Cancer continues to be the leading cause of mortality this century. A recent investigation by the International Agency for Research on Cancer (IARC) estimated that approximately 7.5 million deaths globally resulted from cancer, with approximately 13 million new cases being diagnosed per year. Radiotherapy is currently one of the most common and effective treatment modalities for delivering high curative or palliative ionizing radiation doses. It is estimated that more than one-half of all cancer patients receive radiotherapy during the course of their treatment. Significant developments to radiotherapy delivery techniques have been made within the last decade. For example, electron linear accelerators (LINAC) have been introduced, which generate higher energy photons and electron beams in the megavoltage energy range. These are currently considered the most common sources of clinical ionizing radiation. Modern photon radiotherapy techniques, particularly stereotactic radiosurgery (SRS) and intensity modulated radiotherapy (IMRT), were shown to produce conformal doses to tumors with high precision. However, radiotherapy using photons suffers from a number of issues. For example, they have a high entrance dose and thus, deliver unnecessary radiation to skin and normal surrounding organs/tissues adjacent to the tumor. As a result, other radiotherapy treatment delivery modalities, such as proton therapy, have been gaining interest over the last few years with approximately 80,000 patients treated in 30 centers in the USA, Europe, and Asia.
Proton therapy is currently considered one of the most precise treatment delivery techniques of radiotherapy. Unlike a photon beam which has a high entrance dose and decreases gradually while passing through the body, a proton beam can penetrate through tissues and deposit most of its energy at the Bragg peak, which is located at the end of its track. Proton therapy was shown to provide better dose concentration at the tumor and has a proven role in the management of orbital tumors such as base of skull sarcomas as a result of the increased energy deposition toward the finite range of its beam in tissue. Compared to photon therapy, proton therapy has a much lower entrance dose and no dose beyond the target volume. Because of this unique depth-dose characteristic, proton therapy is able to deliver highly conformal radiation fields to target volumes with minimal side effects. Therefore, it is favored for tumors with irregular shapes or tumors in close proximity to critical organs. Since the proton therapy beam ends completely in the body, direct in vivo verification treatment monitoring is difficult. In order to ensure the effectiveness of proton therapy, there is a need for a device/system that would help evaluate the real-time location of the tumor during treatment.
In view of the foregoing, this invention is developed to provide an implantable radiation–absorbing (radiopaque) capsule for proton therapy range verification and image registration during proton therapy treatment.