July 24, 2008 -- Next week in Houston, thousands of scientists and health professionals will meet at the 50th meeting of the American Association of Physicists in Medicine (AAPM), the largest association of medical physicists in the world. There, from July 27 to July 31, they will present the latest technologies for imaging and treating diseases like cancer and discuss the safety, ethical, and regulatory issues facing the field today.
Almost all the hospitals in the United States today benefit from the work of medical physicists. They help diagnose illness by designing and implementing new and better ways of imaging the human body. They create treatment strategies for fighting cancer and other diseases. They also seek to reduce the risk to people undergoing these treatments.
The Houston area has a large number of medical physicists because of the concentration of universities and hospitals in the area, including The University of Texas M.D. Anderson Cancer Center, which is ranked by U.S. News & World Report as the top hospital in the nation for cancer care.
M.D. Anderson has a large facility dedicated to proton therapy -- a technique that pulses powerful protons (a constituent of atomic nuclei) into tumors, killing the cancer cells therein. The facility began treating patients in 2006 and now treats about 70 people a day. Many of the medical physicists making presentations at AAPM work at the proton therapy facility and will be presenting basic and clinical research on how they optimize proton therapy.
Other presentations will focus on research into developing and applying new technologies for visualizing the body's processes at the molecular and cellular levels and for treating diseases. M.D. Anderson Cancer Center already has a number of medical physicists who are leaders in this research, and it is likely to grow in the future. M.D. Anderson is building a brand-new imaging research center, called the Center for Advanced Biomedical Imaging Research, in collaboration with The University of Texas Health Science Center at Houston, GE Healthcare, and the Texas Enterprise Fund.
This release highlights some of the research being presented at the AAPM meeting by Houston-area medical physicists. Journalists are invited to cover the AAPM meeting in person or remotely. Additional news releases will detail other specific meeting highlights. All news releases will be hosted on the AAPM website (see link below).
1) MODIFYING RADIATION THERAPY MACHINES WILL BENEFIT PEOPLE WITH SMALL TUMORS
"...The risk that exposure to stray radiation during cancer therapy will cause secondary malignancies is small -- it should never deter one from following one's doctor's advice and undergoing radiation therapy for the treatment of cancer. Nevertheless, stray radiation as a potential side effect should always be minimized, and a team of researchers at M.D. Anderson Cancer Center is exploring ways to reduce stray radiation, and the risk it brings, by modifying the radiation delivery machine..." MORE DETAILS BELOW
2) MIXED BEAM THERAPY MAY OFFER ADVANTAGES FOR TREATMENT OF SHALLOW TUMORS
"...Recent work by team of researchers from M.D. Anderson Cancer Center, the Mayo Clinic, and Louisiana State University may bring clinicians closer to the use of mixed beam therapy, which would combine electron and x-ray beams and improve therapeutic outcomes in people with shallow tumors..." MORE DETAILS BELOW
3) GOLD NANOSHELLS HELP VISIBLY HEAT AND DESTROY CANCER
"... Most cancer tumors that have clear borders and are well defined have traditionally been treated successfully by surgical removal. But not all cancers respond to conventional surgery. More importantly, conventional surgery brings risks of complications and long recovery periods that can negatively impact a person's quality of life. To overcome these treatment limits, a group of researchers based at the University of Texas M.D. Anderson Cancer Center, turned to lasers and nanotechnology..." MORE DETAILS BELOW
4) GUIDING LASERS TO THEIR TARGET
"...Like most treatments, laser therapy can benefit from image guidance. A Houston-based company has developed an MRI-guided system that has been tested and is now FDA-approved..." MORE DETAILS BELOW
5) RESEARCHERS QUANTIFY SECONDARY RISKS OF PROTON THERAPY "... Researchers from M.D. Anderson Cancer Center and the Georgia Institute of Technology have completed a study that will help people considering proton therapy for cancer treatment and the physicians who treat them..." MORE DETAILS BELOW
6) PHYSICISTS PROVIDE "GUIDING HANDS" FOR PROTON THERAPY
"... While physicians manage the treatment of people, behind the scenes, proton physicists play a crucial role, providing support and guidelines for treatment planning for calculation of dose distributions, measurements of radiation delivery, measurements of proton beam data, quality assurance of all measuring equipment and of the proton accelerator, and calibration of proton beams, all essential to successful treatment outcomes...." MORE DETAILS BELOW
7) NOVEL INSTRUMENT MAY IMPROVE UPON THE SAFETY AND EFFECTIVENESS OF CERVICAL CANCER BRACHYTHERAPY TREATMENTS
"...To treat cervical cancer, clinicians apply a high dose of radiation directly to diseased tissues, which may be administered using a device called an intracavitary brachytherapy applicator. Researchers at the M.D. Anderson Cancer Center have designed a new applicator made out of special materials that makes it compatible with MRIs, and features a movable shield that both reduces the exposure of healthy tissues to radiation and permits the use of CT and MRI scans..."MORE DETAILS BELOW
1) MODIFYING RADIATION THERAPY MACHINES WILL BENEFIT PEOPLE WITH SMALL TUMORS
The risk that exposure to stray radiation during cancer therapy will cause secondary malignancies is small -- it should never deter one from following one's doctor's advice and undergoing radiation therapy for the treatment of cancer. Nevertheless, stray radiation as a potential side effect should always be minimized, and a team of researchers at M.D. Anderson Cancer Center is exploring ways to reduce stray radiation, and the risk it brings, by modifying the radiation delivery machine.
A recent study examined whether stray radiation was reduced by removing the flattening filter from a standard radiation machine. Currently, the flattening filter is included in all standard radiation machines to ensure uniformity of the radiation beam. However, with current technology, optimal treatments for most radiation machines does not require a uniform beam, rendering the flattening filter completely unnecessary for the majority of radiation treatments. In this case, it may be advantageous to remove it from the radiation machine as it is a source of stray radiation.
This study, one of many undertaken by this group in the last four years, found that there were a large number of patients (particularly those with small tumors) who could benefit from treatment with a radiation machine without the flattening filter. Such equipment would produce less stray radiation, corresponding to a decreased risk of developing a second cancer later in life. In addition to reduced stray radiation, several other benefits to the patient and hospital staff exist such as potentially improved treatments, faster treatment delivery, and less stray radiation to medical personnel.
Modification of traditional radiation equipment will require collaboration with machine manufacturers, and while the logistics of removing the flattening filter are not particularly challenging, what will be more challenging is ensuring that the modified machine remain safe for patient treatments. When the flattening filter is removed, the built-in double checks and triple checks that assure patient safety must be redesigned or at least re-evaluated to ensure they still rigorously ensure safety for people undergoing treatment. This work is a step in reducing stray radiation for patients with small tumors, however, methods to further reduce stray radiation, and thereby further reduce the risk of secondary cancers, will continue to be a priority.
Talk (TH-D-AUD A-5), "Dose Outside the Treatment Volume Following Removal of the Flattening Filter" is at 1:18 p.m. on Thursday, July 31 in Auditorium A. Contact: S. Kry (sfkry@mdanderson.org).
Abstract: http://www.aapm.org/meetings/amos2/pdf/35-8297-12719-983.pdf
2) MIXED BEAM THERAPY MAY OFFER ADVANTAGES FOR TREATMENT OF SHALLOW TUMORS
Recent work by team of researchers from M.D. Anderson Cancer Center, the Mayo Clinic, and Louisiana State University may bring clinicians closer to the use of mixed beam therapy, which would combine electron and x-ray beams and improve therapeutic outcomes in people with shallow tumors.
Intensity-modulated x-ray therapy (IMRT) is a clinical technique that delivers radiation to the tumor volume and spares normal tissues, while an x-ray multi-leaf collimator is used to help "match" the dose distribution to complex tumor shapes. Mixed-beam therapy combines both intensity-modulated electron and x-ray beams using an x-ray multi-leaf collimator to improve target coverage and sparing of critical structures, particularly for cancers of the head, neck and breast. This is possible since the dose from electron beams is reduced quickly as it penetrates through the patient so that there is almost no dose exiting the patient. Using an x-ray multi-leaf collimator to modulate the intensity of electron beams is advantageous because the hardware needed is already available on most existing linear accelerators, though collaboration with the manufacturers of linear accelerators would be required to implement the mixed-beams technique in the clinic.
The mixed-beam technique could be used for people with tumors close to the skin surface, such as parotid, ear or sinus tumors for head and neck patients and in most breast cases. Mixed beam therapy reduces dose to normal tissue resulting in fewer negative side effects, which may lead to fewer secondary malignancies in the future.
Dr. Rebecca Weinberg (RWEINBERG@swmail.sw.org) has taken the first step in realizing the potential of mixed-beam therapy with an x-ray multi-leaf collimator. "There were many other ways of approaching the mixed-beams treatment planning that I was unable to explore due to time constraints and limitation of the currently-available treatment planning software," explains Weinberg. Further research is needed to optimize the mixed electron and x-ray dose distributions, especially reducing dose calculation and clinical treatment delivery times to offer cancer patients the best possible outcome.
Talk (TH-D-AUD B-5), "Electron Intensity Modulation for Mixed-Beam Radiation Therapy with An X-Ray Multi-Leaf Collimator" is at 1:18 p.m. on Thursday, July 31, 2008 in Auditorium B.
Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9349-94925-545.pdf
3) GOLD NANOSHELLS HELP VISIBLY HEAT AND DESTROY CANCER
Most cancer tumors that have clear borders and are well defined have traditionally been treated successfully by surgical removal. But not all cancers respond to conventional surgery. More importantly, conventional surgery brings risks of complications and long recovery periods that can negatively impact a person's quality of life.
To overcome these treatment limits, a group of researchers based at the University of Texas M.D. Anderson Cancer Center, turned to lasers and nanotechnology. They explored an emerging minimally-invasive approach to treating tumors that delivers a lethal dose of laser-generated heat to tumors, known as thermal ablation. To improve thermal ablation, they added a nano-twist that precisely guides and concentrates heat in targeted tumors.
Working with Nanospectra Biosciences, Inc., researchers injected nanoshells made of gold silica into canine models of brain cancer. The nanoshells homed in on the target tumors, where they were taken in by the tumor cells. Next, researchers irradiated the nanoparticle-filled tumor with low-power laser light to selectively heat the tumor-but not the surrounding, healthy tissue. M.D. Anderson researchers added iron-oxide cores to the nanoshells to make them visible by magnetic resonance imaging so researchers could observe the process.
Results from these experiments were supported by numerical modeling studies, and by scanning electron microscope data showing destructive thermal increases near the tumors' blood supplies. "Based on these encouraging early results, we conclude that the use of magnetic resonance temperature imaging and gold nanoshells hold the very real possibility of meeting the long-sought goal of improving the precision of thermal ablation, while sparing healthy tissue," explains M.D. Anderson Cancer Center's R.J. Stafford, Ph.D. (jstafford@mdanderson.org). "Temperature imaging and guidance is an invaluable tool furthering this approach as it moves from feasibility studies to future use in human clinical trials."
Talk (WE-C-351-1), "Characterization of Gold Nanoshells for Thermal Therapy Using MRI" is at 10:00 a.m. on Wednesday, July 30, 2008 in room 351.
Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9309-76032-210.pdf.
4) GUIDING LASERS TO THEIR TARGET
Like most treatments, laser therapy can benefit from image guidance. A Houston-based company has developed an MRI-guided system that has been tested and is now FDA-approved.
Laser induced thermal therapy (LITT) destroys unhealthy tissue, like cancer, with the intense heat supplied from a laser. The laser light is channeled through an optical fiber that can be inserted practically anywhere in the body. One of the biggest challenges in LITT is that the target cannot get too hot, otherwise it will char - thus preventing further laser light from penetrating into the tissue.
To avoid this, physicians have traditionally measured the temperature at some point near the target using a thermometer-like probe. But real-time imaging could provide a non-invasive means to monitor the temperature throughout the target region. In particular, MRI provides a sensitive temperature probe. The frequency of the MRI signal, which depends on the magnetic properties of water molecules, shifts as the temperature of the corresponding tissue changes.
Using this effect, Visualase, Inc., has developed a closed-loop MRI guided LITT system that provides the user with a temperature map of the target region and calculates the corresponding dose (i.e. the likelihood that cells in some region will die from the applied heat). If nearby healthy tissue is receiving too much heat, or if the temperature is approaching the charring temperature, the user can respond by changing the laser power or shutting it off, which helps to increase both the safety and efficacy of the procedure.
Trials of the system were independently performed on canines by R. Jason Stafford (jstafford@mdanderson.org) from the University of Texas M.D. Anderson Cancer Center, and his collaborators. Several LITT lesions were made in the brain, spine and prostate with MRI guidance. The results showed that the machine's calculated dose matched up well with a post-operation assessment. Initial safety studies have also been performed in human patients and the device has recently received FDA approval. Stafford thinks MRI-guided LITT will provide a less invasive alternative to conventional surgery. He is currently working to improve the real-time targeting and heat delivery.
Talk (TH-D-AUD C-8), "Closed-Loop Guidance of Laser Induced Thermal Therapy Using MRI" is at 1:54 p.m. on Thursday July 31, 2008 in Auditorium C.
5) RESEARCHERS QUANTIFY SECONDARY RISKS OF PROTON THERAPY
Researchers from M.D. Anderson Cancer Center and the Georgia Institute of Technology have completed a study that will help people considering proton therapy for cancer treatment and the physicians who treat them. While proton therapy offers great advantages over traditional radiation therapy by delivering radiation dose to the tumor volume while sparing the adjacent healthy tissue/organ, there was concern that secondary neutrons produced along the proton path in the treatment machine and inside the patient could give unwanted dose and pose risks for secondary malignancies.
Prior to this study, there has been very limited measured data of neutron spectrum and dose equivalent from proton therapy in the literature due to the difficulty in measuring high-energy neutrons. However, this team of scientists used a method sensitive to neutrons ranging from thermal energy to 1 GeV to measure the neutron spectral dose equivalent around a mini-phantom using a proton beam simulating treatment typical for children, in order to determine neutron dose equivalent from proton irradiation. It was also critical for the researchers to determine how much of the neutron dose equivalent was generated inside the body since neutrons from the treatment head can be reduced by using low-neutron-generating material, shielding, or scanning beam technique, while neutrons produced inside the body cannot be reduced.
Results showed a maximum neutron dose equivalent of less than 1% of the prescribed proton dose, a low enough dose that it should not be a concern even for children receiving proton therapy. In addition, the major contribution was from neutrons produced in the treatment head, which can be mitigated by using several available techniques. This should provide radiation oncologists confidence that proton irradiation can be used to treat people with cancer, including children, without worrying about secondary malignancies. This also makes a compelling case for new scanned beam proton therapy as compared with passive scattering beam.
Talk (Th-D-AUD-A2), "Measurement of Neutron Spectrum and Ambient Dose Equivalent Around a Mini-Phantom at a Proton Therapy Facility" is at 12:42 p.m. on Thursday July 31, 2008. Contact: Z Wang (zlwang@mdanderson.org).
Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9559-78392-720.pdf.
6) PHYSICISTS PROVIDE "GUIDING HANDS" FOR PROTON THERAPY
Proton therapy offers great benefits as a treatment modality in radiation oncology for a variety of hard to treat tumors. While physicians manage the treatment of people, behind the scenes, proton physicists play a crucial role, providing support and guidelines for treatment planning for calculation of dose distributions, measurements of radiation delivery, measurements of proton beam data, quality assurance of all measuring equipment and of the proton accelerator, and calibration of proton beams, all essential to successful treatment outcomes.
Making the most of the characteristics of proton beams is the role of a team at M.D. Anderson Cancer Center using a proton machine for treatment of cancerous tumors. Proton therapy is a preferred method of treatment where limited radiation dose to critical organs is crucial, an option that may not be feasible to achieve in some instances when people are treated with high energy photon radiation. This is especially valuable in cases such as craniospinal irradiation for pediatric Central Nervous System tumors or in the treatment of people with lung cancer where dose can be restricted to the tumor without affecting nearby tissue and organs.
Currently two techniques are used for delivering proton beams. Passively scattered proton beams deliver uniform dose to the tumor and a small region of adjacent tissue and are shaped laterally by apertures and distally by compensators to reduce the dose to healthy tissue. M.D. Anderson Cancer Center has pioneered a second technique in North America that uses a pencil beam to focus the dose. The pencil beam delivers dose to the tumor at many different spots and multiple layers within the tumor, dramatically reducing the dose to healthy tissue as compared to passively scattered proton beams. The technique does not use apertures and compensators but instead restricts the dose by selecting the spots confined within the tumor. The dose calculation and the accuracy of delivery of these pencil beams is a complex process, but offers great advantages for sparing healthy tissue.
While proton therapy is improving both treatment and quality of life for people with tumors, there is still a great deal to be learned in order to maximize the benefits of this treatment modality. Dose delivery in an inhomogeneous media such as the human body needs to be further understood and investigated in order to assure more accurate dose calculation for optimal dose delivery to the tumor while sparing surrounding tissue, a major advantage offered by proton therapy. The M.D. Anderson team is hoping that their work will benefit others in the field. Dr. Bijan Arjomandy (barjomandy@mdanderson.org), a physicist at the M.D. Anderson Proton Therapy Center in Houston explains, "We hope that by sharing our experiences in developing such a QA program, we will provide an insight for new proton therapy facilities just establishing their programs," he says.
Talk (TH-D-352-6), "An Overview of Comprehensive Proton Machine Quality Assurance at the University of Texas M.D. Anderson Cancer Center" is at 1:30 p.m. on Thursday July 31, 2008 in Room 352.
Abstract: http://www.aapm.org/meetings/amos2/pdf/35-8323-48323-548.pdf
7) NOVEL INSTRUMENT MAY IMPROVE UPON THE SAFETY AND EFFECTIVENESS OF CERVICAL CANCER BRACHYTHERAPY TREATMENTS
To treat cervical cancer, clinicians apply a high dose of radiation directly to diseased tissues, which may be administered using a device called an intracavitary brachytherapy applicator. Imaging the treated areas using computerized tomography (CT) or magnetic resonance imaging (MRI) improves the effectiveness of treatments because the scans allow clinicians to accurately plan the radiation treatments. But when so-called "shielded" applicators, which contain metal shields to protect healthy bladder and rectal tissues from radiation exposure, are used to deliver these treatments, CT images exhibit distortion. Furthermore, the devices themselves are not compatible with MRI scanners.
A new design avoids those problems. The applicator was invented and developed by the faculty at the M.D. Anderson Cancer Center and evaluated by Ph.D. medical physics candidate, Michael J. Price (mjprice@mdanderson.org) for his dissertation work under the direction of Firas Mourtada, Ph.D. It is made out of special materials that makes it compatible with MRIs, and features a movable shield that both reduces the exposure of healthy tissues to radiation and permits the use of CT and MRI scans. Because the shield can be moved out of the path of the scanners' beams, the applicator can be used in conjunction with CT without distortion to the images. In addition, Price says, "the position of the shield can be adjusted as a function of specific patient anatomy," allowing clinicians to tailor treatments for each individual patient. Preliminary studies by the MD Anderson team show that the device may reduce the radiation dose to the rectum by 22% when compared to a commonly used CT/MRI-compatible intracavitary brachytherapy applicator.
Talk (SU-H-AUD C-10), "The Imaging and Dosimetric Capabilities of a Novel CT/MR-Suitable, Anatomically Adaptive, Shielded HDR/PDR Intracavitary Brachytherapy Applicator for the Treatment of Cervical Cancer" is at 5:48 p.m. on Sunday, July 28, 2008.
Abstract: http://www.aapm.org/meetings/amos2/pdf/35-9284-60990-964.pdf.
RELATED LINKS
AAPM home page: http://www.aapm.org
Abstracts and search form http://www.aapm.org/meetings/08AM/MeetingProgram.asp
Press Guide http://www.aapm.org/meetings/08AM/VirtualPressRoom/
Background article about how medical physics has revolutionized medicine:
http://www.newswise.com/articles/view/538208/
HOW TO COVER THE MEETING
Reporters who would like to attend the meeting in person should fill out the press registration form on the AAPM Virtual Press Room. See: http://www.aapm.org/meetings/08AM/VirtualPressRoom/documents/pressregform.pdf.
Reporters who would like to cover the conference remotely will find releases and articles on the Virtual Press Room highlighting many of the interesting and important talks presented at the meeting. Even if you can't make it to Houston, the Virtual Press Room will make it possible to write stories about the meeting from your desk.
ABOUT AAPM
The American Association of Physicists in Medicine (AAPM) is a scientific, educational, and professional nonprofit organization whose mission is to advance the application of physics to the diagnosis and treatment of human disease. The association encourages innovative research and development, helps disseminate scientific and technical information, fosters the education and professional development of medical physicists, and promotes the highest quality medical services for patients. In 2008, AAPM will celebrate its 50th year of serving patients, physicians, and physicists. Please visit the association's Web site at http://www.aapm.org/.
Media contacts:
Jason Socrates Bardi, American Institute of Physics,
301-209-3091 (office) 858-775-4080 (cell)
jbardi@aip.org
Jeff Limmer, AAPM Media Relations Subcommittee Chair
jeffl@aspirus.org