Uniform Margin Research Articles

The effect of uterine motion and uterine margins on target and normal tissue doses in intensity modulated radiation therapy of cervical cancer

In intensity modulated radiation therapy (IMRT) of cervical cancer, uterine motion can be larger than cervix motion, requiring a larger clinical target volume to planning target volume (CTV-to-PTV) margin around the uterine fundus. This work simulates different motion models and margins to estimate the dosimetric consequences. A virtual study used image sets from ten patients. Plans were created with uniform margins of 1 cm (PTVA) and 2.4 cm (PTVC), and a margin tapering from 2.4 cm at the fundus to 1 cm at the cervix (PTVB). Three inter-fraction motion models (MM) were simulated. In MM1, all structures moved with normally distributed rigid body translations. In MM2, CTV motion was progressively magnified as one moved superiorly from the cervix to the fundus. In MM3, both CTV and normal tissue motion were magnified as in MM2, modeling the scenario where normal tissues move into the void left by the mobile uterus. Plans were evaluated using static and percentile DVHs. For a conventional margin (PTVA), quasi-realistic uterine motion (MM3) reduces fundus dose by about 5 Gy and increases normal tissue volumes receiving 30–50 Gy by ∼5%. A tapered CTV-to-PTV margin can restore fundus and CTV doses, but will increase normal tissue volumes receiving 30–50 Gy by a further ∼5%.

Intrafraction Variation of Mean Tumor Position During Image-Guided Hypofractionated Stereotactic Body Radiotherapy for Lung Cancer

Prolonged delivery times during daily cone-beam computed tomography (CBCT)-guided lung stereotactic body radiotherapy (SBRT) introduce concerns regarding intrafraction variation (IFV) of the mean target position (MTP). The purpose of this study was to evaluate the magnitude of the IFV-MTP and to assess target margins required to compensate for IFV and postonline CBCT correction residuals. Patient, treatment, and tumor characteristics were analyzed with respect to their impact on IFV-MTP. A total of 126 patients with 140 tumors underwent 659 fractions of lung SBRT. Dose prescribed was 48 or 60 Gy in 12 Gy fractions. Translational target position correction of the MTP was performed via onboard CBCT. IFV-MTP was measured as the difference in MTP between the postcorrection CBCT and the posttreatment CBCT excluding residual error. IFV-MTP was 0.2 ± 1.8 mm, 0.1 ± 1.9 mm, and 0.01 ± 1.5 mm in the craniocaudal, anteroposterior, and mediolateral dimensions and the IFV-MTP vector was 2.3 ± 2.1 mm. Treatment time and excursion were found to be significant predictors of IFV-MTP. An IFV-MTP vector greater than 2 and 5 mm was seen in 40.8% and 7.2% of fractions, respectively. IFV-MTP greater than 2 mm was seen in heavier patients with larger excursions and longer treatment times. Significant differences in IFV-MTP were seen between immobilization devices. The stereotactic frame immobilization device was found to be significantly less likely to have an IFV-MTP vector greater than 2 mm compared with the alpha cradle, BodyFIX, and hybrid immobilization devices. Treatment time and respiratory excursion are significantly associated with IFV-MTP. Significant differences in IFV-MTP were found between immobilization devices. Target margins for IFV-MTP plus post-correction residuals are dependent on immobilization device with 5-mm uniform margins being acceptable for the frame immobilization device.

Definition and Dosimetric Evaluation of a Clinical Target Volume (CTV) in the Post Implant (CT/MR Fusion) Analysis of Low-Dose-Rate Brachytherapy for Prostate Cancer at Princess Margaret Hospital

Purpose: The extent of extra prostatic extension in low and intermediate risk prostate cancer is mostly confined within a radial distance of 3mm which have implications in evaluating the post-implant dosimetry of LDR brachytherapy. There is a scarcity of data in evaluating the dosimetry around the prostate in the post implant setting. In this study, we defined a CTV and evaluated its dosimetry in the post implant CT/MR scans done at 1 month after the LDR brachytherapy procedure. Materials and Methods: The initial consecutive 71 patients who underwent LDR brachytherapy under a single physician at Princess Margaret Hospital from June 2009 to July 2010 were included in this retrospective study. The margins used in the preplan ultrasound were 3mm anterolaterally 5mm inferiorly and 0mm posteriorly. On the post implant MRI, the CTV was created by adding 3mm uniform margins around the prostate as per guidelines of ESTRO and AAPM. We modified this CTV by editing it back from the bladder wall and rectal wall to respect the anatomic barriers of microscopic spread. We evaluated the dosimetry of prostate and CTV using the dosimetric parameters V80, V90, V100, V150, V200, D80, D90 and D100 after performing the CT/MR fusion. Implants were qualified as optimal if their V100 was >85% and D90 was >90% for the prostate in this analysis and the same indicators were applied for the CTV. Univariate analysis using Wilcoxon rank sum test for continuous variables and Fisher’s exact test for categorical variables was performed to evaluate associations of factors with V100 and D90 for the CTV. Results: The mean (SD) prostate V100 and D90 were 95.5% (4.2) and 117% (10) respectively with only 1 patient having sub optimal implant (V100 <85% and D90 <90%). The mean (SD) V100 and D90 for the CTV were also acceptable at 90.6% (4.9) and 103% (9), respectively. The detailed analysis is given in the table.Tabled 1VariableProstate Mean (SD)CTVMean (SD)V80 (%)99 (1.5)97 (2.5)V90 (%)98 (2.9)94 (2.5)V100 (%)95.5 (4)90.6 (4.9)V150 (%)62 (11)57 (9.3)V200 (%)31 (8)28 (7)D80 (%)131 (11)121 (10)D90 (%)117 (10)103 (9.2)D100 (%)65 (10)55 (8) Open table in a new tab Six patients had V100 <85% and 7 patients had D90 <90% for the CTV. On univariate analysis, the factors which correlated with suboptimal implant for the CTV were edema and seed implantation technique. The mean (SD) edema for patients with V100 <85% was 18% (10) and with D90 <90% was 15% (12). The corresponding values for the optimal implants both in terms of V100 and D90 were 3% (13). Patients implanted with exclusively loose seeds (15 patients only) had higher incidence of implants with V100 <100% and D90 <90% (26%) compared to patients who had strands on the antero-lateral margins (56 patients; 3.5%). The prostate volume (ranging from 18 to 73cc) did not influence the dose coverage of CTV in our study. Conclusions: In this study, we defined the CTV as a 3mm expansion of the prostate to account for extra capsular extension in the post-implant setting for LDR brachytherapy and evaluated its dosimetry. We were able to achieve adequate dose coverage of CTV in most patients with current technique but implants with optimal dosimetry to prostate still may have suboptimal D90 and V100 for the CTV especially in the presence of post-implant edema. A consensus is needed for definition and evaluation of CTV in post-implant setting for LDR prostate brachytherapy.

Is it possible to get adequate dose coverage of a clinical target volume (CTV) to account for the possible extra capsular extension in early-stage prostate cancer by low dose rate (LDR) brachytherapy?

98 Background: There is no consensus for the definition and evaluation of CTV in post-implant setting for LDR prostate brachytherapy to account for extra capsular extension in clinically localized prostate cancer. In this study, we defined a CTV and evaluated its dosimetry in the post implant CT/MR scans done at 1 month after the LDR brachytherapy procedure. Methods: The initial consecutive 71 patients who underwent LDR brachytherapy under a single physician at Princess Margaret Hospital from June 2009 to July 2010 were included in this retrospective study. On the post implant MRI, the CTV was created by adding 3mm uniform margins around the prostate but respecting the anatomical boundaries like bone, bladder and rectum. Post implant dosimetry was based on CT/MR fusion using the dosimetric parameters V80, V90, V100, V150, V200, D80, D90 and D100. Implants were qualified as optimal if their V100 was &gt;85% and D90 was &gt;90% for both prostate and CTV. Univariate analysis was performed to evaluate associations of factors with V100 and D90 for the CTV using Wilcoxon rank sum test and Fisher's exact test. Results: The mean (SD) prostate V100 and D90 were 95.5% (4.2) and 117% (10) respectively with only 1 patient having sub optimal implant (V100 &lt;85% and D90 &lt;90%). The mean (SD) V100 and D90 for the CTV were also acceptable at 90.6% (4.9) and 103% (9), respectively. Six patients had V100 &lt;85% and 7 patients had D90 &lt;90% for the CTV. On univariate analysis, edema and seed implantation technique correlated with sub-optimal implant for the CTV. The mean (SD) edema for patients with V100 &lt;85% was 18% (10) and with D90 &lt;90% was 15% (12). The corresponding values for the optimal implants both in terms of V100 and D90 were 3% (13). Patients implanted with exclusively loose seeds (15 patients only) had higher incidence of sub-optimal implants (26%) compared to patients who had strands on the antero-lateral margins (56 patients; 3.5%). Conclusions: In this study, adequate dose coverage of CTV was achieved in most patients with current technique but implants with optimal dosimetry to prostate still may have sub-optimal D90 and V100 for the CTV. No significant financial relationships to disclose.

The effect of differentiated margin on futures market investors' behavior and structure

PurposeThe purpose of this paper is to empirically analyze the role of differentiated margin system in leading investors' investing behavior and then optimize investor structure in futures markets.Design/methodology/approachUsing economic experimental research method, this paper designs and conducts a futures market experiment according to experimental research's basic norms, thus acquiring needed and credible empirical data.FindingsBy analyzing the experimental data, it is found that compared with situations in futures markets that implement uniform margin system, investors' (especially speculators') futures open position and the ratio of their open position and futures turnover are both significantly higher, in futures markets that implement differentiated margin system. On the other hand, differentiated margin system has no effects on hedgers' futures turnover, but significantly reduces speculators' futures turnover.Research limitations/implicationsThe findings suggest that compared with uniform margin system, differentiated margin system is beneficial to effectively restrict both speculators' and hedgers' speculating behavior and lead hedgers' market participation.Practical implicationsIn order to resolve the problem of unreasonable investor structure in China's futures market, i.e. lack of hedgers and over‐speculating, China's futures market's regulators should reform the margin system and adopt differentiated margin system to lead investors' rational behavior and optimize investor structure.Originality/valueThis paper empirically analyzes and verifies, for the first time, the roles of differentiated margin system in affecting investors' investing behavior. The futures market experiment designed and used in this study is a pioneering and exploratory experiment.

An Advanced 405-nm Laser Diode Crystallization Method of a-Si Film for Fabricating Microcrystalline-Si TFTs

This report describes a crystallization method we developed for amorphous (a)-Si film by using 405-nm laser diodes (LDs). The proposed method has been used to fabricate bottom gate (BG) microcrystalline (µc)-Si TFTs for the first time. A µc-Si film with high crystallinity was produced and high-performance BG µc-Si TFTs with a field effect mobility of 3.6cm2/Vs and a current on/off ratio exceeding 108 were successfully demonstrated. To determine the advantages of a 405-nm wavelength, a heat flow simulation was performed with full consideration of light interference effects. Among commercially available solid-state lasers and LDs with wavelengths having relatively high optical absorption coefficients for a-Si, three (405, 445, and 532nm) were used in the simulation for comparison. Results demonstrated that wavelength is a crucial factor for the uniformity, efficiency, and process margin in a-Si crystallization for BG µc-Si TFTs. The 405-nm wavelength had the best simulation results. In addition, the maximum temperature profile on the gate electrode through the simulation well explained the actual crystallinity distributions of the µc-Si films.

Daily Online Cone Beam Computed Tomography to Assess Interfractional Motion in Patients With Intact Cervical Cancer

To quantify interfraction motion in patients with intact cervical cancer and assess implications for clinical target volume (CTV) coverage and required planning margins. We analyzed 10 patients undergoing external beam radiotherapy using online cone beam computed tomography (CBCT) before each fraction. CTVs were contoured on the planning CT and on each CBCT. Each CBCT was rigidly registered to the planning CT with respect to bony anatomy. The CTV from each CBCT was projected onto the planning CT and compared to the CTV from the planning CT. Uniform three-dimensional expansions were applied to the planning CTV to assess required planning margins. For each fraction, the minimum margin required to encompass the CTV was calculated, and the volume of CTV (on the CBCT) encompassed by the PTV was determined as a function of margin size. A uniform CTV planning treatment volume margin of 15 mm would have failed to encompass the CTV in 32% of fractions. The mean volume of CTV missed, however, was small (4 cc). The mean planning margin (across patients and fractions) required to encompass the CTV was 15 mm. Variation in margin estimates was high, with interpatient variation being the predominant component. Increased rectal volume was associated with posterior (p < 0.0001) and superior (p = 0.0004) shifts in the CTV, whereas increased bladder volume was associated with superior shifts (p < 0.0001). Interfraction motion results in a high probability of missing the CTV using conventional planning margins, but the volume of CTV missed is small. Adaptive radiotherapy approaches are needed to improve treatment accuracy.

Novel Treatment Planning Techniques for Treatment of Chest Wall Lesions using Stereotactic Body Radiotherapy

Materials/Methods: Ten patients with the target volumes attached or near to the chest wall were chosen for this study. Treatment plans using three different techniques were performed retrospectively. These three techniques included conventional 3D planning (3D), forward planning with manual optimization (Field in Field (FIF)) and segmented beams with inverse planning optimization (SIP). A 4DCT simulation was performed using a Philips 16 slice CT scanner. All patients were simulated in the supine position with arms placed above their head and immobilized using a body frame or body fix. These 4D-CT images were fused with helical CT scans and were primarily used for target delineation. Note that all the treatment plans were performed on the free breathing helical CT scans. Plans involved anywhere between 7 -11 noncoplanar beams. 3D conformal plans were designed by manually creating all beam apertures using a uniform margin around the PTV and adjusting the block shape for avoiding critical structures. For FIF technique, 2-3 segments were created for each field. A segment was created by manually moving the MLC leaves into the aperture from the original block edge effectively blocking out an area where too much dose was being delivered. SIP technique uses the same beam angles as the two other techniques. Plans were optimized using direct machine parameter optimization, allowing 1-2 segments per beam. A minimum of 50 to 100 monitor units along with a minimum segment size of 5 to 10 cm was used. Additional structures and optimization constraints were used for inverse planning. The following criteria were used for plan evaluation. All treatment plans had to adhere to the RTOG 0236 protocol. Volume of the PTV covering 90% prescription dose should be at least 99%. Conformality index (CI) was defined as the ratio of the volume of prescription isodose to the volume of PTV. Plans were evaluated for plan quality and time efficiency.

Generalized Diagonal Band Copulas with Two-Sided Generating Densities

Copulas are joint continuous distributions with uniform marginals and have been proposed to capture probabilistic dependence between random variables. Maximum-entropy copulas introduced by Bedford and Meeuwissen (Bedford, T., A. M. H. Meeuwissen. 1997. Minimally informative distributions with given rank correlations for use in uncertainty analysis. J. Statist. Comput. Simulation 57(1–4) 143–175) provide the option of making minimally informative assumptions given a degree-of-dependence constraint between two random variables. Unfortunately, their distribution functions are not available in a closed form, and their application requires the use of numerical methods. In this paper, we study a subfamily of generalized diagonal band (GDB) copulas, separately introduced by Ferguson (Ferguson, T. F. 1995. A class of symmetric bivariate uniform distributions. Statist. Papers 36(1) 31–40) and Bojarski (Bojarski, J. 2001. A new class of band copulas—Distributions with uniform marginals. Technical report, Institute of Mathematics, Technical University of Zielona Góra, Zielona Góra, Poland). Similar to Archimedean copulas, GDB copula construction requires a generator function. Bojarski's GDB copula generator functions are symmetric probability density functions. In this paper, symmetric members of a two-sided framework of distributions introduced by van Dorp and Kotz (van Dorp, J. R., S. Kotz. 2003. Generalizations of two-sided power distributions and their convolution. Comm. Statist.: Theory and Methods 32(9) 1703–1723) shall be considered. This flexible setup allows for derivations of GDB copula properties resulting in novel convenient expressions. A straightforward elicitation procedure for the GDB copula dependence parameter is proposed. Closed-form expressions for specific examples in the subfamily of GDB copulas are presented, which enhance their transparency and facilitate their application. These examples closely approximate the entropy of maximum-entropy copulas. Application of GDB copulas is illustrated via a value-of-information decision analysis example.

SU‐GG‐J‐109: A Study on Image Guided Radiotherapy Using Cone‐Beam Computed Tomography (CBCT) for Head and Neck Cancer IMRT Patient Setup

Purpose: To use our CBCT shift results to determine how much of the CTV to PTV margin is necessary to compensate for the daily setup uncertainty inherent in the treatment of head and neck cancer patients. Method and Materials: To accommodate the daily setup uncertainly, a 3–6 mm uniform margin is used for head and neck IMRT patients to expand CTV to PTV. In order to verify patient setup accuracy, CBCT is taken prior to the treatment. Our protocol calls for CBCT for the first five consecutive fractions, followed by two CBCT every week. Each CBCT is registered to the planning CT to determine the corresponding translational shift. The registration is based on the region‐of‐interest—the rigid bones near the tumor. On the days no CBCT is taken, the average of the previous three calculated translational shifts is used instead. No rotational correction is considered. Results: A total of 22 head and neck IMRT patients were studied with a Siemens Artiste linear accelerator using an MVision CBCT scanner. Each patient had approximately 14 sets of CBCT images taken over the entire course of treatment. The average interfraction shift was 0.6±1.6, 1.4±1.5, 0.1±1.6 mm in the anterior‐posterior, left‐right, and superior‐inferior dimensions, respectively. These data indicate that in the absence of CBCT image guided radiotherapy, a CTV to PTV margin of 2.5, 4.7 and 1.3 mm is needed in the anterior‐posterior, left‐right, and superior‐inferior dimensions, respectively. Conclusion: Our results have shown that asymmetric margins of 2.5, 4.7 and 1.3 mm can be used for CTV to PTV expansion for head and neck cancer radiotherapy if no IGRT presented. Our CBCT protocol will allow a reduction in the CTV to PTV margin. Further investigation needs to be done to find out the specific CTV to PTV margin with different CBCT frequency.

Confirmation of European Brown Rot Caused by Monilinia laxa on Tart Cherry, Prunus cerasus, in Western New York.

Monilinia fructicola (G. Wint.) Honey and M. laxa (Aderh. & Ruhl.) Honey are two pathogens causing brown rot in the United States. While the presence of M. fructicola has been confirmed in all major stone-fruit-production regions in the United States, M. laxa has yet to be detected in much of the eastern production regions. In July 2008, a planting of tart cherries cv. Surefire in Appleton, NY developed severe shoot blight. Blighted shoots (>15% of first-year shoots) were wilted and light brown with the blight encompassing the distal end and often extending into second-year tissue with a distinct sunken margin. Leaves on symptomatic shoots had flushed, but were blighted. Blossom spurs were either blighted at bloom or bore fruit, which were subsequently blighted. Gummosis was commonly observed from cankers at the base of spurs. Both mature and immature mummified fruit in addition to spurs and shoot tissue were sporulating in a manner characteristic of Monilinia (2). Eleven branches displaying symptoms were removed for isolation. Sections of symptomatic shoots (5 cm long) were surface sterilized in 0.6% NaOCl for 1 min and rinsed in sterile dH2O. Cross sections of shoot tissue (3 mm thick), in addition to spores from fruit and spurs, were placed on potato dextrose agar amended with 50 μg/ml of streptomycin sulfate. Following incubation at 24°C for 5 days, 24 colonies exhibiting morphology consistent with that of M. fructicola (uniform colony margin) were obtained, along with nine colonies exhibiting lobed colony margins, commonly associated with M. laxa (3). All colonies resembling M. fructicola were isolated from fruit, whereas those resembling M. laxa were isolated from spurs and shoots. Conidia from both colony morphotypes were lemon-shaped, but those from putative M. laxa isolates were smaller on average (10.75 × 12.0 μm) compared with those from putative M. fructicola isolates (15.75 × 18.25 μm). Confirmation of M. laxa was also accomplished by inoculation of mature green pear (2). Pears inoculated with 104 putative M. laxa conidia per ml produced a region of white-buff colored mycelium but no spores within the inoculated area, while M. fructicola-inoculated pears sporulated abundantly. Identity was further confirmed by PCR amplification of the β-tubulin gene using M. laxa specific primers as previously described (1). Pathogenicity was proven by inoculating flowering shoots of tart cherry trees (cv. Montmorency) in spring 2009. Twenty shoots were spray inoculated with either 104 M. laxa conidia per ml or sterile dH2O and covered with plastic bags for 24 h. Shoots were monitored for symptom development on a weekly basis. Shoots inoculated with M. laxa developed characteristic shoot blight symptoms, while those inoculated with water remained healthy. M. laxa was reisolated from symptomatic shoots and spurs, but not water-inoculated tissues. The presence of M. laxa is reported for the Great Lakes region, which includes New York, but to our knowledge, this report is the first confirmed instance of economically devastating brown rot caused by M. laxa in New York. In the coming seasons, tart cherry growers must consider revising chemical management programs to protect against European brown rot infection during bloom.

SU-GG-T-152: Pediatric Craniospinal Irradiation with RapidArc: A Feasibility Study and Dosimetric Comparison

Purpose: To investigate the feasibility of pediatric craniospinal irradiation (CSI) using RapidArc, and to provide a dosimetric comparison to conventional three-dimensional conformai radiotherapy (3DCRT) techniques. Method and Materials: CT datasets of pediatric patients with a variety of neoplasms were included in this retrospective study. All patients previously received 3DCRT CSI in the supine position. Single planning target volumes (PTVs) were generated for each patient to include the cranial contents and the vertebral column, both with additional uniform volumetric margins. RapidArc treatment plans were created for 6 MV photons using two arcs for the cranial section of the PTV and a single arc for the entire spinal section of the PTV. All RapidArc plans were normalized so that 100% of the prescription dose (36 Gy) was delivered to 95% of the CSI PTV. The RapidArc and 3DCRT CSI plans were compared based on several dosimetric parameters in order to determine organ at risk (OAR) sparing, PTV coverage and PTV homogeneity. Results: The RapidArc CSI plans were able to achieve similar or improved OAR sparing when compared to their original 3DCRT CSI counterparts. As a whole, the RapidArc plans were able to decrease the maximum dose to all of the relevant OARs. However, for some OARs, such as the lungs and bowel, the mean doses were elevated due to the increased number of beam angles. When conformity and dose homogeneity indices were evaluated, the RapidArc plans illustrated improved PTV coverage and superior target volume homogeneity in all cases. Conclusion: The dosimetric results indicate that RapidArc is an advantageous alternative for pediatric CSI. When compared to 3DCRT, the proposed method has the potential to deliver a more uniform dose to the craniospinal PTV, thus minimizing areas of overdose and underdose and eliminating the need for difficult and time-consuming field matching techniques.

An Ultra Low Power and Variation Tolerant GEN2 RFID Tag Front-End with Novel Clock-Free Decoder

In this paper, an ultra low power analog front-end for EPCglobal Class 1 Generation 2 RFID tag is presented. The proposed RFID tag removes the need for high frequency clock and counters used in conventional tags, which are the most power hungry blocks. The proposed clock-free decoder employs an analog integrator with an adaptive current source that provides a uniform decoding margin regardless of the data rate and a link frequency extractor based on a relaxation oscillator that generates frequency used for backscattering. A dual supply voltage scheme is also employed to increase the power efficiency of the tag. In order to improve the tolerance of the proposed circuit to environmental variations, a self-calibration circuit is proposed. The proposed RFID analog front-end circuit is designed and simulated in 0.25µm CMOS, which shows that the power consumption is reduced by an order magnitude compared to the conventional RFID tags, without losing immunity to environmental variations.

Daily Fiducial Based Tracking of Seminal Vesicle Motion in Image Guided Dose Escalated IMRT: Are We Kidding Ourselves Regarding Seminal Vesicle Coverage?

The seminal vesicles (SVs) are often part of the clinical target volume (CTV) when treating prostate cancer. Uniform margins are typically used when expanding the prostate and SV CTV to the planning target volume (PTV), and these margins are decreasing as we move towards image-guided intensity-modulated radiotherapy (IG-IMRT). However little is known about SV motion independent of the prostate when using prostate fiducial markers (FM) for target verification. We investigated SV interfraction motion and SV CTV coverage when matching to prostate FM, in order to determine the impact of this motion on image guidance strategies.

Strategies for Online Organ Motion Correction for Intensity-Modulated Radiotherapy of Prostate Cancer: Prostate, Rectum, and Bladder Dose Effects

To quantify and evaluate the accumulated prostate, rectum, and bladder dose for several strategies including rotational organ motion correction for intensity-modulated radiotherapy (IMRT) of prostate cancer using realistic organ motion data. Repeat computed tomography (CT) scans of 19 prostate patients were used. Per patient, two IMRT plans with different uniform margins were created. To quantify prostate and seminal vesicle motion, repeat CT clinical target volumes (CTVs) were matched onto the planning CTV using deformable registration. Four different strategies, from online setup to full motion correction, were simulated. Rotations were corrected for using gantry and collimator angle adjustments. Prostate, rectum, and bladder doses were accumulated for each patient, plan, and strategy. Minimum CTV dose (D(min)), rectum equivalent uniform dose (EUD, n = 0.13), and bladder surface receiving >or=78 Gy (S78), were calculated. With online CTV translation correction, a 7-mm margin was sufficient (i.e., D(min) >or= 95% of the prescribed dose for all patients). A 4-mm margin required additional rotational correction. Margin reduction lowered the rectum EUD(n = 0.13) by approximately 2.6 Gy, and the bladder S78 by approximately 1.9%. With online correction of both translations and rotations, a 4-mm margin was sufficient for 15 of 19 patients, whereas the remaining four patients had an underdosed CTV volume <1%. Margin reduction combined with online corrections resulted in a similar or lower dose to the rectum and bladder. The more advanced the correction strategy, the better the planned and accumulated dose agreed.

SU-FF-T-176: Rectal and Bladder Dose in Relationship to PTV Percentage Coverage in Prostate IMRT

Purpose: To study the relationship between percentage coverage of planning target volume (PTV) in prostate cancer IMRT and dose received by normal critical structures Method and Materials: Five patients with early stage prostate cancer were selected for this retrospective planning study. For 4 of 5 patients, PTV contains clinical target volume (CTV), which is the prostate gland, plus 0.8 cm uniform margin. For the fifth patient, PTV is formed by expanding CTV (prostate plus 1 cm proximal seminal vesicle) with 0.8 cm uniform margin. The prescription is 74 Gy for the first four patients and 79.2 Gy (last patient) prescribed to 95% iso dose line and dose normalization is to isocenter. For each patient, seven different plans were generated using Varian Eclipse treatment planning system version 8.1 for 18 MV photon beams from Varian 2100C: one 6-field conformal plan and six 7-field IMRT plans with PTV volume coverage raging from 99.5% to 95%. IMRT plans were optimized by iterations to reach the targeted coverage of PTV. Results: A linear correlation between the volume receiving 70 Gy in percentage or cc and PTV volume coverage from 99.5% to 95% has been found for both balder and rectum with R2 better than 0.95 for bladder and 0.91 for rectum for the first four patients. A generalized relationship can be written as (1). All patients have a similar linear slope for bladder (average slope is 0.867±0.083 (SD)) and a slightly different slope for rectum (average slope is 0.545±0.230 (SD)). In equation (1), interception b is dependant of structure volume (bladder and rectum). Conclusions: Volume received 70 Gy by bladder and rectum in IMRT plans for prostate as CTV may have a linear relationship with PTV coverage ranging from 99.5% to 95%. One may use this relationship to guide in treatment planning process.

SU-FF-J-93: Dosimetric Feasibility of Patient-Specific Margins for Prostate Patients Using a Wireless Localization and Tracking System

Purpose: The purpose of this work is to investigate the potential dosimetric benefits of designing patient‐specific margins for prostate cancer patients based on an observation of prostate motion during the initial few treatments using a 4D localizing and tracking system.Method and Materials: 10 prostate cancer patients were localized and tracked using the Calypso Localization System. These patients were treated with a margin of 10 mm in all directions and 7 mm posteriorly from the CTV. All patients were first localized and then tracked for the entire duration of treatment for all fractions. The tracking data was used retrospectively to determine the individualized margin. The daily standard deviations of motion in all three directions were used to ascertain if after a certain number of fractions, the motion could be predicted for the remaining fractions. Another set of plans with a uniform margin of 5 mm was also developed, as this is the typical margin used by centers which performed some form of image guided treatment. Plams with the same constraints were generated for all three of these margin sets. The resulting plans were compared. Results: For all of the 10 patients, 3 standard deviations calculated for the initial 5 days of treatment, resulted in at least 95% coverage of the CTV for the whole treatment. Individualized margins were therefore, calculated based on 3 standard deviations. The individualize margin generally creates the smallest PTV volume. The smaller the margin used to create the PTV, the greater the dosimetric advantage. Conclusion: For all 10 patients, the intra‐fraction motion was predictable based on the initial 5 fractions. It suggests that individualized margin optimization is feasible without compromising on CTV coverage. Based on our data a uniform margin of 5 mm may not be adequate for some patients.

TU-D-BRC-01: Repeated Measures Analysis of Variance of Patient Specific Daily Margins to Assess Interfraction Motion for Cervical Cancer Patients Undergoing IMRT Using Daily CBCT Imaging

Purpose: To analyze interfraction motion in cervical cancer patients based on repeated measures analysis of variance of patient‐specific daily uniform margins obtained using daily CBCTimaging.Methods and Materials: Ten cervical cancer patients (stage IB‐IVA) treated with IMRT were analyzed for this study. A CTV consisting of the regional lymph nodes, upper vagina, parametria, cervix and uterus was contoured on the planning CT and daily CBCTimages. Twenty‐five CBCT scans, corresponding to each fraction were planned and attempted for each patient. The acquired CBCTimages for all the fractions were rigidly registered to the planning CT with respect to bony anatomy. The initial planning CTV was then cast onto the registered daily CBCT and were modified to reflect changes due to organ motion and deformation. Patient‐specific daily margins covering 100% of daily CTV volumes were calculated. Repeated measures analysis of variance (ANOVA) was performed on the patient specific daily margins to quantify inter‐patient and intra‐patient variations in estimated margins. Mean values within the subjects were imputed for the missing fractions. F statistics was used to test the null hypothesis that day of the treatment or fraction number had no effect on daily margins. Results: Patient specific daily uniform margins were used to generate an ANOVA table. The data shows a grand mean of 15.3 mm among all patients and fractions which represents the estimate of the average population margin. In addition, the inter‐patient standard deviation in margins is 5.1 mm and intra‐patient standard deviation is 35.4 mm indicating that the variation between patients is significant. The F statistics (F = 0.654) was significant indicating that the day of the treatment or fraction number had no influence on margin. Conclusion: Margins varied substantially between patients indicating adaptive RT approaches are needed for the treatment of cervical cancer patients.

MO‐D‐BRB‐08: A Hybrid Strategy of Offline Adaptive Planning and Online Image Guidance for Prostate Cancer Radiotherapy

Purpose: In online image‐guided radiotherapy of prostate cancer, the setup error and inter‐fractional motion is eliminated through pre‐treatment imaging and couch correction at each fraction. However, the rotation and deformation is not corrected and only accounted for in planning margin. In this study, we propose a hybrid of online and offline adaptive image‐guidance strategy for both low risk patients (LRP, CTV=prostate) and intermediate risk patients (IRP, CTV=prostate+seminal vesicles). The benefit of margin reduction is evaluated geometrically. Method and Materials: Planning and treatment helical CT images from 25 patients over 412 fractions were used. Online image‐guidance was simulated by matching the center of mass of CTV in treatment CT to planning CT. Offline replanning was performed by constructing the internal target volume (ITV) from the union of position‐corrected CTVs from the first 5 treatment CTs. The volume overlap index (OI) of ITV and CTVs of the remaining fractions were compared with the OIs between PTV from planning CT and the treatment CTVs. Margins from 0 to 10 mm were investigated. Results: The mean ITV volumes are 62.5 and 90.1 cm3 for LRP and IRP, respectively, equivalent to 0.8 and 1.0 mm uniform margin to CTV0 (mean volumes of 55.7 and 78.0 cm3). The margins needed for 99% OI for ITV (V99% = 67.9 and 105.5 cm3) are 1.7 mm and 2.6 mm less than those for the planning CTV (V99% = 84.5 and 144.7 cm3) for LRP and IRP, respectively. Conclusion: The hybrid of online and offline adaptive radiotherapy protocol can effectively account for the patient‐specific interfraction organ motion and setup errors for prostate cancer patients. The planning margin can be reduced further using the hybrid strategy compared with online image guidance alone. Reduced irradiated volume will also lead to decreased toxicity in critical organs.

Ponds and Streams: Wealth and Income in the U.S., 1989 to 2007

Much discussion treats the working definitions of wealth and income as if they were self-evident, but definitional choices can make substantial differences in the overall picture. To provide a clear basis on which to examine family wealth and income their interrelationship, this paper begins with a basic discussion of a range of possible measures of those concepts. Using the measures developed, the paper examines the distributions of wealth and income and their joint properties using data from the 1989-2007 waves of the Survey of Consumer Finances (SCF). Among other things, the data show a complicated pattern of shifts in the wealth distribution, with clear gains across the broad middle and at the top. For income, there is a more straightforward picture of rising inequality. Over this period, wealth as a fraction of income moved up across both the distributions of wealth and income. Nonetheless, their joint copula distributions (a type of distribution with uniform margins) do not show noticeable changes over this time. The consistent pattern is that very high wealth and income and very low wealth and income go together, but in between these poles, the relationship is fairly diffuse. The paper also presents information on the composition of wealth and income over the 18-year period the general patterns of holdings across the distributions did not change markedly, but there were some important shifts. For wealth, debt increased as a share of assets across the wealth distribution, the share of principal residences rose mainly below the median of net worth, the share of tax-deferred retirement accounts rose and the share of other financial assets declined. For income, the clearest change was a general decline in the relative importance of capital income other than that from businesses.