bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐707: Clinical Evaluation of a New Commercial Dose Calculation Algorithm
Authors: Esquivel C , Stathakis S , Sath C , Gutiérrez A , Dorward J , Mihailidis D , Mavroidis P , Papanikolaou N
Published: November 2011

Purpose: A new algorithm, Acuros® XB Advanced Dose Calculation, has been introduced by Varian Medical Systems in the Eclipse planning system for photon dose calculation in external beam radiotherapy. Acuros XB is based on the solution of the linear Boltzmann transport equation (LBTE). In this study we perform a clinical evaluation of the Acuros XB by comparison to other known and tested treatment planning systems and dose calculation algorithms. Methods: Twenty (n=20) patients previously planned with the Pinnacle ver.9.0 treatment planning system and calculated using the collapsed cone convolution superposition algorithm, were recalculated using the Eclipse ver. 10.0 with the Acuros XB dose calculation algorithm. A mixture of treatment sites were chosen, including brain, lung, liver, and pelvis. The metrics chosen for the evaluation were DVH, absolute dose difference, and profiles along the axial, sagital and coronal planes at the isocenter Results: Good agreement was observed between the dose calculations with Acuros and the ones from Pinnacle using the CCCS algorithm. Differences were mostly detected in inhomogeneous media. Maximum differences of 2.5% were observed for lung patients, while, smaller differences were detected for pelvic, brain, and abdominal cases. Conclusions: The new dose calculation algorithm Acuros XB available in Eclipse ver. 10 is in very good agreement with the widely tested and accepted CCCS dose calculation algorithm. More extensive testing of the algorithm might be necessary in order to further evaluate the accuracy of the calculations.
SU‐E‐T‐708: Validation of the New GATE 6.0 Monte Carlo Platform for Radiation Therapy. Investigations on Simulation Parameters
Authors: Perrot Y , Donnarieix D , Breton V , Maigne L
Published: November 2011

Purpose: In this study, we validate the accuracy of the new GATE 6.0 Monte Carlo platform (using GEANT4 9.2 Standard Electromagnetic Physics Package) to model accurate treatment plans in radiation therapy using 18 MV photon beams. Furthermore, we investigate how the specifications of the particle transport management, physic processes and geometry influence the dosimetric accuracy of the results to propose recommendations on the usage of GATE 6.0. Methods: 3D conformational plans were simulated for a lung irradiation using 18MV photon beams from a Varian Clinac 2100C accelerator. The patient volume was derived from CT images and converted into specific format in order to use different voxel sizes. Treatment plans were computed using GATE 6.0 and EGSnrc. Treatment plans obtained with both of the codes were compared using a gamma index evaluation (acceptance criteria 3%/3mm). Investigations on the influence of simulation parameters related to physics or algorithm were examined by qualitative comparisons of DVHs in several regions of interest: PTV and OARs. Results: At first, GATE 6.0 is able to reproduce complex dosimetry in agreement with the well validated Monte Carlo code EGSnrc. Nevertheless, the choice of specific simulation parameters such as cuts, particle production threshold or stepping algorithm showed differences on treatment plans. Users have to fix parameters according to the geometry simulated to ensure a good tracking of particles by taking into account the computation time efficiency. Conclusions: GATE 6.0 provides convivial tools for realistic treatment planning and give comparable results with EGSnrc while the parameters of the simulation are well fixed. These investigations highlight several issues of general interest to users of GATE 6.0 who wish to calculate accurate treatment plans.

We wish to thank the GEANT4 collaboration and the OpenGATE collaboration to their scientific and technical suuport.

This work was partly supported by grants from the European Commission (through the EGI inititative project), by the French National Grid Inititative (France Grilles), and regional authorites (Conseil Général de lˈAllier and Conseil Régional dˈAuvergne).
SU‐E‐T‐770: Compensator‐Based Intensity Modulated Brachytherapy for Cervical Cancer
Authors: Flynn RT , Kim Y , Jacobson GM , Wu X
Published: November 2011

Purpose: Bulky (>40 cc) cervical cancer brachytherapy (BT) tumor dose conformity is often poor since the dose limitations of nearby organs at risk (OARs) prevent the radially symmetric dose distributions from covering tumor extremities. We introduce compensator‐based intensity modulated brachytherapy (CIMBT), a non‐invasive alternative to supplementary interstitial BT that improves the dose conformity to bulky cervical cancer tumors. CIMBT dose distributions are generated by an electronic brachytherapy (eBT) source wrapped in a novel compensator that is covered in varying thicknesses of high‐Z material. Methods: A 3‐D CIMBT treatment planning system prototype was developed that simultaneously optimizes the compensator thickness distribution and the source dwell times at multiple positions. Ir‐192, Xoft Axxent eBT, and CIMBT treatment plans were generated for a stage IB cervical cancer patient with a laterally and posteriorly‐extended 41.3 cc high‐risk clinical target volume (HR‐CTV). The BT doses were escalated as high as possible without compromising the GEC‐ESTRO recommended bladder, rectum, and sigmoid constraints. Results: CIMBT improved HR‐CTV D90 considerably above that of Ir‐192 and eBT. D90‐values for Ir‐192, eBT, and CIMBT were 64, 62 and 90 Gy(EQD2), respectively. Ir‐192 and eBT treatment times were comparable, and the CIMBT delivery time was greater than the eBT case by a factor of 3.4. The user could easily obtain decreased CIMBT treatment times by constraining D90 in the HR‐CTV. No improvement in the dose CIMBT dose distribution was evident for compensator thicknesses greater than 100 μm of gold. Conclusions: Compensator‐based IMBT has the potential to significantly improve cervical cancer dose distributions without the need for supplementary interstitial BT. The physician will have the freedom to optimize the tradeoff between increased delivery time and tumor dose conformity with CIMBT. We expect that patient‐specific compensators can be constructed rapidly in clinical situations using circuit board printing technology.
SU‐E‐T‐772: Volume Matching for Brachytherapy Planning
Authors: Daescu O , Cheung Y , Papiez L
Published: November 2011

Purpose: To perform brachytherapy treatment plan by comparing it with existing data base from earlier treatments of similar type. Method: When brachytherapy target to be treated is closely related in shape and volume to the target treated in the past for which we had well developed plan based on sources energy, activity and spatial distribution we can assume that plan of essentially the same quality will be achieved when the same distribution of sources that was used in the past will be imposed over the new, identical to one in the past treatment volume. The planning strategy under these circumstances relies on matching the volume under consideration with the volume of the target from earlier treatment. Characteristic scalar parameters of volumes will be compared first to filter the database (these will include volume, orientation of principal axes and moments of the characteristic set of the compared volumetric domains). When these parameters match closely between considered volume and one of stored in library volumes they are suspect of close similarity. The next stage of comparisons matches volumes by translating them in 3D space so that the maximal intersection between them is achieved. When closeness criterion is satisfied for this matching the distribution of sources is moved from the old plan to the new target completing the planning process. Results: The program for the algorithm has been written and sequence of plans have been computed for dose distributions obtained by sources placement based on domain comparison planning described above. Conclusion: The excellent agreement between set of plans based on geometrical planning approach and traditional planning optimization approach has been discovered. The domain comparison planning leads to enviable dose distribution in brachytherapy treatment and it is fast enough to be applicable to real time treatments.
SU‐E‐T‐776: External Beam Accelerated Partial Breast Irradiation Using Intensity Modulated Proton Therapy (IMPT)
Authors: Wang X , Zhang X , Amos R , Salehpour M , Zhang S , Sun T , Strom E , Buchholz T , Hoffman K , Woodward W
Published: November 2011

Purpose: To explore advantages and uncertainties of IMPT for accelerated partial breast irradiation (APBI), and compare the dosimetry with passive scattering protons (PSPB) and clinic photon 3D radiotherapy (3DCRT). Method and Materials: Two theoretical proton IMPT plans, i.e. one with two tangential fields (OPPOSED_PAIR) and one with a tangential field and an en face field (ORTHOGONAL_PAIR), were created for 11 patients and compared with PSPB and 3DCRT. The impact of range and patient setup uncertainties and scanned spots mismatching between fields for IMPT plans was evaluated. Results: Compared with 3DCRT, IMPT plans with both beam configurations significantly reduced the dose to lungs, normal breast tissues, heart and breast skin and have significantly better dose coverage for target volume using ORTHOGONAL_PAIR and comparable coverage using OPPOSED_PAIR. Compare with PSPB, IMPT with both beam configurations was significantly better for V90 and V75 of breast skin, and V90 and V75 of ipsilateral normal breast, and comparable for V50 and V30 of breast skin, V100 of ipsilateral normal breast, V5Gy and mean dose of ipsilateral lung, maximum dose of heart and contralateral breast, and mean dose of contralateral lung. IMPT using ORTHOGONAL_PAIR was comparable for V10 of breast skin, V50 and V20 of ipsilateral normal breast, and V10Gy and V20Gy of ipsilateral lung, but significantly worse using OPPOSED_PAIR. For IMPT, CTV coverage of 95% prescription dose was over 90% considering range and patients setup uncertainties, but could drop to 80% with scanned spots mismatching between two beams in worst scenario. The en face beam has significantly more dose fluctuation in chestwall region than tangential beam. Conclusion: IMPT plans showed potential for normal tissue dose reduction and target coverage improvement compared with PSPB and 3DCRT. It is robust considering range and patient setup uncertainties, but vulnerable to the scanned spots mismatching among different beams.
SU‐E‐T‐777: Clinical Implementation of An Automated Segmented MLC Field Approach to Improve Safety of Radiation Treatment Delivery: Eliminating Wedges, External Shields and Physical Junction Shifts
Authors: Davidson MTM , Korol RM , Chin LCL , Ravi A
Published: November 2011

Purpose: As part of routine quality improvement, departmental radiation therapy techniques were reviewed, and technical and operational modifications identified to enhance radiation delivery safety. Our aim was to standardize planning for conventional techniques that exhibit higher potential for delivery errors via automation without compromising plan quality. This was achieved through the use of segmented intensity modulated radiotherapy (IMRT) fields. Methods: A segmented IMRT solution was developed to simulate common fields requiring: a) wedge‐based modulation (eg breast, rectum), b) shielding of anatomical regions (eg midline blocks, island shields) and c) junction shifts during treatment. For cases requiring more intricate beam modulation than what can be provided by a wedge‐like field, a simple inverse‐planned IMRT optimization was devised. Our approach does not depend on anatomical contours, and uses standard 3D conformal beam geometries for delivery and to define planning volumes. All planning strategies were automated using Pinnacle3 scripting to increase planning efficiency and consistency. Results: Compared to standard techniques using wedges, physical blocks, and junction shifts, the developed IMRT protocols resulted in comparable dose distributions. The implementation of scripts in Pinnacle allowed us to improve quality control, as well as planning and delivery efficiency. Delivery safety improvements were also realized. Physical junction shifts can be replaced by intra‐fraction junction feathering (whereby multiple junction shifts are nested within control points, delivered daily) to reduce the dosimetric impact of field edge misalignments and simplify delivery. Regarding physical beam modifiers, the potential for accidents involving dropped devices or errors due to device omission or misalignment is virtually eliminated. Conclusion: Radiation treatment plans that require wedges, physical blocks and junction shifts can be dosimetrically reproduced using simple segmented IMRT fields. Implementation of an MLC‐based delivery offers important benefits in both workflow efficiency and patient safety.
SU‐E‐T‐778: Application of Robust Fluence Approach in IMRT under Clinical Daily Shifts
Authors: Fan Y , Chen Z , Nath R , Decker R
Published: November 2011

Purpose: To verify the applicability of robust fluence approach in IMRT under clinical daily shifts. Method and Materials:Clinical daily setup shifts throughout the prostate IMRT treatments have been acquired and analyzed with OBI and CBCT images. Two patient shifts have been chosen to represent the “good” and “bad” scenarios — more and less of Gaussian‐like distributions of the shift statistics with average standard deviation of 3.5–4 mm. The robust fluencies have been obtained by deconvolution of the static fluence with the corresponding shifts approximated by a Gaussian distribution. To each scenario the doses taken into account the shifts of a typical AP field to a water phantom have been calculated with the static fluence and corresponding robust fluence. The static dose without shifts which is the desired dose was set as the benchmark for comparison. Results: The robust fluence approach can achieve good dose conformality to the static dose, especially for the Gaussian‐like distribution of the shifts. For the shifts having large deviation from the Gaussian distribution (although it is statistically rare) the dose by robust fluence suffers a shift which can be covered by a 2.5 mm margin which is much smaller than a margin‐only approach to keep the same dose conformality for this scenario.This conformality provides the possibility to remove or reduce the margin usually added to target to take into account the geometrical uncertainty. Conclusions: Robust fluence approach is promising to remove or reduce the CTV‐PTV margin and consequently reduce the mean dose to surrounding normal tissue.
SU‐E‐T‐779: Adaptive RapidArc Treatment Planning for Esophageal Cancers Using Cone Beam Computed Tomography
Authors: Sriram P , Syamkumar S A , Kumar J Sam Deva , Prabakar S , Dhanabalan R , Satish K , Vivekanandan N
Published: November 2011

Purpose: To assess the potential of cone beam CT (CBCT) derived adaptive RapidArc treatment for esophageal cancers in reducing the dose to organs at risk (OAR). Methods: Five patients with esophageal cancer were CT scanned in free breathing pattern. The PTV is generated by adding a 3D margin of 1 cm to the CTV as per ICRU 62 recommendations. The double arc RapidArc plan (Clin_RA) was generated for the PTV. Patients were setup using lasers and tattoos and kV‐CBCT scan was acquired daily during first week of therapy, then weekly. Setup errors > 5 mm only were corrected. These images were exported to the Eclipse TPS. The adaptive CTV which includes tumor and involved nodes was delineated in each CBCT image set for the length of PTV. The composite CTV from first week CBCTs was generated using Boolean union operator and 5 mm margin was added circumferentially to generate adaptive PTV (PTV1). Adaptive RapidArc plan (Adap_RA) was generated. NTCP and DVH of the OARs of the two plans were compared. Similarly, PTV2 is generated from weekly CBCTs. PTV2 was evaluated for the coverage of 95% isodose of Adap_RA plan. Results: The PTV1 and PTV2 volumes covered by 95% isodose in adaptive plans were 93.16±1.8% and 94.66±1.45% respectively. The lung V10Gy, V20Gy and mean dose in Adap_RA plan was reduced by 17.36% (p=0.001), 34.86% (p=0.002) and 16.74% (p<0.001) respectively in comparison with Clin_RA. The Adap_RA plan reduces the heart D35% and mean dose by 17.03% (p=0.002) and 17.04% (p=0.002). No significant reduction in spinal cord and liver doses were observed. NTCP for the lung (0.42% vs. 0.08%) and heart (1.41% vs. 0.092%) was reduced significantly in adaptive plans. Conclusions: The adaptive re‐planning strategy based on the first week CBCT dataset significantly reduces the doses and NTCP to OARˈs.
SU‐E‐T‐780: Evaluation of Margin‐Reduction Using a Framework for Image‐Guided Adaptive Radiotherapy (IGART) of Prostate Cancer in the Clinical Setting
Authors: Wen N , Glide‐Hurst C , Chetty I , Nurushev T , Zhong H , Kim J
Published: November 2011

Purpose: This study compares the differences between planned and estimated delivered doses under an IGART framework for prostate cancer treatment, with an emphasis on margin calculation and the resulting dosimetric consequences. Methods: Five patients were enrolled in the protocol. PTVs were generated by adding a 1cm isotropic margin to the CTV, except posteriorly where 6mm was employed to limit rectal dose. Two additional IMRT plans were created: one with a 5mm isotropic expansion except 3mm posteriorly, and a 3mm isotropic margin. Daily CBCTs (acquired for each of 42 fractions for a total of 710 CBCT‐datasets) were used for the daily localization and dose calculation. B‐spline based deformable image registration was performed to register each daily CBCT to reference simulation CT‐datasets (SIM‐CT). Dose was calculated on each daily CBCT and accumulated using spline‐based interpolation on the SIM‐CT to estimate overall dose delivered to the patient using all three margin techniques. Results: For all three margins, the average difference between actual delivered and planned CTV mean doses was within 2%. This discrepancy increased as the margin became smaller. Results were patient‐dependent, ranging from 1% to 11% between planned and delivered CTV mean doses. Dose estimations to organs at risk (mean dose to rectum and bladder) increased in the actual delivered doses (up to 40%). For the isotropic 3 mm margin plan, mean doses to the rectum and bladder were reduced 10% to 40% relative to the conventional margin plan. Conclusions: With IGRT, it is possible to reduce treatment margins in prostate cancer. However, caution should be exercised because IGRT alone cannot fully account for tissue deformation or physiological bladder/rectal filling, which may lead to deficits in PTV coverage. IGART, including an adaptive planning framework, offers the benefit of margin reduction through the evaluation of estimated dose delivery and plan reoptimization.
SU‐E‐T‐781: Reduction of Thread Effect for Superficial Tomotherapy Treatments
Authors: Ehler E , Higgins P , Reynolds M
Published: November 2011

Purpose: Helical tomotherapy can be useful in the treatment of superficial treatment volumes. As a consequence of the helical delivery, a thread pattern is evident in measured dose distributions. This goal of this work is to reduce this effect.Methods: Radiation treatment plans were created utilizing pitches of 0.287, 0.360, 0.430 and 0.500 with a 5 cm field width with the helical tomotherapy treatment planning system (TPS). The plans were delivered to a cylindrical solid water phantom with 1.0 cm bolus. EDR2 film was placed between the solid water and the bolus in the target volume region. Back‐to‐back delivery of procedures with different pitch to constitute a single treatment fraction was considered. Results: The measured percent difference of minima and maxima of the thread pattern was determined to be 5%, 12%, 10%, and 16% for pitch values of 0.287, 0.360, 0.430 and 0.500, respectively. The calculated thread magnitude was within 2% of the measured. Combining procedures with pitches of 0.287 & 0.360 and 0.287 & 0.430 resulted in interference patterns in the threading. For the pitch combination of 0.287 & 0.430, reduced variation (∼3%) was largely observed; however, limited regions of greater magnitude minima and maxima (± 5% of the mean dose) were also observed. An attempt was made to modify the target volume in order to create two plans with equal pitch values that combine to form a destructive interference pattern and, hence, a uniform dose. However, this was not readily achievable with the clinical version of the TPS Conclusions: The thread pattern can be mitigated with the use of a combination of delivery procedures with differing pitch, specifically 0.287 and 0.430. The TPS was able to predict the magnitude of the thread effect within 2% of the measured for the superficial target for all cases considered.
SU‐E‐T‐791: Applications of RapidArc in Cervical Esophageal Cancer Radiation Therapy: A Comparison with Fixed‐Field IMRT in Dosimetry and Implementation
Authors: Chen J , Yin Y
Published: November 2011

Purpose: Comparing fixed‐field intensity‐modulated radiotherapy (f‐IMRT) with intensity‐modulated arc therapy (IMAT) treatment plans in dosimetry and practical application for cervical esophageal carcinoma.Methods: For ten cervical esophageal carcinoma cases, f‐IMRT plan (7 fixed‐fields) and two IMAT plans, namely RA (co‐planar 360° arcs) and RAx (co‐planar 360° arcs without sectors from 80° to 110°, and 250° to 280°). DVHs were adopted for the statistics of above parameters, as well as conformal index (CI), homogeneity index (HI), dose‐volumetric parameters of normal tissues, total accelerator output MUs, and total treatment time.Results: There were differences between RAx and f‐IMRT as well as RA in PTV parameters such as HI, V95% and V110%, but not in CI. RAx reduced lung V5 from (50.9±9.8)% in f‐IMRT and (51.4±10.8)% in RA to (49.3±10.4)% in RAx (P<0.05). However, lung V30, V40, V50 and MLD increased in RAx. There was no difference in the mean heart dose in three plans. Total MU was reduced from 1174.8±144.6 in f‐IMRT to 803.8±122.2 in RA and 736.2±186.9 in RAx (P<0.05) Conclusions: Compared with fIMRT, IMAT reduced low dose volumes of lung and total MU on the basis of meeting clinical requirements.
SU‐E‐T‐794: Effects of Dose Rate Variability for Volumetric Arc Treatments in Prostate Carcinoma
Authors: Mihaylov I , Sternick E , Curran B
Published: November 2011

Purpose: To evaluate the effects of variable versus constant dose rate in volumetric modulated arc (VMAT) treatment planning for prostate cases. Method and Materials:A retrospective investigation on fifteen prostate cases was performed. Two dosimetrically identical linacs were commissioned in Pinnacle TPS. One machine was variable dose rate capable, while the other was constant dose rate capable for VMAT planning purposes. PTVs and OARs (rectum and bladder) were delineated for each case. Two VMAT plans were generated per case: each comprised of a single arc and comparing variable to constant dose rate. Both plans were normalized such that 95% of the PTV was covered by the same prescription dose. Plan quality was evaluated by several dose indices used as DVH objectives in the inverse optimization. In addition, dose inhomogeneity across the PTV was tallied together with MUs and estimated treatment times. Variable dose rare plans were used as reference. Results: The majority of rectum and bladder doses to 10%, 20%, and 40% of the OAR volumes differed by less than 3% between the two plans plans. Even for the cases with larger than 3% deviation the constant dose rate plans were clinically acceptable. Dose inhomogeneity across the PTV however was larger for constant dose rate plans, where for 80% of the cases it was over 3%, while it was within 3% for all variable dose rate cases. The MUs for the two delivering modes were comparable, while the treatment times differed three‐fold. Conclusions: The results indicate that variable and constant dose rate VMAT plans for prostate carcinoma result in comparable target coverage and OAR sparing. Nonetheless, the constant dose rate plans exhibit higher dose inhomogeneity across the target and the clinical applicability should be carefully evaluated for the potential hotspots in undesired location.
SU‐E‐T‐795: Measuring Uncertainty in Dose Delivered to the Cochlea Due to Setup Error during External Beam Treatment of Patients with Cancer of the Head & Neck
Authors: Yan M , Lovelock D , Hunt M , Mechalakos J , Hu Y , Pham H , Jackson A
Published: November 2011

Purpose: To understand the relationship between hearing loss and cochlea dose in patients treated for cancers of the head and neck with external beam IMRT, uncertainties in planned and delivered cochlea doses must be known. We use treatment cone beam scans to determine the positional and dosimetric uncertainty for the cochlea. Methods: Data from 6 head & neck patients with 6 planning CT and 29 Cone Beam CTs taken at time of treatment are used in this study. Patients were treated 70 Gy to the primary target, and between 50–60 Gy to nodal and sub‐clinical disease using IMRT dose painting. We use 6 dimensional rigid body registration to find translational and rotational setup error between the planning CT and Cone Beam CT scans. The Planning CT is rotated and translated so that the cochlea positions match those seen in the cone beam scans and cochlea doses recalculated. Results: We found most probable value of the magnitude of mean error in cochlea position is 0.250.02cm, but it can increase to 7mm in some patients. Uncertainty in the dose to cochlea depends on each treatment plan and relative positions of the cochlea and target volumes. Most of differences in doses to cochlea in our study are around 2% of planned dose. But for some patients this may be as large as 5–9%. Conclusions: Patient setup error introduces uncertainty in the position of the cochlea. Consequent uncertainties in dose heavily depends on the relative position of cochlea w.r.t. the target volumes and the individual treatment plan. Results from this study will be used to model the uncertainty in the dose response of hearing loss.

This research is supported in part by NIH under RO1‐CA129182.
SU‐E‐T‐803: Dosimetric Evaluation for Pulsed Low Dose Rate Radiation Therapy Using RapidArc Delivery Techniques
Authors: Ma C , Lin M , Wang L , Price R
Published: November 2011

Purpose: There has been no consensus standard of care to treat recurrent cancer patients who have previously been irradiated. Pulsed low dose rate (PLDR) radiotherapy has potential to reduce normal tissue toxicities while still providing significant tumor control for recurrent cancers. This work investigates the dosimetry feasibility of PLDR radiotherapy using the RapidArc delivery technique for a dose escalation trial. Methods: Five body sites were investigated including breast, pancreas, prostate, head and neck, and lung. RapidArc plans were generated using the Varian Eclipse system with 6, 10 and 15MV beams. Each plan consisted of two arcs and the plan was delivered 5 times to achieve a daily dose of 2Gy. The dosimetry requirement was to deliver 20cGy/arc with a 3min interval to achieve an effective dose rate of 6.7cGy/min. Monte Carlo simulations were performed to calculate the actual dose delivered to the planning target volume (PTV) considering beam attenuation/scattering and intensity modulation. The maximum, minimum and mean doses to the PTV were analyzed together with the dose volume histograms and isodose distributions. Results: Two full arcs were necessary to achieve superior dose distributions for complex recurrent cancers to spare critical structures effectively. For 9 patients, the mean PTV dose for each arc ranged 18.9–22.6cGy/arc. For breast the minimal and the maximal PTV dose was 8.56 and 31.2cGy/arc, respectively. The RapidArc dose varied between 12.9 and 27.5cGy/arc for pancreas, 12.6 and 28.3cGy/arc for prostate, 12.1 and 30.4cGy/arc for H&N, and 16.2 and 27.6cGy/arc for lung, respectively. Good agreement was achieved between the planned doses and Matrix measurements with 95–98% passing rates Conclusions: Advanced image‐guided radiotherapy can provide superior target coverage and normal tissue sparing for PLDR reirradiation of recurrent cancers, which can be delivered using the RapidArc technique with 10 full arcs and an effective dose rate of 3–10cGy/min.
SU‐E‐T‐806: IMRT Technique for CSI: Better Dose Distribution, Simplified Setup, No Need to Shift Junctions
Authors: Ning H , Chin B , Cheng J , Miller R
Published: November 2011

Purpose: To report an IMRT technique for CSI, which reduces the dose to critical structures in cranial area, improves the dose coverage to PTVs and simplifies the setup. Methods: A supine setup was used for both patient comfort and anesthesia administration in pediatric patients. Patient is immobilized with indexed head rest and face mask, and also with indexed vaclock from the mid‐thigh down to feet. Four half beam (Y1=0) IMRT fields with ISO at the level of the chin to cover the cranial PTV. Cranial PTV is consisted with brain volume plus 5mm margin and portion of the C‐spine superior of the ISO with proper margin. From the first ISO the inferior portion has a PA field (PA1). 2nd PA field (PA2) is added in order to cover the spinal PTV. The spinal PTV is the volume of the spinal canal plus 2cm laterally. The inferior extension of this volume is determined by MRI to cover the thecal nerve. The optimization constrains are applied to maximize the dose coverage of both cranial PTV and spinal PTV, to minimize the dose to parotid glands and lens and to achieve better dose homogeneity. There should be several cm overlap between the two PA fields. During the optimization the leaf sequence forms step wedges in the overlap area and widens the penumbra of these two fields. This makes it more forgiving to the daily patient setup variations. Results: There is 32.8% reduction in mean parotid gland dose, 46.2% reduction for max lens dose without losing dose coverage to brain PTV, compared with the opposite lateral fields setup. The dose homogeneity for the spinal PTV is improved. And the setup is greatly simplified. Conclusions: We have developed a technique which reduces the dose to critical structures and improves the dose coverage and simplifies the setup in CSI.
SU‐E‐T‐807: Measured Data Set for Validation of Bolus Electron Conformal Therapy
Authors: Kavanaugh J , Chu C , Perrin D , Hogstrom K
Published: November 2011

Purpose: To measure sample planes of two 3D dose distributions that can be used to evaluate the accuracy of planning and delivery of bolus electron conformal therapy (ECT). Method: The planning target volumes (PTV) from a parotid and a chest wall patient were modified to a CT image set of a cylindrical polystyrene phantom. A bolus ECT plan for each PTV was developed using .decimal p.d software to design a custom bolus and dose was calculated using Pinnacle. Once acceptable, .decimal fabricated the bolus from machinable wax. Approximately 45 cGy given dose was delivered for each bolus ECT plan, and planar dose measurements were taken in the mid‐sagittal and five transverse phantom planes (±5cm, ±2.5cm, 0cm) using Kodak XV radiographic film sealed within the in‐phantom cassettes. Films were developed and digitized to (0.5mm pixels) using a Vidar DosimetryPRO Advantage, and converted to dose using a film calibration curve created at the time of measurement. Four film measurements were taken in each plane, with the mean dose and standard error being determined at each pixel. The precision of the data was quantified in the low gradient regions (Dose > 90% and Dose <10%) by the mean percent standard error of all pixels and in the high gradient region (90% > Dose > 10%) by the mean distance to dose agreement. Results: The percent average standard errors in the low gradient, high dose region were less than 1.5% for parotid and chest wall measurements and less than 3% in the low gradient, low dose regions. Average distances to agreement in the high gradient region were less than 0.6 mm. Conclusions: For two PTVs bolus, ECT dose distributions in 6 planes were measured and their precision quantified for three dose regions. These data are well‐suited for comparison with calculated electron dose distributions.

This work was supported in part by a research grant from .decimal, Inc.
SU‐E‐T‐808: Improved Normal Tissue Dosimetry Using a Sequential Boost Plan for Locally Advanced Head and Neck Cancer
Authors: Liu T , Brewer M , Dieck G , Edwards J , Yang C , Caudell J
Published: November 2011

Purpose: Simultaneous integrated boost (SIB) fractionation schemes for the treatment of head and neck cancer have become widespread. This usually results in increased total dose to elective regions of the neck. We hypothesized that a sequential boost plan (SEQ) using a lower total dose to the elective neck at a standard fractional dose would result in improved dosimetry to normal tissues. Methods: Nine patients with locally advanced head and neck cancer with primaries in the oropharynx and larynx were selected for this study. SEQ radiotherapy plans were generated to compare with SIB plans. Normal tissue and target dose constraints were kept identical, except for dose to the elective neck target (56 Gy vs. 45 Gy). SIB dose fractionation schema to planning target volumes (PTV) included 70 Gy / 2 Gy fractions to PTV_High, 63 Gy / 1.8 Gy fractions to PTV_Intermediate, and 56 Gy / 1.6 Gy fractions to PTV_elective. SEQ dose fractionation schema included 50 Gy / 2 Gy fractions to PTV_High, 45 Gy / 1.8 Gy fractions to PTV_Intermediate, and 45 Gy / 1.8 Gy fractions to PTV_elective, followed by a boost of 20 Gy / 2 Gy fractions to PTV_High and 18 Gy / 1.8 Gy fractions to PTV_Intermediate. Results: SEQ plans were more likely to have higher percent coverage of the PTV_elective at the 110% and 100% (p < 0.01) prescription dose levels, but not at 95% or 93%. Mean doses to the contralateral parotid, larynx and inferior pharyngeal constrictor were lower with SEQ (p<0.05). Conclusions: The use of SEQ intensity modulated radiotherapy with a previous standard lower total dose (45 Gy in 25 fractions) for treatment of the elective neck in locally advanced head and neck cancer patients may improve the ability to spare normal tissues such as the parotid, larynx, and inferior pharyngeal constrictor.
SU‐E‐T‐809: A Grading‐Study Based Tool to Assist in the Choice of Treatment Modality
Authors: Petersson K , Ceberg C , Engström P , Knoos T
Published: November 2011

Purpose: It is common for radiation oncologists (ROs) today to have a mixed arsenal of radiotherapy treatment modalities at their disposal. To optimize a clinicˈs use of its different treatment modalities, while at the same time giving every patient an optimal treatment, is not a trivial task. The purpose of this study was to give ROs a tool to choose between available modalities. This would help to ensure that the most advanced modality is available for the patients that really benefits from this treatment, and allow for a more optimal use of the clinicˈs assets. This study included different modalities such as 3DCRT, step‐and‐shoot IMRT, and helical tomotherapy. Methods: Twenty‐three patients that had received treatment for tumours in different anatomical regions with the tomotherapy system were chosen. All tomotherapy plans were converted into seven‐beam step‐ and‐shoot IMRT plans using the treatment planning system SharePlan. When feasible, conventional 3DCRT plans were also created by our most experienced planner. A side‐by‐side demonstration of every patientˈs plans was performed. Ten experienced ROs were individually asked to compare and grade the plans. The results were statistically analysed by using Sign test. Results: The results show that for all regions combined, the TT plans were considered somewhat better than the IMRT plans and much better than the 3DCRT plans (p<0.05). Divided into the different anatomical regions, however, the perceived superiority of the TT plans, as compared to step‐and‐shoot IMRT, was only significant for the patients treated in the abdominal and pelvic region. Conclusions: Based on the ROs grading scores obtained in the present study, priority for treatment with the TT system should be given to patients with tumours in the abdominal and pelvic region. Other factors, such as the overall treatment time and the machine occupancy, may also be important for the final choice of treatment.
SU‐E‐T‐813: Using Intensity Modulated Radiation Therapy for Total Body Irradiation — a Phantom Study
Authors: BonCoeur D Vade , Pelloski C , Gupta N , Weldon M , Woollard J , Martin D , McGee M , Boyle D , Glass P , Werner P , Kuhn K , Lu L
Published: November 2011

Purpose: To test the idea of using Intensity Modulated Radiation Therapy (IMRT) for administering Total Body Irradiation (TBI) on a clinical linear accelerator (CLINAC). Methods: A half body phantom which mimics the size of a pediatric patient was used as the basis for planning a total body irradiation with intensity modulated radiation. The phantom consisted of head, neck, left lung, right lung, and torso which were contoured in the 3‐dimensional CT images to apply for IMRT. Within the interior of the phantom both the right and left lungs were present for contouring as organ at risks. The Eclipse treatment planning system (Varian Medical Systems) was used for the simulation of the treatment. A 6 MV beam from a Siemens medical linear accelerator was used for irradiation of the phantom. To perform the quality assurance of an IMRT‐TBI plan, Matrixx OmniPro‐IˈmRT system was used.Results: The doses to different body parts of the phantom were uniformly distributed as demonstrated in the IMRT treatment plan and the dose volume histograms. The total irradiation doses to the lungs and to the body were well under controlled as prescribed. These results indicate that IMRT is a feasible approach for administering Total Body Irradiation. Conclusions: The use of IMRT to deliver total body irradiation may be an acceptable alternative to the conventional method of total body irradiation on a CLINAC.
SU‐E‐T‐816: Application of the Histogram Analysis in Radiation Therapy (HART): An Open Source Software System
Authors: Pyakuryal A , Pokhrel D , Gopalakrishnan M , Jang S , Luo J , Gocer Evgin , Sathiaseelan V , Mittal B
Published: November 2011

Purpose: Histogram Analysis in Radiation Therapy (HART) is an efficient dose‐volume histogram (DVH) computational tool in radiation therapy and radiation oncology research. Various applications of the software were also presented and published earlier in different journals (Med Phys 37(6), p.3217, 2010; J Appl Clin Med Phys 11(1), p.3013, 2010). The main objective of this work was to review the important applications of the program. Method and Materials:MATLAB based codes were primarily designed to read and write a simpler HART format of the DVH statistics, from the standard RTOG data formats exported from the Pinnacle3 treatment planning system (TPS; Philips Healthcare, Best, Netherlands). Various applications such as conventional DVH (cDVH) analysis, and spatial DVH (sDVH; x‐,y‐, and z‐DVHs respectively) analysis, universal‐plan indices (UPI) evaluation, biological modeling based outcome analyses (BMOA), radiobiological dose‐response modeling (DRM), and physical parameterization (PP) modules have been incorporated in the program. The fundamental results obtained in these applications, were thoroughly validated using the primary data derived from the DVH statistics extracted from the Pinnacle3 system. The program also comprises the simple computational mechanism, the graphical simulations, and the flexible interactive modules. Results: HART offers cDVH and sDVH computational modules, UPI evaluations, BMOA features, DRM simulations, and PP modules respectively for the radiotherapy plans. The cDVH and BMOA were the most applicable features among the HART users in the past year. Nearly 50% of the users (N=91) have found the program useful around the globe. The program is also available freely online. Conclusions: Several applications have been upgraded into a simpler, user‐friendly, and automated software package, HART. The program is useful to the medical physics and radiation oncology communities. We further expect to develop HART for various applications in radiotherapy research, and its expansion to other TPSs that utilize DICOM‐RT objects.
SU‐E‐T‐818: Analysis of Internal Margin Based on Organ Deformation for Prostate IMRT
Authors: Suzuki J , Tateoka K , Shima K , Yaegashi Y , Fujimoto K , Saito Y , Nakata A , Nakazawa T , Hareyama M
Published: November 2011

Purpose: The purpose of this study was to predict organ deformation and the possible CTV‐ITV reduction when adopting daily IGRT for prostate cancer patient. Further, to identify any intra‐fraction time trends in organ deformation. And to analyze internal margin for prostate IMRT based on organ deformation. Methods: It was intended to investigate 30 patients treated with prostate IMRT. The pre‐disposal in radiotherapy was implemented by instructing each patient to drink 500 cc of water each time after defecation and urination. CT images for radiation treatment planning were acquired 3 times at 10‐minute intervals for 30 minutes after drinking water. CT images were transferred to treatment planning system. One physician contoured the prostate, rectum, and bladder for all images. The acquired three‐dimensional contour data of the organ were transferred to a customized data processing program. Then, the prostate, rectum and bladder were divided into eight segments. These regions were analyzed with respect to deformation of the entire set of contour points in the 3‐dimensional outline surface in the region of each of the organs. Results: The deformation of the prostate tended to become amplified in the extension direction accompanied by an increase in deformation of the bladder to the anterior and superior direction. But there were not correlated the rectum deformation. The internal margins which not considered organ deformation, were 2.27 mm, 1.76 mm, and 0.99 mm in the L‐R, S‐I, and A‐P direction respectively. However, respect to the organ deformation, these margins were 1.27 mm, 1.56 mm, and 1.53 mm respectively. Conclusions: This analysis based on organ deformation was found to be useful for determination of internal margin. And it will be possible that the extra margin is reduced.
SU‐E‐T‐819: Impact of Dental Extractions on Dose Distribution and Planning for Head and Neck Intensity Modulated Radiation Therapy (IMRT)
Authors: Dubrowski P , Cao F , Gardner P
Published: November 2011

Purpose: To investigate the equivalence of Head and Neck IMRT plans generated on a 1) pre‐dental extraction CT, with teeth to be removed contoured‐out as compared to 2) an actual post dental procedure CT. Ultimate goal is to improve clinic efficiency and through‐put by planning treatment during the patient recovery time from a dental extraction rather then after. Methods: A jaw phantom (constructed using 28 human teeth embedded in Aqua‐Plast mandible structures, submersed in a H&N water tank) was scanned in a clinical CT and 4 significant teeth (3 molars and a bicuspid; most with metal dental fillings) were contoured‐out; assigned HU=0. Simulating the post‐extraction CT, the 4 teeth were physically removed from the jaw. IMRT plans were then generated on these datasets simulating 5 clinically representative situations; critical structures and artefacts contoured and 3 PTVs of varying sizes representing stage T1, T2 and T3 oral cavity cancers were explored. Planning utilized a Pencil‐Beam Convolution algorithm and the Modified Batho tissue heterogeneity correction. Results: No perceptible differences were noted between IMRT plans optimized on pre‐extraction CTs with extracted teeth contoured‐out and plans optimized on the post‐extraction CTs in DVH and isodose coverage. Furthermore, IMRT plans calculated on post‐extraction datasets using fluences from pre‐extraction plans also showed no significant differences, validating the simulation of physical extraction by the contouring‐out process. Finally, plans calculated with teeth not contoured‐out showed underdosing in nearby regions as well as inferior DVHs. Conclusions: Results indicate that clinically comparable plans can be generated by contouring‐out teeth on a pre‐extraction CT. This suggests that our current practice of scheduling a planning CT at least 2 weeks after dental procedure may be unnecessary; instead this time can be used for treatment planning if swelling/jaw‐changes are deemed insignificant, thus saving significant wait times and increasing patient through‐put and clinic efficiency.
SU‐E‐T‐820: Comparison of VMAT and IMRT for Stereotactic Body Radiation Therapy (SBRT) of the Adrenal Metastases
Authors: Zhang Y , Xiao J , Dai J , Zhang Y
Published: November 2011

Purpose: This study is to compare volumetric arc therapy (VMAT) with intensity modulated radiotherapy (IMRT) for stereotactic body radiation therapy (SBRT) of the adrenal metastases. Methods: For 13 patients who have completed SBRT with conventional IMRT technique, new VMAT plans were generated. Plans were optimized with the aim to protect organs at risk and spare healthy tissue while enforcing highly conformal target coverage of clinical prescriptions. IMRT and VMAT plans were designed on Pinnacle3 Version 9.0. All treatment plans were delivered on Elektaˈs Synergy machine. Plan quality and treatment efficiency for VMAT vs. conventional IMRT were evaluated. Results: all plans designed for conventional IMRT and VMAT techniques fulfilled the specific dose constraints. Both VMAT and IMRT resulted in equivalent target coverage but VMAT had an improved conformity index (CI=0.83±0.02 for VMAT and 0.81±0.02 for IMRT, p=0.025). Normal tissue sparing was comparable in both treatment techniques. The mean dose of the unilateral kidney was 10.5±4.6Gy for VMAT and 10.8±4.8Gy for IMRT (p=0.11). The VMAT reduced the total MUs per fraction by 13.1% (1192±261MU for VMAT and 1371±224MU for IMRT, p<0.001). The treatment delivery time for VMAT was 185± 18 seconds per fraction, while IMRT plans presented higher values with an average of 572±79 seconds. Conclusions: For equivalent target coverage and comparable normal tissue sparing, VMAT plans presented improvement in conformity index, and VMAT demonstrates significantly reduced treatment time and fewer MUs to achieve comparable dosimetric plans.