commissioning alignrt with minimal disruption

Another Device to Commission?

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Commissioning AlignRT® with Minimal Disruption

DISCLOSURES

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I have nothing to disclose

INTRODUCTION

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• Technology and complexity in radiation oncology continues to grow at a fast pace

• The need for accurate implementation of SRS/SBRT QA programs is crucial

• Increased pressure to keep cost down and be more efficient

How can physicists provide increased value to clinics with increasing demands,

but maintain a high level of safety?

INTRODUCTION

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• Combine tests to accomplish multiple QA procedures at one time

• Focus first on mission critical processes (think TG-100 and FMEA analysis)

• Use AAPM Task Groups as guidance when developing your program

Now, what about a technology that I don’t know? Like surface imaging?

COMMISSIONING SURFACE IMAGING

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The approach is the same as every other modality in

radiation therapy

• Start out with the Task Group (AAPM TG-147)1 for

recommendations

• Discuss with your clinicians the goals of the system

(motion management for SRS, positioning for breast

patients, etc)

• Prioritize the QA in terms of the clinical need

– Do you need to perform all QA possible?

1 Willoughby, T., et al. “Quality assurance for nonradiographic radiotherapy localization and positioning systems: Report of Task Group 147.” 8 March 2012

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THE TECHNOLOGY

• Stereoscopic camera system that is used for positioning and tracking

• Isocenter is determined from a novel calibration procedure2

• Triangulation provides a 3D reference frame using a speckle pattern on the

patient’s surface

ALIGNRT® INTRODUCTION

2 http://www.visionrt.com/content/core-technology

http://www.visionrt.com/content/core-technology

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COMMON APPLICATION

• Intrafraction motion-management for SRS, SBRT, and respiratory cases

• Positioning for sites where the surface is a good surrogate for the target

– Breast, intracranial, extremities, etc

• General use for all patients

– Gross movements

• The beam can be held (automatically on most systems) when the registered

surfaces are out of the specified tolerance

ALIGNRT® INTRODUCTION

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Start with the clinical use cases to establish QA procedures in conjunction with the

AAPM TG-147

One size may not fit all, and a good QA program will reflect the clinical need

• What site will be treated most often?

• Will it be used for motion-management, positioning, or both?

• Will the beam be held during treatment delivery (dynamic gating)?

• What tolerances will be needed during position and treatment delivery?

CLINICAL USE CASES

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Start by mapping out the workflow and establish an End-to-end test, which

incorporates the complete clinical use case

COMMISSIONING TESTS

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Try to create a test that mimics the clinical use case (E2E)

END-TO-END (E2E) TEST

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EQUIPMENT NEEDED

• Phantom (preferably anthropomorphic) that has a neutral surface for imaging

– Shouldn’t be a ball or cylinder, due to tracking difficulties

– MAX-HD® (Integrated Medical Technologies) a good choice

– STEEV SRS Phantom (CIRS)

– SRS Head Phantom from IROC (clear, so may need taped to image well)

• Detectors such as Gafchromic® film, microchambers/diodes, OSL/TLD

• Electrometer

• 3DOF Head Adjuster (provided by VisionRT) or 6DOF couch for accurate

positioning


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SAMPLE PHANTOMS

MAX-HD STEEV SRS (IROC) SRS Phantom

IMT CIRS IROC CIRS

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SOME NOTES ABOUT EQUIPMENT

• Detectors should be small enough to avoid partial volume effects, especially for

SRS

• Film scanning should use the right calibration procedure

• Make sure film is cut in such a way to ensure reproducibility and localization

– Laser cut films for the phantom are available

• Epson Perfection XL11000 (or the older XL10000) are good choices for film

scanning


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CT SCANNING

• Use the highest resolution protocol possible (small slice thickness ~1mm, high

mAs, etc)

• Try and use the same immobilization techniques that would be used during

treatment

• Set your DICOM origin (CT origin) at a reproducible localization to minimize setup

errors

• If the phantom supports it, try multiple CT scans with different inserts and cubes

– Again, it’s important to know the origin with certainty for film scanning


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CONTOURING

• Many treatment planning systems automatically create the BODY contour, so

review for accuracy

• The Target Volume can be the sensitive volume of the detector or the center of

the film


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TREATMENT PLANNING

• Use a beam configuration that will test the system

– Couch kicks

– VMAT, if applicable, to block cameras

– Dose levels that mimic treatment time (don’t scale MU)

– Use a real plan if available

• Save for a baseline for routine QA


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LOCALIZATION

• Use the AlignRT system to be the primary localization method

• Verify the positioning with CBCT and lasers

– There may be a small deviation with the DICOM because of the BODY

contour

– If so, position initially with CBCT, capture the reference, then reposition

with the AlignRT system

• Use a 6DOF localization technique to position the phantom


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DELIVERY

• Make note of gantry occlusion and deltas

– Some variation is acceptable during blockage, but extreme shifts may

indicate improper lighting, ROI, or calibration conditions

• Watch the deltas for drift over the course of the treatment at the couch base

• When rotating the couch, use the AlignRT readout, not the digital indicators, to

reposition

– Stereoscopic systems trump the internal readouts of the LINAC system,

hence the “STEREO” in stereotactic

– This is especially important in older systems, where couch tolerances are

looser


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ANALYSIS

• Temperature/pressure correct the chamber reading, and use a cross calibration

factor to calculate the ratio of charge/dose (traced by to your ASCL calibrated

detector)

• FilmQA® from Ashland is a good choice for film scanning

– FilmQA analyzes in all 3 RGB channels

– ImageJ is also available for free, but takes some effort to write code

• Always scan the film in the same orientation, and if the calibration films are not

done on the same day, wait a while for the film to develop


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WHAT AM I LOOKING FOR?

Depends on the clinical goals

• Breast patients could be passing 95% with a gamma index at 3%, 3mm with the

film analysis

• SRS programs treating trigeminal neuralgia cases may need 2%, 1mm

• Output measurements should be within 2% of the expected from the TPS, but

can be tough for small cones because of the output factors

If you pass the E2E, the commissioning process got a whole lot better. But…


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WHAT IF IT FAILS?

Start looking at each component of the system closer. You will need it for the

overall QA program anyways. Keep in mind:

1. TG-147 is just part of this. Since an E2E test checks the whole system, it could

be anything outlined in TG-40, TG-142, TG-66, etc

2. Focus on the components that are specific to TG-147, as to not get

overwhelmed


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• Do a “chart check” style review to make sure items transferred properly

– Patient ID

– Isocenter

– Contour (especially BODY)

– Scan orientation

• The coordinate system of the LINAC matches the TPS and DICOM transfer

– For example, the couch coordinates could be opposite if the coordinate

systems don’t match

COMMICATION BETWEEN SYSTEMS

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• Do a “chart check” style review to make sure items transferred properly

– Patient ID

– Isocenter

– Contour (especially BODY)

– Scan orientation

• The coordinate system of the LINAC matches the TPS and DICOM transfer

– For example, the couch coordinates could be opposite if the coordinate

systems don’t match

• If using an interface for shifts, ensure that is correct by using lasers or another

surrogate to confirm AlignRT shifts performed by the LINAC console

COMMICATION BETWEEN SYSTEMS

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• An accurate ROI gives stable real-time deltas for any phantom when there are no

occlusions. If the delta jump at couch base, and no blockage

– Ensure the ROI give a unique view

• I.e., not flat, symmetric, nor broken

– The underlying image is intact

• Check lighting condition or skin tone

• It is equally important to not make the ROI so big it doesn’t detect small

movements

– Like contouring the entire head for SRS – just use the small area in the

open mask

REGION OF INTEREST (ROI)

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• In order to make sure the calibration (both the calibration plate and fine

isocenter) is correct, perform a series of shifts to known positions, and record

the deltas

– Shift 2mm, 1cm, 2cm, 5cm, 10cm in S/I, L/R, and A/P directions

– Kick the couch in increments of 45 degree, for example

– Move the phantom arbitrarily, and see if the 6DOF positioning can get

back to a zero baseline

• If greater than 1mm (for SRS) disagreement is seen, perform isocenter and

monthly calibrations again, and repeat

• Refer to the acceptance testing procedures for vendor baselines as well

SHIFTS

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• With the camera system on for a significant period of time (like an hour or so),

turn the monitoring on and watch the deltas

• Record the values, and if large deviations are seen, repeat after a longer warm

up is achieved

• Compared to infrared based systems, the drift should be quite minimal

SHIFTS

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• With the camera system on for a significant period of time (like an hour or so),

turn the monitoring on and watch the deltas

• Record the values, and if large deviations are seen, repeat after a longer warm

up is achieved

• Compared to infrared based systems, the drift should be quite minimal

SHIFTS

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• With a simple motion phantom, try and move the phantom enough to hold the

beam

• Tighten tolerance to only beam on when the chamber is in position

• Use a simple test plan to isolate it just the motion of the phantom

• Measure with an ion chamber and record the results

– Should be very close to baseline, stationary reading, assuming the

phantom is not shifting during motion, and the gating is working

• This would also test spatial accuracy at the same time

DYNAMIC GATING

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• As with all medical devices, it is up to the medical physicists to stay current with

the latest customer service bulletins and release notes

• The tests outlined are from a clinical medical physicist’s perspective, but are by

no means meant to be prescriptive

• Training and continuing education are equally, and maybe more, important than

a one-time commissioning – as is the continual QA program

VENDOR RECOMMENDATIONS

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• VisionRT has already provided a nice workflow for QA

– DailyQA

• Uses the calibration plate, aligned by the therapists, and analyzes it

for constancy

– MonthlyQA

• Again, using the plate, but overrides the triangulated 3D position of

the system. To be done if the system appears to have changed

– Isocenter Calibration

• Using a phantom with fiducials that can be seen on CT/MV, with the

surface imaged, allows the isocenter of the imaging system to be

correlated to the MV isocenter

ESTABLISHING A QA PROGRAM

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• In addition to the vendor provided phantoms and software, use the results from

the commissioning tests to create baselines for routine QA

ESTABLISHING A QA PROGRAM

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"If it's not written down, it didn't happen“

• Ensure all the tests you do during commissioning, QA, or anything concerning

the system are well documented

• Not only is it good to establish baselines and trends, it is very useful in helping

other centers when they go live with AlignRT

DOCUMENTATION

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• Commissioning any system doesn’t have to be difficult, or even that time-

consuming, any long as the problem is well-defined

• By using clinical use cases as guidance, tests will solidify, and the project can be

focused

• By incorporated E2E tests, and grouping other QA procedures in an effective way,

commissioning and routine QA time can be reduced

CONCLUSIONS

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THANK YOU!

www.alyzenmed.com

1801 South 54th StreetParagould, AR 72450

870.926.0894

[email protected]

Jonathan Rogers, MS, DABR

commissioning alignrt with minimal disruption

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