bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐68: On the Dosimetric Differences Between Single Dwell and Multiple‐Dwell Accelerated Partial Breast Brachytherapy Plans Delivered with a Single Catheter Spherical Balloon
Authors: Nelson C , Kirsner S , Gifford K
Published: April 2010

Purpose: To compare single and multiple‐dwell dose distributions in patients treated with Mammosite (Cytyc Corp., Marlborough, MA) spherical balloons. Methods and Materials: 11 patients from our clinical data base were chosen. For each patient four treatment plans were generated: single dwell centered within the balloon, two, three and four dwells spaced uniformly along the catheter. Plans were generated with the Plato treatment planning system ver. 14.3.5 (Nucletron B.V., TH Veenendaal, The Netherlands) and imported into the Pinnacle3 planning system ver. 8.0h (Phillips Electronics N.V., Eindhoven, The Netherlands) for analysis. DVHs for the PTV, skin and ribs were computed. ANOVA from Matlab® (The Mathworks Inc., Natick, MA) was employed to detect differences in coverage of the 90%, 95%, 100%, 150% and 200% for the PTV, as well as differences in the 100 cGy, 125 cGy and 145 cGy doses to the skin and ribs. Dose difference DVHs were generated for each critical structure to illustrate any differences in the four planning methods. Results: The PTV DVH exhibited no significant difference amongst the four planning methods. The mean coverage of the 90%, 95%, 100%, 150% and 200% in the PTV showed no statistical difference amongst the four planning methods (p=0.8535, 0.6848, 0.4048, 0.7181, 0.6568). However, significant differences in skin doses (100 cGy and 125 cGy) were exhibited (p=0.0054, 0.0269). The single dwell method resulted in a higher percentage of skin receiving 100 cGy and 125 cGy (30% and 32% respectively). Significant differences of the 125 cGy and 145 cGy dose to the rib were also seen. (p=0.0582, 0.0841) The single dwell method resulted in a higher percentage of rib receiving 125 cGy and 145 cGy (29% and 26% respectively). Conclusions: Single and multiple dwell plans can provide similar PTV coverage. However, single dwell plans exhibit higher doses to the skin and ribs.
SU‐FF‐T‐71: Dose Perturbation Due To Contrast Solution In Mammosite Balloon In Ir‐192 HDR Treatment
Authors: Li W , Prasad S
Published: April 2010

Purpose: To determine the dosimetric consequences of radiopaque contrast in balloon used in Mammosite® brachytherapy. Method and Materials: Mammosite brachytherapy is delivered using a balloon catheter placed inside a lumpectomy cavity in a breast. The balloon is filled with a contrast solution to fit inside the lumpectomy cavity. In our institution the treatment is planned using CT images of the breast on an Eclipse treatment planning computer. We have found that the density of the contrast solution can vary significantly depending on the solution inserted in the balloon by the surgeons. CT numbers as high as 3000 Hounsfield Unit (HU) have been found in the mammosite balloon at our institution. The Eclipse treatment planning system does not take into account the heterogeneity of the contrast solution in treatment time calculation. We investigated the effect of the contrast solution on dose using film dosimetry and Varian Varisource 200 HDR unit with an Ir‐192 source. The solution form the balloon of a patient with CT number of 3000 HU was used in our study. A plan was created to deliver a dose which fell within the linear range of Kodak X‐Omat V film. The same geometry and irradiation time was used to irradiate films which under the contrast solution and water respectively. The films were read with a densitometer and the ratio of the optical density gave the dose ratio for the solution relative to water. Results: Solutions with CT numbers of 3000HU and 2000HU showed a reduction in dose of 10% and 5% respectively compared to water. Conclusion: Our study indicates that there can be a dose reduction in mammosite treatments where the CT number of the solution is high compared to water. The appropriate corrections should be made to deliver the intended dose in mammosite treatments with Ir‐192 source.
SU‐FF‐T‐75: Importance of Contamination Signal Removal On HDR Brachytherapy In Vivo Dosimetry When Using a Scintillating Fiber Dosimeter
Authors: Therriault‐Proulx F , Guillot M , Gingras L , Beaulieu L , Beddar S
Published: April 2010

Purpose: To quantify the importance of removing the contamination signal, composed of Cerenkov and fluorescence light, from the output of an in vivo scintillating fiber dosimeter during Iridium‐192 HDR brachytherapy treatments. Method and Materials: The scintillating fiber dosimetry system is composed of a miniature monochrome CCD camera (Apogee Alta U‐4000) detecting light from optical fibers. Two fibers were used for the purpose of this study: one of those had a 3 mm x 1 mm cylindrical scintillator (BCF‐60) coupled to its extremity. Integrating light coming out from both fibers under the same irradiation conditions allows, following proper calibration, to determine the scintillation and the contamination components of the detector signal. This study has been conducted in a solid water phantom. Components of the detector signal have been studied as a function of angular, longitudinal and radial position of the Ir‐192 source with respect to the detecting volume (i.e. scintillator). Results: The contamination component ranged from 4% to 42% of the detector signal, depending on the relative source to scintillator and fiber positions. The highest ratio was obtained when the source was the closest to the scintillator. The lowest was obtained when the source is longitudinally the furthest from the source. The ratio increased from 4% to 10% with the source going from 1cm to 5cm on the radial axis of the scintillator. Angular study reveals that both contamination and scintillation components of the signal varies under 3.4 percents over the complete angles range. Conclusion: Dose determination is proportional to the amount of scintillating light measured. Based on our measurements, the necessity of removing the contamination component of the signal is obvious to obtain an accurate dose calculation. Any scintillating fiber dosimeter for in vivo brachytherapy dosimetry should then include an efficient removal technique of the contamination signal.
SU‐FF‐T‐79: Dosimetric QA Tests of An Online Replanning Technique for Prostate Adaptive Radiotherapy
Authors: Peng C , Ahunbay E , Chen G , Lawton C , Li X
Published: April 2010

Purpose: We have previously developed an online replanning technique to be completed within 8 minutes. In preparation for its clinical implementation, a comprehensive QA test was performed to ensure its dosimetric accuracy and operational efficiency. Method and Materials: The newly developed online replanning technique based on fast aperture morphing and weight optimization has been integrated into a planning system (Prowess). Daily CTs acquired using a CT‐on‐Rails (Siemens) of 3 randomly selected fractions for each of 5 representative prostate cancer cases were used to generate 15 daily plans in total. An independent MU calculation tool (RadCalc) was used to verify the MU numbers. All daily plans were delivered and measured with a 2D diode array (MapCheck). Results: The time required for the entire replanning process starting from loading daily CT to getting the daily plan ready for delivery were less than 8 minutes, comparable to the time of the current IGRT repositioning procedure. The average time required for generating contours of prostate, rectum and bladder, aperture morphing and weight optimization, plan review, and transferring into the delivery system were 3, 2, 1, and 0.5 minutes, respectively. The agreement between MU numbers from RadCalc and from the online replanning tool remained the same as for the original plans and was acceptable (within 5%). The QA passing rates (the agreements between the measured and calculated dose distributions) for daily plans were equivalent to those for the original plans and were acceptable (within 95%). Conclusion: This new online replanning technique is dosiemtrically accurate and practically efficient. Since the daily adaptive plans are not drastically different from the original plan, a QA measurement may not be necessary. A clinical trial to test the feasibility and efficacy of this replanning technique for prostate cancer is being initiated.
SU‐FF‐T‐105: Surface Doses Comparison for Spot Scanned and Passively Scattered Proton Therapy Beams
Authors: Arjomandy B , Sahoo N , Cox J , Lee A , Zhu X , Gillin M
Published: April 2010

Purpose: To evaluate the differences in surface doses deposited from spot scanned and passively scattered proton therapy beams used for treatment of prostate cancer patients. Method and Material: The Proton Therapy Center of UT MD Anderson Cancer Center in Houston is equipped with a Hitachi synchrotron accelerator that delivers proton beams to four treatment rooms. Three of the rooms are equipped with passively scattered proton beams and one is equipped with spot scanning delivery system. The surface doses were measured using a PTW Markus chamber with a 1 mm thick cap in a plastic phantom slab. The calculated skin doses were obtained from the Eclipse treatment planning system (TPS). Markus chamber measurements were compared with the TPS calculated skin doses for fields of 10 patients treated with spot scanning and 10 patients treated with passively scattered proton beams. Results: Comparison of isodose distributions shows a lower dose to skin in case of spot scanned proton treatment fields as compared to the passively scattered proton treatment fields. The average measured surface dose was 11.8% lower for spot scanning than for passive scattering proton beams, with a standard deviation of 0.3%. The average difference in calculated surface doses from the treatment planning system for spot scanning was found to be 6.7% less than that for the passive scattering proton beams with a standard deviation of 0.2%. Conclusions: The results of our study show that the skin dose to patients is considerably lower (11–12% of the prescribed dose) with spot scanning proton beams than with passive scattering proton beams. For a prescribed dose of 76 CGE from two parallel opposed lateral fields, this amounts to a reduction of 4–5 CGE per field with the spot scanning proton beam.
SU‐FF‐T‐114: The Investigation of Dosimetric Reduction On Organs at Risk in Nasopharyngeal Carcinoma for Static IMRT Planning
Authors: Zhu J , Liu M , Yin Y
Published: April 2010

Objective There are two IMRT modes provided by some treatment planning system (TPS), one is static multi‐leaf collimator (MLC) IMRT called ¡°step&shoot¡± and the other one is dynamic MLC IMRT called ¡°sliding window¡±. This work investigated the dose decline on organ at risk (OAR) for nasopharyngeal carcinoma which driven by static IMRT. Methods Ten patients with nasopharyngeal carcinoma were allotted. Their plans were designed in both modes with Varian Eclipse. Under the condition that beam directions and optimization parameters were all the same, the dose on tumor targets and OARs were compared between these two IMRT modes. Then the treatment setup errors were considered and the same comparisons were repeated on the planning risk volume (PRV). Results There were no statistical significance on the maximum point dose, minimum point dose and average dose of the targets between the two IMRT modes. The static IMRT can provide not only the better conformal index for GTV (p=0.036) and PTV (p=0.047), but also the lower dose distribution on parotid‐average (p<0.01), parotid‐V35 (p<0.01), brainstem‐average (p<0.01), brainstem‐maximum (p=0.017), spinal‐cord‐average (p<0.01) and lens‐average (p=0.049). Even the setup errors were considered, the results on PRV of parotid‐average (p=0.033), parotid‐V35 (p=0.012) and spinal‐cord‐maximum (p=0.016) were all the same. Conclusion In comparison with the dynamic IMRT mode, the static one can reduce the dose on some of the nasopharyngeal carcinoma OARs with no dosimetric reduction on the tumor target. This result may be partly responsible for the MLC running mode, static IMRT just deliver the dose to where ever needed, but the dynamic IMRT is beaming on all the time while the MLC sliding all over the beam field.
SU‐FF‐T‐116: A Study of Planning Dose Constraint Template for IMRT Treatment for Patients with Early Stage Nasopharyngeal Carcinoma
Authors: Hu W , Yang H , Wang B , Ding W , Shao M , Yu C , Shan G , Wang W , Zhu H , Xu Q
Published: April 2010

Purpose: To develop a dose constraint template to increase conformity index (CI) of the planning target volume (PTV) and improve intensity‐modulated radiotherapy (IMRT) planning efficiency for patients diagnosed with early stage nasopharyngeal carcinoma (NPC). Methods and Materials: Twenty patients who were diagnosed with early stage NPC under IMRT treatment were selected in this study. The target volumes for all twenty patients were delineated on CORVUS Treatment Planning System (TPS) by oncologists. We started IMRT planning for the first 10 patients. Two dose limiting regions (Dlrs) around PTV were added by extending 1 cm region from PTV in each direction. All the IMRT plans were created and approved according to the dose constraints criteria in RTOG 0225 protocol. The mean values of end points of the extended normal structures from all 10 patients were chosen as the planning dose constraint template. For the other 10 patients, the IMRT treatment plans were performed either with (Plan1) or without dose constraint template (Plan0) derived from the first group of patients. The does distribution and CI for PTV were compared for plan 1 and plan 0, as well as planning optimization time. Results: The clinical target doses from plan 1 were covered well and met the clinical criteria. The doses for normal critical structures of Plan 1 were comparable to Plan0. The CI of Plan1 was increased by 0.08±0.07 and the plan optimization time was decreased significantly. The average planning time for one NPC case was reduced to about 20 minutes excluding contouring time. Conclusions: The usage of dose constraint template together with Dlrs increases the CI of PTV and improves IMRT planning efficiency without sacrificing of target dose coverage and critical structure sparing for patients diagnosed with early stage NPC.
SU‐FF‐T‐122: Investigation of Clinical Performance of Two 4DRT Techniques — RPM and Bellows System
Authors: Song Y , Mizuno K , Obcemea C
Published: April 2010

Purpose The objective of this study was to systematically evaluate the clinical performance of two 4DRT techniques, RPM and Bellows system. Materials and Methods An RPM system was mounted at the distal end of a Philips CT simulator couch. A marker block was positioned on the sternum of a newly released commercial lung phantom. A Bellows sensor was tied around the thorax of the phantom next to the marker block to ensure equal breathing amplitudes. The air pressure generated by an air pump inflated and deflated the lung phantom periodically. It also drove a spherical target in a translational fashion with an 8° rotation at the end of the motion. The performance of the two systems was investigated by applying different motion depths, 0.3, 0.5, 0.75, and 1.0, and motion patterns, sin2(x), sin4(x), and sin6(x), to the lung phantom. The pressure wave was detected by the Bellows sensor and fed into the CT scanner for 4DCT reconstruction. Results The motion wave forms detected by RPM and Bellows system were almost identical in cases of sin2(x), sin4(x), and sin6(x) with a motion depth of 1. At large depths, both systems provided equal sensitivity in detecting breathing signals. At shallow breathing depths, the wave forms detected by RPM were degraded and the peaks were somewhat flattened, while the Bellows system preserved a relatively good wave form. At extremely shallow depths, RPM failed to track the breathing motion while the Bellows system continued to perform normally, providing a superior sensitivity over the RPM. Conclusions RPM failed to detect the breathing signal when the motion amplitude became very small. Bellows System was able to track the respiratory motion continuously even when it is extremely weak.
SU‐FF‐T‐125: Commissioning of Monaco Monte Carlo IMRT Treatment Planning System
Authors: Li J , Doemer A , Cao J , Podder T , Harrison A , Yu Y , Galvin J , Xiao Y
Published: April 2010

Purpose: To commission CMS Monaco IMRT treatment planning system for clinical applications using a standard test suite. Methods and Materials: A system test including IMRT planning and plan delivery was performed for CMS Monaco IMRT treatment planning system, version 1.0.2. Four cases from TG‐119 were studied: one head and neck case, one prostate case, and two C shape cases. IMRT plans were generated with the dose goals set by TG‐119 and were compared with the plans generated using CMS XiO treatment planning system. Analysis metrics were for dose coverage, number of segments, total MU, MU efficiency, number of segments per beam, and delivery time. The IMRT plans were delivered on an Elekta Synergy linear accelerator with step‐and‐shoot technique. This linac has 4‐mm MLC. IMRT QA was performed with field by field review using a diode array device Mapcheck. Results: Monaco plans showed similar target dose coverage as XiO plans and improved organ sparing in some cases. The ratios (Monaco/XiO) of number of total segments, total MU, number of segments per beam, and MU efficiency (Dose/MU) were 0.21–0.76, 0.56–0.77, 0.21–0.50, and 1.31–1.86, respectively. The delivery time of a Monaco plan was shorter than the XiO plan having the same number of beams by approximately 33%. IMRT QA pass rates of the Monaco plans were 93.8%–97.6% for the criteria of 3‐mm, 3%, and 10% threshold, which in three cases were higher than the XiO plans (93.1%–96.6%). Conclusion: The IMRT plans from the Monaco treatment planning system showed advantages over XiO plans. These advantages include smaller number of segments, smaller MU, smaller number of segments per beam, and higher MU efficiency. Additionally, the delivery time was shorter. The QA pass rates were similar to or higher than the XiO plans.
SU‐FF‐T‐129: Comparison of IMRT Planning with Two‐Step and One‐Step Optimization: Strategy for Improving Therapeutic Gain Reducing Integral Dose
Authors: Strigari L , Benassi M , Pressello C , Abate A
Published: April 2010

Purpose: Intensity‐modulated radiotherapy (IMRT) plans are often complex and time consuming both in the optimization and delivery phase, the latter increasing the potential for dosimetric errors. The purpose of this study is to evaluate the effectiveness and efficiency of one‐step optimization with step‐and‐shoot technique as compared to conventional two with sliding windows technique optimization in inverse IMRT planning. Material and methods: The approach generally employed to generate the photon fluence maps is a two‐step process: first the optimization problem is solved generating an ideal matrix of photon fluence, then the fluence profiles are converted into a deliverable photon fluences through a sequencer software using step‐and shoot or sliding window modality of multi‐leaf collimators. Machine parameters can be considered directly in direct machine parameter optimization (DMPO) or in the conversion phase in the two step approach. The Pinnacle IMRT TPS allows both approach. One‐step plans had the maximum number of segments set at 50, 70, 90. Two‐step plans were produced using ideal fluence, with or without smooth filter, converted into a sliding windows sequence. Moreover, the plans were generated allowing or not the split of the beams. Results: All plans showed similar target coverage. Compared to traditional two‐step optimization and dynamic modality, DMPO plans resulted in lower MUs, and lower doses to sensitive structures as well as Normal Tissue Complication Probability. The total MUs and the integral dose were lower for plans with the splitted than the no splitted beams. Conclusion: One‐step optimization is an effective and efficient method for simplifying IMRT plans.
SU‐FF‐T‐135: Dosimetric and Delivery Advantages of a New 160‐Leaf MLC
Authors: Prah D , Kainz K , Peng C , Li X
Published: April 2010

Purpose: To conduct a measurement and treatment planning study on dosimetric and delivery advantages of a new 160 leaf MLC (160MLC, Siemens). Methods and Materials: The uses of 160MLC were compared with a commonly used 58‐leaf MLC (Siemens) and Cerrobend blocks. Radiation leakages and penumbra were measured using films and using a small‐size ionization chamber. A treatment planning system (Xio, CMS) was used to generate (1) isodose distributions for a series of single circular and square fields defined by the MLCs or blocks, and (2) 3DCRT plans for a pituitary adenoma case with a small target volume and closely adjacent organs at risks. Static IMRT plans for a variety of prostate and head and neck cases using Xio and another planning system (Panther, Prowess) were generated and delivered. Results: The 160MLC has lower radiation leakage (0.5% for 160MLC vs. 2% for 58MLC) and narrower penumbra (5–6 mm for 160MLC vs. 9–14 mm for 58MLC calculated between 80/20% isodose lines for a 10×10cm2 field with various MLC rotations), and slightly wider penumbra (within 1 mm) than the blocks. The dose conformity between using 160MLC and blocks determined for a series of circular fields is similar, and higher than that 58MLC. The 3DCRT plans for 160MLC and blocks are comparable and more conformal than that for 58MLC as assessed by DVH parameters. The use of 160MLC reduces the numbers of segments and MU by 13% versus the 58MLC. The average delivery time for the Prowess IMRT plans with 160MLC was 5 minutes. Conclusion: The 160MLC offers several dosimetric and delivery advantages including low leakage, narrow penumbra, conformal dose distributions similar to divergent blocks, reduced numbers of IMRT segments and MU, and reduced IMRT delivery time. These advantages lead to reduced normal tissue doses, without need of Cerrobend blocks, and improved treatment delivery.
SU‐FF‐T‐264: Applications of Optically Stimulated Luminescent Detectors in Patient Dosimetry
Authors: Reft C
Published: April 2010

Purpose: Provide some clinical applications of optically stimulated luminescent detectors (OSLDs) in radiation therapy. These include measurements of in‐vivo absorbed doses to patients receiving total body (TBI) and total skin electron irradiation (TSEI), and measurements of output factors for clinical irregularly shaped electron fields. Method and Materials: The OSLDs used are 0.7 cm diameter, 0.02 cm thick, plastic disks containing encapsulated in a light‐tight plastic holder with dimensions 2.4×1.2×0.2 cm3. TLD 100 LiF thermoluminescent detectors (TLDs) are used to compare the in‐vivo measurements with the OSLD measurements. A diode is used to measure the electron blocked field output factors (BFFs) to compare with those measured with the OSLDs. A Varian CL 2100 provided the 18 MV photons and the 6 MeV high dose rate electrons for the TBI and TSEI irradiations, respectively, and the 6, 9 and 12 MeV electrons for measurement of the BFFs for the patients' blocks. Results: The TBI patient dose measurements are made at the head, umbilicus, and feet, and for the TSEI patients dose measurements are made at eight anatomical sites from the forehead to the shin. The TLD and OSLD measured doses agreed within 1% for the TBI patients and within 3% for the TSEI patients. The electron BFF measurements ranged from 0.55 to 0.94 for 96 to 83% blocking of the open fields at source to surface treatment distances of 113 cm. Conclusion: The agreement between the OSLD and TLD measured patient doses for the TBI and TSET patients show these detectors provide accurate patient dose measurements which can be obtained 8 minutes post radiation. The agreement between the OSLDs and diode for measurement of BFFs, demonstrates that they provide an accurate and convenient method for obtaining BFFs.
SU‐FF‐T‐265: A Study On Output Factor Determination for Kilovoltage X‐Ray Beams
Authors: Kim J , Mackonis E Claridge , Hill R , Kuncic Z
Published: April 2010

Purpose: To evaluate the influence of different detectors in measuring output factors of kilovoltage x‐ray beams and compare with Monte Carlo calculated data. Method and Materials: Four different ionization chambers were used to measure output factors: the Advanced Markus, NACP, PTW Semiflex and NE 2577 ionization chambers. These were used with 2, 4 and 6 cm diameter cones and x‐ray beam energies of 50, 100 and 280 kVp. The measured output factors were determined with the ionization chamber at the surface of a water or Solid Water phantom. Output factors for each field size and beam energy were calculated using the EGSnrc/BEAMnrc Monte Carlo code and derived from backscatter factors published in the AAPM TG61 kilovoltage dosimetry protocol. The BEAMnrc code was used to derive phase space file data for each of the 2, 4 and 6 cm cones and subsequently used to determine the output factor. Results: The agreement in output factor for the four chambers was generally better than 2.5%. The largest difference was found for 2 cm diameter cone and the 280 kVp x‐ray beam. Output factors derived for the same field sizes using the Monte Carlo and TG61 data were greater than the measured output factors. For the 4 cm applicator, the agreement between measured and Monte Carlo calculated data was better than 4% but with differences of up to 10% for the 2 cm diameter cone. These larger differences at the small field size are attributed to the dimensions of the detector and the radiation field size. Conclusion: Each of the four ionization chambers were suitable for output factors for field sizes no less than 4 cm. Output factors at smaller field size require further investigation.
SU‐FF‐T‐266: Characterizing a Multi‐Axis Ion Chamber Array
Authors: Simon T , Fox C , Simon W , Li J , Palta J , Liu C
Published: April 2010

Purpose: To characterize a commercially available multi‐axis ion chamber array for use as a scanning water tank alternative. Method and Materials: The ion chamber array used in this study was the IC Profiler (Sun Nuclear Corporation: Melbourne, FL). We characterized four items of the array: reproducibility, dose linearity, backscatter response, and water tank agreement. Short and long term reproducibility's were established on a 60Co teletherapy unit (Eldorado 6; Atomic Energy of Canada Limited: Mississauga, Canada). The remaining tests were conducted with a Synergy (Elekta: Crawley, UK) linear accelerator (LINAC) operated at a nominal photon energy of 6MV. Results: Over a short time period the array displayed a maximum standard deviation of 0.55% and a mean standard deviation of 0.15%; over a long time period the array displayed a maximum standard deviation of 1.80% and a mean standard deviation of 0.76%. The array was sensitive to startup characteristics of the LINAC when operating in pulsed mode; this affected the dose linearity relative to a Farmer chamber operating under the same geometry. This effect was not observed when the array was operated in continuous mode. Both the array's central axis detector and a Farmer chamber displayed a similar increase in measured signal with increasing backscatter. However, with increasing backscatter (up to 16.6 cm) the arrays in‐beam‐profile shape changed by less than 0.7% relative to a setup with no additional backscatter. The agreement between the array and a scanning water tank differed by less than 1% in the beam. Conclusion: The IC Profiler is a viable option for water tank ‘like’ measurements. The device provides a stable platform with good dose linearity, minimal backscatter response, and uniform profile measurements. Conflict of Interest: This work was supported in part by SBIR Contract No. HHSN261200522014C, the University of Florida, and Sun Nuclear Corporation
SU‐FF‐T‐267: Total Skin Electron Therapy Skin Dose Validation Using Optically Stimulated Luminescent Dosimeters
Authors: Esquivel C , Smith M , Stathakis S , Gutierrez A , Shi C , Papanikolaou N
Published: April 2010

Purpose: Total Skin Electron Therapy skin dose validation using optically stimulated luminescent dosimeters Methods and Materials: The institution's standard of care for total skin electron therapy (TSE) follows the Stanford Technique on a Varian 2300 EX linac that treats the patient standing in six different positions. The patient stands 140 cm from the beam's isocenter. A 9MeV HDTSe electron beam delivers 200 cGy to the skin's surface up to a depth of 0.8 cm with a rapid drop‐off of dose. A 1.2 cm acrylic beam spoiler 30 cm was placed in front of the patient and a sheet of 1mm of aluminum is at the gantry head. Phantom measurements were made to determine suitability of optically stimulated luminescence dosimeters (OSLDs) for in vivo dosimetry of TSE patients. A 30×30×30 cm3 solid water phantom was placed at 100 cm SSD. TLDs, OSLDs and calibrated plane parallel ion chamber were placed at the center of the phantom under 2.1 cm of build up. A dose of 100 cGy was delivered for calibration. For validating the response of the OSLDs, both TLDs and OSLDs were located at different locations around the torso of a Rando phantom. Following the technique described above, the Rando phantom was irradiated to deliver a surface dose of 200 cGy. In addition, in vivo measurements were made for a TSE patient at seven different body points. Results: OSLD phantom measurements were 3% agreement with the ROOS chamber and 4.5% with TLDs during calibration. Skin dose validation of the Rando phantom between TLDs and OSLDs differed by as much as 5.6%. In vivo dosimetry using OSLDs for the patient agreed within 7% for TLDs. Conclusions: Results for both the phantom and patient measurements shows that OSLDs are suitable for in vivo dosimetry in Total Skin Electron beam therapy.
SU‐FF‐T‐269: Comparison of Out‐Of‐Field Doses in Pediatric Patients From Craniospinal Irradiations Using Photon, Electron and Proton Spinal Fields
Authors: Georgiev G , Followill D , Ibbott G , Kry S , Fontenot J , White A , Mahajan A
Published: April 2010

Purpose: Compare the out‐of‐field secondary doses to critical organs in pediatric patients resulting from three different craniospinal irradiation (CSI) treatments. Methods and Materials: A pediatric anthropomorphic Rando phantom was CT scanned for planning purposes following MDACC protocols. Based on the images three different treatment plans employing photon, electron and proton spinal fields, were designed. A common dose prescription for pediatric patients with CNS disease of 36 Gy to the cerebrospinal axis was used for all three plans. The photon and electron spinal fields plans were each delivered three times and the doses at several critical organ sites were measured with TLD. The proton delivery was simulated with MCNPX to calculate the out‐of‐field secondary neutron contribution to the doses at the same critical organ sites. Measured doses for all three treatments were compared. Results: In the majority of the investigated critical organ sites, the doses from the photon spinal fields were higher than from the electron spinal fields. Many of the critical organ doses beyond the spinal target were greater for the photon delivery than for the electron delivery by several orders of magnitude. The entrance doses, as well as the doses lateral to and outside of the target, were up to a factor of two greater for the electron delivery. The expectation for the proton delivery is that the out‐of‐field doses from the secondary neutrons will be less than the conventional electron and photon treatments. Conclusions: An improved clinical treatment decision for pediatric patients can be made using the comparisons between the out‐of field doses for three different treatment methods.

Work supported by CA010953 awarded by NCI, DHHS
SU‐FF‐T‐270: The Neutron Dose in the Maze and at the Maze Door
Authors: Krmar M , Kuzmanovic Z , Ganezer K
Published: April 2010

The Neutron dose was measured at the maze door of a 15 MV therapy accelerator room for three different gantry positions. Two techniques for evaluation of the neutron dose at the maze door the first by Kersey and the second by McGinley, as described in NCRP 151, were compared with measurements. Kersey's method overestimated the dose at the maze door by factors that vary from 2.8 to 5.3, depending on the gantry angle. McGinley's method showed better agreement, although it systematically underestimated the dosage by factors of 0.69 to 0.87, and is also dependent upon the gantry position.

The Neutron dose was measured in the maze, at a distance from the door of up to 5.35 m. The difference between the calculated and measured values increases systematically with the distance to the maze door. McGinley's results are much closer to the measured dosages but the rate of increase in the calculated dosages using Kersey's method is much closer to the corresponding rate of increase in the measured neutron dosages.
SU‐FF‐T‐276: Utilization of Conebeam CT to Accurately Assess TLD Placement for In‐Vivo Dosimetry
Authors: Taylor M , Nautiyal J , Lambert M , Ku L
Published: April 2010

Purpose: Assessing the predicted dose at the thermoluminescent dosimeter (TLD) location is one of difficulties when utilizing in‐vivo TLD dosimetry. Accurate dose prediction at the exact TLD location increases confidence in the measured TLD results. Method and Materials: Prior to localization and treatment, TLDs are placed according to physician's direction. A conebeam CT (CBCT) image set, in treatment position and encompassing all TLD locations, is obtained. The patient's treatment is delivered and the TLDs are sent for analysis (University of Wisconsin, Radiation Calibration Laboratory). The acquired CBCT image set is imported into the Eclipse treatment planning computer and the data set is rigidly fused with the initial treatment planning simulation CT data set. The TLDs are visible on the CBCT data set, allowing for visualization of the TLD location on initial planning CT which contains the calculated dose distribution. The calculated dose at the exact location of the TLD is obtained for comparison to the measured TLDs. Thus, the calculated dose at the exact TLD position is obtained for comparison to the measured TLD results. From 2008 – 2009, three patients underwent treatment for scalp lesions, resulting in twelve TLD measurements from the above described technique. Results: All TLD results were corrected for contribution from the CBCT acquisition. The percentage agreement of measured vs. predicted TLD doses was 0.2 ± 7.5 %. Conclusion: These results indicate that CBCT can be used to predict the dose at the exact TLD location during treatment within 10%. Additionally, CBCT removes uncertainty in TLD location on the patient at the time of exposure.
SU‐FF‐T‐278: Study of Differences in Lateral Penumbra Widths of Passively Scattered and Spot Scanned Proton Therapy Beams
Authors: Sahoo N , Martin C , Zhu X , Ding X , Arjomandy B , Ciangaru G , Gillin M
Published: April 2010

Purpose: To compare the lateral penumbra widths of passively scattered (PS) and spot scanned (SS) proton therapy beams. Method and Materials: Lateral profiles of PS and SS proton therapy beams were measured using Gafchromic EBT films at different depths in plastic water phantom. The distal ranges of the beams, spread out Bragg peak (SOBP) widths, and field sizes are kept same both for the PS and SS beams. The SOBPs in the PS beam are generated by the use of appropriate range modulating wheels, and the field size is defined by apertures of appropriate size. The SOBPs and lateral extend of the radiation field for the SS beams are generated by the superposition of single spots with different energy or range positioned in the required open field area. The air gap between the aperture and the phantom surface for the PS beam was kept at a distance typically used for patient treatment. A calibration curve was used to convert film optical density to dose. Results: The 80–20% penumbra widths for the SS beams were found to be substantially larger than those for the PS beams at all depths. The difference can be as much as 6 to 9 mm at shallow depths (< 20 cm). This difference may be attributed to the larger sizes of lower energy spots in the SS beams, which are responsible for the dose deposited at the shallower depths. It may not be possible to get sharp penumbras in SS beam like those in PS beams where the apertures are used for defining the open field area. Conclusion: Spot scanning beams have larger penumbra widths due do the inherent limitations of the spot sizes. Use of field defining apertures like the ones used in PS beam will help in reducing the penumbra widths in SS beam.
SU‐FF‐T‐284: Accurate Determination of a Linac Radiation Isocenter Using Iterative Analysis of Digitized Star Shot Images
Authors: Chi P , Du W , Yang J
Published: April 2010

Purpose: To develop an accurate method to measure radiation isocenter for linac with sub‐millimeter isocenter radius. Method and Materials: Conventional star shot film is produced for gantry and collimator radiation isocenters. The pattern of gantry rotation and collimator rotation is produced on the same Kodak XV ready pack film by placing the film at vertical, and then horizontal positions at isocenter using a carefully placed “Iso‐Align” device. The beams can be differentiated easily because of the well define length of testing beams for collimator rotation, and penetrating beams of the gantry rotations. The film was digitized and the image was enhanced to show clearly the beam edges and center line of each narrow beam using a public domain image analysis software. Each beam can be described by a linear equation that was obtained through sampling and linear regression of the beam's central line. Using iterative search algorithms and analytical calculations, the location of the isocenter and its radius were obtained. Because gantry isocenter and collimator isocenter were determined on the same image, we were able to measure the lateral deviation between these two isocenters. The impacts of beam arrangements on isocenter determination were also investigated. Results: We applied this method on a Varian Trilogy machine. A 0.2 mm radius was measured for collimator radiation isocenter. The gantry radiation isocenter was measured to be of 0.3 mm radius. The lateral distance between two isocenters was 0.3 mm. The results are highly reproducible. Conclusion: We established a method to determine accurately the radii of the radiation isocenters of a LINAC. The precision of this method had not been achievable by the traditional analysis of a star‐shot film, but it is necessary for evaluating a linac for high precision radiotherapy.
SU‐FF‐T‐285: Daily Verification of Isocenter Alignment for a New Image Guided Radiotherapy System, MHI‐TM2000
Authors: Sawada A , Kaneko S , Takayama K , Nagano K , Miyabe Y , Nakamura M , Narita Y , Kokubo M , Takahashi K , Mizowaki T , Hiraoka M
Published: April 2010

Purpose: The purposes of this study were to propose a fast verification functionality of isocenter alignment of MHI‐TM2000 and to evaluate the accuracy of isocenter alignment for long‐term period. Method and Materials: The verification of isocenter alignment was performed employing lasers, kV X‐ray imaging unit, and MV X‐ray beam unit. First, a cubic water‐equivalent phantom (100×100×100 mm) having a small steel ball at the center was placed on the couch so that the steel ball was aligned to the isocenter using lasers. For each of two orthogonal kV X‐ray images acquired by the corresponding imagers, the steel ball was segmented using a threshold value based on image histogram, and then its centroid was computed. The displacement between the center of the kV X‐ray image and the centroid denotes a positioning error by lasers. After the positioning error was corrected by the couch movement, electronic portal imaging device (EPID) images were acquired at gantry angles of 270, 0, 90, 180 degrees, respectively. The centroid of the steel ball was computed in the same manner. The displacement between the center of the EPID image and the centroid of the ball represents the beam‐axis deviation from the isocenter (beam‐axis error). Results: Daily verification of the laser positioning error and the beam‐axis error were performed from April 2008 to December 2008. The root mean square errors were 0.62 mm for laser positioning and less than 0.40 mm for beam‐axis at each gantry angle. The verification time was within three minutes. Conclusion: We addressed a fast verification functionality of isocenter alignment of MHI‐TM2000. Verification result for long‐term period have proved that the proposed method achieves significant acceleration of daily quality assurance and that MHI‐TM2000 provides isocenter alignment with high accuracy. Conflict of Interest: Research sponsored in part by Mitsubishi Heavy Industries, Ltd.
SU‐FF‐T‐295: Using a 3‐Dimensional Kernel Density Estimator For The Scoring Of Radiotherapy Treatment Volumes Against Multiple Expert Observers
Authors: Jena R , Kirkby N , Burnet N
Published: April 2010

Purpose: Several techniques exist for the numerical assessment of radiotherapy treatment volumes against a ‘gold standard’ volume, such as the conformity index. Such techniques are unable to encompass variations in clinical practice between individuals and institutions, and are ineffective in the assessment of acceptable levels of intra‐observer variation in contouring. We present a novel algorithm based on a three‐dimensional kernel density estimator (3DKDE) to produce a statistic capable of scoring a single target volume against a solution set containing multiple expert volumes. Methods & Materials: The algorithm was coded using a multi‐threaded Pascal compiler. A graphical user interface allows the operator to load multiple expert outlines into the system, calculate the solution space and visualise it in 3D. Individual volumes can then be scored rapidly against all the volumes in the solution space. As a planning exercise, 3 expert observers were asked to contour the GTV for a patient with a resected glioblastoma. Each observer contoured the case on three separate occasions. A solution space with all 9 outlines was constructed to make assessments of inter‐observer and intra‐observer variation. Results: The system provides both a mean kernel density score (k‐score), and voxel‐by‐voxel scores in the form of a k‐score histogram. Similar outlines tend to have similar mean k‐scores and k‐score histogram profiles. Outlying volumes are readily identified by the system. Direct visualisation of the solution space provides information on the conformity between different expert observers, and intra‐observer variation in contouring. Conclusion: The 3DKDE scoring tool is a valuable technique for the quantitative assessment of volume contouring whilst taking into account variation in clinical practice. Further studies are planned to assess the utility of this technique in different disease sites.
SU‐FF‐T‐298: MLC Quality Control Evaluation Combining Dynalog Files and Portal Dosimetry Using Proprietary Software
Authors: Goncalves V , Lopes CP , Sakuraba RK , Cruz JC
Published: April 2010

Purpose: MLC quality control evaluation combining dynalog files and portal dosimetry using proprietary software Method and Materials: The MLC positioning and gap precision plays an important role in the dose delivery for IMRT treatments. The MLC controller verifies the position of each leaf every 50ms, compares with the planned position and generates a log file called dynalog for each carriage. We created a dynamic MLC movement test based on the standard Picket Fence test, but without the 1mm strip and using every 120 leaves. We deliver this test in a daily basis generating the dynalog files and acquiring the portal dosimeter integrated image (PD). Proprietary software was developed in C♯ to correlate the information from dynalog files and the PD exported ASCII file. The evaluation parameters chosen for the dynalog analysis were: 99% of the control point deviations below 1mm, no beam hold off and no errors greater than 2mm. For the PD we compared a measured with a reference image using the gamma method parameters distance to agreement of 2mm and dose difference of 3%, where 99% of the points were below Gamma 1 (score) for a specified ROI. Results: During 2 months 50 dynalogs files and PD were analyzed showing that 44 of them were in accordance with the allowable values limits showing an average score of 99,8% (99,6–100%). However, 6 tests failed showing errors above 1mm and average score 93% (90–96%). It happened due to a reduction in the performance of some MLC motors that lately had to be replaced. Conclusion: The method developed can be a predictor of MLC failures in the morning quality control preventing maintenance and beam hold off's during patient treatments.
SU‐FF‐T‐300: Simple Commissioning and Quality Assurance of a Gating System
Authors: Morin O , Hsu A
Published: April 2010

Purpose: Gating systems rely heavily on technology and automation, which increase the need for quality assurance. This work develops a simple method for commissioning and quality assurance of the complete gating process. Method and Materials: A lung phantom placed on a moving platform and was imaged with CT and 4DCT. The periodic superior‐inferior motion (with adjustable frequency and amplitude) of the phantom was captured with RPM system and reflective marker block. CT images corresponding to 40%–60% expiration phase were selected for QA planning. Simple square fields as well as IMRT plans (using two different collimator angles) were simulated in the treatment planning system. The plans were delivered on a Varian 21Ex with OnBoard Imaging (OBI) capabilities. Radiographic films were inserted in the lung phantom during beam delivery. The phantom was positioned with OBI before the delivery of the plans. Each plan was delivered with and without gating for comparison. Films and dose planes from the planning system were analyzed using commercially available software, which produced dose difference and gamma index maps. Results: The geometric accuracy of dose distribution of gated treatment delivery was verified to be within 5 mm. The nearly perfect sinusoidal motion produced by the platform resulted in more superior‐inferior spread in the dose than initially planned. Intensity profiles were taken on films to document the normal amount of dose spread compared to the delivery of identical plan on static phantom. Analysis of gamma index and dose difference maps show that poor gated delivery result in increased dose outside the target volume and reduced coverage of the target. Conclusion: A rapid method to verify the accuracy of a gating process has been developed using commercially available software. The implementation and needed frequency of the test will be discussed.