement in clinical practice, and to formulate tolerance limits and action limits suitable for the actual process of the institution based on the SPC method. In conclusion, it is expected that the results of this study can provide some references for institutions to optimize the radiotherapy plan verification process, set appropriate pass rate limit, and promote the standardization of plan verification.

Sensitivity Analysis of a 6 MeV Photon Beam Monte Carlo Model.

This study aimed to optimize efficiency in Monte Carlo (MC) simulation using sensitivity analysis of a beam model. The BEAMnrc-based model of 6 MV beam of a Siemens Primus linac was developed. For sensitivity analysis, the effect of the electron source, treatment head, and virtual phantom specifications on calculated percent depth dose (PDD) and lateral dose profiles was evaluated. The optimum mean energy (E) and the full width at half maximum (FWHM) of the intensity distribution of the electron beam were calculated as 6.7 MeV and 3 mm, respectively. Increasing E from 6.1 to 6.7 MeV, increased the PDD in the fall-off region by 4.70% and decreased the lateral profile by 8.76%. Changing the FWHM had a significant effect on the buildup region of PDD and the horns and out-of-field regions of the lateral profile. Increasing the collimators opening by 0.5 mm, PDD increased by 2.13% and the central and penumbra regions of profiles decreased by 1.98% and 11.40% respectively. Collimator properties such as thickness and density were effective in changing the penumbra (11.32% for 0.25 cm increment) and the out-of-field (22.82% for 3 g/cm3) regions of the lateral profiles. Analysis of a 6 MV model showed that PDD profiles were more sensitive to changes in energy than to FWHM of the electron source. The lateral profiles were sensitive to E, FWHM, and collimator opening. The density of the collimator affected only the out-of-field region of lateral profiles. The findings of this study may be used to make benchmarking of an MC beam model more efficient.

The design of integrated gamma ray scanning system for the uranium sample

An integrated gamma ray scanning system has been designed and built to extend that localizes and quantifies highly enriched uranium sample. The detection mechanisms of the two modes (Segmented Gamma Scanner and Tomographic Gamma Scanning) are analyzed respectively. Moreover, the parameters influence of speed and the deviation of the measurement accuracy are analyzed for the uranium sample. In view of these problems, the system has improved by the optimization processing, which include the optimization of the collimator opening for detector, the crosstalk and the time step. Finally, the experimental were investigated and discussed in detail. The single measurement time of the system reduced to about 30 min with an error of less than 5%, so it enhance the measurement accuracy and the speed effectively. The system has broad application prospects in the fields of nuclear safety, radioactive recyclables and non-destructive measurement of nuclear waste.

Design and optimization of an integrated gamma ray scanning system for the uranium sample

Abstract An integrated gamma ray scanning system has been designed and built to extend that localizes and quantifies highly enriched uranium sample. The detection mechanisms of the two modes (segmented gamma scanner and tomographic gamma scanning) are analyzed respectively. Moreover, the parameters influence of speed and the deviation of the measurement accuracy are analyzed for the uranium sample. In view of these problems, the system has improved by the optimization processing, which include the optimization of the collimator opening for detector, the crosstalk and the time step. Finally, the experiment were investigated and discussed in detail. The single measurement time of the system can reduce to about 30 min with an error of less than ±5%, so the measurement accuracy and the speed are enhanced effectively. The system has broad application prospects in the fields of nuclear safety, radioactive recyclables and non-destructive measurement of nuclear waste.

Intensity modulated high dose rate ocular brachytherapy using Se-75

PurposeWe propose an alternative to LDR brachytherapy for the treatment of ocular melanomas by coupling intensity modulation, through the use of a gold shielded ring applicator, with a middle energy HDR brachytherapy source, Se-75. In this study, we computationally test this proposed design using MCNP6. Methods and MaterialsAn array of discrete Se-75 sources is formed into a ring configuration within a gold shielded applicator, which collimates the beam to a conical shape. Varying this angle of collimation allows for the prescription dose to be delivered to the apex of various sized targets. Simulations in MCNP6 were performed to calculate the dosimetric output of the Se-75 ring source for various sized applicators, collimators, and target sizes. ResultsThe prescription dose was delivered to a range of target apex depths 3.5−8 mm in the eye covering targets 10-15 mm in diameter by using various sized applicators and collimators. For a 16 mm applicator with a collimator opening that delivers the prescription dose to a depth of 5 mm in the eye, the maximum percent dose rate to critical structures was 30.5% to the cornea, 35.7% to the posterior lens, 33.3% to the iris, 20.1% to the optic nerve, 278.0% to the sclera, and 267.3% to the tumor. ConclusionsWhen using Se-75 in combination with the proposed gold shielded ring applicator, dose distributions are appropriate for ocular brachytherapy. The use of a collimator allows for the dose to more easily conform to the tumor volume. This method also reduces treatment time and cost, and it eliminates hand dose to the surgeon through the use of a remote afterloader device.

The feasibility of an approximate irregular field dose distribution simulation program applied to a respiratory motion compensation system.

This study optimized our previously proposed simulation program for the approximate irregular field dose distribution (SPAD) and applied it to a respiratory motion compensation system (RMCS) and respiratory motion simulation system (RMSS). The main purpose was to rapidly analyze the two-dimensional dose distribution and evaluate the compensation effect of the RMCS during radiotherapy. This study modified the SPAD to improve the rapid analysis of the dose distribution. In the experimental setup, four different respiratory signal patterns were input to the RMSS for actuation, and an ultrasound image tracking algorithm was used to capture the real-time respiratory displacement, which was input to the RMCS for actuation. A linear accelerator simultaneously irradiated the EBT3 film. The gamma passing rate was used to verify the dose similarity between the EBT3 film and the SPAD, and conformity index (CI) and compensation rate (CR) were used to quantify the compensation effect. The Gamma passing rates were 70.48-81.39% (2%/2mm) and 88.23-96.23% (5%/3mm) for various collimator opening patterns. However, the passing rates of the SPAD and EBT3 film ranged from 61.85% to 99.85% at each treatment time point. Under the four different respiratory signal patterns, CR ranged between 21% and 75%. After compensation, the CI for 85%, 90%, and 95% isodose constraints were 0.78, 0.57, and 0.12, respectively. This study has demonstrated that the dose change during each stage of the treatment process can be analyzed rapidly using the improved SPAD. After compensation, applying the RMCS can reduce the treatment errors caused by respiratory movements.

Application of radiochromic gel dosimetry to commissioning of a megavoltage research linear accelerator for small-field animal irradiation studies.

To develop and implement an efficient and accurate commissioning procedure for small-field static beam animal irradiation studies on an MV research linear accelerator (Linatron-M9) using radiochromic gel dosimetry. The research linear accelerator (Linatron-M9) is a 9MV linac with a static fixed collimator opening of 5.08cm diameter. Lead collimators were manually placed to create smaller fields of 2×2cm2 , 1×1cm2 , and 0.5×0.5cm2 . Relative dosimetry measurements were performed, including profiles, percent depth dose (PDD) curves, beam divergence, and relative output factors using various dosimetry tools, including a small volume ionization chamber (A14), GAFCHROMIC™ EBT3 film, and Clearview gel dosimeters. The gel dosimeter was used to provide a 3D volumetric reference of the irradiated fields. The Linatron profiles and relative output factors were extracted at a reference depth of 2cm with the output factor measured relative to the 2×2cm2 reference field. Absolute dosimetry was performed using A14 ionization chamber measurements, which were verified using a national standards laboratory remote dosimetry service. Absolute dosimetry measurements were confirmed within 1.4% (k=2, 95% confidence=5%). The relative output factor of the small fields measured with films and gels agreed with a maximum relative percent error difference between the two methods of 1.1 % for the 1×1cm2 field and 4.3 % for the 0.5×0.5cm2 field. These relative errors were primarily due to the variability in the collimator positioning. The measured beam profiles demonstrated excellent agreement for beam size (measured as FWHM), within approximately 0.8mm (or less). Film measurements were more accurate in the penumbra region due to the film's finer resolution compared with the gel dosimeter. Following the van Dyk criteria, the PDD values of the film and gel measurements agree within 11% in the buildup region starting from 0.5cm depth and within 2.6 % beyond maximum dose and into the fall-off region for depths up to 5cm. The 2D beam profile isodose lines agree within 0.5mm in all regions for the 0.5×0.5cm2 and the 1×1cm2 fields and within 1mm for the larger field of 2×2cm2 . The 2D PDD curves agree within approximately 2% of the maximum in the typical therapy region (1-4cm) for the 1×1cm2 and 2×2cm2 and within 5% for the 0.5×0.5cm2 field. This work provides a commissioning process to measure the beam characteristics of a fixed beam MV accelerator with detailed dosimetric evaluation for its implementation in megavoltage small animal irradiation studies. Radiochromic gel dosimeters are efficient small-field relative dosimetry tools providing 3D dose measurements allowing for full representation of dose, dosimeter misalignment corrections and high reproducibility with low inter-dosimeter variability. Overall, radiochromic gels are valuable for fast, full relative dosimetry commissioning in comparison to films for application in high-energy small-field animal irradiation studies.

Impact of bowtie filter and detector collimation on multislice CT scatter profiles: A simulation study

To investigate via Monte Carlo simulations, the impact of scan subject size, antiscatter grid (ASG), collimator size, and bowtie filter on the distribution of scatter radiation in a typical realistically modeled third generation 16 slice diagnostic computed tomography (CT) scanner. Full radiation transport was simulated with Geant4 in a realistic CT scanner geometric model, including the imaging phantom, bowtie filter (BTF), collimators and detector assembly, except for the ASGs. An analytical method was employed to quantify the probable transmission through the ASG of each photon intersecting the detector array. Normalized scatter profiles (NSP) and scatter-to-primary-ratio (SPR) profiles were simulated for 90 and 140kVp beams for different size phantoms and slice thicknesses. The impact of CT scatter on the reconstructed attenuation coefficient factor was also studied as were the modulating effects of phantom- and patient-tissue heterogeneities on scatter profiles. A method to characterize the relative spatial frequency content of sinogram signals was developed to assess the latter. For the 21.4-cm diameter phantom, NSP and SPR increase linearly with collimator opening for both tube potentials, with the 90kVp scan exhibiting slightly larger NSP and SPR. The BTF modestly modulates scatter under the phantom center, reducing the prominent off-axis lobes by factors of 1.1-1.3. The ASG reduces scatter on the central axis NSP threefold, and reduces scatter at the detectors outside the phantom shadow by factors of 25 to 500. For the phantoms with diameters of 27 and 32cm, the scatter increases roughly three- and fourfold, respectively, demonstrating that scatter monotonically increases with phantom size, despite deployment of the ASG and BTF. In the absence of a scan subject, the ASG reduces the signal profile arising photons scattered by the BTF. Without ASG, the in-air scatter profile is relatively flat compared to the scatter profile when the ASG is present. For both 90 and 140 kVp photon spectra, the calculated attenuation coefficient decreases linearly with increasing collimation size. For both homogeneous and heterogeneous objects, NSPs are dominated by low spatial frequency content compared to the primary signal. However, the SPR, which quantifies the local magnitude of nonlinear detector response and is dominated by the high frequency content of the primary profile, can contribute strongly to high-spatial frequency streaking artifacts near high-density structures in reconstructed image artifacts. Public-domain Monte Carlo codes, Geant-4 in particular, is a feasible method for characterizing CT detector response to scattered- and off-focal radiation. Our study demonstrates that the ASG substantially reduces the scatter radiation and reshapes scatter-radiation profiles and affects the accuracy with which the detector array can measure narrow-beam attenuation due its inability to distinguish between true uncollided primary and narrow-angle coherently scattered photons. Hence, incorporating the impact of detector array collimation into the forward-projection signal formation models used by iterative reconstruction algorithms is necessary to use CT for accurately characterizing material properties. While tissue heterogeneities exercise a modest influence on local NPS shape and magnitude, they do not add significant high spatial frequency content.

Simulating the approximate irregular field dose distribution in radiotherapy using an ultrasound tracking technique

PurposeThis study used an ultrasound image tracking algorithm (UITA) in combination with a proposed simulation program for the approximate irregular field dose distribution (SPAD) to assess the feasibility of performing dose distribution simulations for two-dimensional radiotherapy. MethodsThis study created five different types of multileaf collimator openings, and applied a SPAD to analyze the matrix position parameters for each regular field to generate a static program-simulation dose distribution map (PDDM), whose similarity was then compared with a static radiochromic film experimental-measurement dose distribution map (EDDM). A two-dimensional respiration motion simulation system (RMSS) was used to reproduce the respiration motion, and the UITA was used to capture the respiration signals. Respiration signals were input to the SPAD to generate two dynamic PDDMs, which were compared for similarity with the dynamic EDDM. ResultsIn order to verify the dose distribution between different dose measurement techniques, the gamma passing rate with 2%/2 mm criterion was used for the EDDM and PDDM, the passing rates were between 94.31% and 99.71% in the static field analyses, and between 84.45% and 96.09% for simulations with the UITA signal input and between 89.35% and 97.78% for simulations with the original signal input in the dynamic field analyses. ConclusionsStatic and dynamic dose distribution maps can be simulated based on the proposed matrix position parameters of various fields and by using the UITA to track respiration signals during radiation therapy. The present findings indicate that it is possible to develop a reusable and time-saving dose distribution measurement tool.

Using Robust Optimization for Skin Flashing in Intensity Modulated Radiation Therapy for Breast Cancer Treatment: A Feasibility Study

PurposeTo study the feasibility and the effectiveness of a novel implementation of robust optimization on 2 sets of computed tomography (CT) data simultaneously for skin flashing in intensity modulated radiation therapy for breast cancer. Method and MaterialsFive patients who received treatment to the breast and regional lymphatics were selected for this study. For each patient, 3 plans were generated using 3 different skin-flashing methods, including (1) a manual flash plan with optimization on the nominal planning target volume (PTV) not extending beyond the skin that required manually postplanning the opening of the multi-leaf collimator and jaw to obtain flash; (2) an expanded PTV plan with optimization on an expanded PTV that included the target in the air beyond the skin; and (3) a robust-optimized (RO) plan using robust optimization that simultaneously optimizes on the nominal CT data set and a simulated geometry error CT data set. The feasibility and the effectiveness of the robust optimization approach was investigated by comparing it with the 2 other methods. The robustness of the plan against target position variations was studied by simulating 0-, 5-, 10-, and 15-mm geometry errors. ResultsThe RO plans were the only ones able to meet acceptable criteria for all patients in both the nominal and simulated geometry error scenarios. The expanded PTV plans developed major deviation on the maximum dose to the PTV for 1 patient. For the manual flash plans, every patient developed major deviation either on 95% of the dose to the PTV or the maximum dose to the PTV in the simulated geometry error scenarios. The RO plan demonstrated the best robustness against the target position variation among the 3 methods of skin flashing. The doses to the lung and heart were comparable for all 3 planning techniques. ConclusionUsing robust optimization for skin flash in breast intensity modulated radiation therapy planning is feasible. Further investigation is warranted to confirm the clinical effectiveness of this novel approach.

001 Pelvic Radiation Reduces Vaginal Blood Flow and Increases Vaginal Smooth Muscle Contraction

Over half of women with cervical cancer will undergo radiation therapy (RT). Following pelvic RT, as many as 85% of women will experience sexual dysfunction including vaginal dryness, decreased arousal and pain. Pelvic irradiation is believed to cause genital tissue injury, fibrosis and decreased genital vasocongestion. The pathological mechanisms underlying these sequelae are poorly understood; therefore, preventive or therapeutic strategies for RT-induced female genital arousal disorder or genital-pelvic pain are lacking. Although several rat models of prostatic RT have been developed to study RT-induced erectile dysfunction, no parallel female model exists. Our objective was to establish a female rat model of pelvic RT and to investigate both acute and chronic changes in post-RT vaginal blood flow and vaginal smooth muscle function. Female Sprague-Dawley rats, 12 weeks of age, were separated into three groups (n=7-8/group): Sham, 4-week RT and 9-week RT. Under anesthesia, a single 20 Gy dose was delivered with the rat shielded beneath a 3D-printed table stand and cerroblend collimator (opening 3x3 cm). Based on 3D imaging of the rat pelvis, the collimator was aligned 0.5 cm superior to the external urethra to target the cervix while maximally sparing neighboring structures. Dose quantity was validated using film irradiated under experimental conditions. At 4 and 9 weeks post-RT, the pelvic nerve was stimulated and vaginal blood flow was measured with a laser Doppler probe. The maximal vaginal blood flow was normalized to mean arterial pressure measured via carotid artery cannulation and total vaginal blood flow was assessed as the area under the curve. Distal vaginal smooth muscle strips were placed in tissue baths and contraction was measured to the adrenergic agonist norepinephrine (NE), to cholinergic agonist carbachol and with electrical field stimulation (EFS). Nitric oxide mediated relaxation of the vaginal tissue was evaluated with DEA-NONOate.

Fast, Low-Dose Megavoltage-Topogram Localization on TomoTherapy: Initial Clinical Experience With Mesothelioma Patients

PurposeThis study aimed to evaluate the potential of megavoltage-topogram (MV-topogram)–based alignment as an alternative to megavoltage computed tomography (MVCT) in reducing setup time and imaging dose for patients with malignant pleural mesothelioma who are receiving TomoTherapy. Methods and MaterialsTwelve patients were enrolled in an ongoing institutional review board approved clinical trial at our institute. Patients were set up with a clinical protocol using red lasers. Anteroposterior (AP) and lateral (LAT) MV-topograms were acquired using gantry angles of 0°/90° with a 1 mm collimator opening, all multileaf collimator leaves open, a couch speed of 4 cm/s, and a 12.5-second scanning time. Routine MVCT scans were performed immediately afterward. The MV-topograms were reconstructed and enhanced using contrast-limited adaptive histogram equalization. Anteroposterior and LAT kilovoltage digital reconstructed topogram images were reconstructed based on TomoTherapy geometry from computed tomography simulation scans. Registrations between MV-topograms and kilovoltage-digital reconstructed topogram images were performed manually, and patients’ daily shifts were recorded. Results were compared against the corresponding daily MVCT shifts. MV-topogram and MVCT doses were measured and recorded using an ion chamber on a cheese phantom with depths between 1 and 14 cm, as well as the times required to acquire the 2 image modalities. ResultsThe mean and standard deviation of shift discrepancies between MV-topogram and MVCT were 0.74 ± 2.08, –0.09 ± 4.46, and 0.45 ± 3.57 mm in the LAT, longitudinal, and vertical directions, respectively. The MVCT imaging doses measured were 14.74 to 26.92 times higher than the MV-topogram doses, depending on depth. On average, MV-topograms with a mean scan length of 50 cm achieved a 5-fold image acquisition time savings over MVCT, with a mean scan length of 38 cm. ConclusionsMV-topograms has the potential to provide alignment performance equivalent to that of MVCT for patients with mesothelioma, with a significant reduction in imaging dose and acquisition time.

EP-1865 A feasibility study: 6 VMAT arcs full collimator opening for hippocampal sparing

EP-1865 A feasibility study: 6 VMAT arcs full collimator opening for hippocampal sparing

Title Design of light element analysis system in BNCT and every NCT

Introduction: The Monte Carlo simulation is used to enhance reliability in the experiments related to nuclear instruments. in addition, that is used to calculate the different components of the neutron and gamma ray fluxes in boron neutron capture therapy(BNCT) and neutron capture (NCT)applications. BNCT is one of the methods in radiotherapy, that is used the neutron beam for kill the cancer cells. The neutron activation analysis(NAA) is the method for identify light elements that the neutron is captured with light elements nucleus and emits characteristic gamma rays. Materials and Methods: the MCNPX code was used for calculation. Boron and other light elements exist in the liver tissue. The BNCT special set geometry was designed. In this designed, light elements analysis is performed simultaneously with the neutron therapy. The effective parameters such as source location, source type, detector location, detector material, patient couch, energy of source, moderator, collimator type, length and thickness of collimator, distance between sample and source, opening of collimator, geometry and location of detector was designed. Results: the best neutron source for BNCT and light element analysis is expanded neutron spectrum produced by the reactor with Paraffin moderator. Neutron Source Generator with every moderator had low efficiency. Collimator made of graphite, graphene and carbon compounds had better neutron output spectrum. Sodium iodide detector is suitable for the detection of light elements gamma rays. The collimator length 20 cm and thickness 6cm. The detectors are placed in a cylindrical arrangement and They should not be exposed to direct neutron radiation. Conclusion: the MCNP study is one of the best methods for BNCT and NCT. the NAA and BNCT is possible Performing Simultaneously. The expanded neutron spectrum from reactors is suitable for NAA and BNCT.

18 SBRT for peripheral lung tumors with linac arctherapy technique: More accurate, fast and safe

Introduction Over the past decade, there have been significant changes in the dosimetric management of peripheral lung tumor treatments with stereotactic radiotherapy. Historically developed on linear accelerators using additional collimators, the treatments are now performed on dedicated accelerators (CyberKnife, Vero, STX TrueBeam, Versa HD for example) with dedicated equipment (positioning imagery, breathing control, contention) and dedicated beam types (Flattening Filter Free). First performed in 3D conformal radiotherapy (3D-CRT), treatments are now indicated in intensity-modulated rotational radiotherapy (VMAT) [1] . Methods This prospective study was conducted on 30 patients with peripheral lung tumor treated by SBRT. The objective was to assess, through metrics (NC, CI, HI, Dmin PTV , and volumes of isodoses 5Gy, 10Gy, D50% and. Dpresc. [2] , the possibility to improve dose distribution and decrease delivery time of SBRT with VMAT and no longer in 3D – CRT. The planning has been conducted with the RayStation v6 TPS. The scheme of radiotherapy was 48Gy in 6 fractions and the average volume of PTV was 18.3 ± 11.8cc. For each patient, the ITV was determined and the PTV achieved by applying margins of 5mm in the cranio-caudal direction and 3mm elsewhere. Two treatment plans were made: one 3D-CRT in 6MV-FFF and the other in VMAT 6MV-FFF with limitation of the movement of the blades. The optimization of the treatment plans was carried out so that 99% of the PTV volume is covered by the prescription isodose with for the 3D-CRT a collimator opening limit of 5 mm and a limit of prescription at Isocenter point of 80%. The metrics of the 30 patients were recorded and compared by a Wilcoxon test. The treatment delivery time was measured for the 3D-CRT technique and the estimate time was provided by the TPS for the VMAT. Results The results are presented in Table 1 and Fig. 1. For almost all of the patients, the coverage of 99% of the PTV was met. Our technique allows to get a better number of conformity (p 0.001) as well as volumes of isodose 10Gy, D50% and Dpresc. smaller (p 0.001). The duration of treatment sessions has been reduced from 150 to 47 sec. Conclusions The limitation of leafs movement, use of partial arcs with only photons flow variation during arc delivery achieve more consistent coverage and lower lung irradiation without interplay effect during irradiation sessions. This technique is now performed in routine.

Assessment of combined use of ArcCheck® detector and portal dosimetry for delivery quality assurance of head and neck and prostate volumetric-modulated arc therapy.

PurposeTo assess the efficiency of combined use of ArcCheck® detector (AC) and portal dosimetry (PDIP) for delivery quality assurance of head and neck and prostate volumetric‐modulated arc therapy.Materials and methodsMeasurement processes were studied with the Gamma index method according to three analysis protocols. The detection sensitivity to technical errors of each individual or combined measurement processes was studied by inserting collimator, dose and MLC opening error into five head and neck and five prostate initial treatment plans. A total of 220 plans were created and 660 analyses were conducted by comparing measurements to error free planned dose matrix.ResultsFor head and neck localization, collimator errors could be detected from 2° for AC and 3° for PDIP. Dose and MLC errors could be detected from 2% and 0.5 mm for AC and PDIP. Depending on the analysis protocol, the detection sensitivity of total simulated errors ranged from 54% to 88% for AC vs 40% to 74% for PDIP and 58% to 92% for the combined process. For the prostate localization, collimator errors could be detected from 4° for AC while they could not be detected by PDIP. Dose and MLC errors could be detected from 3% and 0.5 mm for AC and PDIP. The detection sensitivity of total simulated errors ranged from 30% to 56% for AC vs 16% to 38% for PDIP and 30% to 58% for combined process.ConclusionThe combined use of the two measurement processes did not statistically improve the detectability of technical errors compared to use of single process.

51. Comparison of ORL and prostate VMAT treatment plans verifications by ArcCheck® Sun Nuclear™ 3D detector and Varian™ PDIP® module: assessment of the errors detection sensitivity and the capability of each process

Introduction The complexity of intensity modulation radiation requires a planned dose distribution verification prior treatment. Delivery a patient treatment plan quality assurance can be carried out by EPID, 2D/3D detector or by ionization chamber. In our department, VMAT treatment plans are checked by ArcCheck® Sun Nuclear™ 3D detector and Varian™ PDIP® module. In order to assess the feasibility of reducing the number of verification processes, we studied the detection sensitivity of different errors [1] and the capability of each process. Methods Treatment plans are checked by ArcCheck® Sun Nuclear™ 3D detector + SNC patient™ v6.7.1 software (AC) and Varian™ As 1000 EPID + Varian™ PDIP® v13.0 module (PDIP). For 5 ORL and prostate treatment plans, errors of collimator angulation (1–5°), dose rate (2–3%) and multi-leaf collimator (opening leaves banks from 0.5–1–2 mm) are simulated. Treatment plans are assessed by γ index (3%/3 mm, 2%/2 mm) with a respective passage criteria of 95% and 90% of the total pixels in global and local mode. A database of 80 ORL treatment plans and 30 prostate treatment plans is analyzed in order to check the capability of each process according to the different γ index analysis criterias used. Results As regards the detection sensitivity of errors, according to the analysis criterias of the γ index, the AC and the PDIP respectively make it possible to detect on average: collimator errors from 2° and 3° for the ORL plans and 4° and above 5° for prostate plans; Dose rate errors of 2% for ORL plans and 3% for prostate plans; MLC banks opening errors of 0.5 mm for ORL plans and 0.5 mm and 1 mm for prostate plans. With a fixed analysis criteria, the error detection sensitivity of the AC appears higher than the PDIP. Concerning the database analysis, for the AC, the mean γ indexes with 3%/3 mm global/local mode, and 2%/2 mm global mode are respectively 99,7 [96,3–100]; 95.8 [83.0–100]; 96.8 [81.0–100] for ORL treatment plans and 99.8 [98.8–100]; 98.2 [93.9–100]; 97.6 [90.0–99.8] for prostate treatment plans. The respective CPM capability indices are 5.2; 0.1; 0.9 for ORL treatment plans and 9.2; 1.0; 1.5 for prostate treatment plans. For the PDIP, the mean γ indexes with 3%/3 mm global/local mode and 2%/2 mm global mode are respectively 99.9 [98.8–100]; 97.6 [92.1–100]; 99.0 [93.6–100] for ORL treatment plans and 99.8 [99.0–100]; 99.0 [93.6–99.9]; 98.6 [95.8–100] for prostate treatment plans. The respective CPM capability indices are 17.4; 0.6; 1.5 for ORL treatment plans and 9.8; 1.6; 3.1 for prostate treatment plans. Conclusions The detection sensitivity of the errors appears equivalent between the two processes AC and PDIP by selecting a suited γ index analysis criteria. Analysis with 3%/3 mm local mode appears the most efficient in the detection of error but also leads to a risk of false positive. On a case by case basis, none of the processes can systematically detect the simulated errors.