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Title: Accuracy of two heterogeneity dose calculation algorithms for IMRT in treatment plans designed using an anthropomorphic thorax phantom

Abstract

With the advent of intensity-modulated radiation therapy (IMRT), the inclusion of heterogeneity corrections is further complicated by the conformal delivery of many small beams forming steep dose gradients. Radiation treatment planning has evolved to take into account even small changes in tissue density so that the dose to tumor can be further optimized. However, different treatment planning systems incorporate different heterogeneity correction algorithms, and it is unclear whether any of these algorithms are superior to others in terms of accurately predicting delivered radiation doses relative to measurement in a clinical setting. The purpose of this study was to determine the accuracy of heterogeneity dose calculations from two widely used IMRT treatment planning systems (Pinnacle and Corvus) against measurement. These two systems handle heterogeneity dose corrections by means of a collapsed-cone convolution superposition algorithm and a finite-size pencil-beam algorithm with one-dimensional depth scaling correction, respectively. Treatment plans were generated by each system using an anthropomorphic thorax phantom, routine clinical lung tumor constraints, and a common prescribed dose. Dose measurements made by thermoluminescent detectors (TLDs) and radiochromic film positioned within the phantom's lung and offset tumor insert were then compared with the calculated values. The collapsed cone convolution superposition dose calculation algorithmmore » provided clinically acceptable results ({+-}5% of the normalization dose or 3 mm distance to agreement) in the designed treatment plan and delivery. The pencil-beam algorithm with an effective pathlength correction showed reasonable agreement within the gross tumor volume, overestimated dose within a majority of the planning target volume, and underestimated the extent of the penumbral broadening, yielding only about 60% accuracy when judged by the above criterion. Even judged by a more generous criterion ({+-}7%/7 mm), the results were clinically unfavorable (at only about 80% accuracy). To ascertain the dose in heterogeneous regions such as the tumor-lung interface and the peripheral lung dose near the tumor, the superposition convolution algorithm that accounts for lateral scatter and electron transport should be used. The use of the pencil-beam algorithm with only an effective pathlength correction may result in the dose to the target being overestimated. As a result, a full understanding of any treatment planning system's heterogeneity algorithm is required prior to clinical implementation.« less

Authors:
; ; ; ; ;  [1]
  1. Department of Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 (United States)
Publication Date:
OSTI Identifier:
20951315
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 5; Other Information: DOI: 10.1118/1.2727789; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ACCURACY; ALGORITHMS; CARCINOMAS; CHEST; CORRECTIONS; DOSIMETRY; LUNGS; PHANTOMS; PLANNING; RADIATION DOSES; RADIOTHERAPY; THERMOLUMINESCENT DOSEMETERS

Citation Formats

Davidson, Scott E., Ibbott, Geoffrey S., Prado, Karl L., Dong Lei, Liao Zhongxing, and Followill, David S. Accuracy of two heterogeneity dose calculation algorithms for IMRT in treatment plans designed using an anthropomorphic thorax phantom. United States: N. p., 2007. Web. doi:10.1118/1.2727789.
Davidson, Scott E., Ibbott, Geoffrey S., Prado, Karl L., Dong Lei, Liao Zhongxing, & Followill, David S. Accuracy of two heterogeneity dose calculation algorithms for IMRT in treatment plans designed using an anthropomorphic thorax phantom. United States. doi:10.1118/1.2727789.
Davidson, Scott E., Ibbott, Geoffrey S., Prado, Karl L., Dong Lei, Liao Zhongxing, and Followill, David S. Tue . "Accuracy of two heterogeneity dose calculation algorithms for IMRT in treatment plans designed using an anthropomorphic thorax phantom". United States. doi:10.1118/1.2727789.
@article{osti_20951315,
title = {Accuracy of two heterogeneity dose calculation algorithms for IMRT in treatment plans designed using an anthropomorphic thorax phantom},
author = {Davidson, Scott E. and Ibbott, Geoffrey S. and Prado, Karl L. and Dong Lei and Liao Zhongxing and Followill, David S.},
abstractNote = {With the advent of intensity-modulated radiation therapy (IMRT), the inclusion of heterogeneity corrections is further complicated by the conformal delivery of many small beams forming steep dose gradients. Radiation treatment planning has evolved to take into account even small changes in tissue density so that the dose to tumor can be further optimized. However, different treatment planning systems incorporate different heterogeneity correction algorithms, and it is unclear whether any of these algorithms are superior to others in terms of accurately predicting delivered radiation doses relative to measurement in a clinical setting. The purpose of this study was to determine the accuracy of heterogeneity dose calculations from two widely used IMRT treatment planning systems (Pinnacle and Corvus) against measurement. These two systems handle heterogeneity dose corrections by means of a collapsed-cone convolution superposition algorithm and a finite-size pencil-beam algorithm with one-dimensional depth scaling correction, respectively. Treatment plans were generated by each system using an anthropomorphic thorax phantom, routine clinical lung tumor constraints, and a common prescribed dose. Dose measurements made by thermoluminescent detectors (TLDs) and radiochromic film positioned within the phantom's lung and offset tumor insert were then compared with the calculated values. The collapsed cone convolution superposition dose calculation algorithm provided clinically acceptable results ({+-}5% of the normalization dose or 3 mm distance to agreement) in the designed treatment plan and delivery. The pencil-beam algorithm with an effective pathlength correction showed reasonable agreement within the gross tumor volume, overestimated dose within a majority of the planning target volume, and underestimated the extent of the penumbral broadening, yielding only about 60% accuracy when judged by the above criterion. Even judged by a more generous criterion ({+-}7%/7 mm), the results were clinically unfavorable (at only about 80% accuracy). To ascertain the dose in heterogeneous regions such as the tumor-lung interface and the peripheral lung dose near the tumor, the superposition convolution algorithm that accounts for lateral scatter and electron transport should be used. The use of the pencil-beam algorithm with only an effective pathlength correction may result in the dose to the target being overestimated. As a result, a full understanding of any treatment planning system's heterogeneity algorithm is required prior to clinical implementation.},
doi = {10.1118/1.2727789},
journal = {Medical Physics},
number = 5,
volume = 34,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Purpose: To determine the impact of treatment planning algorithm on the accuracy of heterogeneous dose calculations in the Radiological Physics Center (RPC) thorax phantom. Methods and Materials: We retrospectively analyzed the results of 304 irradiations of the RPC thorax phantom at 221 different institutions as part of credentialing for Radiation Therapy Oncology Group clinical trials; the irradiations were all done using 6-MV beams. Treatment plans included those for intensity-modulated radiation therapy (IMRT) as well as 3-dimensional conformal therapy (3D-CRT). Heterogeneous plans were developed using Monte Carlo (MC), convolution/superposition (CS), and the anisotropic analytic algorithm (AAA), as well as pencil beammore » (PB) algorithms. For each plan and delivery, the absolute dose measured in the center of a lung target was compared to the calculated dose, as was the planar dose in 3 orthogonal planes. The difference between measured and calculated dose was examined as a function of planning algorithm as well as use of IMRT. Results: PB algorithms overestimated the dose delivered to the center of the target by 4.9% on average. Surprisingly, CS algorithms and AAA also showed a systematic overestimation of the dose to the center of the target, by 3.7% on average. In contrast, the MC algorithm dose calculations agreed with measurement within 0.6% on average. There was no difference observed between IMRT and 3D CRT calculation accuracy. Conclusion: Unexpectedly, advanced treatment planning systems (those using CS and AAA algorithms) overestimated the dose that was delivered to the lung target. This issue requires attention in terms of heterogeneity calculations and potentially in terms of clinical practice.« less
  • Purpose: To experimentally validate a rotational kV x-ray source characterization technique by computing CT dose in an anthropomorphic thorax phantom using an in-house dose computation algorithm (kVDoseCalc). Methods: The lateral variation in incident energy spectra of a GE Optima big bore CT scanner was found by measuring the HVL along the internal, full bow-tie filter axis. The HVL and kVp were used to generate the x-ray spectra using Spektr software, while beam fluence was derived by dividing the integral product of the spectra and in-air mass-energy absorption coefficients by in-air dose measurements along the bow-tie filter axis. Beams produced bymore » the GE Optima scanner were modeled at 80 and 140 kVp tube settings. kVDoseCalc calculates dose by solving the linear Boltzmann transport equation using a combination of deterministic and stochastic methods. Relative doses in an anthropomorphic thorax phantom (E2E SBRT Phantom) irradiated by the GE Optima scanner were measured using a (0.015 cc) PTW Freiburg ionization chamber, and compared to computations from kVDoseCalc. Results: The agreement in relative dose between dose computation and measurement for points of interest (POIs) within the primary path of the beam was within experimental uncertainty for both energies, however points outside the primary beam were not. The average absolute percent difference for POIs within the primary path of the beam was 1.37% and 5.16% for 80 and 140 kVp, respectively. The minimum and maximum absolute percent difference for both energies and all POIs within the primary path of the beam was 0.151% and 6.41%, respectively. Conclusion: The CT x-ray source characterization technique based on HVL measurements and kVp can be used to accurately compute CT dose in an anthropomorphic thorax phantom.« less
  • Purpose: In this study, dosimetric comparison of field in field (FIF) and intensity modulated radiation therapy (IMRT) techniques used for treatment of whole breast radiotherapy (WBRT) were made. The dosimetric accuracy of treatment planning system (TPS) for Anisotropic Analytical Algorithm (AAA) and Acuros XB (AXB) algorithms in predicting PTV and OAR doses was also investigated. Methods: Two different treatment planning techniques of left-sided breast cancer were generated for rando phantom. FIF and IMRT plans were compared for doses in PTV and OAR volumes including ipsilateral lung, heart, left ascending coronary artery, contralateral lung and the contralateral breast. PTV and OARsmore » doses and homogeneity and conformality indexes were compared between two techniques. The accuracy of TPS dose calculation algorithms was tested by comparing PTV and OAR doses measured by thermoluminescent dosimetry with the dose calculated by the TPS using AAA and AXB for both techniques. Results: IMRT plans had better conformality and homogeneity indexes than FIF technique and it spared OARs better than FIF. While both algorithms overestimated PTV doses they underestimated all OAR doses. For IMRT plan, PTV doses, overestimation up to 2.5 % was seen with AAA algorithm but it decreased to 1.8 % when AXB algorithm was used. Based on the results of the anthropomorphic measurements for OAR doses, underestimation greater than 7 % is possible by the AAA. The results from the AXB are much better than the AAA algorithm. However, underestimations of 4.8 % were found in some of the points even for AXB. For FIF plan, similar trend was seen for PTV and OARs doses in both algorithm. Conclusion: When using the Eclipse TPS for breast cancer, AXB the should be used instead of the AAA algorithm, bearing in mind that the AXB may still underestimate all OAR doses.« less
  • Purpose To characterize the Cyberknife (CK) robotic system’s dosimetric accuracy of the delivery of MultiPlan’s Monte Carlo dose calculations using EBT3 radiochromic film inserted in a thorax phantom. Methods The CIRS XSight Lung Tracking (XLT) Phantom (model 10823) was used in this study with custom cut EBT3 film inserted in the horizontal (coronal) plane inside the lung tissue equivalent phantom. CK MultiPlan v3.5.3 with Monte Carlo dose calculation algorithm (1.5 mm grid size, 2% statistical uncertainty) was used to calculate a clinical plan for a 25-mm lung tumor lesion, as contoured by the physician, and then imported onto the XLTmore » phantom CT. Using the same film batch, the net OD to dose calibration curve was obtained using CK with the 60 mm fixed cone by delivering 0– 800 cGy. The test films (n=3) were irradiated using 325 cGy to the prescription point. Films were scanned 48 hours after irradiation using an Epson v700 scanner (48 bits color scan, extracted red channel only, 96 dpi). Percent absolute dose and relative isodose distribution difference relative to the planned dose were quantified using an in-house QA software program. Multiplan Monte Carlo dose calculation was validated using RCF dosimetry (EBT3) and gamma index criteria of 3%/3mm and 2%/2mm for absolute dose and relative isodose distribution measurement comparisons. Results EBT3 film measurements of the patient plans calculated with Monte Carlo in MultiPlan resulted in an absolute dose passing rate of 99.6±0.4% for the Gamma Index of 3%/3mm, 10% dose threshold, and 95.6±4.4% for 2%/2mm, 10% threshold criteria. The measured central axis absolute dose was within 1.2% (329.0±2.5 cGy) of the Monte Carlo planned dose (325.0±6.5 cGy) for that same point. Conclusion MultiPlan’s Monte Carlo dose calculation was validated using the EBT3 film absolute dosimetry for delivery in a heterogeneous thorax phantom.« less
  • Purpose: In this study, the comparison of dosimetric accuracy of Acuros XB and AAA algorithms were investigated for small radiation fields incident on homogeneous and heterogeneous geometries Methods: Small open fields of Truebeam 2.0 unit (1×1, 2×2, 3×3, 4×4 fields) were used for this study. The fields were incident on homogeneous phantom and in house phantom containing lung, air, and bone inhomogeneities. Using the same film batch, the net OD to dose calibration curve was obtaine dusing Trubeam 2.0 for 6 MV, 6 FFF, 10 MV, 10 FFF, 15 MV energies by delivering 0- 800 cGy. Films were scanned 48more » hours after irradiation using an Epson 1000XL flatbed scanner. The dosimetric accuracy of Acuros XB and AAA algorithms in the presence of the inhomogeneities was compared against EBT3 film dosimetry Results: Open field tests in a homogeneous phantom showed good agreement betweent wo algorithms and measurement. For Acuros XB, minimum gamma analysis passin grates between measured and calculated dose distributions were 99.3% and 98.1% for homogeneousand inhomogeneous fields in thecase of lung and bone respectively. For AAA, minimum gamma analysis passingrates were 99.1% and 96.5% for homogeneous and inhomogeneous fields respectively for all used energies and field sizes.In the case of the air heterogeneity, the differences were larger for both calculations algorithms. Over all, when compared to measurement, theAcuros XB had beter agreement than AAA. Conclusion: The Acuros XB calculation algorithm in the TPS is an improvemen tover theexisting AAA algorithm. Dose discrepancies were observed for in the presence of air inhomogeneities.« less