bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐307: Peripheral Dose Comparison Between Static and Dynamic Jaw Tracking On a High Definition MLC System
Authors: Perez‐Andujar A , Cheung J , Chuang C
Published: July 2016

Purpose:

To investigate the effect of dynamic and static jaw tracking on patient peripheral doses.

Materials and Methods:

A patient plan with a large sacral metastasis (volume 800cm3, prescription 600cGyx5) was selected for this study. The plan was created using 2‐field RapidArc with jaw tracking enabled (Eclipse, V11.0.31). These fields were then exported and edited in MATLAB with static jaw positions using the control point with the largest field size for each respective arc, but preserving the optimized leaf sequences for delivery. These fields were imported back into Eclipse for dose calculation and comparison and copied to a Rando phantom for delivery analysis. Points were chosen in the phantom at depth and on the phantom surface at locations outside the primary radiation field, at distances of 12cm, 20cm, and 30cm from the isocenter. Measurements were acquired with OSLDs placed at these positions in the phantom with both the dynamic and static jaw deliveries for comparison. Surface measurements included an additional 1cm bolus over the OSLDs to ensure electron equilibrium.

Results:

The static jaw deliveries resulted in cumulative jaw‐defined field sizes of 17.3% and 17.4% greater area than the dynamic jaw deliveries for each arc. The static jaw plan resulted in very small differences in calculated dose in the treatment planning system ranging from 0–16cGy. The measured dose differences were larger than calculated, but the differences in absolute dose were small. The measured dose differences at depth (surface) between the two deliveries showed an increase for the static jaw delivery of 2.2%(11.4%), 15.6%(20.0%), and 12.7%(12.7%) for distances of 12cm, 20cm, and 30cm, respectively. Eclipse calculates a difference of 0–3.1% for all of these points. The largest absolute dose difference between all points was 6.2cGy.

Conclusion:

While we demonstrated larger than expected differences in peripheral dose, the absolute dose differences were small.
SU‐F‐T‐311: Comparison of Measurements From Two Diode Array QA Devices to Deep Point Dose Measurements with Two Treatment Planning Model Settings for Brain VMAT SRT Patient‐Specific QA
Authors: Weethee B , Cheung J , Perez‐Andujar A , Sudhyadhom A , Chen J
Published: July 2016

Purpose:

To investigate the sensitivity of traditional gamma‐index‐based analysis using diode arrays to detect significant dosimetric errors in patientspecific measurements for VMAT brain SRT plans.

Methods:

Quality assurance measurements were performed using an ion chamber and two different diode array devices for four brain SRT treatment plans. All cases were planned with Eclipse AAA RapidArc using 6MV VMAT for a TrueBeam STx. Ion chambers measurements were performed with a PinPoint 3D micro‐ion chamber in both the Standard Imaging Stereotactic Dose Verification (SI) Phantom and in the ArcCheck (AC) cavity plug. Point dose measurements were taken at isocenter within the target. Array measurements were acquired with the ArcCheck and gantry‐mounted MapCheck (MC) and assessed using the SNC patient software with a 3%/3mm absolute dose gamma‐index analysis with global normalization and a 10% dose threshold. Calculations and their corresponding measurements were performed and compared before and after a dynamic leaf gap (DLG) adjustment.

Results:

The measured doses at isocenter dropped from 6.3%–8.7% in the SI phantom and 4.0%–9.3% for AC down to −0.1%–1.1% in the SI phantom and 0.8%–2.9% in the AC after adjusting the DLG. However, the cumulative dose differences to MC's central diode ranged −2.0%–1.9% before the DLG adjustment and were −7.7%–0.2% afterwards. Similarly, the gamma‐index analysis results for MC were found to be 94.1%–100% before the DLG adjustment and 94.4%–100% afterwards. The gamma‐index results from AC were 72.9%–98.7% before and 95.9%–99.7% after.

Conclusion:

Our data suggest that traditional passing criteria using gantry‐mounted MapCheck may not have the sensitivity to catch significant dose errors introduced by DLG settings. ArcCheck measurements did flag some dose differences, however there appears to be a possibility that dose discrepancies may not always be observed for VMAT SRT treatments, and point dose measurements are recommended for verification.
SU‐F‐T‐317: Skin Exposure Outside the Treatment Field During Treatment of Breast Cancer with Tri‐Co‐60 MR‐IGRT System
Authors: Park J , Kim J , Park S , Kim S , Shin K
Published: July 2016

Purpose:

To investigate exposure outside the treatment field when treating breast cancer with tri‐Co‐60 magnetic resonance (MR) image guided radiation therapy (IGRT) system.

Methods:

A total of 7 patients who treated with accelerated partial breast irradiation (APBI) technique were selected prospectively for this study (prescription dose = 38.5 Gy in 10 fractions). Every patient treated with two plans, one was an initial plan and the other was an adaptive plan generated after finishing 5 fractions (a total of 14 plans). Every plan was calculated with and without magnetic field in the treatment planning system. The EBT3 films were attached on the front and the back of 1 cm bolus, and then it was placed on the patient body vertically to cover patient's jaw and shoulder. After measurements, the maximum point dose and the mean dose of whole area of EBT3 film were acquired.

Results:

In the treatment plan with magnetic field, low dose stream outside the patient body was observed, almost reaching the patient's jaw or shoulder, while it was not observed without magnetic field. The average values of the measured maximum and mean doses at the front of bolus were 30.1 ± 11.1 cGy (7.8% of the daily dose) and 14.7 ± 3.3 cGy (3.8%), respectively. At the back of bolus, those values were 6.0 ± 1.9 cGy (1.6%) and 5.1 ± 1.6 cGy (1.3%), respectively. The largest maximum dose at the front was 54.2 cGy (14.1%) while it was 20.7 cGy (5.4%) at the back. The average decrease of the maximum dose by the bolus was 24.0 ± 11.0 cGy.

Conclusion:

Due to magnetic field, dose stream outside the patient body can be generated during breast cancer treatment with the tri‐Co‐60 MR‐IGRT system. Since this dose stream irradiated skin outside the treatment field, it should be shielded.

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015R1C1A1A01054192).
SU‐F‐T‐318: Sensitivity and Stability of OSLDs with Filled Deep Electron/hole Traps Under Pre‐Irradiation and Bleaching Conditions
Authors: Kim J , Park S , Lee H , Kim H , Choi C , Park J
Published: July 2016

Purpose:

This work evaluated the characteristics of optically stimulated luminescence dosimeters (OSLDs) with fully filled deep electron/hole traps (OSLDfull) with the bleaching conditions according to the accumulated dose.

Methods:

The OSLDs were first pre‐irradiated with a Co‐60 gamma ray at more than 5 kGy, so as to fill the deep electron and hole traps. Using a 6‐MV beam, the OSLDfull characteristics were investigated in terms of the full bleaching, fading, dose linearity, and dose sensitivity obtained in response to the accumulated dose values. To facilitate a comparison of the dose sensitivity, OSLDs with un‐filled deep electron/hole traps (OSLDempty) were investigated in the same manner. A long‐pass filter was used to exclude bleaching‐source wavelengths of less than 520 nm. Various bleaching time and wavelength combinations were used in order to determine the optimal bleaching conditions for the OSLD full.

Results:

The fading for the OSLDfull exhibited stable signals after 8 min, for both 1‐ and 10‐Gy. For 4‐h bleaching time and an unfiltered bleaching device, the supralinear index values for the OSLDfull were 1.003, 1.002, 0.999, and 1.001 for doses of 2, 4, 7, and 10 Gy, respectively. For a 65‐Gy accumulated dose with a 5‐Gy fraction, no variation in dose sensitivity was obtained for the OSLDfull, within a standard deviation of 0.85%, whereas the OSLDempty dose sensitivity decreased by approximately 2.3% per 10 Gy. The filtered bleaching device yielded a highly stable sensitivity for OSLDfull, independent of bleaching time and within a standard deviation of 0.71%, whereas the OSLDempty dose sensitivity decreased by approximately 4.2% per 10 Gy for an accumulated dose of 25 Gy with a 5‐Gy fraction.

Conclusion:

Under the bleaching conditions determined in this study, clinical dosimetry with OSLDfull is highly stable, having an accuracy of 1% with no change in dose sensitivity or linearity at clinical doses.

This work was supported by a National Research Foundation of Korea (NRF) grant, funded by the Korea government (MISP) (No. 2014M2B2A4031164), and by the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (HI14C3459).
SU‐F‐T‐320: Assessing Placement Error of Optically Stimulated Luminescent in Vivo Dosimeters Using Cone‐Beam Computed Tomography
Authors: Riegel A , Tariq M , Gomez C , Klein E
Published: July 2016

Purpose:

Optically‐stimulated luminescent dosimeters (OSLDs) are increasingly utilized for in vivo dosimetry of complex radiation delivery techniques such as intensity‐modulated radiation therapy (IMRT) and volumetric‐modulated arc therapy (VMAT). Evaluation of clinical uncertainties such as placement error has not been performed. This work retrospectively investigates the magnitude of placement error using conebeam computed tomography (CBCT) and its effect on measured/planned dose agreement.

Methods:

Each OSLD was placed at a physicist‐designated location on the patient surface on a weekly basis. The location was given in terms of a gantry angle and two‐dimensional offset from central axis. The OSLDs were placed before daily image guidance. We identified 77 CBCTs from 25 head‐and‐neck patients who received IMRT or VMAT, where OSLDs were visible on the CT image. Grossly misplaced OSLDs were excluded (e.g. wrong laterality). CBCTs were registered with the treatment plan and the distance between the planned and actual OSLD location was calculated in two dimensions in the beam's eye view. Distances were correlated with measured/planned dose percent differences.

Results:

OSLDs were grossly misplaced for 5 CBCTs (6.4%). For the remaining 72 CBCTs, average placement error was 7.0±6.0 mm. These errors were not correlated with measured/planned dose percent differences (R2=0.0153). Generalizing the dosimetric effect of placement errors may be unreliable.

Conclusion:

Correct placement of OSLDs for IMRT and VMAT treatments is critical to accurate and precise in vivo dosimetry. Small placement errors could produce large disagreement between measured and planned dose. Further work includes expansion to other treatment sites, examination of planned dose at the actual point of OSLD placement, and the influence of imageguided shifts on measured/planned dose agreement.
SU‐F‐T‐321: The Effect of an Electromagnetic Array Used for Patient Localization and Tumor Tracking On OSLD in Vivo Dosimetry
Authors: Rea A , Kuruvilla A , Gill G , Riegel A , Klein E
Published: July 2016

Purpose:

The purpose of this study was to observe the effect of an electromagnetic array used for patient localization and tumor tracking on optically‐stimulated luminescent in‐vivo dosimetry.

Methods:

A linear accelerator equipped with four photon energies was used to irradiate optically stimulated luminescent dosimeters (OSLDs) at the respective dmax depths and in the buildup region, with and without the presence of an electromagnetic array used for tumor tracking and patient localization. The OSLDs were placed on solid water slabs under 5 mm bolus and on each face of an octagonal phantom, and irradiated using both static beam and arc geometry, with and without the electromagnetic array under our setup. The electromagnetic array was placed 6 cm above the phantom to coincide with similar distances used during patient treatment. Ionization chamber measurements in a water phantom were also taken initially for comparison with the simple geometry OSLD measurements and published data.

Results:

Under simple geometry, a negligible change was observed at dmax for all energies when the electromagnetic array was placed over the setup. When measuring at five millimeter depth, increases of 1.3/3.1/16/18% were observed for energies 4X/6X/10X/15X respectively when the electromagnetic array was in place. Measurements using the octagonal phantom yielded scattered results for the lateral and posterior oblique fields, and showed increases in dose to the OSLDs placed on the anterior and lateral anterior faces of the phantom.

Conclusion:

Placing the electromagnetic array very close to the patient's surface acts as a beam spoiler in the buildup region (at 5 mm depth), which in turn causes an increase in the measured dose reading of the OSLD. This increase in dose is more pronounced when the OSLD is placed directly underneath the electromagnetic array than off to one side or the other.
SU‐F‐T‐324: Experimental Measurement of Optically Stimulated Luminescence Detectors in a MR‐IGRT Environment Toward Assessing Magnetic Field Effects On These Devices and Their Use as An In‐Vivo Dosimeter
Authors: Reilly M , Curcuru A , Yaddanapudi S , Green O
Published: July 2016

Purpose:

To characterize magnetic field effects on Optically Stimulated Luminescence Detectors (OSLDs) for use as an in‐vivo dosimeter in an MRIGRT machine.

Methods:

Landauer OSLD nano‐dots and the MicroStar II reader were used to measure and record OSLDs exposed in and on a solid water phantom in a 10.5 × 10.5 cm2 field, Co‐60, 0.32‐Tesla MR‐IGRT machine ‐ with and without the presence of the magnetic field. Two orthogonal gantry angles were considered to assess orientation effects on the OSLDs with respect to the incident angle of the radiation beam and magnetic field. The same OSLDs were then used (after readout and bleaching) when the magnetic field was restored.

Results:

The measured surface dose decreased by 14.1 ± 1.8% when magnetic field was 'on’ due to contamination electrons being swept away by the field. Doses at both 0.5 cm and 5 cm depth increased by 6.5 ± 0.9% and 8.8 ± 0.5% respectively when the magnetic field was present and the OSLDs oriented with their long axis parallel with the incident beam. This contrasts with an increased dose of 2.7 ± 1.1% when the magnetic field was present and the OSLDs were oriented with their long axis perpendicular to the incident beam.

Conclusion:

Previous works have shown that OSLDs have a dependence on beam incidence angle. Our current work suggests an additional dependence on the presence of the magnetic field when the beam is not perpendicular to the plane of the detector and this effect needs to be considered. Furthermore, the use of an in‐vivo dosimeter was shown to have no effect on image quality during the use of MR guidance. Future work will focus on the use of an electromagnet with a linear accelerator to further characterize these effects.
SU‐F‐T‐325: On the Use of Bolus in Dosimetry and Dose Reduction for Pacemaker and Defibrillator
Authors: Liu W , Zhu D , Trumpore S , Kenneth R , Higgins S , Nath R , Chen Z
Published: July 2016

Purpose:

Special attention is required in planning and administering radiation therapy to patients with cardiac implantable electronic devices (CIEDs), such as pacemaker and defibrillator. The range of dose to CIEDs that can induce malfunction is very large among CIEDs. Significant defects have been reported at dose as low as 0.15Gy. Failures causing discomfort have been reported at dose as low as 0.05Gy. Therefore, accurate estimation of dose to CIED and dose reduction are both important even if the dose is expected to be less than the often‐used 2Gy limit. We investigate the use of bolus in in vivo dosimetry for CIEDs.

Methods:

In our clinic, high‐energy beams (>10MV) are not used for patients with CIED due to neutron production. Solid water phantom measurements of out‐of‐field dose for a 6MV beam were performed using parallel plate chamber at different depth with and without 2cm bolus covering the chamber. In vivo dosimetry at skin surface above the pacemaker was performed with and without bolus for 3 patients with pacemaker <5cm from the field edge.

Results:

Chamber measured dose at depth ∼1 to 1.5cm below the skin surface, where the CIED is normally located, was reduced by ∼6% – 20% with bolus. The dose reduction became smaller at deeper depth. In vivo dosimetry at skin surface also yielded ∼20% – 60% lower dose when using bolus for the 3 patients. In general, TPS calculation underestimated the dose. The dose measured with bolus is closer to the dose at the depth of the pacemaker and less affected by contaminant electrons and linac head leakage.

Conclusion:

In vivo CIED dose measurements should be performed with 1 to 2cm bolus covering the dosimeter on the skin above the CIED for more accurate CIED dose estimation. The use of bolus also reduces the dose delivered to CIED.
SU‐F‐T‐393: Using Commercially Available Software to Prove That Providing Planning Objectives to the Planner Improves Plan Quality
Authors: Younan F , Arnold A , Patel S , Clouser E
Published: July 2016

Purpose:

Use commercially available software to evaluate whether providing planning objectives during the treatment planning process improves overall plan quality in head and neck cases

Methods:

The commercially available software, PlanIQ, was used to evaluate the plan quality of head and neck cases before and after the introduction of an inhouse developed evaluation tool, Integrated Clinical Information System (ICIS). Twenty patients were selected; ten from before the introduction of ICIS and ten that used ICIS during the treatment planning process. These plans only included oropharynx cases. All plans were two or three arc VMAT cases prescribed at two dose levels, 60 Gy and 54 Gy. A PlanIQ algorithm was created with the assistance of physician input. The algorithm consisted of seventy‐four PTV and OAR plan quality metrics and objectives. Each plan was scored based on meeting the objectives provided. Plans were then evaluated by looking at the Plan Quality Metric (PQM) and Adjusted Plan Quality Metric (APQM) score. The PQM score is the overall score which evaluated the treatment plan against the PlanIQ algorithm. The APQM score was customized to the patient‐specific feasibility analysis, adjusting the PQM scores to account for unique challenges like patient‐specific anatomical challenges.

Results:

After introducing ICIS into the workflow, PlanIQ scores improved. On average, target coverage remained the same (p>.05). Individual OAR sparing differed when looking at plans evaluated before ICIS versus plans created with the assistance of the ICIS template. PQM scores increased from 65.16% to 74.07% (p=.004), while the APQM scores increased from 78.26% to 84.05% (p=.008). Overall plan quality improved after providing planners with additional information during the treatment planning process.

Conclusion:

Overall plan quality improves when providing the treatment planner with additional information and guidance during the treatment planning process.
SU‐F‐T‐395: Evaluation of Best Dosimetry Achievable with VMAT and IMRT Treatment Techniques Targeting Borderline Resectable Pancreatic Cancer
Authors: Harpool K , Schnell E , Herman T , Ahmad S , De La Fuente Herman T
Published: July 2016

Purpose:

To determine from retrospective study the most appropriate technique for targeting small borderline operable pancreatic cancer surrounding blood vessels by evaluating the dosimetry and normal tissue sparing achievable using Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT).

Methods:

Treatment plans from ten patients who have undergone treatment with a prescribed dose of 4950 cGy, at 275 cGy per fraction, were analyzed. All plans were replanned using Eclipse TPS (Varian Medical Systems, Palo Alto, CA) with complementary VMAT or IMRT techniques to obtain paired data sets for comparison. The coverage to at least 95% of the planned target volume (PTV) was normalized to receive 100% of the prescription dose. The normal tissue constraints followed the quantitative analysis of normal tissue effects in the clinic (QUANTEC) guidelines and the organs at risks (OARs) were liver, kidneys, spinal cord and bowel. The plan evaluation was based on conformity index (CI), homogeneity index (HI), uniformity index (UI), DVH parameters, and student's‐t statistics (2 tails).

Results:

The VMAT technique delivered less maximum dose to the right kidney, left kidney, total kidney, liver, spinal cord, and bowel by 9.3%, 5.9%, 6.7%, 3.9%, 15.1%, 3.9%, and 4.3%, respectively. The averaged V15 for the total kidney was 10.21% for IMRT and 7.29% for VMAT. The averaged V20 for the bowel was 19.89% for IMRT and 14.06% for VMAT. On average, the CI for IMRT was 1.20 and 1.16 for VMAT (p = 0.20). The HI was 0.08 for both techniques (p = 0.91) and UI was 1.05 and 1.06 for IMRT and VMAT respectively (p = 0.59).

Conclusion:

Both techniques achieve adequate PTV coverage. Although VMAT techniques show better normal tissue sparing from excessive dose, no significant differences were observed. Slight discrepancies may rise from different versions of calculation algorithms.
SU‐F‐T‐398: Improving Radiotherapy Treatment Planning Using Dual Energy Computed Tomography Based Tissue Characterization
Authors: Tomic N , Bekerat H , Seuntjens J , Forghani R , DeBlois F , Devic S
Published: July 2016

Purpose:

Both kVp settings and geometric distribution of various materials lead to significant change of the HU values, showing the largest discrepancy for high‐Z materials and for the lowest CT scanning kVp setting. On the other hand, the dose distributions around low‐energy brachytherapy sources are highly dependent on the architecture and composition of tissue heterogeneities in and around the implant. Both measurements and Monte Carlo calculations show that improper tissue characterization may lead to calculated dose errors of 90% for low energy and around 10% for higher energy photons. We investigated the ability of dual‐energy CT (DECT) to characterize more accurately tissue equivalent materials.

Methods:

We used the RMI‐467 heterogeneity phantom scanned in DECT mode with 3 different set‐ups: first, we placed high electron density (ED) plugs within the outer ring of the phantom; then we arranged high ED plugs within the inner ring; and finally ED plugs were randomly distributed. All three setups were scanned with the same DECT technique using a single‐source DECT scanner with fast kVp switching (Discovery CT750HD; GE Healthcare). Images were transferred to a GE Advantage workstation for DECT analysis. Spectral Hounsfield unit curves (SHUACs) were then generated from 50 to 140‐keV, in 10‐keV increments, for each plug.

Results:

The dynamic range of Hounsfield units shrinks with increased photon energy as the attenuation coefficients decrease. Our results show that the spread of HUs for the three different geometrical setups is the smallest at 80 keV. Furthermore, among all the energies and all materials presented, the largest difference appears at high Z tissue equivalent plugs.

Conclusion:

Our results suggest that dose calculations at both megavoltage and low photon energies could benefit in the vicinity of bony structures if the 80 keV reconstructed monochromatic CT image is used with the DECT protocol utilized in this work.
SU‐F‐T‐401: Three‐Dimensional Conformal Planning Using Low‐Segment Multi‐Criteria Optimization for Hippocampal Avoidance Whole Brain Radiotherapy
Authors: Zhang X , Penagaricano J , Narayanasamy G , Griffin R , Maraboyina S , Paudel N , Peter C , Morrill S
Published: July 2016

Purpose:

Hippocampus avoidance whole brain radiotherapy (HA‐WBRT) has been shown to reduce the risk of neurocognitive dysfunction. This type of treatment has the potential of insurance company payment denial due to increased cost of intensity modulated radiotherapy (IMRT), while the accepted modality for WBRT is three‐dimensional conformal radiotherapy (3DCRT). The purpose of this study is to assess HA‐WBRT treatment plans using 3DCRT and multi‐criteria optimization (MCO) that meets the RTOG 0933 criteria.

Methods:

Ten patients with brain metastases at least 0.5cm away from the hippocampal avoidance region as defined in RTOG 0933 were selected in this study. HA‐WBRT treatment plans with MCO 3DCRT technique (MCO‐3D) was generated with beam arrangements and dose constraints following the RTOG 0933 guidelines. MCO‐3D plans were compared with plans using MCO IMRT techniques (MCO‐IMRT) with same beam arrangements and dose constraints. Evaluation parameters included D98% D2% and dose homogeneity index of PTV, and Dmax and D100% of the hippocampi. The OAR doses were also evaluated.

Results:

For MCO‐IMRT plans, PTV D2% and hippocampi Dmax and D100% met RTOG 0933 objectives in all ten patients (PTV D2%<37.5Gy; Hippocampi Dmax<16Gy and D100%<9Gy). One patient met the RTOG 0933 PTV D98% objective (PTV D98%>25Gy) and 9/10 patients met acceptable variation (PTV D98%<25Gy). For MCO‐3D plans, PTV D2% met RTOG 0933 objective for all patients; 1/10 patient for PTV D98% and 6/10 patients for Hippocampi Dmax and 7/10 patients for hippocampi D100% met RTOG 0933 objective. All the other patients met the RTOG 0933 acceptable variation requirement. (PTV D98%<25Gy; Hippocampi Dmax<17Gy and D100%<10Gy).

Conclusion:

All dosimetric parameters of MCO‐3D plans met the criteria of at least acceptable variation per RTOG 0933. This may be helpful in cases where there is denial of patient's medical insurance coverage due to the use of IMRT for HA‐WBRT.
SU‐F‐T‐403: Impact of Dose Reduction for Simulation CT On Radiation Therapy Treatment Planning
Authors: Liang Q , Shah P , Li S , Miyamoto C
Published: July 2016

Purpose:

To investigate the feasibility of applying ALARA principles to current treatment planning CT scans. The study aims to quantitatively verify lower dose scans does not alter treatment planning.

Method:

Gammex 467 tissue characterization phantom with inserts of 14 different materials was scanned at seven different mA levels (30∼300 mA). CT numbers of different inserts were measured. Auto contouring for bone and lung in treatment planning system (Pinnacle) was used to evaluate the effect of CT number accuracy from treatment planning aspect, on the 30 and 300 mA‐scanned images. A head CT scan intended for a 3D whole brain radiation treatment was evaluated. Dose calculations were performed on normal scanned images using clinical protocol (120 kVP, Smart mA, maximum 291 mA), and the images with added simulating noise mimicking a 70 mA scan. Plan parameters including isocenter, beam arrangements, block shapes, dose grid size and resolution, and prescriptions were kept the same for these two plans. The calculated monitor units (MUs) for these two plans were compared.

Results:

No significant degradation of CT number accuracy was found at lower dose levels from both the phantom scans, and the patient images with added noise. The CT numbers kept consistent when mA is higher than 60 mA. The auto contoured volumes for lung and cortical bone show 0.3% and 0.12% of differences between 30 mA and 300 mA respectively. The two forward plans created on regular and low dose images gave the same calculated MU, and 98.3% of points having <1% of dose difference.

Conclusion:

Both phantom and patient studies quantitatively verified low dose CT provides similar quality for treatment planning at 20–25% of regular scan dose. Therefore, there is the potential to optimize simulation CT scan protocol to fulfil the ALARA principle and limit unnecessary radiation exposure to non‐targeted tissues.
SU‐F‐T‐406: Verification of Total Body Irradiation Commissioned MU Lookup Table Accuracy Using Treatment Planning System for Wide Range of Patient Sizes
Authors: Lewis D , Chi P , Tailor R , Aristophanous M , Tung S
Published: July 2016

Purpose:

To verify the accuracy of total body irradiation (TBI) measurement commissioning data using the treatment planning system (TPS) for a wide range of patient separations.

Methods:

Our institution conducts TBI treatments with an 18MV photon beam at 380cm extended SSD using an AP/PA technique. Currently, the monitor units (MU) per field for patient treatments are determined using a lookup table generated from TMR measurements in a water phantom (75 × 41 × 30.5 cm3). The dose prescribed to an umbilicus midline point at spine level is determined based on patient separation, dose/ field and dose rate/MU. One‐dimensional heterogeneous dose calculations from Pinnacle TPS were validated with thermoluminescent dosimeters (TLD) placed in an average adult anthropomorphic phantom and also in‐vivo on four patients with large separations. Subsequently, twelve patients with various separations (17–47cm) were retrospectively analyzed. Computed tomography (CT) scans were acquired in the left and right decubitus positions from vertex to knee. A treatment plan for each patient was generated. The ratio of the lookup table MU to the heterogeneous TPS MU was compared.

Results:

TLD Measurements in the anthropomorphic phantom and large TBI patients agreed with Pinnacle calculated dose within 2.8% and 2%, respectively. The heterogeneous calculation compared to the lookup table agreed within 8.1% (ratio range: 1.014–1.081). A trend of reduced accuracy was observed when patient separation increases.

Conclusion:

The TPS dose calculation accuracy was confirmed by TLD measurements, showing that Pinnacle can model the extended SSD dose without commissioning a special beam model for the extended SSD geometry. The difference between the lookup table and TPS calculation potentially comes from lack of scatter during commissioning when compared to extreme patient sizes. The observed trend suggests the need for development of a correction factor between the lookup table and TPS dose calculations.
SU‐F‐T‐412: Spatiotemporal Distribution of Dose Rates in VMAT Plans
Authors: Mackeprang P , Volken W , Terribilini D , Frauchiger D , Klippel N , Zaugg K , Aebersold D M , Fix M K , Manser P
Published: July 2016

Purpose:

To assess dose rates in volumetric modulated arc therapy (VMAT) plans.

Methods:

For dose rate analysis, using Monte Carlo methods, dose distributions are calculated in sectors of consecutive DICOM control points and each multiplied with the MU‐rate obtaining dose rate distributions for every voxel at every time‐point during a treatment fraction. Dose rate distributions were calculated for a clinical head and neck, cranial (2 Gy fraction dose) and a SBRT liver treatment case (5 Gy per fraction). To assess optimizer influence on dose rate distributions, five conventionally fractionated head and neck cases were optimized using the progressive resolution optimizer (PRO) versions 2 and 3 (Varian Medical Systems, Palo Alto, CA).

Results:

Firstly, histograms of dose rates over the course of treatment delivery in volumes of interest were generated for the PTV and spine or brainstem of the clinical treatment plans. Secondly, dose rates were assessed as color wash overlay on top of CT slices, allowing the user to explore the dose rate variation over time. For the cases considered, dose rates were spread out over a continuous spectrum with a mean value in the lower half. PRO3 generated plans showed higher maximum dose rates compared to PRO2 (699.80 cGy/min vs. 543.46 cGy/min) and modulation of MU rates in blocks as opposed to gradual modulation.

Conclusion:

Calculation and visualization of dose rate distributions in VMAT have been performed. Dose rates in clinical relevant VMAT cases are spread out over a continuous spectrum with a mean in the lower part for both conventional and SBRT test cases. Different optimization algorithms may lead to substantially different dose rate distributions in the same cases. The development of the Swiss Monte Carlo Plan framework has been partially supported by Varian Medical Systems
SU‐F‐T‐421: Dosimetry Change During Radiotherapy and Dosimetry Difference for Rigid and Deformed Registration in the Mid‐Thoracic Esophageal Carcinoma
Authors: Tao C , Liu T , Chen J , Zhu J , Yin Y
Published: July 2016

Purpose:

This study aimed to analyze dosimetry changes during radiotherapy for the mid‐thoracic esophageal carcinoma, and investigate dosimetry difference between rigid and deformed registration.

Methods:

Twelve patients with primary middle thoracic esophageal carcinoma were selected randomly. Based on first CT scanning of each patient, plans‐o were generated by experience physicists. After 20 fractions treatment, the corresponding plans‐re were created with second CT scanning. And then, these two CT images were rigid and deformed registration respectively, and the dose was accumulated plan‐o with plan‐re. The dosimetry variation of these plans (plan‐o: with 30 fractions, plan‐rig: the accumulated dose with rigid registration and plan‐def: the accumulated dose with deformed registration) were evaluated by paired T‐test.

Results:

The V20 value of total lung were 32.68%, 30.3% and 29.71% for plan‐o, plan‐rig and plan‐def respectively. The mean dose of total lung was 17.19 Gy, 16.67 Gy and 16.51 Gy for plan‐o plan‐rig and plan‐def respectively. There were significant differences between plan‐o and plan‐rig or plan‐def for both V20 and mean dose of total lung (with p= 0.003, p= 0.000 for V20 and p=0.008, p= 0.000 for mean dose respectively). There was no significant difference between plan‐rig and plan‐def (with p=0.118 for V20 and p=0.384 for mean dose). The max dose of spinal‐cord was 41.95 Gy, 41.48 Gy and 41.4 Gy for plan‐o, plan‐rig and plan‐def respectively. There were no significant differences for the max dose of spinal‐cord between these plans.

Conclusion:

The target volume changes and anatomic position displacement of mid‐thoracic esophageal carcinoma should not be neglected in clinics. These changes would cause overdose in normal tissue. Therefore, it is necessary to have another CT scanning and re‐plan during the mid‐thoracic esophageal carcinoma radiotherapy. And the dosimetry difference between rigid and deformed fusions was not found in this study.
SU‐F‐T‐431: Dosimetric Validation of Acuros XB Algorithm for Photon Dose Calculation in Water
Authors: Kumar L , Yadav G , Kishore V , Bhushan M , Samuvel K , Suhail M
Published: July 2016

Purpose:

To validate the Acuros XB algorithm implemented in Eclipse Treatment planning system version 11 (Varian Medical System, Inc., Palo Alto, CA, USA) for photon dose calculation.

Methods:

Acuros XB is a Linear Boltzmann transport equation (LBTE) solver that solves LBTE equation explicitly and gives result equivalent to Monte Carlo. 6MV photon beam from Varian Clinac‐iX (2300CD) was used for dosimetric validation of Acuros XB. Percentage depth dose (PDD) and profiles (at dmax, 5, 10, 20 and 30 cm) measurements were performed in water for field size ranging from 2×2,4×4, 6×6, 10×10, 20×20, 30×30 and 40×40 cm2. Acuros XB results were compared against measurements and anisotropic analytical algorithm (AAA) algorithm.

Results:

Acuros XB result shows good agreement with measurements, and were comparable to AAA algorithm. Result for PDD and profiles shows less than one percent difference from measurements, and from calculated PDD and profiles by AAA algorithm for all field size. TPS calculated Gamma error histogram values, average gamma errors in PDD curves before dmax and after dmax were 0.28, 0.15 for Acuros XB and 0.24, 0.17 for AAA respectively, average gamma error in profile curves in central region, penumbra region and outside field region were 0.17, 0.21, 0.42 for Acuros XB and 0.10, 0.22, 0.35 for AAA respectively.

Conclusion:

The dosimetric validation of Acuros XB algorithms in water medium was satisfactory. Acuros XB algorithm has potential to perform photon dose calculation with high accuracy, which is more desirable for modern radiotherapy environment.
SU‐F‐T‐432: Magnetic Field Dose Effects for Various Radiation Beam Geometries for Patients Treated with Hypofractionated Partial Breast Irradiation
Authors: Lim‐Reinders S , Keller B , McCann C , Sahgal A , Lee J , Kim A
Published: July 2016

Purpose:

Hypofractionated partial breast irradiation (HPBI) is being used at our clinic to treat inoperable breast cancer patients who have advanced disease. We are investigating how these patients could benefit from being treated in an MRI‐linac, where real‐time daily MRI tumor imaging and plan adaptation would be possible. As a first step, this study evaluates the dosimetric impact of the magnetic field for different radiation beam geometries on relevant OARs.

Methods:

Five patients previously treated using HPBI were selected. Six treatment plans were generated for each patient, evaluating three beam geometries (VMAT, IMRT, 3DCRT) with and without B0=1.5 T. The Monaco TPS was used with the Elekta MRI‐Linac beam model, where the magnetic field is orthogonal to the radiation beam. All plans were re‐scaled to the same isocoverage with a prescription of 40Gy/5 to the PTV. Plans were evaluated for the effect of the magnetic field and beam modality on skin V3 0, lung V2 0 and mean heart dose.

Results:

Averaged over all patients, skin V3 0for 3DCRT was higher than VMAT and IMRT (by +22% and +21%, with B0‐ON). The magnetic field caused larger increases in skin V3 0for 3DCRT (+8%) than VMAT (+3%) and IMRT (+4%) compared with B0‐OFF. With B0‐ON, 3DCRT had a markedly lower mean heart dose than VMAT (by 538cGy) and IMRT (by 562cGy); for lung V2 0, 3DCRT had a marginally lower dose than VMAT (by −2.2%) and IMRT (also −2.2%). The magnetic field had minimal effect on the mean heart dose and lung V2 0 for all geometries.

Conclusion:

The decreased skin dose in VMAT and IMRT can potentially mitigate the effects of skin reactions for HPBI in an MRI‐linac. This study illustrated that more beam angles may result in lower skin toxicity and better tumor conformality, with the trade‐off of elevated heart and lung doses.

We are receiving funding support from Elekta
SU‐F‐T‐441: Dose Calculation Accuracy in CT Images Reconstructed with Artifact Reduction Algorithm
Authors: Ng C , Lee V , Chan S , Lee F , Ngan R
Published: July 2016

Purpose:

Accuracy of radiotherapy dose calculation in patients with surgical implants is complicated by two factors. First is the accuracy of CT number, second is the dose calculation accuracy. We compared measured dose with dose calculated on CT images reconstructed with FBP and an artifact reduction algorithm (OMAR, Philips) for a phantom with high density inserts. Dose calculation were done with Varian AAA and AcurosXB.

Methods:

A phantom was constructed with solid water in which 2 titanium or stainless steel rods could be inserted. The phantom was scanned with the Philips Brillance Big Bore CT. Image reconstruction was done with FBP and OMAR. Two 6 MV single field photon plans were constructed for each phantom. Radiochromic films were placed at different locations to measure the dose deposited. One plan has normal incidence on the titanium/steel rods. In the second plan, the beam is at almost glancing incidence on the metal rods. Measurements were then compared with dose calculated with AAA and AcurosXB.

Results:

The use of OMAR images slightly improved the dose calculation accuracy. The agreement between measured and calculated dose was best with AXB and image reconstructed with OMAR. Dose calculated on titanium phantom has better agreement with measurement. Large discrepancies were seen at points directly above and below the high density inserts. Both AAA and AXB underestimated the dose directly above the metal surface, while overestimated the dose below the metal surface. Doses measured downstream of metal were all within 3% of calculated values.

Conclusion:

When doing treatment planning for patients with metal implants, care must be taken to acquire correct CT images to improve dose calculation accuracy. Moreover, great discrepancies in measured and calculated dose were observed at metal/tissue interface. Care must be taken in estimating the dose in critical structures that come into contact with metals.
SU‐F‐T‐522: Dosimetric Study of Junction Dose in Double Isocenter Flatten and Flatten Filter Free IMRT and VMAT Plan Delivery
Authors: Samuvel K , Yadav G , Bhushan M , Tamilarasu S , Kumar L , Suhail M
Published: July 2016

Purpose:

To quantify the dosimetric accuracy of junction dose in double isocenter flattened and flatten filter free(FFF) intensity modulated radiation therapy(IMRT) and volumetric modulated arc therapy(VMAT) plan delivery using pelvis phantom.

Methods:

Five large field pelvis patients were selected for this study. Double isocenter IMRT and VMAT treatment plans were generated in Eclipse Treatment planning System (V.11.0) using 6MV FB and FFF beams. For all the plans same distance 17.0cm was kept between one isocenter to another isocenter. IMRT Plans were made with 7 coplanar fields and VMAT plans were made with full double arcs. Dose calculation was performed using AAA algorithms with dose grid size of 0.25 cm. Verification plans were calculated on Scanditronix Wellhofer pelvis slab phantom. Measurement point was selected and calculated, where two isocenter plan fields are overlapping, this measurement point was kept at distance 8.5cm from both isocenter. The plans were delivered using Varian TrueBeamTM machine on pelvis slab phantom. Point dose measurements was carried out using CC13 ion chamber volume of 0.13cm3.

Results:

The measured junction point dose are compared with TPS calculated dose. The mean difference observed was 4.5%, 6.0%, 4.0% and 7.0% for IMRT‐FB,IMRT‐FFF, VMAT‐FB and VMAT‐FFF respectively. The measured dose results shows closer agreement with calculated dose in Flatten beam planning in both IMRT and VMAT, whereas in FFF beam plan dose difference are more compared with flatten beam plan.

Conclusion:

Dosimetry accuracy of Large Field junction dose difference was found less in Flatten beam compared with FFF beam plan delivery. Even though more dosimetric studies are required to analyse junction dose for FFF beam planning using multiple point dose measurements and fluence map verification in field junction area.
SU‐F‐T‐535: An Android App and Windows Executable with GUI for the Monitor Unit Calculation in KV X‐Ray Therapy
Authors: Pearse J , Chow J
Published: July 2016

Purpose:

We created two applications, one for use on Android and one for use on Windows, to carry out monitor unit (MU) calculations. These applications carried out these long calculations quickly, while avoiding the potential for human error.

Methods:

A general formula for calculating MU for an orthovoltage x‐ray machine was used and implemented in two programs created for Android and Windows. The formula relies on the prescribed dose and fractionation. Other values the formula relies upon are relative exposure factor (REF) and backscatter factor (BSF). These factors are specific to each unit and head in use, and are measured and tabulated prior to use. In the case of a BSF not falling on already known values, the programs were made to automatically use linear interpolation to find an appropriate BSF. The programs also allow for a stand‐off correction, calculated using the inverse‐square law, and an attenuator value that can be arbitrarily input by the user.

Results:

The two programs were built using C#, and use essentially the same types of backends to do their calculations. Differences in the programs are mainly in the graphical user interfaces. The backend was made to mimic the way a human does the same calculations. Previously measured REF and BSF tables for three different x‐ray energies and field size types were loaded into the program beforehand for testing. Both applications were easy to use, and produced the exact same results in all situations. These results matched the same calculations done by hand. Differences were only found when hand calculations use shortcuts to find BSF values that lie outside of the pre‐measured values.

Conclusion:

Our programs can efficiently and effectively calculate MU as well as or better than by hand. The Android version can be useful in the future for emergency situations.
SU‐F‐T‐544: Development of a Clinically Feasible Workflow of 4D MRI‐Based Treatment Planning for Liver SBRT
Authors: Han S , Yin F , Czito B , Palta M , Cai J
Published: July 2016

Purpose:

To develop a clinically feasible workflow of 4D MRI‐based treatment planning for liver SBRT.

Methods:

A clinical workflow based on 4D MRI for liver SBRT was designed to largely simulate the same procedure as 4D CT for lung SBRT. Key features of the workflow include: (1) contouring tumor volume at each phases (2) contouring more structures, (3) assigning CT numbers to structures for dose calculation. Uncertainties (bone delineation, MRI distortion, CT number assignment, etc.) were investigated using five clinical treatment plans of liver SBRT by simulating the following scenarios: homogeneous calculation, calculation with CT number assignment (for each structure separately and for all combined), calculation with and without distortion (mimicked by shirking body structure by 1mm to 5 mm). Dose‐histogram volume (DVF) parameters were collected from the simulated cases and compared to those in the original plan. Lastly, a patient example case of 4D MRI‐based treatment plan was performed to demonstrate the feasibility of the proposed workflow.

Results:

In homogeneous calculation, the average percentage volume error (ΔV30) of liver was 0.40% and maximum average dose error (GTV ΔD95) was 1.08Gy. Between MRI‐based and original plans, liver ΔV30 was 0.28% and maximum average dose error (GTV ΔD95) was 0.75Gy. Basically dose errors and percentage volume error increased as distortion increased. In some special cases, in original plans, the minimum spinal cord max dose error appeared when distortion was 4mm; in MRI‐based plans, the minimum liver ΔV30 appeared when distortion was 3mm. In the example case, mean liver dose was 20.7Gy in 4D MRI‐based plan and 34.2Gy in 4D CT‐based plan.

Conclusion:

A clinically feasible workflow of 4D MRI‐based treatment planning for liver SBRT has been established. Dose uncertainties of the workflow were generally small, except for large MR geometric distortions (> 3 mm).

NIH (1R21CA165384)