| 61. |
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| 62. |
- Johnsson, Stefan
(författare)
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Development and evaluation of an independent system for absorbed dose calculations in radiotherapy
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this work was to develop, implement and evaluate an independent system with which to calculate the absorbed dose, delivered by high-energy X-ray beams, to the prescription point and the depth of dose maximum. The introduction of such a system in the clinical routine may help ensure high-quality treatment and avoidance of errors which may jeopardise the clinical outcome of the treatment (i.e. under- or overdose). A set of equations for calculating the absorbed dose to the prescription point was compiled in a software application (“HandCalc”), which is completely independent of the treatment planning system (TPS). For instance, HandCalc includes models to calculate the absorbed dose from photons scattered in the patient, the transmission of the primary kerma in the patient, the variation of the primary kerma in air with collimator setting (i.e. head scatter), and corrections for heterogeneities in the patient. A new expression for the transmission of the primary kerma in the patient was derived in which the coefficients are strictly defined (and given a physical interpretation) by the first two moments of the spectral distribution of the incident beam. Further investigations also revealed that these moments can be used to determine water-to-air stopping power ratios more accurately than other beam quality indices. In practice, the moments are derived from “in-air equivalent”, narrow-beam measurements using a mini-phantom. The degree of in-air equivalence was investigated with Monte Carlo simulations, which showed that the optimum measurement depth in a mini-phantom is somewhat below the depth of dose maximum. Based upon comparisons with measurements and the TPS, a clinical action level of +/- 4% was chosen for HandCalc. Deviations greater than this are, with all probability, due to erroneous handling of the patient dataset during the preparation phase. An “entrance dose factor” was added in order to correct the dose calculations at the depth of dose maximum where electron equilibrium has not been established. The entrance dose factor was found to vary with beam quality and collimator setting, while no variation was detected with the presence of an acrylic tray (for block support) or with the source-surface distance (SSD). HandCalc was implemented in a hand-held PC which makes dose calculations inside the treatment room at the time of administration of the first fraction possible. An important feature of HandCalc is the built-in report function, which logs results from the calculation for later evaluation. In a study including 700 patients, deviations greater than the action level were found to be due either to limitations in HandCalc or to a systematic deviation between the planned and measured SSD. HandCalc has proven to be a fast and accurate tool for independent dose calculations inside the treatment room and it requires only a limited amount of extra time for the user to perform the calculations. Thus, it can easily be incorporated as part of the daily clinical quality control programme in order to prevent errors which may jeopardise the clinical outcome of the treatment.
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| 63. |
- Bauer, H C, et al.
(författare)
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The Scandinavian Sarcoma Group Register 1986-2001.
- 2004
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Ingår i: Acta orthopaedica Scandinavica. Supplementum. - : Medical Journals Sweden AB. - 0300-8827 .- 0001-6470. ; 75:Supplement 311, s. 8-10
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Tidskriftsartikel (refereegranskat)
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| 64. |
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| 65. |
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| 66. |
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| 67. |
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| 68. |
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| 69. |
- Jestin, P, et al.
(författare)
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Elective surgery for colorectal cancer in a defined Swedish population.
- 2004
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Ingår i: European Journal of Surgical Oncology. - : Elsevier BV. - 0748-7983 .- 1532-2157. ; 30:1, s. 26-33
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Tidskriftsartikel (refereegranskat)abstract
- AIMS: The aim of this study was to describe variability in compliance to clinical guidelines in colorectal cancer surgery related to hospital structure.METHODS: All patients registered in the databases of the Regional Oncologic Centre, operated upon electively for colon cancer between the start of the register in 1997 until 2000 (n=1771) and for rectal cancer between the start of the register in 1995 until 2000 (n=1841) were selected for analysis.RESULTS: There was no difference in 5-year survival rate between colon and rectal cancer (mean follow-up 2.6 and 3.0 years, respectively; p=0.22). There was a significant difference in frequency of preoperative liver scan depending on hospital category with an increase in colon cancer from 39 to 46% (p=0.02) and in rectal cancer from 42 to 64% (p<0.001). For colon cancer there was no difference, according to hospital category, in quotient sigmoid and high anterior resection to left-sided resection. Furthermore, high anterior resection was more common at university and general district hospitals (8%) compared with district hospitals (4%) (p=0.01). Sphincter-saving surgery was more common at university hospitals and district general hospitals than at district hospitals (low anterior/abdomino-perineal resection quotients 2.3, 2.4 and 1.6, respectively; p<0.001).CONCLUSIONS: Population-based audit forms an appropriate and valuable basis for quality assurance projects. In addition to describing compliance to guidelines and pointing to process steps that can be improved, such investigations may also indicate changes due to scientific development. Linked to case-costing data, such results may form an important basis for decisions about modifications in health care.
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| 70. |
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