Xiaoyu Duan1,2, William Giles1, John P Kirkpatrick1,2,3, Fang-Fang Yin1,2,4. 1. Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA. 2. Medical Physics Graduate Program, Duke University, Durham, NC 27705, USA. 3. Department of Neurosurgery, Duke University Medical Center, Durham, NC 27710, USA. 4. Medical Physics Graduate Program, Duke Kunshan University, Kunshan, Jiangsu, 215316, China.
Abstract
PURPOSE: To estimate the combined effect of setup uncertainty on optimal dosimetric margin by analyzing the dose distribution and biological effect in LINAC-based stereotactic radiosurgery (SRS) with dynamic conformal arc (DCA) technique. METHODS: SRS treatment plans were generated from CT scans of the Rando head phantom using four non-coplanar DCA's with total 480-degrees of arc. A single spherical planning target volume (PTV) of 4 different diameters was placed at the center of the phantom to simulate brain lesions. For each PTV, 5 treatment plans were created using identical dose calculation parameters, each with 5 different dosimetric margins. To simulate the effect of setup uncertainty, the isocenter for each plan was shifted to 13 different positions. A marginal dose of 20Gy in a single fraction with 6MV photon beam was prescribed to 49 different percentage isodose surfaces (%IDS). The plan quality was evaluated using Conformity Index (CI), Gradient Index (GI), EUD-based Tumor Control Probability (TCP), Normal Tissue Complication Probability (NTCP), and uncomplicated biological objective function (TCP x (1-NTCP) =p+). RESULTS: A +1mm dosimetric margin could result in a much higher p+ compared to 0mm and 1mm dosimetric margins and a smaller GI while achieving an equivalent p+ in a certain range of %IDS compared to +2mm and +3mm dosimetric margins. With 2mm setup error and +1mm dosimetric margin, the %IDS range optimized for each PTV is: around 80%IDS (10mm diameter); 63~70%IDS (20mm diameter); 66~79%IDS (30mm diameter). CONCLUSION: This simulation study identified the preferred prescription %IDS for a given setup error and dosimetric margin to achieve an optimal dose distribution and favorable biological effect.
PURPOSE: To estimate the combined effect of setup uncertainty on optimal dosimetric margin by analyzing the dose distribution and biological effect in LINAC-based stereotactic radiosurgery (SRS) with dynamic conformal arc (DCA) technique. METHODS: SRS treatment plans were generated from CT scans of the Rando head phantom using four non-coplanar DCA's with total 480-degrees of arc. A single spherical planning target volume (PTV) of 4 different diameters was placed at the center of the phantom to simulate brain lesions. For each PTV, 5 treatment plans were created using identical dose calculation parameters, each with 5 different dosimetric margins. To simulate the effect of setup uncertainty, the isocenter for each plan was shifted to 13 different positions. A marginal dose of 20Gy in a single fraction with 6MV photon beam was prescribed to 49 different percentage isodose surfaces (%IDS). The plan quality was evaluated using Conformity Index (CI), Gradient Index (GI), EUD-based Tumor Control Probability (TCP), Normal Tissue Complication Probability (NTCP), and uncomplicated biological objective function (TCP x (1-NTCP) =p+). RESULTS: A +1mm dosimetric margin could result in a much higher p+ compared to 0mm and 1mm dosimetric margins and a smaller GI while achieving an equivalent p+ in a certain range of %IDS compared to +2mm and +3mm dosimetric margins. With 2mm setup error and +1mm dosimetric margin, the %IDS range optimized for each PTV is: around 80%IDS (10mm diameter); 63~70%IDS (20mm diameter); 66~79%IDS (30mm diameter). CONCLUSION: This simulation study identified the preferred prescription %IDS for a given setup error and dosimetric margin to achieve an optimal dose distribution and favorable biological effect.
Entities:
Keywords:
conformity index; dosimetric margin; normal tissue sparing; setup error; stereotactic radiosurgery; tumor control probability
Authors: G O De Meerleer; L A Vakaet; W R De Gersem; C De Wagter; B De Naeyer; W De Neve Journal: Int J Radiat Oncol Biol Phys Date: 2000-06-01 Impact factor: 7.038
Authors: Lisa J Hazard; Brian Wang; Thomas B Skidmore; Shyh-Shi Chern; Bill J Salter; Randy L Jensen; Dennis C Shrieve Journal: Int J Radiat Oncol Biol Phys Date: 2008-06-17 Impact factor: 7.038