bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐300: Impact of Electron Density Modeling of ArcCHECK Cylindricaldiode Array On 3DVH Patient Specific QA Software Tool Analysis
Authors: Patwe P , Mhatre V , Dandekar P
Published: July 2016

Purpose:

3DVH software is a patient specific quality assurance tool which estimates the 3D dose to the patient specific geometry with the help of Planned Dose Perturbation algorithm. The purpose of this study is to evaluate the impact of HU value of ArcCHECK phantom entered in Eclipse TPS on 3D dose & DVH QA analysis.

Methods:

Manufacturer of ArcCHECK phantom provides CT data set of phantom & recommends considering it as a homogeneous phantom with electron density (1.19 gm/cc or 282 HU) close to PMMA. We performed this study on Eclipse TPS (V13, VMS) & trueBEAM STx VMS Linac & ArcCHECK phantom (SNC). Plans were generated for 6MV photon beam, 20cm×20cm field size at isocentre & SPD (Source to phantom distance) of 86.7 cm to deliver 100cGy at isocentre. 3DVH software requires patients DICOM data generated by TPS & plan delivered on ArcCHECK phantom. Plans were generated in TPS by assigning different HU values to phantom. We analyzed gamma index & the dose profile for all plans along vertical down direction of beam's central axis for Entry, Exit & Isocentre dose.

Results:

The global gamma passing rate (2% & 2mm) for manufacturer recommended HU value 282 was 96.3%. Detector entry, Isocentre & detector exit Doses were 1.9048 (1.9270), 1.00(1.0199) & 0.5078(0.527) Gy for TPS (Measured) respectively.The global gamma passing rate for electron density 1.1302 gm/cc was 98.6%. Detector entry, Isocentre & detector exit Doses were 1.8714 (1.8873), 1.00(0.9988) & 0.5211(0.516) Gy for TPS (Measured) respectively.

Conclusion:

Electron density value assigned by manufacturer does not hold true for every user. Proper modeling of electron density of ArcCHECK in TPS is essential to avoid systematic error in dose calculation of patient specific QA.
SU‐F‐T‐312: Identifying Distinct Radiation Therapy Plan Classes Through Multi‐Dimensional Analysis of Plan Complexity Metrics
Authors: Desai V , Labby Z , Culberson W
Published: July 2016

Purpose:

To determine whether body site‐specific treatment plans form unique “plan class” clusters in a multi‐dimensional analysis of plan complexity metrics such that a single beam quality correction determined for a representative plan could be universally applied within the “plan class”, thereby increasing the dosimetric accuracy of a detector's response within a subset of similarly modulated nonstandard deliveries.

Methods:

We collected 95 clinical volumetric modulated arc therapy (VMAT) plans from four body sites (brain, lung, prostate, and spine). The lung data was further subdivided into SBRT and non‐SBRT data for a total of five plan classes. For each control point in each plan, a variety of aperture‐based complexity metrics were calculated and stored as unique characteristics of each patient plan. A multiple comparison of means analysis was performed such that every plan class was compared to every other plan class for every complexity metric in order to determine which groups could be considered different from one another. Statistical significance was assessed after correcting for multiple hypothesis testing.

Results:

Six out of a possible 10 pairwise plan class comparisons were uniquely distinguished based on at least nine out of 14 of the proposed metrics (Brain/Lung, Brain/SBRT lung, Lung/Prostate, Lung/SBRT Lung, Lung/Spine, Prostate/SBRT Lung). Eight out of 14 of the complexity metrics could distinguish at least six out of the possible 10 pairwise plan class comparisons.

Conclusion:

Aperture‐based complexity metrics could prove to be useful tools to quantitatively describe a distinct class of treatment plans. Certain plan‐averaged complexity metrics could be considered unique characteristics of a particular plan. A new approach to generating plan‐class specific reference (pcsr) fields could be established through a targeted preservation of select complexity metrics or a clustering algorithm that identifies plans exhibiting similar modulation characteristics. Measurements and simulations will better elucidate potential plan‐class specific dosimetry correction factors.
SU‐F‐T‐386: Analysis of Three QA Methods for Predicting Dose Deviation Pass Percentage for Lung SBRT VMAT Plans
Authors: Hardin M , To D , Giaddui T , Li J , Yu Y , Harrison A
Published: July 2016

Purpose:

To investigate the significance of using pinpoint ionization chambers (IC) and RadCalc (RC) in determining the quality of lung SBRT VMAT plans with low dose deviation pass percentage (DDPP) as reported by ScandiDos Delta4 (D4). To quantify the relationship between DDPP and point dose deviations determined by IC (ICDD), RadCalc (RCDD), and median dose deviation reported by D4 (D4DD).

Methods:

Point dose deviations and D4 DDPP were compiled for 45 SBRT VMAT plans. Eighteen patients were treated on Varian Truebeam linear accelerators (linacs); the remaining 27 were treated on Elekta Synergy linacs with Agility collimators. A one‐way analysis of variance (ANOVA) was performed to determine if there were any statistically significant differences between D4DD, ICDD, and RCDD. Tukey's test was used to determine which pair of means was statistically different from each other. Multiple regression analysis was performed to determine if D4DD, ICDD, or RCDD are statistically significant predictors of DDPP.

Results:

Median DDPP, D4DD, ICDD, and RCDD were 80.5% (47.6%–99.2%), −0.3% (−2.0%–1.6%), 0.2% (−7.5%–6.3%), and 2.9% (−4.0%–19.7%), respectively. The ANOVA showed a statistically significant difference between D4DD, ICDD, and RCDD for a 95% confidence interval (p < 0.001). Tukey's test revealed a statistically significant difference between two pairs of groups, RCDD‐D4DD and RCDD‐ICDD (p < 0.001), but no difference between ICDD‐D4DD (p = 0.485). Multiple regression analysis revealed that ICDD (p = 0.04) and D4DD (p = 0.03) are statistically significant predictors of DDPP with an adjusted r2 of 0.115.

Conclusion:

This study shows ICDD predicts trends in D4 DDPP; however this trend is highly variable as shown by our low r2. This work suggests that ICDD can be used as a method to verify DDPP in delivery of lung SBRT VMAT plans. RCDD may not validate low DDPP discovered in D4 QA for small field SBRT treatments.
SU‐F‐T‐387: A Novel Optimization Technique for Field in Field (FIF) Chestwall Radiation Therapy Using a Single Plan to Improve Delivery Safety and Treatment Planning Efficiency
Authors: Tabibian A , Kim A , Rose J , Alvelo M , Perel C , Laiken K , Sheth N
Published: July 2016

Purpose:

A novel optimization technique was developed for field‐in‐field (FIF) chestwall radiotherapy using bolus every other day. The dosimetry was compared to currently used optimization.

Methods:

The prior five patients treated at our clinic to the chestwall and supraclavicular nodes with a mono‐isocentric four‐field arrangement were selected for this study. The prescription was 5040 cGy in 28 fractions, 5 mm bolus every other day on the tangent fields, 6 and/or 10 MV x‐rays, and multileaf collimation.Novelly, tangents FIF segments were forward planned optimized based on the composite bolus and non‐bolus dose distribution simultaneously. The prescription was spilt into 14 fractions for both bolus and non‐bolus tangents. The same segments and monitor units were used for the bolus and non‐bolus treatment. The plan was optimized until the desired coverage was achieved, minimized 105% hotspots, and a maximum dose of less than 108%. Each tangential field had less than 5 segments.Comparison plans were generated using FIF optimization with the same dosimetric goals, but using only the non‐bolus calculation for FIF optimization. The non‐bolus fields were then copied and bolus was applied. The same segments and monitor units were used for the bolus and non‐bolus segments.

Results:

The prescription coverage of the chestwall, as defined by RTOG guidelines, was on average 51.8% for the plans that optimized bolus and non‐bolus treatments simultaneous (SB) and 43.8% for the plans optimized to the non‐bolus treatments (NB). Chestwall coverage of 90% prescription averaged to 80.4% for SB and 79.6% for NB plans. The volume receiving 105% of the prescription was 1.9% for SB and 0.8% for NB plans on average.

Conclusion:

Simultaneously optimizing for bolus and non‐bolus treatments noticeably improves prescription coverage of the chestwall while maintaining similar hotspots and 90% prescription coverage in comparison to optimizing only to non‐bolus treatments.
SU‐F‐T‐389: Validation in 4D Dosimetry Using Dynamic Phantom
Authors: Lin C , Huang T , Lin C , Nien H , Tu P , Lui L , Wu C
Published: July 2016

Purpose:

Tumor motion due to respiration causes the uncertainties during the radiotherapy. This study aims to find the differences between planning dose by treatment planning and the received dose using dynamic phantom.

Methods:

Respiratory motion was simulated by the DYNAMIC THORAX PHANTOM (Model 008A). 4D‐CT scans and maximum intensity projection (MIP) images for GTV were acquired for analysis. The amplitude of craniocaudal tumor motion including 2mm, 5mm, 10mm and 20mm with 3cm2 tumor size were performed in this study. The respiratory cycles of 4‐seconds and 6‐seconds were included as the different breathing modes. IMRT, VAMT, and Tomotherapy were utilized for treatment planning. Ion chamber and EBT3 were used to measure the point dose and planar dose. Dose distributions with different amplitudes, respiratory cycles, and planning techniques were all measured and compared to calculations.

Results:

The variations between the does measurements and calculation dose by treatment planning system were found in both point dose and dose distribution. The 0.83% and 5.46 % differences in dose average were shown on phantom with motions using 2mm amplitude in 4 second respiratory cycle, and 20mm amplitude in 4 second respiratory cycle, respectively. The most point dose overestimation as compared of the calculations was shown the plan generated by Tomotherapy. The underestimations of planar dose as compared of calculations was found in the 100% coverage doses for GTV.

Conclusion:

The loss of complete (100%) GTV coverage was the predominant effect of respiratory motion observed in this study. Motion amplitude and treatment planning system were the major factors leading the dose measurement variation as compared of planning calculations.
SU‐F‐T‐394: Impact of PTV Margins With Taking Into Account Shape Variation On IMRT Plans For Prostate Cancer
Authors: Hirose T , Arimura H , Shibayama Y , Fukunaga J , Umezu Y , Oga S , Sasaki T
Published: July 2016

Purpose:

The purpose of this study was to investigate the impact of planning target volume (PTV) margins with taking into consideration clinical target volume (CTV) shape variations on treatment plans of intensity modulated radiation therapy (IMRT) for prostate cancer.

Methods:

The systematic errors and the random errors for patient setup errors in right‐left (RL), anterior‐posterior (AP), and superior‐inferior (SI) directions were obtained from data of 20 patients, and those for CTV shape variations were calculated from 10 patients, who were weekly scanned using cone beam computed tomography (CBCT). The setup error was defined as the difference in prostate centers between planning CT and CBCT images after bone‐based registrations. CTV shape variations of high, intermediate and low risk CTVs were calculated for each patient from variances of interfractional shape variations on each vertex of three‐dimensional CTV point distributions, which were manually obtained from CTV contours on the CBCT images. PTV margins were calculated using the setup errors with and without CTV shape variations for each risk CTV. Six treatment plans were retrospectively made by using the PTV margins with and without CTV shape variations for the three risk CTVs of 5 test patients. Furthermore, the treatment plans were applied to CBCT images for investigating the impact of shape variations on PTV margins.

Results:

The percentages of population to cover with the PTV, which satisfies the CTV D98 of 95%, with and without the shape variations were 89.7% and 74.4% for high risk, 89.7% and 76.9% for intermediate risk, 84.6% and 76.9% for low risk, respectively.

Conclusion:

PTV margins taking into account CTV shape variation provide significant improvement of applicable percentage of population (P < 0.05). This study suggested that CTV shape variation should be taken consideration into determination of the PTV margins.
SU‐F‐T‐400: Clinical Comparison of An IMRT Plan Computed with Four Algorithms
Authors: Barbiere J , Ndlovu A
Published: July 2016

Purpose:

This work demonstrates clinical differences in a prostate IMRT plan DVH depending on which of four common algorithms is used for computation. Previous comparisons were often based on simple static or re‐optimized IMRT plans which may not be clearly indicative of the clinical end result due solely to the computation algorithm.

Methods:

A step and shoot prostate multiple field IMRT plan was created in Pinnacle with a Collapsed Cone Convolution Superposition (CCCS) algorithm. The computed patient plan with corresponding dose and the control points without dose were both independently exported to Eclipse. Using the same patient image and structure data sets the control points were recomputed with the Anisotropic Analytical Algorithm (AAA) and Acuros XB for dose‐to‐water in medium (AXBwater) and dose‐to‐medium in medium (AXBmedium). All DVH values were measured in Eclipse to eliminated known differences between various DVH systems. A 0.3cm3 volume was created at the isocenter for point dose (PD) comparison.

Results:

The prostate target Acuros dose‐to‐medium in medium is clearly different than the others with a mean value of 101.7 cGy versus 103.8, 103.5 and 103.1 cGy for AAA, CCCS and AXBwater respectively. The difference in other clinical parameters such as volume at 105% dose (V105) is also unexpectedly different with values of 1.6, 23.9, 16.0 and 11.6 % respectively. The mean value in a small volume around the isocenter was 99.6, 102.4, 102.2 and 101.5 respectively which though not a great difference could affect the plan normalization and add to other effects in all regions of interest. The V102 is 25% larger for AAA compared to AXBwater. The variation in V50 for the bladder and rectum was approximately 5%.

Conclusion:

This work demonstrates how an individual plan can be recomputed and compared directly between various algorithms and that clinical parameters can indeed vary according to which algorithm is used for computation.
SU‐F‐T‐404: Dosimetric Advantages of Flattening Free Beams to Prone Accelerated Partial Breast Irradiation
Authors: Galavis P , Barbee D , Jozsef G
Published: July 2016

Purpose:

Prone accelerated partial breast irradiation (APBI) results in dose reduction to the heart and lung. Flattening filter free beams (FFF) reduce out of field dose due to the reduced scatter from the removal of the flattening filter and reduce the buildup region. The aim of this work is to evaluate the dosimetric advantages of FFF beams to prone APBI target coverage and reduction in dose to organs at risk.

Methods:

Fifteen clinical prone APBI cases using flattened photon beams were retrospectively re‐planned in Eclipse‐TPS using FFF beams. FFF plans were designed to provide equivalent target coverage with similar hotspots using the same field arrangements, resulting in comparable target DVHs. Both plans were transferred to a prone breast phantom and delivered on Varian‐Edge‐Linac. GafChromic‐film was placed in the coronal plane of the phantom, partially overlapping the treatment field and extending into OARs to compare dose profiles from both plans.

Results:

FFF plans were comparable to the clinical plans with maximum doses of (108.3±2.3)% and (109.2±2.4)% and mean doses of (104.5±1.0)% and (104.6±1.2)%, respectively. Similar mean dose doses to the heart and contralateral lungs were observed from both plans, whereas the mean dose to the contra‐lateral breast was (2.79±1.18) cGy and (2.86±1.40) cGy for FFF and clinical plans respectively. However for both plans the error between calculated and measured doses at 4 cm from the field edge was 10%.

Conclusion:

The results showed that FFF beams in prone APBI provide dosimetrically equivalent target coverage and improved coverage in superficial target due to softer energy spectra. Film analysis showed that the TPS underestimates dose outside field edges for both cases. The FFF measured plans showed less dose outside the beam that might reduce the probability of secondary cancers in the contralateral breast.
SU‐F‐T‐407: Artifact Reduction with Dual Energy Or IMAR: Who's Winning?
Authors: Elder E , Schreibmann E , Dhabaan A
Published: July 2016

Purpose:

The purpose of this abstract was to evaluate the performance of commercial strategies for artifact reduction in radiation oncology settings. The iterative metal artifact reduction (Siemens iMAR) algorithm and monoenergetic virtual datasets reconstructed from dual energy scans are compared side‐by‐side in their ability to image in the presence of metal inserts.

Methods:

A CIRS ATOM Dosimetry Verification Phantom was scanned with and without a metal insert on a SOMATOM Definition AS dual energy scanner. Images with the metal insert were reconstructed with (a) a tradition single energy CT scan with the iMAR option implemented, using different artifact reduction settings and (b) a monoenergetic scan calculated from dual energy scans by recovering differences in the energy‐dependence of the attenuation coefficients of different materials and then creating a virtual monoenergetic scan from these coefficients. The iMAR and monoenergetic scans were then compared with the metal‐free scan to assess changes in HU numbers and noise within a region around the metal insert.

Results:

Both the iMAR and dual energy scans reduced artifacts produced by the metal insert. However the iMAR results are dependent of the selected algorithm settings, with a mean HU difference ranging from 0.65 to 90.40 for different options. The mean differences without the iMAR correction were 38.74. When using the dual energy scan, the mean differences were 4.53, that is however attributed to increased noise and not artifacts, as the dual energy scan had the lowest skewness (2.52) compared to the iMAR scans (ranging from 3.90 to 4.88) and the lowest kurtosis (5.72 for dual energy, range of 18.19 to 27.36 for iMAR).

Conclusion:

Both approaches accurately recovered HU numbers, however the dual energy method provided smaller residual artifacts.
SU‐F‐T‐415: Differences in Lung Sparing in Deep Inspiration Breath‐Hold and Free Breathing Breast Plans Calculated in Pinnacle and Monaco
Authors: Saenz D , Stathakis S
Published: July 2016

Purpose:

Deep inspiration breath‐hold (DIBH) is used for left‐sided breast radiotherapy to spare the heart and lung. The magnitude of sparing has been shown to be significant. Monte Carlo, furthermore, has the potential to calculate most accurately the dose in the heterogeneous lung medium at the interface with the lung wall. The lung dose was investigated in Monaco to determine the level of sparing relative to that calculated in Pinnacle3.

Methods:

Five patients undergoing DIBH radiotherapy on an Elekta Versa HD linear accelerator in conjunction with the Catalyst C‐RAD surface imaging system were planned using Phillips Pinnacle3. Free breathing plans were also created to clinically assure a benefit. Both plans were re‐calculated in Monaco to determine if there were any significant differences. The mean heart dose, mean left lung, and mean total lung dose were compared in addition to the V20 for left and both lungs. Dose was calculated as dose to medium as well as dose to water with a statistical precision of 0.7%.

Results:

Mean lung dose was significantly different (p < 0.003) between the two calculations for both DIBH (11.6% higher in Monaco) and free breathing (14.2% higher in Monaco). V20 was also higher in Monaco (p < 0.05) for DIBH (5.7% higher) and free breathing (4.9% higher). The mean heart dose was not significantly different between the dose calculations for either DIBH or free breathing. Results were no more than 0.1% different when calculated as dose to water.

Conclusion:

The use of Monte Carlo can provide insight on the lung dose for both free breathing and DIBH techniques for whole breast irradiation. While the sparing (dose reductions with DIBH as compared to free breathing) is equivalent for either planning system, the lung doses themselves are higher when calculated with Monaco.
SU‐F‐T‐416: Dosimetric Comparison of Coplanar and Non‐Coplanar IMRT Plans for Peripheral Lung Lesion
Authors: Kang J , Zhang S , Philbrook S , Paul S , Wang B
Published: July 2016

Purpose:

The purpose of this study was to compare dosimetric parameters of treatment plans between coplanar and non‐coplanar techniques for treating peripheral lung lesions.

Methods:

The planning CT scans of 6 patients in supine positions were used in this study. The size of the PTV ranges from 163 c.c. to 782 c.c.. The locations of PTV are mostly at the peripheral of Lung, some spreading to the mediastinum. For each patient, we generated two IMRT plans, one with and the other without non‐coplanar beams. The non‐coplanar beams were carefully selected so that the beams would never exit patient bodies through the contralateral lung. The IMRT plans were generated with Pinnacle 9.8 treatment planning software. The IMRT optimization objectives were kept the same for the corresponding pairs of plans. All plans were normalized such that 95% of PTV receives the prescription dose (full dose).

Results:

The conformity index (mean±standard deviation of the mean) is 1.49±0.14 and 1.58±0.23 for the coplanar and noncoplanar plans, respectively. The heterogeneity index (mean±standard deviation of the mean) is 7.74 ±2.33 and 6.34±1.40 for the coplanar and non‐coplanar plans, respectively. The maximum heart dose is 60.94±6.22 and 60.42±7.21 Gy, and mean heart dose is 10.22 ±7.57, 9.07 ±6.32 Gy, for the coplanar and non‐coplanar plans, respectively. The ipsilateral lung V20 is 48.0%±2.4% and 47.5%±3.3%, and V5 is 68.2%±10.0% and 69.1%±7.3%, for the coplanar and noncoplanar plans, respectively. Furthermore, with the non‐coplanar beam arrangement, the contralateral lung V20 was reduced from 3.3%±3.7% to 1.3%±0.8%, and the contralateral Lung V5 is reduced significantly from 65.6%±9.3% to 33.5%±20.9% (p value =0.008).

Conclusion:

The IMRT plans with non‐coplanar beam arrangement could reduce the exit dose to the contralateral lung, and therefore reduce the contralateral lung V5 significantly. This method is especially helpful while the lung lesion doesn't have a symmetric shape.
SU‐F‐T‐419: Evaluation of PlanIQ Feasibility DVH as Planning Objectives for Skull Base SBRT Patients
Authors: Jiang W , Wang H , Chi P
Published: July 2016

Purpose:

PlanIQ(Sun Nuclear Corporation) can provide feasibility measures on organs‐at‐risk(OARs) around the target based on depth, local anatomy density and energy of radiation beam used. This study is to test and evaluate PlanIQ feasibility DVHs as optimization objectives in the treatment planning process, and to investigate the potential to use them in routine clinical cases to improve planning efficiency.

Methods:

Two to three arcs VMAT Treatment plans were generated in Pinnacle based on PlanIQ feasibility DVH for six skull base patients who previously treated with SBRT. The PlanIQ feasibility DVH for each OAR consists of four zones – impossible (at 100% target coverage), difficult, challenging and probable. Constrains to achieve DVH in difficult zone were used to start plan optimization. Further adjustment was made to improve coverage. The plan DVHs were compared to PlanIQ feasibility DVH to assess the dose received by 0%(D0), 5%(D5), 10%(D10) and 50%(D50) of the OAR volumes.

Results:

A total of 90 OARs were evaluated for 6 patients (mean 15 OARs, range 11–18 OARs). We used >98% PTV coverage as planning goal since it's difficult to achieve 100% target coverage. For the generated plans, 96.7% of the OARs achieved D0 or D5 within difficult zone or impossible zone (ipsilateral OARs 93.5%, contralateral OARs 100%), while 90% and 65.6% of the OARs achieved D10 and D50 within difficult zone, respectively. Seventeen of the contralateral and out of field OARs achieved DVHs in impossible zone. For OARs adjacent or overlapped with target volume, the D0 and D5 are challenging to be optimized into difficult zone. All plans were completed within 2–4 adjustments to improve target coverage and uniformity.

Conclusion:

PlanIQ feasibility tool has the potential to provide difficult but achievable initial optimization objectives and therefore reduce the planning time to obtain a well optimized plan.
SU‐F‐T‐429: Craniospinal Irradiation by VMAT Technique: Impact of FFF Beam and High Resolution MLC On Plan Quality
Authors: Ganesh T , Sarkar B , Munshi A , Mohanti B
Published: July 2016

Purpose:

Objective of this study was to evaluate the impact of using flattening filter free (FFF) beam with 0.5 cm multileaf collimator (MLC) leaves over conventional flattened beam with 1 cm leaf width MLC on the treatment plan quality in cranio‐spinal irradiation (CSI).

Methods:

For five medulloblastoma cases (3 males and 2 females), who were previously treated by volumetric modulated arc therapy (VMAT) technique using conventional flattened beam shaped by 1 cm width MLC leaves, four test plans were generated and compared against the delivered plan. These retrospective plans consisted of four different combinations of flattened and FFF beams from Elekta's Agility treatment head with 0.5 cm width MLC leaves. Sparing of organs at risks (OAR) in terms of dose to 5%, 50%, 75% and 90% volumes, mean and maximum dose were evaluated.

Results:

All plans satisfied the planning objective of covering 95% of PTV by at least 95% of prescription dose. Marginal variation of dose spillage was observed between different VMAT plans at very low dose range (1–5 Gy). Variation in dose statistics for PTVs and OARs were within 1% or 1 Gy. Amongst the five plans, the plan with flattened beam with 1 cm MLC had the highest number of MUs, 2.13 times higher than the plan with Agility MLC with FFF beam that had the least number of MUs. No statistically significant difference (p≥0.05) was observed between the reference plan and the retrospectively generated plans in terms of PTV coverage, cold spot, hot spot and organ at risk doses.

Conclusion:

In the treatment of CSI cases by VMAT technique, FFF beams and/or finer width MLC did not exhibit advantage over the flattened beams or wider MLC in terms of plan quality except for reduction in MUs.
SU‐F‐T‐438: A Practical Technique to Avoid the Radioactive Otitis Media in Whole Brain Radiotherapy
Authors: Duan J
Published: July 2016

Purpose:

Radioactive otitis media is a common complication in whole brain radiotherapy. In this study, we present a practical technique to avoid the injury for whole brain radiotherapy patients.

Methods:

For this study, 10 whole brain radiotherapy patients with planning CT were selected. For the target, 40Gy/20fractions was prescribed. In the treatment planning, two opposing lateral fields were used, from the left and right side of the patient. The MLC (0.5cm width) was used to shape the fields around the brain with a 10 mm margin to allow for the beam penumbra. For 5 patients, six leafs were positioned to block the auris media. For other patients, there were no leafs blocked to auris media according to the routine technique. The target coverage and the mean dose of the auris media were evaluated to assess the new technique in avoiding the radioactive otitis media.

Results:

The target coverage of new technique decreased by 1.7% (97.6%±1.1% vs. 99.3%±0.5%) compared routine technique. The mean dose of left auris media decreased by 79% (7.92 Gy±0.81Gy vs. 37.82 Gy±2.33Gy). The mean dose of right auris media decreased by 77% (8.8 Gy±0.93Gy vs. 38.4 Gy±2.65Gy). There was no difference for other OARs.

Conclusion:

An excellent sparing of the auris media is achievable while maintaining high coverage to the target volume. The simple technique to deliver whole brain may avoid the radioactive otitis media prospectively.
SU‐F‐T‐448: Use of Mixed Photon Energy Beam in Volumetric Modulated Arc Therapy (VMAT) Treatment Plan for Prostate Cancer
Authors: Manigandan D , Kumar M , Mohandas P , Puri A , Bhalla N
Published: July 2016

Purpose:

To study the impact of different photon beam combination during VMAT planning and treatment delivery.

Methods:

Five prostate patients with no nodal involvement were chosen for the study and only prostate was considered as target (7920cGy/44fractions). In each case, three different VMAT plans were generated with two arcs (200°–160°&160°–200°). First plan used only 6MV in both arcs (6X‐6X) and second utilized 6MV&15MV (6X‐15X), whereas third one used 15MV&15MV (15X‐15X). For consistency, all the plans were generated by the same planner using Monaco− treatment planning system (V5.1) for Elekta Synergy− linear accelerator with 1cm leaf‐width. For plan comparison, target mean dose, conformity index (CI)=Planning target volume (PTV) covered by 95% of prescription dose/PTV were analyzed. Mean doses of bladder, rectum, left femur and right femur were analyzed. Integral dose (liter‐Gray) to normal tissue (patient volume minus PTV), total monitor unit (MU) required to deliver a plan and gamma pass rate for each plan was analyzed.

Results:

The CI for PTV was 0.9937±0.0037, 0.9917±0.0033, and 0.9897±0.0048 for 6X‐6X, 6X‐15X and 15X‐15X, respectively. Mean dose to target slightly increases with the decrease of energy. Mean doses to bladder were 3546.23±692.13cGy, 3487.43±715.53cGy and 3504.40±683.1cGy for 6X‐6X, 6X‐15X and 15X‐15X, respectively. Mean doses to rectum were 4294.60±309.5cGy, 4277.07±279.93cGy and 4290.77±379.07cGy. Mean doses to left femur were 2737.13±545.93cGy, 2668.67±407.12cGy and 2416.77±300.73cGy and mean doses to the right femur were 2682.70±460.81cGy, 2722.58±541.92cGy and 2598.57±481.83cGy. Higher Integral doses to normal tissue observed for 6X‐6X (163.06±24.6 Litre‐Gray) followed by 6X‐15X (154.35±24.74 Litre‐Gray) and 15X‐15X (145.84±26.03 Litre‐Gray). Average MU required to deliver one fraction was 680.75±72.09, 634.81±95.07 and 605.06±114.65. Gamma pass rates were 99.83±0.21, 99.53±0.27 and 99.2±0.20.

Conclusion:

6X‐15X VMAT plan offer dosimetric advantage compared to 6X‐6X in terms of lesser MU and integral dose without significant compromise in plan quality, where as in 15X‐15X, neutron contamination risk is relatively higher.
SU‐F‐T‐457: A Filmless Method for Measurement of Couch Translation Per Gantry Rotation and Couch Speed for Tomotherapy Using ArcCheck
Authors: Yang B , Wong R , Geng H , Lam W , Cheung K , Yu S
Published: July 2016

Purpose:

To develop a filmless methodology based on an ArcCheck for QA measurement of the couch translation per gantry rotation and couch speed of a Tomotherapy unit.

Methods:

Two test plans recommended by TG148 were chosen for this study. A helical plan with 1 cm field size opened the leaves for 180 degrees at the 2nd, 7th and 12th of total 13 rotations and was used to verify if the couch travelled the expected distance per gantry rotation. The other test plan was a static plan with the gantry at 0°, 1cm field width and constant couch movement speed of 0.5mm/s. It was used for couch speed measurement. The ArcCheck was isocentrically set up and recorded movie files which took a snapshot exposure every 50ms. Due to the spiral pattern of diodes distribution, when one of the diodes of the ArcCheck located at the beam center, the dose profile as measured by the row of diodes which surrounded the center diode should have a symmetrical pattern. We divided the profile into left half A and right half B. Then a shape parameter was defined as S=Σ|(A−B)|/Σ(A+B). By searching the local minimum of S parameter, the beam center at different time could be located. The machine trajectory log data were also collected and analyzed for comparison.

Results:

The mean value of measured couch translation and couch speed by ArcCheck had less than 0.05% deviation from the planned values. For couch speed measurement, our result showed a mean value of 0.5002 with an uncertainty ±0.0031, which agreed very well with both the plan setting of 0.5 mm/s and the machine log data of 0.5005 mm/s.

Conclusion:

Couch translation measured using ArcCheck is accurate and comparable to the film‐based measurement. This filmless method also provides a convenient and independent way for measuring couch speed.
SU‐F‐T‐469: A Clinically Observed Discrepancy Between Image‐Based and Log‐ Based MLC Position
Authors: Neal B , Ahmed M , Siebers J
Published: July 2016

Purpose:

To present a clinical case which challenges the base assumption of log‐file based QA, by showing that the actual position of a MLC leaf can suddenly deviate from its programmed and logged position by >1 mm as observed with real‐time imaging.

Methods:

An EPID‐based exit‐fluence dosimetry system designed to prevent gross delivery errors was used in cine mode to capture portal images during treatment. Visual monitoring identified an anomalous MLC leaf pair gap not otherwise detected by the automatic position verification. The position of the erred leaf was measured on EPID images and log files were analyzed for the treatment in question, the prior day's treatment, and for daily MLC test patterns acquired on those treatment days. Additional standard test patterns were used to quantify the leaf position.

Results:

Whereas the log file reported no difference between planned and recorded positions, image‐based measurements showed the leaf to be 1.3±0.1 mm medial from the planned position. This offset was confirmed with the test pattern irradiations.

Conclusion:

It has been clinically observed that log‐file derived leaf positions can differ from their actual positions by >1 mm, and therefore cannot be considered to be the actual leaf positions. This cautions the use of log‐based methods for MLC or patient quality assurance without independent confirmation of log integrity. Frequent verification of MLC positions through independent means is a necessary precondition to trusting log file records. Intra‐treatment EPID imaging provides a method to capture departures from MLC planned positions.

Work was supported in part by Varian Medical Systems.
SU‐F‐T‐471: Simulated External Beam Delivery Errors Detection with a Large Area Ion Chamber Transmission Detector
Authors: Hoffman D , Dyer B , Kumaran Nair C , Stern R , Benedict S , Davis UC
Published: July 2016

Purpose:

The Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large‐area, linac‐mounted ion chamber used to monitor photon fluence during patient treatment. Our previous work evaluated the change of the ion chamber's response to deviations from static 1×1 cm2 and 10×10 cm2 photon beams and other characteristics integral to use in external beam detection. The aim of this work is to simulate two external beam radiation delivery errors, quantify the detection of simulated errors and evaluate the reduction in patient harm resulting from detection.

Methods:

Two well documented radiation oncology delivery errors were selected for simulation. The first error was recreated by modifying a wedged whole breast treatment, removing the physical wedge and calculating the planned dose with Pinnacle TPS (Philips Radiation Oncology Systems, Fitchburg, WI). The second error was recreated by modifying a static‐gantry IMRT pharyngeal tonsil plan to be delivered in 3 unmodulated fractions. A radiation oncologist evaluated the dose for simulated errors and predicted morbidity and mortality commiserate with the original reported toxicity, indicating that reported errors were approximately simulated. The ion chamber signal of unmodified treatments was compared to the simulated error signal and evaluated in Pinnacle TPS again with radiation oncologist prediction of simulated patient harm.

Results:

Previous work established that transmission detector system measurements are stable within 0.5% standard deviation (SD). Errors causing signal change greater than 20 SD (10%) were considered detected. The whole breast and pharyngeal tonsil IMRT simulated error increased signal by 215% and 969%, respectively, indicating error detection after the first fraction and IMRT segment, respectively.

Conclusion:

The transmission detector system demonstrated utility in detecting clinically significant errors and reducing patient toxicity/harm in simulated external beam delivery. Future work will evaluate detection of other smaller magnitude delivery errors.
SU‐F‐T‐477: Investigation of DEFGEL Dosimetry Using MRI
Authors: Matrosic C , McMillan A , Holmes J , Bednarz B , Culberson W
Published: July 2016

Purpose:

The DEFGEL dosimeter/phantom allows for the measurement of 3D dose distributions while maintaining tissue equivalence and deformability. Although DEFGEL is traditionally read out with optical CT, the use of MRI would permit the measurement of 3D dose distributions in optically interfering configurations, like while embedded in a phantom. To the knowledge of the authors, this work is the first investigation that uses MRI to measure dose distributions in DEFGEL dosimeters.

Methods:

The DEFGEL (6%T) formula was used to create 1 cm thick, 4.5 cm diameter cylindrical dosimeters. The dosimeters were irradiated using a Varian Clinac 21EX linac. The MRI based transverse relaxation rate (R2) of the gel was measured in a central slice of the dosimeter with a Spin‐Echo (SE) pulse sequence on a 3T GE SIGNA PET/MR scanner. The R2 values were fit to a monoexponential dose response equation using in‐house software (MATLAB).

Results:

The data was well fit using a monoexponential fit for R2 as a function of absorbed dose (R2 = 0.9997). The fitting parameters of the monoexponential fit resulted in a 0.1229 Gy−1s−1 slope. The data also resulted in an average standard deviation of 1.8% for the R2 values within the evaluated ROI.

Conclusion:

The close fit for the dose response curve shows that a DEFGEL based dosimeter can be paired with a SE MRI acquisition. The Type A uncertainty of the MRI method shows adequate precision, while the slope of the fit curve is large enough that R2 differences between different gel doses are distinguishable. These results suggest that the gel could potentially be used in configurations where an optical readout is not viable, such as measurements with the gel dosimeter positioned inside larger or optically opaque phantoms.

This work is partially funded by NIH grant R01CA190298.
SU‐F‐T‐478: Effect of Deconvolution in Analysis of Mega Voltage Photon Beam Profiles
Authors: Muthukumaran M , Manigandan D , Murali V , Chitra S , Vikraman S , Ganapathy K
Published: July 2016

Purpose:

To study and compare the penumbra of 6 MV and 15 MV photon beam profiles after deconvoluting different volume ionization chambers.

Methods:

0.125cc Semi‐Flex chamber, Markus Chamber and PTW Farmer chamber were used to measure the in‐plane and cross‐plane profiles at 5 cm depth for 6 MV and 15 MV photons. The profiles were measured for various field sizes starting from 2×2 cm till 30×30 cm. PTW TBA scan software was used for the measurements and the “deconvolution” functionality in the software was used to remove the volume averaging effect due to finite volume of the chamber along lateral and longitudinal directions for all the ionization chambers. The predicted true profile was compared and the change in penumbra before and after deconvolution was studied.

Results:

After deconvoluting the penumbra decreased by 1 mm for field sizes ranging from 2 × 2 cm till 20 x20 cm. This is observed for along both lateral and longitudinal directions. However for field sizes from 20 × 20 till 30 ×30 cm the difference in penumbra was around 1.2 till 1.8 mm. This was observed for both 6 MV and 15 MV photon beams. The penumbra was always lesser in the deconvoluted profiles for all the ionization chambers involved in the study. The variation in difference in penumbral values were in the order of 0.1 till 0.3 mm between the deconvoluted profile along lateral and longitudinal directions for all the chambers under study. Deconvolution of the profiles along longitudinal direction for Farmer chamber was not good and is not comparable with other deconvoluted profiles.

Conclusion:

The results of the deconvoluted profiles for 0.125cc and Markus chamber was comparable and the deconvolution functionality can be used to overcome the volume averaging effect.
SU‐F‐T‐480: Evaluation of the Role of Varian Machine Performance Check (MPC) in Our Daily QA Routine
Authors: Juneja B , Gao S , Balter P , Nitsch P
Published: July 2016

Purpose:

(A) To assess the role of Varian MPC in our daily QA routine, and (B) evaluate the accuracy and precision of MPC.

Methods:

The MPC was performed weekly, for five months, on a Varian TrueBeam for five photon (6x, 10x, 15x, 6xFFF, and 10xFFF) and electron (6e, 9e, 12e, 16e, and 20e) energies. Output results were compared to those determined with an ionization chamber (TN30001, PTW‐Freiburg) in plastic and a daily check device (DQA3, Sun Nuclear). Consistency of the Mechanical measurements over five months was analyzed and compared to monthly IsoCal results.

Results:

The MPC randomly showed large deviations (3–7%) that disappeared upon reacquisition. The MPC output closely matched monthly ion chamber and DQA3 measurements. The maximum and mean absolute difference between monthly and MPC was 1.18% and 0.28±0.21% for all energies. The maximum and mean absolute difference between DQA3 and MPC was 3.26% and 0.85±0.61%. The results suggest the MPC is comparable to the DQA3 for measuring output. The DQA3 provides wedge output, flatness, symmetry, and energy constancy checks, which are missing from the current implementation of the MPC. However, the MPC provides additional mechanical tests, such as size of the radiation isocenter (0.33±0.02 mm) and its coincidence with MV and kV isocenters (0.17±0.05 and 0.21±0.03 mm). It also provides positional accuracy of individual jaws (maximum σ, 0.33mm), all the MLC leaves (0.08mm), gantry (0.05°) and collimator (0.13°) rotation angles, and couch positioning (0.11mm) accuracy. MPC mechanical tests could replace our current daily on‐board imaging QA routine and provide some additional QA not currently performed.

Conclusion:

MPC has the potential to be a valuable tool that facilitates reliable daily QA including many mechanical tests that are not currently performed. This system can add to our daily QA, but further development would be needed to fully replace our current Daily QA device.
SU‐F‐T‐481: Physics Evaluation of a Newly Released InCise™ Multileaf Collimator for CyberKnife M6™ System
Authors: Wang L , Chin E , Lo A
Published: July 2016

Purpose:

This work reports the results of the physics evaluation of a newly released InCise™2 Multileaf Collimator (MLC) installed in our institution.

Methods:

Beam property data was measured with unshielded diode and EBT2 films. The measurements included MLC leaf transmission, beam profiles, output factors and tissue‐phantom ratios. MLC performance was evaluated for one month after commissioning. Weekly Garden Fence tests were performed for leaf / bank positioning in standard (A/P) and clinically relevant non‐standard positions, before and after MLC driving exercises of 10+ minutes. Daily Picket Fence test and AQA test, End‐to‐End tests and dosimetric quality assurance were performed to evaluate the overall system performance.

Results:

All measurements including beam energy, flatness and symmetry, were within manufacture specifications. Leaf transmission was 0.4% <0.5% specification. The values of output factors ranged from 0.825 (7.6 mm × 7.5 mm) to 1.026 (115.0 mm × 100.1 mm). Average beam penumbra at 10 cm depth ranged from 2.7mm/2.7mm(7.6 mm × 7.5 mm) to 6.0 mm/6.2mm(84.6 mm × 84.7 mm). Slight penumbra difference (<10% from average penumbra for fields >20 mm) was observed in the direction perpendicular to leaf motion due to the tilting of the leaf housing. Mean leaf position offsets was −0.08±0.07mm and −0.13 ± 0.08 for X1 and X2 leaf banks in 13 Garden Fence tests. No significant difference on average leaf positioning offsets was observed between different leaf orientations and before/after MLC driving exercises. Six End‐to‐End tests showed 0.43±0.23mm overall targeting accuracy. Picket‐Fence and AQA showed stable performance of MLC during the test period. Dosimetric point dose measurements for test cases agreed with calculation within 3%. All film measurements on relative dose had Gamma (2%, 2mm) passing rate of >95%.

Conclusion:

The Incise™2 MLC for CyberKnife M6™ was proven to be accurate and reliable, and it is currently in clinical use.

Stanford was one of the physics evaluation sites for the newly released InCise 2 MLC for Accuray Inc.
SU‐F‐T‐483: An Investigation into the Effect of Varying Temperature On PTP Corrections in TG‐51
Authors: Neba N , Mensah‐Brown N , Howlin T , Howard S , Saleh H
Published: July 2016

Purpose:

To determine the effect on machine output calibration, following the TG‐51 protocol, as the water temperature increasingly deviates from Standard temperature (22°C)

Methods:

A water tank was set up according to TG‐51 protocol. Two sets of measurements were taken and the pressure recorded. The measurements consisted of readings at different temperatures. In the first set, P(ion), P(pol), and P(elec) were assumed constant while they were accounted for in the second. The outputs were normalized to that at 22°C. The first readings were taken after the chamber had equilibrated to the water temperature. The water temperature was then raised at intervals of approximately 1–2°C and measurements taken after 5–10 minutes (as per TG‐51).

Results:

In both measurements, P(TP) was corrected for using equation 10 in TG‐51. The normalized output is expected to be 1.0 with all corrections accounted for. However as the water temperature was gradually increased, the normalized output also varied. The largest discrepancy observed while not accounting for the factors, P(ion), P(pol), and P(elec) was 1.1%, and while accounting for these factors, the largest discrepancy was 1.0%.

Conclusion:

Our results show discrepancies in output measured at different temperatures. Although a lack of equilibrium may explain these discrepancies, it is not as easy to ensure true equilibrium. It is also possible that these discrepancies are real and related to the inherent venting mechanism of the chamber. However, more work would need to be done to investigate this further and to determine if this effect is true across all Exradin and/or other manufacturer chambers. Most importantly, the physicist should perform TG‐51 at room temperature and pressure to better ensure thermal equilibrium. If this is not currently being done, and not enough time is given, especially when the water temperature is “significantly” different from 22°C, the calibration will be less accurate.