bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐410: The Influence of Scanner Parameters On the Accuracy of Film Dosimetry: A Comparison of the Epson Expression 1680 Flatbed and the Vidar VXR‐16 Dosimetry PRO Film Scanners
Authors: Wilcox E , Daskalov G , Nedialkova L
Published: July 2007

Purpose: To investigate the properties of Vidar VXR‐16 Dosimetry PRO™ and Epson Expression 1680 film scanners with Gafchromic EBT and EDR2 radiographic films for dosimetry applications. Method and Materials: The EDR2 and EBT films are irradiated with 10 × 10 cm2 6 MV X‐ray beams in solid water. Dose calibration curves are obtained using an MLC generated stepwedge. Each EDR2 or EBT film is scanned in both vertical and horizontal orientation with Vidar and Epson scanners in transmission mode and analyzed using FilmQA™ (3cognition LLC) software. The RIT (Radiological Imaging Technology, Colorado Springs) software is used with the Vidar only. Epson scans are done without color correction in the 48‐bit RGB mode, resolution 75 dpi. The R channel image is used for analysis. Vidar scans are done with resolution 71 dpi, logarithmic and linear translation tables, and the 16‐bit grayscale image is analyzed. Results: For the EDR2 film no differences are observed for different scan orientations on either Epson or Vidar scanners with both RIT and FilmQA software. The EBT scans show no difference for different scan directions on either scanner. However, artifacts are associated with different translation tables with the Vidar while up to 2% differences are observed in the penumbra with Epson. Scanning measurement, calibration, and background films in the same direction estimates doses on central axis with 2% accuracy for both film types and scanners. However, inconsistent scan directions result in errors up to 10% on Epson and 41%‐45% on Vidar scanner. Conclusion: Calibration curve differences depend on the type of scanner, scanning mode, scanning software, and film orientation. The EDR2 on either scanner reproduces relative profiles and dose to better than 2% regardless of orientation. For the EBT the scanner parameters, orientation, and software corrections become important for accurate dosimetry results and to avoid artifacts.
SU‐FF‐T‐413: The Response Of The Fricke Dosimeter To Sunlight
Authors: Austerlitz C , Mota H , Souza V , Campos D , Gay H , Allison R , Sibata C
Published: July 2007

Purpose: To test the Fricke dosimeter response to sunlight near the Equator. Materials and Methods: Fifty cylindrical glass vials filled with Fricke solution (FS) were placed horizontally floating in a polyethylene water tank in such a way that half of their volumes were underneath the water. These vials were exposed to sunlight 5 hours per day for a period of 10 days in the city of Recife, Brazil (8°3′S, 34°56′W). During the course of the exposure the water temperature was monitored by means of a thermocouple. Every day 5 vials were removed from the water thank, and their optical densities (OD) were measured using a spectrophotometer. The OD was corrected for the mean temperature of the water tank during exposure and the solution's temperature during readout. Vials with Fricke solution were also kept in an oven for 5 hours per day at the same mean temperature as those exposed to sunlight. The change in the OD caused by the sunlight was obtained by subtracting the OD of the exposed vials from the corresponding ones stored in the oven. Both sets of vials were the stored in a refrigerator at 15°C until the next exposure. Results: The mean temperature during the irradiation was 33 ± 1.4 °C. The net OD of the Fricke solution was proportional to the sunlight exposure time with a slope of 0.0010 ODh−1 (r2=0.99). For a 50 hours exposure the net OD was 0.05 (± 5%), which would correspond to an exposure of 14 Gy from a source which produces 0.000023 M of . Conclusions: The FS is relatively sensitive to direct sunlight exposure. Because this dosimeter relies on the oxidation of to by free radicals, it could be evaluated as means to estimate the free radical exposure in humans for various sunlight conditions.
SU‐FF‐T‐414: The Study of Dose Distribution of HDR Brachytherapy for Prostate Cancer with Glass Dosimeter
Authors: Hsu S , Yeh T , Yeh C , Hong J , Kuan W , Chen W , Huang D
Published: July 2007

Purpose: Many international investigations showed that external beam radiotherapy combined with high‐dose‐rate (HDR) brachytherapy will achieve therapeutic effect for prostate cancer. Hence, it is important to determine the treatment precision of in‐vivo dosimetry. However, a number of factors could potentially lead to the discrepancy between the predicted dose and the actually absorbed dose. In this study, in‐phantom measurements simulating the HDR brachytherapy for the treatment of prostate cancer had been performed. Method and Materials: To validate our in‐vivo dosimetry system, a prostate phantom is designed. The innovative glass dosimeter (GD) and rod thermoluminescence dosimeter (TLD) were used in this study. The calibration of the dosimeter results showed the GD is a suitable dosimeter for radiation therapy dosimetry. Results: In this study, the compatibility factor (measured dose/calculated dose by TPS) was analyzed according to the locations in the phantom. For GDs and TLDs, the mean compatibility factor was 1.00±0.03 (range, 0.97 to 1.04) and 1.01±0.03 (range, 0.95 to 1.04) respectively with single source dwell position. In multiple source dwell positions, the mean compatibility factor was 0.98±0.03 (range, 0.93 to 1.02) for GDs. Conclusion: The results showed that the differences in dose between the measurement and calculation were within ±3% with single source dwell position. The measurements simulating the real clinical situations agree with the calculated values within 5%. In this study, results showed that GD displayed ideal properties for phantom‐dosimetry. Phantom‐dosimetry results show that dose delivery after CT‐based planning can be of clinically acceptable accuracy.
SU‐FF‐T‐415: The Use of Advanced Imaging Techniques for Improvement in IMRT Plan Homogeneity and Delivery Efficiency
Authors: Price R , Fourkal E , Li J , Paskalev K , Chen Y , Ma C
Published: July 2007

Purpose: Current RTOG protocols allowing IMRT delivery for prostate cancer limit the hot spot such that <2% of the PTV volume receives 110% of the prescription dose. The purpose of this work was to evaluate the effect of PTV volume on this limit. Methods & Materials: A series of 6 prostate CT data sets was chosen for varying CTV volume. The original, clinically used plans were compared to those generated by decreasing the PTV margins from our standard 8mm (5mm posteriorly) to uniform 5mm and 3mm expansions. Additional plans were generated with a reduction in the number of beam directions as well as decreased input constraints for the rectum. Our routine clinical acceptance criteria were applied to all. All plans were evaluated with respect to hot spot as well as number of segments and MU. Results: PTV reduction alone had little effect on hot spot. Reducing PTV volume and rectal input constraints decreased the hot spot for 3mm PTV expansion to approximately 2% while the additional reduction in the number of beam directions decreased the number of segments and MU on average by 30% and 23%, respectively. A review of our initial data for patients implanted with Calypso transponders indicates that the prostate drifts during treatment by >5mm and >3 mm for 19 and 103 seconds per average treatment (8–17 minutes), respectively. Conclusions: Hot spot generation appears to be a complex function of PTV volume, the number of beam directions and subsequent overlap, and the penalties applied to nearby critical structures during optimization. PTV volume alone contributes minimally for the range of volumes in this study. It is possible to deliver a more efficient and homogeneous plan through localization and PTV reduction and/or active tracking since the prostate migrates out of the volumes studied with minimal frequency.
SU‐FF‐T‐416: The Use of ModuMLC® in Combination with IG‐IMRT for Treating a Very Small Eye Tumor
Authors: Cheng C , Gao Z
Published: July 2007

Introduction: IMRT employing a conventional MLC (1 cm leaf width at isocenter) for small eye tumors may be suboptimal because of its relatively large leaf width compared to the tumor size. The combination of moduleaf (MMLC, 0.25 cm leaf width at isocenter), head immobilization and IG‐IMRT may offer a better alternative. In this study, two IMRT plans are generated for the treatment of a small eye tumor using a conventional MLC (MLC82, 1 cm leaf width), and MMLC with IGRT. Method and materials: A young patient with choroidal hemangioma was treated with a Primatom‐based IG‐IMRT technique. The size of the tumor was delineated to be 4 cm3. A total of 12 Gy in 8 fractions was prescribed to the CTV, and the dose allowed to the right lens (0.12 cm3) was constraint to ⩽ 5 Gy. Treatment planning was carried out on the KonRad inverse planning software. Two plans were generated for a five‐field setup. One was optimized for dose delivery with the MLC82, while the other is optimized for the MMLC. The patient was setup in the treatment couch immobilized with the customized mask and a bite block. Image guidance was performed with a CT‐on‐rail system. Dosimetric measurements were carried out to verify the accuracy of dose delivery for the MMLC plan. Results: The plan for the MLC82 achieves a minimum dose of 7.53 Gy to the PTV and the maximum dose to the right lens is 8.2 Gy. With MMLC, the minimum dose is 12.3 Gy to the PTV while the maximum dose to the right lens is 5.15 Gy. Dosimetric measurement for the MMLC plan yielded good agreement with calculation. Conclusion: The use of IGRT, MMLC and customized mask improves the overall dose delivery accuracy and appears to be a superior choice for treatment of small tumors.
SU‐FF‐T‐417: The Use Radichromic Film for Tomotherapy IMRT Dosimetric Verification
Authors: Turian J , Khelashvili G , Chu J
Published: July 2007

Purpose: To evaluate the adequacy of radiochromic_film/CCD‐flatbed scanner system as a tool for tomotherapy IMRT delivery verification. Methods and Materials: In this study, EBT Gafchromic film and Epson flatbed scanner were used. IMRT plans created using tomotherapy treatment planning were delivered to a phantom which incorporates the film and ion chamber. To obtain accurate and reproducible results a film protocol was setup. First the scanner was evaluated in terms of OD variations due to film position on the scanner, direction of film relative to the motion of CCD‐array, and temperature of the glass during read out. From preliminary findings, a simple protocol was developed in which each film was scanned pre/post irradiation in the same position and orientation. The time between exposure and scan was ⩾ 6 hrs. This protocol is applicable for doses ranging from 0–300 cGy. For scanning, 48‐bit RGB mode was employed and the resolution set to 72 dpi. From the resulting TIFF‐images, the red channel images were extracted, filtered, and analyzed using an in‐house film dosimetry software. Since the pre and post irradiation images were co‐registered, the background was subtracted point by point and the pixel value converted to OD. The measured dose distributions were compared with values calculated by tomotherapy at the location of the film. Comparison between measured and calculated dose distributions is expressed using the γ‐index. Results: The measured dose uncertainty with this protocol is +/− 2.0%. A 2D correction matrix was obtained to account for the nonuniformities of the film, light source, glass plates, and CCD array. For the distributions compared, the passing rates γ ⩽1.0 were larger than 90%. Conclusion: The use of Gafchromic film and an Epson scanner in conjunction with a proper scanning protocol provides an accurate and efficient tool for dosimetric verification of IMRT fields produced by serial tomotherapy.
SU‐FF‐T‐419: Time‐Delay Measurement of Phase Gated Treatment with a Varian Real‐Time Position Management System Using Computed Radiography
Authors: Hanna G , Wang Z , Yin F
Published: July 2007

Purpose: Respiratory gating systems have been developed to reduce treatment uncertainty caused by organ motions related to respiration. The time‐delay between when the gating signal is triggered and when the beam is turned on may affect the actual radiation dose delivered. In this study, we investigated the time delay for a Varian real‐time position management(RPM) respiratory gating treatment system. Method and Materials: A motion phantom with infrared markers was used to simulate a respiration signal. An infrared camera was used to observe the motion of the phantom and to plot out a true position‐versus‐time curve. Computed Radiography(CR) images were taken with a Varian Clinac 21EX at 10% intervals of the simulated breathing cycle with a 2% window. On the CR images, the center of a metal disk attached to the phantom was used to determine the measured position of the phantom relative to a stationary disk. The RPM curve and measured curve were both normalized. The RPM curve was then shifted relative to the measured curve in steps of 0.1milliseconds, and correlation between the two curves was measured at each step using MATLAB. The time shift corresponding to the greatest correlation was defined as the time delay in the gating system. Results: Three measurements were taken and averaged (arithmetic mean) to determine the time delay. The time‐delay between the actual beam‐on time and the RPM beam‐on triggering signal was found to be 0.513 ± 0.077 seconds. Conclusion: This work shows that there is a significant time delay between the gating signal and the time when the radiation beam is turned on for the Varian RPM system. The effect of time‐delay on patient dosimetry needs to be further investigated.

Partially supported by Varian research grant.
SU‐FF‐T‐420: Tomotherapy as a Solution to Minimize Dose to Critical Structures in Previously Irradiatied Areas
Authors: Ku P , Pino‐y‐Torres J , Hsieh H , Chang S , Chen W
Published: July 2007

Purpose: Patients who have had prior radiation therapy often present with recurrent/residual disease in the previously irradiated area. However, additional radiation is often not feasible because the maximum tolerated dose for normal critical organs have already been reached. We present a case of a patient with metastatic endometrial cancer who was retreated to the ninth rib/vertebral body with Tomotherapy although the spine had already received 4500 cGy. Method and Materials: A patient with metastatic disease to the ninth right rib and vertebral body was treated with 4400 cGy in 2003. The patient was recently found to have recurrent/progressive disease in the area of prior treatment. A PET scan was taken prior to treatment and an PET/CT fusion was performed in order to aid in the contouring of the tumor volume. The tumor volume(rib) wrapped around the liver and ended at the ninth vertebral body right next to the spinal cord. A Tomotherapy plan was generated to maximally cover the tumor volume while minimizing the dose to the spinal cord and liver. The positioning of the patient was verified daily with an MVCT. Results: Treatment plans generated using the Tomotherapy treatment planning system and the ability of the Tomotherapy machine to verify patient set‐up daily show that the Tomotherapy unit was able to deliver 6000 cGy to the tumor volume while only delivering a maximum dose of 575 cGy to the spine with an average of only 179 cGy. Dose the liver was kept to a minimum with an average of 1804 cGy. Conclusions: Examination of the dose volume histograms determined that the Tomotherapy unit shows was able to keep at a minimum the doses to the spinal cord and liver and surrounding structures thus making Tomotherapy a useful tool in treating patients with prior radiation.
SU‐FF‐T‐421: Tomotherapy Patient‐Specific Quality Assurance
Authors: Chaudhari S , Goddu S , Mutic S , Grigsby J , Low D
Published: July 2007

Purpose: To verify the patient‐specific dosimetric accuracy of the helical tomotherapy system. Methods and Materials: Tomotherapy is a new and complex delivery system. Varying parameters such as pitch and modulating the beam at various angles during fan‐beam delivery can produce highly conformal dose distributions. Patient‐specific dosimetric verification is thus critical. This study uses a custom‐designed 18×18×18 cm3 phantom made from water‐equivalent plastic and Exradin #a1SL ionization chambers to perform patient‐specific quality assurance (QA) procedures. During treatment, proper positioning of the patient is critical to avoid compromising treatment delivery. Tomotherapy allows roll correction to compensate for patient positioning errors. The roll correction was tested for 5°, 10°, 20°, and 30° using radiographic film dosimetry, the “cheese” phantom and the custom‐designed cuboid phantom. Results: Average ionization chamber correction factors for all patients treated on Tomotherapy were within 1.2%. Film dosimetry for every patient was also performed prior to treatment. Gamma and isodose overlay profiles were analyzed using commercial film analysis software. Results showed no significant dose delivery errors, and all patients passed within 5%. Gamma analysis was performed and showed excellent agreement by comparison with plans without phantom rotation. Gamma values were within 3.3% at 3mm and 5% distance to agreement. A custom leaf‐control file, or sinogram, is created for each patient's plan, and replicated each time the patient plan is to be delivered. Dosimetric verification for three patient plans was performed to verify the integrity of the sinogram replication process. Results for each tested plan agreement within 1% for each patient fraction. Conclusion: Tomotherapy allows for accurate delivery, and accurately applies the roll correction as shown by direct dose distribution measurements. Conflict of Interest: This work supported in part by a grant from Tomotherapy, Inc.
SU‐FF‐T‐422: Total Marrow Irradiation — Conformality, Concern, and Adaptive Process
Authors: Hui S , Verneris M , Dusenbery K
Published: July 2007

Purpose: As a part of a dose escalation total marrow irradiation (TMI) study, we have treated several patients using Tomotherapy. The purpose of this work is to critically review this new methodology in regards to conformality, uncertainty in dosimetric and treatment delivery, multimodality imaging for enhancing conformal avoidance, future adaptive processes, and clinical concerns. Method and Materials: The kVCT, MVCT, PET, and SPECT images were applied in various stages of planning, treatment delivery, boost treatment delivery, and dose reconstructions, using Tomotherapy. Delivered dose was reconstructed using MVCT and kVCT images and compared with expected dose coverage to augment futures of adaptive process. To test the conformality, bone was contoured in four different regions. Clinical concerns about patient treatment and dosimetric uncertainties were also evaluated. Results: A statistical analysis of reconstructed dose showed that a very small fraction (0.2 %) of thoracic bone volume received 10 % less than the prescribed dose. Reconstructed PTV and lung delivered dose were the same as planned dose. SPECT imaging was able to detect skeletal metastasis in one patient while MR, CT, PET failed to detect all the bone metastases. In conjunction with CT images, SPECT image sets were used to explore conformal avoidance of the brain. Treatment procedures for entire bone marrow using Tomotherapy took 80 minutes whereas hemi body marrow irradiation took approximately an hour. Conclusions: Reconstructed dose matched planning dose with reasonable accuracy except in thoracic bone. Application of the appropriate imaging modalities enhances conformality to bone marrow as well as conformal avoidance of critical organs, and also helps in dose escalation. Without the proper margin determined for bone, one may underdose the target, although treatment planning can show good DVH. Current treatment procedures are long and require improvements for patient comfort and for accuracy of the treatment.
SU‐FF‐T‐423: Transmission Properties of Aluminum and Brass Used for Solid IMRT Compensators in Megavoltage Photon Beams
Authors: Butler W , Cyr N , Kurko B , Anderson R
Published: July 2007

Purpose. The design of solid IMRT compensators requires the accurate determination of the linear attenuation coefficient, μ, of the compensating material. For clinical applications, μ is not a single value for a given material. Here we determine μ as a function of beam quality, field size, measurement geometry, and material thickness for two common compensator materials. Methods. The attenuation of brass and aluminum compensator blanks was measured for ten thicknesses ranging from 6 mm to 51 mm and for eleven field sizes ranging from 3×3 cm2 to 25×25 cm2 for each of three photon energies, 6, 10 and 18 MV. Results. The linear attenuation coefficient decreases with photon energy and is lower for aluminum than for brass. As a function of field size, μ attains a maximum value at intermediate field sizes between 5×5 cm2 and 10×10 cm2 and decreases toward smaller and larger field sizes with the lowest values at 25×25 cm2. The range of μ across the spectrum of field sizes spans 14.8% for aluminum and 17.4% for brass. Beam hardening becomes more pronounced as the metal thickness increases so that greater thickness results in a lower μ; however, this effect is less pronounced than the field size effect and varies up to 7.0% for aluminum and 12.2% for brass over the range of thicknesses studied. Conclusion. An approach that designs solid metal compensators using linear attenuation coefficients that reflect typical field sizes (and to a lesser extent the average thickness of the compensator material) for various anatomic sites will reduce the variation between calculated and measured doses when performing quality assurance checks on the compensator.
SU‐FF‐T‐425: Treatment Planning Advantages of Proton Scattered Beam and Intensity Modulated Proton Therapy Over IMRT for Pancreas Tumors
Authors: Ingram M , Kassaee A , McDonough J
Published: July 2007

Purpose: To examine potential treatment planning advantages of proton scattered beam and intensity modulated proton therapy over IMRT for pancreas tumors. Methods and Materials: Five patients with pancreatic tumors were selected. Treatment plans for the conedown phase of the treatment were developed using three different modalities: IMRT, proton scattered beam, and intensity modulated proton therapy (IMPT). The motion of the pancreas was compensated for by using margins equal to those used in IMRT planning. A dose of 1440 cGy in 8 fractions was prescribed to the target. The IMRT plan consisted of 5 coplanar fields and was developed using the Eclipse treatment planning system. The single field proton scattered beam plan was computed using the Eclipse system with an IBA proton nozzle, an aperture block, and a compensator. The IMPT plan was calculated through the use of an in‐house method utilizing GEANT4, a validated Monte Carlo method. The IMPT procedure uses a step and shoot “spot scanning” method with Gaussian beams with an initial width of 8 mm FWHM. Plan optimization for the scanning treatment was performed using the Cimmino algorithm, a feasibility method that utilizes upper and lower dose constraints. Dose distributions, dose volume histograms, and dose statistics were calculated and compared for the three modalities. Results: All plans provided similar coverage of the target. The proton scattered beam plan exhibited better dose homogeneity than the IMRT plan, while the IMPT plan produced noticeable hot spots. These hot spots are a result of the spacing of the Bragg peaks and are avoidable. Both the proton scattered beam and the IMPT plan provided significant sparing of all organs at risk compared to the IMRT plan. Conclusions: Proton therapy in the forms of both scattered beam and IMPT offers organ sparing advantages over IMRT in the treatment of pancreatic tumors.
SU‐FF‐T‐426: Treatment Planning Comparison of Dynamic Multileaf Collimation and Helical Tomotherapy for Spinal Cord Sparing in Head and Neck Re‐Irradiation
Authors: Popple R , Brezovich I , Duan J , Spencer S
Published: July 2007

Purpose: To compare dynamic multileaf collimator (DMLC) and helical tomotherapy (TOMO) IMRT delivery techniques for head and neck re‐irradiation. Method and Materials: Five cases were selected. For each case, a planning target volume (PTV) and the spinal cord were contoured. A 5 mm margin was added to the spinal cord to create a planning organ‐at‐risk volume (PRV). Plans were developed to deliver 60 Gy to 95% of the PTV while minimizing PRV dose. For DMLC delivery, 7 fields in the transverse plane were used. Plans were developed for two secondary collimator configurations, one in which the collimators were set by the optimization engine (DMLC STD) and one in which the PRV was always blocked by a collimator jaw (DMLC BLOCK). For both DMLC STD and TOMO, the optimization parameters were adjusted to minimize the PRV dose without exceeding 69 Gy to a volume of tissue >1 cc. DMLC BLOCK plans were optimized using the same parameters as the DMLC STD plans. The PTV D1cc, spinal cord D0.5cc, and non‐specified normal tissue D1cc were calculated. Results: The TOMO plans were able to both minimize the spinal cord dose and limit the hotspot. The DMLC plans were not able to limit the hotspot to the extent of the TOMO plans. The DMLC BLOCK plans achieved equivalent cord sparing, but with increased dose heterogeneity. The mean spinal cord D0.5cc, was 8.8, 16, and 8.4 Gy for the TOMO, DMLC STD, and DMLC BLOCK plans respectively. The mean PTV D1cc was 67.7, 68.6, and 71.4 Gy and the normal tissue D1cc was 65.2, 68.2, and 71.5 Gy. Conclusion: Dynamic MLC IMRT is capable of producing spinal cord sparing equivalent to helical tomotherapy. However, with current technology, the sparing is at the expense of PTV heterogeneity and larger doses to small volumes of normal tissue.
SU‐FF‐T‐427: Treatment Planning Comparison On Normal Tissue Complication Probability and Tumor Control Probability in the Preoperative Pelvic Irradiation for Rectal Cancer
Authors: Chu K , Wang L , Chao L , Huang D , Hsiao C , Yeh K , Lee Y , Yen S , Chao M
Published: July 2007

Purpose: The surgical operation to remove the tumor is the premier treatment method for rectal cancer, and the radiation therapy is an auxiliary but important way. The radiation treatments for rectal cancer include preoperative irradiation and postoperative irradiation. The purpose of this study is to compare different treatment planning techniques for preoperative pelvic irradiation of rectal cancer. The comparisons include three‐field vs four‐field (box) techniques and the treatment planning with full bladder vs post voiding bladder. Method and Materials: The different planning techniques for the same patient were compared via score function of TCP (Tumor Control Probability) and NTCP (Normal Tissue Complication Probability). The organs contoured include femoral head, intestine, and urinary bladder walls with full bladder and with post voiding bladder for the same PTV. All patients were treated with preoperative irradiation at VGH‐Taipei. These patients include 6 male and 3 female with a mean age of 51.67 (28–76). The clinical stages for all patients are stage II and III rectal cancer (AJCC T2–4 N0–2 M0). The total dose was 4500 cGy with a fraction size of 225 cGy. ANOVA (F‐test) was performed for the results analysis Results: The results from score function show the treatment with 3‐field is better than that with 4‐field. It also shows the treatment with full bladder is better than that with post voiding bladder. Conclusion: In the F test, the P value of field factor (3‐field vs 4‐field) is 0.00024. It means the field factor is a significant factor. The P value of the bladder‐status factor (full or empty bladder) is 0.59 (<0.95). It means the bladder‐status factor isn't significant. Therefore, we conclude the treatment field is a treatment planning factor, but not bladder‐status. However, we need more patients to make a much solid conclusion for the bladder‐status factor.
SU‐FF‐T‐430: Two Beam Segment‐Based Intensity Modulated Radiation Therapy for Solid Tumours of the Brain
Authors: Chin L , Laperriere N , Heaton R
Published: July 2007

We present a novel segment‐based intensity‐modulated radiation therapy (s‐IMRT) technique that utilizes a single lateral and single vertex beam for the treatment of solid brain tumours that eliminates the necessity of employing physical wedges traditionally employed for such treatments. The two beam s‐IMRT method potentially allows for streamlined treatment planning and improved dose calculation accuracy while minimizing quality assurance workload compared to conventional multi‐beam IMRT treatments. The beam segments for lateral beams were generated based on the isodose distributions of a 100% weighted vertex beam while the vertex beam were created from the isodose distribution of a 100% weighted lateral beam. Segment weight optimization was performed using the inverse planning tool of the Pinnacle 7.6 treatment planning software. Segment‐IMRT plans were compared to “best‐case” wedge‐based plans to evaluate differences in dose uniformity, target coverage, and normal tissue sparing. Five patients with solid tumours of the brain were planned for radiation therapy. Overall, the s‐IMRT approach resulted in similar dose distributions as the wedge‐based plans. However, the overall treatment planning time was significantly reduced using s‐IMRT (∼ 60 min. compared to ∼ 150 min.). With the addition of script‐based automated segment generation and optimized inverse planning parameters it is believed that treatment planning time may be further reduced to ∼ 30 min. Furthermore, it is anticipated that the elimination of physical wedges will expedite patient set‐up time for treatments while improving dosimetric accuracy.
SU‐FF‐T‐432: Uncertainty of Dose Calculations with Pencil Beam and Convolution Superposition Algorithms for Stereotactic Treatment of Lung Lesions
Authors: Schell M , Clark D , Liu H , Fu  , Kennedy R , Rosenzweig D
Published: July 2007

Purpose: Tissue heterogeneity perturbs the electron fluence at heterogeneity interfaces. Thus, the dose delivery to lung lesions ranging from 6 mm up through 30 mm in diameter is compromised since the dimensions of the lesions are comparable to the range of the secondary electrons in lung and air. Dose perturbations are evaluated for a range of lesion diameters in lung equivalent phantom material. The impact of the dose algorithm limitations on RTOG protocol requirements is addressed. Methods and Materials: Spherical lesions of 6.4, 12.5, 19.7, and 25.4 mm in diameter and unit density were inserted into lung equivalent material (0.3 g/cm3). The dose distributions were measured with film densitometry and calculated with the dose calculation engine of the ADAC Pinnacle system and the Analytical Anisotropic Algorithm (AAA) and PB algorithm implemented in Varian's Eclipse (v. 7.3.10) treatment planning system (TPS). The Pinnacle TPS uses the adaptive convolution superposition algorithm, which rigorously reproduces x‐ray beam attenuation, and the electron fluence changes at tissue heterogeneity interfaces. Results: The spherical tumor phantoms were irradiated with beam margins of 0, 7, 10, and 25 mm. Dose volume histogram analysis was performed to determine the minimum dose delivery to each lesion as a function of margin size. The pencil beam algorithm overestimates the minimum tumor dose by 5–10%. The Pinnacle and AAA dose calculations agree with the film Dosimetry Conclusion: It was determined that a 7 mm margin for all lesion diameters delivers a minimum tumor dose of 94 % of the prescribed isocenter dose for all lesion diameters. The pencil beam algorithm overestimates the PTV dose by 20% whereas the adaptive convolution superposition and AAA algorithms satisfy the requirements of RTOG 0236.
SU‐FF‐T‐433: Universal Survival Curve and SBRT Hypofractionation
Authors: Timmerman R , Park C , Papiez L
Published: July 2007

Purpose. Available clinical outcomes show that stereotactic body radiation therapy (SBRT) is very efficacious and well tolerated. At the same time, these outcomes show that standard linear quadratic (LQ) models do not provide adequate rationalization for the SBRT hypofractionation. The aim of this analysis is to show that multitarget model can be adapted to provide the proper framework for explaining the radiobiological rationale of the hypofractionated SBRT. Method. Multitarget model leads to a formula defining a curve on the plane characterized by three free parameters with the following geometric interpretation: the initial slope (1/D1), the final slope (1/D0), and quasi‐threshold dose (Dq), which is the D‐intercept of the line defined by the terminal portion of the curve (D denotes the dose). In the range of ablative dose values characteristic for SBRT (8 – 30 Gy) only the final slope (1/D0), and quasi‐threshold dose (Dq) are of clinical relevance. Assuming that the LQ model gives a good description of the survival curve for conventionally fractionated radiation therapy (CFRT), and insisting on the linear, multitarget model type behavior of the survival curve for the high dose per fraction, we construct a universal, survival curve for the arbitrary range of dose per fraction. The additional constraints require the smooth, consistent transition for the universal curve in the dose range separating CFRT and SBRT and demand quantitative consistency with existing data. Results. From universal surviving curve, we derive, for both CFRT and SBRT, two equivalence functions, biologically effective dose (BED) and single fraction equivalent dose (SFED). We find that SFED is the critical parameter for comparison of SBRT regimens as well as for comparison of CFRT and SBRT regimens. Conclusion. The unifying survival curve provides empirically and clinically well justified rationale for the hypofractionation regime of the SBRT treatment modalities.
SU‐FF‐T‐434: Urethra Identification in CT Images Based On 3‐D Model Construction
Authors: Song Y , Song Y , Obcemea C , Muller B , Mychalczak B , Burman C
Published: July 2007

Objective: Prostate IMRT treatment planning requires dose constraints on urethra to minimize acute urinary morbidity under dose escalation or followed by seed implant brachytherapy. However, it is difficult to identify it in CT image since its density is very close to those of the surrounding tissues. Here, we present a novel 3‐D model of urethra in voxel space based on anatomy data and mechanical consideration. Materials and Methods: A urethra model is constructed with a 512×512×50 grid. The first part is embedded in prostate gland and the second part is described as a free suspended string. Since CT images are acquired with the patient lying prone, prostate gland will descend anteriorly due to gravity, resulting in the first part of the urethra model being slightly convex. Assuming that the tissues outside the prostate are uniform, the second part of the urethra will suspend like a string with two ends fixed. From mechanics, the string follows equation
urn:x-wiley:00942405:media:mp1159:mp1159-math-0001 where C1,C2,C3, and C4 are constants determined by the known anatomy data, like prostate size and urethra length, in this voxel space. Considering the statistical uncertainty for each individual patient and this model's simplification, we set a 10 pixel tolerance as the urethra diameter. Results: This model urethra intercepts each slice of CT images with an area that varies in size and location. These intercepted areas will be used as the urethra contours for treatment planning. The urethra volume segmented this way is more accurate than the current manual delineation by visual observation only. Conclusions: The method developed here may be a feasible approach to those organs that human eyes can hardly distinguish from their background in CT images such as the rectum. Its utility in IMRT treatment planning needs to be further explored.
SU‐FF‐T‐435: Use of a Two‐Dimensional Ionization Chamber Array for Proton Therapy Quality Assurance Checks
Authors: Arjomandy B , Sahoo N , Gillin M , Zhu X
Published: July 2007

Purpose: To investigate the characteristics and the suitability of a two‐dimensional ion chamber array detector for proton therapy quality assurance dosimetry measurements. Methods and Material: Matrixx (Scanditronix‐Wellhofer, Bartlett, TN) is equipped with 32 × 32 parallel plate ion chambers with 4.5 mm diameters and separation of 7.5 mm. The water equivalent thickness (WET) for buildup material was determined by measuring the shift of the location of 90% distal dose point measured using plastic water relative to the depth dose measurement in water tank using a Markus chamber. The measured WET of the build up material was found to be 3.9 ± 0.1 mm. The device was used to obtain the profiles and isodose distribution for the patient portals at different depths. The dose distribution calculated by the Eclipse Treatment Planning Systems (TPS) was imported to Matrixx for comparison purpose. The Matrixx was also used for the determination of absolute dose at a calibration point and the monitor units to be used for patient treatment. Results: The point dose measured by Matrixx was found to be within 1% of that measured by a Framer type chamber. However, the penumbra width for open field for 250 MeV measured with matrix was 1.58 cm as compare to 1.24 cm measured in the water tank using a PTW pinpoint chamber. This significant difference in penumbra width is mainly due to the large inter‐chamber separation in Matrixx. The measured 2‐D dose distribution by Matrixx agreed well with that from TPS. Most of the differences in the separation of a given isodose line were within 2mm. Conclusion: The device is found to be well suited for measurement and verification of proton therapy dose distribution of patient treatment fields. Measurements are in real time, which makes this device more convenient compare to film dosimetry.
SU‐FF‐T‐439: Using Electron Beam Modifiers in the DPM Monte Carlo Code for Electron Beam Treatment Planning
Authors: Tyagi N , Tien C , Curran B , Fraass B
Published: July 2007

Purpose: To investigate the feasibility of modeling patient‐specific beam modifiers for electron beams using the DPM MC code. Methods and material: We investigate the applicability of modeling a beam modifier ‘applicator’(vs. a multiple source model or beam fitting approach) inside the DPM code for electron beam dose calculation. DPM is only used for in‐phantom calculations; however, we have included beam modifiers such as Jaws, MLCs and now applicators within the code to improve its clinical applicability. Varian 21EX (Type III) was modeled for beam energies (6, 9 and 12 MeV) using the BEAMnrc MC code. The patient‐independent components were simulated once and the phase space (PS) is stored just below the ion chamber. As a first approximation, a preliminary model of the applicator blocks all the particles through the applicators but allows those in the open beam region. Verification of the beam modifier model with diode measurements and full PS simulations was performed using percent depth doses (PDDs) and profiles for various energies for the standard 15×15 cm2 cutout, and for square and rectangular cutouts from 4×4 to 25×25 cm2 in a homogeneous geometry. Results: PDD calculations with DPM beam modifiers showed agreement within 2% with measurements and full PS simulation for the 6MeV beam. The 9 and 12 MeV PDD calculations showed discrepancies up to 4% in the surface buildup region, and a slightly larger difference in the tail. A full 3‐d simulation currently takes roughly 10mins on 8 processors to achieve a relative uncertainty of less than 1% in voxels > dmax/2 using a 2×2×2 mm3 voxel size. Conclusions: Preliminary investigation of dose calculations with beam modifiers in DPM MC code shows good agreement with measurement. Future work will focus on modeling 16 and 20 MeV beams and their verification in a homogeneous and heterogeneous medium.
SU‐FF‐T‐440: Validation of a New Radiochromic Film Calibration Protocol and a Gel‐Based Phantom for Beta Dosimetry Applications
Authors: Selwyn R , Holmes S , Micka J , Thomadsen B , DeWerd L
Published: July 2007

Purpose: To validate a new film calibration protocol and a gel‐based phantom for use in beta dosimetry by comparing the dose rate measured from a single seed to Monte Carlo simulations. Method and Materials: Two acrylic boxes were constructed and a catheter hole was drilled 2 mm below the surface of one box. A single lumen catheter was placed through the hole and both boxes were filled with porcine gel (90% water and 10% gel). After the gel solidified, a single seed was loaded into the catheter and a sheet of HD‐810 radiochromic film was sandwiched between the two box halves. A Microtek flatbed scanner, an ophthalmic applicator, and a background subtraction technique were used to readout and calibrate the film. A validated Monte Carlo code simulated the seed, phantom, and film geometry. To verify the Monte Carlo simulation, the output was compared to previously published data. Since Monte Carlo provides the dose per starting particle, a highly accurate and precise nondestructive assay of the source seed was required to calculate the absolute dose rate. The recently updated internal pair production branching ratio for and a high‐purity germanium detector were used to assay the seed. The efficiency for detecting 511 keV photons was determined using a certified solution. Results: The dose rate measured with film was 2.70 Gy/min ± 4.7% using a region of interest (ROI) of 0.5 mm × 0.5 mm. The Monte Carlo calculated dose rate was 2.75 Gy/min ± 5.1% for the same ROI using a measured seed activity of 2.64 mCi. Conclusion: Overall, there was a 1.8% difference between the film dose measurement and the Monte Carlo‐based calculation. Together, the HD‐810 radiochromic film, the calibration protocol, and the gel phantom were shown to provide accurate beta dosimetry.
SU‐FF‐T‐442: Validation of the Monte Carlo Model of the Passive Scattering Nozzles at the Proton Therapy Center Houston
Authors: Titt U , Sahoo N , Zhu R , Ding X , Zheng Y , Gillin M , Mohan R
Published: July 2007

Purpose: To validate a Monte Carlo calculation model, simulating the passive scattering nozzles in the Proton Therapy Center Houston (PTCH). Methods and Materials: The passive scattering beam lines at the PTCH use three different snouts for small, medium and large treatment fields. Each snout is used with eight different range modulator wheels to produce flat spread out Bragg peaks (SOBPs) at various proton energies. MCNPX is currently used to simulate the passive scattered proton beams at the PTCH for various research and clinical projects. The validity of the model is crucial and it has to be demonstrated, that the simulations are in agreement with measured data. Proton beam data, measured for commissioning purposes, were compared with the results of Monte Carlo simulations. Tolerance criteria for acceptable agreement was chosen to be 3% dose difference in high dose regions and 2.5 mm distance in high gradient regions. Results: 32 SOBPs and 79 lateral profiles have been compared so far. In three cases, maximum dose differences (in high dose regions) were found to be 3.0 % and one simulated penumbra was found to differ by 2.1 mm when compared to the measurement. Differences for all other cases are below the tolerance level. Conclusion: The Monte Carlo simulation model of the passive scattering nozzles of the PTCH is found to be accurate for the investigated energies and field sizes.
SU‐FF‐T‐443: Validation of Tomotherapy Machine Matching Procedure at the University of Wisconsin
Authors: Jaradat H , Paliwal B , Tome W , Mackie T , Mehta M
Published: July 2007

Purpose: To verify and validate an in‐house developed procedure used to readily transfer treatment plans between two tomotherapy machines without the need to re‐optimize the plan. Easy patient transfer between tomotherapy machines provides smooth patient flow in the clinic and reduces the time needed to complete patients' treatments as scheduled. It also reduces the possibility of introducing errors in the transfer of patients from one machine to another. Method and Materials: Two tomotherapy Hi‐ART machines: Tomotherapy I, running software version 2.1.0.2 and Tomotherapy II running software version 2.2.1.2 (TomoTherapy Inc. Madison, WI.). The Tomotherapy planning was used for comparing treatment plans. The Delivery Quality Assurance (DQA) module of the tomotherapy planning software was used to compare delivered dose to films within the Tomo phantom to the calculated dose from the plans. Results: Comprehensive tests using film and ion chamber dosimetry show that the beam model is true representation of both machines within measurement uncertainty. DQA procedures show that transferred plans are delivered accurately within IMRT acceptable limits (3% of prescribed dose and 3mm distance to agreement). Conclusion: Using this approach the two UW tomotherapy machines were found to be similar and can deliver the same treatment plan within tolerances acceptable by IMRT treatments. On several occasions, tomotherapy treatment plans were transferred between the two tomotherapy machines to avoid treatment cancellation. Tomotherapy treatment plan transfer is accomplished within a reasonable time frame (5–10 minutes per plan) without changing the final outcome of the plans. Conflict of Interest and Disclaimer: R. Mackie has financial interest in TomoTherapy Inc., and potential conflict of interest. The procedure and methods presented here are solely developed by the University of Wisconsin physics for internal use. TomoTherapy Inc. did not participate in this study and they do not support or recommend the procedure presented here.
SU‐FF‐T‐444: Variability of EDR2 Dose Calibration Films Taken for IMRT Dose Verification
Authors: Kuo IL , Ding L , Urie M , Lo YC
Published: July 2007

Purpose: To report the consistency of EDR2 calibration films taken for IMRT absolute dose verification. Method and Materials: 180 sets of dose‐optical (OD) calibration films for IMRT dose validation were taken on 4 Linacs on two campuses using Kodak EDR2 film from Nov. 2005 to Dec. 2006. Each calibration datum contained at least 5 dose points (i.e. 0 cGy, 60 cGy, 120 cGy, 180 cGy and 240 cGy). All calibration films were processed on the same Kodak film processor, were scanned with the same Vidar 1600Pro film scanner, and analyzed using RIT dosimetry software. A second order polynomial function was applied to create the H‐D curve using averaged dose‐OD data from each Linac separately. The range of dose variation (maximum, minimum and standard deviation) was determined. Results: Overall, one standard deviation of the OD corresponded to ±5.3 cGy at 60 cGy, ±8.1 cGy at 120 cGy, ±11.1 cGy at 180 cGy, and ±11.7 cGy at 240 cGy. The maximum and minimum recorded OD numbers of 180 cGy dose point corresponded to 221.4 cGy and 152.5 cGy respectively. Variability was greater for the films taken at one campus and transported (usually overnight) to the main campus for processing and analysis. Had a single dose point film (e.g. 180 cGy) been taken, dose errors (2 SD) of ±24.4 cGy at 240 cGy and ±16.5 cGy at 120 cGy would have occurred. There was no correlation of consistency with processor service. Conclusions: The OD calibration curves with EDR2 film varied significantly, not only in absolute OD value but also in curvature. In order to achieve +/−3% accuracy for IMRT dose verification films, EDR2 calibration films must be taken for each set of IMRT films.