bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐99: Impact of Proper Bladder and Rectum Delineation in the Evaluation of the Effectiveness of IMRT in Prostate Cancer Radiotherapy
Authors: Xu J , Buckey C , Swanson G , Stathakis S , Esquivel C , Gutiérrez A , Shi C , Mavroidis P , Papanikolaou N
Published: April 2010

Purpose This study compares and evaluates different bladder and rectum delineation approaches using IMRT plans for prostate cases. A more comprehensive treatment plan evaluation can be performed using the biologically effective uniform dose (BEUD) together with the complication‐free tumor control probability (P+). Materials and Methods A single physician outlined the prostate planning target volume (PTV), rectum, bladder and femoral heads of 10 consecutive prostate patients. IMRT treatment plans were created with the Pinnacle treatment planning system (TPS). Two different bladder and rectum delineation approaches were examined. In the first approach the whole volume of bladder and rectum were delineated, whereas in the second approach, the delineation included only the volume of the organs lying in the range of 2 margins around the PTV. In the second case, the DVHs were normalized to their volume (2std normalized) and to the volume of the whole organ (2std relative to whole). Results At the optimum dose levels of the dose distributions using the whole volume of bladder and rectum, 2 std relative to the whole volume and 2 std normalized, respectively, the P+ is 67.7%, 51.2% and 32.7% for a BEUDPTV of 86.7 Gy, respectively. The respective total control probabilities, PB are 89.0%, 82.4% and 82.4% whereas the corresponding total complication probabilities, PI are 21.3%, 31.2% and 49.7%. More specifically, the response probabilities of the different tissues are 89.0%, 82.4% and 82.4% for the PTV, 0.0%, 0.0% and 0.01% for bladder and 21.3%, 31.2% and 49.7% for rectum. At the initially prescribed dose level (mean dose to the PTV = 79.4 Gy) the PI values become 6.7%, 12.4% and 27.8%. Conclusions The expected radiation induced bladder and rectum complications using different delineation approaches, should be estimated used appropriate dose‐response parameters, which should have been determined from studies of similar organ delineation methodology.
SU‐FF‐T‐100: The Dosimetric Impact of the New 160MLC On Head and Neck IMRT Treatments
Authors: Rassiah‐Szegedi P , Szegedi M , Cochran D , Zhao H , Huang Y , Wang B , Salter B
Published: April 2010

Purpose: The purpose of this work is to investigate if the change in plan quality with the finer leaf resolution and lower leakage of the 160 MLC would be dosimetrically significant for head and neck IMRT treatment plans. Method and Materials: The 160 MLC™ (Siemens Medical Solutions) consists of 80 leaves of 0.5 cm on each bank, a leaf span of 20 cm and leakage of less than 0.37 % without additional back up jaws. CT image sets of 10 patients of previously treated with stage III and IV head and neck carcinomas (HN) were re‐planned on Prowess 4.6 (Prowess Inc., Ca) using the 160 MLC™ (Siemens Medical Solutions, Erlangen, Germany) and the 120 MLC (Varian Medical Systems, Inc., Ca). The underlying beam data for both the treatment units on the planning system were matched to within 1%. IMRT constraints for both 6 MV plans were identical. We compared dose volume histograms (DVHs), minimum, mean and maximum dose to the organ at risks (OAR), the planning target volume (PTV and conformity index. Results: The dose to the organs at risk were 2 – 5% (i.e 1.5 – 3 Gys for a 70 Gy prescription) lower with the 160 MLC compared to the 120 MLC. The PTV conformity index between the 160 MLC and the 120 MLC were similar. Besides dosimetry, the plans generated on the 120 MLC had multiple split fields resulting in almost double the number of treatment fields. Conclusion: The large field HN plans generated with the 160 MLC are dosimetrically advantageous for critical structures especially when they are located further away from the central axis, without compromising target volume coverage. The 20 cm leaf span also reduces the number of split fields which is likely to reduce delivery time.
SU‐FF‐T‐101: Volumetric Modulated Arc Therapy for the Treatment of Paraspinal Lesions
Authors: Happersett L , Zhang P , Wang K , Jackson A , Yamada Y , Mageras G , Hunt M
Published: April 2010

Purpose: Volumetric Modulated Arc Therapy (VMAT) is a recent treatment modality that synchronizes gantry rotation, multileaf collimator motion and dose rate modulation, usually in a single arc. In this feasibility study, we evaluate the efficacy of VMAT, using an optimization algorithm developed at our institution, for paraspinal stereotactic body radiation therapy (SBRT). Method and Materials: Ten patients with paraspinal lesions were retrospectively planned with VMAT and results were compared to 5 – 8 field treated IMRT plans. Tumor locations varied from C3 to L1. The prescription dose was 24 Gy and cord was constrained to 14 Gy. To compare plan quality, PTV D(99%), D(95%), V(22.8Gy), Dmax, cord Dmax and Dmean, esophagus D(2cc), and lung Dmean were reviewed. Monitor units were assessed to evaluate plan efficiency. Results: Patient averaged PTV D(99%), D(95%), Dmax and V(22.8Gy) were 18.7, 21.7, 29.6 Gy and 92.8% respectively for VMAT and 18.5, 21.8, 28.4 Gy and 93.5% respectively for IMRT. Average cord Dmax was 13.8 and 13.9 Gy for VMAT and IMRT, respectively, but the cord Dmean with VMAT was 34% less than with IMRT. The average esophagus D(2cc) was 14.4 Gy for VMAT and 17.5 Gy for IMRT. The average mean lung dose was 2.8 Gy for VMAT and 2.3 Gy for IMRT. The average MUs were 4817 and 12343 for VMAT and IMRT plans, respectively. Conclusion: PTV coverage was similar for VMAT and IMRT with the exception of slightly higher hot spots with VMAT. For critical structures near the PTV such as cord and esophagus, maximum doses were similar but mean doses were lower with VMAT. Structures farther way from the PTV (e.g. lung) had higher mean doses with VMAT. VMAT plans were more efficient with substantially lower MUs than IMRT. Conflict of Interest (only if applicable): Research agreement with Varian Corporation
SU‐FF‐T‐102: Is Average Fractional Dose Representative of Cumulative Dose for HN‐IMRT?
Authors: Wu Q , Worthy D
Published: April 2010

Purpose: Use of on‐board cone‐beam CT (CBCT) imaging during HN‐IMRT treatment course allows for calculation and reconstruction of the dose delivered to the patient daily. The purpose of this study was to investigate whether the average fractional dose represents the actual cumulative dose to the patient in fractionated radiotherapy. Method and Materials: The CBCT data from 30 patients and 896 treatment sessions were analyzed and applied to HN‐IMRT plans from 12 patients. Dose distribution for each fraction was recalculated based on the actual patient setup error. Two types of analyses and summation were performed for each patient: average of all fractions, AVG, and voxel‐by‐voxel cumulation for all fractions (CUMU). To illustrate the difference, setup errors were also scaled up by different factors. The evaluation was performed using dosimetric indices for targets and OARs. Results: The mean dose for each structure was the same for AVG and CUMU methods. However, other indices were different. In general, the AVG predicts systematically lower target doses than CUMU for both CTV1 and CTV2, up to 4.5% for D95 and 2.6% for D90, at proper margins. The AVG also predicts higher OAR doses (up to 8.1% D1 for cord, brainstem and mandible) than CUMU, except parotid gland in which the V30 and V20 is 11% higher in CUMU than AVG. Conclusion: Significant differences are observed in dose delivered to patients using the average fractional and cumulative dose calculation in the presence of rigid setup error. The differences are smaller at larger margins. The main reason for such differences is that the random setup error is larger than the systematic, and not the same target region gets underdosed at every fraction. Therefore, for fractionated radiotherapy, use of the average fractional dose does not represent the true cumulative dose received by the patient.
SU‐FF‐T‐103: Dosimetric Plan Index (DPI): A New Quantitative Tool for Evaluation of Prostate IMRT Treatment Plans
Authors: Zhang Y , Sathiaseelan V , Karaparukal J
Published: April 2010

Purpose: This study is to present a new quantitative analysis tool for evaluation of prostate IMRT (intensity modulated radiation therapy) plans. Methods and Materials: Based on retrospective analysis of 33 prostate patients (18 with intact prostate and 15 with prostatectomy) for a total of 84 acceptable treatment plans, we developed a new concept, dosimetric plan index (DPI), which integrates the measures of dose conformity, target coverage and OAR (organ at risk) overdose. DPI is defined as: , where CI (conformity index) is defined as the ratio of the volume of a PTV (planned target volume) inside the prescribed IDL (isodose line) to the volume enclosed by the IDL; TC (target coverage index) is defined as the ratio of the volume of a PTV inside the prescribed IDL to the volume of the PTV; DGI (dose gradient index of an OAR) is defined as e−d/λOAR, d is the distance between 95% and 50% IDL, λOAR is the nominal distance that can be commonly achieved in a specified disease site, and it equals to 1 cm for prostate IMRT plans with rectum as an OAR. Results: The target volume and the volume of rectum enclosed by 50% IDL vary dramatically for different acceptable plans. The mean COSI (critical organ scoring index) of these plans is 0.66 ± 0.18 for intact prostate plans and 0.54 ± 0.14 for post‐prostatectomy plans. However, those plans share a common merit that their DPIs are in a much narrower range, 0.63 ± 0.02 for intact prostate plans and 0.59 ± 0.02 for post‐prostatectomy plans. Conclusion: The DPI is a new comprehensive treatment plan scoring tool, accounting for the information derived both from DVH (dose volume histogram) and isodose distribution. It can assist physician/planner to evaluate and optimize treatment plans for target coverage and normal tissue sparing.
SU‐FF‐T‐106: Does Intrafraction Motion Increase Dose to the Inframammary Fold Areas in Whole Breast Treatment Using Direct Machine Parameter Optimization IMRT?
Authors: Hossain S , Xia P , Descovich M , Chen J , Ma L
Published: April 2010

Purpose: Dosimetric uncertainties in the inframmamary fold due to intrafraction breast motion are major clinical concerns for treating large or irregularly shaped breast patients as skin break‐downs commonly occurred near the regions during the course of the treatment. Direct Machine Parameter Optimization (DMPO) IMRT has been well reported for whole breast treatments. The purpose of this study is to investigate whether intrafraction motion affects skin sparing for patients treated with this technique. Method and Materials: A pair of open tangential beams (6 MV) combined with a maximum of 20 DMPO segments of mixed photon energies (6 or 18 MV) was used to create DMPO IMRT plan for a large shaped breast case which was then benchmarked against a standard wedge‐pair plan. In order to constrain the dose to the inframamary fold, a region‐of‐interest starting near the inferior border and extending 3–4 cm superiorly was contoured. Using recorded intrafraction breast movements obtained from an image‐tracked CyberKnife system, transformed treatment plans were created while scaling the average time patterns from the CyberKnife treatment to simulate DMPO IMRT delivery. Results: Transformed DMPO plans received lower dose (90.6±3.1)% to the inframammary region compared to the original DMPO plan (96.0%). V100% for the PTV was slightly reduced from the original 97.5% to 95.0±1.5%. The treatment planning effort and delivery efficiency of DMPO IMRT were found to be similar to the wedge‐pair technique. However, the DMPO method significantly reduced the maximum dose and improved the overall dose uniformity to the inframmamary region. Conclusions: DMPO is an effective and efficient planning technique in skin sparing particularly in the inframammary fold areas for the whole breast IMRT treatments. Our study found no negative impact on such advantage due to intrafraction patient's breathing motion. In addition, the PTV dose coverage was also found to be insensitive to such motion.
SU‐FF‐T‐107: Selective Extended Field IMRT Can Protect Larynx and Adequately Treat the Lower Neck Lymph Nodes in Head and Neck Cancer
Authors: Qi P , Xia P
Published: April 2010

Objectives: Radiation dose to the larynx has been a major concern in the treatment of head and neck cancer. The use of splitting field (SF) IMRT can improve the dose to the larynx but it may result in inadequate tumor coverage and dosimetric uncertainties at the matchline. In this study, we propose a selective extended field (SEF) method to avoid the use of splitting field while reducing the larynx dose and achieving the adequate tumor coverage. Materials and Methods: Five nasopharyngeal patients with the gross tumor volume extended to the lower neck were treated with extended field (EF)‐IMRT. SEF IMRT plans were created by extending only three anterior and anterior oblique beams to the supraclavicular region while the other fields were restricted to the superior of the vocal cord. For comparison, SF‐IMRT plans were also created and matched with the conventional AP field. All plans were compared based on the tumor volume coverage, mean dose to the larynx while meeting other planning requirement in RTOG protocol of 0225. Results: The average doses to 95% (D95) of the pGTVs and pCTV were 67.10 ± 6.56 Gy, 70.65 ± 1.62 Gy, 72.74 ± 1.76 Gy and 55.21 ± 3.41 Gy, 57.17 ± 1.51 Gy, 59.92 ± 1.01 Gy for SF, SEF, and EF‐IMRT plans, respectively. The tumor dose coverage in SF IMRT plans was the worst among three methods. Accordingly, the average mean doses to the larynx were 29.25 ± 5.61 Gy, 29.41 ± 2.99 Gy, 41.87 ± 10.61 Gy, respectively. The mean dose to the larynx in EF‐IMRT plans were the highest among the three methods. Conclusions: The selective extended field IMRT provides adequate tumor dose coverage and protects the larynx with the similar mean dose as the SF method.

Research is supported by Siemens Corporation.
SU‐FF‐T‐109: The Dependence of IMRT Plans On the Maximum Number of Segments
Authors: Kang S , Hwang T , Cheong K , Park S , Lee M , Kim K , Oh D , Bae H
Published: April 2010

Purpose: Pinnacle3 provides an direct aperture based step‐and‐shoot IMRT optimization algorithm, so called direct machine parameter optimization (DMPO). This algorithm is known to result in better plan quality with less monitor units than the previous two‐step optimization. Here, we present the dependence of the IMRT plan quality on the maximum number of segments. Method and Materials: Pinnacle3 (ver 7.4f) with a DMPO option was used for the IMRT plan of the five hypopharyngeal cases. The planning system had been commissioned for a Varian 21‐EX with 120 multileafs upon which larger fields are split into smaller ones due the MLC span limitation. PTVs were contoured for 66 Gy, 59.4 Gy and 56.1 Gy with 33 fractionations. Critical organs delineated were as follows: cord, brain stem, inner ears, parotid glands, and cavity for mucosa. Three‐fold dose shaping rings encompassing the PTVs were also added and seven beams were used. Plans were generated for the number of segments between 20 to 80 and evaluated based on the plan with 80 segments. Results: As the number of segments decreased, the plans generally showed a) a tendency of adopting smaller monitor units, b) a wider low dose region, and c) a more inhomogeneous target dose distribution. However, the IMRT plan for the hypopharyngeal case showed similar DVHs and dose distributions down to 40 segments, which amounts to three segments per beam in average after beam splitting. Conclusion: With the DMPO option, unexpectedly smaller number of segments were found to be enough for the clinically acceptable IMRT plan. We plan to extend this study to nasopharyngeal and maxillary cases. With the evaluation of the plan quality along with the segments, more economical IMRT plan and beam delivery would be possible.
SU‐FF‐T‐111: Head‐And‐Neck IMRT Without Beam‐Splitting
Authors: Lei S , Harter W , Collins S , Xia F , Pang D , Gagnon G
Published: April 2010

Purpose: Varian MLC leaf travel is limited to 14.5 cm. For large PTV, an IMRT field will be split into two or three sub‐fields. Thus a 9‐beam head‐and‐neck plan may end up with 18 or more treatment fields. The purpose of this study is to develop a non‐split IMRT planning technique and compare the quality of non‐split plans with beam‐split counterparts. Method: Varian Eclipse user can choose fixed‐jaws and set field‐size less than 14.5 cm so that IMRT field will not split. A small part of the PTV may be blocked by x‐jaws in a particular beam, but the missing dose from one beam can be covered by other beams at different gantry angles. We compared our previously treated 9‐beam‐split‐18‐field head‐and‐neck IMRT plans with corresponding non‐split plans of 9, 11, and 15 gantry angles. Plan DVH and IMRT QA results were analyzed. Results: Non‐split plans produced the same dose coverage as beam‐split plans. DVH curves of PTV for split and non‐split plans almost overlapped with each other. DVH of organs‐at‐risk were slightly different. Total treatment MU were about the same for all the plans. All IMRT QA plans delivered on a Varian Trilogy passed physics QA criteria, with non‐split plans showing slightly better passing scores. Conclusions: Creating IMRT plans without beam‐splitting is encouraged. Non‐split IMRT plans can be as good as beam‐split plans, but use only half of the number of beams. Quality of non‐split plans improves with increasing number of beams. The amount of improvement was larger for the number of beams going from 9 to 11 than that from 13 to 15, demonstrating a balance of costs and benefits. Cutting the number of beams by half may result in a number of benefits: more accurate dose delivery, shorter treatment time, and increased machine throughput and productivity.
SU‐FF‐T‐112: Dose Sparing of Brainstem and Spinal Cord for Re‐Irradiating Recurrent Head and Neck Cancer with Intensity Modulated Radiotherapy
Authors: Lee C , Chen C , Mah D , Sharma R , Landau E , Garg M , Wu A
Published: April 2010

Purpose: Due to the lifetime dose limit for these critical structures such as brainstem and spinal cord, achieving an additional dose of 60 Gy to patients with recurrent head and neck cancer is challenging for who received a previous dose of ∼60 Gy. Specifically, previously irradiated head and neck patients may be near tolerance dose to their brainstem and spinal cord. In this study, a reproducible IMRT treatment design is presented to spare the doses to brainstem and spinal cord with no compromise of prescribed dose delivery. Method and Materials: Seven patients with previously irradiated, recurrent head‐and‐neck cancers were treated with DMLC IMRT. The jaws of each field were set fixed with the goal of shielding the brainstem and spinal cord at the sacrifice of partial coverage of the planning target volume (PTV) from any particular beam orientation. Beam geometry was arranged to have sufficient coverage of the PTV and ensure that the constraints of spinal cord <10 Gy and brainstem < 15 Gy were met. Results: The mean maximum dose to the brainstem was 12.1 Gy (range: 6.1–17.3 Gy), and the mean maximum dose to spinal cord was 10.4 Gy (range: 8.2–14.1 Gy). For most cases, 97% of the PTV volume was fully covered by the 95% isodose volume. We found empirically that if the angle of cervical spine curvature (Cobb's angle) was less than ∼30 degrees, patients could be treated by 18 fields. Six patients met these criteria and were treated in 25 minutes per fraction. One patient exceeded a 30 degree Cobb's angle and was treated by 31 fields in 45 minutes per fraction. Conclusion: We have demonstrated a new technique for re‐treatment of head and neck cancers. The angle of cervical spine curvature plays an important role in the efficiency and effectiveness of our approach.
SU‐FF‐T‐113: Effect of the Same Plan On Doses to Patients During Radiotherapy with Nasopharyngeal Carinoma
Authors: Yin Y , Bai T , Sun T
Published: April 2010

Purpose To evaluate the feasibility of primitive IMRT plan was used throughout the treatment course in the nasopharyngeal carcinoma. Methods 10 patients with nasopharyngeal carcinoma who had undergone radiotherapy by IMRT was selected. A IMRT plan was designed by Pinnacle3 planning system. During the middle period of the irradiation, the secondary scans were made with the same CT parameters of the first, and then to copy the primitive plan to secondary CT image, The same energy, beam angles, control points, and optimization parameters were used fordose calculations for each paired plans using a treatment optimization system. The two plans were compared using a set of parameters derived from DVHs and dose‐volume statistics. Detailed analysis of the dose distribution of the treatment volume. Result the secondary plan was compared with the first plan. At the Isocenter layer, the mean length was diminute to 8% in the anterior‐posterior direction and 3% in the left‐right direction. PTV1(D95) was decreased to 0.6%–5.3%; the extent of the averaged volume to the right/left parotids was decreased to 13.1%–41.4% and 12.0%–49.0% respectively; The averaged dose to the right/left parotids was increase to 5.6%–45.1% and 3.3%–32.2% respectively; the waving extent of Dmax To the spine cord and brain stem are −4.1%–13.9%, −3.9%–9.3% respectively. Conclusion Our planning study showed that there were the essentiality to modify the plan to correcting the target and normal tissue variation in treatment courses in the nasopharyngeal carcinoma.
SU‐FF‐T‐120: The Impact of Variable Gantry Rotation Speed and Dose‐Rate On the Quality of Aperture‐Modulated Arc Therapy (AMAT)
Authors: Wu X , Both J , Bossart E , Wang K
Published: April 2010

Purpose: From its early inception, DMLC‐based IMRT has differed from Binary MLC‐based helical IMRT by delivering the treatment volumetrically. As the field of IMRT evolved, the demands on its performance converge to three main criteria: quality of dose plans, speed of treatment delivery, and amount of leakage exposure. Many have ventured the approach of DMLC‐based aperture‐modulated arc (AMAT) therapies, indicating their potential to satisfy these three criteria. The traditional arc therapy is delivered with a constant gantry rotation speed and a constant dose rate. It is logical to expect that if the outputs at any transient gantry position can vary, the capacity or flexibility of dose optimization would increase, regardless of the type of aperture modulation algorithms. The technology of arc delivery with varying gantry rotating speed and dose‐rate has recently become available. We conducted a study to investigate the impact of these new arcing parameters. Method and Materials: The study is conducted on the following equipments: a Varian Trilogy linear accelerator, the Varian Eclipse planning system and the Pinnacle SmartArc module. The linac can operate in constant dose‐rate/gantry rotation mode or varying dose‐rate/gantry rotation mode. Plans were derived with constant dose‐rate/gantry rotation and varying dose‐rate/gantry rotation. The comparisons were carried out as objectively as possible based on the three criteria with set benchmarks. Results: From a limited range of examples studied, it is observed that while AMAT with constant dose rate and gantry rotation is capable of producing good dose plans, dose‐rate and gantry rotation variation allows further improvement of the dose plan and the delivery efficiency. MLC inter‐digitation also increases the flexibility of planning and the delivery efficiency. Conclusion: The quality of plan and the treatment delivery efficiency are inter‐related. While plan evaluation is often subjective, a greater technical flexibility undoubtedly increases planning capacity and improves delivery efficiency.
SU‐FF‐T‐121: Dosimetric Comparison Between Intensity‐Modulated Arc Therapy and Helical Tomotherapy Plans for Simultaneous Boost Treatment of Esophageal Cancer
Authors: Han C , Chen Y , Liu A , Schultheiss T , Wong J
Published: April 2010

Purpose: In a previous work, we compared helical tomotherapy (HT) plans with static‐beam IMRT and 3‐dimensional conformal radiotherapy plans for simultaneous boost treatment of esophageal cancer. Recently, intensity‐modulated arc therapy is emerging as a new technique to deliver IMRT. The goal of this study is to compare RapidArc plans with HT plans for esophageal cancer treatment in terms of dosimetric distributions. Method and Materials: Six esophageal cancer patients with locally advanced mid‐distal esophageal carcinoma were treated with chemoradiation with surgery. RapidArc and helical tomotherapy plans were generated retrospectively to deliver 50 Gy to the gross planning target volume (PTV) and 45 Gy to elective PTV in 25 fractions. Plans were normalized so that the prescription isodose volume covers 95% of the gross PTV. RapidArc and helical tomotherapy plans were compared in terms of dose homogeneity to the PTV's, and dose‐volume histograms for critical organs. Results: HT plans achieved slightly better dose homogeneity for the gross PTV, and achieved significantly better homogeneity for the elective PTV (mean homogeneity index: 0.14 vs. 0.33, p < 0.05). HT and RapidArc plans provided comparable dose sparing to the heart (based on V30 and V45) and spinal cord (based on maximum dose). While HT was able to achieve better V15 and V20 to the lungs than RapidArc plans (p < 0.05), the mean dose to the lungs were comparable in both sets of plans. RapidArc plans used significantly less monitor units than HT plans (average MU: 565 vs. 9,975). Conclusion: Both RapidArc and HT achieved highly conformal plans for simultaneous boost treatment of esophageal cancer. HT plans resulted in better dose homogeneity to the electic PTV, while RapidArc plans required shorter delivery time and could potentially lead to less leakage radiation during treatment.
SU‐FF‐T‐127: Perhipheral Dose of Tungsten Powder Compensator (WPC) Based IMRT
Authors: Maurizo A , Jang S , Watchman C , Hamilton R
Published: April 2010

Purpose: To characterize the peripheral dose (PD) of the newly developed compensator system based on tungsten powder (WPC) and to compare with MLC‐based IMRT. Method and Materials:. WPCs molded with different thicknesses of tungsten powder for comparison with MLC‐based plans were loaded into Elekta‐SLi block‐tray. Absorbed doses along the CAX and 2cm outside the field edge were measured for thickness of 1–7 cm at 1cm‐increments, at depths of dmax, 5cm and 10cm for photon energies of 6 and 15MV. Equivalent‐MLC thicknesses were calculated by constraining the total CAX dose and total MU for each compensator thickness. Absorbed doses along the CAX and 2cm outside the field edge were measured for the MLC‐equivalent thickness using Farmer chamber. In addition, PD for a WPC‐based clinical IMRT plan was compared to the equivalent MLC plan. Results: PD with tungsten thickness of 4cm, normalized to 10Gy along the CAX, was found to increase from 35 to 142cGy with increasing field size(5×5cm2 to 20×20cm2 at dmax) and from 74 to 85cGy with depth(dmax to 10cm with 10×10cm2 field). PD at dmax increased 204% by varying tungsten thickness from 1cm to 7cm. PD increased linearly with field size and was energy‐dependant only for the deeper depths where the PD became greater for 6MV than for 15MV. With increasing depth and decreasing field size, WPC‐based PD values became nearer to those of MLC‐based PD in trend. However, at the smallest field (5×5cm2), WPC showed lower PD than MLC. WPC‐based PD of a clinical plan measured 2cm outside the field edge, were ∼60% higher than that of MLC‐based plan. Conclusion: Mean WPC‐based PD was 60% higher than MLC‐based PD, however it was equivalent to 1.5% of the prescription dose of 2Gy/fraction.

Conflict of Interest: Research sponsored by Axellis Ltd.
SU‐FF‐T‐132: Efficiency of Respiratory‐Gated Synchrotron Based Scanning Beam Delivery of Proton Therapy for Lung
Authors: Tsunashima Y , Vedam S , Dong L , Zhang X , Umezawa M , Smith A , Balter P , Mohan R
Published: April 2010

Purpose: To quantify the efficiency of respiratory‐gated synchrotron based scanning beam delivery of proton irradiation for lung tumors. Method and Materials: An in‐house software program was developed to simulate the interaction of the respiratory‐gate signal based on respiratory traces of patients from an external respiratory monitor and the synchrotron magnet operation pattern in scanning beam proton delivery. A simulation study was performed using 10 proton scanning beam plans (total 33 beam angles) for lung tumors. For each plan, 10 patient breathing traces were used to simulate respiratory gated delivery. The total time to deliver each beam was determined for non‐gated and gated modes (30%, 20% and 10 % duty cycles respectively). Efficiency was determined using the effective dose rate (MU/min). The relationship between effective dose rate with and without gating was examined for different irradiated volumes along each beam direction and the number of control points in each plan. Results: The average effective dose rate was 34.2±18.8 (MU/min) for non‐gated treatment. This represented an approximately three fold reduction as compared to the passively‐scattered proton delivery (90.1 MU/min). With gating, effective dose ratios were further reduced to 13.8±4.7, 9.3±3.6 and 3.7±1.7 MU/min for 30%, 20% and 10 % duty cycles respectively. Using an average MU per beam at 70.9, the estimated treatment delivery time for a single beam was 2.1 min for non‐gated treatment, and 5.1, 7.6, and 19.1 min for gated treatment with 30%, 20% and 10 % duty cycles, respectively. No strong relationship was found between the effective dose rate and the irradiated volume or the number of control points. Conclusion: Respiratory gated delivery of pulsed scanning beam proton therapy for lung cancer is less efficient than passively‐scattered proton irradiation. Further studies are needed to improve delivery efficiency in the treatment plan optimization using patient specific breathing patterns.
SU‐FF‐T‐142: Feasibility Study of Linac‐Based IMTMI for Clinical Implementation
Authors: Yeginer M , Aydogan B
Published: April 2010

Purpose: To investigate the treatment planning feasibility of the linac‐based intensity modulated total marrow irradiation (IMTMI) for clinical implementation in patients with hematological malignancies. Method and Materials: Linac‐based IMTMI treatment planning is performed for six patients using Eclipse™ treatment planning system. The planning treatment volume (PTV) consisted of all the bones in the body from head to mid femur except the forearms and hands. Critical organs (OARs) to spare included lungs, heart, liver, kidneys, brain, eyes, oral cavity and bowels and are contoured by a physician on the axial CT images. The three isocenter technique previously developed by our group is employed for the treatment planning in which PTV is divided into three sub‐volumes including head&neck, chest and pelvis. IMTMI treatment plans obtained in this study are evaluated using the dose volume histograms (DVH) and by comparing the IMTMI median organ doses with that of conventional TBI. IMTMI planning is difficult for many reasons. To this end, we investigated a common dose volume objective (DVO) set derived from individual DVOs of adult patients to reduce subjectivity in optimization process and also to decrease the optimization time. Results: Average dose reductions, in comparison to conventional TBI, for critical organs with the linac‐based IMTMI technique ranged from 15% for lung to 61% for lenses while more than 95% of the PTV is covered by 99% of the prescribed dose. The use of common DVO method has reduced the optimization time on average by almost 35% making our linac based IMTMI technique clinically feasible to plan within reasonable time. Conclusion: We demonstrated that clinically superior three isocenter linac‐based IMTMI plans, with good PTV coverage and OAR sparing, can be obtained within reasonable time using our common DVO method proposed in this study. Conflict of Interest: Research sponsored by Varian Medical Systems, Inc.
SU‐FF‐T‐271: Measurement Validation of Attenuation Values of Proton Facility Shielding Materials
Authors: Chen K , Klein E , Zheng Y , Miller W
Published: April 2010

Purpose: Strategies for design and shielding methods vary considerably with proton facilities. Material chosen for shielding is balance of effectiveness and cost. For space‐restricted environments, high‐density materials are desirable. Shielding calculations, whether analytical or statistical rely, on the neutron attenuations properties of chosen materials. The purpose of this study was to measure and calculate attenuation of various materials to be used for shielding. Methods and Materials: We acquired samples of the actual materials to be used to shield neutrons for our new facility. The original calculations relied on analytical methods and classically accepted values for neutron attenuation. Planned materials include: standard concrete (SC)∼136lb/ft3, high‐density concrete (HDC)∼250lb/ft3, Hematite mix (HM), steel (S), and borated polyethylene (BP). For the measurements, we used a 5Ci plutonium‐beryllium (239PuBe) neutron source (1″ in diameter and 5″ in length) with an energy spectrum ranging up to 11MeV. A Bonner‐sphere spectrometer was used for neutron measurements. The material samples were configured in a manner to allow measurements through various paths. A Fortran code was used to reconstruct the neutron spectrum and calculate the neutron dose equivalent. Results: Transmission curves were generated to yield TVL values, which were compared to those used in our analytical calculations. Measured TVL (cm) for the SC, HDC, HM, S, and BP were 55.9, 55.1, 63.1, 35.6, 60.6, respectively. The TVL (cm) used for the calculations were 85.6, 52.4, 32.9 respectively for SC, HDC, and S. Conclusions: Measured TVL values matched analytical calculations very closely, with the exception of standard concrete. The measurements performed in this study assisted in better understanding of attenuation properties of each material and increased our comfort level pre‐construction. As expenditures in the range of millions of dollars were about to be spent, the question of material choices, and the validity of the actual material mix were alleviated.
SU‐FF‐T‐274: Evaluation of a Self‐Contained Orthovoltage X‐Ray Unit
Authors: Alaei P , Gerbi B , Higgins P
Published: April 2010

Purpose: Orthovoltage x‐ray units, designed for non‐human use, are rapidly replacing radioisotope irradiators in small animal and radiobiology research. The beam characteristics of these units, however, are often ignored by researchers. This work characterizes the orthovolatge beam from one of the newer units widely used by researchers in medicine and related fields. Method and Materials: The X‐Rad 320, a self‐contained x‐ray system is commonly used in laboratory and university settings. The unit has a maximum output voltage of 320 kVp and a maximum dose output of 3 Gy/min at 50 cm SSD. The kVp and mA settings are adjustable through a wide range and the SSD can be set between 20 and 90 cm. This work characterizes the beam produced by this system with regard to its flatness, depth dose, collimator scatter factor, and backscatter factor at the location of its adjustable height sample shelf. The validity of the inverse square factor and the accuracy of HVL determination in this system's enclosed environment are also examined. Results: The unit has been calibrated according to AAPM TG‐61 protocol. HVLs for certain beam settings have been determined and depth dose has been measured and compared to published data for the appropriate beam quality. The flatness of the beam for several collimator settings has been measured to ensure uniform irradiation of samples within a given collimator setting. Other beam characteristics such as backscatter and collimator scatter factors have also been measured. Conclusion: Proper characterization of an x‐ray beam and accurate dosimetry is of importance in many of the small animal and radiobiology investigations which may lead to advent of new therapies for humans. This work investigates the beam characteristics of a self‐contained orthovoltage x‐ray unit to ensure accurate and uniform irradiation of samples.
SU‐FF‐T‐280: Evaluation of the Accuracy, and Energy Dependence of the Nano‐Dot Dosimeters
Authors: Dini S , Jamshidi A , Hussain E , Pottes L , Liu G , Meigooni A
Published: April 2010

Purpose: Characteristics and clinical application of the diode, TLD, and Nano‐dot have been studied by various investigators. However, there is a limited publication on clinical application of the Nano‐dot detectors (Landauer®)1. Despite the detailed investigations on characteristics of Nano‐dot, such as time, temperature, and depth, there is no data on energy dependence and accuracy of this dosimeter. The goal of this project is to evaluate the accuracy, energy dependence, and also positional dependence of the Nano‐dots in their clinical applications. Material and method: Accuracy and energy dependence of the Nano‐dot response have been investigated using the megavoltage photon and electron beams from Varian Clinac 2100/EX2 Linear Accelerator. The irradiated in tissue equivalent phantom material were read using a MircoStar reader. The responses of the Nano‐dots were converted to absorbed dose by calibrating the reader using a set of calibrated Nano‐dots which were irradiated in the calibration condition for doses ranging from 0.0 to 400 cGy. The measured absorbed doses for other irradiated Nano‐dots were analyzed as a function of beam energy and dose. Results: The results of these investigations show that the response of the Nano‐dots are very reproduceable (<0.2%). However, up to 5% variation among different Nano‐dots exposed to the same dose and the same beam energy has been observed. These dosimeters are less sensitive to higher energy photon beams. Accurate localization of the Nano‐dots on the patient is a significant factor on clinical application of this detector. Conclusion: Nano‐dots must be carefully calibrated for the different beam energy. Therefore, using the same calibration factors on the MicroStar reader, one has to verify that the results to be corrected appropriately, if it is used for other beam energies.

1. Paul A. Jursinic, “Characterization of optically stimulated luminescent dosimeters, OSLDs, for clinical dosimetric measurements, Med. Phys. 34 (12) 4594–4604 (2007).
SU‐FF‐T‐281: Variation of Beam Characteristics for Physical and Enhanced Dynamic Wedge From a Dual Energy Accelerator
Authors: Chandraraj V , Manickam R , Supe S
Published: April 2010

Purpose: The aim of this study was to compare few of the dosimetric characteristics of a physical and enhanced dynamic wedge from a dual energy (6 and 18 MV) linear accelerator. Materials and Methods: This study used the Varian Clinac‐DHX (S.No.3172) linear accelerator which is equipped with three different type of wedges. To compare the change in beam quality with physical and enhanced dynamic wedge half value layer (HVL) was measured using a 0.14 cc ion chamber covered with brass build up cap positioned at 2 meter distance from the source and the distance from the target to absorber distance was maintained as 1 meter. Transmission measurements were made for varying thickness of white polystyrene phantom placed on the couch. The surface dose with physical and enhanced dynamic wedges were measured using a parallel plate chamber at 85 and 100 cm source to surface distance (SSD), for 6 and 18 MV photons. Results: The HVL was estimated for 6 and 18 MV photons along the central axis and at off‐axis points for the field size of 20 × 20 cm2 with 45° upper physical wedge and compared with that of the enhanced dynamic wedge (EDW). For physical wedged field, at heel edge side HVL value was high compared with the measured that of EDW. It was noticed that, the HVL variation across the beam was significantly high for 6 MV X‐rays than for 18 MV X‐rays. The measured surface dose was found to be more at 85 cm FSD for all the fields. The lower energy photons (6 MV) were found to result in higher surface dose than the higher energy photons (18 MV). Conclusion: The three wedge systems produce significantly different surface doses that should be considered in properly choosing a wedge system for clinical use.
SU‐FF‐T‐283: Proton Beam Dosimetry Using Gafchromic EBT Film
Authors: Zhao Li , Das I
Published: April 2010

Purpose: Gafchromic EBT film characteristics for dose, dose rate, film orientation, air gap, tilt angle, beam energy and temporal stability were investigated in a clinical proton beam dosimetry. Methods and Materials: The EBT film was sandwiched between solid water slabs and irradiated in both parallel and perpendicular arrangements against the beam incident direction. Calibration films were irradiated in the dose range of 20 cGy–1000 cGy at mid spread out Bragg Peak (SOBP) in a reference condition. The optical density changes due to dose, dose rate and proton beam energies were studied. Depth doses measured with EBT film were compared with those obtained with a plane‐parallel ion‐chamber. The responses of the exposed films were measured by a Macbeth TD932 densitometer and a Vidar Dosimetry Pro Advantage™ scanner. Measurements were made at finite time post irradiation for temporal response. Results: There was no noticeable optical density change over dose rates ranging from 32 to 640 cGy min−1. There was an increase in optical density of up to 0.04 units one month after irradiation within the dose range studied. The difference in optical densities between perpendicular and parallel configurations tends to be rather small, within ±0.02 OD units. Air gaps between the film and slabs caused significant perturbation in the depth dose distribution when the film is parallel to the beam axis. By tilting the film plane a few degrees away the beam axis, air gap artifacts was eliminated. Depth dose profiles measured with Gafchromic EBT film agreed with the one measured with an ion chamber although EBT film appears to have an under‐response in the distal end of SOBP. Conclusions: Gafchromic EBT film has unnoticeable dependences of dose rate and proton beam energy. The Gafchromic EBT film could be a useful detector for proton dosimetry measurements with proper precaution and correction.
SU‐FF‐T‐291: Verification of In‐Vivo Dosimetry in TomoTherapy Treatments
Authors: Chen Q , Lu W , Schnarr E , Ruchala K , Olivera G
Published: April 2010

Purpose: The implementation of in‐vivo dosimetry for a TomoTherapy® treatment system is described. The accuracy of the in‐vivo dosimetry is verified with phantom study. The prospect of replacing the film measurement in pretreatment DQA with the in‐vivo dosimetry is studied. Method and Materials: The exit detectors responses for each MLC leaf are measured with a series of solid water stack thicknesses and table heights during a calibration procedure. These measured responses forms a database that is used to reconstruct the incident fluence from the exit detector signal. The database could also be formed by scaling the gold standard database with necessary calibration procedure. The reconstructed incident fluence is then used as input to the dose calculator to get the reconstructed in‐vivo dose. Six different plans (tumor on or off center, under 1.0cm, 2.5cm and 5.0 cm field width respectively) are delivered on a phantom (Tomo® Cheese Phantom). The in‐vivo dose is compared with planned dose and ion‐chamber measurements. DQA plans in patient archives from several clinical sites are retrospectively studied. The in‐vivo dose is compared with the planned dose. Results: The reconstructed incident fluence agreed with the planned fluence within +/− 4%. In‐vivo dose agreed with the planned and ion‐chamber measured dose within +/− 1.5%. The accuracy is well within the normal 3% action level for DQA plan. The in‐vivo dose can be computed within 3 minutes normally in retrospective study mode and it could be computed real‐time during the delivery. Conclusion: TomoTherapy's in‐vivo dosimetry implementation achieves good accuracy. It could be a tool used in a program that performs a filmless DQA that could saves hours of time.

Conflict of Interest: Research sponsored by TomoTherapy Inc
SU‐FF‐T‐294: Design and Validation of a Source Deployment Test for An Intra‐Ocular Sr‐90/Y‐90 Brachytherapy Source
Authors: Holmes S , Micka J , DeWerd L
Published: April 2010

Purpose: To determine whether a well‐type ionization chamber can be used to verify proper source deployment of an approximately 2.5mm long 90Sr/90Y source pellet used to treat wet age‐related macular degeneration; to optimize the measurement geometry; and to verify that the apparatus functions as predicted by the model. Method and Materials: The Monte Carlo code MCNP5 was used to investigate optimal design parameters for a collimating well chamber insert intended to verify whether a 90Sr/90Y brachytherapy source is fully deployed to within 0.25mm of the stainless steel delivery cannula end plug. The source position for measurements was not known a priori with this resolution, so a precise retraction of the source for measured validation of the calculated data was not possible. An alternate method for validation of the MCNP5 model was devised to be substantially similar to the retracted source geometry but to allow corresponding measurements to be made in a well controlled geometry. As part of this investigation, a well chamber transfer standard for reference measurements was established and variations between production models of both straight reference cannulae and treatment cannulae were experimentally determined. Results: The Monte Carlo models indicated that a fully deployed source should generate between 16% and 20% of the open field straight cannula measurement used as a reference value. For the offset source measurements, the measured data concurred with MC values to within 1% (0.1% of the reference signal), thus validating the calculations. Measured variation between reference cannulae was ±0.3% and between clinical cannulae without the collimating insert was ±0.9%. Measurements were reproducible within ±0.2% standard deviation. Conclusion: This work validates the MCNP5 model used to calculate the signal range generated by an acceptably deployed 90Sr/90Y source in the collimating well chamber insert.

Conflict of interest: This investigation was funded in part by NeoVista, Inc.