Upstate New York Association of Physicists in Medicine, Inc.      (A Chapter of the AAPM)
Thursday MAY 5th, 2011

TWIG Auditorium

Rochester General Hospital

1425 Portland Ave

Rochester, NY 14621

 

12:00 pm – 5:00 pm    Sponsoring Vendor Exhibits:

Upstate Linac Services, Sun Nuclear, Resonant Medical Inc., Vision RT., Elekta, BrainLAB AG, CIVCO Medical Solution, LACO Inc, PTW, BARD, Accuray Inc., RAD Technology Medical Systems, IBA Dosimetry , MIM Software Inc.

 

                                   

MEETING SPONSOR

Upstate Linac Services

 

10:00

Business Meeting (Sengupta Room )

11:30

Lunch                                                    Sponsored by  Sun Nuclear & Elekta

12:20

Meeting Introduction

Iris Wang Ph.D., UNYAPM President

Vendor Session

12:20-12:40

Novel Cylindrical 3D Scanner - A fresh new approach - Less subjectivity

 

Jim Ernsberger

Sun Nuclear Corporation

 

Proffered Paper Session

12:50

Study of High-Resolution (HR) and High-Light (HL) Phosphors in the Micro-Angiographic Fluoroscope (MAF) using Generalized Linear Systems Analyses

Sandesh K. Gupta, Amit Jain, Daniel R. Bednarek, Stephen Rudin

1:05

Estimation of confidence intervals for pass rates of low-density 2D IMRT QA planes

D. Bailey, B. Nelms, L. Kumaraswamy, M. Podgorsak

1:20

Adaptive Temporal Filtering Based On the Motion of an Object of Interest for Image Guided Procedures Using the High Resolution Microangiographic Fluoroscope (MAF)

A. Panse, A. Jain, C. Ionita, D. Bednarek, S. Rudin

1:35

A novel hybrid radiotherapy technique combining a VMAT arc with beam angle optimized IMRT fields

Jason Spaans, Lalith Kumaraswamy, Harish Malhotra, Mohammad Bakhtiari,

Matthew Podgorsak, and Daryl Nazareth

1:50

Dose Calculation with MCNP5 in the Buildup Region for 6MV photon beams

Hassan Abbas, Jahangir Satti and C. A. MacDonald

2:05

Evaluation of the Accuracy in the Algorithm used for Optical Patient Alignment.

Juan Carlos Paz Lozada, Daryl Nazareth, and Harish Malhotra

2:20

Attention on Details in Radiation Medicine

Dinko Plenkovich

2:35

Refreshments and Vendor Exhibits – Vestibule        Sponsored by Sun Nuclear & Elekta

Invited Talk

3:00-4:00

SBRT: A paradigm shift from conventional radiotherapy

 

Harish Malhotra, PhD

Roswell Park Cancer Institute

 

 

 

 

 

 

UNYAPM SPRING 2010 MEETING PROCEEDINGS

 

 

ABSTRACTS

 

1)      Study of High-Resolution (HR) and High-Light (HL) Phosphors in the Micro-Angiographic Fluoroscope (MAF) using Generalized Linear Systems Analyses

Sandesh K. Gupta, Amit Jain, Daniel R. Bednarek, Stephen Rudin

Toshiba Stroke Research Center, University at Buffalo, Buffalo, NY, 14214, USA.

Purpose: To investigate if the high light (HL) phosphor with its higher screen efficiency could be replaced with the high resolution (HR) phosphor to achieve improved resolution that is essential for neurovascular procedures without increase in noise resulting from the HR’s decreased light-photon yield. Methods and Materials: We designated the detectors MAF-HR and MAF-HL based on the imaging phosphor HR and HL, respectively, and compared them with a commercial flat panel detector (FPD) (194 micron pixel pitch and 600 micron thick CsI(Tl)). For this comparison, we used the generalized linear-system metrics of GMTF, GNNPS and GDQE which are more realistic measures of total system performance since they include the effect of scattered radiation, focal spot distribution, and geometric un-sharpness. Magnifications (1.05-1.15) and scatter fractions (0.28 and 0.33) characteristic of a standard head phantom were used. Results: In this study, we evaluated the imaging characteristics of the high-resolution, high-sensitivity micro-angiographic fluoroscope (MAF) with 35-micron pixel-pitch when used with different commercially-available 300 micron thick phosphors: the high resolution (HR) and high light (HL) from Hamamatsu. The MAF-HR performed significantly better than the MAF-HL at high spatial frequencies in terms of GMTF and GDQE. Conclusions: Despite significant degradation by inclusion of scatter and object magnification, both MAF-HR and MAF-HL provide superior performance over the FPD at higher spatial frequencies with similar performance up to the FPD’s Nyquist frequency of 2.5 cycles/mm in terms of GMTF and GDQE. Both substantially higher resolution and improved GDQE can be achieved with the MAF using the HR phosphor instead of the HL phosphor.

 

2)      Estimation of confidence intervals for pass rates of low-density 2D IMRT QA planes

D. Bailey, B. Nelms, L. Kumaraswamy, M. Podgorsak

Roswell Park Cancer Institute

Purpose: The most common metric for comparing measured to calculated dose for IMRT QA is a pass rate (%) calculated by percent difference (%Diff) and/or distance-to-agreement (DTA). However, for many dosimeters, the grid of analyzed points corresponds to a low-density 2D or 3D array (of diodes or ion chambers).  In these cases the pass rates for any given %Diff/DTA criteria are not absolute, as they exhibit statistical variability that is a function, in part, on the detector sampling geometry. In this work, we analyze the statistics of various methods commonly used to calculate pass rates, and propose methods for establishing confidence intervals for pass rates obtained with low-density arrays.

Methods and Materials: Dose planes were acquired for 10 prostate IMRT fields and 10 head and neck fields via diode array and EPID. Respective calculated dose planes were created by the TPS. The pass rate for each measured vs. calculated plane pair (both centered to the CAX) was calculated with several common comparison methods: %Diff/DTA composite analysis and gamma evaluation, using both local and global normalization. Specialized software was designed to selectively sample the EPID response (very high data density) down to discrete points to simulate low-density measurements (such as those acquired via diode or ion chamber arrays). The software was used to realign the simulated detector grid at many simulated positions with respect to the CAX, thereby altering the low-density sampled grid. Simulations were repeated with 100 positional iterations using a 1 detector/cm uniform grid, a 2 detector/cm uniform grid, and similar random detector grids (to examine any potential biases introduced by a simple orthogonal low-density grid). For each simulation, composite analysis pass rates were calculated with various %Diff/DTA criteria and for both local and global %Diff normalization techniques.

Results and Conclusions: For both the prostate cases and the H&N cases, the average pass rate obtained with gamma analysis is 2%-5% higher than respective composite analysis, depending on DTA/%Diff tolerances, but regardless of normalization. Meanwhile, the average pass rate obtained via local normalization was 2%-6% lower than global maximum normalization, again depending on tolerance criteria. Repositioning of simulated low-density sampling grids leads to a distribution of possible pass rates for each given QA pair. These distributions can be predicted using a binomial distribution, which can be used to establish confidence intervals that should accompany each analysis. The confidence interval of each pass rate depends largely on the sampling density and the observed pass rate (i.e. the degree of difference between measured and calculated). Any passing rate for a low-density measurement array should be accompanied by a confidence interval indicating the statistical uncertainty of that pass rate.

 

3)      Adaptive Temporal Filtering Based On the Motion of an Object of Interest for Image Guided Procedures Using the High Resolution Microangiographic Fluoroscope (MAF)

A. Panse, A. Jain, C. Ionita, D. Bednarek, S. Rudin

Toshiba Stroke Research Center, SUNY Buffalo, Buffalo NY.

Purpose: To study the effect of temporal filtering on accuracy of localization for static and moving objects and to implement real-time adaptive temporal filtering based on amount of motion detected for the object of interest during fluoroscopy.

Method and Materials:  A phantom consisting of two stents (stainless steel and nitinol) mounted on a stepper motor controlled linear stage, and a stationary third stent (nitinol stent with platinum markers) was assembled. The stent strut sizes ranged between 80 to 100 micron. The new high resolution 35- micron-pixel Microangiographic Fluoroscope (MAF) was used for imaging the stent as it was moved forward 7500 steps and brought back to the original position. Object detection algorithm available in LabVIEW IMAQ Vision software was used to localize the stent using different temporal filtering weights. A real time adaptive temporal filter was developed. Depending on the amount of motion the weight was reduced; more the motion, lesser the weight.

Results: For fixed exposure, stationary object localization accuracy is improved by a factor of 5 for higher temporal filtering compared to no temporal filtering; however, for moving objects the error in localization increased 50 percent due to motion blurring when the filter weight was increased from 4 to 8. Without temporal filtering, the nitinol stent could not be seen. When the stents were stationary, and the temporal filter weight was increased, the nitinol stent could be clearly visualized due to the quantum noise reduction. When the stents were moving, the filter weight was reduced thus reducing the motion blur and improving the visualization of the stainless steel stent struts.

Conclusions: Motion based adaptive temporal filtering can be implemented to aid during interventional procedures by tracking the motion of the high contrast interventional device to improve the visualization of lower contrast neurovascular objects.

 

4)      A novel hybrid radiotherapy technique combining a VMAT arc with beam angle optimized IMRT fields

Jason Spaans, Lalith Kumaraswamy, Harish Malhotra, Mohammad Bakhtiari,

Matthew Podgorsak, and Daryl Nazareth

Roswell Park Cancer Institute

Purpose:  To develop a new radiotherapy delivery technique, which combines the superior dose conformality of an IMRT technique and the efficiency of a VMAT technique.

Methods and Materials:  A simple beam angle optimization algorithm was developed based on field weight, MLC modulation, and patient anatomy to determine the optimal gantry position for placement of IMRT fields.  The use of one, two, or three IMRT fields was investigated.  A VMAT plan was then generated and optimized with the IMRT plan as the base plan.  The resultant VMAT plan delivery was manually merged with the IMRT plan that was initially generated.  This resulted in a single intensity modulated arc which incorporated the additional IMRT fields in static gantry positions.  The resulting hybrid technique delivers dose continuously using an arc technique, and the gantry pauses during its rotation, to deliver each IMRT field. 

Results:  In a retrospective study of prostate and head & neck cases, the new method was evaluated by comparison with clinical VMAT plans.  The hybrid plan, consisting of two optimized IMRT fields and a single arc, provided the best trade-off between low MU’s and favorable dose distribution.  The new technique demonstrated greater sparing of OAR’s than VMAT, with similar coverage of target structures.  For example, the new technique delivered 9% less dose to 40% of the bladder, 13% less dose to 40% of the rectum, and required 10% fewer MU’s.  In addition, the hybrid plan could theoretically be loaded onto the treatment machine as a single arc field.

Conclusions:  This work indicates a new treatment delivery method incorporating both IMRT and VMAT techniques, that results in the efficient delivery of radiation therapy plans.  In comparison with existing treatment techniques, this hybrid technique provides comparable coverage of target volumes with increased sparing of OAR’s and more efficient treatment delivery. 

 

5)      Dose Calculation with MCNP5 in the Buildup Region for 6MV photon beams

Hassan Abbas1, Jahangir Satti2 and C. A. MacDonald1

1.     Center for X-Ray Optics, Physics Department, University at Albany, Albany, NY

2.     Department of Radiation Oncology, Albany Medical Center, Albany, NY

Purpose: Cylindrical ion chamber measurements are known to overestimate the dose in the build up region. Several authors have investigated different measurement methods and MC simulations for accurate PDD predictions in the buildup region. The potential of MCNP5 to provide accurate dose calculations in the buildup region for 6 MV photon beams was studied.

Method: MCNP5 was used to model a 6 MV photon beam for a Varian linear accelerator. Modeling geometry was based on the vendor provided specifications with the primary collimator corrections proposed by Chibani and Ma. Percentage dose depth ionization (PDIs) curves and cross dose profiles were measured using a Farmer ionization chamber for 10×10 and 30×30 cm2 field sizes. The MCNP5 model was benchmarked by comparison with measurements. Dose in the buildup region (at depths ≤ 1.5cm) was calculated with MCNP5 for 2 mm depth voxels for the 10×10 cm2 field size. In order to calculate the dose at clinically significant depths shallower than 2 mm, a polynomial fit of degree 6 was used on MCNP5 computations in the build up region. Dose calculations in the buildup region are compared with reported measurements and MC simulations with other codes.

Results: Depth dose calculations and cylindrical ion chamber PDI measurements agree within 2% beyond dmax for 10×10 and 30×30 cm2 field sizes. Beam profile calculations and measurements at dmax~1.5 cm and at a depth of 10 cm agree within 2% for flat region of the cross profile for both field sizes. MCNP5 calculated PDDs vary from 16.78% to 41.62% within 1 mm from surface for 10×10 cm2 field size for the 6 MV photon beam. These calculations are comparable to accurate measurements and MC simulations reported in literature.

Conclusion:Accurate dose in the buildup region can be calculated by MCNP5.

 

6)      Evaluation of the Accuracy in the Algorithm used for Optical Patient Alignment.

Juan Carlos Paz Lozada, Daryl Nazareth, and Harish Malhotra

Roswell Park Cancer Institute

Purpose: To analyze and evaluate the intrinsic precision of an optical patient alignment system, which we are currently developing, to assist in patient positioning during breast radiotherapy.  Since the breast is a deformable organ of variable size and shape, standard setup procedures may be inadequate to position the breast properly for treatment.

Methods and Materials: This method employs a standard digital camera, and an in-house constructed calibration phantom (CP), composed of ten identifiable reflecting spheres, mounted on a wooden platform. A CT image of the CP was acquired, to determine the 3D configuration of the spheres. For calibration, the CP is placed on the treatment couch and aligned to the collimator crosshairs.  A digital photograph of the CP is acquired, and a centroid-finding technique is applied to this image to obtain the 2D coordinates of the ten spheres.  These 2D coordinates, along with the known 3D model of the spheres, serves as input to an optimization routine based on the downhill simplex algorithm.  The routine solves for the geometry of the camera location; i.e., the rotation and translation relating the camera to the CP, and therefore to the treatment room geometry.  Based on this information about the camera position and orientation, a patient’s 3D CT data can be projected onto the camera’s imaging plane, and displayed on a monitor, superimposed on the real-time patient image, acquired by the camera as live video. This would enable the therapist to view both the patient’s current and desired positions, and guide in proper patient positioning.

Results: A set of 300 simulated images with different rotation angles and translations were created to evaluate the accuracy of the model.  Once the simulated data was obtained we applied the optimization algorithm to calculate the rotation and translation and compared with the known values.  The results showed errors of less than 1 mm in translation and less than 1 degree in rotation.

Conclusion: It suggests that theoretically the system would be a useful tool that can be used to minimize errors due to inconsistent position during breast radiotherapy.

 

7)      Attention on Details in Radiation Medicine

Dinko Plenkovich

Roswell Park Cancer Institute, WCA Cancer Treatment Center, Jamestown, NY

Purpose:  Between January 23, 2010 and February 27, 2011, the New York Times investigative reporter, Walt Bogdanich, published a series of excellent articles about errors which occurred in radiation medicine.  ECRI Institute, a non-profit healthcare research organization, ranked “Radiation Overdose and Other Dose Errors during Radiation Therapy” the top healthcare technology hazard for 2011.  Attention on details during beam output calibration, radiation therapy simulation, treatment planning, patient setup, and treatment delivery can prevent errors and reduce their severity.  Method and Materials: We have reviewed Mr. Bogdanich’s reports and devised procedures to prevent the errors described in them.  The first article discusses the tragic events pertaining to the head-and-neck IMRT patient who was treated for three days with the multileaf collimator fully open.  The radiation oncologist should have allowed sufficient time for the revision and QA of the IMRT plan. Results: We have implemented a visual reminder for the radiation therapists to place the bolus on the patient.  Our method of marking the patient’s skin or the head immobilization mask has greatly reduced the frequency of errors.  Displaying the carina on digitally reconstructed radiographs of the chest patients helps in verification of portal images.  Conclusion:  The use of modern record-and-verify systems has permitted radiation delivery on an “auto pilot.”   Just as an airline pilot has to monitor the instruments and look through the window of the cockpit, the radiation therapist must pay attention to the details of the treatment console and CCTV monitors throughout the treatment.  Just as there are a pilot and copilot in every commercial airplane, there should be two radiation therapists at the controls of a linear accelerator, and there is plenty of work for both of them.

 

Vendor’s session (15 – 30 min)

 

Novel Cylindrical 3D Scanner - A fresh new approach - Less subjectivity

Jim Ernsberger

Sun Nuclear Corporation

 

Invited talk (60 min)

 

SBRT: A paradigm shift from conventional radiotherapy

Harish Malhotra, PhD

Medical Physicist, Assistant Professor

Roswell Park Cancer Institute

Buffalo, NY

 

 

Directions (to Rochester General Hospital):

 

From the West:  New York State Thruway to Exit 47.  490 East to 390 North to 104 (Ridge Road) East to Carter Street exit.  Follow service road to Hospital entrance.  Parking is available in the Ramp Garage.

 

From Rochester Airport (ROC):  390 North to 104 (Ridge Road) East to Carter Street exit.  Follow service road to Hospital entrance.  Parking is available in the Ramp Garage.

 

From the East:  New York State Thruway to Exit 45. 490 West to 590 North to 104 West to Goodman Street/Portland Avenue exit. Follow service road to Portland Avenue and turn left. Hospital is on the right. Parking is available in the Ramp Garage.

 

From the South:  390 North to 590 North to 104 West to Goodman Street/Portland Avenue exit. Follow service road to Portland Avenue and turn left. Hospital is on the right. Parking is available in the Ramp Garage.

 

 

 

Please park in the Portland Ramp (1425 Portland Av). Enter the hospital on the star  (*) floor from the visitor elevator.  Thus you will enter the Polessini Pavilion. The meeting rooms are on the left hand side.

 Vendor exhibits will be in the  Atrium. The Atrium is a 20 second (maybe less) walk from the Twig aud and the meeting rooms