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A Novel Compound 6D-Offset Simulating Phantom and Quality Assurance Program for Precision Image-Guided Radiosurgery and Radiotherapy

Summary

Precision or Stereotactic Image-Guided Radiosurgery and Radiotherapy (IGRT) become common practice in neuroscience and oncology. Treatment system is able to detect patient positional error by computer imaging algorithm and then correct the compound errors by moving the patient on the treatment couch in six dimensions with servo-tracking. The accuracy level of such system reaches 1mm in 3 translational and 1 degree in 3 rotational dimensions. After this precision setup, the patient will then be treated by radiation beams from the clinical Linear Accelerator (Linac). The spatial precision ensures that the Target Volume is fully covered with the desired radiation dose and the Organs At Risk are receiving the minimum dose. Moreover, the Target dose can be escalated to enhance tumor control and the Target margin can be reduced to protect the normal tissues. This type of precision RT modality is currently applied in large volume to many neuro-oncologic, head & neck, spinal, intracranial and extracranial cases worldwide.

Quality Assurance (QA) is a highly important issue in clinical science nowadays, giving a direct proof and measurable evidence of the performance of a certain system. A novel Compound 6D-Offset Simulating Phantom cum Quality Assurance Program for Precision Image-Guided Radiosurgery and Radiotherapy is developed for this purpose. The technology allows the user to carry out routine QA comprehensively and simply in one go. Without this design people did the commissioning works and regular checkings of the IGRT system by separate measurement of the generated offsets rather than by a compound methodology. Natural offsets are random and compound, so a random table of 6-D compound offsets is formulated as part of the QA program. The QA worksheet is another table recording the originally generated 6-D offsets, the detection errors and the correction errors. There will be two sets of random data generated, detected and corrected weekly. All the system performance data will be recorded and documented. The QA pass criterion is 1mm or 1 degree of 6-D errors.

The phantom body is basically a 10cm cube made of perspex. There is an opening at the bottom. The end of the hole is at the centre like a socket. A rod with a ball end is supporting the phantom at the socket. The whole phantom hence can rock and rotate about the supporting ball and rod, simulating the 3-D rotations of Yaw, Roll and Pitch. Generated rotations of roll and pitch are measured by two electronic inclinometers with 0.1 deg resolution. Orthogonal centre-lines are marked on the five faces of the cube with the centre being exactly at the ball-and-socket position. The compound offset once done can be fixed by three screws set to the base-plate. Metallic BB-balls and rods are embedded to the cube for radiological detection by the IGRT system. The three translational random offsets of Vert, Long, Lat are simply done by treatment couch movements. The standard neutral offset configuration is obtained by CT scanning of the phantom with zero offsets in 6 dimensions. The images are sent to the IGRT computer via the planning computer. Two real-time 2-D images are taken with the offset phantom on the treatment couch. When the real-time images are compared to the standard images reconstructed from the CT images, the 6-D offsets are calculated by the system. The detection performance is then evaluated. The system then proceeds to 6-D robotic correction by moving the couch. By a second detection, the robotic mechanical correction performance can also be evaluated.

The Phantom cum QA Program can be applied to all external beam radiation therapy machines with IGRT function. These include the conventional linear accelerators with BrainLAB ExacTrac X-ray Robotic Couch, Linacs with Cone Beam CT/OBI, Novalis, and Cyberknife, etc.

Supplementary Information

Inventor: Ngar, Yuen Kan | Poon, Wai Sang
Priority Number: US8845191B2
IPC Current: A61N000510 | A61B000600 | A61B001900
US Class: 378207 | 378018 | 378205
Assignee Applicant: The Chinese University of Hong Kong
Title: Compound 6D-offset simulating phantom and quality assurance program for precision image-guided radiotherapy and radiosurgery
Usefulness: Compound 6D-offset simulating phantom and quality assurance program for precision image-guided radiotherapy and radiosurgery
Summary: Phantom device for calibrating a robotic couch control system to ensure quality assurance (QA) of IGRT in a patient.
Novelty: Phantom device for calibrating robotic couch control system to ensure quality assurance of image-guided radiation therapy in patient, has markers affixed within body, where marker is configured such that marker position is determined

Industry

Biomedical

Sub Category

Medical Imaging

Application No.

11/MED/427

Others

Inventor(s): Professor POON Wai Sang, Department of Surgery Licensing Status: Available

Country/Region

Hong Kong