bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐572: Normal Lung Tissue Sparing in Radiation Therapy for Locally Advanced Non‐Small Cell Lung Cancer
Authors: Hong C , Ju S , Ahn Y
Published: June 2015

Purpose:

To compare normal lung‐sparing capabilities of three advanced radiation therapy techniques for locally advanced non‐small cell lung cancer (LA‐NSCLC).

Methods:

Four‐dimensional computed tomography (4DCT) was performed in 10 patients with stage IIIb LA‐NSCLC. The internal target volume (ITV); planning target volume (PTV); and organs at risks (OARs) such as spinal cord, total normal lung, heart, and esophagus were delineated for each CT data set. Intensity‐modulated radiation therapy (IMRT), Tomohelical‐IMRT (TH‐IMRT), and TomoDirect‐IMRT (TD‐IMRT) plans were generated (total prescribed dose, 66 Gy in 33 fractions to the PTV) for each patient. To reduce the normal lung dose, complete and directional block function was applied outside the normal lung far from the target for both TH‐IMRT and TD‐IMRT, while pseudo‐ OAR was set in the same region for IMRT. Dosimetric characteristics of the three plans were compared in terms of target coverage, the sparing capability for the OAR, and the normal tissue complication probability (NTCP). Beam delivery efficiency was also compared.

Results:

TH‐IMRT and TD‐IMRT provided better target coverage than IMRT plans. Lung volume receiving ≥–30 Gy, mean dose, and NTCP were significant with TH‐IMRT than with IMRT (p=0.006), and volume receiving ≥20–30 Gy was lower in TD‐IMRT than in IMRT (p<0.05). Compared with IMRT, TH‐IMRT had better sparing effect on the spinal cord (Dmax, NTCP) and heart (V45) (p<0.05). NTCP for the spinal cord, V45 and V60 for the heart, and Dmax for the esophagus were significantly lower in TD‐IMRT than in IMRT. The monitor units per fraction were clearly smaller for IMRT than for TH‐IMRT and TD‐IMRT (p=0.006).

Conclusion:

In LA‐NSCLC, TH‐IMRT gave superior PTV coverage and OAR sparing compared to IMRT. TH‐IMRT provided better control of the lung volume receiving ≥5–30 Gy. The delivery time and monitor units were lower in TD‐IMRT than in TH‐IMRT.
SU‐E‐T‐574: Novel Chance‐Constrained Optimization in Intensity‐Modulated Proton Therapy Planning to Account for Range and Patient Setup Uncertainties
Authors: An Y , Liang J , Liu W
Published: June 2015

Purpose:

We propose to apply a probabilistic framework, namely chanceconstrained optimization, in the intensity‐modulated proton therapy (IMPT) planning subject to range and patient setup uncertainties. The purpose is to hedge against the influence of uncertainties and improve robustness of treatment plans.

Methods:

IMPT plans were generated for a typical prostate patient. Nine dose distributions are computed — the nominal one and one each for ±5mm setup uncertainties along three cardinal axes and for ±3.5% range uncertainty. These nine dose distributions are supplied to the solver CPLEX as chance constraints to explicitly control plan robustness under these representative uncertainty scenarios with certain probability. This probability is determined by the tolerance level. We make the chance‐constrained model tractable by converting it to a mixed integer optimization problem. The quality of plans derived from this method is evaluated using dose‐volume histogram (DVH) indices such as tumor dose homogeneity (D5% – D95%) and coverage (D95%) and normal tissue sparing like V70 of rectum, V65, and V40 of bladder. We also compare the results from this novel method with the conventional PTV‐based method to further demonstrate its effectiveness

Results:

Our model can yield clinically acceptable plans within 50 seconds. The chance‐constrained optimization produces IMPT plans with comparable target coverage, better target dose homogeneity, and better normal tissue sparing compared to the PTV‐based optimization [D95% CTV: 67.9 vs 68.7 (Gy), D5% – D95% CTV: 11.9 vs 18 (Gy), V70 rectum: 0.0 % vs 0.33%, V65 bladder: 2.17% vs 9.33%, V40 bladder: 8.83% vs 21.83%]. It also simultaneously makes the plan more robust [Width of DVH band at D50%: 2.0 vs 10.0 (Gy)]. The tolerance level may be varied to control the tradeoff between plan robustness and quality.

Conclusion:

The chance‐constrained optimization generates superior IMPT plan compared to the PTV‐based optimization with explicit control of plan robustness.

NIH/NCI K25CA168984, Eagles Cancer Research Career Development, The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, Mayo ASU Seed Grant, and The Kemper Marley Foundation.
SU‐E‐T‐576: Obesity as a Factor in Prostate Cancer Treatment Modality and Outcomes
Authors: Njeh C , Stankowski R , Liang H , Kahana B
Published: June 2015

Purpose:

Prostate cancer is the most frequently diagnosed malignancy in American males. To date, no single study has examined the effect of obesity on the outcomes of all three treatment modalities in a single population. We examined the relationship between obesity and prostate cancer treatment decisions as well as outcomes.

Methods:

We conducted a retrospective observational cohort study of the patients treated for prostate cancer with curative intent between January 1998 and December 2010. Wilcoxon ranksum and Chi‐Square tests were used to analyze the association between treatment mode and body mass index (BMI). Cox proportional Hazards models adjusted for risk category, age, and androgen deprivation therapy (ADT) were performed to evaluate the effects of BMI on overall, disease‐free, biochemical recurrence‐free, incontinence‐free, and impotence‐free survival.

Results:

A total of 1681 patients were included in the analysis, including 338 that received BT, 439 that received EBRT, and 904 that received RP. When BMI was assessed as a continuous variable, median BMI was higher in patients treated with BT (29.4) than in those treated with EBRT (28.8) or RP (28.9) (P = 0.0677, Wilcoxon rank‐sum test). After stratifying BMI into two groups (BMI < 29.4 or ≥ 29.4), Chi‐Square test showed that the treatment mode was significantly related to BMI where the proportion of high BMI individuals undergoing was 50.9% for BT, 42.4% for EBRT, and 43.2% for RP (P = 0.0309). Cox proportional hazards modeling was used to assess the relationship between BMI and survival outcomes. For patients receiving EBRT, BMI was a significant risk factor for incontinence‐free survival where HR for incontinence in the lower BMI group was 0.515 (95% CI 0.307–0.865, P = 0.0121).

Conclusion:

BMI appears to be related to prostate cancer treatment decisions, High BMI (≥ 29.4) is associated with poorer incontinence‐free survival for EBRT.

This study was supported by a grant from the Marshfield Clinic Research Foundation
SU‐E‐T‐577: Obliquity Factor and Surface Dose in Proton Beam Therapy
Authors: Das I , Andersen A , Coutinho L
Published: June 2015

Purpose:

The advantage of lower skin dose in proton beam may be diminished creating radiation related sequalae usually seen with photon and electron beams. This study evaluates the surface dose as a complex function of beam parameters but more importantly the effect of beam angle.

Methods:

Surface dose in proton beam depends on the beam energy, source to surface distance, the air gap between snout and surface, field size, material thickness in front of surface, atomic number of the medium, beam angle and type of nozzle (ie double scattering, (DS), uniform scanning (US) or pencil beam scanning (PBS). Obliquity factor (OF) is defined as ratio of surface dose in 0° to beam angle Θ. Measurements were made in water phantom at various beam angles using very small microdiamond that has shown favorable beam characteristics for high, medium and low proton energy. Depth dose measurements were performed in the central axis of the beam in each respective gantry angle.

Results:

It is observed that surface dose is energy dependent but more predominantly on the SOBP. It is found that as SSD increases, surface dose decreases. In general, SSD, and air gap has limited impact in clinical proton range. High energy has higher surface dose and so the beam angle. The OF rises with beam angle. Compared to OF of 1.0 at 0° beam angle, the value is 1.5, 1.6, 1,7 for small, medium and large range respectively for 60 degree angle.

Conclusion:

It is advised that just like range and SOBP, surface dose should be clearly understood and a method to reduce the surface dose should be employed. Obliquity factor is a critical parameter that should be accounted in proton beam therapy and a perpendicular beam should be used to reduce surface dose.
SU‐E‐T‐583: Operated Left Breast and Chest Wall Radiotherapy: A Dosimetric Comparison Between 3DCRT,IMRT and VMAT
Authors: Sarkar B , Roy S , Munshi A , Pradhan A
Published: June 2015

Purpose:

To evaluate the comparative dosimetric efficacy between field and field 3DCRT(FnF), multiple field Intensity modulated radiotherapy (SnS IMRT) and, partial arc volumetric modulated arc therapy (VMAT) in case of post operative left side breast and chest wall irradiation.

Methods:

CT study set of fifteen post‐operative left breast and chest wall patient was tested for a treatment plan of 50Gy in 25 fraction using partial arc VMAT, SnSIMRT and tangential beam 3DCRT . 3DCRT FnF gantry angle was ranging for left medial tangential 290±170 and Lt lateral tangential l14°±120. For IMRT four fixed beam at gantry angle G1300 G1100 G3000 and G3300 was used, in case of insufficient dose another beam G1500 was added. In case of partial arc VMAT, lateral tangential arc G1300‐G1000 and medial tangential arc G2800‐G3100. Inverse optimization was opted to cover at least 95%PTV by 95% prescription dose (RxD) and a strong weightage on reduction of heart and lung dose. PTV coverage was evaluated for it's clinically acceptability depending on the tumor spatial location and its quadrant. Out of the three plans, any one was used for the actual patient treatment.

Results:

Dosimetric analysis done for breast PTV, left lung, heart and the opposite breast. PTV mean dose and maximum dose was 5129.8±214.8cGy, 4749.0±329.7cGy, 5024.6±73.4cGy and 5855.2±510.7cGy, 5340.7±146.1cGy, 5347.2±196.8cGy for FnF, VMAT and IMRT respectively. Ipsilateral lung volume receiving 20Gy and 5Gy was 23.6±9.5cGy and 32.7±10.3cGy for FnF, 18.6±8.7cGy and 38.8±15.2cGy for VMAT and 25.7±9.6cGy and 50.7±8.4cGy for IMRT respectively. Heart mean and 2cc dose was 867.9±456.7cGy and 5038.5±184.3cGy for FnF, 532.6±263cGy and 3632.1±990.6 for VMAT, 711±229.9cGy and 4421±463.7cGy for IMRT respectively. VMAT shows minimum contralateral breast dose 168±113.8cGy.

Conclusion:

VMAT shows a better tumor conformity, minimum heart, ipsilateral lung and opposite breast dose. Cardiac Toxicity and risk of contralateral breast cancer can be reduce using VMAT.
SU‐E‐T‐587: Optimal Volumetric Modulated Arc Radiotherapy Treatment Planning Technique for Multiple Brain Metastases with Increasing Number of Arcs
Authors: Keeling V , Hossain S , Hildebrand K , Ahmad S , Larson D , Sahgal A , Ma L
Published: June 2015

Purpose:

To show improvements in dose conformity and normal brain tissue sparing using an optimal planning technique (OPT) against clinically acceptable planning technique (CAP) in the treatment of multiple brain metastases.

Methods:

A standardized international benchmark case with12 intracranial tumors was planned using two different VMAT optimization methods. Plans were split into four groups with 3, 6, 9, and 12 targets each planned with 3, 5, and 7 arcs using Eclipse TPS. The beam geometries were 1 full coplanar and half non‐coplanar arcs. A prescription dose of 20Gy was used for all targets. The following optimization criteria was used (OPT vs. CAP): (No upper limit vs.108% upper limit for target volume), (priority 140–150 vs. 75–85 for normal‐brain‐tissue), and (selection of automatic sparing Normal‐Tissue‐Objective (NTO) vs. Manual NTO). Both had priority 50 to critical structures such as brainstem and optic‐chiasm, and both had an NTO priority 150. Normal‐brain‐tissue doses along with Paddick Conformity Index (PCI) were evaluated.

Results:

In all cases PCI was higher for OPT plans. The average PCI (OPT,CAP) for all targets was (0.81,0.64), (0.81,0.63), (0.79,0.57), and (0.72,0.55) for 3, 6, 9, and 12 target plans respectively. The percent decrease in normal brain tissue volume (OPT/CAP*100) achieved by OPT plans was (reported as follows: V4, V8, V12, V16, V20) (184, 343, 350, 294, 371%), (192, 417, 380, 299, 360%), and (235, 390, 299, 281, 502%) for the 3, 5, 7 arc 12 target plans, respectively. The maximum brainstem dose decreased for the OPT plan by 4.93, 4.89, and 5.30 Gy for 3, 5, 7 arc 12 target plans, respectively.

Conclusion:

Substantial increases in PCI, critical structure sparing, and decreases in normal brain tissue dose were achieved by eliminating upper limits from optimization, using automatic sparing of normal tissue function with high priority, and a high priority to normal brain tissue.
SU‐E‐T‐589: Optimization of Patient Head Angle Position to Spare Hippocampus During the Brain Radiation Therapy
Authors: Cheon G , Kang S , Kim T , Kim D , Kang Y , Suh T
Published: June 2015

Purpose:

Hippocampus is one of the important organs which controls emotions, behaviors, movements the memorizing and learning ability. In the conventional head & neck therapy position, it is difficult to perform the hippocampal‐sparing brain radiation therapy. The purpose of this study is to investigate optimal head angle which can save the hippocampal‐sparing and organ at risk (OAR) in conformal radiation therapy (CRT), Intensity modulation radiation therapy (IMRT) and helical tomotherapy (HT).

Methods:

Three types of radiation treatment plans, CRT, IMRT and Tomotherapy plans, were performed for 10 brain tumor patients. The image fusion between CT and MRI data were used in the contour due to the limited delineation of the target and OAR in the CT scan. The optimal condition plan was determined by comparing the dosimetric performance of the each plan with the use of various parameters which include three different techniques (CRT, IMRT, HT) and 4 angle (0, 15, 30, 40 degree). The each treatment plans of three different techniques were compared with the following parameters: conformity index (CI), homogeneity index (HI), target coverage, dose in the OARs, monitor units (MU), beam on time and the normal tissue complication probability (NTCP).

Results:

HI, CI and target coverage was most excellent in head angle 30 degree among all angle. When compared by modality, target coverage and CI showed good results in IMRT and TOMO than compared to the CRT. HI at the head angle 0 degrees is 1.137±0.17 (CRT), 1.085±0.09 (IMRT) and 1.077±0.06 (HT). HI at the head angle 30 degrees is 1.056±0.08 (CRT), 1.020±0.05 (IMRT) and 1.022±0.07 (HT).

Conclusion:

The results of our study show that when head angle tilted at 30 degree, target coverage, HI, CI were improved, and the dose delivered to OAR was reduced compared with conventional supine position in brain radiation therapy.

This work was supported by the Radiation Technology R&D program (No. 2013M2A2A7043498) and the Mid‐career Researcher Program (2014R1A2A1A10050270) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&Future Planning.
SU‐E‐T‐594: Out‐Of‐Field Neutron and Gamma Dose Estimated Using TLD‐600/700 Pairs in the Wobbling Proton Therapy System
Authors: Chen Y , Lin Y , Chen H , Tsai H
Published: June 2015

Purpose:

Secondary fast neutrons and gamma rays are mainly produced due to the interaction of the primary proton beam with the beam delivery nozzle. These secondary radiation dose to patients and radiation workers are unwanted. The purpose of this study is to estimate the neutron and gamma dose equivalent out of the treatment volume during the wobbling proton therapy system.

Methods:

Two types of thermoluminescent (TL) dosimeters, TLD‐600 (6LiF: Mg, Ti) and TLD‐700 (7LiF: Mg, Ti) were used in this study. They were calibrated in the standard neutron and gamma sources at National Standards Laboratory. Annealing procedure is 400°C for 1 hour, 100°C for 2 hours and spontaneously cooling down to the room temperature in a programmable oven. Two‐peak method (a kind of glow curve analysis technique) was used to evaluate the TL response corresponding to the neutron and gamma dose. The TLD pairs were placed outside the treatment field at the neutron‐gamma mixed field with 190‐MeV proton beam produced by the wobbling system through the polyethylene plate phantom. The results of TLD measurement were compared to the Monte Carlo simulation.

Results:

The initial experiment results of calculated dose equivalents are 0.63, 0.38, 0.21 and 0.13 mSv per Gy outside the field at the distance of 50, 100, 150 and 200 cm.

Conclusion:

The TLD‐600 and TLD‐700 pairs are convenient to estimate neutron and gamma dosimetry during proton therapy. However, an accurate and suitable glow curve analysis technique is necessary. During the wobbling system proton therapy, our results showed that the neutron and gamma doses outside the treatment field are noticeable.

This study was supported by the grants from the Chang Gung Memorial Hospital (CMRPD1C0682).
SU‐E‐T‐595: Output Factor Calculation for a Uniform Scanning Proton Therapy System
Authors: Hecksel D , Stauffer N , DeFillippo G , Edwards J , Pankuch M
Published: June 2015

Purpose:

To develop an analytical model that predicts dose output factors for patient treatment fields in a uniform scanning proton therapy system.

Methods:

A model to predict output factors for patient specific treatment fields was produced based on the methods developed by Kooy et al. (2003). The Kooy model predicts the output factor based on the ratio of the entrance dose under calibration conditions to that for a given range and modulation corrected for the inverse square effect. Field specific output factors were plotted as a function of a single parameter r, where r = (Range‐Modulation)/Modulation. The model targeted user range 1 sub‐span 3 through user range 2 sup‐span 2 of the IBA uniform scanning proton therapy system. The data set included points measured using the 10 cm and 18 cm snout sizes to eliminate stem effects on the monitor unit chambers. The data was fit using equation 15 from Kooy et al. (2003), and the resulting model was tested against measurements that were not included in the original data set.

Results:

For the range and sub span investigated, 120 data points were tested against the model prediction. The model predicted the output factor within 2% for 96% of the points tested and within 2.5% for 99% of the points tested. All points were within 3% of the predicted values.

Conclusion:

Monitor units for patient treatment fields with proton ranges that fall within the tested interval can be predicted using a model based on the methods developed at MGH. With further evaluation, it will be possible to model all user ranges and sub‐spans of the IBA system. Further testing is also needed to predict output factors using a 25 cm snout which introduces variable scanning pattern sizes and stem effects on the monitor unit chambers.
SU‐E‐T‐596: P3DVHStats ‐ a Novel, Automatic, Institution Customizable Program to Compute and Report DVH Quantities On Philips Pinnacle TPS
Authors: Wu C
Published: June 2015

Purpose:

To implement a novel, automatic, institutional customizable DVH quantities evaluation and PDF report tool on Philips Pinnacle treatment planning system (TPS)

Methods:

An add‐on program (P3DVHStats) is developed by us to enable automatic DVH quantities evaluation (including both volume and dose based quantities, such as V98, V100, D2), and automatic PDF format report generation, for EMR convenience. The implementation is based on a combination of Philips Pinnacle scripting tool and Java language pre‐installed on each Pinnacle Sun Solaris workstation. A single Pinnacle script provide user a convenient access to the program when needed. The activated script will first export DVH data for user selected ROIs from current Pinnacle plan trial; a Java program then provides a simple GUI interface, utilizes the data to compute any user requested DVH quantities, compare with preset institutional DVH planning goals; if accepted by users, the program will also generate a PDF report of the results and export it from Pinnacle to EMR import folder via FTP.

Results:

The program was tested thoroughly and has been released for clinical use at our institution (Pinnacle Enterprise server with both thin clients and P3PC access), for all dosimetry and physics staff, with excellent feedback. It used to take a few minutes to use MS‐Excel worksheet to calculate these DVH quantities for IMRT/VMAT plans, and manually save them as PDF report; with the new program, it literally takes a few mouse clicks in less than 30 seconds to complete the same tasks.

Conclusion:

A Pinnacle scripting and Java language based program is successfully implemented, customized to our institutional needs. It is shown to dramatically reduce time and effort needed for DVH quantities computing and EMR reporting.
SU‐E‐T‐598: Parametric Equation for Quick and Reliable Estimate of Stray Neutron Doses in Proton Therapy and Application for Intracranial Tumor Treatments
Authors: Bonfrate A , Farah J , De Marzi L , Delacroix S , Herault J , Sayah R , Lee C , Bolch W , Clairand I
Published: June 2015

Purpose:

Development of a parametric equation suitable for a daily use in routine clinic to provide estimates of stray neutron doses in proton therapy.

Methods:

Monte Carlo (MC) calculations using the UF‐NCI 1‐year‐old phantom were exercised to determine the variation of stray neutron doses as a function of irradiation parameters while performing intracranial treatments. This was done by individually changing the proton beam energy, modulation width, collimator aperture and thickness, compensator thickness and the air gap size while their impact on neutron doses were put into a single equation. The variation of neutron doses with distance from the target volume was also included in it. Then, a first step consisted in establishing the fitting coefficients by using 221 learning data which were neutron absorbed doses obtained with MC simulations while a second step consisted in validating the final equation.

Results:

The variation of stray neutron doses with irradiation parameters were fitted with linear, polynomial, etc. model while a power‐law model was used to fit the variation of stray neutron doses with the distance from the target volume. The parametric equation fitted well MC simulations while establishing fitting coefficients as the discrepancies on the estimate of neutron absorbed doses were within 10%. The discrepancy can reach ∼25% for the bladder, the farthest organ from the target volume. Finally, the validation showed results in compliance with MC calculations since the discrepancies were also within 10% for head‐and‐neck and thoracic organs while they can reach ∼25%, again for pelvic organs.

Conclusion:

The parametric equation presents promising results and will be validated for other target sites as well as other facilities to go towards a universal method.
SU‐E‐T‐599: Patient Safety Enhancements Through a Study of R&V System Override Data
Authors: Hendrickson K , Vimolchalao S
Published: June 2015

Purpose:

Record and verify (R&V) software systems include safety checks that compare actual machine parameters with prescribed values for a patient's treatment, such as treatment couch position, linac, energy, and MUs. The therapist is warned of a mismatch with a pop‐up and prompted to approve an override in order to continue without changes. Override approval is often legitimate, but the pop‐up can also genuinely indicate a problem that would Result in the wrong treatment. When there are numerous pop‐up warnings, human nature leads us to approve any override without careful reading, undermining the effectiveness of the safety mechanism.

Methods:

Override data was collected from our R&V system for all patients treated between October 8 and 29, 2012, on four linacs and entered into a spreadsheet. Additional data collected included treatment technique, disease site, immobilization, time, linac, and whether localization images were obtained. Data were analyzed using spreadsheet tools to reveal trends, patterns and associations that might suggest appropriate process changes that could decrease the total number of overrides.

Results:

76 out of 113 patients had overrides. Out of the 944 treatments, 599 override items were generated. The majority were due to couch positions. 74 of the 84 overrides on a linac equipped with a 6D couch were due to the use of the rotational corrections and the fact that the 6D couch control does not communicate with the R&V system; translations required to rotate the couch appear to the R&V system as translations outside the tolerance range.

Conclusion:

Many findings were interesting but did not suggest a process change. Proposed process changes include creating site‐specific instead of just technique‐specific tolerance tables for couch shifts. Proposed improvements to the vendor are to facilitate direct communication between the 6D couch and the R&V system to eliminate those override warnings related to lack of communication.
SU‐E‐T‐600: Patient Specific IMRT Verification Using a Phosphor‐Screen Based Geometric QA System: A Preliminary Study
Authors: Lee M , Hu E , Yi B
Published: June 2015

Purpose:

Raven QA (JPLC, MD) is a unified and comprehensive quality assurance system for QA of TG‐142, which use a phosphor screen, a mirror system and a camera. It is to test if this device can be used for IMRT QA dosimetry.

Methods:

A lung IMRT case is used deliver dose to Raven QA. Accuracy of dose distribution of 5cm slab phantom using Eclipse planning system (Varian) has been confirmed both from a Monte Carlo Simulation and from a MapCheck (SunNuclear) measurement. Geometric distortion and variation of spatial dose response are corrected after background subtraction. A pin‐hole grid plate is designed and used to determine the light scatter in the Raven QA box and the spatial dose response. Optic scatter model was not applied in this preliminary study. Dose is normalized to the response of the 10×10 field and the TMR of 5cm depth was considered.

Results:

Time to setup the device for IMRT QA takes less than 5 minutes as other commercially available devices. It shows excellent dose linearity and dose rate independent, less than 1 %. Background signal, however, changes for different field sizes. It is believed to be due to inaccurate correction of optic scatter. Absolute gamma (5%, 5mm) passing rate was higher than 95%.

Conclusion:

This study proves that the Raven QA can be used for a patient specific IMRT verification.

Part of this study is supported by the Maryland Industrial Partnership Grant.
SU‐E‐T‐602: Patient‐Specific Online Dose Verification Based On Transmission Detector Measurements
Authors: Thoelking J , Yuvaraj S , Jens F , Lohr F , Wenz F , Wertz H , Wertz H
Published: June 2015

Purpose:

Intensity modulated radiotherapy requires a comprehensive quality assurance program in general and ideally independent verification of dose delivery. Since conventional 2D detector arrays allow only pre‐treatment verification, there is a debate concerning the need of online dose verification. This study presents the clinical performance, including dosimetric plan verification in 2D as well as in 3D and the error detection abilities of a new transmission detector (TD) for online dose verification of 6MV photon beam.

Methods:

To validate the dosimetric performance of the new device, dose reconstruction based on TD measurements were compared to a conventional pre‐treatment verification method (reference) and treatment planning system (TPS) for 18 IMRT and VMAT treatment plans. Furthermore, dose reconstruction inside the patient based on TD read‐out was evaluated by comparing various dose volume indices and 3D gamma evaluations against independent dose computation and TPS. To investigate the sensitivity of the new device, different types of systematic and random errors for leaf positions and linac output were introduced in IMRT treatment sequences.

Results:

The 2D gamma index evaluation of transmission detector based dose reconstruction showed an excellent agreement for all IMRT and VMAT plans compared to reference measurements (99.3±1.2)% and TPS (99.1±0.7)%. Good agreement was also obtained for 3D dose reconstruction based on TD read‐out compared to dose computation (mean gamma value of PTV = 0.27±0.04). Only a minimal dose underestimation within the target volume was observed when analyzing DVH indices (<1%). Positional errors in leaf banks larger than 1mm and errors in linac output larger than 2% could clearly identified with the TD.

Conclusion:

Since 2D and 3D evaluations for all IMRT and VMAT treatment plans were in excellent agreement with reference measurements and dose computation, the new TD is suitable to qualify for routine treatment plan verification.

Funding Support, Disclosures, and Conflict of Interest: COIs: Frank Lohr: Elekta: research grant, travel grants, teaching honoraria IBA: research grant, travel grants, teaching honoraria, advisory board C‐Rad: board honoraria, travel grants Frederik Wenz: Elekta: research grant, teaching honoraria, consultant, advisory board Zeiss: research grant, teaching honoraria, patent Hansjoerg Wertz: Elekta: research grant, teaching honoraria IBA: research grant
SU‐E‐T‐603: PBS Prostate Plan Robustness: A Tool for Patient Specific Setup Tolerance
Authors: Tang S , Song L , Chen C , Chang C , Chon B , Tsai H , Soffen E , Cahlon O , Mah D
Published: June 2015

Purpose:

Fiducial markers are commonly used for setup of prostate patients using orthogonal radiographs. After aligned with the markers, the displacement of the bony anatomy relative to the planned DRR can be up to 10 mm. Such offset can potentially have significant dosimetric effects because it changes the radiological path length of protons in differing amounts of bone. It is imperative to develop a method to evaluate its impact on target coverage and hence establish patient specific setup tolerance for prostate proton PBS treatment.

Methods:

Prostate patients were planned in RayStation according to the PCG protocol with bi‐lateral beams. The primary planning objectives are: (1) 100% of CTV receives full prescription dose; (2) 98% of the prescription dose covers at least 98% of the PTV; (3) OARs meet criteria per protocol. For each patient 108 dose perturbations were automatically generated using an in‐house script, which considered the isocenter shifting in S‐I and A‐P directions (up to ±15 mm with an interval of 6mm) as well as the range uncertainty (±3.5%). The target coverage was evaluated on the contour shifted along with prostate to mimic the daily treatment.

Results:

The minimum CTV coverage as a function of offsets in S‐I and A‐P directions is presented in a 2D contour map. The offsets along A‐P direction generally have greater impact than along S‐I direction. Both the CTV D98%>98% or CTV V98%>98% are achievable for most patients if the offset is <10 mm in either direction despite of range uncertainties.

Conclusion:

We developed a method to evaluate the plan robustness for proton PBS prostate treatment. It can provide patient specific setup tolerance of bony structure offset. For our current planning approach, a 1 cm displacement is acceptable. This approach can be generalized to other target structures that move relative to bony anatomy.
SU‐E‐T‐605: Performance Evaluation of MLC Leaf‐Sequencing Algorithms in Head‐And‐Neck IMRT
Authors: Jing J , Lin H , Chow J
Published: June 2015

Purpose:

To investigate the efficiency of three multileaf collimator (MLC) leaf‐sequencing algorithms proposed by Galvin et al, Chen et al and Siochi et al using external beam treatment plans for head‐and‐neck intensity modulated radiation therapy (IMRT).

Methods:

IMRT plans for head‐and‐neck were created using the CORVUS treatment planning system. The plans were optimized and the fluence maps for all photon beams determined. Three different MLC leaf‐sequencing algorithms based on Galvin et al, Chen et al and Siochi et al were used to calculate the final photon segmental fields and their monitor units in delivery. For comparison purpose, the maximum intensity of fluence map was kept constant in different plans. The number of beam segments and total number of monitor units were calculated for the three algorithms.

Results:

From results of number of beam segments and total number of monitor units, we found that algorithm of Galvin et al had the largest number of monitor unit which was about 70% larger than the other two algorithms. Moreover, both algorithms of Galvin et al and Siochi et al have relatively lower number of beam segment compared to Chen et al. Although values of number of beam segment and total number of monitor unit calculated by different algorithms varied with the head‐and‐neck plans, it can be seen that algorithms of Galvin et al and Siochi et al performed well with a lower number of beam segment, though algorithm of Galvin et al had a larger total number of monitor units than Siochi et al.

Conclusion:

Although performance of the leaf‐sequencing algorithm varied with different IMRT plans having different fluence maps, an evaluation is possible based on the calculated number of beam segment and monitor unit. In this study, algorithm by Siochi et al was found to be more efficient in the head‐and‐neck IMRT.

The Project Sponsored by the Fundamental Research Funds for the Central Universities (J2014HGXJ0094) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
SU‐E‐T‐606: Performance of MR‐Based 3D FXG Dosimetry for Preclinical Irradiation
Authors: Welch M , Jaffray D
Published: June 2015

Purpose:

Technological advances have revolutionized preclinical radiation research to enable precise radiation delivery in preclinical models. Kilovoltage x‐rays and complex geometries in preclinical radiation studies challenge conventional dosimetry methods. Previously developed gel‐based dosimetry provides a viable means of accommodating complex geometries and accurately reporting dose at kV energies. This paper will describe the development and evaluation of gel‐based ferrous xylenol‐orange (FXG) dosimetry using a 7T preclinical imaging system.

Methods:

To confirm water equivalence, Zeff values were calculated for the FXG material, water and ICRU defined soft tissue. Proton T1 relaxivity response in FXG was measured using a preclinical 7T MR and a small animal irradiator for a dose range of 1–22 Gy. FXG was contained in 50 ml centrifuge tubes and irradiated with a 225 kVp x‐ray beam at a nominal dose rate of 2.3 Gy/min. Pre and post irradiation maps of the T1 relaxivity were collected using variable TR spin‐echo imaging (TE 6.65 ms; TR 500, 750, 1000, 1500, 2000, 3000 and 5000 ms) with 2 mm thick slices, 0.325 mm/pixel, 3 averages and an acquisition time of 26 minutes. A linear fit to the change in relaxation rate (1/T1) for the delivered doses reported the gel sensitivity in units of ms‐1Gy‐1. Irradiation and imaging studies were repeated using three batches of gel over 72 hrs.

Results:

FXG has a Zeff of 3.8 for the 225 kVp spectrum used; differing from water and ICRU defined soft tissue by 0.5% and 2.5%, respectively. The average sensitivity for the FXG dosimeter was 31.5 ± 0.7 ms‐1Gy‐1 (R2 = 0.9957) with a y‐intercept of −29.4 ± 9.0 ms‐1.

Conclusion:

Preliminary results for the FXG dosimeter properties, sensitivity, and dose linearity at preclinical energies is promising. Future work will explore anatomically relevant tissue inclusions to test MR performance.

Student funding provided by The Terry Fox Foundation Strategic Initiative for Excellence in Radiation Research for the 21st Century at CIHR and the Gifford Ontario Student Opportunity Trust Fund.
SU‐E‐T‐609: Perturbation Effects of Pedicle Screws On Radiotherapy Dose Distributions
Authors: Bar‐Deroma R , Borzov E , Nevelsky A
Published: June 2015

Purpose:

Radiation therapy in conjunction with surgical implant fixation is a common combined treatment in case of bone metastases. However, metal implants generally used in orthopedic implants perturb radiation dose distributions. Carbon‐Fiber Reinforced (CFR) PEEK material has been recently introduced for production of intramedullary screws and plates. Gold powder can be added to the CFR‐PEEK material in order to enhance visibility of the screws during intraoperative imaging procedures. In this work, we investigated the perturbation effects of the pedicle screws made of CFR‐PEEK, CFR‐PEEK with added gold powder (CFR‐PEEK‐AU) and Titanium (Ti) on radiotherapy dose distributions.

Methods:

Monte Carlo (MC) simulations were performed using the EGSnrc code package for 6MV beams with 10×10 fields at SSD=100cm. By means of MC simulations, dose distributions around titanium, CFR‐ PEEK and CFR‐PEEK‐AU screws (manufactured by Carbo‐Fix Orthopedics LTD, Israel) placed in a water phantom were calculated. The screw axis was either parallel or perpendicular to the beam axis. Dose perturbation (relative to dose in homogeneous water phantom) was assessed.

Results:

Maximum overdose due to backscatter was 10% for the Ti screws, 5% for the CFR‐PEEK‐AU screws and effectively zero for the CFR‐PEEK screws. Maximum underdose due to attenuation was 25% for the Ti screws, 15% for the CFR‐PEEK‐AU screws and 5% for the CFR‐PEEK screws. Conclusion: Titanium screws introduce the largest distortion on the radiation dose distribution. The gold powder added to the CFR‐PEEK material improves visibility at the cost of increased dose perturbation. CFR‐PEEK screws caused minimal alteration on the dose distribution. This can decrease possible over and underdose of adjacent tissue and thus favorably influence treatment efficiency. The use of such implants has potential clinical advantage in the treatment of neoplastic bone disease.
SU‐E‐T‐611: Photon and Neutron Peripheral Dose Ratio for Low (6 MV) and High (15 MV) Energy for Treatment Selection
Authors: Irazola L , Terron J , Sanchez‐Nieto B , Ortiz‐Seidel M , Sanchez‐Doblado F
Published: June 2015

Purpose:

Differences between radiotherapy techniques and energies, can offer improvements in tumor coverage and organs at risk preservation. However, a more complete decision should include peripheral doses delivered to the patient. The purpose of this work is the balance of photon and neutron peripheral doses for a prostate case solved with 6 different treatment modalities.

Methods:

Inverse and Forward IMRT and 3D‐CRT in 6 and 15 MV for a Siemens Primus linac, using the same CT data set and contours. The methodology described in [1], was used with the TNRD thermal neutron detector [2] for neutron peripheral dose estimation at 7 relevant organs (colon, esophagus, stomach, liver, lung, thyroid and skin). Photon doses were estimated for these organs by terms of the algorithm proposed in [3]. Plans were optimized with the same restrictions and limited to 30 segments in the Inverse case.

Results:

A similar photon peripheral dose was found comparing 6 and 15 MV cases with slightly higher values of (1.9 ± 1.6) % in mean, for the 6 MV cases. Neutron presence when using 15 MV, represents an increase in peripheral dose of (18 ± 17) % in average. Due to the higher number of MU used in Inverse IMRT, an increasing of (22 ± 3) % in neutron dose is found related to Forward and 3D‐CRT plans. This corresponds to photon doses within 44 and 255 mSv along the organs, for a dose prescription of 68 Gy at the isocenter.

Conclusion:

Neutron and photon peripheral doses for a prostate treatment planified in 6 different techniques have been analyzed. 6 MV plans are slightly more demanding in terms of photon peripheral doses. Inverse technique in 15 MV has Result to be the most demanding one in terms of total peripheral doses, including neutrons and photons. [1]Phys.Med.Biol,2012;57:6167–6191.[2]Med.Phys.,2014;41(112105)1–5.[3]Phys.Medica,2014;30:e33.
SU‐E‐T‐612: Photonuclear Activation of Prosthetic Hips in Radiotherapy
Authors: Keehan S , Smith R , Millar J , Esser M , Taylor M , Kron T , Franich R
Published: June 2015

Purpose:

To measure the neutron induced activation of a prosthetic hip when exposed to an 18 MV radiotherapy linac beam to assess the potential dose to patients.

Methods:

A prosthetic hip (Thackray, UK) was placed in a water phantom and irradiated (both in‐field and out‐of‐field) with an 18 MV linac beam. Gamma spectroscopy was used to identify the radioisotopes produced. Following the in‐field irradiation where the induced activity is higher, high sensitivity lithium fluoride Thermoluminescence Dosimeters (TLD‐100H) (Harshaw, USA) were placed on the surface to measure the dose which would be deposited to nearby tissue resulting from the induced radioactivity.

Results:

The radioisotopes produced in the hip prosthesis have been identified as 52V, 53Fe, and 56Mn which have half‐lives of 3.74, 8.51 and minutes respectively. The 378 and 511 keV characteristic peaks of 53Fe do not appear in the spectra collected from hips irradiated in the out‐of‐field region. This isotope is produced by photonuclear interactions within the hip itself. 52V and 56Mn appear in spectra collected from hips irradiated either within the photon beam or in the nearby out‐of‐field region, implying that they are produced by incident neutron radiation produced in components of the linear accelerator.The integrated dose which would be deposited in the tissue immediately surrounding the hip after four hours (1.5 half‐lives of the longest lived product) was measured as approximately 100 µGy, following a 10,000 MU irradiation of the prosthesis. A highly accurate measurement of the dose is challenging because of the irregular shape of the prosthesis.

Conclusion:

The cumulative dose measured at the surface of the hip is 0.0001% of the in‐field dose, and is therefore negligible compared with the doses the patient receives as a consequence of their treatment.
SU‐E‐T‐617: Plan Quality Estimation of Intensity‐Modulated Radiotherapy Cases for Lung Cancer
Authors: Koo J , Yoon M , Chung W , Kim D
Published: June 2015

Purpose:

To estimate the planning quality of intensity‐modulated radiotherapy in lung cancer cases and to provide preliminary data for the development of a planning quality assurance algorithm.

Methods:

42 IMRT plans previously used in cases of solitary lung cancers were collected. Organs in or near the thoracic cavity, such as lung (ipsilateral, contralateral), heart, liver, esophagus, cord and bronchus were considered as organs at risk (OARs) in this study. The coverage index (CVI), conformity index (CI), homogeneity index (HI), volume, irregularity (standard deviation of center‐surface distance) were used to compare PTV dose characteristics. The effective uniform dose (EUD), V10Gy, and V20Gy of the OARs were used to compare OAR dose characteristics.

Results:

Average CVI, CI, HI values were 0.9, 0.8, 0.1, respectively. CVI and CI had narrow Gaussian distribution curves without a singular value, but one case had a relatively high (0.25) HI because of location and irregular shape (Irregularity of 18.5 when average was 12.5) of PTV. EUDs tended to decrease as OAR‐PTV distance increased and OAR‐PTV overlap volume decreased.

Conclusion:

This work indicates the potential for significant plan quality deviation of similar lung cancer cases. Considering that this study were from a single department, differences in the treatment results for a given patient would be much more pronounced if multiple departments (and therefore more planners) were involved. Therefore, further examination of QA protocols is needed to reduce deviations in radiation treatment planning.
SU‐E‐T‐623: Polarity Effects for Small Volume Ionization Chambers in Cobalt‐60 Beams
Authors: Xu Y , Bhatnagar J , Huq M Saiful
Published: June 2015

Purpose:

To investigate the polarity effects for small volume ionization chambers in 60Co gamma‐ray beams using the Leksell Gamma Knife Perfexion.

Methods:

Measurements were made for 7 small volume ionization chambers (a PTW 31016, an Exradin A14, 2 Capintec PR0‐5P, and 3 Exradin A16) using a PTW UNIDOSwebline Universal Dosemeter and an ELEKTA solid water phantom with proper inserts. For each ion chamber, the temperature/pressure corrected electric charge readings were obtained for 16 voltage values (±50V, ±100V, ±200V, ±300V, ±400V, ±500V, ±600V, ±700V). For each voltage, a five‐minute leakage charge reading and a series of 2‐minute readings were continuously taken during irradiation until 5 stable signals (less than 0.05% variation) were obtained. The average of the 5 reading was then used for the calculation of the polarity corrections at the voltage and for generating the saturation curves.

Results:

The polarity effects are more pronounced at high or low voltages than at the medium voltages for all chambers studied. The voltage dependence of the 3 Exradin A16 chambers is similar in shape. The polarity corrections for the Exradin A16 chambers changes rapidly from about 1 at 500V to about 0.98 at 700V. The polarity corrections for the 7 ion chambers at 300V are in the range from 0.9925 (for the PTW31016) to 1.0035 (for an Exradin A16).

Conclusion:

The polarity corrections for certain micro‐chambers are large even at normal operating voltage.
SU‐E‐T‐626: Practical Method to Implement Arc Therapy Using Scanned Particle Beams
Authors: Eley J , Mehta M , Molitoris J , Langner U , Langen K
Published: June 2015

Purpose:

The purpose of this study was to propose a method to implement arc therapy that is compatible with existing particle therapy systems having gantries and pencil‐beam scanning capacities. Furthermore, we sought to demonstrate expected benefits of this method for selected clival chordoma patients.

Methods:

We propose that a desired particle arc treatment plan can be discretized into a finite number of fixed beams and that only one (or a subset) of these beams be delivered in any single treatment fraction; the target should receive uniform dose during each fraction. For 3 clival‐chordoma patients, robust‐optimized, scanned proton beams were simulated to deliver 78 Gy (RBE) to clinical target volumes (CTVs), using either a single‐field plan with a posterior‐anterior (PA) beam or a discrete‐arc plan with 16 beams that were equally spaced throughout a 360‐degree axial arc. Dose‐volume metrics were compared with emphasis on the brainstem, since risk of radiation necrosis there can often restrict application of tumoricidal doses for chordomas.

Results:

The mean volume of brainstem receiving a dose of 60 Gy (RBE) or higher (V60Gy) was 10.3±0.9 cm3 for the single‐field plan and 4.7±1.8 cm3 for the discrete‐arc plan, a reduction of 55% in favor of arcs. The mean dose to the brainstem was also reduced using arcs, by 18%, while the maximum dose was nearly identical for both methods. For the whole brain, V60Gy was reduced by 23%, in favor of arcs. Mean dose to the CTVs were nearly identical for both strategies, within 0.3%.

Conclusion:

Discrete arc treatments can be implemented using existing scanned particle‐beam facilities. Aside from the physical advantages, the biological uncertainties of particle therapy, particularly high in the distal edge, can be reduced by arc therapy via rotational smearing, which may be of benefit for tumors near the brainstem.