Helical Tomotherapy: Image Guidance and Adaptive Dose Guidance

Abstract

Helical tomotherapy is a volumetric image-guided, fully dynamic, intensity-modulated radiation therapy (IMRT) delivery system. The daily use of its pretreatment megavoltage (MV) CT imaging for patient setup verification allows one to correct for interfraction setup error. This is a primary requirement for the accurate delivery of complex IMRT treatment plans, which give differential radiation doses to various target volumes while conformally avoiding normal critical structures. In particular, image guidance using MV CT allows for direct target position verification with the patient in the actual treatment position just prior to therapy delivery. Moreover, since helical MV CT imaging is a slow CT imaging technique, it allows for the encoding of target motion in the resulting MV CT data set, and therefore the pretreatment verification of a motion envelope defined from four-dimensional CT.

American Society for Therapeutic Radiology and Oncology (ASTRO) and American College of Radiology (ACR) Practice Guidelines for Image-Guided Radiation Therapy (IGRT)

“…Fiducial markers do not provide information about changes in the size and shape of tumors that may occur during a several-week course of radiation therapy (9)(10)(11)(12)(13). Various modalities, including orthogonal imaging, ultrasonography, or CT, can be used for real-time imaging of the tumor and surrounding tissues during radiation therapy.…”

“…Recently, megavoltage X-ray CT (MVCT) and in-room MRI have become available for IGRT. Even though MVCT provides images of inferior resolution compared to kVCT, this modality results in better soft tissue imaging in anatomic regions adjacent to metallic prostheses, such as dental fillings in patients with head and neck cancers, and hip prostheses in patients with pelvic tumors (13).…”

Analysis on Setup Variation According to Megavoltage Computed Tomography System

“…In this way, we can minimize an inter-fractional set-up error day to day. Furthermore, when planning a treatment with an MVCT image, we are able to perform a stereotactic radiation treatment by confirming a planned dosage and assessing the changes of normal organs and tumor [3]. However, the image quality of MVCT is not as good for distinguishing the soft tissues from low-contrast resolution [3,4].…”

“…Furthermore, when planning a treatment with an MVCT image, we are able to perform a stereotactic radiation treatment by confirming a planned dosage and assessing the changes of normal organs and tumor [3]. However, the image quality of MVCT is not as good for distinguishing the soft tissues from low-contrast resolution [3,4]. Therefore, when it comes to parenchymal tumor, it is difficult to distinguish the soft tissues from mediastinal tumor even when we can find the location and size of tumor with the MVCT images [5].…”

High-performance GPU-based rendering for real-time, rigid 2D/3D-image registration and motion prediction in radiation oncology

“…Methods for retrieving this additional image information range from ultrasound [6,7], magnetic resonance imaging [8] and, most important, kilovoltage and megavoltage x-ray imaging, either by means of planar radiography [9,10] or 3D modalities [11,12]. Non-rigid registration [13] techniques can be employed to simulate the deformation of the tumor [14,15] between treatment sessions.…”