FIRST CQ M SKIN DOSE M R F - agenda.infn.it€¦ · QUALITY CONTROL RADIOCHROMIC FILM MEASUREMENTS...

QUALITY CONTROL RADIOCHROMIC FILM MEASUREMENTS

FIRST CQ MEASUREMENTS AND SKIN DOSE

MEASUREMENTS WITH RADIOCHROMIC

FILMSSYRMA-3D Collaboration Meeting

Anna Veronese

17 February 2017

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QC PHANTOM MATERIALS

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QC PHANTOM

Acquisition and Reconstruction Parameters:

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QC PHANTOM IMAGES35 keV High Dose:

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QC PHANTOM IMAGES35 keV High Dose:

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QC PHANTOM MEASUREMENTS

Average CT number of water:

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QC PHANTOM MEASUREMENTSAverage CT number of water:

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Noise and Uniformity:

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Noise and Uniformity:

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CT Number Linearity:

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CT Number Linearity:

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QC PHANTOM MEASUREMENTS RESULTS

Synthesis of the Results:

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QC PHANTOM MEASUREMENTS RESULTSSynthesis of the Results:

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QC PHANTOM MEASUREMENTS RESULTS

What we learned:• Nylon isn’t Nylon... It’s Delrin!• Plexiglas absorbs ≈water @ 35 keV;• Low Contrast Details are unresolved;• Ring artefacts affect uniformity especially in the central

area;• PVC generated streaking artefacts: is it too absorbing?

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SKIN DOSE MEASUREMENTS USING RADIOCHROMIC

Aim:• Measure the dose to the

patient’s skin;• Different irradiation

modalities.

Radiochromic Films:• GafChromicTM XR-QA2;• Sensitive 1-200 mGy;• Properly Calibrated.

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MEASUREMENTS AT THE SYRMEP BEAMLINESYRMEP Beamline @Elettra:• Elettra @ 2.4 GeV;• Laminar SR beam 3 mm height (@slits);• Energy 38 keV;• IOC gives the air-Kerma.

(a) (b)

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MEASUREMENTS AT THE SYRMEP BEAMLINE

Cylindrical Phantom 10 cm in diameter on patient’s support:• diameter, symmetry and µ similar to breast;• two pieces of films tightly wrapped around it to simulate

patient’s skin.

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MEASUREMENTS AT THE SYRMEP BEAMLINE

Four different irradiation modalities on different pieces of film:

• 180◦

• 360◦

• 0◦-180◦- step - 0◦-180◦

• 0◦-180◦- step - 180◦-360◦

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0◦-180◦- STEP - 0◦-180◦

Radiochromic film scan:

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0◦-180◦- STEP - 0◦-180◦Profile of horizontal dose distribution:

• Minimum dose: 18% of the maximum dose;• MGDt = 6.9 mGy→ Dose up to 205% of MGDt.

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0◦-180◦- STEP - 0◦-180◦

Profile of vertical dose distribution:

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0◦-180◦- STEP - 0◦-180◦

• Maximum peak-to-valley difference: 33% of the maximumdose.

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0◦-180◦- STEP - 180◦-360◦

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0◦-180◦- STEP - 180◦-360◦Profile of horizontal dose distribution for odd slices:

• Minimum dose: 20% of the maximum dose.24 / 42

0◦-180◦- STEP - 180◦-360◦Profile of horizontal dose distribution for even slices:

• Minimum dose: 20% of the maximum dose.• MGDt = 6.9 mGy→ Dose up to 170% of MGDt.

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0◦-180◦- STEP - 180◦-360◦Profile of vertical dose distribution: we see three differentpatterns

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0◦-180◦- STEP - 180◦-360◦Profile of vertical dose distribution:

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• Maximum peak-to-valley difference: 34% of the maximumdose.• MGDt = 6.9 mGy→ Dose up to 120% of MGDt.

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CONCLUSIONS AND COMMENTS

We were able to measure the dose to the skin in differentirradiation conditions:• In 180◦the non irradiated skin receives > 10% of the

maximum dose;• 0◦-180◦- step - 0◦-180◦gives high areas of superposition

(with this step);• 0◦-180◦- step - 180◦-360◦is a good intermediate irradiation

(less superposition).

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FUTURE MEASUREMENTS

In the future we would like to repeat the measure with...• Different step between slices to study the superposition;• Different energies;• Different doses.

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THE END

Thank you for you kind attention!

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WHAT IS THE MEAN GLANDULAR DOSE (MGD)?• For the whole volume irradiated, MGD(mGy) is calculated

from the total energy deposited (Eg) in the total glandularmass of the breast (Mg), as:

MGD = Eg/Mg

• For a partial irradiation, MGDv (mGy) can be calculatedfrom the energy (eg) deposited only in the glandular massof the directly irradiated breast volume (mg), as:

MGDv = eg/mg

• Considering the scattered radiation coming outside of theirradiated volume, MGDt is the ratio between the totalenergy deposited in the whole breast (Eg) and theglandular mass in the irradiated volume (mg):

MGDt = Eg/mg

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180◦

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180◦

Profile of horizontal dose distribution:

• Minimum dose: 9.5% of the maximum dose;• MGDv = 7,8 mGy→ Dose up to 240% of MGDv.

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VERTICAL BEAM PROFILE

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VERTICAL BEAM PROFILEProfile of vertical dose distribution:

• 1200 dpi scan: 1 pixel=2 µm;• FWHM=3,61 mm;• Magnification: 20%.

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360◦

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360◦

Profile of horizontal dose distribution:

• Maximum variation: 24% of the maximum dose;• MGDv = 7.8 mGy→ Dose 175% - 130% of MGDv.

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DOSE EVALUATION

The dose is proportional to the change in reflectance of the film:

• Films have to be scanned both before and after irradiation;• PV (pixel value) change is evaluated as:

∆R = Rbefore − Rafter =PVbefore

216 − PVafter

• A piece of control film is never irradiated:

∆Rcontrol = Rcontrolbefore − Rcontrol

after =PVcontrol

before216 −

PVcontrolafter216

• The net change in reflectance is:

net∆R = ∆R−∆Rcontrol

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CALIBRATION PROCEDUREWe want a dose-response curve for the specific energy (38 keV):

• Obtained plotting the air Kerma Kfilm as a function of thecorresponding film response net∆R;• 3 4×4 cm film pieces exposed at the same time;• Different values if air-Kerma (1-20 mGy);

• Best fitting funtion logarithm one: Kfilm = a +b net∆R

ln (net∆R)

Net DeltaR (a.u.)0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

20 / ndf 2χ 4.61 / 6

Prob 0.5947a 0.1166± 0.6549 b 5.681±169 −

/ ndf 2χ 4.61 / 6Prob 0.5947a 0.1166± 0.6549 b 5.681±169 −

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OTHER QC PROTOCOL MEASUREMENTS

Ideas for other measurements:• Air Slits and Vacuum Slits control;• µ curve to verify energy;• Phantom to verify bed movement;• CTDI to check dose.

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FIRST CQ M SKIN DOSE M R F - agenda.infn.it€¦ · QUALITY CONTROL RADIOCHROMIC FILM MEASUREMENTS...

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