Surgery – Radioactive substance applied to body for therapy
Reexamination Certificate
1998-10-30
2001-03-13
Gilbert, Samuel G. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
C600S003000
Reexamination Certificate
active
06200255
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the use of a computerized dosimetry system for planning the spatial configuration of radioactive seeds and the associated dose intensity distribution inside and surrounding a planning target volume in the irradiation of cancerous tissue.
More particularly, the present invention relates to a method of and a system for using artificial intelligence to determine the most appropriate seed configuration for a given prostate shape and size, with minimal human intervention.
In the treatment of prostate cancer, a method is often employed to implant numerous radioactive seeds in a carefully preplanned pattern in three dimensions within the prostate. That procedure serves to deliver a known amount of radiation dosage concentrated around the prostate, while at the same time sparing radiation-sensitive tissues, such as the urethra, the bladder and the rectum. Customarily, 60 to 120 seeds are placed through 15 to 30 needles in the inferior (feet) to superior (head) direction (see FIG.
1
). These needle positions are selected from a 13×13 grid of 0.5 cm evenly spaced template holes, which are used to achieve precise needle insertion. The number of these holes that intersect with the prostate cross section, and therefore are potentially usable, is typically about 60 (see FIG.
2
). The number of mathematical combinations is therefore greatly in excess of 10
16
, each of which is a potential treatment plan but is associated with different degrees of cancer control and the likelihood of treatment complications.
In current clinical practice, the design of a suitable seed configuration which is customized to the anatomy of a patient is achieved by a highly trained medical physicist or dosimetrist only by using trial-and-error manual iterations. The practitioner usually starts with an initial needle configuration based on experience or rules of thumb, and then adjusts the radioactive strength per seed or the locations of certain needles or both, until the calculated dose intensity distribution satisfies a set of clinical considerations. That process requires between 15 minutes and 2 hours, depending on the experience of the treatment planner and the geometric complexity of the relationship between the prostate and the surrounding anatomic structures.
These known treatment planning processes are typically aided by one of several available commercial computerized treatment planning systems. Such treatment planning systems enable the user to outline the prostate in relation to a template grid, to turn on or off any available needle positions and seed positions within each needle, and to examine the resultant dose distribution in two or three dimensions. Examples of such planning systems include those offered by Multimedia Medical Systems (MMS) of Charlottesville, Va., SSGI Prowess, of Chico, Calif., Nucletron Plato, from Columbia, Md., Computerized Medical Systems (CMS) Focus, of St Louis, Mo., Radiation Oncology Computer Systems (ROCS), of Carlsbad, Calif., ADAC Laboratory's Pinnacle, of Milpitas, Calif. and Theraplan, available from Theratronics International Ltd. of Kanata, Ontario, Canada.
In a number of such known commercial treatment planning systems, for example, those available from MMS and SSGI, the initial needle configuration that otherwise would have to be turned on by the human treatment planner is automatically set up by the computer system. That initial setup is based on simple rules of thumb, such as uniform loading, peripheral loading or modified peripheral loading. In a number of instances, the manufacturer claims that its planning system offers “automatic planning”, “geometric optimization”, or “real-time dosimetry”. However, none of these commercial planning systems offer true optimization in that the automatically loaded seeds are not designed based on customized dosimetric calculations. Rather, they are designed to fill the space of the prostate in some predetermined manner. Therefore, such known automatic seed loading techniques are designed to save between 15 to 30 mouse clicks by the operator (or about 1 minute of operation). However, the user is still required to apply his or her expert knowledge to iteratively improve upon this initial design in order to achieve customized planning for any individual patient. Thus, there are two significant drawbacks of the above-mentioned current techniques: First, the complete treatment planning process is under the manual guidance of a radiation planning expert using trial and error techniques; and second, the adjustment of the delivered dose is achieved by varying the radioactive strength per seed until an isodose surface with the desired shape and size is scaled up or down to the prescription dose, i.e., these techniques will suffer when the activity per seed is fixed, as at the time of surgical implantation in the operating suite.
Because of these two severe drawbacks, the currently available commercial treatment planning systems are not suitable for intraoperative treatment planning in the surgical suite, where the patient is placed under anesthesia in volatile conditions and where the cost per minute is very high. The variability of human performance, experience and stress, and the general inability of humans to manage large amounts of numerical data in 1 to 2 minutes are also factors that deter current practitioners from performing intraoperative treatment planning.
Although not designed for the express purpose of intraoperative optimized treatment planning, four previously published articles have described methods to automate the dosimetric planning (rather than simple geometric planning) for prostate seed implant brachytherapy. The references, features and deficiencies of these methods are as follows:
1. Roy J N; Wallner K E; Chiu-Tsao S T; Anderson L L; Ling C C. [“CT-based optimized planning for transperineal prostate implant with customized template.”
International Journal of Radiation Oncology Biology and Physics,
21:483-9 1991] This is an early attempt at computerized optimization and automation of dosimetric planning. The authors start from a manual design of the needle configuration, and use a least square computer algorithm to find the best seed loading pattern within the needles. The major limitation of this approach is that once the needle pattern is fixed by the human planner, only superficial degrees of freedom exist for the computer algorithm to optimize the dosimetry. For example, only the seed spacing within each needle can be varied, which is inconsistent with the standard technique of 1 cm uniform spacing. In addition, the least square optimization method is known to be unable to search widely for the best overall treatment plan in this multi-modal problem; it tends to settle for the nearest local optimal solution because there is no mechanism to test other design patterns which initially may be suboptimal. In general, any optimization method that presumes an existing fixed needle configuration (either designed manually by the dosimetric planner or automatically loaded based on geometric rules) does not allow sufficient variation in the possibilities of dose distribution to produce the optimal treatment plan.
2. Yu Y; Schell M C. [“A genetic algorithm for the optimization of prostate implants.”
Medical Physics,
23:2085-91 1996] This is the first attempt in using an “intelligent” computer algorithm, viz., the genetic algorithm, to explore the world of dosimetric possibilities for prostate brachytherapy planning. It is a theoretical work, not directly applicable to real-life prostate shapes and sizes. In fact, the prostate is schematically represented by ellipsoids of various sizes and elongations. The genetic algorithm is of an off-the-shelf generic kind, where the template is linearized into a string of bits, and not encoded by two dimensional genetic templates such as in the present invention. The article describes the use of a utility function for dosimetric comparison of competing treatment plans, which
Blank Rome Comisky & McCauley LLP
Cadugan Joseph A.
Gilbert Samuel G.
University of Rochester
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