bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐785: Evaluation of HybridArc‐‐a Novel Treatment Planning and Delivery Approach
Authors: Robar J
Published: November 2011

Purpose: This investigation focuses on possible dosimetric and efficiency advantages of HybridArc—a novel treatment planning approach combining optimized dynamic arcs with IMRT beams. Application of this technique to two disparate sites, complex cranial tumors and prostate, was examined. Methods: HybridArc plans were compared to either dynamic conformal arc (DCA) or IMRT plans, in order to determine whether HybridArc offers a synergy through combination of these two techniques. Plans were compared with regard to target volume dose conformity, target volume dose homogeneity, sparing of proximal organs at risk, normal tissue sparing and Monitor Unit (MU) efficiency. Results: HybridArc produced improved and comparable dose conformity for cranial and prostate cases, respectively, compared to IMRT. Using the DCA technique produced inferior results on average in this regard, for both sites. For prostate cases, HybridArc also offered the advantage of improved dose homogeneity in the target volume compared to IMRT. Both arc‐based techniques distribute peripheral dose over larger volumes of normal tissue compared to IMRT, while HybridArc involved slightly greater volumes of normal tissues compared to DCA. Compared to IMRT, cranial cases required 38% more MUs, while for prostate cases, MUs were reduced by 7%. Conclusions: HybridArc is capable of improving dose conformity and dose homogeneity for cranial and prostate cases, respectively. MU efficiency may depend on the complexity of the case.

This work results from a collaboration with Brainlab, AG but no financial support has been received by this company during the course of the investigation.
SU‐E‐T‐790: The Effect of Pulmonary Emphysema on Lung SBRT Dosimetry
Authors: Yang W , Lobo M , Dunlap N , Read P , Benedict S , Sheng K , Larner J
Published: November 2011

Purpose: The purpose of this study is to systematically analyze the effect of pulmonary emphysema (PE) on the dosimetric results for intensity modulated arc therapy (IMAT). Methods: One patient diagnosed with non‐small cell lung cancer was chosen as the model patient. Hypothetic tumors with volumes of 2cc, 48cc and 169cc were contoured in the right middle lung. GPU based helical tomotherapy IMRT planning system is used in the study. 50 Gy in 5 fractions were prescribed to planning target volume (PTV). The planning parameters include a jaw size of 2.5 cm and 1cm, a pitch of 0.287 and 0.1, and dosimetric constrains according to RTOG 0813. To simulate emphysema lung density was overwritten from 0.05 to 0.4 g/cc. The dosimetric results such as tumor coverage, R50, and lung V20 were analyzed. Results: All plans satisfy 95% of PTV receiving 50Gy prescription. Lung density has a significant effect on the dosimetric results for all tumor sizes studied. For plans with jaw size of 2.5 cm and pitch of 0.287, R50 increases by as much as 92%, 55% and 35% for PTV of 2cc, 48cc and 169cc, when the lung density was reduced from 0.3 to 0.05 g/cc. Similarly, lung V20 increases by 32%, 20% and 18% for PTV of 2cc, 48cc and 169cc, respectively. Interestingly, for plans with jaw size of 1cm and pitch of 0.1, although the R50 for different tumor sizes follows similar trend as 2.5cm plans, the effect of lung density on V20 is non‐linear. For PTV of 2cc and 48cc, V20 plot shows a peak with varying lung densities. Conclusions: Systematic planning studies show that lower lung densities generally result in poorer dosimetry due to the greater difficulty to achieve electron equilibrium. Therefore, the lung density should be taken into consideration in the lung SBRT protocol.
SU‐E‐T‐792: Dosimetric Influence of Carbon Fiber Couchtop on Volumetric‐Modulated Arc Therapy
Authors: Hu Z , Dai J
Published: November 2011

Purpose: To evaluate the dosimetric influence of carbon fiber couchtop on Volumetric‐modulated arc therapy (VMAT). Methods: In this study, a carbon fiber couchtop has been incorporated into Pinnacle3 9.0 treatment planning system, with the help of model‐based segmentation (MBS) function. This was done by generating the couch topˈs model from contours of the couchtop, together with the density information. Ten cases previously treated with VMAT in our institute were selected, six head‐and‐neck (HN), two thoracic, two abdomen cases. For each case, a VMAT plan was optimized without the couchtop model, and the final dose calculation was performed twice, with (WI plan) or without (WO plan) the couchtop model. Dual arcs with full or partial gantry rotation were used according to each caseˈs geometry. The MU of WI plan was set to the same value of the WO plan for comparison. Dose indices for targets and OARs were determined from dose—volume histograms.Results: The comparison for the 10 cases showed that the WI plans achieved worse target volume coverage than WO plans, with an average difference of 3.3% in V100% (target volume that receives 100% of the prescription dose). Especially for small boost volumes, the difference larger that 11% in V100% was observed. The largest difference in mean dose of the target volumes was 1.0 Gy. For almost all the OARs, the mean doses for WI plan were smaller than those for WO plans Conclusions: In conclusion, the carbon fiber couchtop significantly affects the dose delivered to the target volume(s) in volumetric‐modulated arc therapy, and should be included in treatment planning to avoid any discrepancy between the prescribed dose and delivered dose.
SU‐E‐T‐793: Static‐Gantry and Rotational IMRT with Flattening Filter Free versus Flattening Filtered Beams
Authors: Chen G , Hu X , Kainz K , Chang Y , Li X
Published: November 2011

Purpose: The flattening filter free (FFF) photon beams offer high dose rate, greatly speeding up treatment delivery. This work aims to evaluate the impact of FFF beam on treatment planning for both static‐gantry (sIMRT) and rotational IMRT (rIMRT). Methods: Both FFF and flattening filtered (FF) photon beams from a Siemens Artiste machine, calibrated to deliver 1 cGy/MU at dmax with a 10×10 cm, 2 field, were used in our study. Both sIMRT and rIMRT plans were generated with either FFF or FF beams for 10 previously treated cases, using a planning system based on direct aperture optimization algorithm (Panther, Prowess). The plans were compared based on dose‐volume histograms with parameters including dose uniformity for planning target volume (PTV) and equivalent uniform dose for organs at risk (OAR), as well as monitor unit (MU) numbers. Results: In general, the plan qualities for rIMRT plans are equal to or slightly better than those for sIMRT, while the plan quality of a FFF‐beam plan is slightly worse than that for the corresponding FF‐beam plan. The plan quality of a FFF‐beam rIMRT plan is close to that for the FF‐beam sIMRT plan, and the former has slightly worse dose uniformity in PTV but slightly better OAR sparing. Both rotational delivery and the use of FFF‐beam require more MUs, with the latter to more extent. The MU increase can be up to 34% for large PTV and complicated OAR configurations. However, FFF‐beam rIMRT has the advantages of high delivery efficiency with overall treatment time reduced by up to 30%. Conclusions: Plan quality degrade associated with FFF beams can be compromised with rotational IMRT technique. The overall treatment time can be reduced with FFF beams, even though the total MUs are increased. FFF beams are more advantageous for a small sized target or less complicated OAR geometry.
SU‐E‐T‐796: Assessment of Dose Distribution and Delivery Efficiency of Two Volumetric Modulated Arc Therapy Planning Techniques for Breast Cancer
Authors: Tsai P
Published: November 2011

Purpose: To assess the dose distribution and delivery efficiency on two different Volumetric Modulated Arc Therapy (VMAT) planning techniques for breast cancer. The beam‐on time (BOT) was measured for the possibility of incorporating patient motion management system with VMAT. Methods: Three treatment scenarios were assessed: Whole Breast Irradiation (WBI), WBI plus supraclavicular lymph node (WBI+SC) and bi‐lateral WBI (BL‐WBI). Six partial arcs (P‐ARC) (50 degree per arc for WBI and WBI+SC; 80 degree per arc for BL‐WBI) and two full arcs (F‐ARC) planning techniques were compared. The targets and organs‐at‐risk (OAR) were contoured on the CT images. All plans were optimized with the same objectives in Eclipse treatment planning system and were normalized to V95% equal to 95% on PTV in 50.4Gy prescription dose. Results: For all the plans, the PTVs received 55.44Gy were less than 1c.c.. P‐ARC technique has superior dose distribution to the F‐ARC in terms of V20Gy for lungs, V25Gy for hearts and mean doses for right breast. The volume received the low integral dose on the P‐ARC (V5Gy ∼50%) is approximately half in comparison to the F‐ARC (V5Gy =100%) on the ispli‐lateral lung and heart. The total BOT and the MU per plan was less in P‐ARC than in F‐ARC, especially the BL‐WBI. The BOT per arc is 13 seconds (P‐ARC) and 40 seconds (F‐ARC) respectively on the WBI and WBI+SC scenarios. For the BL‐WBI, average BOT per arc was 20 seconds (P‐ARC) and 85 seconds (F‐ARC). Conclusions: Our P‐ARC achieved excellent PTV coverage while maintaining extremely low doses to OARs in comparison to the F‐ARC. If the breathing holding technique is applied, the patient is able to achieve one breath holding per arc using the P‐ARC technique. The efficiency of the P‐ARC technique could provide the patient comfort and achieve precise treatment.
SU‐E‐T‐801: VMAT for the Treatment for Cervical Carcinoma and Para‐Aortic Nodes
Authors: Lee C
Published: November 2011

Purpose: The PTV of cervical carcinoma and para‐aortic nodes is unique for its large width and length which pose a challenge to VMAT because of the MLC leaf length, speed and gantry rotation speed restrictions. This study establishes a field arrangement for VMAT and assesses the differences between VMAT and IMRT plans. Methods: Six patients were randomly selected for the study. The CTV included the areas of subclinical risk around the GTV and associated lymph node drainage sites. The PTV margin includes a 0.7cm expansion around the lymph nodes and 0.5cm margin elsewhere. Organs at risk included rectum, bladder, small bowel and kidneys. Six plans, each consisting of three arcs (collimator angle 90 degrees on one and 0 on others) and 9 field IMRT plans were generated with Eclipse treatment planning system and delivered with a 6MV beam and 120 leaf MLC. Planning goals for both VMAT and IMRT plans were: V100 of the PTV covered by 98% prescription dose with a maximum dose <112%, V15 < 33% for both kidneys, V40<60% for bladder and rectum and mean small bowel dose < 30Gy. Treatment time was measured from when the beam data was loaded into the treatment console to the end of beam delivery. Results: The average PTV was 1850cm3. The PTV coverage met the constraints on all plans. The average rectal V40 (VMAT: 56%; IMRT: 62%), bladder V40 (VMAT: 55%; IMRT: 59%) and mean small bowel dose (VMAT: 23Gy; IMRT: 24Gy) were comparable. The mean left and right kidneys V15 were substantially reduced with VMAT (VMAT: 15%; IMRT: 28.1%) and (VMAT: 14.1%; IMRT: 29.5%). VMAT reduced the average MU from 2581 to 662 resulting mean delivery time of 791s to 292s. Conclusions: VMAT results substantial kidney sparing for the same coverage while reducing treatment time and monitor units.
SU‐E‐T‐812: Case Studies with the Monaco Treatment Planning System
Authors: Culberson W
Published: November 2011

Purpose: To compare different plan and delivery techniques with the Monaco Treatment Planning System (TPS) and identify which techniques achieve the goals of short treatment times and good DVHs. Methods: Monaco is an IMRT‐only TPS that is capable of creating plans with step‐and‐shoot, DMLC, consolidated DMLC, and VMAT delivery techniques. We are using Monaco Version 2.04 and delivering treatment plans with an Elekta Infinity linear accelerator and Model MLCi2 multi‐leaf collimator. In this study, a prostate case and a head and neck case are planned using each delivery method. The plan DVH and treatment times are compared to identify the best plan for treatment. Our department treats an average of 50–60 patients per day on a single accelerator, so shorter treatment times weigh heavily on the selection of the best treatment plan. Results: For the Head and Neck treatment plan, the DVH of a seven‐field DMLC treatment plan was favored over the VMAT technique because of better target coverage. Furthermore, the treatment delivery time was faster with the DMLC than it was for the VMAT. Because of this, the DMLC plan was selected for its increased delivery efficiency and favorable DVH. For the prostate plans, the DVHs were comparable with each delivery method, but the treatment times were significantly shorter with VMAT delivery. The treatment times were 9 minutes, 6 minutes, 4 minutes, and 3 minutes for step‐and‐shoot, DMLC, consolidated DMLC, and VMAT, respectively. Because the DVHs were comparable, VMAT was selected for its increased delivery efficiency. Conclusions: Although VMAT is a faster delivery technique with a comparable DVH for prostate treatments, DMLC is chosen for a head and neck treatment. This study highlights the importance of analyzing the various delivery techniques available when using the Monaco treatment planning system to select the best treatment plan.
SU‐E‐T‐817: Comparison of a Hybrid Planning Technique with Standard IMRT Planning
Authors: Estabrook W , Willoughby T
Published: November 2011

Purpose: To determine if a hybrid planning technique consisting of a combination of dynamic‐conformal arcs and IMRT beams meets or exceeds dosimetric markers defined by IMRT‐only planning techniques. Method and Materials: In an IRB approved protocol for retrospective review, eleven cranial CT data sets consisting of different lesion sizes and shapes were contoured and planned for radiotherapy. Planning was to clinical guidelines and doses for each tumor. Hybrid plans used 5 non‐coplanar, MLC‐dynamic arcs (with fixed dose rate) with 2–4 IMRT beams. IMRT‐only plans used 9–14 non‐coplanar beams. Brainlabˈs iPlan 4.1 was used to plan all cases and generate respective DVH values. Normal tissue was defined as external contour, minus the target structure. Conformity/Gradient Index (a normalized value with 100 representing optimal), low‐to‐intermediate isodose volumes, and hotspots (D1cc=dose to 1cc) were used as dosimetric benchmarks. Results: Comparing CGI for each data set, the average score for the hybrid plans was 77, while for IMRT‐only it was 73. The radius related to the gradient component of the CGI score shows that hybrid plans gave, on average, a 0.38 mm tighter dose gradient between RX isodose to 50% of prescription. The volume of the 25% isodose line was on average 33cc smaller with the hybrid plan than the IMRT only plan. Lastly the maximum dose (D1cc) showed little difference between techniques. Conclusions: This planning analysis indicates that the standard IMRT approach to fractionated cranial treatments can be improved by creating a hybrid plan consisting of IMRT beams and dynamic‐conformal arcs. The hybrid technique reduced dose gradients, improved conformality, and reduced volumes of low‐to‐intermediate isodose lines. It should be noted that both techniques required approximately the same amount of time to plan with an estimated reduction in treatment time due to fewer couch angles.
SU‐E‐T‐823: Implication of the Spatial Resolution of the Conventional Dose‐Volume Histogram Analysis in the Radiation Therapy Treatments
Authors: Pyakuryal A , Pokhrel D , Jang S , Gopalakrishnan M , Sathiaseelan V , Mittal B
Published: November 2011

Purpose: The detection of the local‐spots of interest is important in evaluation of radiotherapy treatment plans. The conventional dose‐volume histogram (DVH) analysis loses the spatial information of the dose‐distribution such as “hot” and “cold” spots in the evaluation process. However, the cDVH can be resolved into the components of spatial‐DVHs (sDVHs; x‐,y‐ and zDVHs respectively). The objective of this work was to assess the accuracy of IMRT plans using a noble approach of sDVH analysis in the open‐source software system, Histogram Analysis in Radiation Therapy, HART (J Appl Clin Med Phys, Vol.11 (1), p. 3013, 2010). Method and Materials:The contours of the regions‐of‐interest along z‐direction were reformatted to generate contours along x‐, and y‐ planes respectively, using RTOG format of the IMRT plans of 10 head and neck cancer patients (N=10). The dose computed along z‐planes of the CT slices were used to compute dose‐volume matrices along x‐,y‐ and z‐planes respectively, using the user‐friendly HART program. The sDVH data‐points were validated with the cumulative‐DVH (cDVH) statistics of the corresponding organs. The sDVH statistics were utilized to assess the dose‐distribution in organs‐at‐risk such as salivary glands and larynx. Results: HART extracted more than 7000 sDVH statistics in 15–20 minutes for 20–30 organs using the dual‐core processor of 3GB RAM. The hot‐spots estimated from the sDVH analyses, were consistent with the cDVH analyses at higher resolution (1 mm). The low‐density hot‐spots (< 5% per slice) were symmetrically polarized in 3D‐space in 57 ±12% and 93 ±2% of the slices (N=10) of parotid glands and larynx respectively, however high‐density hot‐spots were detected in 90 ±8% of the slices (N=10) of the submandibular glands. Conclusions: The sDVH analysis is an accurate and efficient approach for the in‐depth analysis of the radiotherapy plans and the radio‐biological outcomes of the treatments, using the HART program.
SU‐E‐T‐826: Dosimetric Comparison of Intensity‐Modulated Proton Therapy and 3D Proton Radiotherapy with Passively Scattered Beams for Primary Prostate Cancer
Authors: Dimofte A , James P , Kassaee A , McDonough J , Tochner Z
Published: November 2011

Purpose: To evaluate the dose distributions for treatment of primary prostate tumor using plans with intensity modulated proton therapy (IMPT) and plans with 3D conformal proton beam using passive scattering beams. Methods: We generated treatment plans for five patients with two different proton treatment planning technique (IMPT and 3D conformal) using opposed lateral beams. The 3D conformal plans included passively scattered beams with appropriate beam compensators to conform the dose along the distal region of each beam. IMPT planning applies the spot scanning beam and uses the dose optimization process to reduce the dose to normal tissue and provide adequate prescription dose to prostate. The planning target volume (PTV) included prostate and margins to account for dosimetric and setup uncertainty. The total prescription dose (PD) for each plan is 79.2 Gy. We require that 99% of the clinical target volume (prostate) is covered by 98% of PD (D99%=78.4 Gy) and the PTV dose criteria is D98%=75.2 Gy. The dose for rectum and bladder for volumes of 20% and 40% (D20%, D40%) was optimized such that D20% and D40% are less than or equal to 60 Gy and 40 Gy respectively. The index of conformality (CI) was evaluated using the ratio of PTV volume to that of volume covered by 95% of PD. Results: The PTV dose coverage is achieved for both techniques but IMPT plans showing better dose homogeneity and lower maximum dose. Overall, the D20% and D40% slightly decreased for rectum for all plans. However, for bladder, there is higher dose reduction for IMPT plans as compared to 3D proton plans. The CI was improved for IMPT plans. Conclusions: The IMPT technique results in plans with better PTV coverage and lower dose to organ at risk as compared to plans with passively scattered beams.
SU‐E‐T‐843: Direct Segment Optimization of Conformal Plans: Achieving Equivalence with Beamlet IMRT
Authors: Fraass B , Steers J , Matuszak M , McShan D
Published: November 2011

Purpose: Use of inverse planning to improve conformal treatment plan quality has concentrated on optimization of beamlet‐based IMRT plans. The few direct aperture‐based optimization methods are all based on optimizing a beamlet‐based plan, followed by sequencing which identifies the many apertures to be optimized. In contrast, direct segment optimization (DSO), described here, directly optimizes conformal and few‐segment plans using inverse planning. This work compares DSO‐optimized plans versus beamlet IMRT and forward‐planned 3DCRT plans for a series of clinical sites. Methods: Our in‐house beamlet‐based inverse planning system has been enhanced to support DSO with an improved and reimplemented perturbational version of the Edge/Octree calculation algorithm and a multilayer search strategy. DSO optimizes MLC segment shapes, weights and/or jaw positions for multiple field plans (including VMAT). In our inverse planning infrastructure, beamlet, multi‐segment and conformal plans can all be optimized using the same cost functions, dose points, and plan evaluation metrics, making quantitative comparisons between techniques straightforward. Inverse planned DSO 3DCRT plans are compared to forward planned 3DCRT and beamlet IMRT plans for brain, liver, lung, and other sites. Results: For many tested patient geometries, DSO achieves equivalent plan quality to the beamlet IMRT plan optimized with the same cost function, though there are certain situations where IMRT is expected to (and does) perform better. The DSO plans use significantly fewer MU, require less treatment time, are less sensitive to motion, and do not require pre‐treatment IMRT QA checks, so they may be significantly easier to implement in the clinic. Conclusions: Optimization of 3DCRT and multi‐segment plans using DSO results in plan evaluation metrics virtually equivalent to beamlet IMRT plans optimized with the same cost function and beam directions, for many geometries. DSO may potentially lead to important efficiency savings for many clinical protocols.

Supported in part by NIH P01‐CA59827
MO‐D‐BRB‐10: Optical Surface Imaging for Online Rotation Correction and Real‐Time Motion Monitoring with Threshold Gating for Frameless Cranial Stereotactic Radiosurgery
Authors: Li G , Ballangrud A , Kuo L , Kang H , Kirov A , Lovelock D , Yamada Y , Mechalakos J , Amols H
Published: November 2011

Purpose: To develop an image‐guided procedure for online head‐rotation correction and real‐time motion monitoring with threshold gating for clinical frameless stereotactic radiosurgery (SRS) using video‐based optical 3D surface imaging (AlignRT) to ensure accurate tumor localization and clinically‐acceptable head motion at all treatment couch angles during treatment. Methods: Eight patients, immobilized with a deep‐head mold and a mouth‐piece fixed to the couch, were treated with single‐fraction frameless SRS. The planning target volume was defined by a 3.0mm‐margin around the gross tumor volume for these patients with brain metastasis. A ceiling‐mounted AlignRT system with three camera pods was used to correct residual head rotation before cone‐beam computed tomography (CBCT) setup, verify setup at all treatment couch angles, and monitor the head motion with 1.0mm gating threshold for beam hold. The external contour of the planing CT and on‐site surface reference images were used for setup verification and motion monitoring, respectively, using the maximum visible skin surface within the entire mid‐to‐upper face as the region of interest. An anthropomorphous head phantom and an adjustable platform (accuracy of 0.1 mm) were used to determine the geometric accuracy of frameless setup procedure and AlignRT motion detection. Results: The phantom experiment shows that the motion detection accuracy was less than 0.1 mm. For these patients, <1 degree head rotation was achieved at the setup by using surface‐image‐guided head repositioning. The patient head motion was found to be <1.0mm for 98% of the time after CBCT setup, while the beam‐hold gating was used for <1% of beam‐on time. The required workload and machine time of this procedure are similar to those of conventional frame‐based SRS. Conclusions: This non‐invasive frameless SRS procedure provides accurate and reliable means to perform clinical SRS. The image‐guided setup and motion control provides adequate accuracy, yet more convenient to the patients, comparing with frame‐based SRS. This research is in part supported by VisionRT through a clinical research agreement.
MO‐D‐BRC‐07: Reducing Artifacts in Cone‐Beam CT Images Caused by the Presence of An Array Used for Tracking Transponders during Radiotherapy
Authors: Maurer J , Godfrey D , Wu Q
Published: November 2011

Purpose: To compare two methods for reducing artifacts in cone‐beam CT (CBCT) images caused by the presence of an electromagnetic array used for tracking transponders during radiotherapy. Methods: A pelvis phantom was imaged using a gantry mounted CBCT system at two dose levels typical for prostate imaging. Both dose protocols acquired approximately 670 projections at 125 kVp. Tube currents and pulse widths were 80 mA/13 ms and 63 mA/10 ms for standard and low dose scans. The phantom was imaged with and without the array in position. The two methods used to reduce artifacts were: 1) filtering projection images prior to reconstruction, and 2) halving the dose per projection and doubling the number of projections. The filtering method replaced pixel values with neighboring values when pixels differed from neighboring pixels by a threshold percentage. 18, 22, 26 and 30% thresholds were investigated. Artifact reduction was quantified by computing difference images between the ‘corrected’ reconstructions and the image reconstructions for the phantom without the presence of the array. The filtering method was also applied to a prostate patient data set. Results: Average pixel values of the difference images were reduced by 6.4 and 7.3% for the 18% threshold filtered reconstructions for low and high doses, respectively, compared with difference images between the unaltered reconstructions with and without the panel. Reductions were 4.4 and 4.9% for other thresholds for low and high dose images. 8.6 and 19.6% reductions were calculated for low and high dose images using increased projection numbers. Improved soft tissue visibility was noted in the filtered patient reconstructions. Conclusions: Both filtering and increasing projection numbers reduced artifacts caused by the presence of an electromagnetic array in CBCT imaging. Quantitative and visual analyses suggested that greater artifact reduction was achieved with increased projection numbers.
MO‐D‐BRC‐08: Improving the McKinnon‐Bates 4D‐CBCT Reconstruction Algorithm through Prior Destreaking
Authors: Sun M , Star‐Lack J
Published: November 2011

Purpose: On‐board 4D cone‐beam computed tomography (CBCT) is being actively pursued to help guide radiotherapy treatments of lung tumors. Among the existing 4D‐CBCT methods, the McKinnon‐Bates algorithm (MKB) has the advantage of being computationally efficient and not requiring additional scan time compared to a conventional 3‐D acquisition taking on the order of 1 minute. The resulting images, however, can suffer from temporal hysteresis and ghosting artifacts that hinder tumor delineation and determination of motion trajectories. This work describes an improvement to the MKB algorithm that reduces or eliminates the ghosting artifacts and restores tumor conspicuity in the lungs. Methods: Temporal blurring and ghosting are identified as being caused by motion‐induced streaks in the 3D image that serves as the MKB prior and which, ideally, should be a time‐averaged image of all respiratory phases. A prior destreaking method, using tissue thresholding and boundary erosion operations, is then proposed to remove the streaks without introducing new artifacts in the final phase images. The method is tested on simulated data using the XCAT phantom and on in vivo data from lung tumor patient. Image quality improvements are assessed in moving and static tissue. Results: The prior destreaking technique successfully removed motion‐induced streaks from the prior images, and the subsequent MKB reconstructions provided accurate spatial and temporal information. The lung tumor patient exhibited +/ −6 mm of diaphragm motion that was not seen in the original MKB reconstruction, but was clearly recorded after prior destreaking was employed. Phantom images were similarly improved. Conclusions: The MKB algorithm is enhanced by destreaking the prior image, and the proposed thresholding‐ and erosion‐based technique is proven to be effective and efficient. This approach enables 4D‐CBCT images to be acquired and reconstructed in a sufficiently short period of time forIGRT.

All authors are employees of Varian Medical Systems.
MO‐D‐220‐02: Assessing Intra‐Tumor Hemodynamics and Oxygen Concentration Using Photoacoustic Computed Tomography
Authors: Stantz K , Cao N , Shaffer M
Published: November 2011

Purpose:The goal is to develop a method to non‐invasively assess intra‐ tumor pO2 using photoacoustic imaging. It is well established that the oxygen status of a tumor plays a critical role in the therapeutic response and resistance, resulting in treatment failure and poor disease‐free and overall survival. Clinical techniques, such as polarographic electrode, photoluminescence‐quenching, or pimonidazole, are invasive and lack the patho‐physiological etiology leading to hypoxia. A biophysical model is proposed to determine local pO2 based on fusing hemodynamic measurements acquired from dynamic contrast‐enhanced and spectroscopic photoacoustic imaging (DCE‐PCT and PCT‐S). Methods: MCF7 and MCF7/VEGF xenograft breast tumors were first scanned within a prototype PCT scanner to obtain parametric maps of oxygen saturation and hemoglobin concentration and within a clinical CT scanner to obtain dynamic contrast‐enhanced data (DCE‐CT) to obtain parametric maps of perfusion, fractional‐plasma‐volume, and fractional‐interstitial‐volume. These maps were fused based on a mathematical model of tissue oxygen delivery, and compared to measurements taken with an OxyLite probe. To replace DCE‐CT, a new generation of PCT scanner was developed to acquire DCE‐PCT data and realize physiological maps. Mice with MDA‐ MB‐231 xenograft breast tumors were i.v. injected with ICG, and scanned prior to and every 12‐seconds for up to 4‐minutes and at 15‐minutes post‐ injection. These contrast‐enhance curves were fit compartmental models to obtain maps of tumor perfusion and fractional plasma volumes. Results: Preliminary results comparing pO2 measurements implementing biophysical models and PCT‐S and DCE‐CT and OxyLite probe measured a linear correlation of R2=0.82, and a slope of 0.975(±0.10) and an intercept of − 0.093(±2.2)mmHg. The first parametric maps of tumor perfusion and fractional plasma volume using DCE‐PCT will be presented and compared to DCE‐CT, and ICG kinematics identifying regions of high extravasation. Conclusions: A biophysical model of pO2 based on hemodynamic data and physiological maps in breast tumors obtained from photoacoustic imaging has been demonstrated.

NIH/SBIR Funding from OptoSonics, Inc, OptoSonics, Inc., 108 Straight Road, Oriental, NC 28571; Consulting for Endra, Inc, 35 Research Drive, Suite 100, Ann Arbor, MI 48103.
MO‐F‐BRA‐05: Comparison of Organ Dosimetry for Astronaut Phantoms: Earth‐Based vs. Microgravity‐Based Anthropometry and Body Positioning
Authors: Bahadori A , Shavers M , Baalen M Van , Semones E , Bolch W
Published: November 2011

Purpose: To use NASA radiation transport codes to compare astronaut organ dose equivalents resulting from solar particle events (SPE), geomagnetically trapped protons, and free‐space galactic cosmic rays (GCR) using phantom models representing Earth‐based and microgravity‐based anthropometry and positioning. Methods: The University of Florida hybrid adult phantoms were scaled to represent male and female astronauts with 5th, 50th, and 95th percentile heights and weights as measured on Earth. Another set of scaled phantoms, incorporating microgravity‐induced changes, such as spinal lengthening, leg volume loss, and the assumption of the neutral body position, was also created. A ray‐tracer was created and used to generate body self‐shielding distributions for dose points within a voxelized phantom under isotropic irradiation conditions, which closely approximates the free‐ space radiation environment. Simplified external shielding consisting of an aluminum spherical shell was used to consider the influence of a spacesuit or shielding of a hull. These distributions were combined with depth dose distributions generated from the NASA radiation transport codes BRYNTRN (SPE and trapped protons) and HZETRN (GCR) to yield dose equivalent. Many points were sampled per organ. Results: The organ dose equivalent rates were on the order of 1.5–2.5 mSv per day for GCR (1977 solar minimum) and 0.4–0.8 mSv per day for trapped proton irradiation with shielding of 2 g cm−2 aluminum equivalent. The organ dose equivalents for SPE irradiation varied considerably, with the skin and eye lens having the highest organ dose equivalents and deep‐seated organs, such as the bladder, liver, and stomach having the lowest. Conclusions: The greatest differences between the Earth‐based and microgravity‐based phantoms are observed for smaller ray thicknesses, since the most drastic changes involved limb repositioning and not overall phantom size. Improved self‐shielding models reduce the overall uncertainty in organ dosimetry for mission‐risk projections and assessments for astronauts.

This research was supported by NASA GSRP Grant NNX09AK14H and NASA Bioastronautics Contract NAS9‐02078.
MO‐F‐BRB‐03: A GPU‐Based Finite‐Size Pencil Beam (FSPB) Algorithm with 3D‐ Density Correction for Radiotherapy Dose Calculation
Authors: Gu X , Jelen U , Li J , Jia X , Jiang S
Published: November 2011

Purpose: To develop an accurate and efficient finite size pencil beam (FSPB) dose calculation engine for online adaptive radiotherapy. Methods: The new GPU‐based 3D‐density correction FSPB dose calculation engine (g‐DC‐FSPB) is built on our previously published ultrafast FSPB (g‐FSPB) computational framework. The new dose engine correctly accounts for medium heterogeneities by providing both lateral and longitudinal density corrections and its GPU implementation is designed to maximize the data‐ parallel strength of GPU and minimize the memory‐conflict issues. Results: Dosimetric evaluations of the g‐DC‐FSPB dose calculation algorithm against MCSIM Monte Carlo dose calculation algorithm are conducted on 10 IMRT treatment plans with heterogeneous treatment regions (5 head‐and‐ neck cases and 5 lung cases). For head and neck cases, when cavities exist near the target, the improvement with the 3D‐density correction is significant. However, when there are high‐density dental filling materials in beam paths, the improvement is small and the accuracy of the new algorithm is still unsatisfactory. On the other hand, significant improvement of dose calculation accuracy is observed in all lung cases. Especially when the target is in the middle of the lung, the accuracy improvement with the 3D‐density correction is dramatic. Regarding the efficiency, because of the appropriate arrangement of memory access and the usage of GPU intrinsic functions, the dose calculation with the g‐DC‐FSPB algorithm for an IMRT plan on can be accomplished well within 1 second (except for one case) a NVIDIA Tesla C1060 card. Conclusions: We have implemented a GPU‐accelerated 3D‐ density correction FSPB dose calculation engine and systematically evaluated its dosimetric accuracy and computational efficiency. Compared to the original g‐FSPB algorithm, the new g‐DC‐FSPB algorithm significantly improve accuracy with slightly scarification of the computation efficiency (about 5–15% slower in terms of the total computation time), indicating that this algorithm is more suitable for online IMRT replanning.
MO‐F‐BRC‐02: A Method for 4D Tumor Tracking Using Dynamic 2D Orthogonal MRI
Authors: Tryggestad E , Roland T , Shea S
Published: November 2011

Purpose: Current methods for deriving tumor motion in the pre‐treatment setting, e.g. 4D‐CT or planar x‐ray fluoroscopy, fail to address breathing motion variability and result in imaging dose to the patient. “4D” treatment planning and delivery methods, most of which are under development, typically rely on a robust characterization of motion. Implementation of these beneficial 4D methods may be hindered by deficiencies in pre‐ treatment imaging. To characterize motion and associated variability over extended durations, we have developed a technique employing 2D dynamic MRI acquired in orthogonal planes intersecting the tumor. Methods: 2D balanced steady‐state free precession (bSSFP; TR=2.9 ms; TE=1.22 ms; flip angle=77–79°) MRI was acquired continuously over >4 minutes with interleaved sagittal and coronal planes in two healthy (lung and abdomen) volunteers at 1.5 T using a MAGNETOM Espree MRI (Siemens). In‐plane resolution was 2 mm and the slice thickness was 5 mm. The imaging grid was 160×160 and 176×176 for the lung and abdominal volunteer, respectively. The resulting frame rate was 4 frames/sec. Synchronous with image acquisition, an external respiratory trace was collected at 50 Hz. Results: 4D tracking of normal anatomy was successfully performed using custom software (Matlab, The Mathworks Inc.). Rectangular template matching was employed via normalized cross‐correlation‐based optimization. MRI frames were up‐sampled (4×) to provide improved tracking resolution (0.5 mm). Image feature positions in 3D as a function of time were derived by interpolating 2D data from each plane onto a regular temporal grid according to the frame rate. Conclusion: In patients, this technique will be employed to derive the mean tumor trajectory and the breathing phase‐dependent tumor position uncertainty over the imaging duration. The external respiratory trace provides important data, allowing for careful study of its viability as a surrogate. Future efforts will involve modifications to the bSSFP sequence for significant improvements in speed.

This work was made possible, in part, by research personnel support from Siemens.
MO‐F‐214‐01: A Novel Dosimetry System Useful for Accurate and Optimal Total‐Skin Electron‐Beam Therapy
Authors: Li S , Micaily B , Chan P , Liu Z , Miyamoto C
Published: November 2011

Purpose: We are introducing a dosimetric system for calculation of dose distribution within patients from total skin electron beam (TSEB) in order to avoid large dose variations and frequent setup changes for accurate and safe TSEB therapy of mycosis fundoides. Methods: Custom cylindrical phantoms were made of a set of buckets filled with water and wrapping with bolus outside. Films placed at depths of interest in the cylindrical phantoms and flat solid water phantom were irradiated using 6‐MeV high‐dose‐rate TSEB from an Elekta Synergy linear accelerator. Horizontal and vertical fluence profiles as well as depth‐dose curves were measured by positioning the flat phantom at various locations. Curvature factors were determined by the dose curves across the films in the cylindrical phantom and quantified as functions of the curvature radius and the angle between the TSEB and local surface norm. The off‐axis and curvature factors were used in calculation of the skin‐depth dose distribution in any body parts for individual beams. Sum of the doses from all beams provides the total skin dose distribution. The calculation requires only the toward beam body surfaces that can be captured with 3D cameras. Results: Repeated phantom experiments confirmed the dose calculation accuracy within 5%. Computer simulation for patients with different body shapes and treatment setup using the Stanford technique agreed with the results of in‐vivo dose measurements. Dose variation from different techniques including changes from 60 to 45 degree turntable angles for oblique beams in Stanford technique and rotation TSEB were simulated. Conclusions: This simple and accurate dosimetric system allows users to predict total skin dose distribution and distribution changes with different treatment techniques. Importantly, it allows users to plan and optimize TSEB treatment.
MO‐F‐214‐02: A New, High Resolution 2D Dose Measurement Device Based on a Few Scintillating Fibers and Tomographic Reconstruction
Authors: Goulet M , Gingras L , Archambault L , Beaulieu L
Published: November 2011

Purpose: To develop and validate a novel type of 2D dosimeter based on the tomographic reconstruction of the dose projections obtained using long scintillating fibers. Methods: 50 parallel scintillating fibers (diameter, 1mm; length, 6 to 20cm) were aligned in a 30cm diameter cylindrical masonite phantom with a 90cm source‐to‐surface distance and a 100cm source‐to‐fibers distance. The fibers were disposed so that the effective detection area of the scintillating fibers was a 20cm diameter disk. Both ends of each scintillating fiber were coupled to clear optical fibers to enable light collection by a single CCD camera using an f/2, 50mm focal length lens. 7 IMRT segments and 2 square fields were acquired using 18 projections over a 170 degrees rotation of the device. Dose reconstructions were conducted using a total‐variation minimization reconstruction algorithm. 8 monitoring units were programmed for each projection and the reconstructed dose grid pixel resolution was set to 1×1mm,2,. Results: Using a non‐optimized algorithm on a 2GHz CPU, each reconstruction was performed in less than 6 minutes. 3%/3mm gamma tests conducted between the reconstructed IMRT dose distributions and the dose calculated with the treatment planning system Pinnacle,3, were on average successful for 99.6% of the dose pixels for the region over 10% of the maximum dose. For both square fields and the whole summed IMRT field, 100% of the dose pixels were successful to the gamma test. Conclusions: Using tomographic reconstruction on the projections acquired with rotating scintillating fibers, one is able to perform 2D dosimetry of simple and IMRT fields with great accuracy and resolution using only a limited number of scintillating fibers. The underlying concept of tomographic dosimetry and the small number of fibers needed to reconstruct a given 2D dose distribution offer a world of new dosimetric possibility, both applicable to 2D and 3D dosimetry.
MO‐F‐214‐07: Online Monitoring of Radiotherapy Treatments Using a Novel Optical Attenuation‐Based Transmission Detector
Authors: Goulet M , Gingras L , Beaulieu L
Published: November 2011

Purpose: To present and characterize a fluence monitoring transmission detector for the online quality control of radiotherapy treatments. This work presents extended detection capability of the detector using a new formalism for the representation of the beam quality control. Methods: Sixty 27‐cm scintillating fibers were aligned in the direction of motion of each of the 60 leaf pairs of a 120 leaves Millenium MLC on a Varian Clinac iX. Because of the significant light attenuation in scintillating fibers, combined information from the two sides of each fiber allowed for both position coding and integral fluence information of the incident fluence passing thought each MLC leaf pair. The whole device was placed in the accessory tray of the linac to enable fluence verification during the treatment delivery. The impact of a wide range of delivery errors was evaluated using a graphical representation of the treatment validity. The influence of the transmission device on the radiation beam was also evaluated. Results: The presented online detector allowed the detection of MLC leaf positioning errors below 1 mm, symmetric leaf displacement of 1.6mm, blocking jaws errors of 2mm and absolute dose rate de‐calibration of less than 1 %. The formalism used for the graphical representation of the beam quality control allowed the instantaneous detection of critical delivery errors such as deleted segments or wrong energy selection. The fluence monitor also achieved a uniform beam transmission of 98.3%. Conclusions: This work shows that an optical attenuation—based detector can be used to monitor both intuitively and precisely the incident fluence during radiotherapy delivery. The performance of such a system would enables real‐time quality control of the incident fluence both in current MLC‐driven treatments and in future adaptive radiotherapy procedures where new treatment plans will have to be delivered without passing thru the current standard quality control chain.

This research is supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC) support Grant No.262105
MO‐F‐110‐02: A New Model‐Based Dose Calculation Algorithm for Kilovoltage X‐ Rays
Authors: Pawlowski J M , Ding GX
Published: November 2011

Purpose: There is an increasing need to develop fast and accurate dose calculation algorithms for kilovoltage (kV) x‐rays. This study describes a new model‐based method and presents initial results of its calculation accuracy. Methods: The new approach calculates the radiation dose to patients by calculating the dose to water‐like media first. This is done by assuming all voxels in a patient CT data set are water, but with densities scaled according to a CT‐number‐to‐density calibration. The dose distribution to water‐like media with physical density considered is calculated by summation of pencil beam percent depth‐dose curves, considering the incident x‐ray fluence profiles and empirical x‐ray scatter factors. The beam modeling parameters were obtained by the Monte Carlo method. The final dose distribution calculated for the actual physical media is obtained using medium‐dependent correction (MDC) factors. The MDC factor at a voxel is expressed as a function of an intermediate quantity, the effective bone depth, which is calculated from patient CT data. The accuracy of this new approach was tested for calculating the dose resulting from a kV cone‐beam CT scan by comparing to Monte Carlo calculations. Results: The calculated dose using the new approach was shown to agree with Monte Carlo within 3% for the mean dose to bone, and within 1% for the mean dose to soft‐tissue. The dose to bone was on the order of 2–3 times the dose to soft‐tissue. The computation time of the new approach is significantly less than Monte Carlo. Conclusions: The new approach was shown to be very promising and has potential to extend current model‐based dose calculation algorithms to the kV energy range.