1. Field
The embodiments described below relate generally to the delivery of radiation therapy to a patient according to a “dynamic strobe” delivery scheme. In some embodiments, the “dynamic strobe” delivery scheme may encompass and/or seamlessly combine with one or more other radiation therapy delivery methods.
2. Description
According to conventional radiation therapy, a beam of radiation is directed toward a tumor located within a patient. The radiation beam delivers a predetermined dose of therapeutic radiation to the tumor according to a treatment plan. The delivered radiation kills cells of the tumor by causing ionizations within the cells. A major concern is limiting the damage to healthy tissue surrounding the tumor.
FIG. 1 illustrates a conventional patient treatment process that includes radiation therapy. According to some examples of process 100, image data of a patient is acquired, and a target volume and critical internal structures are identified based on the image data during diagnosis (105). A radiation dose is prescribed (110) for achieving desired results with respect to the target volume while minimizing damage to the critical structures. Next, a treatment plan for delivering the dose is determined (115).
The treatment plan is then delivered (125) to the patient during several sessions, or “fractions”, spaced over some period of days. Prior to each fraction, the patient is positioned (120) as required by the treatment plan. Such positioning may involve the use of lasers, skin markers, etc.
Various methods or modes of radiation therapy delivery have been proposed and utilized. A radiation therapy delivery system typically includes hardware and a control system optimized for one specific mode of radiation therapy delivery. Some modes of radiation therapy delivery include, for example, conventional IMRT, Dynamic Modulated Arc Therapy, CT-Guided IMRT (Intensity Modulated Radiation Therapy), and Volumetric Modulated Arc Therapy.
In a conventional IMRT system, beams with modulated intensity are generated at a number of fixed positions or angles around the patient. These beams are then delivered with the gantry stationary at each fixed position. The beam intensity is modulated by either superimposing several shapes at a fixed position (“Step and Shoot IMRT”) or by moving leaves of a multileaf collimator (“MLC”) across the beam with varying speeds (“Sliding Window IMRT”). In a Dynamic Modulated Arc therapy system the gantry of the delivery system performs a contiguous rotational motion (360 degrees or less per arc). Throughout the rotational motion, the beam remains on at constant dose rate, and the MLC leaves constantly re-form to maintain a shape which is conformal with the shape of the tumor, as viewed from the respective angle. The throughput of Dynamic Modulated Arc therapy is greater than in conventional IMRT, but requires more sophisticated control of the MLC leaves.
In a CT-Guided IMRT system, such as a TomoTherapy® system provided TomoTherapy Incorporated, a linear accelerator is mounted in a ring-shaped gantry and moves in a 360 degree rotation around the patient. The beam is always on during this motion and is partially blocked or unblocked by rapidly opening and closing the MLC leaves as the gantry rotates. In a Volumetric Modulated Arc Therapy system, such as provided by the RapidArc™ radiotherapy technology from Varian Medical Systems, an L-shaped gantry performs a 360 degree rotation around the patient. The beam is constantly on and the dose rate may be modulated. Also, the MLC leaves are in constant motion, thus creating different shapes as the gantry rotates. These latter two systems require complex and expensive components for synchronizing and controlling motion of the gantry and the MLC leaves.
During the treatment planning stage (115), a decision is made regarding which delivery mode to use. The decision may be based on a number of factors, including for example the patient's diagnosis, delivery system constraints, time issues related to schedules and availability of the patient and/or radiation therapy systems, etc. After the specific mode of delivery is decided, a treatment plan that is adapted to the delivery mode is determined.
Selection of a delivery mode involves trade-offs or compromises as described above. Other radiation therapy delivery modes which may be particularly suitable to certain applications are desired.