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Evaluation of automatic treatment planning using iterative method, for permanent seed implantation of the prostate

Seiron, Kristian (2006)
Medical Physics Programme
Abstract (Swedish)
Purpose: The aim of this study was to investigate if the inverse planning available in the dedicated planning program VariSeed 7.1, can generate plans of equal quality to plans generated through manual planning.Materials and Methods: In this study the dedicated permanent seed implantation planning system VariSeed 7.1. (Varian, Paolo Alto California) was used for inverse planning, using a dose-volumehistogram based optimization algorithm. Seven patients with different prostate sizes and shapes were randomly selected amongst those patients that had already gone through the implantation. For each of these patients six sets of dose volumetric requirements with different weight factors and placement restrictions were investigated. The tests... (More)
Purpose: The aim of this study was to investigate if the inverse planning available in the dedicated planning program VariSeed 7.1, can generate plans of equal quality to plans generated through manual planning.Materials and Methods: In this study the dedicated permanent seed implantation planning system VariSeed 7.1. (Varian, Paolo Alto California) was used for inverse planning, using a dose-volumehistogram based optimization algorithm. Seven patients with different prostate sizes and shapes were randomly selected amongst those patients that had already gone through the implantation. For each of these patients six sets of dose volumetric requirements with different weight factors and placement restrictions were investigated. The tests were organized so to shift priority from good prostate dose coverage at the first tests to sparing the organs at risk. Decreasing the dose to the organs at risk was achieved by increasing the weight factors to the organs at risk or prohibiting seed placement close to them. The dose-volumetric criteria for a good dose plan are as follows: Prostate V100 > 96%, Prostate V150 < 65%, Urethra D30 < 150% and finally V69 < 3 cm3 for the rectum. The algorithm was confined to use Rigid Absorbable Permanent Implant Device (RAPID) strands with no loose seeds; the algorithm was also restricted from placing seeds in the middle of the prostate. The calculation time and number of needles allowed was set high so that these conditions did not affect the planning results negatively, they where set to 200 seconds and 40 needles respectively. Results: The results from the tests show that the algorithm generates acceptable dose coverage for large prostates when priority is put mainly upon achieving acceptable dose coverage of the target and little priority is put on the organs at risk. The target dose coverage decreases with decreasing prostate size. Acceptable dose coverage of the target was achieved for all prostate sizes when an extra 3 mm placement area around the prostate was added. The rectum and the urethra both received acceptable doses throughout all the tests. However, the dose received by the urethra was lower when using the manual planning method. The seed geometry produced by the optimization algorithm was very randomized and clustered. The clustering of the seeds generated few large high dose volumes, compared to several small high dose volumes generated with the manual planning. The treatment margins around the target were also too thin for the automatic planes.Conclusion: From a dose-volumetric point of view the inverse planning method can generate plans with acceptable dose coverage for both the target and the organs at risk. However in the presented study, the urethra received a lower dose using the plans generated manually with the peripheral loading method, than with the automatic optimized plans. Shifting dose coverage priority to minimize the urethra dose means compromising target dose coverage. The seed geometry put forward by the algorithm is randomized and clustered compared to the manual peripheral loading. Thus the algorithm generates large high dose volumes compared to the manual peripheral loading were several smaller high dose volumes are created. (Less)
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author
Seiron, Kristian
supervisor
organization
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Strålterapi
language
English
id
2156974
date added to LUP
2011-09-13 14:03:04
date last changed
2011-09-13 14:03:04
@misc{2156974,
  abstract     = {Purpose: The aim of this study was to investigate if the inverse planning available in the dedicated planning program VariSeed 7.1, can generate plans of equal quality to plans generated through manual planning.Materials and Methods: In this study the dedicated permanent seed implantation planning system VariSeed 7.1. (Varian, Paolo Alto California) was used for inverse planning, using a dose-volumehistogram based optimization algorithm. Seven patients with different prostate sizes and shapes were randomly selected amongst those patients that had already gone through the implantation. For each of these patients six sets of dose volumetric requirements with different weight factors and placement restrictions were investigated. The tests were organized so to shift priority from good prostate dose coverage at the first tests to sparing the organs at risk. Decreasing the dose to the organs at risk was achieved by increasing the weight factors to the organs at risk or prohibiting seed placement close to them. The dose-volumetric criteria for a good dose plan are as follows: Prostate V100 > 96%, Prostate V150 < 65%, Urethra D30 < 150% and finally V69 < 3 cm3 for the rectum. The algorithm was confined to use Rigid Absorbable Permanent Implant Device (RAPID) strands with no loose seeds; the algorithm was also restricted from placing seeds in the middle of the prostate. The calculation time and number of needles allowed was set high so that these conditions did not affect the planning results negatively, they where set to 200 seconds and 40 needles respectively. Results: The results from the tests show that the algorithm generates acceptable dose coverage for large prostates when priority is put mainly upon achieving acceptable dose coverage of the target and little priority is put on the organs at risk. The target dose coverage decreases with decreasing prostate size. Acceptable dose coverage of the target was achieved for all prostate sizes when an extra 3 mm placement area around the prostate was added. The rectum and the urethra both received acceptable doses throughout all the tests. However, the dose received by the urethra was lower when using the manual planning method. The seed geometry produced by the optimization algorithm was very randomized and clustered. The clustering of the seeds generated few large high dose volumes, compared to several small high dose volumes generated with the manual planning. The treatment margins around the target were also too thin for the automatic planes.Conclusion: From a dose-volumetric point of view the inverse planning method can generate plans with acceptable dose coverage for both the target and the organs at risk. However in the presented study, the urethra received a lower dose using the plans generated manually with the peripheral loading method, than with the automatic optimized plans. Shifting dose coverage priority to minimize the urethra dose means compromising target dose coverage. The seed geometry put forward by the algorithm is randomized and clustered compared to the manual peripheral loading. Thus the algorithm generates large high dose volumes compared to the manual peripheral loading were several smaller high dose volumes are created.},
  author       = {Seiron, Kristian},
  keyword      = {Strålterapi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Evaluation of automatic treatment planning using iterative method, for permanent seed implantation of the prostate},
  year         = {2006},
}