bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐610: Evaluation of the Performance of the Segmentation Methods Used in the CMS XiO Step‐And‐Shoot IMRT
Authors: Jurkovic I , Mavroidis P , Stathakis S , Esquivel C , Chyle V , Papanikolaou N
Published: July 2013

Purpose: The aim of this work is to evaluate the performance of the segmentation methods used in the CMS XiO radiotherapy treatment planning system. Methods: For this study, fifteen patients with different types of cancer (prostate, head and neck, pancreas, esophagus, lung) were selected. For each patient, two treatment plans were produced using the sliding window segmentation and the smart sequencing methods. The plans were optimized based on the same clinical objectives. The analysis was based on the dose volume histograms (DVHs) of the PTV and organs at risk, the isodose distributions, maximum global dose, total number of segments, total number of monitor units (MU) per plan, and the average number of MUs per segment. Results: The study showed a statistically significant reduction in the total number of monitor units (mean:25.1%, range:7.0%– 35.5%) when the smart sequencing segmentation method was used (p=1.2E‐7). However, this reduction in the total number of monitor units did not reduce the total number of MLC segments per plan. The number of MLC segments per plan varied regardless of the site being treated. The plans that used the smart sequencing segmentation method had higher global maximum doses ranging between 106%–118% of the prescription dose, while the corresponding range for the sliding window method was 104%– 111%. The average number of monitor units per MLC segment was 2.5 for the smart sequencing method (range:2.0–3.1), and 3.7 for the sliding window segmentation method (range:2.6–5.0). Conclusion: This study shows that while smart sequencing segmentation method significantly reduced the total number of monitor units it did not reduce the total number of segments per plan. The smart sequencing segmentation method also produced a higher global maximum dose in all the cases, but with no additional sparing of the relevant organs at risk.
SU‐E‐T‐611: Investigating VMAT Planning Technique to Reduce Rectal and Bladder Dose in Prostate Cancer Treatment Plans
Authors: Rana S , Cheng C
Published: July 2013

Purpose: The purpose of this study was to compare the dosimetric quality of new partial‐double arc (partial‐DA) technique in volumetric‐modulated arc therapy (VMAT) planning of prostate cancer. Methods: In this retrospective study, twelve cases of low‐risk prostate cancer were included. For each case, a full‐double arc (DA) plan was created using two arcs in Varian Eclipse (version 11). The partial‐DA plans were then created using identical dose‐volume optimization values and beam parameters as in full‐DA plans except for arcs which included anterior (30degree) and posterior (60degree) avoidance sectors. All plans were calculated by analytical anisotropic algorithm. For planning target volume (PTV), maximum dose (Dmax), mean dose (Dmean), and conformity index (CI) were evaluated. For bladder and rectum, volumes that received 70,50,40,and 20Gy (V70,V50,V40 and V20, respectively),and Dmean were compared. For femoral heads, V20 and Dmean were evaluated. Additionally, monitor units (MUs) and integral dose were compared. Results: Doses to PTV were comparable in partial‐DA and full‐DA plans with an average difference ±0.2%. The CI (1.24; p=0.960) was same for both sets of plans. Dose to rectum was always lower in partial‐DA plans by average differences of 1.8%(p=0.183) for V70, 9.2%(p=0.014) for V50, 22.6%(p<0.000) for V40, 19.4%(p=0.028) for V20, and 9.5%(p<0.000) for Dmean. Similarly, dose to bladder was always lower in partial‐DA plans by average differences of 10.2%(p=0.002) for V70, 31.0%(p=0.001) for V50, 40.9%(p=0.001) for V40, 21.8%(p=0.001) for V20, and 18.5%(p<0.000) for Dmean. In contrast, partial‐DA technique delivered higher dose to femoral heads by average differences of 52.2%(p<0.000) for V20 and 21.2%(p<0.000) for Dmean. Partial‐DA plans produced higher number of MUs (7.5%,p=0.005) and integral dose (5.5%,p<0.000). Conclusion: In comparison to full‐DA technique, our purposed partial‐DA technique reduced rectal and bladder dose significantly but with higher femoral head dose, which was nonetheless within planning criteria, for the same PTV coverage.
SU‐E‐T‐613: A Multi‐Isocenter IMRT Approach of Large Fields to Reduce the Hot Or Cold Spots Caused by Setup Error
Authors: Liu B , Zhou S , Song S
Published: July 2013

Purpose: To reduce the hot and cold spots introduced by setup error of multi‐isocenter IMRT for large fields. Methods: A patient with entire peritoneal cavity as PTV for IMRT on Trilogy are studied, with prescription of 3000 cGy to the PTV and 3600 cGy to gross disease in 20 fractions. The PTV dimension on the Sup‐Inf direction is 46 cm, thus two isocenters (one in the abdominal region and one in the pelvis) are used. Eight beams with gantry angles 320°, 280°, 240°, 200°, 160°, 120°, 80°, 40° are used for each isocenter, and the two groups of eight beams overlap for 13cm. We intentionally vary the inferior boarder of the abdominal fields and the superior boarder of the pelvis fields, so that there are 4 pairs of beams with different inferior boarders for the 8 abdominal fields and also 4 pairs of beams with different superior boarders for the 8 pelvis fields: the benefit of this beam setup is that only 2 out of the 8 beams will contribute to hot or cold spot when setup errors are introduced. Setup errors are simulated by shifting the isocenters in the Sup‐Inf direction in the Pinnacle system Results: Our method and IMRT without varying superior and inferior boarder give similar plans: V27s are 94.8% vs 95.1%; mean liver doses are 2720 cGy vs 2721 cGy; mean kidney doses are 1795 cGy vs 1774 cGy. However, for 0.3 cm inferior shift of the abdominal isocenter, hot spots are 3400cGy vs 3850 cGy; for 0.3 cm superior shift of the abdominal isocenter, the cold spot are 2700 cGy vs 2400 cGy. Conclusion: Our IMRT approach for large field can significantly reduce the hot and cold spots introduced by setup error.
SU‐E‐T‐614: A Comparison of IMRT Plans for the ViewRay MR‐Guided RT System with TomoTherapy and Pinnacle
Authors: Saenz Daniel , Bayouth John , Paliwal Bhudatt
Published: July 2013

Purpose: To begin to assess the treatment planning capabilities of the ViewRay MR‐guided radiotherapy system. Methods: Treatment plans created using ViewRay software were compared with previously completed Pinnacle and TomoTherapy plans from patients in our clinic. Sites such as pancreas were chosen due to the soft‐tissue contrast which makes them candidates for MR‐image guidance with ViewRay. CT images and structure sets were exported from their original planning systems and imported into ViewRay. MR images were not the focus of this investigation since we required a direct comparison with existing plans utilizing CT. ViewRay plans were created as equivalently as possible with the original planning environment, matching prescription and normal structure priorities. The resulting isodose lines were visually assessed for conformality. Dose‐volume histograms were extracted from ViewRay and plotted together with those from the original planning system. Finally, ViewRay plans were also examined by their ability to meet QUANTEC dose restraints. Results: A pancreas plan created using the images of a patient who underwent IMRT with Tomo Therapy resulted in satisfactory conformality assessed by the coverage of the 98% isodose line. The DVH demonstrated shallower dose fall‐off for the PTV compared with TomoTherapy, as expected for a Cobalt‐60 based treatment. Normal tissue DVH lines for View Ray surpassed QUANTEC dose constraints or performed as well as Tomo Therapy for all structures except kidney. Comparison with non‐IMRT Pinnacle cases also exhibited good conformality and satisfied QUANTEC restraints. Conclusions: View Ray created a feasible plan generally matching most normal tissue restrictions. Of course, the IMRT gold‐standard Tomo Therapy outperformed View Ray regarding the steepness of DVH dose fall‐off. In the future, more cases will be studied to perform a more complete analysis. Also, we will investigate the Co‐60 dose profiles to assess penumbra directly. The View Ray TPS has the potential for comparable plans in the hands of experienced planners.
SU‐E‐T‐617: Commissioning the Eclipse Pencil Beam for Low Energy X‐Rays
Authors: Cherven M , Burmeister J , Rakowski J , Snyder M
Published: July 2013

Purpose: To use an existing treatment planning system to configure a low energy beam in order to evaluate the possibility of applying such a beam to intensity modulated radiation therapy (IMRT). It has been shown that low energy photons combined with heavy metal contrast can provide a higher relative biological effectiveness (RBE) through Auger electron production. Achieving a higher RBE may provide additional treatment options for patients with tumor types, such as glioblastoma, that are resistant to megavoltage therapy. Methods: A set of low energy photon beam data was generated using Monte Carlo simulation, put into appropriate w2CAD formatting, and imported into Varian Eclipse TPS to provide a set of depth dose curves and profiles. Additional beam data was calculated and a low energy beam was configured using the Pencil Beam Convolution algorithm. Treatment plans investigating dose distribution of the beam utilizing IMRT techniques were created to evaluate the usefulness of this technique. Results: The Eclipse TPS is able to model the dose distributions that would be produced by a low energy beam in a solid water phantom. In theory we could apply this model to IMRT treatment techniques to provide a more conformal dose distribution. Dose enhancement due to heavy metal contrast will initially be included as a simple scaling of the dose within the target region. The inclusion of heterogeneity corrections is difficult due to the enhanced photoelectric effect in bone at low energies, and is under investigation. Conclusion: Eclipse is capable of modeling a low energy photon beam using the pencil beam algorithm for calculation on homogeneous phantoms. Further investigation is needed to determine the ability of the treatment planning system to assist in low energy photon treatment planning, with the eventual goal of providing a higher RBE therapy option for resistant tumor types.
SU‐E‐T‐618: Development of a Graphic User Interface for An In‐House Monte Carlo Based Treatment Planning System for Mixed Beam Radiation Therapy
Authors: Eldib A , Lin M , Jin L , Li J , Ma C
Published: July 2013

Purpose: Mixed beam radiation therapy (MBRT) has been shown by many investigators to be a promising modality. In our institution, we have developed an in‐house Monte Carlo based treatment planning system for MBRT treatment planning. The aim of the current work is to develop a graphic user interface (GUI) for this system and to promote its clinical application. Methods: We have used the MCBEAM code for treatment head simulation and for generating phase space files to be used as radiation source input for our treatment planning system. The MCPLAN code was used as a Monte Carlo dose calculation engine. An interface was constructed to facilitate the input of all required parameters for the planning process. The planner can also input all Monte Carlo simulation parameters or simply use the default values already stored in the program. A display window interface was developed to show the virtual patient phantom and the planner can easily explore the different patient transversal CT cuts by using a scroll bar. The planner could then place the beams after mouse clicking to select the target isocenter. The planner could visually change the beam angles. The virtual phantom is generated using another interface, named MCDICOM. MCDICOM was developed for creating a virtual phantom with 3D rectilinear voxel geometry for Monte Carlo dose calculation based on DICOM‐compatible export from other treatment planning system. Results: The GUI for MBRT treatment planning provided a great tool for gantry angle selection. It streamlines the treatment planning process by integrating all seperate codes into one running environment. The GUI interface improved the operation efficiency for our in‐house treatment planning system. Conclusion: Our GUI based program can facilitate the clinical implementation of MBRT and its widespread clinical applications. This work has been supported by a UICC American Cancer Society Beginning Investigators Fellowship funded by the American Cancer Society
SU‐E‐T‐623: Comparison of Planned and Delivered Doses for Prostate Cancer Using a Deformable Image‐Guided Adaptive Radiation Therapy (IGART) Method
Authors: Ellis R , Traughber B , Bao A , Pereira G , Kaminsky D , Pirozzi S , Shen Z , Liu I , Nelson A , Piper J
Published: July 2013

Purpose: To evaluate an IGART scheme for prostate cancer that uses deformable CBCT image registration to track daily delivered dose (accumulated over time) to targets and organs‐at‐risk and allows comparison to the original treatment plan. Methods: Six patients treated with external beam radiation therapy for high risk prostate cancer were evaluated. Daily CBCTs were obtained for setup evaluation for all 45 fractions. Contours were transferred from the planning CT to the Day 1 CBCT to serve as the surrogate planning CT for deformation. Dose was applied automatically to each CBCT based on the recorded shift for that day. The daily CBCTs were deformed back to the first CBCT to sum the dose over the course of treatment. Contours were also deformed from the Day 1 CBCT to each subsequent day to allow for daily DVH evaluation. The accumulated delivered dose (summed from each daily treatment) and the planned dose were compared in terms of min, mean, max doses to structures: bladder, rectum, and PTV. Results: The average percentage differences between planned and delivered doses were: bladder — Dmin (8.2 +/− 13.4), Dmean (7.3 +/− 12.7), Dmax (−4.2 +/− 2.7); rectum — Dmin (−16.4 +/−41.4), Dmean (0.8 +/−9.8), Dmax (−3.2 +/−2.3); PTV — Dmin (−16.7 +/− 12.9), Dmean (−3.8 +/−2.7), Dmax (−4.1 +/− 2.9). Conclusion: An IGART scheme for prostate cancer using daily CBCTs and deformable registration was evaluated and found to be feasible. Further work is planned using a larger cohort of patients to evaluate the impact of dose differences between planned and delivered doses. Aaron Nelson and Jonathon Piper are owners and employees of MIM Software Inc. Sara Pirozzi, Ian Liu, and Zhilei Shen are employees of MIM Software Inc.
SU‐E‐T‐630: Feasibility Study of Volumetric Modulated Arc Therapy with Constant Dose Rate for Endometrial Cancer
Authors: Yang R , Wang J , Xu F , Li H , Zhang X
Published: July 2013

Purpose: To investigate the feasibility, efficiency, and delivery accuracy of volumetric modulated arc therapy with constant dose rate (VMAT‐CDR) for whole pelvic radiotherapy of endometrial cancer. Methods: The nine‐field intensity‐modulated radiotherapy (IMRT), volumetric modulated arc therapy with variable dose rate (VMAT‐VDR), and VMAT‐CDR plans were created for 9 patients with endometrial cancer undergoing whole pelvic radiotherapy. The dose distribution of planning target volume (PTV), organs at risk (OARs) and normal tissue (NT) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. For each VMAT‐CDR plan, a dry run was performed to assess the dosimetric accuracy with MatriXX from IBA. Results: Compared with IMRT, the VMAT‐CDR plans delivered a slightly greater V20 of bowel, bladder, pelvis bone and normal tissue, but significantly decreased the dose to the high dose region of rectum and pelvis bone. The monitor units decreased from 1105 with IMRT to 628 with VMAT‐CDR. The delivery time also decreased from 9.5 min to 3.2 min. Very similar dose distribution was found in the VMAT‐VDR and VMAT‐CDR plans. The average gamma pass rate was 95.6% at the 3%/3 mm criteria with MatriXX pre‐treatment verification for nine patients. Conclusion: Volumetric modulated arc therapy with constant dose rate can achieve comparable plan quality with significant shorter delivery time and smaller number of MUs compared with IMRT for endometrial cancer patients undergoing whole pelvic radiotherapy. It can be accurately delivered and be an alternative to IMRT on the linear accelerator without variable dose rate capability. This work is supported by the grant project: National Natural Science Foundation of China (No. 81071237).
SU‐E‐T‐631: A Fixed Jaw Method to Protect Critical Organs in Intensity‐Modulated Radiotherapy
Authors: Chen J , Dai J
Published: July 2013

Purpose: For some patients to be treated with IMRT, extremely low tolerances of critical organs(such as lens, ovaries and testicles) could not be met during treatment planning. The aim of this work is to introduce a new planning method to overcome this problem. Methods: In current planning practice, jaw positions are automatically set to cover all target volumes by planning system(eg, Pinnacle3 system). Because of such setting, critical organs may be fully blocked by MLC, but sit in the field shaped by collimator jaws. These critical organs receive doses from MLC leaf transmission and leakage. To reduce their doses further, we manually fixed jaw positions to block them. This method has been used for different treatment sites in our clinic. Here we take 8 patients with radical hysterectomy plus ovarian transposition as example, to demonstrate its performance. For each patient, two treatment plans were generated with the same optimization parameters: the original plan(called O‐plan), and the plan with fixed jaw positions(named F‐plan). In F‐plan, the jaws were manually fixed to block the ovaries. Results: For target coverage, the mean CI of F‐plan was remarkable lower than O‐plan(p<0.05). Meanwhile, for the critical organ sparing, the mean dose of left and of right ovary were much lower in F‐plan than O‐plan(p<0.05). V20, V30 and V40 of bladder were also lower with the F‐plan (p<0.05). The maximum dose to the spinal cord PRV of the O‐plan and the F‐plan were with significant differences(p<0.01). But there were 1.4 times MUs in F‐plan compared with the O‐plan, thus the treatment time could be longer by using the F‐plan. Conclusion: A fixed‐jaw method was developed to protect critical organs. Since it results in better plan quality but more MUs, it is recommended to be used only clinical requirements to critical organs cannot be met with regular method.
SU‐E‐T‐632: Study the Effect of Grid Size On Head and Neck IMRT Dosimetry
Authors: Srivastava S , Das I , Cheng C , Nohadani O
Published: July 2013

Purpose: In IMRT, ICRU‐83 requires dose prescription to be at D50% also as mean dose. Dosimetry is impacted by the calculational grid size that is studied for head and neck IMRT with special consideration on the tumor control probability (TCP) and normal tissue complication probability (NTCP). Methods: Five head and neck patients treated with IMRT and daily IGRT were chosen for this study. Using Eclipse treatment planning system (TPS) treatment plans were generated for different grid sizes in the range 1.0 mm−5.0 mm for the same optimization criterion with a 6MV photon beam. The desired dose volume constraints were kept the same to provide uniform dose to the PTV. The dose volume histogram (DVH) was recorded for all IMRT plans and dosimetric data were compared. ICRU‐83 dose points such as D2%, D50% and D98% were also calculated. In addition, TCP and NTCP were calculated using LQ Poisson model and Lyman Kutcher Burman model respectively from DVH data. Results: The PTV mean dose decreases with increasing grid size from 1mm to 5mm with an average decrease of 1.5%. It is also found that TCP decreases with increase in grid size with an average decrease of 1.6%. Mean dose and NTCP for the right parotid increases with increase in grid size with an average increase in mean dose by 1.6% and NTCP by 4.8%. Similar patterns were observed for all other OARs: left parotid, mandible, brainstem and spinal cord. Conclusion: It is concluded that smallest possible grid size should be used for accurate dose calculation in head and neck IMRT planning. Smallest calculational grid also improves TCP for target volumes and reduces NTCP for normal tissues. The grid size effect is most important for smaller structures such as cochlea, optic chiasm and lens.
SU‐E‐T‐633: Hypofractionated Prostate Treatment in a Single VMAT Arc
Authors: Clemente F , Perez‐Vara C , Couselo M , Lopez‐Carrizosa C , Ibanez C , de Miguel M Martin , Saez J , Zapatero J , Jerviz V , Dominguez M
Published: July 2013

Purpose: Several publications have proposed during the last years hypofractionated treatment schedules in prostate cancer. Such schedules have been possible because the α/ß ratio for prostate carcinoma is comparable to, and even lower than, the surrounding late‐responding normal tissues. This work shows the scheme adopted in our institution for hypofractionated prostate cancer treatment and plan evaluation based in DVH parameters. Methods: Monaco 3.10 (CMS, Elekta) is the inverse planning system used for volumetric‐modulated arc therapy (VMAT). Treatments are delivered with an Elekta Synergy linac. Daily cone‐beam CT corrections are performed as image‐guided radiation therapy technique. The fractionation schedule, with the assumption that α/ß = 1.5 for targets and 3.0 Gy for OARs, consists on 28 fractions, delivering 2.5 Gy to prostate gland, 2.0 Gy to seminal vesicles and 1.8 Gy if lymph nodes are included. Dose‐volume constraints are taken from QUANTEC reviews and they are adapted to our fractionation scheme according the linear‐quadratic model (assuming the previous α/ß ratios): V45.4<50%, V54.5<35%, V59.0<25%, V63.6<20%, V68.2<50% for rectum; V59.0<50%, V63.6<35%, V68.2<25%, V72.7<15% for bladder; Dmax<45.4 Gy for femoral heads; Dmean<45.4 Gy for penile bulb Results: Valid single VMAT arc plans are generated by the TPS. Target volumes preserve the optimal homogeneity and coverage, as well as OARs maintain their dose‐volume parameters under those imposed by QUANTEC: V45.4=(20.3±5.9)%, V54.5=(11.7±4.4)%, V59.0=(8.9±4.0)%, V63.6=(6.5±3.1)%, V68.2=(4.1±2.4)% for rectum; V59.0=(12.2±7.3)%, V63.6=(9.5±6.5)%, V68.2=(6.5±5.6)%, V72.7=(2.7±4.0)% for bladder; Dmax=(35.3±4.6) Gy for femoral heads; Dmean=(42.3±3.7) Gy for penile bulb. Mean treatment time is 310±43 s. Conclusion: VMAT in conjunction with IGRT techniques are powerful tools to cover a hypofractionated prostate cancer treatment program. It is possible to generate optimal plans to treat target volumes as well as to accomplish QUANTEC constraints. VMAT technique allows the delivery of the treatment in a single arc, with a significant reduction in treatment time.
SU‐E‐T‐634: Accuracy of Patient Dose Calculation for Lung VMAT Plans: Comparison of Multiple TPS
Authors: Wang X
Published: July 2013

Purpose: To evaluate the discrepancy in patient dose calculation for lung VMAT SBRT plans calculated either using the same type treatment planning systems (TPS) commissioned in different hospitals or the different type TPS commissioned in the same hospital.Methods: 10 lung SBRT cases have been calculated using four different TPS. TPS A, B, and C are Pinnacle3 (version 9) and each one is commissioned in a different hospital for 6 MV photon beams (Varian Trilogy, 120 MLC). Therefore, beam data and parameters used in these TPS are not exactly the same. The TPS D is Eclipse (version 10) and uses the same machine data as the TPS A. The variations of PDD (10)/PDD (20) ratios for three 6 MV beams are within 0.5%. MU are rescaled for TPS A, B, and C to get a normalized dose in a reference condition. TPS A and D use the same MU. The Dmean for IGTV and PTV, D50, D99, D2 for PTV, D2cm, cord Dams, Dmean, V20 and V10 for lung are used for comparison. Cases with large discrepancy are also recalled in typically used lung QA phantoms (ROTG and Quasar). Results: The doses calculated using different Pinnacle TPS have no clinical significantly discrepancy. The largest discrepancy in PTV mean dose is 3%. In most cases the dose discrepancy between the Eclipse and Pinnacle is also small but the largest discrepancy is up to 7% in PTV mean dose. Dose calculation in lung phantoms cannot predict the corresponding discrepancy in patients. Conclusion: The same type PTS even commissioned in different hospitals will have minimum calculated discrepancy. Using different type TPS have largest discrepancy especially for a tumour surrounded unusual lower density lung volume. Centralized modeling with comprehensive QA will improve dose calculation accuracy to achieve a standardized treatment.
SU‐E‐T‐635: Volumetric Modulated Arc Therapy for the Treatment of Cervical Cancer in Lieu of HDR Brachytherapy
Authors: Merrow C , De Boer S , Podgorsak M
Published: July 2013

Purpose: To investigate the use of VMAT to deliver the following conceptual GYN brachytherapy (BT) dose distributions: 1. traditional pear‐shaped dose distribution with substantial dose gradients, 2. homogeneous dose distribution throughout PTV (BT prescription volume), and 3. increased dose to PTV without OAR overdose. Methods: A tandem and ovoid BT treatment plan, with the prescription dose of 6 Gy to point A was exported into the VMAT treatment planning system (TPS) and became the baseline for further comparative analysis. The 200%, 150%, 130% 100%, 75% and 50% dose volumes were converted into structures for optimization and evaluation purposes. The 100% dose volume was chosen to be the PTV. Five VMAT plans were created to duplicate the Ir‐192 tandem and ovoid inhomogeneous dose distribution. Another five VMAT plans were generated to deliver a homogeneous dose of 6 Gy to the PTV. An additional five VMAT plans were created to increase the dose to the PTV with a homogeneous dose distribution. All plans used BT dose constraints. Results: On average in the first set of plans, the dose given to 99% of the 200‐100% dose volumes agreed within 2% of the BT plan, the 75% dose volumes were within 5% and the 50% dose volumes were within 6.4%. In the second set, the 100% dose volume was within 1% of the original plan. In the last set the maximum increase of dose to the PTV was 8 Gy with similar doses to OARs as the other VMAT plans. The maximum increase of dose was 2.50 Gy to the rectum. The maximum decrease of dose was 0.70 Gy to the bladder. Conclusion: VMAT was successful at reproducing brachytherapy dose distributions. Alternative dose distributions have the potential to be used in lieu of brachytherapy. However, differences in radiobiology need to be further investigated.
SU‐E‐T‐636: Impact of Different Intensity Levels On Step and Shoot IMRT Plan Quality and Deliverability
Authors: Manigandan D , Sharma S , Biswas A , Mohanty B , Subramani V , Chander S , Julka P , Rath G
Published: July 2013

Purpose: To evaluate the impact of different intensity‐levels on step and shoot IMRT plan quality and deliverability. Methods: Five previously treated patients of carcinoma rectum (pre‐operative) were studied. Planning target volume (PTV) and organ at risk (OAR) i.e. bladder and bowel were contoured. Step and shoot IMRT plans (6MV, 45Gy/25fraction prescribed at 95% isodose) were created in Eclipse TPS for Varian CL2300C/D linear accelerator at 300MU/min. During optimization, dose volume constraints and priorities were kept constant and only intensity‐levels were varied as follows: 5, 10 and 15. Plan quality was analyzed in terms of maximum and mean doses of PTV, coverage index (CI=PTV covered by prescription dose/PTV), heterogeneity index (HI)=D5/D9 5 (D5=dose received by 5% of PTV and D9 5=dose received by 95% of PTV), OAR mean‐doses and normal tissue integral‐dose (NTID) (liter‐Gray). Total monitor units (MUs) required to deliver a plan was noted. Deliverability of treatment plans were verified with I‐matriXX array and compared with TPS dose‐plane using gamma index of 3% dose difference and 3mm distance to agreement (DTA) criteria. Results: Maximum dose to PTV was 5219.06±54.55cGy, 5071.30±49.01cGy and 5053.26±71.85cGy for 5, 10 and 15 intensity‐levels, respectively. Mean dose to the PTV was 4655.02±27.29cGy, 4664.00±23.29cGy and 4659.98±22.01cGy. The CI of PTV was 0.8573±0.07, 0.9661±0.02 and 0.9686±0.01 and HI of PTV was 1.0800±0.02, 1.0701±0.01, and 1.0677±0.01 for 5, 10 and 15 intensity‐levels. Mean dose to bladder was 3491.88±365.15cGy, 3513.98±387.04cGy and 3501.93±380.91cGy. Bowel mean dose was 1352.05±365.20cGy, 1369.65±378.76cGy and 1369.53±375.30cGy. NTID (liter‐Gray) was 144.64±11.88, 145.77±12.85 and 145.60±12.73. Total MU required to deliver a plan was 1060±307, 1081±309 and 1061±303. Gamma pass rate was 99.65±0.35%, 99.81±0.16% and 99.87±0.12%. Conclusion: : PTV coverage and homogeneity increases with increase in intensity‐level. Plan quality was better at intensity‐level 5 in terms of OAR mean‐doses, NTID and total MU. Gamma pass rates were improved with increase of intensity‐level.
SU‐E‐T‐637: IMRT for Pancreas and Prostate Cancer Using Pulsed Low Dose Rate Delivery Techniques
Authors: Li J , Lang J , Wang P , Kang S , Lin M , Chen X , Guo M , Chen F , Ma C
Published: July 2013

Purpose: Reirradiation of patients previously treated with radiotherapy is vastly challenging. Pulsed low dose rate (PLDR) external beam radiotherapy has the potential to reduce normal tissue toxicities while still providing significant tumor control for recurrent cancers. This work investigates treatment planning techniques for IMRT‐based PLDR treatment for various sites, including pancreatic and prostate cancer cases. Methods: Treatment plans were generated with 10 gantry angles using the step‐and‐shoot delivery technique, which can be delivered in three‐minute intervals to achieve an effective low‐dose rate of 6.67cGy/min. The IMRT plans were compared with the 3DCRT plans and RapidArc plans in this study. Results: For the ten pancreas cases investigated, the mean PTV dose for each gantry angle in the IMRT plans ranged from 17.6 cGy to 22.4 cGy. The maximum doses ranged between 22.9 cGy and 34.8 cGy. The minimum doses ranged from 8.2 cGy to 17.5 cGy. For the ten prostate cases investigated, the mean PTV doses for individual gantry angles ranged from 18.8 cGy to 22.6 cGy. The maximum doses per gantry angle were between 24.0 cGy and 34.7 cGy. The minimum doses per gantry angle ranged from 4.4 cGy to 17.4 cGy. Conclusion: A significant reduction in the OAR dose was achieved with IMRT compared with 3DCRT. For most OARs, no significant differences were observed between IMRT and RapidArc. Compared with 3DCRT, IMRT could provide superior target coverage and normal tissue sparing for PLDR reirradiation of recurrent pancreatic and prostate cancers. PLDR IMRT is an effective treatment choice for recurrent cancers in most cancer centers.
SU‐E‐T‐638: Influence of Dose Rate On Step and Shoot IMRT Plan Quality and Deliverability
Authors: Sharma S , Manigandan D , Biswas A , Mohanty B , Subramani V , Chander S , Julka P , Rath G
Published: July 2013

Purpose: To study the influence of dose rate on step and shoot IMRT plan quality and deliverability. Methods: Five previously treated patients of carcinoma rectum (pre‐operative) were studied. Planning target volume (PTV) and organ at risk (OAR) i.e. bladder and bowel were contoured. Step and shoot IMRT plans (6MV X‐rays, 7‐beam, 45Gy/25fraction) were generated in Eclipse TPS at 300MU/min for Varian CL2300C/D linear accelerator. Then plan was re‐optimized by keeping dose volume constraints, priorities and all other parameters constant, only the dose rate was varied as follows: 400MU/min, 500MU/min and 600MU/min. Therefore, four different plans were generated for each case at 300– 600MU/min. Plan quality was analyzed by means of PTV maximum and mean‐doses, coverage index (CI=PTV covered by prescription dose/PTV) and OAR mean‐doses. Total monitor units (MUs) and treatment time required to deliver a plan was also noted. Deliverability of plans were verified with I' matriXX ion‐chamber array and compared with TPS dose‐plane using gamma index of 3% dose difference and 3mm distance to agreement criteria. Results: Maximum dose to the PTV was 5063.66±99.76cGy, 5083.56±104.54cGy, 5062.74±96.65cGy and 5062.72±92.13cGy for 300–600MU/min dose rates, respectively. Mean‐dose to PTV was 4659.08±26.05cGy, 4660.50±26.09cGy, 4656.34±25.78cGy and 4656.18±24.01cGy. The CI for PTV was 0.9520±0.020, 0.9528±0.022, 0.9497±0.023 and 0.9505±0.023. Mean‐dose to the bladder was 3644.78±452.68cGy, 3642.52±452.15cGy, 3641.56±450.71cGy and 3639.98±450.90cGy for 300‐600MU/min, respectively. Bowel mean dose was 1666.60±747.77cGy, 1665.46±747.49cGy, 1665.84±746.44cGy and 1665.50±744.97cGy. Total MUs were 1063±319, 1059±315, 1062±315 and 1080±353. Total time required to deliver a plan was 8.75±1.02min, 8.34±0.90min, 7.78±0.79min and 7.53±0.65min. Gamma pass rate was 99.86±0.08%, 99.80±4.04%, 99.74±0.10% and 99.61±0.28%. Conclusion: Plan quality in terms of PTV coverage, maximum and mean‐dose to OAR showed almost similar results for all dose rates. The time required to deliver a plan was reduced with increase in dose rate. However, gamma pass rate was slightly decreased with increase in dose rate.
SU‐E‐T‐639: Convex Imputing for Automatic Treatment Planning
Authors: Sayre G , Low D , Ruan D
Published: July 2013

Purpose: To improve plan quality and consistency and to automate the treatment planning process by developing a novel data‐mining method that learns a task‐specific objective formulation from previously optimized cases using a convex imputing approach. Methods: General clinical planning objectives are hard to quantify and DVH conditions are challenging to optimize directly, often requiring numerous iterations of human intervention that incurs manpower cost and risk of practice inconsistency. In this work, we address treatment planning using a new data‐mining perspective that learns the weighting factors of user‐defined convex penalties from previously optimized cases. The imputed weighting factors and corresponding penalties are then used to optimize future cases. To test our method, we imputed weighting factors from clinically‐derived prostate cases. The imputed weighting factors were then inserted into an optimization engine to drive generation of new plans. DVHs were then calculated from the imputed plans and compared to DVHs of the clinical plans. Results: Dose‐volume metrics calculated from the imputed plans showed excellent correlation with the original plans for each structure of interest: 1) PTV coverage R^2 = 0.782, 2) V_R_70Gy R^2 = 0.968, 3) V_R_65Gy R^2 = 0.983, 4) V_R_60Gy R^2 = 0.989, 5) V_R_50Gy R^2 = 0.9952, 6) V_Bl_75Gy R^2 = 0.857, 7) V_Bl_70Gy R^2 = 0.9989, 8) V_Bl_65Gy R^2 = 0.9993, and 9) bulb mean dose R^2 = 0.9776. Furthermore, the inter‐case averages of these metrics deviated by at most 3 units and on average by 0.84 units. All imputed plans were clinically acceptable. Conclusion: This pilot study demonstrates the feasibility and great potential of utilizing the developed convex imputing approach to achieve dose plans that match the true planning goals of a dose planner and/or an institution. This work is supported in part by an AACR career development award and a TRDRP exploratory grant.
SU‐E‐T‐640: Using An Open Source Interior Point Optimization Solver for Intensity Modulated Radiotherapy Treatment Planning
Authors: Tiwari P , Chen Y , Xie Y , Deasy J
Published: July 2013

Purpose: To support IMRT research, we developed an open‐source, computationally efficient, and flexible optimization solver that can solve a wide range of problem formulations, including constrained optimization, convex and non‐convex polynomial functions, and hierarchical optimization formulations. Methods: The solver is an adaptation and modification of the open‐source Interior Point Optimization Solver (IPOPT), with some performance enhancements. Previously, we implemented the IMRT optimization based on the commercial Mosek solver. Mosek can solve convex linear and quadratic problems but cannot solve convex or non‐convex polynomials of higher orders. This limits the ability to model IMRT optimization using more appropriate metrics like gEUD. Therefore, we implemented the optimization problem using C++ interface of IPOPT. IPOPT can use the Newton or Quasi‐Newton method to solve the optimization problem. In the Newton method, the exact Hessian matrix provided by the user is used to find the direction in each iteration while in the Quasi‐Newton method the Hessian matrix is approximated from the Jacobian matrix. After integrating IPOPT with CERR, we found that the Newton method converges more quickly than the Quasi‐Newton method. To increase the computational efficiency, we incorporated the uBLAS matrix library. Results: Few compared the modified IPOPT code to Mosek for a set of convex quadratic problems using realistic, anonymized treatment planning data and dose data accessed using CERR. These problems have a unique global minimum and both solvers were observed to give the same results for eight head and neck planning datasets. The median speedup of IPOPT compared to Mosek was a factor of 3.5. Conclusion: Our IPOPT implementation provides an open‐source framework to model the IMRT optimization using complex objective functions; is integrated with CERR; and our C++ implementation of the optimization problem gives increased control over the optimization process. This tool provides a basis for future IMRT treatment planning research. Memorial Sloan‐Kettering Cancer Center
SU‐E‐T‐642: A Patient Population Based Approach for Disease Site Specific Intensity‐Modulated Radiation Therapy (IMRT) Treatment Planning
Authors: Zhang H , Stanojevic D , Meyer R , D' Souza W
Published: July 2013

Purpose: To develop and evaluate a population based planning scheme for disease site specific IMRT treatment planning. Methods: A database of previously treated locally advanced head and neck patients from our institution was retrospectively used for this study. The treatment targets involved primary tumor, high risk and low risk nodal volumes. Organs‐at‐risk (OARs) included both parotids, oral cavity, brain stem and the spinal cord. Nine‐beam IMRT plans were generated using the Pinnacle3 planning system for 80% of patients. These plans served as the population basis. Thousands of apertures from these cases were extracted. From these apertures, prospective case‐specific apertures were either selected from the population basis or derived using machine learning for each of the remaining 20% of the patients. Aperture‐based 3D dose distributions were calculated in parallel using Monte Carlo‐based Kernel Superposition (MCKS) via a high throughput computing environment. Aperture weights of each case were optimized via an in‐house developed progressive dose optimization (PDO) approach. The PDO approach involved solving the DO problem by dividing the problem into sub‐problems, each of which was solved while maintaining a global view of the full problem. Our approach was compared with conventional IMRT and two‐arc volumetric modulated arc therapy (VMAT). Results: On average, the improvements achieved using population approach in parotid gland mean dose were 16% and 15%, in the maximum dose to the spinal cord were 21% and 28%, in mean oral cavity dose were 10% and 24% and in maximum brain stem dose were 6% and 15% compared with conventional IMRT and two‐arc VMAT. t‐test showed that these improvements were significant (p < 0.001). Dose homogeneity for all PTVs (tumor and nodes) was higher for population based approach as well. Conclusion: Population based planning approach resulted in superior plan quality compared with conventional IMRT and VMAT.
SU‐E‐T‐647: Fast Treatment Planning for Arc Therapy Using Maximum Intensity Regularized Quadratic Optimization (MIRQO)
Authors: Niu T , Zhu L
Published: July 2013

Purpose: Arc therapy is an emerging technique to achieve effective and efficient dose delivery by rotating the gantry of Linac through one or more arcs with the radiation beam continuously on. Treatment planning in arc therapy is a difficult optimization problem mainly due to the non‐convex physical constraints of deliverable apertures and a large amount of optimization variables. The stochastic searching scheme is initially introduced to minimize the non‐convex objective and referred to as direct aperture optimization (DAO). However, the number of segments is pre‐fixed in the DAO approaches, and the typical random search scheme in the optimization is computationally intensive. Beamlet‐based optimization (BBO) is an alternative way for arc therapy planning and achieves high computation efficiency. This method fails to fully incorporate the physical constraints of arc therapy into planning process and has limited efficacy. In this work, a regularization‐based algorithm is proposed to overcome the drawbacks of the BBO method. Methods: Instead of smoothing the beamlet intensity maps as in BBO, we include a maximum intensity constraint in the optimization objective to enforce the signal level consistency. An aperture rectification algorithm is then applied to generate single‐or multi‐arc deliverable apertures. The new scheme is referred to as the maximum intensity regularized quadratic optimization (MIRQO). Results: On a prostate and a head‐and‐neck patient, MIRQO successfully generates a fluence map with over 70% of non‐zero intensities approaching the maximum value and readily rectifiable into single segment. The computation time of MIRQO is one order of magnitude less than that of DAO. Conclusion: MIRQO maintains an efficient form of quadratic optimization, with an additional advantage of approaching the non‐convex constraints using convex approximation. By providing an efficient and effective planning scheme, our method is promising to explore the ultimate potential of arc therapy.
SU‐E‐T‐648: Multi‐Criteria Optimization for Real‐Time Planning of Lung Cancer Radiotherapy
Authors: Watkins WT , Song WY , Merrick JR , Weiss E , Hugo GD , Siebers JV
Published: July 2013

Purpose: Multi‐criteria optimization (MCO) is implemented for planning lung cancer radiotherapy treatments to clarify patient‐specific tradeoffs and allow real‐time plan decision making. Methods: For four locally advanced lung cancer patients (P1–P4), a basis set of MCO plans are constructed and compared to plans determined from fixed‐objective (FO) optimization for organs at risk (OARs). All optimized plans include constraints on target‐D95>70 Gy and spinal cord Dmax<45 Gy. Five MCO basis plans are designed per patient through weight variation of four non‐zero dose‐volume objectives (DVOs) for ipsilateral lung (iLung), contralateral lung (cLung), heart, and esophagus. The five basis plans are optimized according to: (1) simultaneous minimization of four OAR‐DVOs and (2–5) weight variation for one OAR‐DVO. Results: Patient‐specific tradeoffs between OAR objectives are revealed with MCO which are not evident in FO‐optimization. For P1, MCO basis plans vary iLung‐V20 from 46% to 65% and show that V20<46% is not achievable; the FO iLung‐V20 is 54%. For P2,the FO‐plan trades off a 1% reduction in iLung‐V20 for a 29% increase in esophagus‐V20. An interpolated MCO plan, in this case, takes advantage of this tradeoff to reduce esophagus V20 by from 41% to 8%. P3 shows increasing heart‐V20 by 35% (from 20% to 55%) results in a 7% (34%‐27%) reduction in iLung‐V20. With P4, MCO reveals a tradeoff between the two lungs; varying iLung‐V20 from 23% to 30% corresponds to cLung‐V20 varying from 23% to 17%. The FO plan treats cLung up to the V20 objective (to 29%) without penalty. MCO shows the ability to reduce OAR dose‐volumes, but often led to increased PTV hotspots. Conclusion: Analysis of MCO plans clarifies conflicting objectives and exposes inherent limitations due to patient geometry. Real‐time planning is possible with a small set of MCO plans, and achieves plans which are superior to FO‐optimization. Supported by NIH P01‐CA‐116602 and Philips Medical Systems
SU‐E‐T‐649: Planning Margins Validation for Concurrent Treatment of Prostate and Pelvic Lymph Nodes Under Daily Image Guided Delivery
Authors: Ferjani S , Stephans K , Tendulkar R , Xia P
Published: July 2013

Purpose: To validate prostate planning margins for concurrent treatment of the prostate and pelvic lymph nodes (PLN) under daily kilo‐voltage cone beam (KV‐CBCT) imaging guidance while applying MLC and iso‐center shifting methods to compensate for inter‐fractional prostate motion. Methods and Materials: Ninety‐four daily KV‐CBCTs from five patients, who received IMRT treatment with a clinical planning margin to the prostate of 8mm/6mm posterior (M(8,6)) and 5mm to the PLN, were selected. Three additional IMRT plans were created for each patient with the prostate planning margins of 6mm/4mm posterior (M(6,4)), 4mm/2mm posterior (M(4,2)) and 2mm uniform margin (M(2,2)). The PLN planning margin remained 5mm. Subsequently, each plan was applied to the daily KV‐CBCT using MLC and iso‐center shifting methods. Daily D95 of the prostate and D95 of the PLN, and D5 of the rectum and D5 of the bladder were evaluated for adequate planning margins. Results: For both the MLC and iso‐center shifting methods, D95 of the prostate was greater than or equal 97% of the prescription dose in 97.8% (100%), 98.9% (97.9%), 95.8% (97.9%), and 93.7%(96.8%) of 94 fractions, for M(8,6), M(6,4), M(4,2), and M(2,2) respectively. Accordingly, D95 of the PLN was greater than or equal 97% of the prescription dose in 98.9%(100%), 100%(98.9%), 98.9%(98.9%), and 100%(98.9%), for M(8,6), M(6,4), M(4,2), and M(2,2) respectively. For the rectum, D5 exceeded 105% of the original IMRT D5 for the MLC‐shift (and iso‐center shift) plans in 16%(14.9%), 14.9%(16.4%), 5.4%(12.2%) and 4.3%(12.2%) for these four planning margins respectively. For the bladder, D5 exceeded 105% of the original IMRT D5 for the MLC‐shift (and iso‐center shift) plans in 0%(1.1%), 6.4% 3.2%), 13.9%(4.3%), and 8.6%(4.3%), respectively. Conclusion: With 5 mm planning margin to the PLN, both MLC and iso‐center shifting methods can reduce the prostate planning margin to 4mm/2mm posterior while achieving adequate targets coverage. This research was supported by the United States Army Medical Research and Materiel Command (USAMRMC) (Grant No. W81XWH‐080‐0358)
SU‐E‐T‐650: Evaluation of Novel IMRT Auto‐Planning Tool for Nasopharyngeal Carcinoma Cases
Authors: Jeong K , Bzdusek K , Kumar P , Tome W
Published: July 2013

Purpose: Evaluation of newly developed auto‐planning tool for automatic IMRT plan optimization. Methods: A pre‐defined treatment template is used to configure an auto‐planning engine. A template consists of beam configurations, a prescription, PTV and/or PRV expansions, optional isocenter placement, isodose and DVH display settings, prioritized IMRT optimization goals, and IMRT parameters. The auto‐planning engine uses prioritized optimization goals to formulate optimization objectives. Multiple optimization loops iteratively reformulate and adjust the optimization objectives to meet the goals and further drive down organ at risk sparing with minimal compromise to the target coverage. Ten clinically approved head and neck IMRT plans were selected for test. Target dose levels were 70 Gy, 60 Gy, and 56/54 Gy for high‐, intermediate‐, and low dose level PTVs. Objectives of brainstem, spinal cord, parotid gland, oral cavity, and larynx were selected as a common planning objectives. Target doses were normalized so that the highest PTV dose coverage will be the same as clinically approved plans. Maximum brainstem, spinal cord, and parotid gland doses were compared. Mean dose to normal organs, which were defined as mean doses of the entire bodies except the targets, were also compared. Results: Using the auto‐planning tool, we could achieve similar or better results compared with clinically approved plans. For the brainstem and the spinal cord doses, maximum doses were lower in auto‐plans in most cases. For the parotid glands, mean doses were lower in auto‐plans in all cases. NTCPs were lower in auto‐plans for all cases. Mean doses to normal tissues were lower in the auto‐generated plans for all cases. Conclusion: Using the auto‐planning tool, we could achieve the better IMRT plans with less work and time. WA Tome has a research grant from Philips Healthcare.