Dynamic radiation treatment techniques, such as intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), are typically used with a radiotherapy system, such as a linear accelerator (linac), equipped with a multi-leaf collimator (MLC) to treat pathological anatomies (tumors, lesions, vascular malformations, nerve disorders, etc.) by delivering prescribed doses of radiation (X-rays, gamma rays, electrons, protons, and/or ions) to the pathological anatomy while minimizing radiation exposure to the surrounding tissue and critical anatomical structures. Use of the MLC allows the radiotherapist to treat a patient from multiple angles while varying the shape and dose of the radiation beam, thereby providing a greatly enhanced ability to deliver radiation to a target within a treatment volume while avoiding excess irradiation of nearby healthy tissue. IMRT and VMAT, which are complex techniques involving the synchronous occurrence of gantry rotation, MLC motion, and dose rate modulation, are rapidly growing as radiation therapy techniques due to their ability to quickly deliver highly conformal dose distributions.
Quality assurance is an integral component in the workflow of clinical radiotherapy. After creating a clinical treatment plan, the performance of the different machine components to deliver the intended plan is checked in a pre-treatment verification step, which confirms that the treatment system is capable of delivering the intended dose distribution using the installed collimation devices, e.g., jaws or MLC. Different measurement methods can be applied, such as ion chamber or diode arrays that directly measure the delivered dose distribution without the patient in the beam and before the first treatment.
Recently, errors in the delivery of a radiation therapy have resulted in injury to patients, some with fatal consequences, despite pre-treatment verification. In particular, because this verification occurs without the patient in place, it cannot account for changes in setup, such as system errors or misalignment, that may inadvertently expose the patient to harmful radiation during treatment. Moreover, dose to the patient can be affected by significant changes in patient anatomy, such as weight loss or significant tumor shrinkage. Thus, a need exists for monitoring dose delivery during treatment of the patient, to account for potential errors, such as missing beam limiting devices, patient positioning errors, mismatch between treatment plan and patient, etc. and to account for anatomical changes.