bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐243: Impact of Intra‐Fractional Tumor Motion for Hypo‐Fractionated Lung Radiosurgery Using Hi‐Art TomoTherapy System
Authors: Wu H , Sourivong P , Jang S , Katz S , Massey J , Rosen L
Published: July 2007

Purpose: To investigate the effect of intra‐fractional tumor motion on the dosimetric accuracy of the helical TomoTherapy for the treatment of hypofractionated lung radiotherapy cases using the TomoTherapy Hi‐Art System. Methods and Materials: A movable phantom system was developed with the TomoPhantom, motor/gear set, and remote‐speed controller to find the impact of the breathing tumor motion or dosimetry. A pre‐selected phantom case, which simulated a case of hypo‐fractionated lung Image Guided‐Intensity Modulated Radiosurgery was used to investigate the intra‐fractional tumor motion. The phantom was moved in the superior‐inferior direction with the displacement distances of no‐movement, 1.5cm, and 3cm. Four different breathing cycle patterns (i.e., no‐movement, 3sec, 5sec, and 8sec) were used to perform measurements. The dosimetric accuracy of a clinical DQA plan was analyzed using EDR2 film and #a1SL ion chamber imbedded inside the phantom. Results: Ion chamber measurements for the four different breathing cases were within ± 2% tolerance range compared to the no‐movement case. For the longitudinal dose profile, the dose coverage for the tumor decreased as the speed of cycling increased from no‐movement to 3sec. For the 3cm displacement distance case, the Full Width at 80% and 90% Maximum for the 3‐second cycle case were reduced by 13∼24% approximately ±3∼6mm compared to the no‐movement case due to breathing. However, breathing motion model here did not play an important role in the Full Width at Half Maximum. For the 1.5cm displacement distance case, the Full Width at 80% Maximum for the 3‐second cycle case was reduced by 5% (2.6mm) compared to the no‐movement. No hot/cold spots in the treatment region were found. Conclusions: Based on this preliminary study, it appears that in order to maintain dosimetric accuracy, a minimal 6mm clinical setup margin was necessary to account for the lung motion in the longitudinal direction.
SU‐FF‐T‐244: Impact of the Isocenter Shift as a Function of Couch and Gantry Angles On the Stereotactic Radiosurgery (SRS) Dose
Authors: Fan J , Paskalev K , Li J , Fourkal E , Jin L , Lin T , Luo W , Ma C
Published: July 2007

Purpose: The most important component of the pre‐treatment QA for radiosurgery is the verification of the target position in the beam. There are some generally accepted rules for the alignment test, e.g., the positioning differences should be within 1 mm or better. However, the impact on delivered dose of the shift in different directions during gantry and couch rotation may not be the same. Detailed investigations are desired to find out the relationship between the shift functions and the final dose distributions. Method and materials: In this study, the impact on the delivered dose was evaluated by Monte Carlo simulations using an EGS4‐based code MCSIM. The code was modified for arc therapy so that it can be used to do patient dose calculation for any given arc range and couch angle. A two‐step investigation has been carried out in this research. First, several assumed meaningful shift functions of gantry and couch movement were implemented into the Monte Carlo simulation to find out the dose impact from each component. Then actual shift functions based on measurements were used to evaluate the dose change due to the isocenter uncertainties for a real machine. A SRS plan for a brain tumor (9 arcs with a 10 mm cone) was used in these simulations. Results and conclusions: Based on the results from the assumed shift functions and the measured shift functions, we found that the isodose line shift is generally less than 0.5 mm on our Trilogy and Primart, which is much smaller than the isocenter uncertainties. Also big differences were mainly found in the high dose region (>90% of the maximum dose). The isodose line shift at the typical dose prescription 2457_4level, e.g., 70% or 80%, has been reduced to 0.2∼0.3 mm, which is comparable to the imaging uncertainties.
SU‐FF‐T‐245: Impact of Volume Effect of Detectors in Multiple Points Absolute Dose and the Choice of Plane of Measurement in 2D Planar Dose Verification in Patient Specific IMRT QA
Authors: Subramani V , Rath GK , Chander S , Ganesh T , Joshi RC , Gopishankar N , JhothyBasu S
Published: July 2007

Purpose: To evaluate the volume effect of detector's in multiple points dose in small and large field IMRT verification and to compare the planar dose distribution between fixed‐fields coronal‐plane and multifield axial‐plane verification methods. Method and Materials: Patient‐specific dosimetric verification was conducted for 20 patients of nasopharynx's small‐field, SIB‐IMRT large‐field and prostate tumors. Eclipse‐Helios system, Clinac‐2300C/D linear accelerator, Med‐Tec IMRT phantom and ionchambers of 0.6, 0.13 and 0.015cm3 and MOSFET detectors were used. For each patient, 15 IMRT plans were generated. The multiple points doses were measured at multifield and fixed‐fields on‐axis, 4‐offsets and inhomogeneous points. The agreements between calculated and measured doses were found for small and large field IMRT verification. For relative dosimetry, EDR2 films, Virtual Water phantom for fixed‐fields coronal‐plane and IMRT Body phantom for multifield axial‐plane verifications RITsystem and Vidar scanner were used. The agreements between calculated and measured dose distributions between two methods were compared using various gamma criteria. Results: The agreements between measured and calculated doses using 0.6 and 0.13cm3 chambers at multifield and fixed‐fields on‐axis points were within 4.7% ±2.3. The dose differences of 6% ±1.7, 19.7% ±5.5, and 12.1% ±3.2 at offset1 to 3 points were found. The 0.015cm3 chamber and MOSFET detectors were showed the dose differences of upto 8.4% in large field verification. The mean differences in percentage of pixels passing the gamma criteria of 3mm/5% were 98.2% ±0.9 and 90% ±5.4 for fixed‐fields coronal‐plane and multifield axial‐plane verifications. Conclusions: This study is useful in evaluating the detector's response at high and low dose, outside the fields and inhomogeneous points dose verification. In offset points, 0.6cm3 is more accurate than 0.13cm3 chamber in both small and large field verification. The fixed‐fields coronal‐plane verification is more accurate, however, the multifield axial‐plane is clinically realistic method of verification and to be adopted.
SU‐FF‐T‐248: Improved Accuracy in Radiotherapy Dosimetry of High‐Energy Photon and Electron Beam Using Optically Stimulated Luminescence
Authors: Yukihara E , Mardirossian G , Mirzasadeghi M , Guduru S , Ahmad S
Published: July 2007

Purpose: The interest in the Optically Stimulated Luminescence (OSL) technique for radiotherapy dosimetry originates from its precision and advantages over thermoluminescence (TL) technique. Previously we demonstrated that a precision of <0.7% for a single measurement can be achieved using the appropriate readout methodology. In this study we used a newly designed dosimeter holder to improve the dosimeter positioning and demonstrate the accuracy of the OSL technique for determining the percent‐depth‐ dose (PDD) in a variety of photon and electron beams. Method and Materials: PDD curves were obtained with the OSL technique for 6 and 18 MV photons beams, and 6, 9, 12, 16, and 20 MeV electron beams. The OSL dosimeters placed on dosimeter holder were irradiated in water phantom at different depths. The holder is made of a Plastic Water™ frame with thin nylon strings running across the frame to support the dosimeters, improving the dosimeter positioning. The OSL measurements were performed using an automated Risø TL/OSL‐DA‐15 reader without monitoring the mass of the dosimeters or the reader sensitivity. Results: In the low‐gradient region of the depth‐dose curves the difference between the OSL and ionization chamber PDD was typically less than 1% for all beams. In the high‐gradient region, the distance‐to‐agreement was typically less than 1 mm. The reproducibility in the position of the dosimeters show that the maximum difference due to position around dmax (depths between 8 and 16 mm) was 1.1% for 6 MeV electron. Conclusion: Using accurate positioning device and proper data analysis technique the OSL demonstrated highly precise and accurate dose readings for variety of photon and electron high energy beams. These results show that OSL is a viable alternative to TLDs, offering an easy readout method and additional advantages such as the absence of dose‐rate or temperature dependence.
SU‐FF‐T‐258: IMRT Planning Comparisons Between Elekta Synergy‐S and Elekta Synergy
Authors: Guo FQ , Ho K , Wu C , Yang C , Liu T , Stern R , Purdy J
Published: July 2007

Purpose: To compare IMRT planning between Elekta Synergy (ES) and Elekta Synergy‐S (ES‐S), which has a new “beam modulator” MLC design. Method and Materials: ES‐S is equipped with a “Beam Modulator” MLC (4 mm leaf width at isocenter), which provides a maximum field size of 21cm×16cm. IMRT plans for two patients (prostate cancer and parotid cancer disease sites) were generated for both ES and ES‐S. Planning CTs were obtained using Philips AcQSim and CT data were transferred into Pinnacle3 TPS 8.0. IMRT plans for each patient were calculated with two machine models, ES‐S and ES, with minimum segment areas of 1.6×1.6 cm2 and 2×2 cm2 respectively. All other calculation configurations are the same. Dose volume histograms (DVH) were generated and exported into Excel for comparison. Results: For prostate site, PTV DVH for ES‐S demonstrates more conformality than that for ES, possibly because ES‐S has smaller segment area. However, in the low dose region, bladder and rectum DVHs show higher doses from ES‐S versus ES. This may be due to more scatter and leakage doses from MLC of ES‐S. Same trend is observed for the parotid patient. While PTV DVH for ES‐S is slightly more conformal than that for ES, doses for cord expansion, left parotid, and brain stem expansion for ES‐S are slightly higher in low dose region compared to corresponding DVHs for ES. Conclusions: Preliminary results indicate IMRT plans with ES‐S provide slightly better conformality for target volume but slightly higher doses for critical structures in low dose region. For these two sites, there does not appear to be clinically significant differences for IMRT plans between Elekta Synergy‐S and Elekta Synergy. More case example studies are planned and findings will be discussed in depth including practical considerations such as transfer of treatment plans between the two types of machines.
SU‐FF‐T‐260: In‐Vivo Dosimetry Verification of a 3D Treatment Plan Prescription Dose at a Depth Beyond Dmax Using Diodes
Authors: Roa D , Song H , Ahmad M , He Q , Al‐Ghazi M
Published: July 2007

Purpose: To provide an in‐vivo verification using diode detectors of a patient prescription dose calculated by a three‐dimensional treatment planning algorithm. Method and Materials: Three models of diodes specially designed for high‐energy photon beams (6‐MV Isorad and QED, and the 20‐MV QED diode detectors manufactured by Sun Nuclear Corporation, Melbourne, Florida) were used to measure the percent depth dose (PDD) of a 6‐MV and 20‐MV photon beams produced by a Varian 2300 C/D Linac. These diodes were not water proof and the measurements were performed at multiple depths in a solid‐water phantom. Results: The measured PDD curves agree within 2% with clinical PDD curves scanned in a water tank to depths up to 25 cm. This allows scaling of the diode dose reading measured at the patient skin to a depth inside the patient which is usually the prescription point or the isocenter for a multiple beam SAD treatment as defined in a 3D treatment plan.

In‐vivo measurements were performed on real patients. The doses scaled to the measurement depth were summed for all beams and compared with the calculated value from the treatment planning system (TPS). The treatment sites and agreement are listed below.

‐ 10 head and neck cases thus far, 0.4%–6.7% difference between calculated and measured doses,

‐ 8 pelvis cases thus far, 1.9%–6.5% difference between calculated and measured doses,

‐ 6 breast cases thus far, 2.3%–5.4% difference between calculated and measured doses,

4 chest cases thus far, 1.3%–6.7% difference between calculated and measured doses. Conclusion: An in‐vivo dosimetric method has been developed to measure delivered dose to the prescription point at a depth within the patient. Overall agreement between the measured and TPS‐calculated dose to the prescription point falls within ± 7% as recommended by the TG‐62 protocol.
SU‐FF‐T‐268: Internal Mammary Lymph Node Irradiation After Breast Conservation Surgery: Analysis for the Correlation Between Radiographic Pulmonary Change and Dose‐Volume Histogram Parameters
Authors: Kim J , Jeong K , Kim Y , Lee I , Shim S , Kim J , Suh C
Published: July 2007

Purpose: To evaluate the association between radiation pneumonitis (RP) and dose‐volume histogram (DVH) parameters and to provide practical guidelines to prevent RP in radiation therapy (RT) for breast cancer including internal mammary lymph nodes (IMNs). Method and Materials: Eighteen patients with early breast cancer who underwent partial mastectomy were involved in this study. Entire breast, supraclavicular lymph nodes, and IMNs were irradiated with total 50.4 Gy in 28 fractions. Partially wide tangential field technique and Photon‐electron mixed field technique were used. Radiological pulmonary change (RPC) was examined according to modified Arriagada classification and symptomatic radiation pneumonitis (SRP) according to RTOG/EORTC morbidity scoring scheme. DVH parameters were compared between two groups, one with grade<2 RPC and the other with grade⩾2 RPC. Results: Of the 18 patients, 8 developed RPC with grade 2 (44%) and other 10 patients did not develop RPC with grade 0 (56%). Only one patient developed SRP with grade 1. For mean lung dose (MLD), V10 (percent lung volume receiving equal to and more than 10 Gy), V20, V30, V40, and normal tissue complication probability (NTCP), means values were 21.3±1.2 Gy, 37.0±10.4%, 30.1±7.1%, 26.4±6.7%, 20.2±6.1%, and 32.5±9.1% for the group with grade<2 RPC, respectively and 23.0±3.4 Gy, 41.0±10.1%, 35.1±6.3%, 31.3±5.1%, 24.9±5.1%, and 52.9±22.7% for the group with grade⩾2 RPC, respectively. In the logistic regression test, V20, V30, V40, and NTCP showed statistically significant differences between two groups. MLD and V10, however, did not show significant differences between two groups. Conclusions: Among DVH parameters, V20, V30, V40, and NTCP could be used as predictors of RPC after RT of IMNs in breast cancer. In clinical practice, we can suggest that RPC is not likely to be developed below the values of 28% for V20, 26% for V30, 19% for V40, and 30% for NTCP.
SU‐FF‐T‐269: Intracranial Applications of IMRT Based Stereotactic Radiosurgery to Treat Multiple Or Large Irregular Lesions
Authors: Wang J , Rice R , Pawlicki T , Mundt A , Murphy K
Published: July 2007

Purpose: For multiple brain metastases, or large irregular lesions, the linac‐based multi‐arc stereotactic radiosurgery approach with circular collimators may not be feasible to provide conformal dose coverage, or to deliver treatment in a realistic time period tolerated by patient. We are reporting our experience using Intensity Modulated Radiosurgery (IMRS) to treat such intracranial lesions. Method and Materials: The frameless localization system was used for patient setup and target localization during treatment. The image fusion of MR and CT scans was used for better tumor definition. PTV margin was normally 1–3 mm. Critical structures, as well as the normal brain were delineated for optimization and plan evaluation. Fine tuned inverse optimization procedure gave satisfactory conformal PTV dose coverage and critical organ sparing. QA procedure included independent point dose calculation and planar dose verification, plus daily calibration of infrared camera vs. linac isocenter. The patient setup was guided by the infrared camera through the fine adjustment in three‐translational and three‐rotational degrees for isocenter localization. Orthogonal KV images were taken by on board imager (OBI) before treatment and the overlay of KV images with DRRs ensured the accuracy of IMRS treatment. Results: Ten patients were treated using IMRS. It was found that properly selected 8 to 12 fixed beams with a single isocenter were sufficient to achieve good dose coverage and organ sparing. Utilizing portal dosimetry and KV images provided excellent quality assurance for the IMRS plan and patient setup. The treatment time was less than 60 minutes to deliver dose of 16–18 Gy. Conclusion: IMRS treatment of multiple brain metastases or large irregular lesion enables saving of treatment time and gives the benefits of dose‐conformity and organ‐sparing, easy plan QA, and patient setup verification.
SU‐FF‐T‐270: Investigating the Temporal Effects of Respiratory Gated IMRT Treatment Delivery On in Vitro Survival: A Theoretical and Experimental Study
Authors: Keall P , Chang M , Benedict S , Thames H , Vedam S , Lin P
Published: July 2007

Purpose: Respiratory gated radiotherapy changes radiation delivery compared to conformal radiotherapy (CRT) in two ways: the beam is periodically turned on and off and treatment time is increased. IMRT also changes radiation delivery in two ways: only part of the tumor is irradiated at any given time and the treatment time is increased. The aim of this research was to experimentally and theoretically investigate the temporal effects of respiratory gated and IMRT treatment delivery on in vitro survival. Method and Materials: Four radiation delivery methods were investigated: CRT, IMRT, gated CRT and gated IMRT. Experiments were designed to isolate the effects of periodic irradiation (gating), partial tumor irradiation (IMRT) and extended treatment time (gating and IMRT). For the experimental studies V79 Chinese hamster cells were irradiated to 2Gy with four delivery methods and a clonogenic assay performed. The theoretical calculations used the incomplete repair model. The biological parameters of the model were taken from a previous publication studying V79 cells; the remaining parameters of the model were determined from the biological experiments. Results: Treatment times ranged from 1.67 (CRT) to 15minutes (gated IMRT). Survival fraction (SF) calculations ranged from 68.2% for CRT to 68.7% for gated IMRT. For the same treatment time (5minutes), gated delivery alone and IMRT delivery alone both had calculated SF of 68.3%. The experimental values ranged from 65.7(±1.0)% to 67.3(±1.3)% indicating no significant differenced between the experimental observations and theoretical calculations. Conclusion: Of the three temporal effects of radiation delivery caused by gating and IMRT, extended treatment time was the dominant effect compared with periodic irradiation (gating) and partial tumor irradiation (IMRT). Care should be taken clinically to ensure that the use of gated IMRT does not significantly increase treatment times by evaluating appropriate duty cycles for respiratory gating and the complexity of IMRT delivery.
SU‐FF‐T‐273: Investigation of the Beam Penumbra Effect On IMRT Dose Conformity and Uniformity
Authors: Lin T , Li J , Fan J , Jin L , Luo W , Price R , Chen L , Fourkal E , Ma C
Published: July 2007

Purpose: To investigate the effect of beam penumbra and intensity variation on IMRT dose distributions and to determine an optimal beam penumbra for IMRT dose delivery. Method and Materials: Differences in accelerator/MLC geometry may have a significant effect on IMRT dose conformity and uniformity. The beam penumbra is affected by photon energy, source size and the distance from the collimator to the patient. In this work, we have investigated the beam penumbral effect on IMRT dose distributions based on ten real IMRT cases (6 prostate, 2 breast and 2 head and neck) originally planned with the Corvus inverse planning system. Monte‐Carlo dose calculations were performed with different penumbra settings, which correspond to three accelerator models, Siemen‐Primus, Primart and Varian‐21Ex. A variety of beam penumbra settings were considered, including the primary and extrafocal source size and the distance from the MLC to the patient. Film measurements were performed to verify a penumbra effect model and the Monte Carlo calculations. Results: The results show that the dose for 95% of the target volume is not significantly affected by the difference in the beam penumbra. Siemen‐Primus and Primart have slightly larger geometrical beam penumbra and result in slightly larger doses to nearby critical structures. The Varian‐21Ex has smaller MLC leaves (5mm) and smaller beam penumbra but gives more heterogeneous target dose distributions (hot and cold spots). A beam overlapping model is used to explain these results. Conclusions: Smaller MLC leaves may improve dose conformity but introduce more target dose heterogeneity. The hot spots can be partially explained by the overlapping of MLC segments while larger beam penumbra can smear out the overlapping effect. An optimal beam penumbra can lead to the best target dose uniformity.
SU‐FF‐T‐274: Investigation of the Use of Transmission Type Detectors for Daily IMRT Patient Dose Reconstruction
Authors: Papanikolaou N , Eller C , Esquivel C , Shi C , Mavroidis P , Stathakis S
Published: July 2007

Purpose: To study the feasibility of using transmission type detectors for daily IMRT patient dose reconstruction and verification. Methods and Materials: Because of the complexity of IMRT there is a need for quality assurance for every patient. However, the daily delivered intensities may vary slightly from the planned ones. In this work we investigated the use of transmission type detectors and films for the verification of daily dose delivered to the patient. Films were placed at various distances from the source in air to measure the beam intensity. The fluence maps were also reconstructed from calculations of the TPS at the same planes. Monte Carlo simulations of the same geometries were performed and the intensity maps were also extracted at the same planes. Intead of film, a tray mounted transmission detector can also be used. Results: The film measurements were compared to TPS predicted intensity maps. Corrections based on the Monte Carlo study were applied to remove the electron contamination from the measured intensity maps since it was not accounted by the TPS. MC results indicate that the corrections due to the contaminant electrons can be 15 to 20% for 6MV beams. The corrected measured intensity map was used to calculate and reconstruct the daily dose to the patient using Monte Carlo. The results show good agreement between measurements using films and Monte Carlo calculations. Conclusions: Transmission detectors such as films can be used in order to compare the delivered intensity maps against the TPS predicted ones. The dose to the patient can be reconstructed using Monte Carlo based on the delivered intensity map and the dose can be potentially verified for each fraction, especially if a cone beam CT is performed daily.
SU‐FF‐T‐278: Is Monte Carlo Calculation Necessary for Prostate Patients with Hip Prostheses?
Authors: Ludlum E , Mu G , Chuang C , Xia P
Published: July 2007

Purpose: To determine whether Monte Carlo calculation should be used for all IMRT patients with metal implants by comparing the dose distributions from two commercial dose calculation engines for patients with hip prostheses undergoing concurrent treatment of prostate and pelvic lymph nodes. Method and Materials: IMRT treatment plans from four patients with hip prostheses, including two patients with bilateral prostheses, were optimized using the Corvus planning system, which calculates dose using a finite size pencil‐beam algorithm with an equivalent path‐length correction to account for tissue heterogeneities. The plans were subsequently calculated with Monte Carlo (Peregrine) for another final dose calculation. All plans were normalized and assessed based on changes in dose coverage. Results: For patients with bilateral prostheses, the dose to 95% (D95) decreased 8.7% for the prostate when calculated with Peregrine, with a corresponding decrease of 9.5% for the lymph nodes. For patients with a unilateral prosthesis, the D95 decreased 8.2% for the prostate, and 7.9% for the lymph nodes. The percentage decreases in the D5 and D20 for the bladder were 8.2% and 9.0%, and 7.3% and 8.2% for the rectum, respectively, for patients with bilateral prostheses. For patients with a unilateral prosthesis, the D5 and D20 were 13.9% and 11.0% lower for the bladder and 7.8% and 8.8% lower for the rectum, respectively. Conclusion: This study shows that IMRT plans for patients with extensive tissue heterogeneities can produce very different dose distributions, depending on the dose calculation engine used. Future studies will investigate whether the discrepancies are due to the dose calculation algorithms, or to the tissue heterogeneity correction methods. In addition, a third dose calculation engine (Pinnacle), which uses a superposition‐convolution algorithm, will be included, and phantom measurement studies will be conducted. Conflict of Interest: This research is supported by Siemens Medical Solutions.
SU‐FF‐T‐400: The Application of a Simplified Framework for the Treatment of Left Breast Cancer Using Deep Inspiration Breath‐Hold (DIBH) for Reduced Heart Dose
Authors: Guan H , Hammoud R , Pradhan D
Published: July 2007

Purpose: A simplified framework for deep inspiration breath‐hold (DIBH) was developed and used for patient simulation. This report presents the details of using the framework for left breast patient treatment. Materials and methods: For each patient, two plans were made, one with the free breathing CT and the other with the DIBH CT. Organ structures (left breast, heart and left lung) were contoured separately on each set of CT. Dose volume histograms (DVH) and dose statistics were used for comparison. Before treatment, the framework was set to patient in the same way as for simulation. Patient setup was made at DIBH such that P point's SSD (anterior) matches that from the simulation DIBH CT. Portal images were taken at DIBH and compared to DRRs generated from the DIBH CT for setup. Because the RPM inside the treatment room and that inside the simulation room had different setups, in case the DIBH amplitudes were different, the two gating threshold lines can be shifted and overlaid to the captured DIBH signal before treatment. The RPM system can guide the linac to turn on or off the radiation automatically. Results: Comparing the two plans based on two CT sets, it was found that the left breast dose coverage was similar. While the absolute DVH for left lung was higher with DIBH, the relative DVH was similar or even lower because of the much enlarged lung volume. The heart volume did not change much but the dose was appreciably reduced. One breath hold was generally enough for the treatment of each beam. We did find that the DIBH portal images matched better to DRRs generated from DIBH CT than with free breathing CT. Conclusion: The framework was successfully applied for the treatment of three left breast patients with reduced heart dose.
SU‐FF‐T‐402: The Development of a New Radiochromic Film Protocol for Three‐Dimensional and Beta Dosimetry
Authors: Griffin S , Selwyn R , De Werd L
Published: July 2007

Purpose: To develop a film‐specific correction factor for radiochromic film (RCF) when exposed to in a parallel geometry and to use this technique with three‐dimensional and beta dosimetry. Method and Materials: Radiochromic films were placed in a Virtual Water™ phantom at 100 SSD and exposed to radiation using both parallel and orthogonal exposure techniques. The dose rate was determined using an Exradin #a12 ionization chamber at 5 cm depth in the same phantom. Response curves were generated for each technique using a novel film readout protocol employing an i900 Microtek flatbed scanner and localized background subtraction. Several film readout techniques were investigated including transmission and reflective modes. All films were scanned simultaneously using a film template to ensure millimeter alignment for pre‐ and post‐irradiation scans. A correction factor was determined to account for the different response of RCF to parallel and orthogonal exposures. This correction factor was then applied to a parallel exposure to allow comparison with an orthogonal exposure from a NIST‐traceable ophthalmic applicator. The ophthalmic exposure was conducted using a certified technique. Results: The depth dose exposure method resulted in an average over response at depths > 1 cm of 5% and 15% and was proportional to film thickness. Film‐specific correction factors were determined for EBT and HD‐810 radiochromic films. Using these correction factors, the parallel exposure method was within the 3.5% uncertainty of the ophthalmic applicator. An accurate film readout protocol was essential to obtaining precise results and it was determined that the reflective black and white protocol was the most reliable and reproducible. Conclusion: A “many points” calibration method was developed using a single film exposed to in a parallel (on‐edge) geometry. This technique, along with a film‐specific correction factor, allows for improved accuracy when applied to 3D and beta dosimetry.
SU‐FF‐T‐403: The Dose‐Volume Differences by Set‐Up Error for Prostate
Authors: Lo C , Huang D , Hong J
Published: July 2007

Purpose: To simulate the dose‐volume changes by set‐up errors for prostate. Method and Materials: Patient set‐up errors consist of two parts, one for the systematic error, and one for random error. A prostate patient was treated with IMRT has 7.0mm margin in posterior and 9.0mm margin in others. To simplify analysis, the first numerical simulation was no random error present. The systematic errors had a shift of 1.0mm, 2.0mm, and 3.0mm along each axis. Next, the simulation had 1.0mm, 2.0mm, and 3.0mm standard deviation in random error only. We compared the receiving dose of the 95% volume of prostate (D95%), the volume of receiving dose more than 90% and 70% of the prescribed dose (V90% and V70%) for rectum and bladder in each numerical simulation cases. Results: In our simulation cases, the receiving dose of prostate (D95%) is more than 99.95% prescribed dose. A systematic error within 3.0mm in Rt‐Lt direction, the percent volume change of bladder and rectum (V90% and V70%) are less than 2.5%. In the Sup‐Inf direction, no large percent volume change of rectum was found. There are more than 3% volume changes for bladder in the 3.0mm shift of Sup‐Inf direction. The worse results are the percent volume change of rectum in the Ant‐Post. More than 6% volume changes for rectum in 1.0mm shift to anterior.

No more than 2.5% volume changes for bladder and rectum within 3.0mm standard deviation (SD) in Rt‐Lt and Sup‐Inf direction. Up to 3.0mm SD in Ant‐Post, rectum volume (V90%) had 5.6% changes apparently. Otherwise, random error has less volume changes than systematic error in our data. Conclusions: The rectum volume change is sensitive to systematic error in Ant‐Post direction. Set‐up should be accuracy in Ant‐Post direction than others. Also, accuracy is more important than precision.
SU‐FF‐T‐408: The IAEA Initiative to Standardize Nuclear Data for Heavy Charged‐Particle Radiotherapy
Authors: Paganetti H , Jaekel O , Lomax A , Palmans H , Molina J Quesada , Sobolevsky N , Vatnitsky S , Noy R Capote
Published: July 2007

Purpose: Protons and heavy ions loose energy via atomic and nuclear interaction processes. When simulating charged‐particle beam characteristics, for example absorbed dose distributions or secondary particle fluences, accurate physics descriptions are required. Sophisticated computing techniques, e.g. Monte Carlo, are applied for high accuracy calculations. However, the availability of high‐quality cross‐section data for the simulation of heavy charged‐particle interactions is far from being satisfactory. For example, the intra‐nuclear cascade models that are employed for cross‐section calculations are strictly valid only at high energies (>200 MeV per nucleon). Data libraries of charged‐particle interactions are needed to validate the calculations using nuclear models and for direct use in calculations. Method and Materials: The new IAEA coordinated research project on heavy charged‐particle interaction data for radiotherapy comprises of a program to compile and evaluate charged‐particle nuclear data for therapeutic applications. Plan is to review data and parameterizations for protons and heavy ions. Sensitivity analysis for different applications will be done with different codes for representative examples. The outcome will be a recommendation of preferred universal parameterization for all applications. Further, the aim is to work with code developers of the Monte Carlo codes FLUKA, Geant4, MCNPX, and SHIELD‐HIT in order to implement reference models for use in charged‐particle therapy simulations. Results: This presentation will discuss the sensitivity of nuclear interaction data for various applications in heavy charged‐particle therapy. We will discuss the nuclear interaction component in patient dose calculations, neutron background estimations, absolute dosimetry, and PET imaging for treatment verification. Based on these examples we will outline the specific aims of the IAEA initiative. Conclusion: The IAEA initiative aims at standardizing the use of charged‐particle nuclear interaction data for Monte Carlo simulations in proton and heavy ion therapy in order to improve the accuracy and compatibility of dosimetric studies.
SU‐FF‐T‐418: Therapeutic Advantage of GRID Therapy Using a Multileaf Collimator
Authors: Dou K , Hafendorfer J , Aryal P , Ashburn J , Johnson E , Meigooni A , Zwicker R
Published: July 2007

Purpose: Dosimetry of megavoltage spatially fractionated (GRID) radiation therapy using a multileaf collimator (MLC GRID) was carried out using films. Its therapeutic advantage was assessed based on dosimetric measurements by a linear quadratic model. Therapeutic advantages obtained from MLC GRIDs were compared with a Cerrobend GRID. Materials and Methods: A Varian Clinac 2100EX linear accelerator equipped with an MLC was used for the MLC GRID therapy. The two MLC GRID blocks were denoted by MLC5 and MLC10, representing 5×5 and 10×10 mm openings projected at isocenter, respectively. Cerrobend GRID blocks were used for comparison with MLC GRIDs. A linear‐quadratic (LQ) model was used to calculate the survival fraction (SF) of tumor and normal tissues. Therapeutic gain was obtained by the SF ratios of normal tissues under an MLC GRID to that under equivalent open field. Results: 5×5 and 10×10 mm GRIDS (i.e., MLC5 and MLC10 GRIDs) were created using a MLC using 6 MV and 18 MV x rays. Their dose distributions were measured at different depths using a film dosimetry. The peak‐to‐valley dose ratios at the depth of maximum dose at 100cm SSD were found to be 19% for MLC5 and 17% for MLC10. Therapeutic ratios varied from 0.9 to 45 for a wide range of tumor sensitivities at single fraction doses of up to 30 Gy. MLC10 GRID therapy showed a higher therapeutic gain than MLC5 and an 8mm Cerrobend GRID block. Conclusion: With high, single‐fraction doses, MLC GRID radiotherapy exhibited a significant therapeutic advantage over the open field radiotherapy when the tumor cells were more radioresistant. Dosimetric properties of MLC GRIDs allowed for therapeutic evaluation using a modified LQ model. One of the GRIDs investigated, MLC10 showed a great increase in therapeutic benefit compared to MLC5 and a Cerrobend GRID block with 8mm apertures.
SU‐FF‐T‐429: Treatment Planning Modeling and Dose Delivery Advantages of Standard Linac Without Flattening Filter
Authors: Bayouth J , Shukla H , Pavord D , Nixon E , Siochi R
Published: July 2007

Purpose: The objective of this study is to determine the accuracy with which treatment planning systems can model dose distributions generated by conventional linear accelerators without the flattening filter, and the potential benefits. Method and Materials: Data was collected on a Siemens Oncor linear accelerator, where the flattening filter has been removed and energy tuned to match a standard 6 MV x‐ray beam but with dose rates of 1000 MU/min. Data was acquired to model and commission four treatment planning systems (Philips Pinnacle, CMS Xio, Nomos Corvus, and Siemens Konrad). Comparisons included: TPS model parameters w/ and w/o flattening filter, measured and computed %dd and profiles, conventional and IMRT dose distributions both via planning and delivery measurements in phantom. Results: Beam energy spectrum characteristics show only a modest softening in the beam since beam tuning matched the filtered 6 MV. Differences are seen in the off‐axis fluence and off‐axis energy softening: the fluence is reduced linearly away from the central axis and the energy spectrum is only slightly reduced by comparison. Dose profiles and %dd were accurately modeled to within 2% and 2mm for all field sizes 2–40 cm. When applied to IMRT treatment plans, the model produced equivalent dose distributions for head‐and‐neck, CNS, and prostate plans; the number of monitor units was slightly increased (∼15%) but the number of segments was identical. Delivery times at 1000 MU/min were shorter (20% reduction), and the IMRT plans delivered had a 30–50% reduction in the number of pixels showing dose‐differences beyond 5%. Conclusion: Treatment planning systems are not only capable of modeling the dose distributions produced without flattening filters, they perform superior than with the filter present, and can reduce common dosimetric errors observed in IMRT phantom studies.

Research sponsored by Siemens Medical Solutions corporation.
SU‐FF‐T‐436: Using a 3D Diode Array System to Verify 3D Dose Distribution
Authors: Xue T
Published: July 2007

Purpose: We have been used a 3D diode array to verify 3D dose distributions from IMRT plans, and SRS plans using conical arcs or dynamical arcs. Some of the results are reported here. We are also going to study the possibility of using this diode array for routine QA of the treatment machine and the treatment planning system. Method and Materials: IMRT plans are developed on Varian Eclipse, and delivered on Varian Trilogy treatment unit by using sliding window technique. The SRS plans are developed on a BrainLab IPlan Dose, and delivered on the Trilogy. The 3D diode array is the Delta4 system from Scandidos. Delta4 has 1069 type Si diodes on two planes in a cylindrical PMMA phantom. In the treatment planning systems, a patient plan is copied to the phantom, and recalculated. The plan and dose distribution are transferred to the Delta4 system by using DICOM RT. In the Delta4 software, the planned dose and measured dose are compared by using 2D isodose display, profile comparisons, percentage dose deviation, and DTA and Gamma index. Results: We have used this method to verify 61 IMRT plans. The average percent diodes with deviation of 5% or less is 84.5%; the average distance to agreement (DTA) of 3mm or less is 86.7%. The average Gamma Index (5% and 3mm) of 1.0 or less is 91.8%. We have also used this system to verify the isocenter dose of BrainLab SRS plans, each using a cone from 7.5 mm to 30 mm with 180 degree arc. The average absolute difference between measurement and plan isocenter dose is 1.8%. Conclusion: The 3D diode system is a good tool to verify 3D dose distribution.
SU‐FF‐T‐437: Using a Matrix Detector for Helical Delivery QA
Authors: Woo M
Published: July 2007

Purpose: To investigate the possibility of extending the matrix detector for IMRT QA in Helical beam delivery Method and Materials: Matrix detectors, usually consisting of arrays of ion chambers or diodes, are a valuable tool for linac QA. A common method for IMRT is to irradiate the matrix with the detector plane perpendicular to the beam axis with each of the number of IMRT beams (typically 7 to 9) and the measured dose compared to the planned one. To evaluate the complete beam delivery, the individual distributions have to be combined. This is different from the standard means of using films for helical treatments as delivered by the Tomotherapy linac. In this work we want to investigate the possibility of extending the matrix detector for IMRT QA in such complex treatments. The proposed method is to configure the matrix as a phantom for setting up a delivery QA (DQA) plan, and then deliver the treatment plan beams on it as usual, taking care not to irradiate the electronics housing of the matrix. The detector plane will be designated in the DQA plan as the dose plane for comparison to the calculated one. A major concern is the angular dependency of the detectors on the direction of incidence of the radiation beams. This work aims to evaluate this limitation and to assess the usefulness of the device within the scope of this limitation Results: Preliminary measurements indicate quantitative agreement between calculated plan and measurements. More extensive results will be presented. Conclusion: The matrix detector has the potential to provide a fast QA tool for Tomotherapy and allows a dynamic view as radiation is being delivered. We propose to exploit this dynamic property to establish useful QA procedures to provide checks and analysis to a complex sequence of beam delivery.
SU‐FF‐T‐438: Using Diode Dosimeters to Characterize Dose in the Buildup Region of High‐Energy Photon Beams
Authors: Song H , Roa D , Ahmad M , Luo W , Yin F , Chen Z
Published: July 2007

Purpose: For external photon beams, the depth dependence of the stopping power ratio between air and water in the buildup region is difficult for accurate quantitative characterization. Qualitatively the depth dependence increases as the photon energy increases above the cobalt‐60 energy. As a result, the depth dependence is often ignored and the “uncorrected” percentage depth dose curves are being used in many clinics. However, accurate knowledge on dose in the buildup region is important for applications such as the tangential beam setup. This work is to look for a dosimeter that measures with ease the correct photon beam PDD curves for all depth in phantom including the buildup region and beyond. Method and Materials: The PDDs of a 10 MV photon beam at field size of 10×10 cm2 and 100 cm SSD was scanned in a water‐tank with a cylindrical (Scanditronix, RK) ion chamber, a parallel‐plane (NACP) ion chamber, and a diode dosimeter (Scanditronix, designed for photon field with back‐scatter absorber). The raw scan readings were corrected only for the effective point shifts as defined for depth beyond dmax. The Monte Carlo code EGS was used to generate the “true” PDD curve. Results: The ion chambers, diode and EGS show good agreement beyond the dmax region. In the buildup region, the diode matches the EGS curve within 3% while the two ion chamber curves differ from the EGS curve by 5% to 20%. Conclusion: A scanning diode dosimeter can be designed to generate true PDD curves, with a simple effective point correction, for both the buildup region and beyond for high energy photon beams. The ease of use afforded by such diode dosimeters would mean more availability of true PDD curves at clinic, including the dose buildup region.
SU‐FF‐T‐441: Validation of a New Serial Tomotherapy IMRT System
Authors: Pavord D
Published: July 2007

Purpose: To evaluate the function and accuracy of a new serial tomotherapy system. Method and Materials: The new nomosSTAT IMRT system from Nomos Division of North American Scientific integrates several devices into one package. The new system removes the controller box from the Mimic collimator and transfers the functions to a computer placed in the accelerator control area linked to a touch‐screen monitor inside the treatment room. The new system is connected to the CORVUS planning station by standard network cabling, eliminating the need to transfer a plan via disk. In addition to automating the multileaf collimator control functions, the AutoCrane table indexing device is now computer controlled.

The accuracy and reliability of the new system was validated. This included data transfer integrity, proper functioning of all controls, mechanical accuracy, and dosimetric accuracy. Multiple plans were transferred for both 1cm and 2cm treatment modes. Multiple table angle plans were also tested. Results: The plan data was found to be transferred accurately in all cases. The function of each control was verified as well as the ability to recover from an error. The mechanical accuracy of the AutoCrane device was found to be better than 0.1mm for the In/Out direction and 0.4mm for the Left/Right direction. The gantry angle inclinometers were found to be accurate to within 0.5 degrees when compared to an independent digital level. Two plans for each delivery width were verified with ion chamber and film measurements. The ion chamber measurements were within 3% of expected. Film dosimetry showed that at least 93% of pixels agreed within 4%, 4mm criteria. Repeat measurement of individual plans agreed within 1%. Conclusion: The new nomosSTAT system was therefore found to be acceptable for clinical treatment. Conflict of Interest: Research sponsored by Nomos Division of North American Scientific corporation.
SU‐FF‐T‐446: Verification of a Beam Model in a Treatment Planninng System Using An Monte Carlo Approach
Authors: Wieslander E , Knoos T
Published: July 2007

Todays treatment planning systems (TPSs) have to be able to calcualate the dose distribution for very complex beams, i.e. highly modulated multi‐leaf collimator (MLC) beams, to meet clinical requirements. To achieve a high accuracy it is common to separate the dose calcualtion into a beam modelling phase, describing the beam exiting the accelerator, followed by a subsequent dose calculation in the patient.

The aim of this work was to set up the Monte Carlo (MC) code system EGSnrc (incl BEAMnrc and DOXYZnrc) to study the head scatter as well as the transmission through MLC and diaphragms for an linear accelerator (Elekta Precise). These MC results are then be compared the beam model used in a commercial TPS (MasterPlan, Nucletron B.V.). Vendors data regarding the geometry of the treatment head of the linac was the basis for simulations performed with BEAMnrc. The collimation in the MLC direction consists of the leafs complemented with backup diaphragms. The characteristics of the electron beam, i.e. energy and spot size, impinging on the target have been varied to match measured data.

Phase spaces from simulations of the treatment head were used to extract the scatter from, e.g., the flattening filter and the collimating structures. Similar data for the source models used in the TPS were extracted from the treatment planning system, thus a comprehensive analysis was possible.

Simulations in a water phantom, with DOSXYZnrc, were used to study the modelling of the MLC and the backup diaphragm by the TPS. The results from this study will be helpful to understand the limitations of the model in the TPS and also providing knowledge for further improvements of the TPS source modelling.