A method to implement full six-degree target shift corrections for rigid body in image-guided radiotherapy.

Treatment position setup errors often introduce temporal variations in the position of target relative to the planned external radiation beams. The errors can be introduced by the movement of a target relative to external setup marks or to other relevant landmarks that are used to position a patient for radiotherapy. Those variations can cause dose deviations from the planned doses and result in suboptimal treatments where part of the target is not fully irradiated or a critical structure receives more than desired radiation doses. Clinically available technology for image-guided radiotherapy can detect variations of target position. In this study, a method has been developed to correct for target position variations and restore the original beam geometries relative to the target. The technique involves three matrix transformations: (1) transformation of beams from the machine coordinate system to the patient coordinate system as in the patient geometry in the approved dosimetric plan; (2) transformation of beams from the patient coordinate system in the approved plan to the patient coordinate system that is identified at the time of treatment; (3) transformation of beams from the patient coordinate system at the time of treatment in the treatment patient geometry back to the machine coordinate system. The transformation matrix used for the second transformation is determined through the use of image-guided radiotherapy technology and image registration. By using these matrix transformations, the isocenter shift, the gantry, couch and collimator angles of the beams for the treatment, adjusted for the target shift, can be derived. With the new beam parameters, the beams will possess the same positions and orientations relative to the target as in the plan for a rigid body. This method was applied to a head phantom study, and it was found that the target shift was fully corrected in treatment and excellent agreement was found in target dose coverage between the plan and the treatment.

[1]  K. Brock,et al.  Determination of ventilatory liver movement via radiographic evaluation of diaphragm position. , 2001, International journal of radiation oncology, biology, physics.

[2]  D P Dearnaley,et al.  Portal imaging protocol for radical dose-escalated radiotherapy treatment of prostate cancer. , 1998, International journal of radiation oncology, biology, physics.

[3]  T E Schultheiss,et al.  A comparison of daily CT localization to a daily ultrasound-based system in prostate cancer. , 1999, International journal of radiation oncology, biology, physics.

[4]  J O Deasy,et al.  Tomotherapy: a new concept for the delivery of dynamic conformal radiotherapy. , 1993, Medical physics.

[5]  R L Siddon,et al.  Solution to treatment planning problems using coordinate transformations. , 1981, Medical physics.

[6]  Harry Keller,et al.  Optimal stochastic correction strategies for rigid-body target motion. , 2003, International journal of radiation oncology, biology, physics.

[7]  D. Jaffray,et al.  Cone-beam computed tomography with a flat-panel imager: magnitude and effects of x-ray scatter. , 2001, Medical physics.

[8]  G T Chen,et al.  Online repositioning during treatment of the prostate: a study of potential limits and gains. , 1993, International journal of radiation oncology, biology, physics.

[9]  J. Fowler,et al.  Image guidance for precise conformal radiotherapy. , 2003, International journal of radiation oncology, biology, physics.

[10]  M Wannenmacher,et al.  Combined error of patient positioning variability and prostate motion uncertainty in 3D conformal radiotherapy of localized prostate cancer. , 1996, International journal of radiation oncology, biology, physics.

[11]  J. Kapatoes,et al.  Megavoltage CT image reconstruction during tomotherapy treatments. , 2000, Physics in medicine and biology.

[12]  Ning J Yue,et al.  Comparison of an image registration technique based on normalized mutual information with a standard method utilizing implanted markers in the staged radiosurgical treatment of large arteriovenous malformations. , 2002, International journal of radiation oncology, biology, physics.

[13]  J Wong,et al.  Adaptive modification of treatment planning to minimize the deleterious effects of treatment setup errors. , 1997, International journal of radiation oncology, biology, physics.

[14]  M. Roach,et al.  Prostate volumes and organ movement defined by serial computerized tomographic scans during three-dimensional conformal radiotherapy. , 1997, Radiation oncology investigations.

[15]  R Mohan,et al.  A method of incorporating organ motion uncertainties into three-dimensional conformal treatment plans. , 1996, International journal of radiation oncology, biology, physics.

[16]  W Swindell A 4-MV CT scanner for radiation therapy; spectral properties of the therapy beam. , 1983, Medical physics.

[17]  M J Murphy,et al.  The Cyberknife: a frameless robotic system for radiosurgery. , 1997, Stereotactic and functional neurosurgery.

[18]  K L Lam,et al.  A mathematical model for correcting patient setup errors using a tilt and roll device. , 1999, Medical physics.

[19]  H Alasti,et al.  Portal imaging for evaluation of daily on-line setup errors and off-line organ motion during conformal irradiation of carcinoma of the prostate. , 2001, International journal of radiation oncology, biology, physics.

[20]  F. Yin,et al.  Dosimetric characteristics of Novalis shaped beam surgery unit. , 2002, Medical physics.

[21]  Radhe Mohan,et al.  Evaluation of mechanical precision and alignment uncertainties for an integrated CT/LINAC system. , 2003, Medical physics.