bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐25: Investigating the Impact of Polymer‐Coating On the Dosimetric Characteristics of a 103Pd Brachytherapy Source Using Photon Spectroscopy
Authors: Chen Z , Kim J , Nath R
Published: July 2013

Purpose: Synthetic polymers have been used to coat the surface of existing low‐energy brachytherapy sources to improve their fixity in tissue in order to minimize seed migration in the patient. The purpose of this study was to evaluate the effects of the polymer‐coating on the photon energy spectra emitted by Pd‐103 seeds and to estimate its impact on the dosimetric characteristics of these seeds. Methods: Two Pd‐103 AnchorSeeds (Biocompatibles, Inc) and two Pd‐103 TheraSeeds (Theragenics Corporation) were used in this study. The AnchorSeed is made from the TheraSeed by coating its surface with bio‐absorbable polymeric anchoring rings and ribs. Photon energy spectra emitted by these seeds were measured using a high‐resolution, high‐purity Germanium (HPGe) photon spectrometer. The effects of polymer coating on the dose rate constant were quantified by comparisons of the coated seed with a non‐coated seed. Results: The relative photon energy spectrum emitted by the AnchorSeed was nearly identical to that emitted by the TheraSeed without polymer coating. The dose‐rate constants determined from the emitted photon energy spectra for the two seed models were identical to the third digit after the decimal point (0.679 ± 0.037 cGyh‐1U‐1). Because the basic dosimetric property of a brachytherapy seed is fundamentally determined by the photon characteristics emitted by the seed, effects of the polymer‐coating on the relative dosimetry data of TheraSeed is also expected to be minimal. Using a preexisting photon spectrometer, these measurements and calculations were completed in about 10 working hours. Conclusion: The polymer coating used in the AnchorSeed has minimal impact on its dosimetric characteristics compared to the non‐coated TheraSeed. We also demonstrate that photon spectroscopy provides a ready tool for the evaluation of impact of various coatings or other material changes in the seed manufacture process.
SU‐E‐T‐26: Determination of Field Parameters for Unflattened Photon Beams Using a Universal Scaling Factor
Authors: Chen Y , Shih R , Afghan M , Gopal A , Chen H
Published: July 2013

Purpose: To investigate unflattened and flattened photon beam profiles and to propose a new method in determining field parameters for unflattened beams. Methods: For flattened beams, field parameters of field size, etc., are defined according to the profile scaled the dose at central axis (D_CAX) to 100%. For unflattened beams, Siemens presents a table of scaling factors (to D_CAX) which are field size and energy dependent. The M. D. Anderson group presented a method to match the dose level at the inflection point for an unflattened beam to that for the corresponding flattened beam. By investigating cross‐plane and in‐plane profiles for the flat beams of Siemens Artiste 6 and 10 MV, Varian 21EX 6 and 10 MV, Trilogy 6 and 18 MV at different field sizes and depths, it was observed that the ratio of the dose at the inflection point (D_IP) to D_CAX remains unchanged within an uncertainty. Therefore, it is proposed to scale any unflattened beam profile by defining its D_IP to this value. After the scaling, the common definitions of field size, penumbra, and asymmetry remain the same. Results: The ratio (D_IP/D_CAX) approaches a Gaussian distribution, yielding a mean of 54% with standard deviation of 2% for all data. The differences between the field sizes determined by this new method and those by Siemens scaling factors are mostly within 1 mm for Artiste 7 UF and 11 UF unflattened beams in a wide range of field sizes and depths. Varying this scaling factor in the 95% confidence interval leads to a variation within ±1 mm for field size determination.Conclusion: This study demonstrates reasonability in use of single “54%” scaling factor to the inflection point for all unflattened beam profiles. The proposed method would provide simplification in determining field parameters for unflattened beams. This work is supported in part by a Siemens research fund.
SU‐E‐T‐28: Commissioning of OSLDs as An In‐Vivo Dosimeter in INTRABEAM Radiotherapy for Early Stage Breast Cancer
Authors: Pillai S , Crilly R , Laub W
Published: July 2013

Purpose: To commission OSLDs for estimating skin dose for patients undergoing INTRABEAM radiation therapy for early stage breast cancer. Methods: Intrabeam system, using low energy X‐rays of 20keV effective energy, 0.64mm of Al HVL, deliver 20Gy to the spherical applicator surface. Optically Stimulated Luminescence Dosimeters (OSLDs Landauer screened nanoDOTs) were used for this study. OSLDs were water proofed using 3M Tegaderm film and held by a custom made solid water holder. OSLDs were irradiated in water at distances from the applicator surface ranging from 5mm up to 40mm. Measurements were repeated three times for each depth. Depth dose data in water as provided by the manufacturer is applied for estimating the delivered dose to OSLDs. Irradiated OSLDs were analyzed using microStar reader after giving a minimum 10 minutes delay to allow suppression of ambient phosphorescence. Calibration curves (Dose vs Counts) were generated for each applicator/probe combination and validated by performing comparisons in plastic water using PTW MARKUS planeparallel Ionization chamber and virgin OSLDs. Results: Calibration curves were generated for spherical applicators with diameters ranging from 2.5cm to 5cm. OSLD calibration curves were validated by performing a set of measurements in plastic water using ionization chamber & OSLDs. The results were within ±6% as expected based on the OSDL sensitivity uncertainty and OSLD positioning uncertainty. The reproducibility of OSLD measurements were ±2% (1σ). Conclusion: OSLDs can be used for in vivo dosimetry for intrabeam therapy and can accurately measure skin dose for patients receiving INTRABEAM therapy. Immediate reading and the ease of use provide added advantages to use OSLDs as an in vivo dosimeter. This calibration method incorporates the energy spectrum change with depth and hence the change in OSLD sensitivity with energy.
SU‐E‐T‐30: Estimation of Dynamic Leaf Gap for IMRT Dose Calculation
Authors: Yao W , Goodyear D , Gillard M , Corsten M
Published: July 2013

Purpose: To obtain the proper dynamic leaf gap (DLG) of a Millennium 120 MLC such that the calculated dose matches the measured. Methods: The DLG for round leaves is often measured via extrapolating the size of fields formed by sweeping synchronized MLC leaves to the size under which the measured dose equals the MLC transmission. In this situation, the tongue and groove effect would be minimal. However, practical IMRT fields are formed by non‐synchronized MLC leaves. Therefore, we measured doses from both synchronized and non‐synchronized dynamic fields. Each non‐synchronized field had fixed but different neighbouring leaf extensions (tongue‐and‐grove, T&G). The DLG was obtained for each set. Doses calculated with various values of DLG and transmission rate (TR) were compared with the measured dose. The relative discrepancies were put into a lookup table as function of gap and T&G. The table was used to estimate the pass rate of patient IMRT plans, in which each field was decomposed into sub‐fields. Each sub‐field was formed by a pair of opposite leaves. The T&G was calculated from the neighbouring leaves formed the sub‐field. Results: The extrapolated DLG was 1.8, 1.6, 1.7, 2.5 and 1.6mm for the T&G 0, 5, 10, 15 and 20mm, respectively. The MLC TR was 1.6%. For typical patient IMRT plans, the T&G values were broadly distributed from 0 to 20mm but with median around 15mm. From investigating many combinations of TR and T&G, we see the pass rate was extremely sensitive to the combination, and the highest pass rate went to the combination of transmission 1.6% and T&G 2.3mm. This Result excellently agreed with IMRT QA. Conclusion: The extrapolated DLG depends on the T&G. The proper value of DLG can be estimated from the study of non‐synchronized sweeping gaps and T&G distributions in typical patient IMRT plans.
SU‐E‐T‐31: The Evaluation of Dosimetric Characteristics of OSLDs Based On Output Correction Factor in Low Energy
Authors: Han S , Kim K , Park S , Lee S , Yi C , Kim H , Jung H , Kim M , Ji Y
Published: July 2013

Purpose: The output of General X‐ray unit (low energy) has variation against 60Co unit. So it is necessary to minimize output variation when evaluating dosimetric characteristics of optical stimulated luminance dosimeters (OSLDs). Considering output variation of X‐ray unit, we evaluated dosimetric characteristics of OSLDs in low energyMethods: The OSLDs that used were nanoDotTM Dosimeter (Landauer Inc, Glenwood, USA) and this dosimeter had never been irradiated. Through single irradiate them (test dose was 7mGy), we certified batch homogeneity and sampled dosimeters with variation of radiation sensitivity within ± 1.5% among them. Using to these dosimeters certified reproducibility considering output variation every time when irradiated OSLDs. Through this process, we certified element correction factor (ECF) and coefficient of variation (COV) about each OSLD. Based on these OSLDs, we studied linearity, energy dependence and angular dependenceResults: The batch homogeneity was 1.21% of the coefficient of variation (after sampling). The average value of COV about reproducibility of OSLDs was reduced from 1.3% to 0.96% after applying to output correction factor. The linearity was that the correlation of between dose and count was fitted by linear function (R2 =0.997). The energy dependence study showed a range of ion chamber‐to OSLD rations from 0.23 (24.7 keV) to 0.27 (34.5 keV). According to energy, the range of angular dependence was from 0.1% to 8.4% variation when each degree was normalized by zero degreeConclusion: Considering output correction factor, reduced uncertainty occurred in general x‐ray unit. We acquired information that was ECF, COV of OSLDs in low energy. Using to these OLDs, It is feasible to measure patient dose of diagnostic radiography and Cone beam computed tomography for radiotherapy
SU‐E‐T‐34: In‐House Computer Controlled Automatic 2D RFA and Dosimeteric Comparison with BJR‐25 Report
Authors: Senthilkumar S , Vinothkumar P
Published: July 2013

Purpose: The main purpose of this work was to fabricate an indigenous computer controlled two dimensional Radiation Field Analyzer (2D RFA) for external beam radiotherapy machines to measure the output, PDD, TMR, TPR and isodose profile automatically. The 2D RFA is fast, accurate, simple and easy to setup. Methods: This 2D RFA consist of water phantom, DC stepper motor, electronic circuit, acrylic chamber holding assembly, Buzzer and LED. An automatic ionization chamber movement tool was fabricated for radiation dose measurement in X direction using a DC stepper motor. There was an arrangement helping to move the ionization chamber in the Y direction. A cylindrical rod was made of acrylic and the other setup also made up of the same low atomic number material to avoid the scatter contribution from the water phantom. An easy mechanism was provided to fix the movable chamber holder setup in the water phantom. Results: The beam output, PDD, isodose profile for different field sizes and, off‐axis ratio were measured for external beam radiotherapy machines using the 2D RFA device with a 0.6cc farmer type ionization chamber. The device was used to measure the dose profiles for various field sizes at various depths. The values were normalized at 0.5cm depth. The measured values and values obtained by BJR25 were compared. The measured values agreed well with those published in the BJR25 report. The average difference was found the maximum variation of 2 percentage. Conclusion: Dosimetry is important for external beam teletherapy machines. The routine machine output calibrations can be performed with this device. From this, it can be concluded that it is very suitable for routine radiotherapy dosimetery produces. Salient features of the 2D RFA is its speed, accuracy, simplicity, and low cost.
SU‐E‐T‐36: Determination of the Beam Quality Correction Factor for the Liquid Ioinization Chamber in a Clinical Photon Beam
Authors: Choi Sang Hyoun , Kim Woo Chul , Kim Seong Hoon , Kim Chan Hyeong , Ji Young Hoon , Kim Kum Bae , Shin Dong oh
Published: July 2013

Purpose: The beam quality correction factor Koo0 of microLion chamber is still unknown and should be determined for the application of the chamber to the reference dosimetry. The objective of this study is to calculate the beam quality correction factor of microLion chamber for the high energy 6MV photon beam from Clinac iX (Varian, USA) using two alternative ways; Monte Carlo simulation, in particular EGSnrc system and experimental decision. Methods: For the present work the Cobalt60 gamma beam (Theratron780) is employed as beam source in the calibration beam quality and the high energy 6MV photon beam from the Linac (Clinac iX) is selected as quality of user beam. We have employed the egs cavity code, the EGSnrc user code, to model microLion chamber. Results: The correction factor of the PTW30013 chamber is given 0.995 for the photon beam quality TPR20,10 of 0.663. We get the Result of 1.024(±0.58%) for the TPR20,10 factor of the microLion chamber for the 6MV photon beam with its beam quality TPR20,10 of 0.663 using Monte Carlo simulation. The correction factor is calculated for the microLion chamber and for the 6MV photon beam with its beam quality of 0.665 is and shows good agreements within 0.56% with the one measured (1.024). Conclusion: The beam quality correction factor of the microLion chamber was determined with its correction factor unknown for the 6MV photon. The results from two methods were in good agreements within acceptable uncertainties. There remains a problem that uncertainties associated with microLion chamber should be studied further, but we think the averaged factor 1.0212 could be used for the microLion chamber and for the same photon beam quality as in this study in the reference dosimetry.
SU‐E‐T‐38: The Evaluation of High Dose and Dosimetric Characteristics of Optical Stimulated Luminance Dosimeters in the 60CO Unit
Authors: Han S , Kim K , Park S , Jung H , Lee S , Kim H , Yi C , Kim M , Ji Y
Published: July 2013

Purpose: We aimed to evaluate optical stimulated luminance dosimeters (OSLD) to estimate high dose in 60Co unit and to compare to advanced study about OSLDMethods: OSLDs were grouped into three groups by radiation sensitivity (serial No.) and each groups consisted of dosimeters with variation of radiation sensitivity within ± 1.5% among them by sampling. When we evaluated dosimetric characteristics of OSLD, indicated used OSLD groups in list of evaluation of the dosimetric characteristics of them. OSLD had supra‐linear response from more than 3 Gy. So the correlation of between dose delivered from 60Co and count was fitted by quadratic function. We compared to calculation dose and delivery dose in more than 3 GyResults: The reproducibility was 0.76% of the coefficient of variation, the batch homogeneity was within 1.5 % of the coefficient of variation and the depletion by repeat reading was 0.04% per reading. The half time of count decay curve after irradiation according to reading time was 0.68 min. (1 Gy), 1.04 min. (5 Gy), and 1.10 min. (10 Gy), respectively and the count decay was stable after 11 min, After stability, coefficient of variation was within 0.4%.The removal rate of count by optical annealing time (30min.) after OSLD reading was 88% (1 Gy), 90% (5 Gy), and 92% (10 Gy), respectively and was 99% when they were annealed for 4hour. The diff. % of between delivery dose form 60Co unit and calculated dose from fitting model was within ± 4.0%. But the OSLDs irradiated dose above 20 Gy changed their radiation sensitivity. So it is necessary to use carefully them and to calibrate radiation sensitivity of themConclusion: Considering to uncertainty of count for procedure, if delivery dose was calculated, it is feasible to use OSLD for evaluation of high dose in 60Co unit. Acknowledgement:This research was supported by the Ministry of education, Science and Technology(MEST)
SU‐E‐T‐164: Comparing Measurement Derived (3DVH) and Machine Log File Derived Dose Reconstruction Methods for VMAT QA in Heterogeneous Patient Geometries
Authors: Tyagi N , Yang K , Yan D
Published: July 2013

Purpose: To extend the 3DVH analysis to heterogeneous patient geometries for VMAT delivery and comparing its accuracy using machine log file derived dose reconstruction method Methods: A total of 10 patient plans were selected from a regular fractionation plan to complex SBRT plans. Treatment sites in the lung and abdomen were chosen to explore the effects of tissue heterogeneity on the respective dose reconstruction algorithms. Delivered plan in the patient geometry was reconstructed by using ArcCheck Planned Dose Perturbation (ACPDP) within 3DVH software, and by converting the machine logfile to Pinnacle3 9.0 treatment plan format. In addition, delivered gantry angles between machine logfile and 3DVH 4D measurement was also compared to evaluate the accuracy of the virtual inclinometer within the 3DVH. Results: Measured ion chamber and 3DVH derived isocenter dose agreed with planned dose within 0.3±0.7 Gy and −0.5±0.8 Gy respectively. Machine log file reconstructed doses and TPS dose agreed to within 2 Gy in PTV and OARs over the entire treatment course. 3DVH reconstructed dose showed a difference of up to 3.2 Gy in maximum PTV doses compared to planned dose in hypo lung patients due to plan heterogeneity. For majority of normal structures, dose differences were within 1 Gy except for few cases, where a maximum point dose difference of up to 2.2 Gy in proximal bronchial tree dose for a hypo lung patient was seen. The average Virtual Inclinometer Error (VIE) was − 0.65±1.6° for all patients, with a maximum error of −5.16±4.54° for an SRS case. Conclusion: Both methods are capable of taking into account the plan delivery errors. 3DVH is more sensitive to these errors compared to machine log file.
SU‐E‐T‐173: Patient‐Specific IMRT QA for Large Volume CyberKnife Plans Using MatriXX
Authors: Veltchev I , Lin M , Price R , Ma C
Published: July 2013

Purpose: The recent introduction of CyberKnife M6 FM and FIM models expands the field of robotic radiotherapy into the domain of large volume tumors. The increased complexity of CyberKnife plans with MLC requires at least 2D dosimetric verification in a phantom before the patient is treated. We describe a protocol for IMRT QA using an array of ionization chambers (MatriXX, IBA) for IMRT QA of large‐target CyberKnife plans. Methods: We developed post‐processing software that reads the dose frame sequence recorded by the MatriXX and applies a number of CyberKnife‐specific correction factors to each frame. Individual beams are located within the frames and angular correction factors are applied depending on beam angle. In addition, the background evolution is tracked in the “beam‐off” frames which are subsequently subtracted from the “beam‐on” frames according to a predictive model. Results: The clinical passing rates are significantly improved when the per‐frame analysis software was introduced in our IMRT QA procedure. We present a number of cases, for which the passing rates are increased from an average 80% in the raw data to 95% after correction. The MatriXX is found to have additional advantages, for it allows vertex beams, which are often part of the predefined paths in the planning software. Conclusion: The per‐beam correction strategy described in this work is found to improve the passing rates of CyberKnife plans designed for target volumes in excess of 40cc. Such large target volumes will be commonly treated with the new MLC enabled CyberKnife robot. Point dose verification remains a viable option for smaller targets, for which the spatial averaging in the MatriXX chambers hinders the performance of the device.
SU‐E‐T‐177: Radiochromic Film: Towards a Public Calibration Function
Authors: Lewis D , Yu X , Chan M
Published: July 2013

Purpose: To assess the possibility of using a public calibration function for radiochromic film dosimetry in dose QA of highly conformal treatment plans. Methods: EBT3 film calibration strips (3.5×20cm2 from lots A101212 and A011713) were exposed on a Varian Trilogy at a facility to a 10×10cm2 open field at doses of 80,160,320 cGy using 6MV photons. Together with a strip of unexposed film from the same lot the exposed films were digitized in a single scan using different Epson 10000XL scanners at two different facilities. The dose‐response data for each color‐channel from each facility were generated using the same calibration function X(D) = a + b/(D‐c), where X(D) is the response at dose D and a, b and c are the coefficients. Different batches of EBT3 film were exposed to a VMAT beam. These films, plus two reference strips exposed to doses of zero and 160 cGy, were digitized on the scanners at the two facilities. Using the multi‐channel dosimetry method and One‐scan protocol (Med Phys, 39:6339‐49, 2012) the recorded doses on the VMAT films were calculated and the results were compared with the VMAT plan using a Gamma index of 3%/3mm. Results: The passing rates obtained for dose maps calculated for all combinations of VMAT images and calibration functions were nearly unchanged, using the One‐scan protocol. Also, in all cases a passing rate of >99% was obtained for Gamma index of 3%/3mm. On the other hand, if the One‐scan protocol was not employed, the dose maps for VMAT images and calibration functions from different scanners showed poor correlation with the treatment plan. This is probably due to the scan‐to‐scan variability. Conclusion: We have found that it is feasible to use a public calibration function for a given radiochromic film lot using the same methodology, One‐scan protocol, for patient‐specific QA.

Two of the authors are the employees of Ashland Inc., the manufacturer of GafChromic film.
SU‐E‐T‐178: Dosimetric Evaluation of Gated and Non‐Gated IMRT Treatments Using Portal Dose Image Prediction Software
Authors: Karunakaran Kaviarasu , Raj Arunai Nambi , Murthy K Krishna , Babu Ananda Giri , Prasad B Durga
Published: July 2013

Purpose: The aim of the study is to compare the planar dose of IMRT fields on RPM gated delivery (for different duty cycles) with non‐gated delivery. Methods: Clinac NovalisTx Linear Accelerator equipped with Real‐Time Position Management (RPM) gating system is used to deliver the gated treatments. Varian Eclipse Treatment Planning System is used to perform the IMRT Planning. Quality Assurance of IMRT fields are performed on Electronic Portal Imaging Detector (aS1000) with Portal Dosimetry software. Portal Dose Image Prediction software is used to analyze the gamma of planar doses for gated to the reference of non‐gated IMRT delivery. In this retrospective study, 60 IMRT fields from various IMRT plans were analyzed and compared for three different duty cycles (20%, 30% & 40% Duty cycle, which are generally used for treatment) of gated delivery with that of non‐gated delivery. The measured dose planes were analyzed for gamma agreement with criteria of 1% to 1mm. In addition to that, the measured dose planes of gated & non‐gated delivery are compared with the TPS Calculated dose planes for gamma with criteria of 3% to 3mm. Results: The mean values of average area gamma greater than one for measured planar doses for 60 IMRT fields of 20%, 30% and 40% duty cycles were 1.50, 0.79 and 0.58 respectively for the gated delivery to the reference of non‐gated delivery. Conclusion: The Gamma results suggest that the gated deliveries for various duty cycles are comparable with the normal non‐gated delivery. The Results exhibits that the increase in duty cycle reduces the deviation between the gated and non‐gated delivery. This deviation is attributed due to the frequent breakage of beam for 20% duty cycles compared with the 30% and 40% duty cycles.
SU‐E‐T‐179: Evaluating Treatment Couch Dosimetric Effects in Spine SBRT Treatment Planning
Authors: Winey B , Wolfgang J , Speier C , Crawford B
Published: July 2013

Purpose: To evaluate the dosimetric effects of the treatment couch on skin dose and field attenuation for Spine SBRT. Methods: Measurements were acquired with an Elekta Synergy S in a 10.4 cm x 10.4 cm open 6 MV field with a Marcus parallel plate ionization chamber for varying thickness of water equivalent plastic. Measurements were repeated with and without the Hexapod carbon fiber treatment couch. A program was written to superimpose a CT scan of the treatment couch onto the patient planning CT. Dose calculations were performed with and without the treatment couch in a solid water phantom in Raystation Treatment planning software and compared to the measured values. All doses are in reference to Dmax of the open field without couch. Results: The measurements displayed a 69% higher dose (93% versus 24%) at the surface with the addition of the couch due to the electron contamination from the couch. Our beam model in Raystation underestimates the surface dose by 10% and agreement is achieved at 7 mm and within 4% at 4 mm depth. At depths greater than Dmax, the couch introduced an attenuation factor of 2%. Conclusion: A carbon fiber couch significantly affects the surface dose for beams that pass through the couch. The couch introduces electron contamination that increases the dose by 69% at the surface. High doses to the skin can cause skin erythema. Couch dose enhancement combined with high dose fractions and several beams passing through the couch for spine SBRT treatments should be accurately modeled to evaluate the actual dose delivered to the skin.
SU‐E‐T‐180: Empirical Determination of Output Factors for Proton Therapy Fields Using a Uniform Scanning Proton Beam and 10cm Snout
Authors: Aaron E , Cheng C , Lamba M
Published: July 2013

Purpose: he output factor of a proton field is affected by energy, width of spread‐out Bragg Peak (SOBP), source to measurement point distance, shape and size of the aperture, and the thickness of the compensator. It is generally measured in a water phantom to determine MU needed for each treatment field. This is time consuming and labor intensive. Previous studies employed empirical fits to measured data and then applied correction factors to account for various parameters. In this study, we have developed an empirical model to determine the output factors for proton fields with a 10cm snout using a cubic equation. Methods: Measured output factors with (OFclosed) and without (OFopen) a compensator for 693 fields delivered with the uniform scanning beam were analyzed. The measurements were made for various ranges, SOBP widths, air gaps, aperture shapes and sizes using a 10cm snout. 3D empirical equations for predicting OFclosed and OFopen were determined by fitting the data to several 3D curves and evaluating each fit. Results: The proposed model uses a simplified cubic fit. The distribution of closed measured OF vs predicted OF for this model has a mean of 1.000 and 0.013 the standard deviation and agrees within 3% of measured data 88.9% of all fields. The current model being used has a mean of 0.994 and a standard deviation of 0.009 and agrees within 3% of measured data 98.2% of all fields. Conclusion: We have shown that a simplified cubic fitting of the measured data allows for calculation of output factor with a single equation of the form OF=f(Inverse Square Law Correction, SOBP, Range). This empirical equation may be used to double check the OFclosed obtained with the separate model that is currently used. The model will significantly reduce the QA time required for measurements
SU‐E‐T‐196: Pretreatment Patient Clinical Objective IMRT Quality Assurance Using a 3D Diode Array
Authors: Ren L , Zhang Y , Yang Y , Adamson J , Yin F
Published: July 2013

Purpose: To evaluate the accuracy and sensitivity of a patient clinical objective IMRT QA tool using a 3D diode array. Methods: A 3D QA device (Delta4, Scandidos Inc.) with 2 orthogonal diode array planes was used for IMRT QA. The diode spacing is 5mm in central 6cmx6cm region and 1cm in the peripheral 20cmx20cm region. 3D volumetric dose is interpolated from the measured planar dose. The Delta4 Anatomy software (Anatomy) calculates the entrance energy fluence for each beam, which is then applied to the patient anatomy to calculate dose to the patient using a pencil‐beam dose calculation algorithm. The accuracy of Anatomy was evaluated in both solid water phantom using open fields and in patient anatomy using a prostate IMRT plan. The dose calculated by Eclipse was used as the gold standard. The sensitivity of the Anatomy was also evaluated by introducing leaf positioning errors in the delivery of a spine SBRT plan. Results: Excellent agreement between Anatomy and Eclipse was achieved for the solid water phantom with open fields. Discrepancy was observed for the PTV DVH calculated in patient anatomy using the prostate IMRT plan. This is mainly due to sharp dose fall‐off outside PTV and phantom setup errors during QA. Good agreement between Anatomy and Eclipse was achieved for bladder and rectum DVH. For spine case with introduced 1cm single leaf positioning error, the traditional gamma analysis using Delta4 still showed 95% pass rate using 3%, 3mm criteria. However, Anatomy showed 40% increase of cord max dose due to this error, which was consistent with Eclipse. Conclusion: Patient clinical objective QA using Delta4 Anatomy can potentially provide valuable information about the clinical significance of the QA results. It can potentially catch clinically significant delivery errors that would otherwise be missed in the traditional QA process using gamma analysis. Funding from Scandidos Inc.
SU‐E‐T‐204: Preliminary Study of the Comparison of Patient‐Specific QAs Using the Diode and Ionization Chamber Based Dosimetry Systems
Authors: Gupta S , Zhang X , Han E , Liang X , Sharma S , Morrill S , Hardee M , Penagaricano J , Ratanatharathorn V
Published: July 2013

Purpose: Patient QA comparison by using the ArcCHECK diode cylindrical and PTW 2D ionization chamber array based dosimetry systems for in‐homogenous and small field size tumor. Methods: Four head and neck (HN), 4 lung and 3 brain tumor patients were selected to study the behavior of in‐homogeneity on QA and, 3 SRS and SRT patients were selected to investigate small field size effect. The detectors used for this study are the PTW Seven29 2D ion‐chamber planar array (PTW, Freiburg, Germany) and the ArcCHECK cylindrical array (Sun‐Nuclear, FL). All the patient QA plans were generated using the Eclipse (version‐11) TPS; all the treatment plans were delivered on the TrueBeam‐STX Accelerator and measured by both the systems. A gamma‐index criterion of minimum 3% (3 mm) is used to evaluate the QA results. The Local‐Dose and the Van‐Dyk criteria are used to calculate the gamma, respectively. Results: The QA results show that gamma‐index scores are higher than 94% (3mm, 3%) for both the systems for the brain and lung patients; whereas for the HN patients, the gamma‐index score is 86% and 98% for the PTW and ArcCHECK, respectively. For the small field size, the gamma‐index scores (3%, 3 mm) are higher than 98% for the ArcCHECK; whereas the gamma‐index score is lower for the PTW. Conclusion: The tumor inhomgeneity does not affect the QA results since both systems give similar QA results for the brain and lung patients. However, ArcCHECK is better as compared to the PTW for the HN patients; this may be due to the relatively higher sensitivity of the diode and could pick up the lower signal for low dose area. For the SRS and SRT QAs, there will be volume averaging effect because of the large sensitive volume; hence, the PTW system may not be a good choice of detectors for these QAs.
SU‐E‐T‐205: Development of Institutional Consistency Metrics for the Prevention of Injurious and Reportable Radiation Delivery Errors
Authors: Molloy J , Langner U , Gerring S , Lewis D , Otageri P , Yagelski J , Gillie M , Greist T
Published: July 2013

Purpose: Radiotherapy treatment techniques are too complex for humans to assess the reasonableness of machine settings. Contrary to conventional wisdom, generalized logical tests, such as comparison to institutional norms, can be applied to patient‐specific machine settings. Such tests can be automatically applied to machine settings immediately prior to the point of treatment delivery and have a powerful potential to reveal and prevent potentially injurious errors. Methods: We tested two consistency metrics, one each for conventional (Mc,conv) and IMRT (Mc, IMRT) treatments. The metrics assess the weighted, total number of monitor units in a proposed treatment. Refinement of the IMRT metric was tested for the larynx category and incorporated an optimized exponential. The performance of Mc,conv was tested using Receiver Operator Characteristic (ROC) analysis. A deviation of > 2σ was flagged as an error by the metric, and ground truth was determined by full dose calculation, with either 20% or 5% dose thresholds considered indications of significant errors. The ROC analysis was performed for purely dosimetric errors, as well as for a cadre of dosimetric and geometric errors. Results: The standard deviations in the metrics used for conventional and step‐and‐shoot IMRT treatments are less than 13%, and 17%, respectively. The optimized exponential in the IMRT metric reduced the standard deviation of the larynx population from 14 % to 6 %, thus improving the predictive power of the metric. ROC analysis indicates that the metrics sensitivity to dosimetric errors is strong at both the 20% and 5% dose threshold levels. Even when geometric errors are included, the metric retains good predictive power for maximum dose. Conclusion: Comparison of patient‐specific treatment delivery parameters to institutional norms can reveal dosimetric errors of less than 20%. These methods have the potential to prevent potentially injurious radiation therapy errors from propagating to treatment. Varian Corporation research grant
SU‐E‐T‐218: Octavius 4D: Commissioning and Clinical Implementation of a New Device for VMAT Verifications
Authors: Gimeno‐Olmos J , Meseguer V Carmona , Lliso‐Valverde F , Martinez T Garcia , Pujades‐Claumarchirant MC , Palomo R , Ballester F , Perez‐Calatayud J
Published: July 2013

Purpose: To commission a new device for pre‐treatment patient specific verification of VMAT plans, which is capable of reconstructing 3D dose with high resolution. Methods: Octavius 4D system (PTW) consists of an ion chamber array embedded in a cylindrical phantom which, assisted by an inclinometer, rotates synchronously with the gantry. For VMAT plans, it measures planar dose distributions as a function of gantry angle in order to compute the resulting 3D dose distribution. There are two options for the ion chamber array: Octavius 729 (general purpose) and Octavius 1000 SRS (small field size, high resolution). We have used three linacs: two Varian Clinac iX and one TrueBeam with MLC HD 120, and the TPS has been Eclipse (v.10.0). The commissioning measurements consisted of the following tests: (1) homogeneity in response; (2) linearity with dose; (3) reproducibility; (4) leakage current, pre‐and post‐irradiation; (5) verification of typical VMAT and SBRT plans, comparing TPS‐calculated versus measured dose using 3D local gamma index (3%, 3 mm criteria). Results: We found the following results for Octavius 729 (and, in brackets, for Octavius 1000 SRS): (1) Homogeneity between chambers was 1.9% (0.8%). (2) Excellent linearity for both cases, with r2 value better than 0.999. (3) Reproducibility was 0.52% (0.08%). (4) Leakage increases with previously measured dose and shows its largest variation for large field sizes, fluctuating between −0.33 and +0.33 cGy/min (between −0.006 and +0.020 cGy/min). (5) Verifications of typical clinical plans, performed with the adequate array, showed a mean pass ratio of 89.3% (98.7%). Conclusion: Octavius 4D system together with Octavius 729 is an adequate tool for VMAT patient specific QA. With Octavius 1000 SRS, this capability is extended to those treatments requiring better resolution, as is the case for SBRT.
SU‐E‐T‐219: Illustration of Electron Beam Loss of Field Edge Fidelity (Beam Shape) and Uniformity with Air Gap
Authors: Lightfoot D
Published: July 2013

Purpose: Clinical use of electron beams frequently involves elaborate field shapes and/or matching of edges with adjacent poton fields. Treatment on accasion requires an extended Source Skin Distance (SSD). The optical projection of the field shape on the patient at the extended SSD does not depict the impact of the increased distance on shape and uniformity. The purpose of this presentation is to illustrate some examples of the impact Methods: Shape and dosimetric quantities measured on films exposed cross‐beam at 1 cm depth in plastic water at standard and extended SSD are compared with optical projections of shape and TPS calculations of dosimetric quantities. Results: Small field sizes of low energy electron beams have a small Effective SSD or f‐air and show a greater impact of extended distance on field shape and uniformity. For example, an f‐air value of 0.9 indicates that a net 10 percent of the beam directed towards the measurement point at the standard SSD is scattered away at the extended SSD. The scattering causes an outward bowing of straight edges, a rounding of sharp corners, loss of shape detail and a loss of uniformity of dose. Conclusion: When substantial departure from Inverse Square Law (ISL) is evident in extended SSD Electron Beam calculations it is advisable to evaluate the altered shape and uniformity so that clinical relevance can be judged. Substantial departure from ISL may mean more than a 5 or 10 percent departure from ISL or an air gap of more than 5 or 6 cm. Facilities ought to establish acceptable f‐air and air gap limits or action levels. Careful attention to minimizing air gaps as much as possible minimizes discrepancy between optically projected and actual shape and uniformity.
SU‐E‐T‐225: Factors Influencing Point A Treatment Volume for Tandem/Ring Applicators
Authors: Wilkinson D , Kolar M
Published: July 2013

Purpose: To study factors affecting the treatment volume (V100) for tandem/ring HDR brachytherapy. V100 values are used for patient specific treatment plan second checks. Methods: Treatment plans generated using Oncentra 4.1 (Nucletron/Elekta) for 28 patients involving a 2.6 cm ring with various tandem lengths (4 to 8 cm) were analyzed. All plans were prescribed to point A and no optimization was applied. Original plans were manipulated to alter dwell positions and the position of point A relative to the applicator to simulate gaps between the ring and external os. Dose volume histograms (dvh) were obtained for the treatment volume and in a subset of the study population for bladder and rectum according to GEC‐ESTRO guidelines. Results: Statistically significant differences in V100 were found for two different applicators having differing dwell position loadings. The differences were less than 10%. Increasing the distance from the ring surface to point A by 2 or 5 mm caused an increase in V100 of approximately 6% and 16% respectively for applicators with 4 or 6 cm tandems. The effect on organs at risk (bladder and rectum) according to GEC‐ESTRO dvh analysis showed changes of up to 20% with different dwell position ratios. Conclusion: The use of V100 values for treatment time verification should be supplemented with verification of the V100 itself. Not only does the size of the applicator affect V100 but also tandem/ring dwell positions need to be taken into account.
SU‐E‐T‐228: Automatic Second Check of RT Treatment Record Using Event Triggered Audit
Authors: Hadley S , Chen X , Weyburne G , Keranen W
Published: July 2013

Purpose: To enhance patient safety and radiation therapy quality assurance by implementing an immediate computer‐based audit of radiation therapy treatment record. Provide an automatic second check of the RT record in a paperless environment. Replace some aspects of weekly physics chart checks with a computer‐based audit of the treatment. Method: A software agent receives signals from a system we have developed, EventNet, when sentinel events occur in the TMS. Audits are triggered when a “treatment canceled”, and one of the many “treatment complete” signals are received. The treatment canceled audit assumes the patient treatment was canceled and verifies that no treatment happened. The treatment completed audit assumes that a treatment occurred and checks the treatment history parameters and dose summary against the scheduled plans, session, daily and total doses. The agent extracts the plan(s) and the day's treatment history from the TMS with a DICOM query and sends that data to a web service that compares the history against the plan. If the audit succeeds, the agent quietly adds an entry to a log file. When it fails the agent alerts staff via pager, email, or SMS message. Results: The agent is able to catch events from the TMS and trigger one of two audit processes. Basic audits of the treatment histories works as designed. Intentional variation in treatment parameters in test cases are caught and trigger the immediate alert. Conclusion: Immediate audit of the RT record is better than waiting for weekly physics chart check to verify plan parameters. Rather than have a physicist seek out variations in treatments by checking every treated parameter, a software agent can provide a basic audit and alert the physicist if needed. This brings more focus on patient treatments that require oversight and could free up valuable time for other QA tasks.
SU‐E‐T‐231: Breathing Pattern of Patients with and Without SBRT Immobilization Device
Authors: Michalski D , Huq M , Bednarz G , Lalonde R , Yang Y , Heron D
Published: July 2013

Purpose: To investigate the effect of SBRT immobilization device on patients breathing pattern. Methods: SBRT requirements for setup errors are more stringent than for standard radiation therapy. The patients are placed in an immobilization device and tumor motion management is applied if respiration induced tumor motion exceeds 0.5 cm. Patients' respiration pattern is a crucial component of the performance of gating technology. For our ongoing IRB approved project we acquire pretreatment 4DCT scan of patients immobilized in a device and with immobilization foil removed.These scans provided 20 pairs of breathing tracks of the Varian RPM external block placed on patients abdomen. The motion amplitude and time was read from the files. Cubic spline based resampling of the track was applied to space the point evenly. Recursive moving average filter covering 1 second was applied to demarcate peaks and troughs and identify the individual respiratory cycles. The Fourier low pass filter of 1Hz was applied to remove the high frequency noise that is not related to respiration. The base line drift was extracted applying ideal Fourier low pass filter of 0.1Hz. The descriptive statistics was used for respiratory peaks, troughs and their variability. The normality of the data was ascertained with Box‐Cox transformation. Period, exhalation and inhalation time were analysed. Welch t‐test for means and F‐test for variances was used. To examine the characteristics of the distribution Shapiro‐Wilk and Kolgomorov‐Smirnov test were used. Results: The base drift affects motion but does not have an effect on respiration cycles. Peaks has smaller than troughs variability. Shannon entropy and Lempel‐Ziv multilevel complexity are statistically dissimilar for both scans. The same is for other extracted parameters. Immobilization reduces base line shift. Conclusion: Immobilization devices tends to reduce the drift in patient breathing which can be viewed as a time dependent systematic error. We wish to acknowledge the support of Varian Medical Systems for this project through a research grant.
SU‐E‐T‐233: Application of Failure Modes and Effects Analysis to COMS Eye Plaque Brachytherapy
Authors: Tseng T , Palaniswaamy G , Deb N , Mutyala S , Rangaraj D
Published: July 2013

Purpose: Failure mode and effects analysis (FMEA) is a systematic technique performed to identify possible failures in the process and help in developing corresponding quality assurance (QA) procedure to avoid such failures. This project was designed to study the process, develop QA procedures, and evaluate safety and reliability of the COMS eye plaque brachytherapy procedure in our department. Methods: The eye plaque implantation procedure was divided into three sub‐processes: pre‐implant preparation, implant, and removal. The possible failure modes were identified by staff members involved in the treatment process. Each mode was quantified using an RPN (Risk Priority Number) score based on the multiplication of three factors: severity (S), frequency of occurrence (O), and detection failure (D). All factors are on a scale of 1 (low) to 10 (high) and determined by the consensus of the staff members. Larger RPN values represent more critical failure modes. Results: A process map was developed for the COMS eye plaque implantation. Twenty‐one failure modes were identified and the potential effects were analyzed by staff members and the RPN scores were averaged. The averaged RPN scores range from 35 to 281.25. Of the top four RPN values (>260), three were related to errors occurring in the pre‐treatment localization step which would cause incorrect dose estimation to the target and organ at risk. Incorrect seed activity ordered/received can also cause a critical error leading to incorrect dose delivery. Potential causes of these failures included human errors, failure in the communication between ophthalmologist, physicists, and the seeds manufactures, and imaging equipment malfunction. Conclusion: FMEA can be a useful tool within the Radiation Oncology department to prospectively examine specific treatment policies and procedures. The results would be useful in developing QA procedure to decrease the possibility of high RPN failure modes.
SU‐E‐T‐234: An Automated Tool for Treatment Plan Quality Evaluation and Clinical Trial Quality Assurance
Authors: Wang J , Chen W , Studenski M , Cui Y , Lee A , Xiao Y
Published: July 2013

Purpose: Develop an automated plan‐quality evaluation program for multi‐institutional clinical trials to improve case review efficiency. This program is generally applicable to routine clinical process to raise practice quality level. Methods: In this study, we developed an automated plan‐quality evaluation program which combines MIMVista, Java/MATLAB, and extensible markup language (XML). More specifically, MIMVista is used for data visualization; Java and its powerful function library are implemented for calculating dosimetry parameters; and to improve the clarity of the index definitions, XML is applied. The accuracy and the efficiency of the program were evaluated by comparing the results of the program with the manually recorded results in two RTOG trials. Results: A slight difference of about 0.2% in volume or 0.6Gy in dose between the automated program and manual recording was observed. According to the criteria of indices, there was no significant difference between the two methods. The evaluation time was reduced from 10–20 minutes to 2 minutes by applying the automated plan‐quality evaluation program. Conclusion: Quality review efficiency was much improved by using this automated plan‐quality evaluation tool. Accuracy was also improved as human error was eliminated. This tool will be made freely available to benefit general clinical practice.