bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐825: Influence of the Multileaf Collimator Step Size in Step&shoot IMRT for Head&neck Treatments
Authors: Almada M , Venencia C , Descamps C , Garrigo E , Pipman Y
Published: November 2011

Purpose: The purpose was to analyze the influence of the step size during head&neck IMRT treatments. Methods: Ten patients with head&neck IMRT treatment plan were selected. Treatment plans were done using nine 6MV photon‐beams on a Primus linac (Siemens) with Optifocus MLC (10mm leaf width) and a dose rate of 200MU/min. The TPS used was Konrad v2.2 (Siemens) with leaves step size of 10, 5 and 3mm. For each step‐size, plans were evaluated in terms of MU, segments number, treatment time, PTVˈs (66Gy and 50Gy) dose uniformity and OAR (parotids and spinal cord) doses. Variations between measured and calculated total plan doses were obtained using solid water phantom and PTW PinPoint ionization chamber. Results: The MU number for 10mm step‐size plans was 624 [495,770] and increased 51% [36%, 87%] for 5mm and 124% [93%, 171%] for 3mm. The segments number for 10mm step‐size plans was 111 [99,129] and increased 41% [27%, 52%] for 5mm and 102% [71%, 125%] for 3mm. The treatment time for 10mm step‐size plans was 11.47min [11.08min, 12.45min] and increased 24% [9%, 33%] for 5mm and 65% [27%, 74%] for 3mm. Reducing the step‐size from 10mm to 5mm leads to better PTV_66Gy dose uniformity within ICRU50 tolerance (no difference observed between 5mm and 3mm). Step‐size diminution from 10mm to 3mm leads to a better coverage of PTV_50Gy especially in patient surface regions. For all the studied plans there are no differences in the parotids mean doses and spinal cord maximum dose. The variation between measured and calculated doses was 1.1% for 10mm step‐size. It increased 1.7% and 2.4% for 5mm and 3mm respectively. Conclusions: Using 10mm step‐size produces plans with adequate OAR doses. PTV Dose uniformity and volume coverage could be improved by 5mm step‐size whereas 3mm step‐size produces larger treatment times without advantages in dose distribution.
SU‐E‐T‐827: The Impact of Artefact Contouring on the Optimization of Head and Neck Cancers Using IMRT
Authors: Nuraney N , Cao F
Published: November 2011

Purpose: IMRT planning of head and neck (H&N) cancers routinely employs artefact contouring in the oral cavity due to dental restorations (DR). The differentiation between teeth and soft tissue in the region immediately surrounding these DR however is uncertain. A study was carried out on patients with varying number of DR/artefacts to determine the impact on optimization. Methods: Five H&N patients who had been planned using IMRT were selected with varying PTV locations, degrees of DR and artefacts. These patients were originally planned with the artefacts surrounding the DR contoured and the density of these converted to water/soft tissue (HU=0). The DR were given a maximum CT number assigned for our CT scanner (HU∼2700). These patients were then re‐optimized (using identical constraints as in the original plan) without any compensation for artefacts. Optimizations were carried out in both scenarios using the Eclipse™ planning system Pencil Beam (PBC)8.6.15 and then carried out using the AAA algorithm with/without artefacts contouring as well. Results: In the cases where the PTV didnˈt overlap the teeth/DR, DVH as well as axial slice comparisons showed insignificant differences between contouring the artefacts or not. In those cases where the PTV did overlap the DR, a difference was seen between the two optimizations; with and without artefacts converted to water/soft tissue. For large PTV volumes, this may not translate into a significant effect based on DVH comparisons since the volume of DR artefact is relatively small compared to the PTV volume. However, for smaller PTV volumes, the impact could be quite significant. This effect was seen using both algorithms: PBC and AAA. Conclusion: For H&N cancers with PTVs within the oral cavity, artefact contouring does have an impact on the optimization of IMRT plans and the proper contouring of DR artefacts can minimize the impact.
SU‐E‐T‐829: Dosimetric Comparison of Three Different External Beam Partial Breast Irradiation Techniques: Three‐Dimensional Conformal Radiotherapy, Intensity‐Modulated Radiotherapy and Volumetric Modulated Arc Radiotherapy
Authors: Sun T , Li J , Xu M , Liu T , Lin X , Zhang G
Published: November 2011

Purpose: To compare the dosimetric differences of three‐dimensional conformal radiotherapy (3D‐CRT), inverse intensity‐modulated radiotherapy (IMRT) and volumetric modulated arc radiotherapy(V‐MAT) for external beam partial breast irradiation. Methods: Twelve patients with breast cancer receiving breast‐conserving surgery and external beam partial breast irradiation were enrolled in the study.Three treatment techniques including 3D‐CRT, IMRT and V‐MAT were designed for each patient.The dose distribution in the target,the dose to the organs at risk,total MU and delivery time were compared. Results: 3D‐CRT plans showed the worst conformity in target.V‐MAT plans provided the lowest target coverage and homogeneity in target.All three plans met the clinical requirement.3D‐CRT plans showed the lowest values for the V5,V10 and mean dose and the highest values for V30 in the ipsilateral lung. No statistically significant differences were observed in V20 of the ipsilateral lung between three plans.The ipsilateral normal breast volume receiving 5Gy,10Gy,30Gy and 34Gy doses were significantly lower in IMRT and V‐MAT compared with 3D‐CRT.V‐MAT showed the lowest values in ipsilateral normal breast volume receiving 15Gy,20Gy and 25Gy doses.For V5,mean and max dose in heart,the mean dose in contralateral lung and the mean,max dose in thyroid, IMRT and 3D‐CRT showed the highest and lowest value respectively.The MUs were 417.6±34.4,772.8±54.4 and 631.0±109.0 respectively in 3D‐CRT,IMRT and V‐MAT.The delivery times were 9–10min, 8–10min and 1–1.1 min respectively in 3D‐CRT,IMRT and V‐MAT. V‐MAT could significantly reduced the delivery time. Conclusions: All three plans met the clinical requirement.V‐MAT significantly reduced the irradiated volume of high dose region in the ipsilateral normal breast,but the other dosimetric parameters didnˈt show better in V‐MAT compared with IMRT.V‐MAT significantly decreased the delivery time.Overall,V‐MAT showed a similar or better dose distribution and could significantly reduce the delivery times compared with 3D‐CRT and IMRT.
SU‐E‐T‐830: A Plan Comparison Study between Three Different Intensity Modulated Arc Therapy Techniques
Authors: Varadhan  , Yerich S , Overbeck C , Kristupaitis D , Weber M
Published: November 2011

Purpose: Intensity Modulated Arc Therapy (IMAT) is gaining widespread attention from various radiation oncology vendors and several centers are implementing them clinically. The aim of this study is to compare Plan quality between Rapid Arc (Varian), Volumetric Modulated Arc Therapy (Elekta) and Smart Arc (Pinnacle) for the same dataset and plan objectives. Methods: 3 anonymized prostate cancer cases with the same DICOM RT structure set were used to compare between the 3 IMAT delivery schemes. The Rapid Arc plans were generated using Eclipse Treatment Planning System (TPS), the VMAT plans were generated using MONACO TPS, and the Smart Arc plans were generated using Pinnacle TPS. The Dose Volume Histograms (DVH) was exported for each plan and plotted together to compare the DVH between 3 different TPS for each patient. In each case the plan objectives were kept the same. Also, the RT dose files were compared from the 3 different delivery methods by importing them into a 3rd party software. Results: To achieve the same plan quality, the Rapid Arc plans were generated using 2 arcs. There was no substantial improvement in plan quality when 2 arcs were used in VMAT plans using MONACO, therefore plans were generated using only one 360 degree arc for both VMAT and Smart Arc plans. The VMAT plans have more dose heterogeneity across the target volume while organs at risk sparing varied depending on the case. The Smart Arc plans had the lowest total monitor units among the 3 delivery methods while the Rapid Arc plans had the largest because 2 arcs were needed to achieve same plan quality.Conclusion: All 3 IMAT methods produced acceptable plans for Prostate IMRT. The relative strengths of each system varied depending on the complexity of the case and there is a trade off between each delivery method.
SU‐E‐T‐831: Four‐Dimensional CT in the Study of Internal Target Volume and Dose Distribution for Lung Cancer
Authors: Bai T , Li J , Yin Y , Lu J , Zhu J , Liu T
Published: November 2011

Purpose: For the effect of breathing motion, it is difficult to confirm the tumor accurately in lung cancer in the intensity‐modulated radiotherapy (IMRT). This study is to confirm the internal target volume (ITV) and compare the volumetric and dosiology differences between 3D‐CT and 4D‐CT, using 4D‐CT technology. Methods: Eight patients with primarily lung cancer were enrolled and both 3D and 4D‐CT were taken. For each patient, 3D‐CT was taken as reference image and clinical target volume (CTV) was defined on it. Extended CTV with setup margin was defined as PTV‐3D; for each respiratory phase, CTV were drawn separately and mixed together as ITV, which was extended as PTV‐4D. Design different IMRT plans on PTV‐3D and 4D separately for each patient with same prescription doses, field degrees and optimization target functions. The differences of target volumes, dose distributions on targets and organs as risk (OAR) were compared. Results: The volume is (150.67±86.67)cm3 for PTV‐3D and (130.17±79.89)cm3 for PTV‐4D, which is 13.61%(8.51%∼23.53%)smaller. There is no significant difference of target conformal index (CI)and homogeneity index (HI). About the dose on OARs (including lung, heart and spinal‐cord), 4D plans have lower dose to the 3D plans: V5, V10, V20 and V30 for total‐lung is cut separately from 41.25%, 29.75%, 21.25%, 13.00% to 38.13%, 27.00%, 17.25%, 9.13%; mean lung dose (MLD) is cut from 1103.63cGy to 911.21cGy; mean heart dose is cut from 450.43cGy to 372.20cGy; maximum dose for spinal‐cord is cut from 3162.83cGy to 2967.63cGy. Conclusions: 4D‐CT technology can be used to bridge the gap of missing or extending the target volume on 3D radiotherapy. It will bring better accuracy an lower dose on OARs as well.
SU‐E‐T‐833: A Phantom Study to Measure Increased Testicular Dose from Elective Lymph Node IMRT Compared with Prostate Irradiation Alone
Authors: Schubert L , Chen S , Zhou S , Enke C , Wahl A
Published: November 2011

Purpose: To verify the accuracy of treatment planning calculations indicating increased testicular doses from pelvic lymph node irradiation Methods: IMRT prostate plans with and without lymph node irradiation were created on an anthropomorphic phantom (RANDO®, The Phantom Laboratory) using Pinnacle3 version 8.0m treatment planning software (Philips Medical Systems). Nine beam plans were generated for a Siemens Oncor linear accelerator using 6 and 15 MV energies. For the prostate with lymph node irradiation plan, the prostate PTV and lymph node CTV were prescribed 45 Gy followed by a 34.2 Gy boost to the prostate PTV. For the prostate only plan, the prostate PTV was prescribed 79.2 Gy. Plans were normalized such that 95% of the prostate PTV received the same dose or greater in 1.8 Gy fractions. Measurements were acquired at locations on the phantom that corresponded with where the testicles would have been located on a human. MOSFET detectors (Best Medical) and a 0.6 cm3 farmer ion chamber (PTW) provided a total of ten measurements per plan. Measured doses with lymph node irradiation were compared to those without lymph node irradiation. Measurements were then compared with calculations from the respective treatment plans. Results: Both measurements and treatment planning calculations resulted in a dose increase to the testicular region in the IMRT prostate plan with lymph node irradiation. MOSFET measurements showed a 40% dose increase with lymph node irradiation (3.65 ± 0.21 Gy) compared to prostate irradiation alone (2.61 ± 0.17 Gy). Ion chamber readings also showed a similar percent increase (42%). The increase in calculated doses provided by the treatment plan was 50% (3.43 Gy with lymph node irradiation versus 2.28 Gy without). Conclusions: Phantom measurements have verified treatment planning calculations that indicate an increase in testicular dose for IMRT prostate treatments due to the addition of lymph node irradiation.
SU‐E‐T‐834: Comparison of Rapidarc, IMRT and 3D Conformal Planning for Treatment of Chestwall, and Regional Nodes
Authors: Dumane V , Powers A , Sheu R , Green S , Svoboda A , Lo Y
Published: November 2011

Purpose: To investigate the application of Rapidarc as a technique to improve the dosimetric plan quality for the treatment of the chestwall and regional nodes when 3D conformal planning using the partially wide tangents (PWT) technique requires the irradiation of more than 3 cm of the ipsilateral lung and/or the heart in order to achieve coverage to the IMNs, and to compare it with IMRT. Methods: The PWT plan was done using the field in field technique. IMRT planning consisted of 6 beams at five gantry angles, chosen to minimize the entrance or exit through the contralateral structures. The arc range for the Rapidarc plan was similar to IMRT. Dose calculation was performed with the AAA algorithm in Eclipse V 8.9. Dose prescribed was 5040 cGy. Results: PTV D95 and V95 for both the Rapidarc and IMRT plans were 98% and 97% respectively. The same for 3D was lower by 4%–5% respectively. Rapidarc reduced the left lung mean dose compared to 3D and IMRT by as much as 19 Gy. The V20 Gy and V10 Gy were lower with Rapidarc by as much as 45% and 50%. The total lung mean dose was lower with Rapidarc by 8 Gy while the V20 Gy and V10 Gy reduced by 22% and 25%. Heart doses more than 25 Gy were identical with 3D and Rapidarc while IMRT gave a mean heart dose that was higher by 11 Gy. The mean dose to the contralateral organs was higher with Rapidarc by 3 Gy compared to 3D. Conclusions: For the same coverage, Rapidarc was able to better spare critical organs compared to IMRT. Compared to 3D, Rapidarc had better coverage and lower ipsilateral and total lung dose and identical volumes of heart irradiated above 25 Gy.
SU‐E‐T‐835: Volumetric Modulated Arc Therapy Assisted by Active Breathing Control for Hepatocelluar Carcinoma Radiotherapy: A Planning Study
Authors: Gong G , Yin Y
Published: November 2011

Purpose: To investigate the feasibility of volumetric modulated arc therapy, RapidArc (RA), assisted by active breathing control (ABC) for hepatocellular carcinoma (HCC) radiotherapy. Methods: Twelve patients with HCC after TACE underwent 3D‐CT scanning assisted by ABC at end inspiration hold (EIH), end expiration hold (EEH), and free breathing (FB). Three treatment plans were designed as 3D‐CRT, IMRT, and RA. The volumes of liver, normal liver (the liver volume minus the PTV), GTV, PTV in three breathing status were compared. The conformity index (CI), the dose homogeneity index (HI) of target volume, and the maximum dose, minimum dose, the monitor unit, treatment time, the dose‐volume parameters of normal liver, stomach, duodenum were compared.Results: There was no significant difference in the volumes of liver, normal liver, and GTV at three breathing status (p > 0.05); but the PTV at FB was larger than that at EEH and EIH (p < 0.05), The overall CI and HI for RA was better than IMRT and 3D‐CRT at three breathing status (p < 0.05). The mean dose, V20, V30, V40 of normal liver were 3D‐CRT > RA > IMRT (p < 0.05). For the mean normal liver dose, the V10 was FB > EEH > EIH. For the V20, V30 and V40 of normal liver at FB was greater than that of EEH and EIH. The D5cm3 of duodenum was EIH > FB > EEH (p < 0.05). The monitor unit for IMRT, RA and 3D‐CRT were 626.33 ± 113.98, 550.28 ± 122.56 and 254.06 ± 18.56 respectively. The treatment time for IMRT, RA and 3D‐CRT were 540 ± 45s, 130 ± 10s, 135 ± 10s respectively Conclusions: RA assisted by ABC for HCC radiotherapy was feasible, with better dose distribution, fewer monitor unit, less treatment time and sparing more OARs.
SU‐E‐T‐836: Dosimetric Comparison of Intensity‐Modulated Radiotherapy and Volumetric Modulated Arc Radiotherapy for the Treatment of Multiple Intracranial Metastases
Authors: Lin X , Sun T , Yin Y , Liu T , Lu J
Published: November 2011

Purpose: To evaluate the dosimetric differences of intensity‐modulated radiotherapy (IMRT) and volumetric modulated arc radiotherapy (V‐MAT)for multiple intracranial metastases. Methods: Ten patients with multiple intracranial metastases were included in this analysis. Three treatment techniques were designed for each patient: intensity‐modulated radiotherapy with seven fixed field(IMRT), volumetric modulated arc radiotherapy with single 358° coplanar arc(V‐MAT1) and volumetric modulated arc radiotherapy with double 358° coplanar arcs(V‐MAT2) . Dose prescription was 60Gy to PTV in 30 fractions. All plans were normalized to the mean dose to PTV.The dose distribution in the target,the dose to the organs at risk,total MU and delivery time in three techniques were compared. Results: The best conformity and homogeneity in PTV were observed in V‐MAT2 plans,no statistically significant differences were observed between IMRT and V‐MAT1.For the maximum dose in lens,eyes and brainstem,the two V‐MAT plans were significantly lower than IMRT plan(p<0.05). For the maximum dose in optic nerves,the V‐MAT2 plans were statistically lower than IMRT plan(p<0.05).For the mean dose to normal brain tissue, no statistically differences were observed in the three techniques. V‐MAT2 plans showed the highest values in the normal brain tissue volume receiving 5Gy and 10 Gy doses.In the normal brain tissue volume receiving 20Gy,30Gy and 40 Gy doses,IMRT and V‐MAT2 plans showed the highest and lowest values respectively. Compared with IMRT plans,the average monitor units reduced 29% and 24% in V‐MAT 1 and V‐MAT2 plans and the delivery time was significantly shorter in V‐MAT plans. Conclusions: Comparing to IMRT plans, V‐MAT plans showed similar or better in the target dose distribution,reduced irradiation doses on organs in risk and moreover significantly decreased the monitor units and delivery time.
SU‐E‐T‐837: Comparison Between Step&shoot and Dynamic MLC Based IMRT for Prostate Treatment
Authors: Venencia C , Delgado J , Zunino S , Besa P , Pipman Y
Published: November 2011

Purpose: To compare step&shoot and dynamic MLC‐based IMRT for prostate treatment. Methods: Patient data with prostate cancer was selected. Same beam geometries and energy were used. Treatment plan includes simultaneous irradiation of prostate to 82Gy and seminal vesicles to 64Gy (41 fractions). Plans were normalized to achieve 82Gy minimum dose to prostate. Step&shoot was delivered using Primus linac (Optifocus MLC, 10mm leaf‐width, 200MU/min) and Konrad v2.2 TPS (Siemens). MLC step‐size of 0.5cm, minimum of 3 MU per segment and 15 intensity levels was used. Dynamic was delivered using Clinac 21EX (Millenium MLC, 0.5cm leaf‐width, 300MU/min) and Eclipse v8.1 TPS (Varian). MLC step‐size was 0.2cm. Plans dose distributions were compared in PCRT3D TPS (TRF). Optimization and dose calculation time, treatment time, MUs, PTVs and OAR DVH analysis and treatment plan QA were compared for both techniques. Results: Optimization and dose calculation time was 220seg for S&S and 360seg for dynamic. Total MU was 508 for S&S and 577 for dynamic. D98% (V82Gy) for PTV prostate were 81.5Gy (95.7%) for step&shoot and 80.1Gy (84.6%) for dynamic respectively. D98% (V64Gy) for PTV seminal vesicle were 64.2Gy (98.2%) for S&S and 62Gy (92.3%) for dynamic respectively. Rectum, V40Gy, V65Gy and EUD were 56.6cc, 21.2cc and 65.1Gy for S&S and 55.7cc, 19.7cc and 63.3Gy for dynamic respectively. Bladder V65Gy and EUD were 27.4cc and 47.9Gy for S&S and 24.4cc, and 46.2Gy for dynamic. Femoral head D10% were 40.4Gy for S&S and 39.3Gy for dynamic. Treatment time was 531seg for S&S and 271 seg for dynamic. Both treatment plans QA are within tolerances. Conclusions: Both IMRT modalities could be used for prostate treatment. Calculation time and MU are lower with S&S. D98%, V82Gy and V64Gy are slightly better using S&S. OAR doses are few percent better using dynamic. Treatment time is 50% less with dynamic.
SU‐E‐T‐838: Inverse‐Planned Multi‐Beam Intensity‐Modulated Radiation Therapy versus Three‐Dimensional Conformal Radiotherapy for Left Breast Cancer Patients after Mastectomy
Authors: Rakhno E , Crass J , Thompson P , Chakravarthy A
Published: November 2011

Purpose: The purpose of this study was to compare dose distribution and normal tissue sparing in the treatment of left chest wall, as well as supraclavicular nodes (SCV), and, in one case, internal mammary nodes (IMN) for patients undergoing post mastectomy radiation using three‐dimensional conformal radiotherapy (3D‐CRT) vs. multi‐beam intensity‐modulated radiotherapy (IMRT). Methods: To date, a total of five patients were randomly selected for comparison. All the planning target volumes (PTV) were contoured according to the Breast Cancer Atlas for the Radiation Therapy Planning from Radiation Therapy Oncology Group (RTOG). A dose of 5040cGy was prescribed in 28 fractions to each PTV. Two plans were evaluated for each patient, one with beam split tangents and an additional supraclavicular field for 3D‐CRT, and the other one with five inverse‐planned IMRT beams. To obtain the desired skin dose, bolus was used every other day. Dose comparison metrics included: PTV homogeneity index (HI) and conformity index (CI), V30 and V5, and mean and maximum doses to normal tissue structures, such as heart, left lung, right lung, contralateral chest wall, and V20 to both lungs. Results: Compared to a conventional 3D‐CRT plan, the five‐field IMRT significantly improved PTV HI and CI, and marginally reduced heart and left lung maximum doses without compromising PTV coverage, but at the same time increased contralateral chest wall and lung dose, and heart V5. Conclusions: Five‐field IMRT plan provides far superior target volume coverage and comparable heart V30 and lung V20 to a conventional plan, while increasing low dose to contralateral side. The use of five beams —instead of 9 or 11, as recommended by other studies‐ reduces the treatment time and, consequently, possible setup and internal organ motion errors. Further clinical studies are needed to determine whether IMRT improves tumor control or reduces acute or late toxicities when compared to 3D‐CRT.
SU‐E‐T‐841: The Potential of Probablistic Optimization for Tumor Motion with IMRT
Authors: Kissick M , Flynn R , Mackie T , Mo X , Zhao D , Campos D , Yan Y
Published: November 2011

Purpose: To demonstrate the feasibility of using probabilistic optimization for helical tomotherapy (HT) treatment planning of intrafraction moving targets: an alternative to motion management by active tracking. Methods: Realistic but regular purely transverse elliptical motion was produced with the Washington University 4D Motion Phantom to supplement previous work that contained either transverse and longitudinal or just longitudinal motions with varying amount of randomness and drifts. Dose perturbations due to motion were measured with Gafchromatic EBT film. A small (12cm diameter, 12 cm long) Virtual WaterTM cylindrical phantom is used in a Hi‐Art IITM (TomoTherapy Inc., Madison, WI) HT device. The treatment plan consists of a 9 cm ring target (98% gets the prescribed dose) with a 4 cm diameter central avoidance region (gets half the prescribed dose on average) for 9 cm along the length of the cylinder. Results: The transverse motion needs to be much larger than average transverse respiratory motions for lung tumors for the motion to cause unacceptable blurring. This and other studies demonstrate that HT is robust to breathing motion interference with the beamlet modulation, but care must be taken in the longitudinal direction for irregular breathing with a low frequency drift that interferes with the couch motion. Within the target, less than a 1% dose perturbation is observed between 0.10 < (gantry period)/(breathing period) < 10. Conclusions: With reasonable care to approximately regularize the patientˈs breathing, the dose distribution exhibits a dominantly ‘blurred’ response to the motion, so a single motion probability distribution function (pdf) can approximate the respiratory motion well enough to enable the use of probabilistic optimization. HTˈs delivery over multiple gantry rotations and patient breathing cycles enables sufficient dose smoothing for probabilistic optimization to apply to hypofractionated HT deliveries.

The author, T. Mackie, has ownership interests in TomoTherapy, Inc., which is commercializing helical tomotherapy. This work was funded by NIH/NCI K25 CA119344.
SU‐E‐T‐842: Robust Optimization of Dose Painting Treatment Plans Using Dosimetric Margins
Authors: Bradshaw T , Bowen S , Jeraj R
Published: November 2011

Purpose: Uncertainties in dose delivery due to setup or motion can be accounted for by robust IMRT optimization. In dose painting, the transformation of functional imaging data to non‐uniform dose prescriptions introduces large additional uncertainty, resulting in prescribed dose uncertainty at every voxel. We have developed and tested an optimization method for dose painting treatment plans that is robust to dose prescription uncertainty. Methods: An optimization method was developed that constrains dose at a voxel to within a range, as opposed to conventional single‐dose constraints. Ranges were based on uncertainties in the image‐to‐dose transformation as determined by a previously presented uncertainty model. Treatment plans for head‐and‐neck cancer patients were generated using both robust and conventional methods. Mean, deviation, and range in plan quality were compared when different prescribed‐dose distributions were sampled. The metric for plan quality was the percent PTV receiving planned dose within ±5% of its prescribed dose (Q(0.95–1.05)). Results: The pooled standard deviation in Q(0.95–1.05) was significantly lower (p<0.01) for the robust method (SD=19%) than the conventional method (SD=25%), indicating less overall spread in plan quality. The mean Q(0.95–1.05) for all patients was 73% for the robust method and 71% for the conventional method, which was not significantly different (p>0.05). Conventional plans performed better when no prescription uncertainties were introduced (nominal case), and robust plans performed better under large prescription uncertainties. Conclusions: Robust optimization using dosimetric margins produced significantly less spread in plan quality than did conventional optimization. While the methods yielded similar mean Q(0.95–1.05) values, plan quality under worst‐case‐scenario dose prescriptions was improved using the robust method. This advantage was more significant for dose‐painting plans with high dose‐escalation. Eventual incorporation of probability density functions for dose prescriptions into objective functions may enable more precise implementation of dose painting in prospective clinical trials.
SU‐E‐T‐844: Efficient IMRT Optimization by Appropriate Determination of Weighting Factors Using a New L1‐Solver: TFOCS
Authors: Kim H , Zhu L , Kim T , Xing L
Published: November 2011

Purpose: Recently, a new IMRT optimization containing a total‐variation (TV) with quadratic programming was proposed, which simplifies fluence‐map by generating piece‐wise constant solution. In practice, however, the traditional quadratic programming takes large memory space and the convergence rate is not ideal. As thus, determination of weighting factors of different structures remained to be trial‐and‐error in nature due to time limitation. This study proposes a new efficient method of appropriately determining weighting factors of critical structures using the profits given by a new L1‐solver, Template for First‐Order Conic Solver (TFOCS). Methods: The flexibility in defining the constraints in optimization with guaranteed convergence rate by TFOCS solver allows for modifying the process of determining weighting factors and optimizing beamlet‐intensity map. To specify the relationship of weighting factors of structures, an optimizing process with only PTV is performed. Based on the residues of structures, prescribed residues on PTV and OAR, and the size of matrices, weighting factors are finally determined. With determined parameters, PTV and OAR, a fluence‐map optimization is executed by TFOCS. To validate this method, head‐neck patient data was used. Results: The proposed method shows the efficiency in IMRT optimization by offering the proper weighting factors. With the new optimizing process, dose deliverability and quality of dose distribution are well balanced by properly defining the residues on PTV and OAR. With relatively large prescribed residue on OAR, it only demands 35 segments for 7 beams configuration for treatment. Contrarily, small prescribed residue adds the complexity in fluence‐map, requiring 50 segments with better dose conformality. Conclusions: The proposed method offers the effective way of determining weighting factors of different structures with guaranteed convergence rate and flexible constraint setting through a new L1‐solver TFOCS.
SU‐E‐T‐845: Benefits from Achillesˈ Heel of Intensity‐Modulated Proton Therapy via Worst‐Case Robust Optimization
Authors: Liu W , Zhang X , Li Y , Chen W , Mohan R
Published: November 2011

Purpose: to minimize the influence of ranger and patient setup uncertainties in intensity‐modulated proton therapy (IMPT), thus achieving the goal of “what you see is what you get” results in IMPT. Methods: A new efficient optimization scheme, which uses memory‐distributed parallelization on a multi‐processor system, is devised. Our method minimizes the possible hot spots in target volumes by penalizing not only underdosing but also overdosing in the target volumes in the objective function. Range and setup uncertainties are considered simultaneously with some simplifications. The optimization is done using the L‐BFGS method and parallelized with beamlet domain decomposition. Our approach is essentially not restrained by the memory available at one computing node and can easily be expanded to address more demanding problems in the future. Results: Compared with conventional treatment plans optimized based on planning target volumes (PTVs), our method yields plans that are considerably less sensitive to range and setup uncertainties and provides better protection for organs at risk. After robust optimization, the dose distribution is static to the CTV regardless of range and/or setup uncertainties, therefore reducing the sensitivity of the CTV coverage. This unique characteristic allows that the dose distribution is not necessarily conformal inside the whole volume of PTV, but rather a much smaller volume enclosing the CTV. Better normal tissue protection is thus accomplished by underdosing the margin of the PTV while not compromising the CTV coverage. Conclusions: Our results demonstrate the importance of robust optimization and challenge the effectiveness of the use of PTV to account for uncertainties in IMPT planning. Actually we can get some benefits rather than impediments from the sensitive dose distribution to uncertainties of IMPT. Thus, ideally all IMPT plans should be robustly optimized and our approach has great potential to make previously unreliable IMPT plans reliable.
SU‐E‐T‐846: Considering Marker Visibility during Planning Optimization for Dynamic Intensity‐Modulated Radiation Therapy
Authors: Zhao B , Dai J
Published: November 2011

Purpose: To retrospectively compare different topogram‐based patient body size indices and to determine if attenuation‐area product (AAP) is more accurate as a basis for optimizing scan protocol and minimizing patient dose in body CT of adults. Method: Thirty‐seven non‐contrast CT scans of thorax or abdomen exam were studied retrospectively, with patient age ranges from 21 to 67 years old. The individual patient body attenuation of the scanned region was computed from reconstructed images as the gold standard, after first converting image pixel values from HU values to μa values (μ is the attenuation coefficient and a is the area per pixel). Four topogram‐based body size indices (diameter (D), girth (G), projection area (sqrtPA), and AAP) were computed and compared to the gold standard using regression analysis. D was calculated by averaging the coronal and sagittal diameters, G by modeling the patient cross‐section as an ellipsoid, sqrtPA as the square root of the summation of the detector channel data. AAP was computed by multiplying the sqrtPA by the area per pixel, after accounting for patient mis‐centering, table attenuation, scanner geometry and detector pitch angle. The goodness of fitted linear models in correlation with gold standard was described by 95% confidence intervals (CIs). Results: Regression analysis resulted in different linear models. Preliminary results showed diameter and girth were similar in correlation with patient body attenuation with 95% CIs of ±2.8cm and 3.1cm. PA was better than both D and G; however, AAP was most accurate with a 95% CI of 1.3cm. At this time, we are analyzing more patient data sets. Conclusion: AAP may potentially be an automated, accurate patient size index as a basis for protocol optimization and dose minimization in adult body CT. Patient mis‐centering and pixel area corrections are critical for accurately estimating patient body size from topograms.

This research work was funded by National Natural Science Foundation of China (Grant No. 10975187)
SU‐E‐T‐847: Reducing Gated IMRT Delivery Times: Dual‐Gating
Authors: Geneser S , Kielar K , Kim T , Xing L
Published: November 2011

Purpose: Respiration‐gated radiation therapy delivers the beam at either inhale or exhale phases. To increase the duty cycle of gating and improve the treatment efficiency, we propose delivering radiation at both inhale and exhale windows. This work presents a treatment planning method that enables dual‐gated delivery while maintaining plan quality.Methods: The accumulated dose is a weighted sum of the dose distributions of the two phases. We minimize the least squares difference between the prescribed and computed accumulated doses under a set of dose‐volume (DVH) constraints. Optimization produces a single set of beam apertures for delivery at both inhale and exhale phases. We evaluate the optimization framework for our novel delivery scheme using a 4D phantom undergoing 1, 2, and 3 cm periodic motion in the superior‐inferior (SI) direction and compare the resultant dose distributions against the IMRT exhale gated distribution.Results: The dual‐gated technique produces highly conformal dose distributions for all testing cases. Compared to gating at exhale, the dual‐gated plans exhibit similar adjacent sensitive structure sparing (with the exception of the ipsilateral lung) while providing nearly identical PTV coverage. Indeed, the PTV DVH remains essentially unchanged for increased SI motion. However, the ipsilateral lung receives intermediate doses for large SI translation. For a target prescription of 60 Gy, over 61.7% of the ipsilateral lung receives a dose greater than 10 Gy for 3 cm motion. For 2 cm, 1 cm, and no motion in SI direction, the ipsilateral lung volume receiving a dose higher than 10 Gy is 39.5%, 36.9%, and 32.8%, respectively. The dose to the tissue surrounding the PTV is inversely proportional to the overlap of the inhale and exhale PTVs Conclusions: Dual‐gated delivery is a promising option for increasing duty cycle and thus improving treatment efficiency for tumors undergoing respiratory‐motion.
SU‐E‐T‐849: Optimal Sequencing to Reduce Treatment Time while Improving the Quality of Intensity‐Modulated Brachytherapy with Fixed‐Angular Fan‐Beams
Authors: Liu Y , Flynn R , Kim Y , Wu X
Published: November 2011

Purpose: To develop an optimal shield‐sequencing algorithm and evaluate its feasibility of a rotating shield intensity shield intensity modulated brachytherapy (RS‐IMBT) with a fixed emission angle.Methods: We use an electronic brachytherapy source (Xoft Axxent) with a tungsten (gold) partial‐shield, and test a range of emission angle (32 ∼ 76). Large tumor (>= 40cc) at BT was tested for cervical cancer. In shielding sequencing optimization, a nontrivial network transformation scheme was utilized which makes the global optimum is efficiently achieved with the shortest path and network flow algorithms. We employed the objectives that based upon GEC‐ESTRO recommendations. D90 of high risk CTV receives a prescription dose (Rx) while organs‐at‐risk (OAR: rectum & sigmoid (bladder) D2cc <=75 (90) EQD2 (equivalent dose in 2Gy fraction) Gy from external beam radiotherapy and BT. The feasibility was tested using the metric of plan conformality (D90 in high risk CTV and D2cc in OAR) and treatment delivery time. Results: The shielding sequencing algorithm improves significantly tumor coverage (D90) with favor OAR sparing in an acceptable delivery time increase. The D90 (100% Rx) was improved from 41% Rx from conventional, Point‐A plan. D2cc of OAR was kept under the recommended limits. The increase of delivery time was recorded as less than 5 times higher when 72 degree emission angle and with unshielded source combined. Optimization time was less than 2 seconds. Conclusion: Globally optimal shielding‐sequencing with beamlets overlapping significantly improves tumor coverage of high risk CTV for large tumor without compromising OAR sparing but with less than 5 times delivery time increase. RS‐IMBT technique shows promising approach for large, non‐isotropic shape tumor that is currently investigated using intracavitary plus interstitial approach or performed by conventional interstitial technique.

The research was supported, in part, by NIH grants R01‐EB004640 and K25‐CA123112, andNSF grants CCF‐0830402 and CCF‐0844765.
SU‐E‐T‐850: Selection of Initial DVH Constraints for IMRT Planning Based on Target Dose Gradient Characteristics
Authors: Zhang L , Court L , Choi B , Palmer M , Dong L
Published: November 2011

Purpose: One major obstacle for IMRT planning is to set up proper DVH constraints for organs at risk (OARs). Inexperienced IMRT planners often set OAR constraints using generic clinical guidelines, which may not always produce the best organ sparing. The goal of this study is to incorporate dose gradient information to set up the most likely achievable OAR dose tolerance. Methods: We investigated the dose falloff characteristics from typical IMRT plans. We found that the fastest dose falloff from a prostate plan can be universally used to describe the best scenario of dose gradient near the PTV. We also found the multi‐field near‐field dose falloff is different from the far‐field dose falloff, which is usually described by the attenuation of a single beam. We used an open‐field un‐modulated dose calculation to simulate the far‐field dose falloff. Also, we calculated the Euclidean distance map to translate the dose fall‐off to regional dose distribution. This dose distribution solely based on the distance from PTV and dose gradient information was reloaded back into the original plan. The DVHs calculated from this dose‐gradient plan represents the best scenario of OAR sparing. Those DVH values for OARs were used as initial estimation of DVH objective function for IMRT planning. Results: We applied our approach to 2 head‐and‐neck patients, 2 lung patients, and 2 prostate patients. We found the 40% dose falloff from the target dose prescription best represents the dose distribution in the near‐field. IMRT plans re‐optimized based on OAR constraints set by the dose‐gradient method produced better OAR sparing than the clinical plans for bladder (in prostate plans), heart (in lung plans), and oral cavity (in head‐and‐neck plans). All other organs produced similar results. Conclusions: We have designed a novel approach to incorporate dose gradient information as dose constraints for IMRT optimization.
SU‐E‐T‐851: An Inter‐Institutional Comparison of Knowledge‐Based IMRT Treatment Planning for Prostate Cancer
Authors: Chanyavanich V , Das S , Lo J
Published: November 2011

Purpose: To evaluate the feasibility of using a site‐specific database of prior plans to generate new prostate IMRT plans for cases drawn from an outside institution. Methods: The assembled database consists of 250 retrospective prostate IMRT treatment plans collected over a three‐year period at our institution. A case‐similarity algorithm based on mutual information was implemented to identify similar patient cases by matching 2D beamˈs eye view projections of contours. Ten randomly selected query cases from an outside institution were each matched against our site‐specific database of prior clinically approved plans. Treatment parameters including fluences and optimization weights from the best‐matched case were adapted to generate new IMRT treatment plans. We conducted a comparison of the differences in plan quality between the new semi‐automated plans and the original, manually generated plans. A simple plan quality (PQ) metric based on the area under the curve (AUC) of each structure of the DVH plot was used to quantitatively score the dose‐volume coverage for the PTV, rectum, and bladder. Results: For ten cases, the mean percentage difference in AUC between the new plan and the original plan was 0.4% for the PTV, indicating very comparable PTV coverage. The mean percentage difference in AUC was −3.6% for the rectum, and −9.3% for the bladder, indicating greater dose sparing for these two critical structures. This indicates that our new semi‐automated plans are very comparable in plan quality to the original, manually‐generated plans Conclusions: It is feasible to utilize a site‐specific knowledge base of prior plans to generate new, clinically acceptable treatment plans for cases drawn from an outside institution. This semi‐automated approach has the potential to improve the efficiency of the treatment planning process while ensuring that the extent of dose‐sparing is consistent and clinically acceptable.
SU‐E‐T‐853: Robust Multicriteria Optimization for IMPT
Authors: Chen W , Craft D
Published: November 2011

Purpose: A time and memory efficient projection algorithm for solving large scale IMPT treatment plans in a multicriteria setting has been published. However, the more conformal dose distribution of IMPT compared with that of IMRT comes with its sensitivity to uncertainties such as proton range uncertainty and set‐up error. To design a practically efficacious IMPT treatment system, robustness has to be accounted for to reduce the uncertainties. Methods: A nominal scenario and eight worst‐case scenarios (six extreme patient positions,proton beam undershoot and overshoot) are used to sample the uncertainty space. A solution can be constrained using a subset or all of the nine scenarios to be robust given any realization of the random errors. Moreover, the best quality plan can be pursued by navigating the Pareto space constituted by a number of optimal plans according to their own criteria of optimality. The method deals with very fine dose grid and tens of thousands modulated proton beamlets, therefore fully utilizes the potential of IMPT. Results: A base of skull case with 1mm dose‐grid resolution is applied to demonstrate the robustness of the solution. Compared to the plan obtained by the same problem formulation but considering only the nominal scenario, the DVH band of the robust plan is more stable, meaning the dose distribution varies little under even the worst scenario. The optimization for each task takes only seconds on a standard computer, making a computationally friendly interface possible to the planner. Conclusions: The uncertainty pertinent to the IMPT procedure can be reduced during treatment planning by optimizing some best plans that emphasize different treatment objectives and then interactively seeking for a compromised one from the Pareto solution space. The method works very fast for rather fine dose grid and sufficiently large beamlet numbers, thus streamlines the IMPT treatment process.
SU‐E‐T‐855: The Correlation Analysis of IMRT Dosimetry Errors and Parameters of Beams
Authors: Liu D , Chi Z , Cao Y , Li R , Han C
Published: November 2011

Purpose: To study the relationships of IMRT plansˈ beam characteristic parameters, furthermore in order to research the effect of parameters settings on the absolute dose accuracy. Methods: Forty‐three esophageal carcinoma cases were planned with the Pinnacle 7.6c TPS using appropriate optimization parameters and dose constraints. All the plans were transplanted into solid water phantom. DOSE1 dosimeter and 0.13cc ion Farmer Chamber (IBA Corp) were used to measure the absolute dose and obtained the dosimetry errors later. The parameters of the 43 casesˈ statistics were collected, and their relations were analyzed. Then we summarized the dosimetry errors, made comparison and analyzed the relativity between the beam parameters and absolute dose verification errors. Results: 1. The describing parameters of beams feature were related. (1) Beam numbers were significantly correlated with beam segment numbers and total MUs, both p‐values were equal to 0.000, but were not distinctly connected with average beam segment numbers and average MUs. (2) Beam segment numbers were prominently interrelated with average beam segment numbers, total MUs and average MUs. (3) Average beam segment numbers were negatively correlated with average MUs and the statistical correlation coefficient was −0.358, yet had no relationship with total MUs. (4) The relationship between total MUs and average MUs was significantly correlated, and the p‐value was 0.003. 2. There was an obvious interrelation between dose accuracy and parameter settings, all of the p‐values were almost 0.000. Dose deviation was positively correlated with the total number of fields, segments, MUs and average segment numbers, while was negatively connected with average MUs.

Conclusions: For the purpose of decreasing the absolute dose verification errors, the quantity of beam angles and beam segments should be reduced, considered the aspect of the designing of treatment plans.
SU‐E‐T‐857: Comparison of Nasopharyngeal Carcinoma IMRT Plans from Four Commercial Treatment Planning Systems (TPS)
Authors: Cao Y , Chi Z , Li R , Han C , Zhu S
Published: November 2011

Purpose: Different treatment planning systems (TPS) use different treatment optimization and leaf sequencing algorithms. This work compares nasopharyngeal carcinoma (NPC) IMRT plans optimized with four commercial TPSs to investigate the plan quality in terms of target conformity and delivery efficiency. Methods: Five nasopharyngeal carcinoma cases were planned with the Corvus, Monaco, Pinnacle and Xio TPSs by experienced planners using appropriate optimization parameters and dose constraints to meet the clinical acceptance criteria. Plans were normalized for at least 95% of PTV to receive the prescription dose (Dp). Dose‐volume histograms and isodose distributions were compared. Other quantities such as Dmin (the minimum dose received by 99% of CTV/PTV), Dmax (the maximum dose received by 1% of CTV/PTV), D100, D95, D90, V110%, V105%, V100% (the volume of GTV/CTV/PTV receiving 110%, 105%, 100% of Dp), conformity index(CI), homogeneity index (HI), the Dmax of spinal cord, brain stem, nerves and lens，the volume of receiving 30Gy (V30) and the mean dose to parotids (Dmean) were evaluated. Total segments and MUs were also compared. Results: While all plans meet target dose specifications and normal tissue constraints, the maximum GTVCI of Pinnacle plans was up to 0.43 and the minimum of Corvus plans was only 0.17, these four TPSs PTVCI had comparable and no difference. The GTVHI, CTVHI and PTVHI of Pinnacle plans are all very low and show a very good dose distribution. Corvus plans provided the lower, better protection of normal tissue. The Monaco and Pinnacle plans require significantly less segments and MUs to deliver than the Corvus plans. Conclusions: To deliver on a Varian linear‐accelerator, the Pinnacle plans show a very good dose distribution. Corvus plans provided the lower, better protection of normal tissue. The Monaco and Pinnacle plans have faster beam delivery.