Surgery – Radioactive substance applied to body for therapy
Reexamination Certificate
2001-10-01
2004-04-13
Gilbert, Samuel G. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
Reexamination Certificate
active
06719683
ABSTRACT:
FIELD OF THE INVENTION
The invention herein described relates to radiotherapy and more particularly to an apparatus and method for treatment planning for radiotherapeutical procedures.
BACKGROUND OF THE INVENTION
Conformal radiation therapy typically employs a linear accelerator as the source of a radiation beam or beams used to treat a tumor and/or other internal anomaly, herein referred to generally as a target volume. The linear accelerator has a radiation beam source which may be rotated about the patient to direct the radiation beam toward the target volume from different angles. Various means have been employed to control the rotation, intensity, shape and/or direction of the radiation beam in accordance with a predetermined treatment program designed to apply a desired radiation dose to the target area while minimizing the dose of radiation to surrounding healthy tissue and/or adjacent healthy organs, hereinafter referred to generally as a non-target volume. Overall, the goal of conformal radiation therapy is to confine the delivered radiation dose to only the treatment volume while minimizing the dose of radiation to the non-target volume. Accordingly, a treatment plan (also referred to as treatment solution) is desired that optimizes the radiation dose to the target area while minimizing the amount of radiation delivered to the surrounding non-target volume.
Existing techniques to optimize treatment planning during radiation oncology include forward treatment planning and the more recent inverse treatment planning. The forward treatment problem is to compute the dose distribution in a tissue given a treatment plan. The inverse treatment problem is to find a treatment plan whose execution will achieve a desired dose distribution.
More particularly, forward treatment planning typically involves loading patient scan data in a computer. Usually a three-dimensional (3D) data set of the patient is used, such as that obtained by CT, MRI or other imaging techniques. The treatment planner then virtually places therapeutic radiation beams within the scan data, adjusting the shape, size, direction and/or intensity of the radiation beam or beams. Next the planning system calculates the resulting dose distribution. If the treatment planner is not satisfied with the results, he/she changes one or more of the beam parameters and starts the calculation again. In an iterative process the treatment planner tries to achieve the desired dose distribution. This can be a tedious and time consuming task.
Inverse treatment planning directly defines the desired dose distribution instead of defining beam parameters. The desired dose distribution may be defined in different ways, e.g., by drawing on the two-dimensional (2D) CT slices. Typically the desired dose distribution is specified by marking forbidden areas (constraints) on a Dose Volume Histogram (DVH) sketch. The DVH is a standard radiotherapy treatment verification tool. Based on the desired dose distribution regardless of how represented, a computer calculates the ideal beam parameters using known optimization techniques. Inverse planning systems are typically used in conjunction with Intensity Modulated RadioTherapy (IMRT) treatments.
Ideally the treatment planner would like to set the constraints in a way that the target volume (e.g., a tumor) receives 100% of the prescribed dose, while the risk organs and the healthy tissue (non-target volume) receive absolute zero dose. As the beam typically intersects healthy tissue (and sometimes even the risk organ, e.g., if the tumor is surrounded by a risk organ) the aforesaid very strict constraints cannot be kept. That is, there is no treatment plan that can satisfy these strict constraints. Requiring the treatment planner to change the constraint settings and to try again is time consuming and against the idea of inverse planning. Conversely, if the constraints are too loose the patient doesn't receive the best possible treatment.
Thus, a need exists for an inverse planning system which can react effectively to the problem presented when not all desired constraints can be kept, while still allowing the system to generate a plan better than the desired one.
SUMMARY OF INVENTION
The present invention provides an inverse planning system (method and apparatus) which can react effectively to the problem presented when not all desired constraints can be kept, while still allowing the system to generate a plan better than the desired one. To this end and according to one embodiment of the invention, an inverse planning method for radiotherapy treatment of a target volume in a body comprises the steps of: using a computer to calculate the results (dose distribution) of multiple treatment solutions (proposed radiation beam arrangements); and simultaneously displaying the calculated results for at least two of the treatment solutions for comparison by a treatment planner to enable the treatment planner to select a desired one of the treatment solutions.
In a specific embodiment, the inverse planning method includes a non-constrained step of using a computer to obtain the multiple treatment solutions at two or more discrete calculations yielding X% of a prescribed dose throughout the target volume and (100-X)% protection of a non-target volume, where X has a position value between 0 and 100.
In a specific embodiment, the inverse planning method includes the step of identifying a first objective function indicating a desired distribution of dose in a plurality of volume elements within the target volume, the step of identifying a second objective function indicating a desired distribution of dose in a plurality of volume elements within the non-target volume, and the constrained step of using a computer to obtain the multiple treatment solutions at two or more discrete calculations weighting the first objective function at Y% and the second objective function at (100-Y)%.
In a specific embodiment, the multiple treatment solutions are obtained from calculations combining the non-constrained and constrained steps with variable weighting, thereby enabling consideration of the objective functions without eliminating the possibility to improve the treatment plan beyond the objective functions.
In a specific embodiment, the identifying steps include receiving the first and second objective functions from a treatment planner.
In a specific embodiment, the first and second objective functions are represented by dose volume histograms of desired dose distribution data for the target volume and the non-target volume, respectively.
In a specific embodiment, the calculations of the treatment solutions are set as default calculations or are defined by the treatment planner.
In a specific embodiment, the calculated results are displayed as 2D and/or 3D dose-distributions and resulting histograms.
In a specific embodiment, one or more parameters of the first and second objective functions are displayed.
In a specific embodiment, the inverse planning method includes the step of sequentially displaying different pairs of calculated results.
The invention also provides an apparatus for carrying out the method of the invention. More particularly, the invention provides an apparatus for inverse planning a radiotherapy treatment of a target volume in a body comprising a display and a logic device which calculates the results (dose distribution) of multiple treatment solutions (proposed radiation beam arrangements) and causes to be simultaneously displayed on the display the calculated results for at least two of the treatment solutions for comparison by a treatment planner to enable the treatment planner to select a desired one of the treatment solutions.
REFERENCES:
patent: 5373844 (1994-12-01), Smith et al.
patent: 5458125 (1995-10-01), Schweikard
patent: 6301329 (2001-10-01), Surridge
patent: 6327490 (2001-12-01), Spetz
patent: 6385286 (2002-05-01), Fitchard et al.
BrainLAB AG
Gilbert Samuel G.
Renner , Otto, Boisselle & Sklar, LLP
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