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- Das, Indra J., et al.
(författare)
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Accelerator beam data commissioning equipment and procedures : report of the TG-106 of the Therapy Physics Committee of the AAPM
- 2008
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 35:9, s. 4186-4215
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Forskningsöversikt (refereegranskat)abstract
- For commissioning a linear accelerator for clinical use, medical physicists are faced with many challenges including the need for precision, a variety of testing methods, data validation, the lack of standards, and time constraints. Since commissioning beam data are treated as a reference and ultimately used by treatment planning systems, it is vitally important that the collected data are of the highest quality to avoid dosimetric and patient treatment errors that may subsequently lead to a poor radiation outcome. Beam data commissioning should be performed with appropriate knowledge and proper tools and should be independent of the person collecting the data. To achieve this goal, Task Group 106 (TG-106) of the Therapy Physics Committee of the American Association of Physicists in Medicine was formed to review the practical aspects as well as the physics of linear accelerator commissioning. The report provides guidelines and recommendations on the proper selection of phantoms and detectors, setting up of a phantom for data acquisition (both scanning and no-scanning data), procedures for acquiring specific photon and electron beam parameters and methods to reduce measurement errors (<1%), beam data processing and detector size convolution for accurate profiles. The TG-106 also provides a brief.discussion on the emerging trend in Monte Carlo simulation techniques in photon and electron beam commissioning. The procedures described in this report should assist a qualified medical physicist in either measuring a complete set of beam data, or in verifying a subset of data before initial use or for periodic quality assurance measurements. By combining practical experience with theoretical discussion, this document sets a new standard for beam data commissioning.
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- Cheng, Chee-Wai, et al.
(författare)
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Dosimetric comparison of treatment planning systems in irradiation of breast with tangential fields
- 1997
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Ingår i: International Journal of Radiation Oncology, Biology, Physics. - 0360-3016. ; 38:4, s. 835-842
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The objectives of this study are: (1) to investigate the dosimetric differences of the different treatment planning systems (TPS) in breast irradiation with tangential fields, and (2) to study the effect of beam characteristics on dose distributions in tangential breast irradiation with 6 MV linear accelerators from different manufacturers. METHODS AND MATERIALS: Nine commercial and two university-based TPS are evaluated in this study. The computed tomographic scan of three representative patients, labeled as "small", "medium" and "large" based on their respective chest wall separations in the central axis plane (CAX) were used. For each patient, the tangential fields were set up in each TPS. The CAX distribution was optimized separately with lung correction, for each TPS based on the same set of optimization conditions. The isodose distributions in two other off-axis planes, one 6 cm cephalic and the other 6 cm caudal to the CAX plane were also computed. To investigate the effect of beam characteristics on dose distributions, a three-dimensional TPS was used to calculate the isodose distributions for three different linear accelerators, the Varian Clinac 6/100, the Siemens MD2 and the Philips SL/7 for the three patients. In addition, dose distributions obtained with 6 MV X-rays from two different accelerators, the Varian Clinac 6/100 and the Varian 2100C, were compared. RESULTS: For all TPS, the dose distributions in all three planes agreed qualitatively to within +/- 5% for the "small" and the "medium" patients. For the "large" patient, all TPS agreed to within +/- 4% on the CAX plane. The isodose distributions in the caudal plane differed by +/- 5% among all TPS. In the cephalic plane in which the patient separation is much larger than that in the CAX plane, six TPS correctly calculated the dose distribution showing a cold spot in the center of the breast contour. The other five TPS showed that the center of the breast received adequate dose. Isodose distributions for 6 MV X-rays from three different accelerators differed by about +/- 3% for the "small" patient and more than +/- 5% for the "large" patient. For two different 6 MV machines of the same manufacturer, the isodose distribution agreed to within +/- 2% for all three planes for the "large" patient. CONCLUSION: The differences observed among the various TPS in this study were within +/- 5% for both the "small" and the "medium" patients while doses at the hot spot exhibit a larger variation. The large discrepancy observed in the off-axis plane for the "large" patient is largely due to the inability of most TPS to incorporate the collimator angles in the dose calculation. Only six systems involved agreed to within +/- 5% for all three patients in all calculation planes. The difference in dose distributions obtained with three accelerators from different manufacturers is probably due to the difference in beam profiles. On the other hand, the 6 MV X-rays from two different models of linear accelerators from the same manufacturer have similar beam characteristics and the dose distributions are within +/- 2% of each other throughout the breast volume. In general, multi-institutional breast treatment data can be compared within a +/- 5% accuracy.
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- Das, Indra J., et al.
(författare)
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Report of AAPM Task Group 155 : Megavoltage photon beam dosimetry in small fields and non-equilibrium conditions
- 2021
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Ingår i: Medical physics (Lancaster). - : John Wiley & Sons. - 0094-2405 .- 2473-4209. ; 48:10, s. E886-E921
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Tidskriftsartikel (refereegranskat)abstract
- Small-field dosimetry used in advance treatment technologies poses challenges due to loss of lateral charged particle equilibrium (LCPE), occlusion of the primary photon source, and the limited choice of suitable radiation detectors. These challenges greatly influence dosimetric accuracy. Many high-profile radiation incidents have demonstrated a poor understanding of appropriate methodology for small-field dosimetry. These incidents are a cause for concern because the use of small fields in various specialized radiation treatment techniques continues to grow rapidly. Reference and relative dosimetry in small and composite fields are the subject of the International Atomic Energy Agency (IAEA) dosimetry code of practice that has been published as TRS-483 and an AAPM summary publication (IAEA TRS 483; Dosimetry of small static fields used in external beam radiotherapy: An IAEA/AAPM International Code of Practice for reference and relative dose determination, Technical Report Series No. 483; Pal-mans et al., Med Phys 45(11):e1123, 2018). The charge of AAPM task group 155 (TG-155) is to summarize current knowledge on small-field dosimetry and to provide recommendations of best practices for relative dose determination in small megavoltage photon beams. An overview of the issue of LCPE and the changes in photon beam perturbations with decreasing field size is provided. Recommendations are included on appropriate detector systems and measurement methodologies. Existing published data on dosimetric parameters in small photon fields (e.g., percentage depth dose, tissue phantom ratio/tissue maximum ratio, off-axis ratios, and field output factors) together with the necessary perturbation corrections for various detectors are reviewed. A discussion on errors and an uncertainty analysis in measurements is provided. The design of beam models in treatment planning systems to simulate small fields necessitates special attention on the influence of the primary beam source and collimating devices in the computation of energy fluence and dose. The general requirements for fluence and dose calculation engines suitable for modeling dose in small fields are reviewed. Implementations in commercial treatment planning systems vary widely, and the aims of this report are to provide insight for the medical physicist and guidance to developers of beams models for radiotherapy treatment planning systems.
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- Das, Indra J., et al.
(författare)
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Small fields : nonequilibrium radiation dosimetry
- 2008
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 35:1, s. 206-215
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Forskningsöversikt (refereegranskat)abstract
- Advances in radiation treatment with beamlet-based intensity modulation, image-guided radiation therapy, and stereotactic radiosurgery (including specialized equipments like CyberKnife, Gamma Knife, tomotherapy, and high-resolution multileaf collimating systems) have resulted in the use of reduced treatment fields to a subcentimeter scale. Compared to the traditional radiotherapy with fields > or =4 x 4 cm2, this can result in significant uncertainty in the accuracy of clinical dosimetry. The dosimetry of small fields is challenging due to nonequilibrium conditions created as a consequence of the secondary electron track lengths and the source size projected through the collimating system that are comparable to the treatment field size. It is further complicated by the prolonged electron tracks in the presence of low-density inhomogeneities. Also, radiation detectors introduced into such fields usually perturb the level of disequilibrium. Hence, the dosimetric accuracy previously achieved for standard radiotherapy applications is at risk for both absolute and relative dose determination. This article summarizes the present knowledge and gives an insight into the future procedures to handle the nonequilibrium radiation dosimetry problems. It is anticipated that new miniature detectors with controlled perturbations and corrections will be available to meet the demand for accurate measurements. It is also expected that the Monte Carlo techniques will increasingly be used in assessing the accuracy, verification, and calculation of dose, and will aid perturbation calculations of detectors used in small and highly conformal radiation beams.
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