bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐159: Determination of the MLC Scatter, MLC Transmission and Dosimetric Gap in Dynamic IMRT as a Function of Field Size, Depth and Beam Energy
Authors: Zygmanski P , Rosca F , Kadam D
Published: July 2006

Purpose: To develop a dynamic MLC test for the determination of the MLC scatter, transmission and dosimetric gap for large field size and complex geometry IMRT. Materials and Methods: A series of dynamic MLC tests was designed and performed with ionization chamber in a solid water phantom as a function of field size, depth, MLC gap size for 6,10MV 2100Ex: open beam (OB), closed MLC (cMLC), and dynamic sweeping gap (dMLCgap). Based on a generalized fluence model, MLC scatter, direct MLC transmission (no scatter) and dosimetric gap (due to rounded leaves) were determined. IMRT planning system predictions and measurement doses were compared at the central axis and outside of the field edges. Dose errors were corrected using the generalized fluence model. Results: MLC scatter is responsible for field size dependence of cMLC‐to‐OB dose ratio (1.45% for size=5cm×5cm, 1.8% for size=14cm×30cm, 6MV). MLC scatter is rather uniform within and outside of the field edges, and decreases only slightly with depth. Direct MLC transmission (no MLC scatter) changes with depth up to 10% (6MV), 5% (10MV) due to beam hardening. In dynamic MLC delivery, MLC scatter is significant for large field sizes (14cm×30cm) and low average fluence 〈φdMLC〉: MLC scatter=1%–5% for clinically realistic 〈φdMLC〉 =30%–10%, (〈φOB〉=100%, 〈φcMLC〉 ≈1.5% by definition). Dose errors of 1%–8% for large sizes and sweeping gaps 1.0cm–0.1cm were corrected when the modified fluence model (including MLC scatter) was used instead of the Eclipse fluence. Conclusions: Many commercial IMRT planning systems do not account for the MLC scatter. It is suggested that the OB‐cMLCd‐MLCgap test be used for commissioning of the IMRT when field sizes are large and average fluence 〈φdMLC〉 is low. MLC parameters in IMRT planning system may need to be adjusted separately for each IMRT class depending on field size and fluence complexity (or 〈φdMLC〉).
SU‐FF‐T‐162: Development of a Patient‐Specific Lung Phantom Using 3D Imaging and Rapid Prototyping
Authors: Hanlon J , Oakley M , Bednarz B , Xu X George
Published: July 2006

Purpose: Physical human phantoms have been widely used in verification of external radiotherapy treatment plans, study of exposures outside of the target regions, and calibration of whole‐body counter for nuclear medicine procedures and for radiation safety bioassays. Existing phantoms are mostly crude in anatomical representations, although realistic 3D images of patients are available. This paper presents a method of fabricating a physical phantom of the lung using patient‐specific medical images and computer aided design (CAD) and manufacturing (CAM). Methods: Medical images have been used to construct the VIP‐Man model from Visible Human images. The voxelized data from the lung of VIP‐Man were translated into 3D polygon mesh models. The models were then corrected and scaled to the actual size of the organ. A 3D rapid prototyping machine (i.e., a 3D printer) was used to develop a physical mold of 3D polygon mesh lung. The mold was filled with lung tissue‐equivalent foam, which matched the density and effective atomic number of the lung tissue. Results: Using the methods described above the lung of the VIP‐Man model in STL format was used to fabricate an identical 3D tissue‐equivalent phantom. Conclusions: A method has been developed to rapidly prototype physical lung phantoms using CAD and CAM capabilities. Currently, there is no method that automates this complicated process of creating 3D organ phantoms. A major research effort in this task is to develop an integrated software method that will streamline image processing and 3D printing.
SU‐FF‐T‐163: Development of An Inverse Optimization Package for Non‐Uniform Dose Distribution Based On Spatially Inhomogeneous Radiosensitivity
Authors: Chen G , Ahunbay E , Li X
Published: July 2006

Purpose: To develop an inverse optimization algorithm that is capable of generating non‐uniform dose distribution with sub‐regional dose escalation based on spatially inhomogeneous radiosensitivity in the target, while keeping the critical structure doses as low as possible. Method and Materials: A matlab package with GUI was developed. The software system reads in structure contours, reference 3D‐dose distribution (e.g., conventional uniform dose), dose to each voxel from all beamlets, as well as the voxel radiosensitivity from biological images. This system is able to optimize beamlet weights based on sequential quadratic programming (SQP) method to achieve maximum equivalent uniform dose (EUD) for target and minimum EUD for critical structures. The beamlets were generated using a commercial planning system (XiO, CMS). The EUD was calculated based on 3D‐dose distribution and spatial radiosensitivity distribution which is extracted from biological images. Constraints that limit the doses to critical structures not to exceed the corresponding maximum for the reference plan are applied. Sample spatial radiosensitivity distributions based on physiological MRI of brain tumor were used to test the developed system. DVHs and EUDs for the uniform and non‐uniform dose distributions are compared. Results: Using the newly develop system, we have generated non‐uniform 3D‐dose distributions for selected patient cases. Sub‐regional dose escalation can be as high as 30% of the uniform dose as planned conventionally. The target EUDs are found to be higher than those for the uniform dose planned ignoring the spatial inhomogeneous radiosensitivity. The EUDs for organs at risk are found to be equal or lower than those for the uniform dose plans. Conclusion: We have developed a package that is capable of generating non‐uniform dose distributions optimized for spatially inhomogeneous radiosensitivity. Sub‐regional dose escalation may lead to increased treatment effectiveness as indicated by higher EUDs. The current development will impact biological image guided radiotherapy.
SU‐FF‐T‐166: Different Method of IMRT Planning for Breast Treatment
Authors: Khalifeh A , Abdulhay I , Elasmar H
Published: July 2006

Purpose: To compare three different methods of IMRT planning for breast treatment. Method and Material: Breast IMRT plans are conducted for several Patients using Pinnacle PHILIPS system. Three IMRT methods have been utilized; the first is Forward Planning (FP) technique using segment weight optimization for selected set of objectives such as GTV, PTV, lung, heart, etc. The second method is Inverse planning (IP) technique using Direct Machine Parameters Optimization (DMPO) with same objectives used in FP plus an extra segment to account for flash. The third is IP technique using DMPO with same objectives used in FP plus an extra objective called “Flash Planning Target (FPT)” defined by expanding the PTV by 2.5–3.0 cm in the interior direction of the breast depending on the required amount of flash. The “FTP” objective is defined as a uniform dose with 80% or higher of the prescribed dose with an extremely minimum dose in the order of 1E‐15. “FPT” objective is included in the DMPO to generate sufficient flash (due to breathing parameter) which could not have happen without including this objective in the IP optimization. Comparing all methods, IP technique using the two DMPO methods will allow having a Flash for most of the treatment without defining segments and they will give better coverage of the breast from the superior and inferior direction with better controlling the dose to the surrounding organs. Results: Using the “FPT” objective along with DMPO techniques provide the open segment higher percentages for each beam with some other segments generated by Pinnacle not by the planner are superior over FP method. Conclusion: Inverse planning techniques using DMPO technique mentioned above will give a better coverage of the breast from the superior and inferior direction with better controlling the dose to the surrounding healthy tissues.
SU‐FF‐T‐167: Digital Data Integrity QA for Multi‐Institutional Clinical Trials
Authors: Straube W , Bosch W , Matthews J , Haynes R , Purdy J
Published: July 2006

Purpose: The Image‐guided Therapy QA Center (ITC) as part of the NCI‐sponsored Advanced Technology QA Consortium (ATC) has nearly 15 years experience in performing data integrity QA review for multi‐institutional advanced technology clinical trials that require digital data submission. This presentation will report on that experience. Method and Materials: Participants in some advanced technology multi‐institutional clinical trials must be able to submit imaging data as well as RT objects (CT, RT Structure Set, RT Dose, and RT Plan) to the ITC for protocol compliance QA review of contoured volumes and dose coverage/heterogeneity. Data are sent via FTP or on media. However, prior to that QA review, experienced personnel at the ITC carefully review each digital data set in regard to completeness of protocol required elements, format of data, and possible data corruption. Results: Thus far over 3000 data sets have been submitted to ITC. Unfortunately, data often need resubmission due to problems discovered by ITC. Errors in submission can be divided into five categories: 1) misuse of UI of treatment planning system (TPS), 2) misunderstanding of protocol requirements, 3) non‐uniformity of DICOM export implementations by TPS vendors, 4) user error with digital data transfer software, and 5) updated TPS software, whose data export feature no longer is ATC compliant. Statistics of number of resubmissions required as well as specific details of these problems will be presented. Conclusion: Digital data submission of complete 3D data set is essential for QA of advanced technology clinical trials. However, collection of these data requires review and troubleshooting by experienced personnel to ensure subsequent protocol compliance QA and later still, quality data analysis. A significant portion of the ITC workload involves digital data integrity QA to ensure quality of submitted digital data. Support: NIH U24 Grant CA81647.
SU‐FF‐T‐169: Dose Calculation Accuracy in the Presence of High‐Z Materials Using Megavoltage CT for Treatment Planning
Authors: Hecox R , Gibbons J , Followill D , Ibbott G
Published: July 2006

Purpose: Verify the accuracy of the dose calculation algorithm in the presence of a hip prosthesis when planning with megavoltage CT (MVCT) images of the TomoTherapy Hi‐Art II planning system. Methods and Materials: Artifacts from imaging high‐Z materials are greatly reduced in MVCT compared to kilovoltage CT (kVCT). This may allow more accurate treatment planning for patients with metallic implants. The Radiological Physics Center's (RPC) pelvic phantom was modified to accommodate a commercial Co‐Cr‐Mo hip prosthesis and imaged with both kVCT and MVCT. On the TomoTherapy Hi‐Art II planning system, the MVCT‐to‐density table was extended to high‐Z materials by including stainless steel and lead in the calibration. Contours were drawn on kVCT images without the prosthesis present and fused to the MVCT image set. Helical tomotherapy plans were created using the MVCT images with no constraints on beam entry or exit location. The delivered dose distribution was measured using TLDs in the PTV and EBT radiochromic film in the coronal and sagittal planes. Criteria based on TG‐53 recommendations were used for comparison between measurements and calculations. Results: Dose calculation with MVCT images resulted in minor variations between calculated and measured dose. It was found that on average 97% of the dose distribution measured with film agreed with the treatment planning system to within +/−5% or 3mm. Profiles across the PTV also showed good agreement between measurement and calculation. The average TLD dose at the center of the PTV was 96.0% of the expected dose. Conclusion: Using dose calculations based on MVCT images, it is possible to accurately calculate the dose distribution in the pelvic region while treating through a high‐Z prosthetic implant. Work was supported by PHS grant CA10953 and CA081647 awarded by NCI.
SU‐FF‐T‐170: Dose Delivery to Curved Structures in Intra‐Operative High Dose Rate (IOHDR) Brachytherapy
Authors: Oh M , Wang Z , Malhotra H , Jaggernauth W , Podgorsak M
Published: July 2006

Purpose: To investigate the magnitude of overdosage / underdosage for curved surfaces in intra‐operative high dose rate (IOHDR) brachytherapy when the original treatment plan assumed a planar geometry. Method and Materials: The archived IOHDR brachytherapy treatment plans of 5 cases were used in this study. Plans of 3 patients treated in our facility were chosen for the different treatment surface areas and two plans with square fields were developed to compare with irregular shape of clinical cases. Phantoms with four various radii (5 cm to 13.5 cm) were used to simulate the treatment planning geometries which were calculated in 2‐dimensional plans. EDR2 radiographic film dosimetry was used to evaluate the dose distribution for each case. Each film was digitized with 0.17 mm resolution using a film dosimetry system and converted to dose. Results: A 2‐D planar implant was designed to deliver a dose of 200 cGy to the prescription depth. This implant applicator was then wrapped around curved phantoms of different radii and the identical treatment was delivered for each curved structure. However, the actual doses delivered to the prescription points were about 9 % (5.5 % for small treatment area − 3 catheter × 4 cm2) higher for the convex with respect to the prescription point with 5 cm radius at 1 cm prescription distance. The actual delivered dose was increased linearly proportional to decreasing of the radius of convex. Conclusion: In IOHDR clinical cases, 2‐dimensional planning geometry is typically used without considering the curved shape of the patient's structure. Our measurements have shown an overdosage when the original planar treatment plan was delivered in a convex setting resulting in an increase in the prescription depth which may be clinically relevant.
SU‐FF‐T‐171: Dose Differences Due to Air Pockets in Mammosite Treatments for Partial Breast Irradiation
Authors: Huang Y , Blough M , Esquivel C , Papanikolaou N
Published: July 2006

Purpose: To evaluate the effect of air pockets on the delivered dose for MammoSite® treatments using Monte Carlo (MC) calculations, conventional treatment planning system (TPS), and TLD measurements. Method and Materials: A solid water phantom was designed and fabricated to simulate a MammoSite® treatment with an air pocket outside the balloon. Dose measurements were performed using TLD‐100s with dimensions of 3 mm × 3 mm × 0.9 mm and sensitivity of ±3%. The phantom was composed of twelve slabs of 30 cm × 30 cm Plastic Water with varying thicknesses to provide different measurement distances from the balloon surface. The balloon volume was 34 cc, with a diameter of 4 cm. No contrast medium was added to the balloon to avoid possible dose effects due to the contrast. Hemisphere‐shaped air pockets with different radii were milled on top of the balloon surface. An MC algorithm with geometric modeling based on the phantom design was created for dose comparison. The dose discrepancies from the TPS, TLD measurements, and MC calculations were compared. Results: For a 25 mm air pocket, measured doses from TLDs at various locations of the customized phantom and MC results agreed with each other. The maximal discrepancy between TLDs and MC at different measured points was 3.68%. Dose differences between TPS and MC calculation at the air pocket was 6.37%, and less than 5% at locations other than air pockets. Doses will also be shown for a larger air pocket (5 mm radius). Conclusion: The air pocket located outside of MammoSite® balloon does affect the dose to surrounding tissue and this dose can be represented using MC calculations.
SU‐FF‐T‐177: Dose‐Volume Histogram Objectives in Multi‐Criteria IMRT Optimization
Authors: Halabi T , Craft D , Bortfeld T
Published: July 2006

Purpose: Dose‐volume histogram (DVH) constraints are frequently used in IMRT planning. For example, a DVH constraint may state that 5% (but no more) of the voxels in the planning target volume may receive a dose below the prescription level. We want to find out if the percentage of violating voxels can be reduced. We are also interested in the “price” of this reduction of violating voxels, in terms of dose to other voxels and other structures. Methods and Materials: We introduce DVH objectives into IMRT planning. Here the objective is to minimize the number of voxels that violate a given dose constraint. We then integrate DVH objectives into a multi‐criteria optimization (MCO) framework, to analyze the trade offs between DVH objectives and other planning objectives. Relaxation of mixed integer programs (MIPs) used to produce the trade off curve yields a good approximation. This is contrary to relaxation of an MIP with DVH constraints in the conventional framework. A heuristic then fine tunes the relaxation results. Results: Our methods are applied to two clinical cases with both a dose‐volume objective on the tumor and a maximum dose objective on OAR. The trade off curve between those two objectives is calculated in around 20 minutes with the relaxed MIPs compared to 40 hours with the nominal MIPs. The two techniques differ on average by only .77% tumor volume coverage and the heuristic reduces this difference to .35%. Conclusion: The use of DVH objectives (instead of DVH constraints) has the potential to lead to better trade offs in IMRT treatment planning. Surprisingly, DVH objectives simplify the numerical handling of the problem and reduce calculation times.
SU‐FF‐T‐179: Dosimetric Characteristics of a Titanium Clad 90Y Plaque for Irradiation of Sarcomas of the Spine
Authors: Mauceri T , Folkert M , Munro J , Chen
Published: July 2006

Purpose: A foil encased in polycarbonate plaque has been used to irradiate the dura for sarcomas of the spine. The plaque is applied to the dura intraoperatively after radiation therapy and surgery. Rapid falloff of % DD allows the surface of the dura to be treated and the spinal cord a few millimeters below to be spared. Fabrication of a polycarbonate plaque is a difficult process. Radiation and heat damage from the nuclear reactor used to activate the foil will compromise the polycarbonate housing. Requiring the plaque to be assembled in a glove box after the foil has been activated. This process limits design parameters. A new plaque design incorporating a foil encapsulated in titanium has been developed to facilitate the manufacturing process. The plaque may be assembled before activation allowing for more flexibility in design. Method and Materials: To study the dosimetric characteristics of this new plaque design, a flat plaque was constructed for measurements with radiochromic film. Surface profiles and %DD were measured and compared to previous results for a polycarbonate encapsulated foil and to MCNP calculations generated for the new plaque. Surface profiles were evaluated using a Therapeutic Width Index (TWI), defined as the width of the surface profile at 90% divided by the width of the foil. Results: The titanium plaque's %DD measurements agreed well with the MCNP calculations and with the polycarbonate plaque measurements. Surface profiles for the titanium plaque were measured and the average TWI was 0.88. The average TWI for the polycarbonate plaque was 0.77. The increase in TWI for the titanium plaque corresponds to a 30% increase in useful treatment area. Conclusion: Similar %DD characteristics and an increase in useful treatment area show the new plaque design to be clinically acceptable.
SU‐FF‐T‐181: Dosimetric Comparison of a Semi‐Conductor Array (MapCheck), EDR2 Film and Ion‐Chamber in the Commissioning of Enhanced Dynamic Wedges On a Varian Linear Accelerator (21 EX)
Authors: Oh M , Malhotra H , Podgorsak M
Published: July 2006

Purpose: To evaluate the accuracy of Mapcheck, EDR2 film and ion‐chamber for enhanced dynamic wedge (EDWs) on a Varian Linear Accelerator (21‐EX). Method and Materials: Dosimetric measurements for the entire range of available field‐sizes (4×4cm2 to 30×30cm2) for both 6‐ and 23‐MV photon beams on 21‐EX were performed as a part of commissioning of EDWs. Eclipse computed dose profiles in the coronal plane at 5cm depth for 100MUs were compared with measurement using a 445 diode‐array (MapCheck; Sun Nuclear Corp.) after calibrating it for relative and absolute dosimetry. Planar dose measurements were also repeated using EDR2 radiographic film. Each film was digitized with 0.17mm resolution using the RIT 113 film dosimetry system (Radiological Imaging Technology) and converted to dose using an appropriate H&D curve. These measurements were also compared with those made using a 0.6cc Farmer chamber. Results: For the majority of the EDWs and field size geometries, the CAX dose values between MapCheck measurement and Eclipse computed values were within 2% except for very large wedge angles at large field sizes. Interestingly, for field sizes less than 10×10cm2, the results of MapCheck device demonstrated a better agreement to the TPS computed values than those of ion‐chamber measurement which could be attributed to the miniature size of the diode detector. Also, EDR2 film dosimetry showed consistent 2‐3% over‐response for all wedge angles and field sizes which was very evident at the toe region of EDW. Conclusion: The three measurement detection systems were used to verify the beam profiles and depth doses of EDW. Our results have demonstrated the superiority of MapCheck device in the commissioning and routine QA of EDW over EDR2 film that had an inherent over‐response of 2–3% despite an appropriate H&D curve. The only disadvantage of the Mapcheck device was its restrictive measurement area of 20×20cm2.
SU‐FF‐T‐183: Dosimetric Comparison Of Gamma Knife Vs. CyberKnife Radiosurgery For Patients With Tumors Near Optic Apparatus
Authors: Yu C , Aho C , Liu C , Giannotta S
Published: July 2006

Purpose: We reviewed our 10‐year experience with GK radiosurgery (GKRS) and recent experience with CK radiosurgery (CKRS) for patients with tumors near optic apparatus to make a dosimetric comparison between the two modalities. Method and Materials: From 1994 to 2004, a total of 186 patients (165 GKRS and 21 CKRS) with tumors near the optic apparatus were treated. The majority of this group included 80 meningiomas and 93 pituitary adenomas. Dosimetric parameters, such as, the conformity index, tumor coverage, the closest distances and the maximum radiation doses to optic apparatus and brainstem were evaluated between the two modalities. Results: Mean tumor volume was 4.5cm3 (0.2 to 20.7cm3) for GKRS and 11.0cm3 (0.9 to 38.7cm3) for CKRS. The maximum doses to optic apparatus and brainstem were significantly higher (p < 0.05) even though the closest distances to the structures were very similar. For a subgroup of GKRS patients (n=40) with a mean of tumor volume equivalent to that of CKRS, radiation dose to brainstem was virtually comparable. The mean conformity index was1.35 for CKRS, 1.68 for all GKRS patients (n=165) and 1.49 for the subgroup of GKRS (n=40) in favor of CKRS. The mean tumor coverage was 98.4% for CKRS, 96.0% for all GKRS patients, and 90.9% for the subgroup in favor of CKRS also. Conclusion: CKRS provides excellent radiation conformity and tumor coverage by means of the non‐isocentric beam delivery. However, due to the limits of beam access, the dose fall‐off for CKRS is less rapid, resulting in higher radiation doses to the critical structures. GKRS is best used for small tumors located at least 2mm from the visual pathways. CKRS can be used but is not limited to tumors abutting the optic apparatus or for tumors greater than 3 millimeters in size. This is accomplished via dose fractionation.
SU‐FF‐T‐184: Dosimetric Comparison of LDR, HDR, and IMRT for the Treatment of Advanced Stage Cervical Cancer
Authors: Gaballa H , Roy J , Fontenla D , Marin L , Lim M , Pipman Y
Published: July 2006

Purpose: While perineal template‐based LDR Brachytherapy has been the treatment of choice for advanced stage cervical cancers, recently, there is increasing interest in HDR and IMRT treatments for this disease. This study compares LDR, HDR and IMRT dose distributions, using biological effective doses (BED's), based on a Linear‐Quadratic model. 1 Methods and Materials: Afterloading needles were implanted in the OR using Syed‐ Neblett templates. A physician outlined the target, the rectum, and the bladder volumes on CT‐MRI fused images. Images and structures were transferred to Pinnacle‐III, Plato, and Corvus planning systems, used for LDR, HDR, and IMRT, respectively. Dosimetry parameters for the target (D100, D90, D50, D10) and for rectum and bladder (D50, D30, D20, D10), were transformed to BED's for comparison. Results: Three patients were analyzed in this study. Plans were created for the same BED doses in these three modalities. Dosimetry parameters were normalized to D90. Average D100 values in LDR, HDR, and IMRT were 56%, 55% and 87% of D90, respectively. Although dose coverage in the target region was comparable in LDR and HDR, average value of D10 was higher in HDR than LDR (by 25%). However, average D30 and D50 values were comparable in LDR and HDR. In IMRT, average D10 was only about 8% higher than D90, indicating superior dose homogeneity. Rectum and bladder doses were lower in IMRT and in HDR compared to LDR. Conclusion: While dose inhomogeneity in the target region was higher in HDR than LDR, normal structure doses were lower. IMRT provided better dose homogeneity and target coverage, and delivered lower doses to normal structures than LDR. Therefore, HDR and IMRT seem to be better for the treatment of advanced stage cervical cancer. IMRT has the added advantage of being non‐invasive. (1)C. C. Ling, et. al. Radiotherapy and Oncology, 25 (1992) 103–110.
SU‐FF‐T‐185: Dosimetric Comparison of Tandem and Ovoids Vs. Tandem and Ring for Intracavitary Gynaecologic Applications
Authors: Levin D , Menhel J , Rabin T , Alezra D , Pfeffer R , Symon Z
Published: July 2006

Purpose: To evaluate dosimetric differences in Tandem and Ovoid (TO) and Tandem and Ring (TR) gynaecologic brachytherapy applicators. Method and Materials: 10 patients with cervical cancer (stages II–IV) were treated with three brachytherapy applications: either one TO and two TR, or one TR and two TO applications. All patients underwent CT scans at 2.5 mm slice thickness. Contrast was inserted into the bladder prior to scan. Patients were prescribed 8 Gy to ICRU points A, with additional optimization goals of maintaining the traditional pear‐shaped dose distribution and limiting bladder and rectum doses to below 6 Gy. ICRU bladder and rectum point doses, as well as mean and maximum doses were calculated. Maximum dose was defined as the highest dose received by 2cc of the organ. Total treatment time and volumes treated to 95%, 85% and 50% of the prescription dose were also compared. Data were analyzed using the Mann‐Whitney rank‐sum test. Results: There were no significant differences between TO and TR applicators in doses to prescription points or to critical organs. However, there was a significant difference (p<0.05) between the applicators in the treated volumes and total treatment time. The TO treated larger volumes over a longer time. The treated volumes were also found to be significantly different between applicators within each patient (p<0.05, Chi‐square). Conclusion: Our results demonstrate that the two applicators, whilst delivering prescription doses to points A and keeping critical organ doses within tolerance, treat significantly different volumes. It is unclear if this difference is clinically advantageous or not. TO applicators may be treating healthy tissue unnecessarily, or TR applicators may be underdosing tumor tissue. Further investigation with appropriate imaging modalities is required for accurate delineation of target volumes. Clearly, the TR and TO are not identical, and should not be used interchangeably without further study.
SU‐FF‐T‐186: Dosimetric Effect of Patient Rotational Setup Errors On Prostate IMRT Plans
Authors: Fu W , Yang Y , Li X , Heron D , Huq M , Yue N
Published: July 2006

Purpose: To determine dose delivery errors that could result from systematic and random rotational setup errors for prostate patients treated with IMRT. Methods and Materials: Five prostate cancer patients treated with IMRT technique had their dose distributions re‐evaluated to assess the impact of systematic and random rotational setup errors. The IMRT treatments were delivered in three phases: 54 Gy to 95% of PTV1 (prostate and seminal vesicle plus a 10mm margin), 16.2 Gy to 95% of PTV2 (prostate plus a 5mm margin), and 5.4Gy to 95% of PTV3 (which was PTV2 excluding rectum). Rotational setup error can be equivalently simulated with matrix transformed equations by using the gantry, collimator and couch angles of treatment beams. Systematic rotational setup error ΔΦ was simulated around each of the three Cartesian axes (denoted as ΔΦLR, ΔΦAP, ΔΦSI) respectively. The dosimetric effect of random rotational setup error (Δσ) was also simulated with normal probability distribution. Various dosimetric parameters for the targets and surrounding normal organs were evaluated with respect to the IMRT plan used for treatment. Results: The cumulative dosimetric deviations of target (prostate) were within 1% when ΔΦ and Δσ were up to ±5° and 3° respectively. For OARs, when ΔΦLR=ΔΦAP=ΔΦSI=5° was simulated, the V40Gy and V70Gy of rectum deviated by 5.8±3.6% and 6.1±11.8% respectively, the V40Gy and V65Gy of bladder deviated by −1.0±2.9% and −1.9±4.4%. When ΔσLR=ΔσAP=ΔσSI=3° was simulated, the V40Gy and V70Gy of rectum deviated by −0.4±0.4% and −2.9±3.2%, the V40Gy and V65Gy of bladder deviated by 1.6±1.5% and 0.6±1.5%. Conclusions: For three phases sequential boost prostate IMRT technique, the rotational setup errors do not have a significant dosimetric impact on the cumulative target coverage when ΔΦ and Δσ were up to ±5° and 3° respectively. However, reduction of rotational setup errors can decrease doses to surrounding normal structures.
SU‐FF‐T‐190: Dosimetric Impacts of Smaller Pencil Beam Utilizing in Smaller Intracranial Lesions On Intensity Modulation Serial Tomotherapy
Authors: Cheng CY , Salter B , Cheek D , Fuss M
Published: July 2006

Purpose: To test the dosimetric feasibility of using a smaller size circular pencil beam on small intracranial lesions in serial tomotherapy based radiosurgery. Method and Materials: An in‐house post collimation device (Gizz) was developed to refine the NOMOS Peacock pencil beams to an array of 5 mm diameter circular pencil beams. Beam characteristics were investigated and implemented into the treatment planning system. Eighteen patients with small irregular intracranial lesions (0.19 to 3.21c.c, mean 1.21c.c) were selected in groups of arteriovenous malformation (n = 6), acoustic neuroma (n = 6), and metastatic lesion (n = 6). Plans were calculated with the refined smaller size circular pencil beam and a 4 mm x 10 mm rectangular pencil beam in Corvus 6.0. A novel strategy of normalizing plans to 97% target volume covered by 100% prescription line was adopted. Plan quality was characterized, for the purposes of the study, by conformity and homogeneity indices, mean, maximum and minimum does to target and critical structures, and volume of healthy tissue receiving various dose levels. Results: This new pencil beam provided a better two‐dimensional resolution than three available commercial rectangular pencil beams. Due to adjacent gap spaces from this new physical design, a new couch indexing approach was proposed. Clinical selected cases experienced an average 15% conformity improvement utilizing this smaller pencil beam associated with better normal tissue avoidance. Results reflected that the performance of this device is dependent on target coverage, target volume, and beam displacement location. Conclusion: Smaller pencil beam is an option to improve the target comformality for small irregular lesions in serial tomotherapy based radiosurgery. Future works on optimized pencil beam size, shape, isocenter shift should be accomplished.
SU‐FF‐T‐194: Dosimetric Validation of Tomotherapy in Hetergeneous Media
Authors: Chaudhari S , Goddu S , Mutic S , Esthappan J , Kawamura S , Low D
Published: July 2006

Purpose: Helical Tomotherapy is a relatively new treatment modality that is being used to treat lesions that lie within and near low‐density organs. Accurate dose calculations are critical to the effective use of this modality. This study quantified the Tomotherapy treatment planning system (TPS) convolution‐superposition‐based dose calculation accuracy in heterogeneous media. Method and Materials: This evaluation required a custom fabricated dosimetry phantom with lung‐equivalent and water‐equivalent media. The phantom consisted of an 18×18×18 cm3 cuboid constructed from slabs of water‐equivalent and lung‐equivalent materials (LN300 Gammex RMI, Middleton, WI (ρ ∼0.3g/cc), and Balsa wood (ρ ∼0.1g/cc) and imaged on a CT scanner. Dose measurements were conducted using both film and ionization chambers using the same phantom geometry. Evaluations were conducted using an esophageal treatment plan, delivering 1.8 Gy/fraction, was superimposed onto the phantom CT‐datasets and computed the dose distributions using the Tomotherapy treatment planning system. Radiochromic film (EBT, International specialty Products, Wayne, NJ) sheets were inserted between slabs of virtual water and lung equivalent material LN‐300. Experiments were repeated with radiographic film (Kodak EDR2, Eastman Kodak, Rochester, NY) with balsa wood. Calibration curves for absolute dosimetry for both types of film were generated from additional film exposures and ion chamber measurements on the Tomotherapy unit. Ionization‐chamber measurements were performed to confirm the film dosimetry. Results: Doses measured inside the water‐equivalent plastic were within 2% of the computed doses by the Tomotherapy planning system. Measurements with radiochromic film in LN‐300 material verified that the planning system computed the doses within 5%. Similar results were observed with EDR2 film in Balsa wood. Conclusions: The dose calculation accuracy of TPS was measured to be within 5% in lung material and within 2% in water‐equivalent plastic. This work supported in part by Tomotherapy, Inc.
SU‐FF‐T‐195: Dosimetry Audit for Tomotherapy Using Alanine/EPR
Authors: Duane S , Nicholas D , Palmans H , Schaeken B , Sephton J , Sharpe P , Thomas R , Tomsej M , Tournel K , Verellen D , Vynckier S
Published: July 2006

Purpose: To provide an audit of ion chamber‐based dosimetry for IMRT delivered by helical tomotherapy. Method and Materials: Three treatment plans were selected from the commissioning of a TomoTherapy Hi‐Art II machine using a 30 cm diameter cylindrical Virtual Water (“cheese”) phantom. For each plan, measurements were made at 6 points: two in the target volume, two in the steep dose‐gradient region just outside the target volume, and two in the low‐dose region far from the target volume, which was a 6 cm diameter cylinder. Absorbed dose was measured using two independent alanine/EPR dosimetry systems and two Exradin A1SL ion chambers. The planned dose in the target volume was 2 Gy per fraction, and 9 or 10 fractions were delivered to the phantom loaded with alanine dosimeters. The ion chambers had been calibrated in a 60Co beam at Ghent University Dosimetry Laboratory, and correction factors were applied for beam quality and ion recombination as recommended by TomoTherapy Inc. Four or five alanine dosimeter pellets were used per measurement position. The NPL alanine dosimeters were read out using a Bruker EMX spectrometer, and the ZNA‐Middelheim alanine dosimeters were read out using a desktop Bruker EMS‐104 spectrometer. Results: In the target volume, ion chamber and alanine doses agreed to better than 2%. The statistical uncertainty in absorbed dose measured using a single alanine pellet was 0.06 Gy at NPL and 0.3 Gy using the desktop spectrometer. On average, absorbed dose measured using the ZNA‐Middelheim alanine system was 3% higher than the dose measured using the NPL alanine system. Conclusions: Dosimetry audit of IMRT delivered by helical tomotherapy using alanine/EPR is both convenient and independent of the assumptions made in analysing ion chamber measurements.
SU‐FF‐T‐196: Dosimetry for Linear Sources in Heterogeneous Prostate Phantom
Authors: Dimofte A , Zhu T , Finlay J
Published: July 2006

Purpose: To characterize the light distribution from linear diffusing optical fibers in a prostate‐simulating phantom. The light distribution depends on the geometry and optical properties of the phantom and on the geometry of the light sources. Light distributions were measured in homogeneous and inhomogeneous phantoms. Method and Materials: Measurements were performed in homogeneous and inhomogeneous prostate simulating phantoms with linear light sources of lengths (1 – 5 cm) placed in the phantom through transparent catheters. The optical fluence rate was measured using isotropic detectors at various distances from the linear source using a computer‐controlled stepper motor. Results for a point source were also presented to predict the light fluence rate for linear sources with the intensity distribution of the linear sources taken into account. Attempts were made to predict the light fluence rate distribution in 3D using calculation with a kernel‐based method. Results: The profiles of linear sources with lengths between 1 and 5 cm were scanned at 0.3, 0.5 and 0.7cm away using isotropic detectors in homogeneous and inhomogeneous phantoms. The increase of light fluence in lower absorption region in an inhomogeneous phantom is due to the increase of effective optical penetration depth. Scans measured around a 5cm linear source show a clear difference in optical properties for the case when the detector passes through the urethra, prostate tissue and tumor. Conclusion: We have demonstrated the ability to characterize the light distribution inside the prostate using a methodology compatible with clinical measurement. Our method is sensitive enough to differentiate between the optical properties of the prostate, tumor and urethra in our model system.
SU‐FF‐T‐262: Image‐Guided Non‐Invasive Stereotactic Radiosurgery
Authors: Shiu A , Wang C , Woo S , Wang H
Published: July 2006

Purpose: The objective of this study is to demonstrate that the use of image registration and a non‐invasive head frame for SRS can achieve the same accuracy as the current invasive head‐ring SRS technique. Method and Materials: First, a head phantom was used to evaluate the accuracy of this procedure for aiming the target. Then, two SRT patients fixed with the GTC frame were treated with the proposed technique for ten treatments. The five‐point GTC alignment device was used to aid the repositioning of the GTC frame with respect of the original setup. This alignment device minimized the misalignment of the GTC frame in AP, lateral, and axial translations and the angular deviations about each of these axes on roll, tilt, and spin. Prior to each treatment, a daily CT scan with a localization device was acquired. Daily CT images were registered with planning CT and MRI images. The 9 rods on the daily CT images were then identified, such that all the target, critical structures, and external contours from the planning images were transferred to the daily stereotactic coordinates. A new plan was generated. Results: In the head phantom study, the daily isocenter setup was verified to be within 0.2 mm accuracy based upon the portal images verse the planned DRRs. Optimized the dose distributions for each daily CT images of ten treatments, the mean deviations of the daily isocenter from the planned isocenter are 0.2±0.12, −0.4±0.24, and −0.1±0.07 mm in AP‐, LAT‐, and VERT‐direction, respectively. The comparison of dose‐volume histograms is clearly revealed the prescribed dose enclosed the PTV for every treatment. Conclusions: The image‐guided noninvasive frame SRS has the capability of delivering high level accuracy of dose to the lesion without the discomfort from the pins fixed to the patient's skull.
SU‐FF‐T‐264: Impact of Heterogeneous Activity Distributions On the Tumor Absorbed Dose Distribution for An In‐Vivo Colorectal Cancer Model
Authors: Roberson P , Buchsbaum D
Published: July 2006

Purpose: To compare the heterogeneous uptake distribution of intact and domain deleted monoclonal antibodies with simulated activity distributions used to derive the dosimetric impact of heterogeneous uptake. Method and Materials: A total of 4 tumors with approximate masses of 0.1 g (∼5mm diameter) and 0.5 g (∼10mm diameter) were chosen for this study. Tumor activity distributions were reconstructed in 3D using serially sectioned LS174T tumors grown on the flank of athymic nude mice. The mice received an injection of either 177Lu‐PA‐DOTA‐HuCC49 or 177Lu‐PA‐DOTA‐HuCC49dCH2 monoclonal antibody. Simulated distributions of similar dimensions were created for comparison. All distributions were normalized to 100 uCi/g uptake and convolved with dose point kernels for a short range (I131) and a long range (Y90) isotope. Compared were radial profiles for activity density and dose rate, mean dose and tumor central dose. Results: The activity distributions are much more erratic for tumor uptake compared to the simulated distributions. There is also variation in minimum and maximum activity density between tumors. The simulated distributions under‐estimated the tumor size dependence of the average dose for both isotopes by about 10%. The central dose for the small tumor were overestimated for Y90 and bracketed for I131. The central dose for the larger tumors was under‐estimated for both isotopes. Conclusion: The simulated distributions did not well represent the large variation in uptake observed in tumors. Compared to the simulated distributions, dose due to Y90 performed better for the 0.5 g tumors, but worse for the 0.1 g tumors and dose due to I131 performed better for the 0.5 g tumors and similar for the 0.1 g tumors. The heterogeneity of uptake in tumors are not well represented by a single simulated distribution because of the wide variation in local uptake.
SU‐FF‐T‐265: Impact of Linac Isocenter Shifts On Stereotactic Radiosurgery Dose
Authors: Sethi A , Glasgow G , Gao M , Ke Y , Rusu I , Melian E
Published: July 2006

Introduction: Of the various sources of error in Stereotactic radiosurgery, linac isocenter shift can be the largest. We present a method of quantifying this error using Winston Lutz (WL) QA films and evaluate its impact on patient dose. Methods and Materials: WL films (5mm ball and 10mm cone) were acquired for 16 gantry and couch angles for a NOVALIS linac. Films were scanned at high‐resolution (89 μm) and analyzed using RIT software to determine differences between ball and radiation field centroids. An algorithm was developed to transform these to patient reference frame and map out shifts between target and linac isocenter for all allowed gantry and table angles. For this study, a patient with trigeminal neuralgia (70Gy with 6 arcs and 4mm cone) was considered. The impact on delivered dose was evaluated by weighting each treatment arc with its appropriate isocenter shift. Also for comparison, the treatment plan was recalculated using the maximum shift observed in film data. Results: Minimum target dose (Dmin) in the original patient plan was 54.6Gy and target D95 was 61.6Gy. When maximum shift was used to modify treatment plan, DVH data erroneously showed 30% target underdosage: Dmin = 38.5Gy; D95 = 44.2Gy. However, for the “weighted‐arc” plan, Dmin = 53.9Gy and D95 = 61Gy were within 1% of the original plan. Therefore, in evaluating dose delivered to the patient, it is important to consider the impact of isocenter shift on each treatment arc for highly accurate treatments. In appropriate cases, this method can also be used to compensate for gantry‐table combinations that may fall outside the acceptable limits (> 1 mm). Conclusions: We have presented a method that allows quantitative evaluation of dose errors that result due to shifts in linac isocenter as a function of gantry and table angles.
SU‐FF‐T‐267: Implementation of ATC Method 1 for Clinical Trials Data Review at the Quality Assurance Review Center
Authors: Bosch W , Matthews J , Ulin K , Urie M , Yorty J , Straube W , FitzGerald T , Purdy J
Published: July 2006

Purpose: To develop the capability at the Quality Assurance Review Center (QARC) to receive and review digital radiation therapy treatment planning data (TPD) for clinical trial case review. Method and Materials: A system of software (“ATC Method 1”) developed at the Image‐guided Therapy QA Center (ITC) as part of the Advanced Technology QA Consortium (ATC) to receive, process, and review volumetric TPD for clinical trials was ported to a Linux workstation at QARC. The system includes an FTP server for receiving TPD (in DICOM or RTOG data exchange format) from protocol participants, utilities for importing TPD into a local file format, and the web‐based Remote Review Tool (RRT) for QA of ROIs, isodoses, DVHs, and dose statistics. (Proprietary software components were used by special arrangement with CMS, Inc.) Results: Software installation and maintenance were performed remotely at QARC by ITC personnel, with weekly teleconferences to coordinate the development effort. ITC software was adapted to better support the QARC QA process. RRT enhancements include selectable DVHs, distance measurement tool, and image grayscale presets. QARC software was adapted to support RRT invocation directly from the QARC database user interface. The system is in use for six COG, CALGB, ACOSOG, and ECOG protocols; 28 cases from 15 institutions have been received and reviewed (3/1/06). Conclusion: Widespread use of new treatment modalities such as IMRT, makes use of 3D datasets essential for complete evaluation of ROI delineation and assessment of agreement of dosimetric parameters with protocol requirements. This project demonstrates that ATC Method 1, successfully used in support of RTOG trials for many years at ITC, can be implemented at other QA centers. The effort required, however, was significant and tools must be tailored to each individual QA center's computer infrastructure/QA process. Supported by NIH U24 Grant CA81647 and NCI‐H Grant 5U10CA02951.