The introduction of Intensity Modulated Radiation Therapy (IMRT) has revolutionized the field of radiation therapy. IMRT allows the delivery of highly conformal radiation treatment to well-defined target volumes while sparing the surrounding healthy tissue. However, there are many challenges associated with the proper execution of IMRT treatments. The process of intensity modulation in an IMRT field is accomplished through the delivery of many smaller beam segments by a sophisticated method, which synchronizes the production of the radiation beam with the dynamic motion of a Multileaf Collimator (MLC) assembly. The MLC assembly has several metal strips, referred to as fingers or leaves, which are used to shape the radiation beam. Accurate delivery of radiation dose and precise positioning of the leaves of the MLC assembly is essential. Small deviations from the intended energy fluence pattern of the beam segments can have much greater consequences to the patient treatment outcome compared to similar errors in other forms of radiation therapy.
Additionally, the workflow of modern radiation therapy involves a sophisticated network of software modules, hardware systems and the interaction of many multidisciplinary healthcare professionals. To ensure that the planned IMRT treatment is delivered as intended, great efforts are required, involving costly staff and machine time, to perform Quality Assurance (QA) tests. Current standard practice for IMRT patient plan QA involves a fragmented approach developed from QA procedures traditionally used for standard radiotherapy treatments, including: 1) planned dose verification through an ion chamber point dose measurement (requiring time on a treatment machine), or through the use of a secondary dose calculation software tool; 2) verification of beam fluence using either film or an electronic portal imaging device, both of which also require time on a treatment machine; and 3) manual checks of patient field parameters entered into a Record-and-Verify (R&V) system.
The need for time on a treatment machine to perform some or all of these QA procedures is costly in terms of staffing and infrastructure resources since either time must be scheduled on the machine during the normal treatment day, resulting in less time available for patient treatment, or the QA must be performed by staff outside of normal working hours. As well, QA of the IMRT patient plan and delivery system is typically performed prior to the first treatment session only. During the actual treatment sessions, which consists of 30 to 40 daily fractions, the control system of the treatment machine and the R&V system are relied upon to accurately deliver the treatment. However, after the initial pre-treatment QA, no independent checks are performed to ensure that the treatments are being delivered as intended, and so treatment errors introduced in subsequent sessions can go undetected. Common mistreatment scenarios can involve human errors as well as software and hardware malfunctions. For instance, the built-in radiation monitoring systems that are integrated into the treatment machine do not provide information of the radiation conditions following the final beam shaping devices, and so are insensitive to the MLC assembly and associated potential errors. In addition, leaf position sensors for the MLC assembly are not independent of the treatment machine and software, and therefore cannot detect all errors reliably. The current practice of IMRT is therefore vulnerable to errors and may lead to treatment incidences. However, up to now, there is no integrated, comprehensive QA solution that is available to meet the complexities associated with modern radiation therapy processes to provide workflow efficiency and integrated on-line treatment verification.