Cancer Research Highlights

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 (.(JavaScript must be enabled to view this email address)) 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:

One of the most effective means of treating cancers is via radiation therapy. However, ionization and its by-products damage both the cancer and normal cells. Accuracy and precision of the radiation delivered to the tumor and the ability to spare normal tissue determine patient outcomes. Recently, high energy proton beams have been shown to be more precise in delivering energy to the tumor than photon beams, but even with advanced treatment planning, the delivery of the beam to the tumor may deviate from the treatment plan due to the complications of the anatomy and motion of patients.

The ability to see the location and measure the amount of energy delivered during the treatment in real time would allow radiation oncologists to adjust the energy delivered to the tumor assuring that the prescribed energy is delivered at right location. Since high energy protons and photons induce gamma rays via interaction with nuclei in the human body by imaging the gamma rays, one could see the location and measure the amount of energy delivered during treatment. Unfortunately, the penetration power of the emitted gamma rays is too high to be stopped and imaged with conventional medical imaging modalities in real time.

Using principles adapted from gamma ray astronomy, a research team at the University of Florida is working to develop a modality capable of imaging the gamma rays in 3D. The team has designed an imager using a new material, LaBr3, with high stopping power. The researchers are now optimizing the design and doing bench-top testing, which has demonstrated the feasibility of this concept with a precision of about 5mm at 10 cm distance.

As the next step, the team will prototype and test the imager in radiation therapy clinical facilities using proton and photon beams. Dr. Yuxin Feng, a member of the Florida team, believes that the challenge of accelerating image reconstruction speed to achieve real or near real time imaging is achievable with the development of image reconstruction and computing power, making real-time imaging in proton therapy a reality.

Talk (TU-D-352-3), “A Design of Compton Cameras for Imaging Gamma Emission in Proton Therapy” is at 1:54 p.m. on Tuesday July 29, 2008 in Room 352.

Ductal carcinoma in situ (DCIS), the development of cancer cells within the milk ducts of breast tissue, is thought to be a possible precursor of invasive cancer, prompting research to understand its underlying biology-and detect it early. Now medical physics graduate student Neha Bhooshan of the University of Chicago, her advisor Professor Maryellen Giger, and their colleagues have developed an automated computer image analysis technique to ultimately characterize and diagnose DCIS and other breast carcinomas.

The method is similar to the computer-aided detection techniques currently used to identify suspicious features on mammograms for further study by radiologists. It makes use of differences in the morphology of DCIS and other malignant and benign breast lesions, and in their response to the contrast agents used in magnetic resonance imaging (MRI) scans. For example, malignant and benign breast lesions vary in the rates at which they take in and eliminate MRI contrast agents; malignant lesions rapidly take in and wash out the contrast because they have a greater proliferation of blood vessels, while benign lesions have a slow and persistent uptake. The computer program compares seven such features in breast MRI scans taken before and after the administration of contrast, and calculates a numerical value that characterizes the tumor subtype.

To test the program’s validity, the researchers used it to analyze MRI scans of 131 benign and 203 malignant breast lesions, including 79 lesions that had been pathologically diagnosed as DCIS and 124 as invasive ductal carcinoma (IDC). The system was able to differentiate benign and malignant lesions, and to distinguish DCIS and IDC lesions. Bhooshan believes computer-aided diagnosis can be applied to the image analysis of other types of cancer and may become more common in the clinical setting.

Talk (SU-HH-AUD C-07), “Classification of Breast Carcinoma Subtypes Using Computer-Extracted Morphological and Kinetic Features in DCE-MRI” is at 5:12 p.m. on Sunday, July 26, 2008 in Auditorium C.

Breathing is a major complication for radiation treatment of lung cancer. The latest technology plans to tackle the problem by moving the radiation beam in unison with the breath. To help in the tracking, researchers have devised a new algorithm - similar to one used by the post office - that can predict where a tumor will be one second beforehand.

Breathing is a problem in radiation treatment not only for lung cancer, but also for cancers in other parts of the abdomen. Medical physicists have traditionally dealt with this motion by shooting a beam that broadly covers the area in which the tumor is located. Because there will be plenty of healthy tissue inside this big margin of error, the beam strength has to be turned down low.

A better way to treat cancer is to use intense, highly-focused beams that only strike the tumor. This is why the next generation of radiation treatments have robotic arms or special shutters that can move the beam up and down to stay centered on a moving target. But these new techniques will require a precise way to track where the tumor is inside the chest.

Nadeem Riaz and collaborators at Stanford University School of Medicine have a model that accurately predicts a tumor’s motion using its last eight positions. The algorithm, which improves its performance by learning from its mistakes, is also used by the post office to automatically read zip codes on letters. The researchers tested their program on data from a previous radiation treatment in which a tumor was tracked with X-ray images and found it worked better than another simple model at predicting where the tumor will be one second into the future. One second should be enough time, Riaz says, for newly-developed technologies to redirect their radiation beams.

Talk (TH-C-AUD C-07), “Prediction of Fiducial Motion in Respiratory Tumors for Image-Guided Radiotherapy” is at 11:12 a.m. on Thursday July 31, 2008 in Auditorium C.

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.

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.

Source: American Institute of Physics (AIP)

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