Commissioning Guide

The purpose of this commissioning guide is to describe the process of configuring the eRT application for clinical use. This requires modeling the actual electron treatment machines in terms of physical geometry (e.g. SAD, rotation directions and limitations, applicator sizes/names), beam parameters (e.g. treatment energies, energy spectrum, beam flatness), and other facility information/preferences (e.g. CT Curves, location/shipping address, planning defaults). As the beam modeling/commissioning steps are critical to ensuring the safety and quality of patient treatments, it is also essential that the qualified medical physicist (QMP) responsible for the facility has a sufficient understanding of the dose calculation technique used by the eRT application. As such, this guide also serves to provide this information.

The first step in preparing eRT for clinical use will be to gather the data needed to create a model of the local treatment facility. This model will include the follow information:

The following section describes the hierarchy of data used to define an Organization within the decimal eRT application.

There are three main levels for how decimal eRT stores its organization configuration data:

1. Organization
   1. A legal entity that provides electron radiation treatments to patient. An Organization may be a network / group or individual and the data stored at this level contains preferences and basic information that applies broadly to the entity.
   2. This is where preferences that improve organization wide standardization are stored, such as dose map colors, treatment plan report settings, and material properties.
   3. An Organization will contain 1 or more Sites.
2. Site(s)
   1. A site is an individual treatment facility. The site stores the shipping address, CT curves, dicom export/import settings, QA options, and a list of physicians and treatment (disease) sites.
   2. A Site contains one or more Treatment Machines.
3. Treatment Machine
   1. A detailed model of an electron therapy treatment machine. The majority of the configuration data, including all commissioning data, is stored within a treatment machine.
   2. The treatment machine defines all physical machine geometry, as well as the electronic machine model (e.g. name, accessory IDs).
   3. The treatment machine also stores the list of available electron treatment energies and the commissioning data necessary to ensure accurate dose calculations are achieved.

A single Organization can have one or multiple [1 - n] Sites (locations where treatments occur), and a Site can have one or multiple [1 - n] Treatment Machines. This relationship is detailed in the table below:

decimal eRT dose calculations follow the pencil beam redefinition algorithm as described in Pencil-beam redefinition algorithm for electron dose distributions that allows for electron dose calculations using beam limiting devices. It is recommended that users familiarize themselves with the PBRA as described in the above reference as it provides critical information regarding the equations used in the dose engine, how tissue heterogeneities are handled, and the value ranges for the modeling parameters. A description of the model accuracy and a set of calculation inputs and expected outputs can be found in the Acceptance Testing section of this user guide.

As a semi-analytical calculation model, the PBRA requires only simple measurement data results in order to fully commissioning the system. with more details.

Interpolation processes are necessary within many contexts for an application such as eRT. Specifically, users should be aware of the following contexts where interpolation is used:

1. Dose Calculation (internal)
2. MU Determination
3. Dose Result Displays
4. Dose Volume Histograms (DVHs)
5. Dose Exporting
6. The Dose Profile tool

In all such cases, eRT will use a linear interpolation approach whenever data falls within the range of the provided minimum and maximum values. Note, for 2D or 3D calculations, this refers to bi-linear or tri-linear interpolation as appropriate.

The following is an overview of the use of interpolation throughout the treatment planning process.

Since users provide commissioning data for all electron energies utilized at their site, there is no interpolation across energies. However, data is provided at discrete field sizes and SSD positions that may not exactly match the commissioning data. This is the first use of interpolation, whereby user supplied PDDs are interpolated to the appropriate field size and SSD for the beam at hand. This interpolation uses a combination of electron beam theory and user provided data to generate a PDD that accurately reflects the intermediate beam conditions (see interpolation reference for details). The off-axis-ratios and other beam parameters are linearly interpolated as needed. Following the PDD determination, the PBRA then computes dose on a beam-aligned, divergent grid. The next interpolation occurs to transfer the dose data from this beam aligned grid onto a patient-aligned, equally spaced grid. This uses standard trilinear interpolation. Dose within this patient-aligned grid is displayed on-screen within the eRT application. This same dose is also used for DVH computations and all other dose statistics provided by the eRT application. DVH and all volume-based dose statistics are computed using the dose at the center of each voxel in this dose grid, but volumes are computed by accounting for the actual portion of the voxel contained within the structure/region at hand. The dose from this patient-aligned dose grid is directed exported by the eRT application such that no further interpolation is needed.

As described in the above section, eRT will not extrapolate data other than by extending the first/last data value as appropriate (this is in essence, a zero-order extrapolation).