The dosimetry system for radiochromic film dosimetry consists of:

• Gafchromic™ radiotherapy/radiology films
• a flatbed scanner
Our first option in terms of accuracy would be the Epson Expression 10000-12000XL, followed by the Epson Perfection V700-850 models, all of which have been extensively studied in the literature.
• scanner software
• Radiochromic.com

The recommended accessories are:

• gloves
• a guillotine
• a frame to center the film on the scanner
• a transparent compression (glass) sheet, when scanning in transmission mode
Technical drafts for frames and compression sheets for the Epson Expression 10000-12000XL and Epson Perfection V700-850 scanners can be found here.

The dosimetry system

A calibration is necessary to convert the response of the dosimetry system into a dose distribution.

Radiochromic.com allows you to calibrate with fragments irradiated with unflattened fields.

Step 1:

Irradiate several fragments with known doses using unflattened fields.

Unflattened fields

Step 2:

Irradiate, scan and upload the film.

Only the central part of the scanner should be used.

Step 3:

Click on CALIBRATION.

Step 4:

Select an existing study or insert a new one.

Step 5:

Insert an identifier for the calibration.

Step 6:

Select the calibration film.

Step 7:

Select Unflattened fields.

Advanced options

Step 8:

Click on Reference doses. The ‘Dose ROIs’ menu will appear.

Step 9:

Associate ROIs with their doses. A minimum of three dose ROIs is needed. The Dose ROIs for Unflattened fields are circles with known dose and diameter. For each ROI, introduce the diameter (d) and the dose (D), then select a rectangle that encloses completely the field. The application will find the center of the field and select a centered ROI with diameter d and dose D.

Dose ROIs

Step 10:

Click on Request calibration.

Step 11:

The calibration is in progress. The result will be saved in My Work.

Convert film pixel values into doses.

Step 1:

Calibrate the film lot.

Step 2:

Irradiate, scan and upload the film.

Step 3:

Click on DOSIMETRY.

Introducing dosimetry data

Step 4:

Select an existing study or insert a new one.

Step 5:

Insert an identifier for the dosimetry.

Step 6:

Select the film.

Step 7:

Select the calibration.

Optional: Noise reduction

Apply a square median filter to the dose distribution to reduce the noise (a 3×3 square median filter is recommended).

Advanced options

Step 8:

Click on Response correction.

Step 9 (recommended):

Inter-scan correction: select an unexposed ROI in order to correct inter-scan variations. Use the central part of the scan to avoid the lateral artifact.

The unexposed film fragment from the calibration can be used to correct inter-scan variations. We recommend keeping this fragment in the same position when scanning every film until a new calibration is made.

Step 10 (optional):

Dose rescaling: rescale doses in order to match the film dose with the known dose of a ROI. To apply dose rescaling, before the irradiation, cut a strip from the film to measure. This strip should be irradiated with a known homogeneous dose and scanned together with the rest of the film (and the unexposed strip). Finally, select a ROI of the exposed strip centered on the scan and introduce its dose.

In Radiochromic.com, the re-calibration correction is optional and composed of inter-scan correction and dose rescaling.

Response correction

Step 11:

Submit the request.

Step 12:

The dosimetry is in progress. The result will be saved in My Work.

Radiochromic film dosimetry is affected by many sources of uncertainty. An incorrect protocol for film irradiation and scanning, as well as inherent uncertainties of the dosimetry model, may produce errors in film doses, resulting in differences between the expected dose distribution and the dose calculated with film dosimetry. As a consequence, additional tests may be required to verify the accuracy of the dose distribution.

Upload film scans to Radiochromic.com.

Step 1:

Click on FILM UPLOAD.

Introducing film data

Step 2:

Select an existing study or insert a new one.

Step 3:

Insert an identifier for the film.

Step 4 (recommended):

Introduce film statistics.

Statistics assist you in describing your films. Furthermore, they are processed to improve the accuracy of your results.

Step 5:

Upload the film scans following irradiation.

Step 6 (optional):

Upload the film scans prior to irradiation.

Film scans

Step 7:

Select film orientation. This is CRITICAL if lateral corrections are applied. Click on the arrows to select the direction of movement of the scanner lamp on the film scans.

Film orientation

Step 8:

Click on Upload scans. The average film scans will be calculated and uploaded. They will be saved in My Work.

Average film scans

In My Work

Radiochromic.com does not record or use patient data. Do not enter patient data to identify items or studies.

Upload dose planes or image maps (e.g., EPID images) to Radiochromic.com.

Supported image formats:

• DICOM-RT dose 3D
• DICOM-RT dose 2D
• DICOM-RT image
• TIFF single channel
• Comma Separated Values
• XiO and Monaco (Elekta)
• iPlan (Brainlab)
• ADAC Pinnacle (Philips)
• OmniPro I'mRT (IBA) .opg file

Import dose distributions in CSV format

Import dose distributions in comma-separated values format. Doses should be in Gy and positions in mm. Follow the format of the example below:

Comma-separated values format

Compare dose distributions by evaluating the 2D γ-index.

Step 1:

Select evaluation (Image A) and reference (Image B) dose distributions.

Noise in the evaluation distribution artificially improves the γ-index. Given that film dosimetries are noisier than uploaded dose planes, the film dosimetry should be the reference distribution while the dose plane should be the evaluation distribution.

Step 2:

Pre-register both images by flipping, translating, and rotating Image A. Alternatively, register them with the Registration functionality.

Step 3:

If necessary, scale or increment the doses of Image A by a fixed value with Transform / Math.

If you are using a dose plane calculated by the TPS, you can introduce the daily output of the accelerator as dose scaling. If you are using a dose plane measured with a 2D dosimeter, you can introduce the dose scaling factor necessary to correct for the distance between the plane of the film and the plane of measurement of the dosimeter.

Step 4:

Open the Gamma index menu by clicking on the Gamma button .

Step 5:

Introduce the inputs of the Gamma.

Gamma: inputs

Input / Study:

Select an existing study or insert a new one.

Input / ID:

Insert an identifier for the gamma comparison.

Input / Normalization:

Select between global and local gamma normalization. Global gamma can be normalized at Dmax or at a specified Dnorm.

Input / Tolerance Dose:

Select dose tolerance as a percentage of Dmax or Dnorm (global normalization) or of the local dose (local normalization).

Input / Tolerance Distance:

Insert the distance tolerance in mm.

Input / Threshold:

Insert the threshold dose. Points with doses lower than the threshold dose are excluded. The threshold dose is a percentage of Dmax or Dnorm.

Input / Tolerance Distribution:

Select the distribution from which global gamma dose tolerances and the threshold dose are calculated. Either the reference or the evaluation dose distribution can be used. (Default: Evaluation)

Input / Fine registration:

If selected, the automatic fine registration will improve your manual registration.

Input / Relative dosimetry:

If selected, the application will consider that the images contain relative doses. In order to optimize the γ-index results, doses in Image A will be scaled.

Both the automatic scaling in relative dosimetry and the automatic fine registration use evolutionary algorithms to optimize the gamma index results. Repeated calculations can deliver slightly different results because of the random nature of evolutionary algorithms.

Input / Maximum gamma:

The maximum gamma value restricts the search space around each reference point. (Default: 2.0)

Input / ROI (optional):

The edges of the reference dose distribution have misleadingly high γ-index values. They are excluded by default with the automatic ROI. Alternatively, you can select a different ROI manually.

Step 6:

Click on Calculate. The gamma is in progress. The result will be saved in My Work.

In My Work

Step 7:

You can change Gamma inputs to launch several Gamma Index calculations in parallel. For instance, you can change tolerances, apply relative dosimetry, etc., and click on Calculate again.

In My Work:

Click on the Fast Gamma button to re-evaluate Gamma Index comparisons.

Fast Gamma

Locate and obtain the dimensions of the radiation isocenter by analyzing a starshot test.

Step 1:

Load an image of a starshot test (e.g., film, EPID, CR, etc.).

Starshot image

Step 2:

The axes of the star should have lower values than the background. If this is not the case, click on the Complement button to calculate the complementary image.

Starshot : complement

Step 3:

Click on the Starshot button .

Step 4:

Introduce the inputs of the test.

Starshot: input

Input / Fiducial:

Lock the cursor and align it with the fiducial/laser isocenter if marked on the image. Otherwise, lock the cursor in a position close to the center of the star.

Input / ROI (optional):

Prevent labels and other artifacts from interfering in the calculation by selecting a ROI.

Step 5:

Click on Calculate. Results will show after few seconds.

Starshot: output

Output / Isocenter coordinates:

Position of the radiation isocenter.

Output / Isocenter radius:

Radius of the radiation isocenter.

Output / Detected beams:

Number of detected beams.

Output / Distance fiducial-isocenter:

Distance between fiducial and radiation isocenter.

Results

Step 6:

Click on Report to get the results in a PDF file.

Troubleshooting 1:

The axes of the star have higher values than the background. Click on the Complement button to calculate the complementary image.

Starshot: error

Troubleshooting 2:

The cursor is far from the center of the star. Lock the cursor in a position closer to the isocenter.

Troubleshooting 3:

Excessive noise, large beam widths, beams too close to each other, image artifacts, etc., can induce errors in the location of the beams.

Check the accuracy of MLC positions with the Picket Fence test.

Step 1:

Load an image of a picket fence test (e.g., film, EPID, CR, etc.).

Picket fence image

Step 2:

The beam lines should be horizontal and have higher values than the background. If this is not the case, transform the image by rotating it and/or calculating the complementary image.

Prepare the picket fence image

Step 3:

Click on the Picket Fence icon .

Step 4:

Introduce the inputs of the test.

Picket fence: input

Input / MLC:

Select the MLC model.

Input / Auto-correct Translation:

Automatically remove any small offset of the isocenter position on the x-axis. (Default: checked)

Input / Auto-correct Rotation:

Remove any small rotation of the beam lines. (Default: checked)

Input / Isocenter:

Introduce the position of the isocenter on the X-axis either manually or by locking the cursor near the center of the MLC on the X-axis. Use this field to introduce EPID offsets with respect to the isocenter.

Input / Distance scaling:

Introduce distance scaling (i.e., Source to Imager Distance / Source to Axis Distance). (Default: 1.0)

Input / Tolerance:

Tolerance for errors of leaf positions. (Default: 0.5 mm)

Input / Leaf end threshold:

By default, the leaf end is located at the position of the 50% isodose between the peak of the signal and the background (i.e., the FWHM), which is appropriate when working with doses. You can change the threshold level to locate the leaf end more accurately when pixel values do not correspond to doses (e.g., with EPIDs). (Default: 50 %)

Input / ROI (optional):

Delineate the ROI (i.e., the MLC region).

MLC ROI

Step 5:

Click on Calculate. Results will show after few seconds.

Picket fence: output

Output / Passing rate:

Percentage of leaf positions within tolerance.

Output / Mean absolute error:

Mean absolute leaf position error.

Output / Maximum absolute error:

Maximum absolute leaf position error.

Picket fence: results

Step 6:

Click on Report to get the results in a PDF file.

The accuracy of the results depends on the image resolution and the signal-to-noise ratio. Better resolution and less noise produce more accurate results.

Troubleshooting 1:

The beam lines are vertical. Transform the image by rotating it.

Troubleshooting 2:

The beam lines have lower values than the background. Click on the Complement button to calculate the complementary image.

Verify the coincidence of light and radiation field.

Step 1:

Load an image of a light-radiation test.

Light-radiation image

Step 2:

Click on the Light-radiation icon .

Step 3:

Introduce the inputs of the test.

Light-radiation: input

Input / Field definition:

Select between Inflection points and FWHM. The FWHM follows the standard definition of radiation field as delimited by the 50% isodose of the beam profile. However, this definition requires that films are converted into dose distributions. When working with pixel values, an approximation to the radiation field can be obtained by the inflection points of the profiles.

Input / Nominal field size:

Introduce the nominal dimensions of the field on each semiaxis.

System of coordinates for QA tests

Input / Light points:

Introduce the points that mark the limits of the light field on each semiaxis. Enable them in Inputs and place them on the canvas. Light points shall correspond to the correct semiaxis and be located on the crosshair.

Input / ROI:

Select a ROI that encompasses the radiation field.

Light-radiation: canvas

Step 4:

Click on Calculate. Results will show after few seconds.

Light-radiation: output

Output / Light-radiation angle:

Rotation between light and radiation field.

Output / Light-radiation displacement:

Distance between radiation and light field. It is positive/negative when the radiation field is larger/smaller than the light field.

Output / Crosshair-light distance:

Light field dimensions on each semiaxis.

Output / CAX coordinates:

For symmetric nominal field sizes only: central axis coordinates of the radiation field.

Output / CAX distance to crosshair:

For symmetric nominal field sizes only: distance between the crosshair and the central axis.

Light-radiation: results

Step 5:

Click on Report to get the results in a PDF file.

Troubleshooting 1:

The light points shall correspond to the correct semiaxis and be located on the crosshair.

Troubleshooting 2:

The ROI shall encompass the radiation field, not extend beyond the image, and avoid labels and other artifacts.

This test uses evolutionary algorithms to recognize the radiation field. Repeated calculations can deliver slightly different results because of the random nature of evolutionary algorithms.

Analysis of the radiation field, including field size, central dose statistics, flatness, symmetry, penumbra, etc.

It can analyze rectangular and circular fields (e.g., cones) of WFF photons, FFF photons, and electron beams.

It is the QA test of choice for also measuring small fields and output factors.

Available protocols for flatness and symmetry:

Photons WFF:

• WFF IEC / Elekta™:   "IEC 60976. Medical electrical equipment - Medical electron accelerators - Functional performance characteristics." IEC (2007).
• WFF TG45 / Varian™:   Biggs, P.J., et al. "AAPM code of practice for radiotherapy accelerators: report of AAPM Radiation Therapy Task Group No. 45." Medical Physics 21 (1994): 1093.

Photons FFF:

• FFF Elekta™:   "Versa HD Product Data." Elekta AB.
• FFF Varian™:   "TrueBeam System Specifications." Varian Medical Systems, Inc. (2011)
• FFF AERB of India:   Sahani, G., et al. "Acceptance criteria for flattening filter-free photon beam from standard medical electron linear accelerator: AERB task group recommendations." Journal of Medical Physics/Association of Medical Physicists of India 39.4 (2014): 206.

Electrons:

• Electrons IEC / Elekta™:   "IEC 60976. Medical electrical equipment - Medical electron accelerators - Functional performance characteristics." IEC (2007).
• Electrons TG45 / Varian™:   Biggs, P.J., et al. "AAPM code of practice for radiotherapy accelerators: report of AAPM Radiation Therapy Task Group No. 45." Medical Physics 21 (1994): 1093.

Step 1:

Load an image with a dose distribution of a rectangular or circular radiation field.

Radiation field image

Step 2:

Click on the Radiation field icon .

Step 3:

Introduce the inputs of the test.

Radiation field: input

Input / Protocol for flatness and symmetry:

If you want to calculate flatness and symmetry, select one of the available protocols.

Input / Field geometry:

Select between rectangular and circular field.

Input / Apply field rotation:

Apply rotations while recognizing the rotation field. Do not apply rotations on fields with circular symmetry (e.g., cones and very small fields). (Default: checked)

Input / Central dose diameter:

Central dose statistics are measured for a circle with this diameter centered on the field. (Default: 1.0 mm)

Input / Averaging area:

Side of the area that averages pixel values for flatness and symmetry calculations. (Default: 10 mm)

Input / Field definition isodose:

Isodose that delimits the radiation field. (Default: 50%)

Input / Nominal field size:

Nominal field size dimensions.

Input / Crosshair coordinates (optional):

Lock the cursor and align it with the crosshair if the crosshair is marked on the image.

Input / ROI (optional/mandatory):

Select a ROI that encompasses the radiation field. This input is mandatory when applying the FFF AERB protocol.

Step 4:

Click on Calculate. Results will show after few seconds.

Radiation field: output

Output / Radiation field center:

Coordinates of the center of the radiation field.

Output / Radiation field size:

Dimensions of the radiation field.

Output / Radiation field rotation:

Rotation of the radiation field.

Output / Central dose statistics:

Statistics of the distribution of values within the central dose diameter.

Output / CAX distance to crosshair:

If the crosshair is introduced: distance between the crosshair and the central axis.

Output / Penumbras:

For rectangular fields except for FFF Elekta™ and FFF Varian™: distance between the 80-20% isodoses on each semiaxis.

Output / Flatness and Symmetry:

According to the different protocols, the outputs for flatness and symmetry are:

Photons WFF IEC / Elekta™:

Flatness

Symmetry

Maximum ratio of absorbed dose

Photons WFF TG45 / Varian™:

Flatness in the X and Y axes and both diagonals.

Symmetry in the X and Y axes and both diagonals.

Photons FFF Elekta™:

Symmetry

Isodose values on each semiaxis at different distances from the CAX.

Photons FFF Varian™:

Flatness

Symmetry

Isodose values on each semiaxis at different distances from the CAX.

Distances from the CAX to different isodoses on each semiaxis.

Photons FFF AERB of India:

Symmetry

Distances from the CAX to different isodoses on each semiaxis.

Electrons IEC / Elekta™:

Flatness: distance between the 90% isodose and the edge on each semiaxis and the diagonals.

Symmetry

Maximum ratio of absorbed dose

Electrons WFF TG45 / Varian™:

Flatness in the X and Y axes and both diagonals.

Symmetry in the X and Y axes and both diagonals.

Radiation field: results

Step 5:

Click on Report to get the results in a PDF file.

Troubleshooting 1:

The image must contain a dose distribution. If the image is a film scan, pixel values should be converted into doses.

Troubleshooting 2:

Rotation recognition may fail if the field has circular symmetry.

Troubleshooting 3:

The sample of central dose pixels may be empty if the central dose diameter is too small. As a consequence, the program will return an error.

This test uses evolutionary algorithms to recognize the radiation field. Repeated calculations can deliver slightly different results because of the random nature of evolutionary algorithms.

All your uploaded and calculated data are in My Work.

Open My Work:

Click on the Radiochromic.com logo to open My Work.

Open My Work

List of items:

Select a list of items according to Study and Category.

My Work menu

Archive / Restore studies:

Archived Studies are only accessible in My Work.

Edit studies:

Rename a study.

My Work buttons

Open My Item:

Click on an Item from the list and examine it.

In My Item:

Open the item in Analysis, Download it, print a Report or ask for Support from My Item.

My Item buttons