Comparisons of treatment optimization directly incorporating random patient setup uncertainty with a margin-based approach
- 11 August 2009
- journal article
- research article
- Published by Wiley in Medical Physics
- Vol. 36 (9Part1), 3880-3890
- https://doi.org/10.1118/1.3176940
Abstract
The purpose of this study is to incorporate the dosimetric effect of random patient positioning uncertainties directly into a commercial treatment planning system's IMRT plan optimization algorithm through probabilistic treatment planning (PTP) and compare coverage of this method with margin-based planning. In this work, PTP eliminates explicit margins and optimizes directly on the estimated integral treatment dose to determine optimal patient dose in the presence of setup uncertainties. Twenty-eight prostate patient plans adhering to the RTOG-0126 criteria are optimized using both margin-based and PTP methods. Only random errors are considered. For margin-based plans, the planning target volume is created by expanding the clinical target volume (CTV) by 2.1 mm to accommodate the simulated 3 mm random setup uncertainty. Random setup uncertainties are incorporated into IMRT dose evaluation by convolving each beam's incident fluence with a sigma = 3 mm Gaussian prior to dose calculation. PTP optimization uses the convolved fluence to estimate dose to ensure CTV coverage during plan optimization. PTP-based plans are compared to margin-based plans with equal CTV coverage in the presence of setup errors based on dose-volume metrics. The sensitivity of the optimized plans to patient-specific setup uncertainty variations is assessed by evaluating dose metrics for dose distributions corresponding to halving and doubling of the random setup uncertainty used in the optimization. Margin-based and PTP-based plans show similar target coverage. A physician review shows that PTP is preferred for 21 patients, margin-based plans are preferred in 2 patients, no preference is expressed for 1 patient, and both autogenerated plans are rejected for 4 patients. For the PTP-based plans, the average CTV receiving the prescription dose decreases by 0.5%, while the mean dose to the CTV increases by 0.7%. The CTV tumor control probability (TCP) is the same for both methods with the exception of one case in which PTP gave a slightly higher TCP. For critical structures that do not meet the optimization criteria, PTP shows a decrease in the volume receiving the maximum specified dose. PTP reduces local normal tissue volumes receiving the maximum dose on average by 48%. PTP results in lower mean dose to all critical structures for all plans. PTP results in a 2.5% increase in the probability of uncomplicated control (P+), along with a 1.9% reduction in rectum normal tissue complication probability (NTCP), and a 0.7% reduction in bladder NTCP. PTP-based plans show improved conformality as compared with margin-based plans with an average PTP-based dosimetric margin at 7100 cGy of 0.65 cm compared with the margin-based 0.90 cm and a PTP-based dosimetric margin at 3960 cGy of 1.60 cm compared with the margin-based 1.90 cm. PTP-based plans show similar sensitivity to variations of the uncertainty during treatment from the uncertainty used in planning as compared to margin-based plans. For equal target coverage, when compared to margin-based plans, PTP results in equal or lower doses to normal structures. PTP results in more conformal plans than margin-based plans and shows similar sensitivity to variations in uncertainty.Keywords
Funding Information
- National Institutes of Health (P01CA116602, T32CA113277)
This publication has 40 references indexed in Scilit:
- Evaluation of dosimetric margins in prostate IMRT treatment plansMedical Physics, 2008
- IMRT optimization including random and systematic geometric errors based on the expectation of TCP and NTCPMedical Physics, 2007
- An Adaptive Off-Line Procedure for Radiotherapy of Prostate CancerInternational Journal of Radiation Oncology*Biology*Physics, 2007
- A robust approach to IMRT optimizationPhysics in Medicine & Biology, 2006
- Simulation and visualization of dose uncertainties due to interfractional organ motionPhysics in Medicine & Biology, 2006
- Robust optimization for intensity modulated radiation therapy treatment planning under uncertaintyPhysics in Medicine & Biology, 2005
- Errors and margins in radiotherapySeminars in Radiation Oncology, 2004
- High-precision prostate cancer irradiation by clinical application of an offline patient setup verification procedure, using portal imagingInternational Journal of Radiation Oncology*Biology*Physics, 1996
- Optimal radiation beam profiles considering the stochastic process of patient positioning in fractionated radiation therapyInverse Problems, 1995
- Volume and Heterogeneity Dependence of the Dose-Response Relationship for Head And Neck TumoursActa Oncologica, 1995