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Evaluation of the NCI IMRT benchmark for clinical trials
S260
I. J. Radiation Oncology
● Biology ● Physics
Volume 57, Number 2, Supplement, 2003
Conclusions: Soluble rodent ScFv antibodies to radiation-inducible neoantigens, P-selectin and ␣2b integrin chain, were developed by phage antibody library technology. MALDI-TOF mass spectrometry was shown to be an effective modality for high-throughput screening of selective binding of P-selectin and ␣2b antibodies to irradiated mice tumors. Work was supported by grants R21-CA89888, R01-CA70937, R01-CA58508, P30-CA68485, R01-CA88076, R01CA89674, and Lung Cancer SPORE P50-CA90949.
1001
IMRT QA Analysis: What To Do With Unresolved Discrepancies?
R.A. Price, J. Li, J. Yang, S.W. McNeeley, L. Chen, E. Fourkal, M. Ding, W. Xiong, L. Qin, G. Mora, C.C. Ma Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, PA Purpose/Objective: To date, we have treated approximately 800 patients with IMRT at this institution using the Siemens Primus or Primart linear accelerators and the SMLC delivery technique. Prior to the initial patient treatment, each plan is evaluated and a series of QA tests are performed including absolute dose verification. This verification is a comparison between the dose calculated in phantom by the treatment planning system and the dose measured in phantom during irradiation. Our clinical acceptance criteria dictate that the values should agree to within ⫾ 3% for treatment to begin. Values exceeding this limit trigger additional analysis, measurement and double-checking prior to patient treatment. An example is given where the mean deviation value was ⫺6.5% with a maximum deviation measured of ⫺8.8%. The focus of this work is to analyze the accuracy of our dosimetry QA procedure and address discrepancies that are significantly greater than ⫾ 3%. Materials/Methods: All IMRT treatment plans are generated using the Corvus treatment planning system. Once a satisfactory plan is obtained a hybrid plan is generated. This plan utilizes the leaf sequences and associated MU designed for the patient plan and calculates dose on a virtual phantom. The physical phantom is then irradiated under the same conditions using the same leaf sequences. An absolute dose comparison is made by comparing dose in the physical phantom as measured using a 0.125cc PTW ionization chamber with dose predicted at the same point(s) in the virtual phantom by the treatment planning system. Agreement to within ⫾ 3% indicates that the plan is appropriately deliverable as far as absolute dose is concerned. Values exceeding this limit prompt additional investigation. This investigation includes reassessing the treatment plan and hybrid plan for errors in data extraction, investigation of input data into the R&V system for accuracy and completeness, and investigation of deliverability with respect to beam placement. The phantom irradiation is then repeated to eliminate errors due to improper setup. Discrepancies outside a ⫾ 4% window are verified using Monte Carlo simulations of both the dose in the virtual phantom and dose in the original patient CT data set. With agreement between the original Corvus calculated relative dose distributions and the distributions generated in film and Monte Carlo simulations, the MU can be scaled appropriately to bring the absolute dose into our acceptable range. When agreement is not present the individual patient plans are regenerated with changes in input parameters and/or beam directions. Results: Upon evaluation of our absolute dose data it was found that the agreement between measured dose and dose predicted by the planning system in phantom was within ⫾ 1% for 37.9% of the cases, ⫾ 2% for 68.6% and ⫾ 3% for 93.6% of the cases. The discrepancies were more than 3% and more than 4% in only 6.4% and less than 1% of all cases, respectively. Monte Carlo calculation of absolute dose compares to within 2% of dose in phantom or the patient CT data set in the non-gradient portion of the dose distribution associated with the target as tested for 20 prostate cases. Conclusions: There appear to be some intensity maps that are not deliverable to within our clinical acceptance criteria even though the planning system generated a leaf sequence and associated MU set. Verification of absolute dose as well as the relative dose distribution is essential especially in these cases. While MU scaling may result in acceptable delivery, verification of the resultant dose distribution is needed since the Siemens linacs allow for integer MU delivery only. Monte Carlo can serve as an independent dose verification tool in the QA process. Evaluation of different leaf sequencing options is made for these cases and comparisons made using both measurement and Monte Carlo simulations.
1002
Evaluation of the NCI IMRT Benchmark for Clinical Trials
M.J. Engler, M.J. Rivard Department of Radiation Oncology, Tufts-New England Medical Center, Boston, MA Purpose/Objective: The objective of this study was to evaluate the capabilities of the NCI IMRT benchmark (NCIB) to characterize different IMRT beams and planning techniques, and to propose benchmark anatomy that may improve on capabilities of the NCIB. Materials/Methods: The NCIB consists a hemi-cylindrical CTV half-surrounding a cylindrical critical normal tissue structure (NT) (1). For cranial applications, the shared longitudinal axis of both structures is oriented along the craniocaudal axis. The NCIB resembles a model used by Hunt et al (2) to characterize an IMRT system. Dosimetric goals of the NCIB were to deliver prescribed dose (PD) to 100% of CTV, keep NT dose ⬍ 60% of PD, and thereby create a dose gradient (⌬D) of 40% over the 3-mm gap between CTV and NT. Nine years of clinical experience with NOMOS IMRT systems was applied to obtain plans approaching the goals. Plans were generated with Corvus software using beam data from Varian linacs with 10 ⫻ 8 mm2 beamlets from a MIMiC collimator, 10 ⫻ 4 mm2 beamlets from a Beak-MIMiC collimator, and Millennium MLC beams. To improve plans, a cylindrical region of avoidance (ROA) was inserted around the NT. To control maximum dose location within the CTV, an ROA was placed around the surface of the CTV opposite the NT. Comparisons were made between plans using different IMRT beams, with and without ROAs, and with single and multiple couch angles. Metrics for comparison were ⌬D and CTV dose uniformity. Results of comparisons were applied to design benchmarks with variable gap (g) between CTV and
Proceedings of the 45th Annual ASTRO Meeting
NT, extent to which CTV surrounded NT (␣), structure shape (⍀), and structure orientation relative to anatomic axes (, ). Cones and deformed cylinders with curved axes were applied to more realistically represent clinical anatomy. Ability of the Corvus planning system to satisfy dosimetric criteria was tested by obtaining plans over ranges of {g, ␣, ⍀, , }. CTV dose uniformity and ⌬D were then determined as functions of a variable NT dose constraint. Results: Maximum ⌬D achievable for the NCIB was ⬃ 20%, half of the goal (Figure: isodose lines from 10 –90% in 10% increments). Plans with a single couch angle were superior to those with multiple couch angles because the structures had constant diameter and were aligned with the gantry axis. All three collimators produced similar plans, partly because structures were of constant diameter and aligned with the gantry rotational axis, and partly because similar objective functions were used. The ability to meet dosimetric goals was substantially enhanced by increasing g, decreasing ␣, and introducing ROAs. The ability to differentiate between IMRT collimators and single versus multiple couch angle plans was achieved with benchmark anatomies having structure shape and orientation different from those of the NCIB. Conclusions: The NCIB was limited in its ability to differentiate between plans obtained with different collimators, and unable to characterize possible advantages of using unconventional or multiple couch angles. To better characterize IMRT planning and delivery systems, it is proposed that benchmarks contain structures such as cones and deformed cylinders, and that these structures have variable orientation relative to anatomic axes. 1. IMRT QUESTIONNAIRE & BENCHMARK, Quality Assurance Review Center, Providence, RI. Available at: http:// www.qarc.org/benchmarks/IMRTbenchmark.pdf. 2. Hunt MA, Hsiung C-Y, Spirou SV, et al. Evaluation of concave dose distributions created using an inverse planning system. Int J Radiat Oncol Biol Phys 2002;54(3):953–962.
1003
Errors in Radiation Oncology: A Study in Pathways and Dosimetric Impact
E.E. Klein, R.E. Drzymala, J.A. Purdy Radiation Oncology, Washington University, St. Louis, MO Purpose/Objective: As the complexity for treating patients increases, so does the risk of error. This is partially due to the increased options for ancillary devices and introduction of new treatment procedures and techniques. This has not necessarily come simultaneously with an increase in automated independent checking capabilities. Some publications have suggested that record and verify systems (R&V) may contribute in propagating errors as these systems have been considered for efficiency rather than for assurance. And though the dosimetric consequences may be obvious in some cases, a detailed study does not exist. In this effort, we examined potential errors in terms of scenarios, pathways of occurrence, and dosimetry. Our goal is to prioritize error prevention according to likelihood of event and dosimetric impact Materials/Methods: For conventional photon beam treatment, we investigated errors of incorrect SSD, energy, omitted wedge (physical, dynamic, or universal) or compensating filter, incorrect wedge or compensating filter orientation,
S261
I. J. Radiation Oncology
● Biology ● Physics
Volume 57, Number 2, Supplement, 2003
Conclusions: Soluble rodent ScFv antibodies to radiation-inducible neoantigens, P-selectin and ␣2b integrin chain, were developed by phage antibody library technology. MALDI-TOF mass spectrometry was shown to be an effective modality for high-throughput screening of selective binding of P-selectin and ␣2b antibodies to irradiated mice tumors. Work was supported by grants R21-CA89888, R01-CA70937, R01-CA58508, P30-CA68485, R01-CA88076, R01CA89674, and Lung Cancer SPORE P50-CA90949.
1001
IMRT QA Analysis: What To Do With Unresolved Discrepancies?
R.A. Price, J. Li, J. Yang, S.W. McNeeley, L. Chen, E. Fourkal, M. Ding, W. Xiong, L. Qin, G. Mora, C.C. Ma Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, PA Purpose/Objective: To date, we have treated approximately 800 patients with IMRT at this institution using the Siemens Primus or Primart linear accelerators and the SMLC delivery technique. Prior to the initial patient treatment, each plan is evaluated and a series of QA tests are performed including absolute dose verification. This verification is a comparison between the dose calculated in phantom by the treatment planning system and the dose measured in phantom during irradiation. Our clinical acceptance criteria dictate that the values should agree to within ⫾ 3% for treatment to begin. Values exceeding this limit trigger additional analysis, measurement and double-checking prior to patient treatment. An example is given where the mean deviation value was ⫺6.5% with a maximum deviation measured of ⫺8.8%. The focus of this work is to analyze the accuracy of our dosimetry QA procedure and address discrepancies that are significantly greater than ⫾ 3%. Materials/Methods: All IMRT treatment plans are generated using the Corvus treatment planning system. Once a satisfactory plan is obtained a hybrid plan is generated. This plan utilizes the leaf sequences and associated MU designed for the patient plan and calculates dose on a virtual phantom. The physical phantom is then irradiated under the same conditions using the same leaf sequences. An absolute dose comparison is made by comparing dose in the physical phantom as measured using a 0.125cc PTW ionization chamber with dose predicted at the same point(s) in the virtual phantom by the treatment planning system. Agreement to within ⫾ 3% indicates that the plan is appropriately deliverable as far as absolute dose is concerned. Values exceeding this limit prompt additional investigation. This investigation includes reassessing the treatment plan and hybrid plan for errors in data extraction, investigation of input data into the R&V system for accuracy and completeness, and investigation of deliverability with respect to beam placement. The phantom irradiation is then repeated to eliminate errors due to improper setup. Discrepancies outside a ⫾ 4% window are verified using Monte Carlo simulations of both the dose in the virtual phantom and dose in the original patient CT data set. With agreement between the original Corvus calculated relative dose distributions and the distributions generated in film and Monte Carlo simulations, the MU can be scaled appropriately to bring the absolute dose into our acceptable range. When agreement is not present the individual patient plans are regenerated with changes in input parameters and/or beam directions. Results: Upon evaluation of our absolute dose data it was found that the agreement between measured dose and dose predicted by the planning system in phantom was within ⫾ 1% for 37.9% of the cases, ⫾ 2% for 68.6% and ⫾ 3% for 93.6% of the cases. The discrepancies were more than 3% and more than 4% in only 6.4% and less than 1% of all cases, respectively. Monte Carlo calculation of absolute dose compares to within 2% of dose in phantom or the patient CT data set in the non-gradient portion of the dose distribution associated with the target as tested for 20 prostate cases. Conclusions: There appear to be some intensity maps that are not deliverable to within our clinical acceptance criteria even though the planning system generated a leaf sequence and associated MU set. Verification of absolute dose as well as the relative dose distribution is essential especially in these cases. While MU scaling may result in acceptable delivery, verification of the resultant dose distribution is needed since the Siemens linacs allow for integer MU delivery only. Monte Carlo can serve as an independent dose verification tool in the QA process. Evaluation of different leaf sequencing options is made for these cases and comparisons made using both measurement and Monte Carlo simulations.
1002
Evaluation of the NCI IMRT Benchmark for Clinical Trials
M.J. Engler, M.J. Rivard Department of Radiation Oncology, Tufts-New England Medical Center, Boston, MA Purpose/Objective: The objective of this study was to evaluate the capabilities of the NCI IMRT benchmark (NCIB) to characterize different IMRT beams and planning techniques, and to propose benchmark anatomy that may improve on capabilities of the NCIB. Materials/Methods: The NCIB consists a hemi-cylindrical CTV half-surrounding a cylindrical critical normal tissue structure (NT) (1). For cranial applications, the shared longitudinal axis of both structures is oriented along the craniocaudal axis. The NCIB resembles a model used by Hunt et al (2) to characterize an IMRT system. Dosimetric goals of the NCIB were to deliver prescribed dose (PD) to 100% of CTV, keep NT dose ⬍ 60% of PD, and thereby create a dose gradient (⌬D) of 40% over the 3-mm gap between CTV and NT. Nine years of clinical experience with NOMOS IMRT systems was applied to obtain plans approaching the goals. Plans were generated with Corvus software using beam data from Varian linacs with 10 ⫻ 8 mm2 beamlets from a MIMiC collimator, 10 ⫻ 4 mm2 beamlets from a Beak-MIMiC collimator, and Millennium MLC beams. To improve plans, a cylindrical region of avoidance (ROA) was inserted around the NT. To control maximum dose location within the CTV, an ROA was placed around the surface of the CTV opposite the NT. Comparisons were made between plans using different IMRT beams, with and without ROAs, and with single and multiple couch angles. Metrics for comparison were ⌬D and CTV dose uniformity. Results of comparisons were applied to design benchmarks with variable gap (g) between CTV and
Proceedings of the 45th Annual ASTRO Meeting
NT, extent to which CTV surrounded NT (␣), structure shape (⍀), and structure orientation relative to anatomic axes (, ). Cones and deformed cylinders with curved axes were applied to more realistically represent clinical anatomy. Ability of the Corvus planning system to satisfy dosimetric criteria was tested by obtaining plans over ranges of {g, ␣, ⍀, , }. CTV dose uniformity and ⌬D were then determined as functions of a variable NT dose constraint. Results: Maximum ⌬D achievable for the NCIB was ⬃ 20%, half of the goal (Figure: isodose lines from 10 –90% in 10% increments). Plans with a single couch angle were superior to those with multiple couch angles because the structures had constant diameter and were aligned with the gantry axis. All three collimators produced similar plans, partly because structures were of constant diameter and aligned with the gantry rotational axis, and partly because similar objective functions were used. The ability to meet dosimetric goals was substantially enhanced by increasing g, decreasing ␣, and introducing ROAs. The ability to differentiate between IMRT collimators and single versus multiple couch angle plans was achieved with benchmark anatomies having structure shape and orientation different from those of the NCIB. Conclusions: The NCIB was limited in its ability to differentiate between plans obtained with different collimators, and unable to characterize possible advantages of using unconventional or multiple couch angles. To better characterize IMRT planning and delivery systems, it is proposed that benchmarks contain structures such as cones and deformed cylinders, and that these structures have variable orientation relative to anatomic axes. 1. IMRT QUESTIONNAIRE & BENCHMARK, Quality Assurance Review Center, Providence, RI. Available at: http:// www.qarc.org/benchmarks/IMRTbenchmark.pdf. 2. Hunt MA, Hsiung C-Y, Spirou SV, et al. Evaluation of concave dose distributions created using an inverse planning system. Int J Radiat Oncol Biol Phys 2002;54(3):953–962.
1003
Errors in Radiation Oncology: A Study in Pathways and Dosimetric Impact
E.E. Klein, R.E. Drzymala, J.A. Purdy Radiation Oncology, Washington University, St. Louis, MO Purpose/Objective: As the complexity for treating patients increases, so does the risk of error. This is partially due to the increased options for ancillary devices and introduction of new treatment procedures and techniques. This has not necessarily come simultaneously with an increase in automated independent checking capabilities. Some publications have suggested that record and verify systems (R&V) may contribute in propagating errors as these systems have been considered for efficiency rather than for assurance. And though the dosimetric consequences may be obvious in some cases, a detailed study does not exist. In this effort, we examined potential errors in terms of scenarios, pathways of occurrence, and dosimetry. Our goal is to prioritize error prevention according to likelihood of event and dosimetric impact Materials/Methods: For conventional photon beam treatment, we investigated errors of incorrect SSD, energy, omitted wedge (physical, dynamic, or universal) or compensating filter, incorrect wedge or compensating filter orientation,
S261