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21 Tomotherapy: preliminary experience with a new methodology for RT
Symposia
Monday, October 25, 2004 $9
A small percentage of the genes present on the arrays met the stringent criteria for differential expression that was applied in this analysis. The selected genes included regulators of vascular development and angiogenic remodelling (Jagged-I, KLF-5), as well as genes involved in inflammatory pathways (TSA-1). The present study demonstrated that the microarray approach is an effective tool in identifying candidate genes that were not previously known to be associated with molecular and cellular biological processes in normal tissues after irradiation. Further studies will be required to evaluate the functional role of the differentially expressed genes in the development of vascularmediated normal tissue injury.
Novel technology in radiotherapy 21 Tomotherapy: preliminary methodology for RT
experience
with
a
new
R. Ca/andrino. G.M. Cattaneo, S. Broggi, S. Molinel/i, C. Fiorino Istituto Scientifico San Raffaele, Servizio Fisica Sanitaria, Milano, Italy Commercial clinical helical Tomotherapy unit (Hi-Art 2 System) is a new modality for radiation treatments: it's the first treatment unit dedicated to intensity modulated radiotherapy (IMRT) with a fully integrated image-guided radiotherapy system with the on-board mega-voltage CT (MVCT) capability. The Tomotherapy system uses a 6 MV accelerator, a 64-leaf binary multileaf collimator and xenon image detector array mounted on a rotating slip-ring: the radiation is delivered in an helical way, obtained by concurrent gantry rotation and couch/patient travel; together, these components allow continuous intensity modulated rotational delivery of radiation with fan beam entry from 360-degree. Optimisation process in Tomotherapy represents a special challenge: pre-optimisation step, where the main free parameters (field size, pitch, modulation factor) are determined and beamlets pre-calculated; optimisation step where the dose constraints are selected and the plan optimised accordingly by using an iterative last-square minimisation technique and a post-optimisation step, where the dose distribution is finally recalculated to account dosimetric and mechanical MLC's characteristics (time leaf latency; Tongue-groove effect). Convolution/superpositJon (C/S) dose calculation is employed for ultimate dose calculation. The availability of a CT scanner on board allows a number of verification processes: a MVCT scan before the treatment can be fused with a planning CT scan to determine the correct setup of the patient. The CT detector signal during treatment could be used to reconstruct the effectively delivered dose to the patient to be compared with the expected one. The capability to reduce the uncertainty in the patient set-up and the ability of this IMRT technique to produce very large dose gradients and rapid dose falioff outside the target makes it desirable to reduce margins limiting the high dose volume in adjacent structures by offering the possibility to increase the biologically effective dose to the target. In this presentation different aspects of the Tomotherapy process will be summarised: commissioning test, QA procedures, treatment plans examples and clinical aspects will be described.
22 Robotic approaches in patient positioning: 4 weddings ... and a funeral? R. Ferrand Centre de Protonth6rapie d'Orsay, Orsay Cedex, France The major evolution in radiotherapy towards targeted irradiation and high conformation has led to a quest for precision at every step of the treatment process. And patient positioning is one of the crucial and hardest issues to solve since it depends on the patient himself: immobilisation, Iocalisation, displacement and error compensation .... Furthermore, although a precise patient positioning must also be fast (to minimise patient motion), speed and precision are usually incompatible, unless a reliable and automated procedure assists in reaching such an optimisation. For years, radiotherapy and robotics ignored each other, one in the medical world, the other mostly focused to industry (space, cars,...). As conformal therapy emerged, patient positioning became a "six degrees of freedom problem" as well as a "4D problem" (time dimension), for which robotics can bring elegant, fast, precise but also reliable answers, based on a strong industrial experience. Several examples, based on the use of industrial robots, have already proven the high potential of today's system adapted to a medical use. From the specification required today in patient positioning, we will consider the different fields (target Iocalisation, motion calculation and correction, real time tracking, automation) where the links between the robotics concepts and radiotherapy will certainly be reinforced in the future, with as final goal a safe, highly precise, fully automated, patient positioning. 23 Cyberknife: user's point of view P. Francescon Ospedale San Bortolo, Medical Physics, Vicenza, Italy CyberKnife is an innovative radiosurgery device based on a compact linear accelerator mounted on a robotic arm, and on a x-ray imaging system allowing non-isocentric, frameless operations. The non-isocentric approach is the main characteristic which allows highly conformal isodose shapes; it is possible thanks to a robotic arm with 6 degrees of freedom. The Linac source is positioned at 80 cm from the virtual isocenter; 100 positions can be assumed by the source on a sphere centered on this point, and from each position 12 directions can be reached, leading to 1200 different beams in total. Not all these directions will probably be used, but it is thanks to such a flexibility, and to the different weighting of the beams, that highly conformal shapes can be achieved. The Linac is a compact, 6MV unit with circular collimators ranging from 5 to 60mm. Compared to conventional stereotactic radiosurgery systems, the CyberKnife provides enhanced ability to avoid critical structures, thanks to highly conformal dose distribution, dose fractionation (allowed by reliable relocation) and potential to target multiple tumors at different locations during a single treatment. The localization system is based on the comparison between a set of digitally reconstructed radiographs (DRRs), generated from a CT scan, and actual x-ray pictures taken from orthogonal directions. From the comparison of the two pairs of images it is possible to calculate six parameters that describe the translation and rotation errors. After an initial alignment which is performed by moving the treatment couch, the system tracks further movements and accounts for them by redefining the frame of reference - that is, patient movements are corrected by correcting the position of the robot.
Monday, October 25, 2004 $9
A small percentage of the genes present on the arrays met the stringent criteria for differential expression that was applied in this analysis. The selected genes included regulators of vascular development and angiogenic remodelling (Jagged-I, KLF-5), as well as genes involved in inflammatory pathways (TSA-1). The present study demonstrated that the microarray approach is an effective tool in identifying candidate genes that were not previously known to be associated with molecular and cellular biological processes in normal tissues after irradiation. Further studies will be required to evaluate the functional role of the differentially expressed genes in the development of vascularmediated normal tissue injury.
Novel technology in radiotherapy 21 Tomotherapy: preliminary methodology for RT
experience
with
a
new
R. Ca/andrino. G.M. Cattaneo, S. Broggi, S. Molinel/i, C. Fiorino Istituto Scientifico San Raffaele, Servizio Fisica Sanitaria, Milano, Italy Commercial clinical helical Tomotherapy unit (Hi-Art 2 System) is a new modality for radiation treatments: it's the first treatment unit dedicated to intensity modulated radiotherapy (IMRT) with a fully integrated image-guided radiotherapy system with the on-board mega-voltage CT (MVCT) capability. The Tomotherapy system uses a 6 MV accelerator, a 64-leaf binary multileaf collimator and xenon image detector array mounted on a rotating slip-ring: the radiation is delivered in an helical way, obtained by concurrent gantry rotation and couch/patient travel; together, these components allow continuous intensity modulated rotational delivery of radiation with fan beam entry from 360-degree. Optimisation process in Tomotherapy represents a special challenge: pre-optimisation step, where the main free parameters (field size, pitch, modulation factor) are determined and beamlets pre-calculated; optimisation step where the dose constraints are selected and the plan optimised accordingly by using an iterative last-square minimisation technique and a post-optimisation step, where the dose distribution is finally recalculated to account dosimetric and mechanical MLC's characteristics (time leaf latency; Tongue-groove effect). Convolution/superpositJon (C/S) dose calculation is employed for ultimate dose calculation. The availability of a CT scanner on board allows a number of verification processes: a MVCT scan before the treatment can be fused with a planning CT scan to determine the correct setup of the patient. The CT detector signal during treatment could be used to reconstruct the effectively delivered dose to the patient to be compared with the expected one. The capability to reduce the uncertainty in the patient set-up and the ability of this IMRT technique to produce very large dose gradients and rapid dose falioff outside the target makes it desirable to reduce margins limiting the high dose volume in adjacent structures by offering the possibility to increase the biologically effective dose to the target. In this presentation different aspects of the Tomotherapy process will be summarised: commissioning test, QA procedures, treatment plans examples and clinical aspects will be described.
22 Robotic approaches in patient positioning: 4 weddings ... and a funeral? R. Ferrand Centre de Protonth6rapie d'Orsay, Orsay Cedex, France The major evolution in radiotherapy towards targeted irradiation and high conformation has led to a quest for precision at every step of the treatment process. And patient positioning is one of the crucial and hardest issues to solve since it depends on the patient himself: immobilisation, Iocalisation, displacement and error compensation .... Furthermore, although a precise patient positioning must also be fast (to minimise patient motion), speed and precision are usually incompatible, unless a reliable and automated procedure assists in reaching such an optimisation. For years, radiotherapy and robotics ignored each other, one in the medical world, the other mostly focused to industry (space, cars,...). As conformal therapy emerged, patient positioning became a "six degrees of freedom problem" as well as a "4D problem" (time dimension), for which robotics can bring elegant, fast, precise but also reliable answers, based on a strong industrial experience. Several examples, based on the use of industrial robots, have already proven the high potential of today's system adapted to a medical use. From the specification required today in patient positioning, we will consider the different fields (target Iocalisation, motion calculation and correction, real time tracking, automation) where the links between the robotics concepts and radiotherapy will certainly be reinforced in the future, with as final goal a safe, highly precise, fully automated, patient positioning. 23 Cyberknife: user's point of view P. Francescon Ospedale San Bortolo, Medical Physics, Vicenza, Italy CyberKnife is an innovative radiosurgery device based on a compact linear accelerator mounted on a robotic arm, and on a x-ray imaging system allowing non-isocentric, frameless operations. The non-isocentric approach is the main characteristic which allows highly conformal isodose shapes; it is possible thanks to a robotic arm with 6 degrees of freedom. The Linac source is positioned at 80 cm from the virtual isocenter; 100 positions can be assumed by the source on a sphere centered on this point, and from each position 12 directions can be reached, leading to 1200 different beams in total. Not all these directions will probably be used, but it is thanks to such a flexibility, and to the different weighting of the beams, that highly conformal shapes can be achieved. The Linac is a compact, 6MV unit with circular collimators ranging from 5 to 60mm. Compared to conventional stereotactic radiosurgery systems, the CyberKnife provides enhanced ability to avoid critical structures, thanks to highly conformal dose distribution, dose fractionation (allowed by reliable relocation) and potential to target multiple tumors at different locations during a single treatment. The localization system is based on the comparison between a set of digitally reconstructed radiographs (DRRs), generated from a CT scan, and actual x-ray pictures taken from orthogonal directions. From the comparison of the two pairs of images it is possible to calculate six parameters that describe the translation and rotation errors. After an initial alignment which is performed by moving the treatment couch, the system tracks further movements and accounts for them by redefining the frame of reference - that is, patient movements are corrected by correcting the position of the robot.