Isocenter Verification in Radiotherapy Clinical Practice Using Virtual Simulation: An Image Registration Approach

Isocenter Verification in Radiotherapy Clinical Practice Using Virtual Simulation: An Image Registration Approach

George K. Matsopoulos (National Technical University of Athens, Greece), Pantelis A. Asvestas (Technological Educational Institute of Athens, Greece), Vasiliki Markaki (National Technical University of Athens, Greece), Kalliopi Platoni (University of Athens, Greece) and Vasilios Kouloulias (University of Athens, Greece)
DOI: 10.4018/978-1-4666-8828-5.ch010
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Abstract

This chapter presents an overview of the procedures that are used for the verification of the patient position during radiotherapy. Furthermore, a method for the verification of the radiotherapy isocenter prior to treatment delivery is proposed. The method is based on the alignment of two Computed Tomography (CT) scans: a scan, which is acquired for treatment planning, and an additional verification scan, which is acquired prior to the treatment delivery. The proposed method was applied to CT scans, acquired from 20 patients with abdominal tumors and 20 patients with breast/lung cancer. The results of the proposed method were compared with the ones obtained using conventional methods, indicating that the estimated isocenter displacement can be translated into patient setup error inside the treatment room.
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Introduction

According to the World Health Organization (WHO), chronic diseases (also known as not noncommunicable diseases) are long duration diseases that are not passed from person to person (World Health Organization, 2014). The main types of chronic diseases are cardiovascular diseases (like heart attacks and stroke), cancers, respiratory diseases (such as chronic obstructed pulmonary disease and asthma) and diabetes. Cancers can be considered the most serious chronic diseases with significant impact on the patients. According to Ferlay et al. (2013), “there were 14.1 million new cancer cases, 8.2 million cancer deaths and 32.6 million people living with cancer (within 5 years of diagnosis) in 2012 worldwide. 57% (8 million) of new cancer cases, 65% (5.3 million) of the cancer deaths and 48% (15.6 million) of the 5-year prevalent cancer cases occurred in the less developed regions. The overall age standardized cancer incidence rate is almost 25% higher in men than in women, with rates of 205 and 165 per 100,000, respectively. Male incidence rates vary almost five-fold across the different regions of the world, with rates ranging from 79 per 100,000 in Western Africa to 365 per 100,000 in Australia/New Zealand (with high rates of prostate cancer representing a significant driver of the latter). There is less variation in female incidence rates (almost three-fold) with rates ranging from 103 per 100,000 in South-Central Asia to 295 per 100,000 in Northern America. In terms of mortality, there is less regional variability than for incidence, the rates being 15% higher in more developed than in less developed regions in men, and 8% higher in women”.

One of the most common methods for cancer treatment is radiation therapy, which is a clinical modality dealing with the use of ionizing radiations in the treatment of patients with malignant neoplasias (and occasionally benign diseases) (Halperin, Brady, Perez, & Wazer, 2013).

Radiation therapy (or Radiotherapy) plays a central role in dealing with benign and malignant tumors and is an important way to alleviate the clinical symptoms of the disease when treatment is not feasible. Approximately 60% of all cancer patients in Europe and the United States of America are subjected to radiation therapy (external or internal), which either is the main method of treating cancer or used in combination with chemotherapy or surgical removal of the tumor (Halperin et al., 2013). The term radiotherapy usually refers to external irradiation of the tumor region with the aim of delivering the maximum dose to the tumor with the least possible impact on healthy tissue. This can be achieved by splitting and administering the total radiation dose in successive sessions, in order to destroy cancer cells while leaving the possibility of healthy cells to recover.

Key Terms in this Chapter

Affine Transformation: A geometric transformation that preserves points, straight lines and planes.

Virtual Simulation: Delineation of the tumor volume and the radiosensitive normal tissue and visualization of the field apertures using CT dataset.

Isocenter: The point in space relative to the treatment machine about which various components of the linear accelerator rotate.

Linear Accelerator: Device used for external beam radiation treatments for patients with cancer.

Radiotherapy: The use of ionizing radiation in order to remove of cancerous tumor or to prevent tumor recurrence after surgery.

Electronic Portal Imaging: Imaging of radiation field placement using digital means.

Simulator: Medical device used in oncology clinics to perform the simulation for the external beam radiotherapy treatment.

Image Registration: A procedure, involving a spatial transformation that brings homologous point in two images into correspondence.

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