Respiratory Gating with IMRT

Presented by:Katherine Adams

Respiratory Gating & IMRT

• Conforms to target• Higher doses to target tissue• Less side effects from normal tissue• Sharp dose gradient between target tissue and

normal tissue

• Target location important• Misjudgment causes

• Underdose target• Overdose normal tissue

Treatment Planning• The prescription dose is targeted to a region that consist

of the gross tumor volume, clinical target volume and the planning target volume.

• These margins need to be considered to make sure that the target volume remains in the field during treatment

• The resulting margins in conventional therapy can be as high as 3 to 5 cm depending on the anatomy treated. – GTV: visible or palpable tumor– CTV: GTV + microscopic disease– PTV: CTV + margin to account for

• Variations in treatment setup• Patient motion• Organ motion

Tumor Motion

Tumor Motion

• The previous slide showed a video clip of a 4DCT that shows the movement and location of a lung tumor during respiration.

• Internal structures can move a significant amount- The diaphragm and liver can move up to 3 cm and the pancreas, kidney and thorax can move up to 2 cm

• Respiratory gating is used to minimize the increased margins of the treatment volume that are directly related to respiratory movements

Tracking Respiration

• External Marker– RPM by Varian– Reflective markers

“learn” the patient’s breathing pattern

– Camera system• Sends signal • Reflected off markers• Respiratory waveform

created– Shape represents

tumor movement

• Internal Markers– Implanted gold seeds– Use flouroscopy to

locate

http://www.biij.org/2007/1/e40/fig1.jpg

Respiratory Waveform

• Peaks: inspiration• Troughs: expiration• Patient coached until a waveform that matches the

patient’s normal breathing pattern is attained. • Cycle divided into phases

Inspiration

Expiration

Inspiration

Expiration

PHASES

CT Images• Spiral CT acquires its

images with a moving table during many different phases of the breathing cycle

• The resulting image is a blurred snapshot of the structure and may contain motion artifacts

4D CT• CT table stationary

– Info for complete cycle– Divided into phases

• Table moves to next position– Cycle repeats

• Information is gathered for each phase and combined to construct an image that represents the location of the anatomy at that precise moment.

• Exhalation = Beam on– Anatomy is relatively

stationary– More reproducible

• More phases included– More efficient

treatment

Beam Off

Beam On

Beam On

Treatment Planning

Cancer Treatment with Respiratory Gating

System automatically shuts down until normal

breathing pattern is

reestablished.

Irregular Respiration

Beam On

Beam On

Beam Off

Normal Respiration Normal Respiration

Beam Off

Inspiration

Expiration

Inspiration

ExpirationExpiration

Beam On

Irregular Respiration

Cancers Treated

• Tumors subject to respiratory motion:– Lung– Breast

• Maximum inhalation– Inflates lung- minimizing amount in field– Separates breast from heart

– Pancreatic– Stomach– Liver– Prostate– Whole abdomen for ovarian cancer

Patient Eligibility

1. Consistent and periodic respirations– Inadequate lung function prohibits

2. Tumor movement must correlate with breathing movement

– More accurate prediction of target location

3. Sufficient overall tumor movement– Yet within 5mm displacement during “Beam

On” time to increase treatment efficiency.

Alternative Methods

• Require invasive surgical procedures submitting patient to infection:– Intraoperative radiation therapy– Interstitial brachytherapy

• Uncomfortable breath holds that many cannot withstand due to decreased pulmonary function:– Deep inspiration breath hold (DIBH)– Active breathing control (ABC)

• Continuous Monitoring Required!!– Waveform pattern to match the actual

breathing pattern– Beam on time to correlate with the appropriate

phase of the cycle– The beam is actually turning on and off at the

right times

Role of the Radiation Therapist

http://www.varian.com/us/oncology/radiation_oncology/clinac/rpm_respiratory_gating.html

THE END

• ANY QUESTIONS...???

References• Brandner, E., Heron, D. E., Wu, A., Huq, M. S., Yue, N. J.,Chen, H. C., (2006).

Localizing Moving Targets and organs using motion-managed CTs. Medical Dosimetry, 31(2), 134-140.

• Bucsko, J. K., (2004, November). Managing Respiratory Motion. Radiology Today, 5(23), 33. Retrieved February 27, 2008, from http://www.radiologytoday.net/archive/rt_110804p33.shtml

• Butler, L.E., Forster, K. M., Stevens, C. W., Bloch, C., Liu, H. H., Tucker, S. L., (2004). Dosimetric benefits of respiratory gating: a preminary study. Journal of Applied Clinical Medical Physics, 5 (1), 16-24.

• Carlson, A. H., (2007, October). Breathing New Life into Respiratory Gating. Medical Imaging, 42. Retrieved February 27, 2008, from http://www.medicalimagingmag.com/issues/articles/2007-10_04.asp

• Garsa, A.A., Andrade, R. S., Heron, D.E., Beriwal, S., Kim, H., Brandner, E., (2007). Four-dimensional computed tomography-based respiratory-gated whole abdominal intensity-modulated radiation therapy for ovarian cancer: a feasible study. International Journal of Gynecological Cancer, 17, 55-60.

• Huntzinger, C., (n.d.). The Revolution in Radiation Therapy. In Looking Forward- The Future is in Motion. Varian Medical systems. Retrieved February 27, 2008, from varian.mediaroom.com/file.php/mr_varian/spinsite_docfiles/147/VRM395+IMRT+White+Paper+Final+Jan+2005.pdf -

References• Jiang, S. B., (2006). Technical aspects of image guided respiration-gated radiation

therapy. Medical Dosimetry, 31(2), 141-151.• Keall, P., Vedam, S., George, R., Bartee, C., Siebers, J., Lerma, F., (2006). The

clinical implementation of respiratory-gated intensity-modulated radiotherapy. Medical Dosimetry, 31(2), 152-162.

• Kornmehl, C., (2005). Every Move You Make. Image, 18(10). Retrieved February 25, 2008, from http://www.rt-image.com/030705FO

• Korreman, S., Mostafavi, H., Le, QT., Boyer, A., (2006). Comparison of respiratory surrogates for gated lung radiotherapy without internal fiducials. Acta Onclolgica, 45, 935-942.

• Rosenzweig, KE., Yorke, E., Amols, H., Mageras, GS., Giraud, P., Katz, MS., (2005). Tumor Motion Control in the Treatment of Non Small Cell Lung Cancer. Cancer Investigation, 23, 129-133.

• Saw CB, Brandner E, Selvaraj R, Chen H, Saiful Huq M, Heron DE, (2007). A review on the clinical implementation of respiratory-gated radiation therapy, Biomedical Imaging and Intervention Journal 3(1):e40. Retrieved February 25, 2008, from http://www.biij.org/2007/1/e40/>

• Underberg, R., van Sornsen de Koste, JR., Lagerwaard, FJ, Vincent, A., Slotman, BJ., Senan, S., (2006). A dosimetric analysis of respiration-gated radiotherapy in patients with stage II lung cancer. Radiation Oncology. 1:8, Retrieved February 27, 2008, from http://www.ro-journal.com/content/pdf/1748-717X-1-8.pdf.