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Anand's Talk

Faculty Seminar

Aman Anand

on 24 October 2012

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Transcript of Anand's Talk

Proton Therapy – Current Trends and inherent uncertainties Aman Anand, Ph.D. Medical Physics Resident,
U.T. M.D. Anderson Cancer Center
Houston, TX - 77030
Tel: 713-745-9808
Email: aanand@mdanderson.org Overview Background
Proton Therapy at MDACC
Proton Dosimetry -- Scanning beam system
Synopsis (water and patient specific)
My work at PTCH
Characterization of pencil beams -- Novel procedures
Creation of a Data Library system.
Alternate dosimeters for QA
Conclusion Next best radiation would deliver most dose within the target volume, and relatively little dose outside. Ideal Radiation for treating cancer would deliver entire dose within the target ! 1946: First Proton based therapeutic treatment was proposed Beam Delivery Capabilities at PTCH Beam delivery capable of both scanning and double scattering Focus of my work - Scanning Beam System 94 energies with ranges : 4.0- 30.6 cm
Range step size adjustable at 0.1 g/cm2
Maximum Field Size capabilities: 30x30 cm
Beam Spot Size in air --> Energy dependent (5-14) mm sigma
Each scanning pulse is 4.4 seconds, with 2.1 seconds between pulses.
A new pulse is required to change energy Courtesy Hitachi Systems Ltd. What does it take?
Choosing right tools and equipments for characterization

Making measurements, modeling, and optimizing the beam characteristics

Understanding the treatment planning system requirements

Carefully identifying “knowns” and “unknowns”

Choosing mitigation strategies.

Validation period

A.K.A. Commissioning a proton therapy center

AAPM Task Group (N/A) Basic Requirements TPS Input – Monte Carlo, In Air Spot Profiles.

TPS Dose Validation – Point measurements, 2D film measurements.

TPS MU Validation – Point measurements, function of field size.

Electronic Medical Record Testing such as Mosaiq interfaces with Hitachi Control

Safety testing and Machine QA

Designing Patient specific QA Procedures .

In room Imaging P+ Dosimetry Explained We Ought to Know what we don't know The Whole Ball Game Changes From Water to Humans Uncertainties - clinical perspective Paganetti et. al Widely discussed -- Summarised

Setup Uncertainties
Range Uncertainties
Anatomical Changes
Motion Uncertainties U. Schneider et al. Phys. Med. Biol. 41, 111-124 (1996).
B. Schaffner , Phys. Med. Biol. 43, 1579-1592 (1998).
Paul Scherrer Institute, Switzerland Stoichiometry TPS Aspect "Painting" a perfect picture For estimating the optimal energy, spacing and margins for delivering volumetric dose : It is important we characterize our pencil beams How to Characterize Proton Pencil Beam Proton Pencil Beam Characterization Nuclear interactions occur along the proton beam path up until the last few mm of the their end of range
Consequences of nuclear interactions:

Reduce number of primary protons in the beam; a 160 MeV beam loses about 20% of its protons in this manner before end of range;

Produce a halo of scattered primary protons and secondary protons that add a “tail” the lateral dose profile of a beam;

Create heavily ionizing fragments with a very high stopping power, thus increasing the relative biological effectiveness (RBE) local to the site of interaction; Procedure to compute planar integral spot dose from pencil beams Possible methods of characterization For proton beams of diameter < 15 mm, the depth-dose distribution is degraded as compared to that of a broad beam.

As a result the energy deposited at the Bragg Peak is smeared out Assumptions of rotational symmetry and Gaussian distribution Would not be true
& thus One of the requirements for Eclipse TPS is to measure integral dose The challenge is the detector size effect A possible method studied Challenge Solution Total Dose = DB + LTDCF*DB Validation Various uncertainties estimated

Water Tank Setup and quantifying profile reproducibility
Quantifying FWHMs Sigma
How to address energy dependencies on profiles’ reproducibility? – remains unanswered
Peak Spot Dose measurements
along the beams direction from broad beam measurements
Perpendicular to the beam, reproducibility error is less than 0.1%
Bragg Peak Chamber Measurements
Along the beams direction
Perpendicular to the beams direction
ADCL Calibration uncertainty – Fixed
Detector Size Effect- WIP Results EBT2 for Proton Dosimetry ? Future Research interests:

Radiobiology and "newer" charged particle dosimetry.
"Non destructive evaluation of tissue using dielectric spectroscopy, and nano dosimetry of microcellular structures." Conclusion Remarks Lot has been done. Lot more lies ahead 1954: First patient treated at LBL
1961: HCL treatment of CNS tumors
1990: First hospital proton treatment at LLUMC Proton Therapy at M.D. A. 1840 Old Spanish Trail Houston A great deal of understanding : Characterization of pencil beams However there are also nuclear interactions within the medium
Which leads to additional dose deposition in the lateral profiles "Halo" doses Principal genesis of the Bragg peak is the loss of energy due to Coulomb interactions with atomic electrons. This varies as a function of depth. Paganetti et.al.
Pedroni et. al.
Slide courtesy R. Amos For Relative dosimetry Absolute Dosimetry Just like conventional Treatment, except the effect gets magnified Outcome of TPS depends on what we provide Other Works For QA Role of Thank you for your time Narayan Sahoo, Ph.D. Ron Zhu, Ph.D. Michael T. Gillin, Ph.D Richard Amos, M.Sc. Uwe Titt, Ph.D. Radhe Mohan, Ph.D. Rajat Kudchadker Ph.D Suzuki Kazumichi, Ph.D Michael Taylor, B.S. James Kerns, M.S. Hitachi Ltd. Varian Health Systems Gabriel Sawakuchi, Ph.D. Luis Perles, Ph.D. Yupeng Li, M.S Xiaodong Zhang , Ph.D Falk Poenisch, Ph.D.
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