Impact of Geometric Uncertainties on Dose Calculations for Intensity Modulated Radiation Therapy of Prostate Cancer

IMRT uses non-uniform beam intensities within a radiation field to provide patient-specific dose shaping, resulting in a dose distribution that conforms tightly to the planning target volume (PTV). Unavoidable geometric uncertainty arising from patient repositioning and internal organ motion can lea...

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Main Author: Jiang, Runqing
Language:en
Published: 2008
Subjects:
Online Access:http://hdl.handle.net/10012/3570
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spelling ndltd-WATERLOO-oai-uwspace.uwaterloo.ca-10012-35702013-01-08T18:50:59ZJiang, Runqing2008-01-29T14:38:20Z2008-01-29T14:38:20Z2008-01-29T14:38:20Z2007http://hdl.handle.net/10012/3570IMRT uses non-uniform beam intensities within a radiation field to provide patient-specific dose shaping, resulting in a dose distribution that conforms tightly to the planning target volume (PTV). Unavoidable geometric uncertainty arising from patient repositioning and internal organ motion can lead to lower conformality index (CI), a decrease in tumor control probability (TCP) and an increase in normal tissue complication probability (NTCP). The CI of the IMRT plan depends heavily on steep dose gradients between the PTV and organ at risk (OAR). Geometric uncertainties reduce the planned dose gradients and result in a less steep or “blurred” dose gradient. The blurred dose gradients can be maximized by constraining the dose objective function in the static IMRT plan or by reducing geometric uncertainty during treatment with corrective verification imaging. Internal organ motion and setup error were evaluated simultaneously for 118 individual patients with implanted fiducials and MV electronic portal imaging (EPI). The Gaussian PDF is patient specific and group standard deviation (SD) should not be used for accurate treatment planning for individual patients. Frequent verification imaging should be employed in situations where geometric uncertainties are expected. The dose distribution including geometric uncertainties was determined from integration of the convolution of the static dose gradient with the PDF. Local maximum dose gradient (LMDG) was determined via optimization of dose objective function by manually adjusting DVH control points or selecting beam numbers and directions during IMRT treatment planning. EUDf is a useful QA parameter for interpreting the biological impact of geometric uncertainties on the static dose distribution. The EUDf has been used as the basis for the time-course NTCP evaluation in the thesis. Relative NTCP values are useful for comparative QA checking by normalizing known complications (e.g. reported in the RTOG studies) to specific DVH control points. For prostate cancer patients, rectal complications were evaluated from specific RTOG clinical trials and detailed evaluation of the treatment techniques. Treatment plans that did not meet DVH constraints represented additional complication risk. Geometric uncertainties improved or worsened rectal NTCP depending on individual internal organ motion within patient.enDose gradientGeometric uncertaintiesIMRT optimizationProstate cancerDose calculationProbability density functionEffective uniform doseImpact of Geometric Uncertainties on Dose Calculations for Intensity Modulated Radiation Therapy of Prostate CancerThesis or DissertationPhysics and AstronomyDoctor of PhilosophyPhysics
collection NDLTD
language en
sources NDLTD
topic Dose gradient
Geometric uncertainties
IMRT optimization
Prostate cancer
Dose calculation
Probability density function
Effective uniform dose
Physics
spellingShingle Dose gradient
Geometric uncertainties
IMRT optimization
Prostate cancer
Dose calculation
Probability density function
Effective uniform dose
Physics
Jiang, Runqing
Impact of Geometric Uncertainties on Dose Calculations for Intensity Modulated Radiation Therapy of Prostate Cancer
description IMRT uses non-uniform beam intensities within a radiation field to provide patient-specific dose shaping, resulting in a dose distribution that conforms tightly to the planning target volume (PTV). Unavoidable geometric uncertainty arising from patient repositioning and internal organ motion can lead to lower conformality index (CI), a decrease in tumor control probability (TCP) and an increase in normal tissue complication probability (NTCP). The CI of the IMRT plan depends heavily on steep dose gradients between the PTV and organ at risk (OAR). Geometric uncertainties reduce the planned dose gradients and result in a less steep or “blurred” dose gradient. The blurred dose gradients can be maximized by constraining the dose objective function in the static IMRT plan or by reducing geometric uncertainty during treatment with corrective verification imaging. Internal organ motion and setup error were evaluated simultaneously for 118 individual patients with implanted fiducials and MV electronic portal imaging (EPI). The Gaussian PDF is patient specific and group standard deviation (SD) should not be used for accurate treatment planning for individual patients. Frequent verification imaging should be employed in situations where geometric uncertainties are expected. The dose distribution including geometric uncertainties was determined from integration of the convolution of the static dose gradient with the PDF. Local maximum dose gradient (LMDG) was determined via optimization of dose objective function by manually adjusting DVH control points or selecting beam numbers and directions during IMRT treatment planning. EUDf is a useful QA parameter for interpreting the biological impact of geometric uncertainties on the static dose distribution. The EUDf has been used as the basis for the time-course NTCP evaluation in the thesis. Relative NTCP values are useful for comparative QA checking by normalizing known complications (e.g. reported in the RTOG studies) to specific DVH control points. For prostate cancer patients, rectal complications were evaluated from specific RTOG clinical trials and detailed evaluation of the treatment techniques. Treatment plans that did not meet DVH constraints represented additional complication risk. Geometric uncertainties improved or worsened rectal NTCP depending on individual internal organ motion within patient.
author Jiang, Runqing
author_facet Jiang, Runqing
author_sort Jiang, Runqing
title Impact of Geometric Uncertainties on Dose Calculations for Intensity Modulated Radiation Therapy of Prostate Cancer
title_short Impact of Geometric Uncertainties on Dose Calculations for Intensity Modulated Radiation Therapy of Prostate Cancer
title_full Impact of Geometric Uncertainties on Dose Calculations for Intensity Modulated Radiation Therapy of Prostate Cancer
title_fullStr Impact of Geometric Uncertainties on Dose Calculations for Intensity Modulated Radiation Therapy of Prostate Cancer
title_full_unstemmed Impact of Geometric Uncertainties on Dose Calculations for Intensity Modulated Radiation Therapy of Prostate Cancer
title_sort impact of geometric uncertainties on dose calculations for intensity modulated radiation therapy of prostate cancer
publishDate 2008
url http://hdl.handle.net/10012/3570
work_keys_str_mv AT jiangrunqing impactofgeometricuncertaintiesondosecalculationsforintensitymodulatedradiationtherapyofprostatecancer
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