David J Eaton1, Kevin Alty2. 1. 1 National Radiotherapy Trials Quality Assurance Group (RTTQA), Mount Vernon Hospital , Northwood , UK. 2. 2 Radiotherapy Physics, Leeds Cancer Centre , Leeds , UK.
Abstract
OBJECTIVE: Uncertainties in radiotherapy target structures are partly dependent on differences between volume calculation and margin growing methods in treatment planning systems (TPS). These uncertainties are exacerbated with very small structures such as those common in stereotactic radiosurgery. METHODS: Data from a national commissioning programme for SRS was used to assess variation in reported volumes for six benchmark cases, including malignant and benign indications. Reported volumes were compared both with and without any margins added according to local practice. RESULTS: 137 plans were submitted, with a total of 311 structures and covering seven TPS. For volumes < 1 cm3 agreement was within 0.05 cm3, and for volumes > 1 cm3 agreement was within 5%. Systematic differences were seen between TPS, partly because of different methods for calculating the end slice volume. About one third of structures had a margin added, of 1-2 mm. Most TPS over-grew the volumes, compared to the approximation of a perfect sphere, especially Pinnacle and Eclipse. CONCLUSION: Differences between volume calculation methods may lead to 5-10% variation in reported volumes from different TPS. This should be taken into account when comparing multicentre studies, and it is recommended that a minimum volume of 0.05 cm3 be used for any near-point doses to allow more consistent comparisons. When margins are added to small structures, there may be up to 40% difference to nominal margin size. Such differences are still small compared to interobserver variation in delineation. Advances in knowledge: This study quantifies the potential uncertainties in clinical volume calculation and margin growth with small radiosurgical targets.
OBJECTIVE: Uncertainties in radiotherapy target structures are partly dependent on differences between volume calculation and margin growing methods in treatment planning systems (TPS). These uncertainties are exacerbated with very small structures such as those common in stereotactic radiosurgery. METHODS: Data from a national commissioning programme for SRS was used to assess variation in reported volumes for six benchmark cases, including malignant and benign indications. Reported volumes were compared both with and without any margins added according to local practice. RESULTS: 137 plans were submitted, with a total of 311 structures and covering seven TPS. For volumes < 1 cm3 agreement was within 0.05 cm3, and for volumes > 1 cm3 agreement was within 5%. Systematic differences were seen between TPS, partly because of different methods for calculating the end slice volume. About one third of structures had a margin added, of 1-2 mm. Most TPS over-grew the volumes, compared to the approximation of a perfect sphere, especially Pinnacle and Eclipse. CONCLUSION: Differences between volume calculation methods may lead to 5-10% variation in reported volumes from different TPS. This should be taken into account when comparing multicentre studies, and it is recommended that a minimum volume of 0.05 cm3 be used for any near-point doses to allow more consistent comparisons. When margins are added to small structures, there may be up to 40% difference to nominal margin size. Such differences are still small compared to interobserver variation in delineation. Advances in knowledge: This study quantifies the potential uncertainties in clinical volume calculation and margin growth with small radiosurgical targets.
Authors: Christos Melidis; Walther R Bosch; Joanna Izewska; Elena Fidarova; Eduardo Zubizarreta; Kenneth Ulin; Satoshi Ishikura; David Followill; James Galvin; Annette Haworth; Deidre Besuijen; Catharine H Clark; Clark H Clark; Elizabeth Miles; Edwin Aird; Damien C Weber; Coen W Hurkmans; Dirk Verellen Journal: Int J Radiat Oncol Biol Phys Date: 2014-12-01 Impact factor: 7.038
Authors: Julia Stanley; Peter Dunscombe; Harold Lau; Paul Burns; Gerald Lim; Hong-Wei Liu; Robert Nordal; Yves Starreveld; Boris Valev; Jon-Paul Voroney; David P Spencer Journal: Int J Radiat Oncol Biol Phys Date: 2013-12-01 Impact factor: 7.038