Algorithms used in heterogeneous dose calculations show systematic error as measured with the Radiological Physics Center’s anthropomorphic thorax phantom used for RTOG credentialing Stephen F. Kry Ph.D. 1 , Paola Alvarez M.S. 1 , Andrea Molineu M.S. 1 , Carrie Amador B.S. 1 , James Galvin Ph.D. 2 , and David Followill Ph.D. 1 1 Radiological Physics Center, The University of Texas MD Anderson Cancer Center, Houston, TX 2 Radiation Therapy Oncology Group, Philadelphia, PA Wednesday, October 31, 2012 ASTRO Annual Meeting Boston, MA
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Algorithms used in heterogeneous dose calculations show systematic error as measured with the Radiological Physics Center’s anthropomorphic thorax phantom.
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Algorithms used in heterogeneous dose calculations show systematic error as
measured with the Radiological Physics Center’s anthropomorphic thorax phantom
used for RTOG credentialing
Stephen F. Kry Ph.D.1, Paola Alvarez M.S.1, Andrea Molineu M.S.1,
Carrie Amador B.S.1, James Galvin Ph.D.2, and David Followill Ph.D.1
1Radiological Physics Center, The University of Texas MD Anderson Cancer Center, Houston, TX
2Radiation Therapy Oncology Group, Philadelphia, PA
Wednesday, October 31, 2012 ASTRO Annual Meeting
Boston, MA
Introduction
• Dose calculation in thorax is challenging because of heterogeneous environment.
• Homogeneous and low quality heterogeneous dose calculations (e.g., Batho-corrected pencil beam) are highly inaccurate
• These algorithms are no longer allowed in NCI-sponsored clinical trials
Introduction
• Dose calculation in thorax is challenging because of heterogeneous environment.
• Homogeneous and low quality heterogeneous dose calculations (e.g., Batho-corrected pencil beam) are highly inaccurate
• These algorithms are no longer allowed in NCI-sponsored clinical trials
Introduction
• Dose calculation in thorax is challenging because of heterogeneous environment.
• Homogeneous and low quality heterogeneous dose calculations (e.g., Batho-corrected pencil beam) are highly inaccurate
• These algorithms are no longer allowed in NCI-sponsored clinical trials
• Convolution-Superposition/AAA algorithms are generally considered accurate
Verify dose delivery:
• RPC phantoms (treated like a patient)
Verify dose delivery:
• RPC phantoms (treated like a patient)
RPC phantoms:• Long history of use• Homogeneous phantoms:
– Average agreement of TLD and TPS: <1% • (Ibbott G et al. Technol Ca Res Treat 2006;5:481)
• Thoracic phantom– 2 TLD in center of lung target (3 cm x 5 cm)– Film in 3 planes
Irradiations• In this study:
– 304 irradiations– 6 MV irradiations– IMRT or 3D CRT– Moving or static– Various algorithms– All used heterogeneity
corrections
• Evaluate– TLD dose (vs TPS)– Planar agreement
• DTA or gamma
TLD Measurement vs TPS calculation
0.92
0.96
1.00
1.04
1.08
1/14/2004 10/10/2006 7/6/2009 4/1/2012
Date
Me
as
ure
d/C
alc
ula
ted
MC
0.994
TLD Measurement vs TPS calculation
0.92
0.96
1.00
1.04
1.08
1/14/2004 10/10/2006 7/6/2009 4/1/2012
Date
Me
as
ure
d/C
alc
ula
ted
MC PB
0.994
0.951
TLD Measurement vs TPS calculation
0.92
0.96
1.00
1.04
1.08
1/14/2004 10/10/2006 7/6/2009 4/1/2012
Date
Me
as
ure
d/C
alc
ula
ted
MC PB C/S AAA
0.994
0.951
0.963
TLD Dose Findings
• Measured doses systematically lower than calculated doses for C/S AAA algorithms (p<0.0001)
• No significant difference between C/S AAA algorithms
• For C/S AAA algorithms:• No significant difference between IMRT (mean=0.963) and 3D CRT
(mean=0.964) irradiations (p=0.7)
• No significant difference between moving (mean=0.961) and static (mean=0.964) irradiations (p=0.5)
• No significant trend versus irradiation date (p=0.2)