bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐59: A Novel Multi‐Beam Dynamic IMRT with Fixed‐Jaw Technique for Left Breast Cancer Patients with Regional Lymph Nodes Radiotherapy
Authors: Wang J , Yang Z , Hu W
Published: June 2015

Purpose:

This study was to investigate the dosimetric benefit of a novel intensity modulated radiation therapy (IMRT) technique for irradiating the left breast and regional lymph node (RLN).

Methods:

The breast and RLN (internal mammary node and periclavicular node) and normal tissue were contoured for 16 consecutive left‐sided breast cancer patients previously treated with RT after lumpectomy. Nine equi‐spaced fields IMRT (9 ‐field IMRT), tangential multi‐beam IMRT (tangential‐IMRT) and IMRT with fixed‐jaw technique (FJT‐IMRT) were developed and compared with three‐dimensional conformal RT (3DCRT). Prescribed dose was 50 Gy in 25 fractions. Dose distributions and dose volume histograms were used to evaluate plans.

Results:

All IMRTs achieved similar target coverage and substantially reduced heart V30 and V20 compared to the 3DCRT. The average heart mean dose had different changes, which were 9.0Gy for 9‐field IMRT, 5.7Gy for tangential‐IMRT and 4.2Gy for FJT‐IMRT. For the contralateral lung and breast, the 9‐field IMRT has the highest mean dose; and the FJT‐IMRT and tangential‐IMRT had similar lower value. For the thyroid, both 9‐field IMRT and FJT‐IMRT had similar V30 (20% and 22%) and were significantly lower than that of 3DCRT (34%) and tangential‐IMRT (46%). Moreover, the thyroid mean dose of FJT‐IMRT is the lowest. For cervical esophagus and humeral head, the FJT‐IMRT also had the best sparing.

Conclusion:

All 9‐field IMRT, tangential‐IMRT and FJT‐IMRT had superiority for targets coverage and substantially reduced the heart volume of high dose irradiation. The FJT‐IMRT showed advantages of avoiding the contralateral breast and lung irradiation and decreasing the thyroid, humeral head and cervical esophagus radiation dose at the expense of a slight monitor units (MUs) increasing.
SU‐E‐T‐60: A Plan Quality Index in IMRT QA That Is Independent of the Acceptance Criteria
Authors: Kim D , Kim S , Kang S , Kim T , Kim K , Park S , Cho M , Shin D , Suh T
Published: June 2015

Purpose:

In IMRT QA, plan quality evaluation is made based on pass rate under preset acceptance criteria, mostly using gamma‐values. This method is convenient but, its Result highly depends on what the acceptance criteria are and suffers from the lack of sensitivity in judging how good the plan is. In this study, we introduced a simple but effective plan quality index of IMRT QA based on dose difference only to supplement such shortcomings, and investigated its validity.

Methods:

The proposed index is a single value which is calculated mainly based on point‐by‐point comparison between planned and measured dose distributions, and it becomes “1” in an ideal case. A systematic evaluation was performed with one‐dimensional test dose distributions. For 3 hypothetical dose profiles, various displacements (in both dose and space) were introduced, the proposed index was calculated for each case, and the behavior of obtained indices was analyzed and compared with that of gamma evaluation. In addition, the feasibility of the index was assessed with clinical IMRT/VMAT/SBRT QA cases for different sites (prostate, head & neck, liver, lung, spine, and abdomen).

Results:

The proposed index showed more robust correlation with the amount of induced displacement compared to the gamma evaluation method. No matter what the acceptance criteria are (e.g., whether 3%/3mm or 2%/2mm), it was possible to clearly rank every case with the proposed index while it was difficult to do with the gamma evaluation method.

Conclusion:

IMRT plan quality can be evaluated quantitatively by the proposed index. It is considered that the proposed index would provide useful information for better judging the level of goodness of each plan and its Result is independent of the acceptance criteria.

This work was supported by the Radiation Technology R&D program (No. 2013M2A2A7043498) and the Mid‐career Researcher Program (2014R1A2A1A10050270) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&Future Planning.
SU‐E‐T‐67: A Quality Assurance Procedure for VMAT Delivery Technique with Multiple Verification Metric Using TG‐119 Protocol
Authors: Katsuta Y , Kadoya N , Shimizu E , Matsunaga K , Inoue M , Majima K , Jingu K
Published: June 2015

Purpose:

A successful VMAT plan delivery includes precise modulations of dose rate, gantry rotational and multi‐leaf collimator shapes. The purpose of this research is to construct routine QA protocol which focuses on VMAT delivery technique and to obtain a baseline including dose error, fluence distribution and mechanical accuracy during VMAT.

Methods:

The mock prostate, head and neck (HN) cases supplied from AAPM were used in this study. A VMAT plans were generated in Monaco TPS according to TG‐119 protocol. Plans were created using 6 MV and 10 MV photon beams for each case. The phantom based measurement, fluence measurement and log files analysis were performed. The dose measurement was performed using 0.6 cc ion chamber, which located at isocenter. The fluence distribution were acquired using the MapCHECK2 mounted in the MapPHAN. The trajectory log files recorded inner 20 leaf pairs and gantry angle positions at every 0.25 sec interval were exported to in‐house software developed by MATLAB and determined those RMS values.

Results:

The dose difference is expressed as a ratio of the difference between measured and planned doses. The dose difference for 6 MV was 0.91%, for 10 MV was 0.67%. In turn, the fluence distribution using gamma criteria of 2%/2 mm with a 50% minimum dose threshold for 6 MV was 98.8%, for 10 MV was 97.5%, respectively. The RMS values of MLC for 6 MV and 10 MV were 0.32 mm and 0.37 mm, of gantry were 0.33 degree and 0.31 degree.

Conclusion:

In this study, QA protocol to assess VMAT delivery accuracy is constructed and results acquired in this study are used as a baseline of VMAT delivery performance verification.
SU‐E‐T‐71: A Radiochromic Film Based Quantitative Assessment of Thermoplastic Mask Bolus Effect in Head and Neck IMRT/VMAT
Authors: Kalavagunta C , Lin M , Snider J , Xu H , Schrum A , Vadnais P , Marter K , Suntharalingam M , Prado K
Published: June 2015

Purpose:

To quantify the factors leading to thermoplastic mask bolus‐associated‐increased skin dose in head and neck IMRT/VMAT using EBT2 film.

Methods:

EBT2 film placed beneath a dual layer 3‐point ORFIT head, neck and shoulder mask was used to test the effect of mask thickness, beam modulation, air gap, and beam obliquity on bolus effect. Mask thickness was varied based on the distribution of 1.6mm Orfilight layer on top of 2 mm Efficast layer. Beam modulation was varied by irradiating the film with an open field (no beam modulation) and a step and shoot field (beam modulation). Air gap between mask and film was varied from 0 to 5mm. Beam obliquity was varied by irradiating the film at gantry angles of 0°, 35°, and 70°.Finally, film strips placed on a Rando phantom under an Orfit mask, in regions of expected high dose, were irradiated using 5 IMRT and 5 VMAT plans with various modulation levels (modulation factor 2 to 5) and the results were compared with those obtained placing OSLDs at the same locations.

Results:

An 18–34% increase in mask bolus effect was observed for three factors where the effect of beam obliquity ≥ beam modulation > mask thickness. No increase in mask bolus effect was observed for change in air gap. A 6–13% increase in dose due to mask bolus effect was observed on film strips.

Conclusion:

This work underlines the role of beam obliquity and beam modulation combined with thermoplastic mask thickness in increasing mask bolus‐associated skin dose in head and neck IMRT/VMAT. One possible method of dose reduction, based on knowledge gained from this work, is inclusion of skin as an avoidance structure in treatment planning. Another approach is to design a mask with the least amount of thermoplastic material necessary for immobilization.
SU‐E‐T‐73: A Robust Proton Beam Therapy Technique for High‐Risk Prostate Cancer Whole Pelvis Irradiation: Bilateral Opposed Single Field Uniform Dose (SFUD) Plan with Lateral Penumbra Gradient Matching
Authors: Ding X , Wu H , Rosen L
Published: June 2015

Purpose:

To develop a clinical feasible and robust proton therapy technique to spare bowel, bladder and rectum for high‐risk prostate cancer patients

Methods:

The study includes 3 high‐risk prostate cancer cases treated with bilateral opposed SFUD with lateral penumbra gradient matching technique prescribed to 5400cGyE in 30 fx in our institution. To treat whole pelvic lymph node chain, the complicated ‘H’ shape, using SFUD technique, we divided the target into two sub‐targets (LLAT beam treating ‘90 degree T‐shape’ and RLAT beam treating ‘: shape’) in Plan A and use lateral penumbra gradient matching at patient's left side. Vice verse in Plan B. Each plan deliver half of the prescription dose. Beam‐specific PTVs were created to take range uncertainty and setup error into account. For daily treatment, patient received four fields from both plan A and B per day. Robustness evaluation were performed in the worst case scenario with 3.5% range uncertainty and 1, 2, 3mm overlap or gap between LLAT and RLAT field matching in Raystation 4.0. All of cases also have a Tomotherapy backup plan approved by physician as a dosimetric comparison.

Results:

The total treatment time take 15–20mins including IGRT and four fields delivery on ProteusONE, a compact size PBS proton system, compared to 25–30min in traditional Tomotherapy. Robustness analysis shows that this plan technique is insensitive to the range uncertainties. With the lateral gradient matching, 1, 2, 3mm overlap renders only 2.5%, 5.5% and 8% hot or cool spot in the junction areas. Dosimetric comparisons with Tomotherapy show a significant dose reduction in bladder D50%(14.7±9.3Gy), D35%(7.3±5.8Gy); small bowel and rectum average dose(19.6±7.5Gy and 14.5±6.3Gy respectively).

Conclusion:

The bilateral opposed(SFUD) plan with lateral penumbra gradient matching has been approved to be a safe, robust and efficient treatment option for whole pelvis high‐risk prostate cancer patient which significantly spares the OARs.
SU‐E‐T‐79: A Study of the Effect of Clinical Tumor Volume Displacement On the Dosage of Post Modified Radical Mastectomy Intensity‐Modulated Radiation Therapy Plans for Left‐Sided Breast Cancer
Authors: Zhang W , Ma C , Li D , Wu F
Published: June 2015

Purpose:

To explore the effect of clinical tumor volume (CTV) displacement on the dosage of intensity‐modulated radiation therapy (IMRT) plans for left‐sided breast cancer after modified radical mastectomy.

Methods:

We created 2 sets of IMRT plans based on PTV0.5 and PTV0.7 (with CTV displacement of 0.5cm and 0.7cm respectively) for each of the ten consecutive left‐sided breast cancer patients after modified radical mastectomy, and compared the difference in PTV coverage and organ at risk (OAR) sparing between the two groups. And then, we compared the difference in PTV coverage in IMRT plans based on PTV0.5 between the group with properly estimated CTV displacement (presuming the actual CTV displacement was 0.5cm) and the one with underestimated CTV displacement (presuming the actual CTV displacement was 0.7cm). The difference in results between the corresponding two groups was compared using paired‐sample t‐test. P values less than 0.05 were considered statistically significant.

Results:

IMRT plans derived from PTV0.5 had more homogenous PTV coverage, and less heart, left lung, right breast, right lung, left humeral head and B‐P radiation exposure, as well as less total Mu as compared with the ones stemmed from PTV0.7 (all p<0.05). IMRT plans with appropriate estimation of CTV displacement had better PTV coverage compared with the ones with underestimated CTV displacement (all p<0.01).

Conclusion:

The IMRT plans with smaller CTV displacement in post modified radical mastectomy radiotherapy for left‐sided breast cancer has dosimetrical advantages over the ones with larger CTV displacement. Underestimation of CTV displacement can lead to significant reduction of PTV coverage. Individually quantifying and minimizing CTV displacement can significantly improve PTV coverage and OAR (including heart and left lung) sparing.

This work was supported by the Medical Scientific Research Foundation of Guangdong Procvince (A2014455 to Changchun Ma)
SU‐E‐T‐83: A Study On Evaluating the Directional Dependency of 2D Seven 29 Ion Chamber Array Clinically with Different IMRT Plans
Authors: Kumar Syam , C.P Aswathi
Published: June 2015

Purpose:

To evaluate the directional dependency of 2D seven 29 ion chamber array clinically with different IMRT plans.

Methods:

25 patients already treated with IMRT plans were selected for the study. Verification plans were created for each treatment plan in eclipse 10 treatment planning system using the AAA algorithm with the 2D array and the Octavius CT phantom. Verification plans were done 2 times for a single patient. First plan with real IMRT (plan‐related approach) and second plan with zero degree gantry angle (field‐related approach). Measurements were performed on a Varian Clinac‐iX, linear accelerator equipped with a millennium 120 multileaf collimator. Fluence was measured for all the delivered plans and analyzed using the verisoft software. Comparison was done by selecting the fluence delivered in static gantry (zero degree gantry) versus IMRT with real gantry angles.

Results:

The gamma pass percentage is greater than 97 % for all IMRT delivered with zero gantry angle and between 95%–98% for real gantry angles. Dose difference between the TPS calculated and measured for IMRT delivered with zero gantry angle was found to be between (0.03 to 0.06Gy) and with real gantry angles between (0.02 to 0.05Gy). There is a significant difference between the gamma analysis between the zero degree and true angle with a significance of 0.002. Standard deviation of gamma pass percentage between the IMRT plans with zero gantry angle was 0.68 and for IMRT with true gantry angle was found to be 0.74.

Conclusion:

The gamma analysis for IMRT with zero degree gantry angles shows higher pass percentage than IMRT delivered with true gantry angles. Verification plans delivered with true gantry angles lower the verification accuracy when 2D array is used for measurement.
SU‐E‐T‐85: A Systematic Analysis of Mono‐Isocentric Techniques for the Treatment of Multiple Metastasis
Authors: Papanikolaou N , Narayanasamy G , Stathakis S , Pappas E , Kirby N , Mavroidis P , Crownover R , Gutierrez A
Published: June 2015

Purpose:

In this planning study, we compared two mono‐isocentric techniques for the treatment of multiple brain metastasis. We hypothesize that, dynamic conformal arc delivery produces significantly more efficient plans of similar quality when compared to volumetric modulated arc therapy (VMAT).

Methods:

Recently published clinical data demonstrated a benefit in treating multiple brain metastasis (more than four mets) with SRS. A number of publications showed the feasibility of planning such patients with VMAT. In our study, we planned ten SRS patients with three to eight brain metastasis. The Varian eclipse system used four arcs with a VMAT optimized delivery whereas the Brainlab multiple elements software (MME) selected between 3 and 7 optimized arcs to deliver the prescribed dose using a hybrid conformal arc technique (non‐IMRT).

Results:

We have found that both planning systems achieved the goal to deliver the prescribed dose to the 99.5% of the tumor volume. The tumor doses ranged from 18 to 24Gy, following the RTOG criteria, with most tumors receiving 24Gy. The VMAT and MME plans had varying maximum doses for each tumor and were on average at least 132% of the prescribed dose. We found that once the segmentation and the plan objectives were specified the MME plan was the fastest to compute (less than 3min) whereas the VMAT took on average an hour to calculate with the AAA engine and 15 minutes with the Acuros engine (dose grid resolution of 1mm).

Conclusion:

Patients with multiple brain metastasis can be treated very efficiently using a mono‐isocentric non‐IMRT delivery technique. Whereas VMAT produces equivalent plans, it takes longer to both compute and deliver with the added complexity of IMRT delivery.

UTHSCSA, division of medical physics has a research grant with Brainlab
SU‐E‐T‐90: Accuracy of Calibration of Lithium‐6 and ‐7 Enriched LiF TLDs for Neutron Measurements in High Energy Radiotherapy
Authors: Keehan S , Franich R , Taylor M , Lonski P , Kron T
Published: June 2015

Purpose:

To determine the potential error involved in the interpretation of neutron measurements from medical linear accelerators (linacs) using TLD‐600H and TLD‐700H if standard AmBe and 2⁵2Cf neutron sources are used for calibration without proper inclusion of neutron energy spectrum information.

Methods:

The Kerma due to neutrons can be calculated from the energy released by various nuclear interactions (elastic and inelastic scatter, (n,α), (n,p), (n,d), (n,t), (n,2n), etc.). The response of each TLD can be considered the sum of the neutron and gamma components; each proportional to the Kerma. Using the difference between the measured TLD responses and the ratio of the calculated Kerma for each material, the neutron component of the response can be calculated. The Monte Carlo code MCNP6 has been used to calculate the neutron energy spectra resulting from photonuclear interactions in a Varian 21EX linac. TLDs have been exposed to the mixed (γ‐n) field produced by a linac and AmBe and 2⁵2Cf standard neutron sources.

Results:

For dosimetry of neutrons from AmBe or 2⁵2Cf sources, assuming TLD‐700H insensitivity to neutrons will Result in 10% or 20% overestimation of neutron doses respectively.For dosimetry of neutrons produced in a Varian 21EX, applying a calibration factor derived from a standard AmBe or 2⁵2Cf source will Result in an overestimation of neutron fluence, by as much as a factor of 47.The assumption of TLD‐700H insensitivity to neutrons produced by linacs leads to a negligible error due to the extremely high Kerma ratio (600H/700H) of 3000 for the assumed neutron spectrum.

Conclusion:

Lithium‐enriched TLDs calibrated with AmBe and/or 2⁵2Cf neutron sources are not accurate for use under the neutron energy spectrum produced by a medical linear accelerator.
SU‐E‐T‐98: An Analysis of TG‐51 Electron Beam Calibration Correction Factor Uncertainty
Authors: Lee P , Alvarez P , Taylor P , Lowenstein J , Molineu A , Kry S , Followill D
Published: June 2015

Purpose:

To analyze the uncertainty of the TG‐51 electron beam calibration correction factors for farmer type ion chambers currently used by institutions visited by IROC Houston.

Methods:

TG‐51 calibration data were collected from 181 institutions visited by IROC Houston physicists for 1174 and 197 distinct electron beams from modern Varian and Elekta accelerators, respectively. Data collected and analyzed included ion chamber make and model, nominal energy, ND,w, I5₀, R5₀, k'R5₀, dref, Pgr and pdd(dref). k'R5₀ data for parallel plate chambers were excluded from the analysis.

Results:

Unlike photon beams, electron nominal energy is a poor indicator of the actual energy as evidenced by the range of R5₀ values for each electron beam energy (6–22MeV). The large range in R5₀ values resulted k'R5₀ values with a small standard deviation but large range between maximum value used and minimum value (0.001–0.029) used for a specific Varian nominal energy. Varian data showed more variability in k'R5₀ values than the Elekta data (0.001–0.014). Using the observed range of R5₀ values, the maximum spread in k'R5₀ values was determined by IROC Houston and compared to the spread of k'R5₀ values used in the community. For Elekta linacs the spreads were equivalent, but for Varian energies of 6 to 16MeV, the community spread was 2 to 6 times larger. Community Pgr values had a much larger range of values for 6 and 9 MeV values than predicted. The range in Varian pdd(dref ) used by the community for low energies was large, (1.4–4.9 percent), when it should have been very close to unity. Exradin, PTW Roos and PTW farmer chambers ND,w values showed the largest spread, ≥11 percent.

Conclusion:

While the vast majority of electron beam calibration correction factors used are accurate, there is a surprising spread in some of the values used.
SU‐E‐T‐103: An Evaluation of Multiple Irradiations of the IROC Houston QA Center Anthropomorphic Liver Phantom
Authors: Alvarez P , Molineu A , Lujano C , Nguyen T , Followill D
Published: June 2015

Purpose:

Analyze the results from irradiations of an anthropomorphic liver phantom based on irradiation technique and number of isocenters used for the SBRT delivery.

Methods:

The phantom consists of a water‐fillable plastic shell that has a polystyrene insert, representing the liver which includes two Solid WaterTM targets (PTV1 and PTV2) mimicking liver metastases. The two targets, PTV1 and PTV2 are non‐coplanar and are an ovoid 2 cm in diameter and 2.5 cm long and a 3 cm diameter sphere, respectively. Each PTV houses one TLD and 2 planes of radiochromic film. The phantom and a motion table to simulate respiratory motion is sent to institutions sthat are instructed to design and deliver a stereotactic treatment plan that delivers 6 Gy to ≥ 95% of each PTV. The maximum motion of the phantom on the motion table was 1 cm in the superior‐inferior direction.

Results:

Irradiations from 93 institutions have been analyzed. The acceptance criteria are ±7% for the TLD and 85% of the pixels in a region surrounding each PTV passing a ±7%/4 mm global gamma analysis. Sixty‐seven (71%) irradiations meet this criteria. The majority, 74 (80%), of the irradiations were performed with IMRT. 73% of the IMRT deliveries were within criteria and 68% of the 3D CRT delivery were within criteria. 32 of the irradiations had a single isocenter plan, 50 were performed with two isocenters and 11 irradiations were performed with CyberKnife and TomoTherapy units where the concept of isocenter is not applicable. The pass rate for the single, dual and no isocenter irradiations were 69%, 74% and 73%, respectively and are not statistically different.

Conclusion:

The pass rate for the anthropomorphic liver phantom is approximately 70%. There does not seem to be any correlation with number of isocenters used or irradiation technique used for the delivery.

This work was supported by PHS CA180803 awarded by NCI, DHHS
SU‐E‐T‐104: An Examination of Dose in the Buildup and Build‐Down Regions
Authors: Tome W , Kuo H , Phillips J
Published: June 2015

Purpose:

To examine dose in the buildup and build‐down regions and compare measurements made with various models and dosimeters

Methods:

Dose was examined in a 30×30cm 2 phantom of water‐equivalent plastic with 10cm of backscatter for various field sizes. Examination was performed with radiochromic film and optically‐stimulated‐luminescent‐dosimeter (OSLD) chips, and compared against a plane‐parallel chamber with a correction factor applied to approximate the response of an extrapolation chamber. For the build‐down region, a correction factor to account for table absorption and chamber orientation in the posterior‐anterior direction was applied. The measurement depths used for the film were halfway through their sensitive volumes, and a polynomial best fit curve was used to determine the dose to their surfaces. This chamber was also compared with the dose expected in a clinical kernel‐based computer model, and a clinical Boltzmann‐transport‐equation‐based (BTE) computer model. The two models were also compared against each other for cases with air gaps in the buildup region.

Results:

Within 3mm, all dosimeters and models agreed with the chamber within 10% for all field sizes. At the entrance surface, film differed in comparison with the chamber from +90% to +15%, the BTE‐model by +140 to +3%, and the kernel‐based model by +20% to −25%, decreasing with increasing field size. At the exit surface, film differed in comparison with the chamber from −10% to −15%, the BTE‐model by −53% to −50%, the kernel‐based model by −55% to −57%, mostly independent of field size.

Conclusion:

The largest differences compared with the chamber were found at the surface for all field sizes. Differences decreased with increasing field size and increasing depth in phantom. Air gaps in the buildup region cause dose buildup to occur again post‐gap, but the effect decreases with increasing phantom thickness prior to the gap.
SU‐E‐T‐105: An FMEA Survey of Intensity Modulated Radiation Therapy (IMRT) Step and Shoot Dose Delivery Failure Modes
Authors: Faught J Tonigan , Johnson J , Stingo F , Kry S , Court L , Balter P , Followill D
Published: June 2015

Purpose:

To assess the perception of TG‐142 tolerance level dose delivery failures in IMRT and the application of FMEA process to this specific aspect of IMRT.

Methods:

An online survey was distributed to medical physicists worldwide that briefly described 11 different failure modes (FMs) covered by basic quality assurance in step‐ and‐shoot IMRT at or near TG‐142 tolerance criteria levels. For each FM, respondents estimated the worst case H&N patient percent dose error and FMEA scores for Occurrence, Detectability, and Severity. Demographic data was also collected.

Results:

181 individual and three group responses were submitted. 84% were from North America. Most (76%) individual respondents performed at least 80% clinical work and 92% were nationally certified. Respondent medical physics experience ranged from 2.5–45 years (average 18 years). 52% of individual respondents were at least somewhat familiar with FMEA, while 17% were not familiar. Several IMRT techniques, treatment planning systems and linear accelerator manufacturers were represented. All FMs received widely varying scores ranging from 1–10 for occurrence, at least 1–9 for detectability, and at least 1–7 for severity. Ranking FMs by RPN scores also resulted in large variability, with each FM being ranked both most risky (1st ) and least risky (11th) by different respondents. On average MLC modeling had the highest RPN scores. Individual estimated percent dose errors and severity scores positively correlated (p<0.10) for each FM as expected. No universal correlations were found between the demographic information collected and scoring, percent dose errors, or ranking.

Conclusion:

FMs investigated overall were evaluated as low to medium risk, with average RPNs less than 110. The ranking of 11 FMs was not agreed upon by the community. Large variability in FMEA scoring may be caused by individual interpretation and/or experience, thus reflecting the subjective nature of the FMEA tool.
SU‐E‐T‐106: An Institutional Review of Using Commercially Available Software to Evaluate Treatment Plan Quality for Various Treatment Sites and Beam Deliveries
Authors: Esquivel C , Patton L , Walker S , Lawson S
Published: June 2015

Purpose:

Use Sun Nuclear Quality Reports™ with PlanIQ™ to evaluate different treatment delivery techniques for various treatment sites.

Methods:

Fifteen random patients with different treatment sites were evaluated. These include the Head/Neck, prostate, pelvis, lung, esophagus, axilla, bladder and abdomen. Initially, these sites were planned on the Pinnacle 3 V9.6 treatment planning system and utilized nine 6MV step‐n‐shoot IMRT fields. The RT plan, dose and structure sets were sent to Quality Reports™ where a DVH was recreated and the plans were compared to a unique Plan Algorithm for each treatment site. Each algorithm has its own plan quality metrics and objectives, which include the PTV coverage, PTV maximum dose, the prescription dose outside the target, doses to the critical structures, and the global maximum dose and its location. Each plan was scored base on meeting each objective. Plans may have been reoptimized and reevaluated with Quality Reports™ based on the initial score. PlanIQ™ was used to evaluate if any objective not met was achievable or difficult to obtain. A second plan using VMAT delivery was created for each patient and scored with Quality Reports™.

Results:

There were a wide range of scores for the different treatment sites with some scoring better for IMRT plans and some better for the VMAT deliveries. The variation in the scores could be attributed to the treatment site, location, and shape of the target. Most deliveries were chosen for the VMAT due to the short treatment times and quick patient throughput with acceptable plan scores.

Conclusion:

The tools are provided for both physician and dosimetrist to objectively evaluate the use of VMAT delivery versus the step‐n‐shoot IMRT delivery for various sites. PlanIQ validates if objectives can be met. For the physicist, a concise pass/fail report is created for plan evaluation.
SU‐E‐T‐107: An Investigation Into Attenuation Effects On the Energy Spectrum for 137Cs Using Monte Carlo Techniques
Authors: Taneja S , Bartol L , Culberson W , DeWerd L
Published: June 2015

Purpose:

The calibration of radiation protection instrumentation including ionization chambers, scintillators, and Geiger Mueller (GM) counters used as survey meters are often done using 137Cs irradiators. During calibration, irradiators use a combination of attenuators with various thicknesses to modulate the beam to a known air‐kerma rate. The variations in energy spectra as a result of these attenuators are not accounted for and may play a role in the energy‐dependent response of survey meters. This study uses an experimentally validated irradiator geometry modeled in the MCNP5 transport code to characterize the effects of attenuation on the energy spectrum.

Methods:

A Hopewell Designs G‐10 137Cs irradiator with lead attenuators of thicknesses of 0.635, 1.22, 2.22, and 4.32 cm, was used in this study. The irradiator geometry was modeled in MCNP5 and validated by comparing measured and simulated percent depth dose (PDD) and cross‐field profiles. Variations in MCNP5 simulated spectra with increasing amounts of attenuation were characterized using the relative intensity of the 662 keV peak and the average energy.

Results:

Simulated and measured PDDs and profiles agreed within the associated uncertainty. The relative intensity of the 662 keV peak for simulated spectra normalized to the intensity of the unattenuated spectra ranged from 0.16% to 100% based on attenuation thickness. The average energy for simulated spectra for attenuators ranged from 582 keV with no attenuation to 653 keV with 5.54 cm of attenuation. Statistical uncertainty for MCNP5 simulations ranged from 0.11% to 3.69%.

Conclusion:

This study successfully used MCNP5 to validate a 137Cs irradiator geometry and characterize variations in energy spectra between different amounts of attenuation. Variations in the average energy of up to 12% were determined through simulations, and future work will aim to determine the effects of these differences on survey meter response and calibration.
SU‐E‐T‐111: An Iterative Approach to Modelling Dosimetric Properties of a Varian MLC
Authors: DiCostanzo D
Published: June 2015

Purpose:

In effort to efficiently and accurately model MLC parameters for use in Varian Eclipse treatment planning system (TPS), an iterative technique for characterizing the dosimetric properties of MLCs has been developed.

Methods:

The initial characterization of the dosimetric leaf gap (DLG) and MLC transmission was performed using varied sizes of moving gaps and transmission measurements through central axis of the radiation beam. These values were determined during the initial data collection. After the initial values were determined and entered into the TPS, two plans were calculated to test the veracity of DLG and transmission independently. The plan used to determine the DLG has openings of varied sizes which are affected differently by the DLG. A large field uniform fluence that required a MLC carriage shift was used to determine the transmission value independent of DLG. After characterizing the dosimetric properties of the MLC independently, clinical IMRT plans were tested and used to tweak the final values.

Results:

This approach to modelling MLC dosimetric properties was employed for: standard 120 leaf MLC (SDMLC) and 120 leaf high definition MLC (HDMLC). Both types were successfully commissioned, tested, and approved for clinical use on 4 SDMLC machines and 2 HDMLC machines. The pass rate of clinical IMRT plans was 96.9% for 6MV and 98.3% for 10MV for SDMLC and 96.3% for 6MV, 96.5% for 6FFF, and 97.5% for 10FFF for HDMLCs using MapCheck2 with gamma analysis of 2%/2mm and 10% threshold. The final DLG and transmission parameters for 6X were 0.5mm and 0.01, and 1.35mm and 0.02 for HD and SD MLCs respectively.

Conclusion:

This iterative approach of determining dosimetric properties of MLCs is viable for both SDMLC and HDMLC and multiple energies. This approach accurately and efficiently determines the values needed for commissioning MLCs when they are employed for modulated therapies.
SU‐E‐T‐112: An OpenCL‐Based Cross‐Platform Monte Carlo Dose Engine (oclMC) for Coupled Photon‐Electron Transport
Authors: Tian Z , Shi F , Folkerts M , Qin N , Jiang S , Jia X
Published: June 2015

Purpose:

Low computational efficiency of Monte Carlo (MC) dose calculation impedes its clinical applications. Although a number of MC dose packages have been developed over the past few years, enabling fast MC dose calculations, most of these packages were developed under NVidia's CUDA environment. This limited their code portability to other platforms, hindering the introduction of GPU‐based MC dose engines to clinical practice. To solve this problem, we developed a cross‐platform fast MC dose engine named oclMC under OpenCL environment for external photon and electron radiotherapy.

Methods:

Coupled photon‐electron simulation was implemented with standard analogue simulation scheme for photon transport and Class II condensed history scheme for electron transport. We tested the accuracy and efficiency of oclMC by comparing the doses calculated using oclMC and gDPM, a previously developed GPU‐based MC code on NVidia GPU platform, for a 15MeV electron beam and a 6MV photon beam in a homogenous water phantom, a water‐bone‐lung‐water slab phantom and a half‐slab phantom. We also tested code portability of oclMC on different devices, including an NVidia GPU, two AMD GPUs and an Intel CPU.

Results:

Satisfactory agreements were observed in all photon and electron cases, with ∼0.48%–0.53% average dose differences at regions within 10% isodose line for electron beam cases and ∼0.15%–0.17% for photon beam cases. It took oclMC 3–4 sec to perform transport simulation for electron beam on NVidia Titan GPU and 35–51 sec for photon beam, both with ∼0.5% statistical uncertainty. The computation was 6%–17% slower than gDPM due to the differences in both physics model and development environment, which is considered not significant for clinical applications. In terms of code portability, gDPM only runs on NVidia GPUs, while oclMC successfully runs on all the tested devices.

Conclusion:

oclMC is an accurate and fast MC dose engine. Its high cross‐platform portability makes it clinically attractive.
SU‐E‐T‐113: An Unified Imaging and Robotic Couch Quality Assurance Procedure and Automation Software
Authors: Schreibmann E , Elder E
Published: June 2015

Purpose:

To introduce a quality assurance (QA) procedure for the robotic 6DoF couches integrates the couch and imaging components QA procedures into a simple workflow.

Method:

Current QA procedure for the imaging systems is to carefully align a phantom at isocenter and measure in images acquired using the on‐board imaging (OBI) system if the phantom appears aligned with the isocenter. For the robotic couches a complementary procedure offsets a phantom from to measure the couch's ability to reposition the phantom at isocenter. We propose a two‐in –one procedure that starts with a phantom displaced with random positions and orientation and asks the imaging system to align it back at isocenter. Accuracy is measured by comparing the repositioned phantom againts the treatment field. A software module was also implemented to analyze, quantify and report the results.

Results:

The procedure has been implemented clinically using a SRS calibration phantom (VisionRT, London, UK) and the automated software version that is able to detect errors of less than 0.1 mm or 0.1 degrees. The software detects the markers locations with a combination of contouring and intensity filters to compute the shifts/rotations needed to reposition the phantom to it's ideal location using a interactive closest point algorithm to match markers segmentations as extracted from imaging with a mesh representation of their expected location according to the phantom specifications. Once the shifts are send to the couch for repositioning, the procedure is repeated to measure the residual error in imaging to measure robotic couch repositioning accuracy and the phantom location against the graticule is verified.

Conclusions:

A simplified QA procedure and the associated software are presented to streamline the quality assurance of imaging and 6D couch components into a single, easy‐to‐use procedure.
SU‐E‐T‐114: Analysis of MLC Errors On Gamma Pass Rates for Patient‐Specific and Conventional Phantoms
Authors: Sterling D , Ehler E
Published: June 2015

Purpose:

To evaluate whether a 3D patient‐specific phantom is better able to detect known MLC errors in a clinically delivered treatment plan than conventional phantoms. 3D printing may make fabrication of such phantoms feasible.

Methods:

Two types of MLC errors were introduced into a clinically delivered, non‐coplanar IMRT, partial brain treatment plan. First, uniformly distributed random errors of up to 3mm, 2mm, and 1mm were introduced into the MLC positions for each field. Second, systematic MLC‐bank position errors of 5mm, 3.5mm, and 2mm due to simulated effects of gantry and MLC sag were introduced. The original plan was recalculated with these errors on the original CT dataset as well as cylindrical and planar IMRT QA phantoms. The original dataset was considered to be a perfect 3D patient‐specific phantom. The phantoms were considered to be ideal 3D dosimetry systems with no resolution limitations.

Results:

Passing rates for Gamma Index (3%/3mm and no dose threshold) were calculated on the 3D phantom, cylindrical phantom, and both on a composite and field‐by‐field basis for the planar phantom. Pass rates for 5mm systematic and 3mm random error were 86.0%, 89.6%, 98% and 98.3% respectively. For 3.5mm systematic and 2mm random error the pass rates were 94.7%, 96.2%, 99.2% and 99.2% respectively. For 2mm systematic error with 1mm random error the pass rates were 99.9%, 100%, 100% and 100% respectively.

Conclusion:

A 3D phantom with the patient anatomy is able to discern errors, both severe and subtle, that are not seen using conventional phantoms. Therefore, 3D phantoms may be beneficial for commissioning new treatment machines and modalities, patient‐specific QA and end‐to‐end testing.
SU‐E‐T‐116: Analysis of Patient Specific VMAT QA Passing Rates with Delta4 for Matched Machines
Authors: Keller J , Hardin M , Giaddui T , Kremmel E , Peng C , Doyle L , Yu Y , Harrison A
Published: June 2015

Purpose:

To test whether unified vendor specified beam conformance for matched machines implies volumetric modulated arc radiotherapy(VMAT) delivery consistency.

Methods:

Twenty‐two identical patient QA plans, eleven 6MV and eleven 15MV, were delivered to the Delta⁴(Scandidos, Uppsala, Sweden) on two Varian TrueBEAM matched machines. Sixteen patient QA plans, nine 6 MV and seven 10 MV, were delivered to Delta⁴ on two Elekta Agility matched machines. The percent dose deviation(%DDev), distance‐to‐agreement(DTA), and the gamma analysis(γ) were collected for all plans and the differences in measurements were tabulated between matched machines. A paired t‐test analysis of the data with an alpha of 0.05 determines statistical significance. Power(P) was calculated to detect a difference of 5%; all data except Elekta %DDev sets were strong with above a 0.85 power.

Results:

The average differences for Varian machines (%DDev, DTA, and γ) are 6.4%, 1.6% and 2.7% for 6MV, respectively, and 8.0%, 0.6%, and 2.5% for 15MV. The average differences for matched Elekta machines (%DDev, DTA, and γ) are 10.2%, 0.6% and 0.9% for 6 MV, respectively, and 7.0%, 1.9%, and 2.8% for 10MV.A paired t‐test shows for Varian the %DDev difference is significant for 6MV and 15MV(p‐value6MV=0.019, P6MV=0.96; p‐value15MV=0.0003, P15MV=0.86). Differences in DTA are insignificant for both 6MV and 15MV(p‐value6MV=0.063, P6MV=1; p‐value15MV=0.907, P15MV=1). Varian differences in gamma are significant for both energies(p‐value6MV=0.025, P6MV=0.99; p‐value15MV=0.013, P15MV=1). A paired t‐test shows for Elekta the difference in %DDev is significant for 6MV but not 10MV(p‐value6MV=0.00065, P6MV=0.68; p‐value10MV=0.262, P10MV=0.39). Differences in DTA are statistically insignificant(p‐value6MV=0.803, P6MV = 1; p‐value10MV=0.269, P10MV=1). Elekta differences in gamma are significant for 10MV only(p‐value6MV=0.094, P6MV=1; p‐value10MV=0.011, P10MV=1).

Conclusion:

These results show vendor specified beam conformance across machines does not ensure equivalent patient specific QA pass rates. Gamma differences are statistically significant in three of the four comparisons for two pairs of vendor matched machines.
SU‐E‐T‐121: Analyzing the Broadening Effect On the Bragg Peak Due to Heterogeneous Geometries and Implementing User‐Routines in the Monte‐Carlo Code FLUKA in Order to Reduce Computation Time
Authors: Baumann K , Weber U , Simeonov Y , Zink K
Published: June 2015

Purpose:

Aim of this study was to analyze the modulating, broadening effect on the Bragg Peak due to heterogeneous geometries like multi‐wire chambers in the beam path of a particle therapy beam line. The effect was described by a mathematical model which was implemented in the Monte‐Carlo code FLUKA via user‐routines, in order to reduce the computation time for the simulations.

Methods:

The depth dose curve of 80 MeV/u C12‐ions in a water phantom was calculated using the Monte‐Carlo code FLUKA (reference curve). The modulating effect on this dose distribution behind eleven mesh‐like foils (periodicity ∼80 microns) occurring in a typical set of multi‐wire and dose chambers was mathematically described by optimizing a normal distribution so that the reverence curve convoluted with this distribution equals the modulated dose curve. This distribution describes a displacement in water and was transferred in a probability distribution of the thickness of the eleven foils using the water equivalent thickness of the foil's material. From this distribution the distribution of the thickness of one foil was determined inversely. In FLUKA the heterogeneous foils were replaced by homogeneous foils and a user‐routine was programmed that varies the thickness of the homogeneous foils for each simulated particle using this distribution.

Results:

Using the mathematical model and user‐routine in FLUKA the broadening effect could be reproduced exactly when replacing the heterogeneous foils by homogeneous ones. The computation time was reduced by 90 percent.

Conclusion:

In this study the broadening effect on the Bragg Peak due to heterogeneous structures was analyzed, described by a mathematical model and implemented in FLUKA via user‐routines. Applying these routines the computing time was reduced by 90 percent. The developed tool can be used for any heterogeneous structure in the dimensions of microns to millimeters, in principle even for organic materials like lung tissue.
SU‐E‐T‐126: Application of PIPSpro and EPID for Quality Assurance of Medical Accelerators
Authors: Lin Z , Peng X , Lu J
Published: June 2015

Purpose:

The purpose is to study applying PIPSpro and EPID for routine quality assurance of medical accelerators.

Methods:

(1) The coincidence of Light field and radiation field: Placed the FC‐2 phantom on the treatment couch at the 100cm SSD. Using jaw set 10×10 cm2 or 15×15 cm2 field. Verified that the light field aligns with the engraved squares on the phantom. Placed the Crosshair Marker phantom on the top of the FC‐2 phantom with the cross‐hair and spherical marker aligned to the center of the light field. Acquired images with EPID and the images should be exported preferably in DICOM format. Analyzed Follow the recommended procedures in the radiation light field module of PIPSpro software.(2)MLC QA:Set up the MLC phantom on the treatment couch at isocenter. Positioned the EPID imager at the highest possible position without colliding with either the couch or the phantom. Created and delivered four different patterns for testing the MLC leaf position, leaf width, multi‐port and leaf transmission. (3)Radiation isocenter test: Included the isocenter of collimator rotation, gantry rotation and couch rotation. Set the jaws of the collimator to create a thin field as 0.4cm × 20cm.Irradiated film or EPID using an equidistant 15° spacing angles with rotating collimator, gantry and couch respectively.

Results:

We analyzed imagers from EPID and film with PIPSPro software. As a Result, we acquired the specifications of medical accelerators quickly. In the meantime, the results were saved to database for trending and future analysis.

Conclusion:

Quality assurance of medical accelerator is very important. We used PIPSpro and EPID for routine detection, not only improved our efficiency, but also saved the cost. It is an good method.
SU‐E‐T‐127: Application of TG‐119 for Evaluation of Proton Spot Scanning Based Planning and Treatment Delivery
Authors: Saini J , Cao N , Bowen S , Bloch C , Wong T
Published: June 2015

Purpose:

The clinical test cases presented in AAPM TG‐119 are used to evaluate the accuracy of treatment planning and delivery through spot scanning proton beams.

Methods:

An IBA spot scanning delivery system has been commissioned to be used with the RayStation treatment planning system. Various test cases provided in TG‐119 were used for planning and delivery verification. The CT dataset and structures as provided by TG‐119 were imported into a mock patient. The plans were optimized using the multi field optimization (MFO) to achieve the desired goals. The planner was given the flexibility to achieve the given dose‐volume goals by creating appropriate objectives and constraints. Beams were delivered to a phantom and measurements were performed at multiple depths using the MatrixxPT detector array. The analyses were performed on beam by beam basis and quantified using the gamma index. A tolerance of 3%/3 mm in 2D was used for gamma index analysis along with dose threshold of 10%.

Results:

The clinical goals for targets and critical structures were met or improved for all cases except the C‐Shape target with difficult constraints. The minimum gamma index using the 3%/3mm as a criterion is 93.3% for one of the planes measured for C‐Shape target. Using 2%/2mm as a criterion, the minimum gamma index drops to 70%. Only Prostate target has all the planes above >90% pass using the 2%/2mm criterion.

Conclusion:

The overall accuracy of the treatment planning and delivery is deemed clinically acceptable. The test cases with highly modulated beams can have steep gradients in the dose profiles that can reduce the gamma index pass rate. Gamma analysis based on 3D data may be needed for routine use of 2%/2mm criterion. In addition, improvements in modelling of spot profiles in dose engine may be required for further improving the gamma index pass rate.