Intensity-modulated proton therapy patient treatments

Introduction

Intensity-modulated proton therapy (IMPT) can begin only after a number of other processes have been completed, including simulation and treatment planning. For both proton and photon treatments, radiation oncology has evolved to the point in which the treatment parameters, defined in the treatment planning process, are included in the radiation oncology electronic medical record (EMR) to be uploaded to the delivery system for each treatment field on each day. At the completion of daily treatment for a specific patient, the delivery system downloads a number of parameters of the treatment delivered on that day. The delivery system may also have its own logs, which contain a history of operations at specific times on a specific day. These treatment delivery logs are the ultimate source of truth because they record the details as to the actions taken by the treatment device. It is necessary on limited occasions to consult the treatment logs to confirm the individual treatment on a specific day.

IMPT is an example of a very complex treatment technique that would be impossible to deliver without the use of an EMR to upload the treatment parameters. In addition to the treatment parameters, patient-specific referenced images are also uploaded to the delivery system so that a comparison can be made to daily patient setup images. It is not unusual that there are devices or systems from multiple vendors involved in the IMPT treatment process. For example, at MD Anderson Cancer Center (MDACC), the treatment delivery system is provided by vendor H (Hitachi), the EMR system by vendor E (Elekta), and the treatment planning system (TPS) by vendor V (Varian). A key to this successful digital communication is the Digital Imaging and Communications in Medicine (DICOM) standard. DICOM was developed by the American College of Radiology and the National Electrical Manufacturers Association to aid the distribution and viewing of medical images. The first version of DICOM was released in 1985. DICOM for radiation therapy came later, in 1995, with DICOM Working Group 7. Information on this industry standard can be found on the DICOM homepage, dicom.nema.org . DICOM is a very successful, mature standard that has evolved over time and continues to evolve. DICOM makes IMPT possible in the multivendor environment.

DICOM defines many basic radiation therapy ion beam attributes, including beam type (static or dynamic), radiation type (photon, proton, ion), scan mode (none, uniform, modulated, modulated spec), and so on. DICOM uses the concept of control points for radiation therapy treatments. Control point 0 has the cumulative meter set weight set to zero and defines all initial parameters (e.g., gantry, table, collimator). Control points are important in IMPT delivery. A new control point is defined for each energy change. Each control point has a specific number of spots and monitor units (MUs).

Treating with individual spots (packets of protons), which change energy and location, is different than treating with large fields, either protons or photons. The concept of dose, energy deposited per unit mass, needs reflection when treating with spots; for example, the unit mass involved and the instantaneous dose rate. One potential unique catastrophic failure would be the corruption of data or failure of devices such that all spots were delivered to the same physical location over and over and over.