Skip header and navigation

2 records – page 1 of 1.

Biological consequences of MLC calibration errors in IMRT delivery and QA.

https://arctichealth.org/en/permalink/ahliterature125426
Source
Med Phys. 2012 Apr;39(4):1917-24
Publication Type
Article
Date
Apr-2012
Author
Vitali Moiseenko
Vincent Lapointe
Kerry James
Lingshu Yin
Mitchell Liu
Todd Pawlicki
Author Affiliation
British Columbia Cancer Agency, Vancouver Cancer Centre, Vancouver, British Columbia, Canada.
Source
Med Phys. 2012 Apr;39(4):1917-24
Date
Apr-2012
Language
English
Publication Type
Article
Keywords
Calibration
Canada
Humans
Neoplasms - radiotherapy
Quality Assurance, Health Care - standards
Radiometry - standards
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted - standards
Radiotherapy, Conformal - instrumentation - standards
Reproducibility of Results
Sensitivity and specificity
Abstract
The purpose of this work is threefold: (1) to explore biological consequences of the multileaf collimator (MLC) calibration errors in intensity modulated radiotherapy (IMRT) of prostate and head and neck cancers, (2) to determine levels of planning target volume (PTV) and normal tissue under- or overdose flagged with clinically used QA action limits, and (3) to provide biologically based input for MLC QA and IMRT QA action limits.
Ten consecutive prostate IMRT cases and ten consecutive head and neck IMRT cases were used. Systematic MLC offsets (i.e., calibration error) were introduced for each control point of the plan separately for X1 and X2 leaf banks. Offsets were from?-?2 to 2 mm with a 0.5 mm increment. The modified files were imported into the planning system for forward dose recalculation. The original plan served as the reference. The generalized equivalent uniform dose (gEUD) was used as the biological index for the targets, rectum, parotid glands, brainstem, and spinal cord. Each plan was recalculated on a CT scan of a 27 cm diameter cylindrical phantom with a contoured 0.6 cc ion chamber. Dose to ion chamber and 3D gamma analysis were compared to the reference plan. QA pass criteria: (1) at least 95% of voxels with a dose cutoff of 50% of maximum dose have to pass at 3 mm/3% and (2) dose to chamber within 2% of the reference dose.
For prostate cases, differences in PTV and rectum gEUD greater than 2% were identified. However, a larger proportion of plans leading to greater than 2% difference in prostate PTV gEUD passed the ion chamber QA but not 3D gamma QA. A similar trend was found for the rectum gEUD. For head and neck IMRT, the QA pass criteria flagged plans leading to greater than 4% differences in PTV gEUD and greater than 5% differences in the maximum dose to brainstem. If pass criteria were relaxed to 90% for gamma and 3% for ion chamber QA, plans leading to a 5% difference in PTV gEUD and a 5%-8% difference in brainstem maximum dose would likely pass IMRT QA. A larger proportion of head and neck plans with greater than 2% PTV gEUD difference passed 3D gamma QA compared to ion chamber QA.
For low modulation plans, there is a better chance to catch MLC calibration errors with 3D gamma QA rather than ion chamber QA. Conversely, for high modulation plans, there is a better chance to catch MLC calibration errors with ion chamber QA rather than with 3D gamma QA. Ion chamber and 3D gamma analysis IMRT QA can detect greater than 2% change in gEUD for PTVs and critical structures for low modulation treatment plans. For high modulation treatment plans, ion chamber and 3D gamma analysis can detect greater than 2% change in gEUD for PTVs and a 5% change in critical structure gEUD since either QA methods passes the QA criteria. For gEUD changes less than those listed above, either QA method has the same proportion of passing rate.
PubMed ID
22482613 View in PubMed
Less detail

IMRT quality assurance using a second treatment planning system.

https://arctichealth.org/en/permalink/ahliterature147102
Source
Med Dosim. 2010;35(4):274-9
Publication Type
Article
Date
2010
Author
Muhammad Naeem Anjum
William Parker
Russell Ruo
Ismail Aldahlawi
Muhammad Afzal
Author Affiliation
McGill University Health Center, Department of Medical Physics, Montreal General Hospital, Quebec, Canada.
Source
Med Dosim. 2010;35(4):274-9
Date
2010
Language
English
Publication Type
Article
Keywords
Equipment Failure Analysis
Humans
Neoplasms - radiotherapy
Quality Assurance, Health Care - methods - standards
Quebec
Radiometry - instrumentation - standards
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted - instrumentation - standards
Radiotherapy, Conformal - instrumentation - standards
Reproducibility of Results
Sensitivity and specificity
Abstract
We used a second treatment planning system (TPS) for independent verification of the dose calculated by our primary TPS in the context of patient-specific quality assurance (QA) for intensity-modulated radiation therapy (IMRT). QA plans for 24 patients treated with inverse planned dynamic IMRT were generated using the Nomos Corvus TPS. The plans were calculated on a computed tomography scan of our QA phantom that consists of three Solid Water slabs sandwiching radiochromic films, and an ion chamber that is inserted into the center slab of the phantom. For the independent verification, the dose was recalculated using the Varian Eclipse TPS using the multileaf collimator files and beam geometry from the original plan. The data was then compared in terms of absolute dose to the ion chamber volume as well as relative dose on isodoses calculated at the film plane. The calculation results were also compared with measurements performed for each case. When comparing ion chamber doses, the mean ratio was 0.999 (SD 0.010) for Eclipse vs. Corvus, 0.988 (SD 0.020) for the ionization chamber measurements vs. Corvus, and 0.989 (SD 0.017) for the ionization chamber measurements vs. Eclipse. For 2D doses with gamma histogram, the mean value of the percentage of pixels passing the criteria of 3%, 3 mm was 94.4 (SD 5.3) for Eclipse vs. Corvus, 85.1 (SD 10.6) for Corvus vs. film, and 93.7 (SD 4.1) for Eclipse vs. film; and for the criteria of 5%, 3 mm, 98.7 (SD 1.5) for Eclipse vs. Corvus, 93.0 (SD 7.8) for Corvus vs. film, and 98.0 (SD 1.9) for Eclipse vs. film. We feel that the use of the Eclipse TPS as an independent, accurate, robust, and time-efficient method for patient-specific IMRT QA is feasible in clinic.
PubMed ID
19944590 View in PubMed
Less detail