UNYAAPMmeetingletterhead

Upstate New York Association of Physicists in Medicine, Inc.      (A Chapter of the AAPM)

Spring Meeting – May 6, 2010

Staybridge Suites-ROCHESTER UNIVERSITY

1000 GENESEE STREET

ROCHESTER, NY 14611

 

12:00 pm – 4:00 pm    Sponsoring Vendor Exhibits:

Resonant Medical Inc., Varian, TomoTherapy Inc., IBA, Elekta, Sun Nuclear, BrainLAB AG, CIVCO Medical Solutions, Upstate Linac Services, LLC        

                       

10:00

Business Meeting

11:10

Lunch                                                    Sponsored by  Sun Nuclear & Elekta

12:00

Meeting Introduction

Michael Schell Ph.D., UNYAPM President

Vendor Session

12:05

ViewRay

Will Wells

Proffered Paper Session

12:20

External beam dose perturbation from non-radioactive I-125 seeds: film and Monte Carlo measurements

James P. Steinman, and Harish K. Malhotra

12:30

High Resolution CCD based Micro-Angiographic Fluoroscopic x-ray detector in Single Photon Counting mode for radionuclide imaging.

A. Panse, A. Jain, W. Wang, R. Yao, D. Bednarek, S. Rudin

12:40

Risk of secondary cancer resulting from unaccounted exposures associated with Gamma Knife® radiosurgery for the model 4C and Perfexion

Tuan-Anh Tran, Vincent Wu, Richard P. Harvey III, Dheerendra Prasad, and Matthew B. Podgorsak

12:50

Reduction of effective dose using region-of-interest techniques for neuroangiography

Kamaljit K Gill, Daniel R. Bednarek, and Stephen Rudin

1:00

Loss of biological effects from prolonged treatment times for sliding window IMRT versus VMAT treatment techniques

Jonathan Schmitt and Zhou Wang

1:10

Study of the Effect of the Line-Focus Principle on Generalized MTF for the Microangiographic Fluoroscope (MAF) System

Sandesh Kumar Gupta, Amit Jain, Danial R. Bednarek, and Stephen Rudin

1:20

Influence of water temperature during absolute calibration on patient dose delivery

Tuan-Anh Tran, Vincent Wu, James P. Steinman, Khalid Hassan, Harish K. Malhotra, and Matthew B. Podgorsak

1:30

Refreshments and Vendor Exhibits – Vestibule        Sponsored by Sun Nuclear

                                                         Error Reduction in Radiation Oncology Discussion

2:00-4:00

Panel Discussion

Moderator: Michael Schell Ph.D.


Driving Directions to the University of Rochester Medical Center, Helen Wood Hall, 255 Crittenden Blvd

Google map link

 

From the West:  New York State Thruway to Exit 47.

  -  Take exit #47/LEROY (RT-19)/ROCHESTER onto I-490 E (Toll applies) - go 19.63 mi

  -  Take exit #9B/AIRPORT onto I-390 S - go 2.9

  -  Take exit #17/SCOTTSVILLE RD. - go 0.2 mi

  -  Turn Left on SCOTTSVILLE RD(RT-383) - go 0.6 mi

  -  Bear Right on ELMWOOD AVE - go 0.7 mi

  -  Turn Right on Kendrick Rd - go 0.2 mi

  -  Turn Left on Crittenden Blvd - go 0.2 mi

Parking is available in the Visitors lot next to Helen Wood Hall, and also in Ramp Garage.

 

From Rochester Airport (ROC):

  -  Take exit #9B/AIRPORT onto I-390 S - go 2.9

  -  Take exit #17/SCOTTSVILLE RD. - go 0.2 mi

  -  from there follow the directions as above

 

From the East: New York State Thruway to Exit 46.

  -  Take exit #46/ROCHESTER/CORNING onto I-390 N toward ROCHESTER (Toll applies) - go 6.9mi

  -  Take exit #16/E HENRIETTA RD/W HENRIETTA RD (RT-15) - go 0.2 mi

  -  Turn Right on E HENRIETTA RD(RT-15A) - go 0.9 mi

  -  Bear Right on MT HOPE AVE(RT-15) - go 0.2 mi

  -  Turn Left on Crittenden Blvd - go 0.3 mi

 

From the South:  390 North and follow the directions above when coming from the East.

 

 

Visitor

Parking

 
 


                                      

UNYAPM SPRING 2010 MEETING PROCEEDINGS

 

 

ABSTRACTS

 

External beam dose perturbation from non-radioactive I-125 seeds: film and Monte Carlo measurements

James P. Steinman, and Harish K. Malhotra

 

Purpose:  Large numbers of radioactive seeds are often used in prostate brachytherapy procedures.  External beam radiotherapy is often used to salvage failed brachytherapy treatments ignoring their presence.  Present study attempts to quantify the dose perturbation due to these seeds as a function of energy, depth, field size, number of seeds, etc. during external beam treatments. 

Method and Materials:  A number of non-radioactive I-125 seeds were procured.  Film measurements were primarily carried out using Kodak XV2 layered above and below an I-125 seed placed in a groove on a Lucite plate with 5-cm buildup and 10-cm backscatter at 95-cm SSD.  The phantom was irradiated with and without seed with 6 MV photons with a 1x1cm² field size.  Monte-Carlo simulations were done using DOSXYZnrc and compared with Gafchromic-EBT2 film.  Effect of energy, depth, and field size including metals of various Z of the seed’s dimensions was also studied.  Study also looked into effect of 3 seeds spaced 0.5-cm vertically and effect of two opposing fields. 

Results:  XV film measurements for a single and three I-125 seeds show a localized dose enhancement of 6.3% upstream but reduction of 10.9% downstream.  With two opposing fields, a cold spot around the seed of ~3 percent was observed.  Increasing beam energy and field size decreased the effect. Use of higher Z of materials greatly increased perturbation.  Varying depth did not change effect.  DOSXYZnrc and EBT2 film verified maximum dose enhancement of 15% upstream and -20% downstream of the I-125 seed surface.  In general, the range of the dose perturbation was noticed up to ~2-mm upstream and ~5-mm downstream. 

Conclusion:  Presence of I-125 seeds causes dose perturbation which depends on energy, field size, depth, and material.  With multiple seeds spaced apart and multi-field external beam radiotherapy, the net perturbation may not be clinically significant.

 

High Resolution CCD based Micro-Angiographic Fluoroscopic x-ray detector in Single Photon Counting mode for radionuclide imaging.

A. Panse, A. Jain, W. Wang, R. Yao, D. Bednarek, S. Rudin

Toshiba Stroke Research Center, SUNY Buffalo, Buffalo NY.

 

This experiment demonstrates the use of the high-resolution Micro-Angiographic Fluoroscopic (MAF) detector in single-photon counting (SPC) mode for nuclear medicine imaging. The MAF uses a CCD camera and fiber-optic taper, has 1024 x 1024 pixels with an effective pixel size of 35 microns and is capable of real-time imaging at about 30 fps. A 300 micron cesium-iodide phosphor is coupled to a light image intensifier (LII) through a fiber optic taper. Large variable gain of the LII provides quantum-limited operation with essentially no additive instrumentation noise and enables the MAF to operate in both energy-integrating (EI) and the very-sensitive low-exposure SPC modes. A custom-made phantom, with hot rods ranging from 0.9mm diameter to 2.3mm diameter, filled with 1 mCi of 125I (35.5 keV) was used as a test object. The collimator used, was a medium-energy, gamma-camera collimator with 1-mm diameter parallel holes and was placed between the phantom and the MAF.  Data was acquired at 20 fps. Two algorithms to localize the events were used. (i) Simple threshold and (ii) Weighted Centroid method. When the data was processed, we could see a pattern corresponding to the collimator holes in the images. To remove this pattern, the collimator was moved multiple times in random directions after equal intervals of time to maintain approximately same exposure per position.  The image generated with the simple threshold method is more blurred than the weighted centroid method. In both the cases, all the hot rods could be clearly identified. Currently we are limited by the collimator resolution for radionuclide imaging. This experiment enabled us to show that the same MAF can be used in both nuclear-medicine imaging and x-ray imaging. : This work received support from: NIH Grants R01EB002873 and R01EB008425

 

Risk of secondary cancer resulting from unaccounted exposures associated with Gamma Knife® radiosurgery for the model 4C and Perfexion

Tuan-Anh Tran, Vincent Wu, Richard P. Harvey III, Dheerendra Prasad, and Matthew B. Podgorsak

 

Purpose:  Gamma Knife Radiosurgery is a highly precise modality for the treatment of intracranial diseases; however, there is potential for unaccounted exposures during treatment.  These extracranial and intracranial exposures are measured for both the Gamma Knife model-4C and Perfexion™; measured doses from this study are used to determine the lifetime potential for fatal secondary cancer and risks of aggregated detriment to exposed organs. 

Method and Materials:  Additional, unaccounted dose associated with treatment coordinate repositioning from intershot transit (model-4C) and shutter effects (Perfexion) was measured with an ionization chamber positioned throughout a spherical phantom.  Organ doses were measured for a typical treatment for both models using film dosimetry (Gafchromic EBT) and a Rando phantom.  The Linear-No Threshold (LNT) model is used to determine lifetime risk of radiation induced second cancer formation to various anatomical structures.

Results:  Intershot transit and shutter add intracranial exposure that is unaccounted for by the GammaPlan treatment planning system.  The LNT-model predicts a lifetime fatal cancer risk as high as 6.2 incidences per 100,000 people for the model-4C, and 4.8 incidences per 100,000 for the Perfexion, assuming a homogeneous exposure to the brain.  Considering areas around the target-site in the brain as separate organs, this model predicts increased fatal cancer risk of 50 and 132 incidences per 100,000 for the Perfexion™ and model-4C, respectively.  The lifetime risk of fatal lung cancer can be 18 and 31 incidences per 100,000 for the Perfexion™ and model-4C, respectively.  Fatal thyroid cancer risk is 1 and 2 in 100,000 incidences for the Perfexion™ and model-4C, respectively.  Organ dose is lower for the Perfexion than the model-4C, reducing overall risk.

Conclusion:  Appropriate accounting for and minimization of intershot transit and shutter effects may reduce secondary cancer formation, especially when treating pediatric patients, patients with benign disease or those with greater life expectancy.

 

Reduction of effective dose using region-of-interest techniques for neuroangiography

Kamaljit K Gill, Daniel R.  Bednarek, and  Stephen Rudin

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

 

Purpose: We evaluate the reduction of effective dose (ED) obtained by limiting the field of view (FOV) to a region of diagnostic or interventional interest in neuroangiographic imaging. The effect on dose of combining higher-dose ROI with a reduced-intensity peripheral field using dual detectors for cone-beam CT is investigated. Region-of-interest (ROI) imaging has the potential to reduce effective dose, while improving image quality by reducing scatter and providing increased resolution.

Method and Materials: We used the PC program for X-ray Monte Carlo (PCMXC, STUK, Helsinki, Finland) to calculate the ED for three FOV’s: 20x20 cm for fluoroscopic flat panel, 3.6x3.6 cm FOV for the high resolution microangiographic fluoroscope (MAF), and 20x3.6 cm FOV for dual-detector cone beam CT, which is used to prevent truncation artifacts. These calculations were done for 3 beam filters selectable on the Toshiba Infinix C-Arm unit: 1.8 mm Al, 0.2 mm Cu and 0.3 mm Cu. For this study, the primary region of interest is the circle of Willis. The ED is calculated at constant air kerma at the image receptor of 1 microgray and at constant mAs as a function of kVp for all FOV’s. For attenuation calculations, the AAPM head phantom (Report 31) was used and “spectrum processor 78” was used for determining the exposure at the entrance skin for constant air kerma at the receptor of 1 microgray. We calculated the integral ED for 210 frames over 210 degrees LAO/RAO around the head for the Toshiba C-arm to get the total dose for CBCT. 

Results: Effective dose per detector exposure decreases with increasing kVp for all three beam filters and for all FOV’s. Compared to the FPD, use of the MAF detector allows a reduction of ED by a factor ranging between 50 to 70 over the range of beam filters and kVp’s used

Conclusions: The decrease in effective dose is very much dependent on the ROI size. Using the MAF we get a substantial reduction in effective dose per detector exposure.(Support: Toshiba Medical Systems, NIH R01EB002873)

 

Loss of biological effects from prolonged treatment times for sliding window IMRT versus VMAT treatment techniques

Jonathan  Schmitt and  Zhou Wang

Roswell Park Cancer Institute

 

Purpose: Intensity Modulated Radiation Therapy (IMRT) is an effective method of maximizing dose conformity while minimizing damage to healthy tissue. These benefits are achieved by using highly variable spatiotemporal radiation fields. The spatial effects of IMRT are commonly used as a technique to evaluate treatment quality. However, the use of spatial information alone neglects the fact that cell survival is directly related to the temporal dose deposition. This study uses the linear quadratic (LQ) model, with the Lea-Catcheside dose protraction factor in order to investigate the change in biological effectiveness between IMRT modalities, including sliding window (DMLC) and volumetric modulated arc therapy (VMAT).

Methods: The temporal dose deposition was calculated using Eclipse treatment planning software. For both a prostate and head/neck plan, a specific coordinate was chosen in the tumor and the dose was calculated as a function of time. The dose-time relationship was used to calculate the protraction factor and the biological effective dose (BED) with varying repair half-times and α/β ratios. The BED results were normalized to an ideal treatment delivery when the dose is deposited instantaneously (G(t) = 1).

Results: Switching from VMAT to DMLC, for both the prostate and head/neck treatments, revealed a significant drop in the biological effects. A comparison of the DMLC and VMAT techniques showed a reduction in BED of 4.5% and 3.3% for head/neck (α/β = 10) and prostate (α/β = 6) treatments respectively. These results are due to the significant difference in treatment times for the DMLC and VMAT treatment techniques.

Conclusion: By comparing sliding window and VMAT techniques it is clear that temporal dose deposition is an important characteristic in determining the biological effects from different treatment modalities. A comparison of the biological effects clearly indicates that it is advantageous to rapidly irradiate the tumor volume. Although this study was theoretical, it is expected that an empirical study will reveal the same biological effects. 

 

 

 

 

 

Study of the Effect of the Line-Focus Principle on Generalized MTF for the Microangiographic Fluoroscope (MAF) System

Sandesh Kumar Gupta, Amit Jain, Danial R. Bednarek, and Stephen Rudin

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

Purpose: The Generalized MTF (GMTF) is known to provide a metric for the performance of the total imaging system, which includes the effect of scatter, geometric un-sharpness due to finite focal spot size and object magnification. The effective focal spot size changes as we move along the direction of tube axis due to the Line-Focus Principle, and changes minimally in the direction perpendicular to the tube axis. Therefore, the effect of the Line-Focus Principle on the Generalized MTF can be studied along the direction of the tube axis. In this report, we evaluate the newly developed high-resolution, small-field-of-view (3.6x3.6cm2) MAF detector, which requires the use of a small effective focal spot to maintain the high spatial frequency components of the system GMTF. Method and Materials: Three different focal spots, three different object magnifications, and three different positions along the tube axis direction are used for comparison. Focal spot measurements were performed with a pin-hole assembly using the same technique parameters (70 kVp, 4 mAs) and a magnification for the pin-hole of 2.18. X-ray intensity values were determined for all the focal spot sizes and locations in the field. Results: The generalized MTF was found to be degraded at higher spatial frequencies as focal spot size and object magnification increased. The Generalized MTF was found to be improved towards the anode direction for each focal spot. We give a comparison between small and medium focal spots in terms of resolution and intensity along the tube axis direction. X-ray intensity was reduced by 9% toward the anode side for each focal spot as compared to the central axis. Conclusions: This work demonstrates that high Generalized MTF with only a minimal reduction in x-ray intensity can be achieved using the Line-Focus Principle. (Support from: NIH Grants R01EB002873 and R01EB008425)

 

 

Influence of water temperature during absolute calibration on patient dose delivery

Tuan-Anh Tran, Vincent Wu, James P. Steinman, Khalid Hassan, Harish K. Malhotra, and Matthew B. Podgorsak

 

Purpose:  Calibrations of medical linear accelerators and other specialized radiation delivery units are typically completed in water at room temperature (20-25 C).  However, delivery of therapeutic radiation is to a human body whose temperature ranges from 28-37 C.  Currently, there are corrections for several parameters in TG-51, but none account for body temperature.  Does the temperature influence the amount of dose absorbed? 

Method and Materials:  A closed water tank was constructed to allow transmission measurements of high energy photon beams through water with temperature ranging from 7-45 C.   The ionization chamber was isolated from the heat of the tank; any effects from temperature are measured indirectly through transmission.  Percent depth dose (PDD) measurements were also obtained to study the temperature effects at various depths. 

Results:  Measured data shows an increased transmission with temperature; however, the relationship is non-linear.  The change in transmission is slower than the change in water density, indicating more dose is deposited for the same MU as temperature of a medium increases.  At 37 C, the 6 MV and 23 MV beams transmit 0.4925% and 0.3394% less than expected, respectively.  The PDD shift towards a greater depth with increasing temperature indicates temperature dependence.

Conclusion:  If the beam transmission through the water is equal with density change, the transmitted beam should change equally with density if there is no temperature effect.  However, if we observe a deviation between the transmitted beam and the density, then the water temperature may cause a deviation.  Therefore, for a given beam, the absorbed dose will increase with increasing temperature.  This indicates greater dose than predicted resulting from energy of the water molecules.  Since TG-51 requires the use of PDD, and PDD is shown to depend on temperature, then the absolute dose calibration will be different depending on the temperature of the environment.