Patient Specific Quality Assurance for IMRT and VMAT based on Radiochromic Film Dosimetry with EBT2/EBT3 Film Sou-Tung Chiu-Tsao, PhD Quality MediPhys LLC, Denville, NJ Presentation at the New Jersey Medical Physics Society Jun. 12, 2012

Disclosure Statement Consultant to Ashland Inc. (Formerly ISP)

Background Safety and quality of radiation therapy Machine equipment QA Complex treatment modalities Imaging devices Immobilization/support devices Skin dose issue

Complex Treatment Modalities SRS (Stereotactic Radiation Surgery, single fx) SRT (Stereotactic Radiation Therapy, multiple fx) SBRT (Stereotactic Body Radiation Therapy) Helical Tomotherapy IMRT (Intensity Modulated Radiation Treatment) VMAT (Volumetric Modulated Arc Therapy) SRS, SRT, SBRT Stereotactic delivery of target dose Multiple arcs Multiple fixed gantry fields defined by stationary or dynamic MLC Helical tomotherapy Helical delivery of MLC fields

IMRT Fixed gantry angle Constant output rate Multileaf collimator (MLC) leaves move during the treatment Non-uniform beam intensity Technique Sliding window Step and shoot

VMAT Arc delivery of IMRT MLC leaf motion Gantry rotation Output rate variation VMAT: the divergent ray paths, leaf positions and segment weighting at each gantry angle. The reconstructed parallel rays and associated intensity-modulated beam are shown for every 4th angle. From a set of unmodulated VMAT fields, the parallel rays are spatially modulated Vmat by definition is an arc therapy. It utilizes an arc sweeping 360 degree. There are three mechanical axes during vmat delivery. Gantry rotation, mlc aperture shaping, and dose rate modulation. During gantry rotation, both mlc aperture and dose rate are modulated according to the designed tx plans. At certain beam angle, if the required dose is too high and can not be handled by dose rate modulation, gantry will slow down to compensate dose delivery. Webb_PMB_2009_54_4345-4360_VMAT_considerations.pdf Figure 4. The diagram shows the patient in the centre. Magenta dotted lines show the divergent ray paths from a source at each of 72 gantry angles at 5◦ angular spacing. The moving source rotates along a circle indicated by the outermost circle in the diagram. The next-in concentric circle shows the position of the leaves at each gantry angle. Beneath the leaves (i.e., the next circle in) the segment weighting is plotted as a grey rectangle of varying height and intensity which both vary in proportion to the segment weighting. Beneath this (next circle in), the reconstructed bixel maps from re-sorted parallel rays are shown with the associated parallel rays (black dotted lines). It can be seen that these re-sorted rays have an intensity modulation. Webb & McQuaid, PMB 2009; 54: 4345-4360.

VMAT/IMRT Prostate VMAT IMRT Evolving rapidly MU ~ 300 30 50 70 90 100 105 % Evolving rapidly MU ~ 300 Less treatment time Output rate varies with angle Rotating gantry Single arc, Multiple arc Partial arc, Split arc Established MU ~ 600 More treatment time Output rate remains fixed Fixed gantry angle for each field So close up to the target, the dose distributions are fairly similar with vmat perhaps being slightly more conformal. Zooming out, however, we see significant differences in the dose distributions. With imrt, we see doses of 30-50% corresponding to the 5 treatment fields. However, with vmat, the 30 and 50% regions are dispersed all the way around the patient. Our ability to control the distribution of dose outside of the target is something that we are still learning how to do using the parameters available to us during optimization. Basically, though dose is delivered from all directions as the gantry moves around the patient with the multileaf collimator shape adjusting to conform to the target and block the normal tissues to the best of it’s ability.

Patient Specific QA Pre-treatment QA Consult, diagnostic data gathering Decision making on Prescription dose to target Tolerance doses to organs at risk (OAR) Treatment planning CT scan simulation Delineation of contours of target and OARs Treatment planning calculation Pre-treatment QA On-treatment, in vivo monitoring Post-treatment analysis Skin dose

Pre-Treatment QA 2D dosimetry 3D, 4D dosimetry Ion chamber array Diode array: MapCHECK Radiochromic film: EBT2, EBT3 film EPID 3D, 4D dosimetry Gel Delta4 (2 perpendicular diode arrays ) ArcCHECK 4D Monte Carlo simulation Lobo_PMB_2010_55_4431_DOSXYZnrc_MC_QA_RapidArc_VMAT_TomoTherapy_cyberKnife.pdf

Planar Dose: Gamma Index Solid: TPS Dotted: EBT2 Film Planar Dose: Gamma Index Gamma index: Distance difference: Dose difference: DTA criterion: ∆d Dose diff criterion: ∆D Low, Med Phys 2003; 30: 2455-2464.

Pre-Treatment QA Procedure: EBT2/3 Film Import Plan via DICOM Flatbed Scanner Results cGy Film Export via R&V System Expose Phantom

Film Dosimetry Radiographic film, Kodak XTL, XV2, EDR2 Radiochromic film, Ashland (Formerly ISP) XR-QA, XR-RV2, EBT, EBT2, EBT3, MDV3, HDV2 Fine spatial resolution Darker shade with higher dose

EBT2 and EBT3 Films Contains yellow marker dye Color: yellow to green Less sensitive to ambient light EBT2 EBT3 Clear Polyester - 50 mm Adhesive Layer 25 m Active Layer 28 175 Matte Polyester - 120 m Active Layer 28 Matte Polyester - 120 m Asymmetric Symmetric

Matte Polyester in EBT3 Film

Common Setup for IMRT QA EDR2 Film EBT2/3 Film Measurement probe for absolute point dose Film for 2D dose distribution Solid Water

EBT2/3 Film in Phantom on Couch in Coronal Plane IGRT couch

EBT2/3 Film Dosimetry Technical Considerations Note model and lot # Note film orientation and alignment Control time between irradiation and scanning Environmental factors: humidity, temperature Store in dark envelopes Scanner influence, uniformity, and software

Tips for Scanning EBT2/EBT3 Film for IMRT and VMAT QA Scan all films in the same orientation Landscape or portrait orientation Place the film at the center of the scanner bed Practical spatial resolution for IMRT/VMAT QA 72 dpi, i.e. 0.35 mm per pixel Use 48 bit color mode, red, green, blue channels Use transmission mode Disable color correction feature Drop this slide?

Epson 10000XL Flatbed Scanner Landscape orientation of film on the scanner bed Transparency adapter Coating direction Scanning direction Scanner bed 10000XL 10000XL

Epson 10000XL Flatbed Scanner Portrait orientation of film on the scanner bed Coating direction Scanning direction 10000XL

EBT2/3 Film Image w/48 Bit Color Mode EBT2/3 film RGB image consists of 3 components Separated into 3 images in red, green and blue channels Red is highest contrast catch phrase. Blue image is RGB image--combined channels. FILMQA automatically takes from red channel

Absorption Spectra of EBT2/3 Film Before exposure After exposure of 2 Gy 636 nm 585 nm 420 nm Courtesy: Dr. David Lewis

Absorption Spectra of EBT2/3 Components Active component Signals in red and green channels Marker dye Signal in blue channel Courtesy: Dr. David Lewis

Data Analysis Method Single channel method Triple channel method Red channel only Green channel only Blue channel only Triple channel method Red, green and blue channels Removes film and scanner artifacts Allows compensation for film thickness variation Significantly improves the accuracy of dose map Micke, Lewis and Yu, “Multi-channel film dosimetry with non-uniformity correction”, Med. Physics 37, 2523-2534 (2011).

IMRT/SBRT QA, EBT2 Film D(cGy) Single field SBRT patient QA with EBT2 film (Red Channel data) Lung CA: 2000 cGy x3 Solid line: Film Dotted line: TPS 98% 3 % 3 mm Highest isodose line is for 200 cGy? 2 cm

IMRT, H&N Field, EBT3 Film 98% 2 % 2 mm Thcik line: TPS Thin line: EBT3

SBRT Lung Treatment EBT2 film used for patient QA Small field size Require fine spatial resolution, which is NOT achievable with diode or ion chamber array

cGy D(cGy) 95% 3% 3mm Composite of 3 fields SBRT patient QA OAR cGy 95% 3% 3mm D(cGy) Composite of 3 fields SBRT patient QA with EBT2 film (Red channel data) Lung CA: 2000 cGy x3 Solid line: Film Dotted line: TPS Add spatial scale Composite 3 fields 2000cGy/fx x 3 fx? Or 2000cGy total in 3 fx? Why is the highest isodose line is for 550 cGy? 2 cm

Brain SRS QA, EBT2 Film 97% 2 % 2 mm 96% 2 % 2 mm 2 cm 2 cm Solid line: iPlan, Dotted line: EBT2 Chan, International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 2012, 1, 1-7.

VMAT QA, EBT2 Film Red channel data Solid line: Film. Dotted line: TPS 96% 3 % 3 mm D(cGy) Add spatial scale Red channel data 2 cm Solid line: Film. Dotted line: TPS

Prostate VMAT QA, EBT2 Film Ozawa_strategy-for-VMAT-Juntendo-0843.pdf Ozawa_9AOCMP_Eleckta_VMAT_QA_EBT_EBT2.pdf Ozawa, ESTRO 2009 and 9th AOCMP 2009

VMAT, Double Arc, EBT3 Film Scanned Image, Portrait Orientation Coating direction Scanning direction Application Film 1.7 Gy 0 Gy Reference Films

VMAT, Double Arc, EBT3 Film Isodose Curve comparison 96.4% 2 % 2 mm Thick line: TPS, Thin line: EBT3 Film

IMRT QA (Single Field) EBT2 vs. TPS MapCHECK vs. TPS Agreement Discrepancy cGy cGy Solid line: Measurement, Dotted line: TPS

Radiochromic EBT/EBT2/EBT3 Film Fine spatial resolution (e.g. 0.35 mm) No angular dependence of film response van Battum, Med. Phys. 2008; 35: 704-716. Lin, Master’s thesis, Taichung, Taiwan, 2006. Suitable for IMRT and VMAT QA Immediate visualization of color change Drawback: Scan film after radiation exposure and then perform quantitative data analysis

Thank You. We have come a long way in radiation therapy. To assure the safety and quality of treatment, More work to be done, Further progress to be made, Future refinement to be achieved. Thank You.