- Email: [email protected]
244 Fluctuation in speed and amplitude of lung tumor motion detected by real-time tumor-tracking radiotherapy system
$86
March 1 2 -
15
Poster Presentations
connecting the corresponding feature points between the images. The feature point tracking was carried out using point pattern matching with a probabilistic relaxation method. This quantification technique enables us to track the realistic local motion of any positions inside the whole lung without any burden on a patient. Gridding interpolation of the obtained vectors into all voxels inside the lung volume was carried out. The deformed CTV was estimated from a CTV defined at an initial CT image. Dynamic 3D-CT images were scanned with synchronization of conventional respiratory waveform, and the motion-quantification technique was verified. Results: More than 2000 bifurcations were derived from each lung 3D-CT image. The feature point tracking process made them correspond and more than 1000 displacement vectors were obtained. The probabilistic reaxation method was found to be effective in preventing mismatched point tracking. The averaged error distance of the displacement vectors was estimated to be N0.2 mm, where the voxel size was 0.625 m m x 0.625 mm x 1 ram. Taking account of the thinning algorithm etc., this motion-evaluation technique includes an uncertainty of ~1 voxel in all directions. However, it is expected that the accuracy of this technique is sufficiently high for radiation therapy. The occupied volume per vector was estimated as 2.2 cc/vector. This vector density seems to be enough for gridding interpolation. The CTV deformation using the interpolated motion data was correctly confirmed. Synchronization of the conventional respiratory waveform enables to estimate the motion at any respiratory phase. Clinical verification of the technique using dynamic 3D-CT (4DCT) data is in progress. Conclusions: This 3D motionquantification technique enables us to track the lung motion at each position in the lung without any fiducial markers. The accuracy is expected to be within 1-voxel. The method can automatically estimate the deformation of the target volume. This technique is expected to be a powerful tool for radiotherapy, such as motion quantification for actual 4D-CT images, dose estimation in moving targets and normal tissues, and 4D treatment planning. 3D lung motion, Anatomical feature, Topology 243 V I S U A L I Z A T I O N OF DOSE D I S T R I B U T I O N ENDOBRONCHIAL SURFACE USING BRONCHOSCOPY
ON THE VIRTUAL
S. Minohara, M. Baba, 7-. Yashiro, K. Kagei, N. Hirasawa, T. Miyamoto, S. Kandatsu Research Center for Charged Particle Therapy, National Institute of Radiological Sciences Objective: To estimate effects of irradiation on lung tumor around bronchi, we developed the visualizing application of planning dose distribution on virtual bronchoscopic images. In the treatment planning, the calculated dose distribution is displayed on axial CT images, or sagittal and coronal reconstruction images. However the real dose distribution in the patient would be affected with respiratory motion and reproducibility of target position, and in generally it is difficult to directly observe the tissue response by irradiation except for the skin surface. Especially in particle radiotherapy, dose at boundary of planning target volume is important to clinical result because the lateral shape and the depth end of particle beam are very sharp. Actual bronchoscopy can be advanced to peripheral bronchi under direct vision, and is useful for the radiotherapy to evaluate effects of the irradiation on tumor and normal tissues. Therefore the comparison of tissue responses by actual bronchoscopic findings and planning dose distribution on virtual bronchoscopy would be important to evaluate the accuracy of irradiation and the dose response. So we developed the software to superimpose the color map of planning dose distribution on virtual bronchoscopic images. Material and methods: Respiratory gated CT images using multi-detector CT scanner (GEYMS Ltd. Light Speed Ultar16, 0.5 seconds/rotation) is taken for the patient of lung cancer. Treatment planning is performed to a set of gated CT image using a HIPLAN which is treatment planning system for carbon-ion radiotherapy developed our institute. Then the isocenter information file, dose distribution files at each filed and a set of CT volume file are inputted to application software
of virtual bronchoscopy. We developed this application based on commercial software of virtual bronchoscopy (AZE Ltd. Virtual Place Advance Plus. Ver.2). After the geometrical adjustment and interpolation with CT images and dose distribution, the 3-dimensional voxel data set is reconstructed. Each voxel is defined as x, y, z, CT value, and dose at each field. Using volume rendering technique, virtual bronchoscopic images are reconstructed. The pixel of image at endobronchial surface on virtual bronchoscopy has the value of dose where the pixel intersects the voxel. In proportion as the dose, pixels at endobronchial surface are visualized by color map. Results: Planning dose distribution at each filed or total filed was visualized on the endobronchial surface of virtual bronchoscopy, and was simultaneously displayed on axial, sagittal and coronal multiplanar reconstruction CT images, too. It is easy to change the dose distribution of total filed to each filed. When the observing point on virtual bronchoscopy is moved on the 3-dimensional bronchoschopic image by interactive exploration, the bronchoschopic image with dose map was obtained in real-time. On each cross-sectional CT image, the location and the direction of the observing point were simultaneously displayed and moved in association with the bronchoschopic image. In addition, the value of dose at any point on virtual endobronchial surface is possible to search by computer-mouse operation. Thus we can observe the dose distribution at any point with any angle on virtual endobronchial surface. Conclusions: We developed the unique dose distribution display system on virtual bronchoscopic images. This system is emerging as a useful approach for evaluation of pulmonary dose response in comparison of actual bronchoscopic images. 244 FLUCTUATION I N SPEED AND A M P L I T U D E OF LUNG TUMOR M O T I O N DETECTED BY REAL-TIME T U M O R TRACKING RADIOTHERAPY SYSTEM S. Onodeara, M. Fujino, K. Fujita, R. Onimaru, H. Aoyama, G. Sharp, H. Shirato Department of Radiology, Hokkaido University School of Medicine, Japan Objective: Accurate knowledge about lung tumor motion is a key step in four-dimensional radiotherapy (4DRT). We describe what we have found about inter-fractional and intrafractional changes in the amplitude and speed of internal tumor motion using a real-time tumor-tracking radiotherapy (RTRT) system which records the trajectory of the internal fiducial marker near the tumor. One of the most important steps is the accurate registration of the tumor position at the right phase of internal tumor motion. 4D setup method--that is, a method for setting up tumors in motion at the right time and with the right coordinates--is also reported. M a t e r i a l and Methods: A fiducial marker was implanted into or near the lung tumor. During treatment planning and daily setup in the treatment room, the trajectory of the internal fiducial marker was recorded for 1 to 2 minutes at the rate of 30 times per second by the RTRT system. To maximize gating efficiency, the patient's position on the treatment couch was adjusted using the 4D setup system. Inter-fractional and intra-fractional changes in the absolute amplitude and speed of the fiducial marker were analyzed using the data for 21 patients with lung tumors. In total, 60 treatment days, or 3 treatment days for each patient in average, were used for the analysis. Results: The trajectory of the marker detected in the 4D setup system was well visualized and used for daily setup. Various degrees of inter-fractional and intra-fractional changes in the absolute amplitude and speed of the internal marker were detected. The achievable efficiency varied considerably among patients. Even in the same patient, the achievable efficiency of the irradiation varied considerably among treatment days. Thirtythree percent (20/60) of average absolute amplitudes were longer than 10 mm along the RL, CC, and AP directions in 21 patients. The standard deviation of the absolute amplitude was larger than 5 mm in 23% (14/60). The maximum speed of the marker exceeded 20 mm/s in 33% of the treatment days, with the highest speed at 94 mm/s. The estimated achievable efficiency of the gated radiotherapy was 62.4% +19.0% with the use of a 4-2 mm gating window. The actual treatment
Poster P r e s e n t a t i o n s
time was 25 4- 13 (mean 4- standard deviation) minutes for 10.5 4- 1.7 Gy. The number of readjustments necessary per irradiation treatment day was 4.1 4- 4.1, prompted by baseline shifting of the tumor position in most patients. The actual efficiency was grossly estimated as 28%. Conclusion: Interfractional and intra-fractional changes in the absolute amplitude and speed of lung tumors were detected. The present findings showed that the variation of the absolute amplitude of the trajectory among patients was remarkable not only in the cranio-caudal direction but also in the lateral and antero-dorsal directions. Even with real-time tracking technology, it will be difficult to make pursuing radiotherapy clinically feasible. The 4D setup using tumor motion trajectories with fine on-line remote control of the treatment couch was shown to be useful for reducing the uncertainty of tumor motion and to increase the efficiency of gated irradiation. 245 I O N I Z I N G R A D I A T I O N AS AN EXPERIMENTAL TOOL I N STUDIES OF ADULT NEUROGENESIS I N M A M M A L I A N BRAIN
J.M. Wojtowicz Department of Physiology, University of Toronto, Canada Objective: Ionizing radiation has been the method of choice in experiments requiring a blockade of cell division in adult brain. Specifically, the phenomenon under investigation is the adult neurogenesis that occurs in all mammals, including humans. Neurogenesis results in the production of thousands of new neurons per day in young individuals. This rate tapers off to very low levels by middle-age. The prime objective of the current studies on neurogenesis is to determine the functional role of young neurons as opposed to the mature pre-existing neurons. Material and Methods: We have used gamma irradiation at 1-10 Gy directed to the head of experimental animals (Long Evans or Sprague-Dawley adult rats). In most experiments we used two fractions repeated at 24hr interval. Animals were anaesthetised prior to irradiation with pentobarbital (60mg/kg) i.p. Control animals were also anesthetized but not irradiated. Results: The main experimental approach was to abolish the neuronal production and study the consequences on physiology and behaviour. In using the gamma irradiation we aimed to achieve a selective blockade of cell division of neuronal stem cells or precursor cells in the brain without significant effects on mature neuronal population. We verified the effectiveness of irradiation on cell division using selective histological markers of cell division (bromodeoxyuridine and Ki-67). We further showed that young neuronal production is blocked by using markers of immature neurons (doublecortin and PSA-NCAM). For example, irradiation by 7.5Gy resulted in the reduction of cell division by 77% and reduction of the number of immature neurons by 90%. In this and previous experiments the effects of irradiation on neurons were more pronounced than the effects on non-neuronal proliferating cells such as gila cells. The effects of irradiation were irreversible i.e. cell proliferation did not recover at 3 months after irradiation. We did not observe any evidence of prolonged inflammation after the irradiation. Behavioral tests comparing learning in control vs. irradiated rats show specific deficits that can be attributed to the missing young neurons. For example, the learning of the contextual fear conditioning task that depends on the hippocampus, part of the brain that contains a large number of dividing neurons, was impaired in the irradiated group. A cued fear conditioning task that is known to be hippocampus independent was not impaired. Physiological tests show that synaptic plasticity attributed to the young neurons was selectively blocked by irradiation. Conclusion: Ionizing radiation is a surprisingly effective and flexible tool in inhibiting production of new neurons in the adult brain of experimental animals. However, these results suggest that whole head irradiation of human patients at the clinically relevant doses may result in strong inhibition of ongoing neurogenesis in the hippocampus and perhaps other brain regions that may contain the dividing stem cells. Avoidance of normal functional targets related to cognition such as the
March 12 - 15
$87
hippocampus would appear to be essential in future clinical strategies involving irradiation. 246 THE POTENTIALS OF TOMOTHERAPY I N S I M U L T A N E O U S INTEGRATED BOOST (SIB) "MUCOSA-SPARING" I R R A D I A T I O N OF N A S O P H A R I N X CANCERS
C. Fiorino, I. Dell'Oca*, A. Pierelli, G.M. Cattaneo, E. De Martin, S. Broggi, N. Di Muzio*, F. Fazio °*, R. Calandrino. Medical Physics, Institute H. S. Raffaele, Milano, Italy; *Radiotherapy, Institute H. S. Raffaele, Milano, Italy; °IBFM CNR, University of Milano Bicocca, Institute H. S. Raffaele, Milano, Italy Purpose: A Tomotherapy unit (HiArt 2) was recently installed at our Institute and clinically activated. In order to explore the potentials of -I-i- in the field of HNC, a number of planning studies comparing Linac-IMRT technique (Varian 600CD Linac, inversely optimised by the Helios/Eclipse system) vs l-iplanning were activated. In current investigation four nasopharinx patients (stage IIb-IVb) were considered for the comparison. Materials and methods: A SIB technique delivering 54 Gy, 61.5 and 64.5 Gy in 30 fractions respectively to non-positive nodes (PTVl), positive nodes (PTV2) and tumour (PTV3) was planned with IMRT and -FI. In both situations (i.e. IMRT and -FI-) the same "minimum" constraints for PTV coverage and for parotids, spinal cord, brain stem, mandible and optical pathways (OARsetl) were used for planning optimization. Moreover, a number of other structures were defined for planning purposes: mucosae outside PTV (including oral cavity and tongue), larynx, thyroid, esophagous, inner ear, sub-mental connective tissue, brain, lungs apex (OARset2). The planner was asked to spare as much as possible these additional structures without compromising PTV coverage and the sparing of OARsetl. The comparison was performed considering a number of dose-volume parameters, like mean and maximum dose, or fraction of volume V receiving at least a certain dose d (Vd). Results: Excellent PTV coverage was obtained with both techniques with a better homogeneity of the dose distribution within each PTV together with a better coverage with TT (for instance: V50 Gy for PTVl: 98.2 % for IMRT; 99.7 % for q-I). Concerning OARsetl, both techniques were generally able to satisfy our constraints; however, -FI- was able to reduce the mean parotid dose (from 31.3 Gy of IMRT to 30.0 Gy) and the spinal cord Dmax (from 41.2 Gy to 37.8 Gy). Concerning OARset2, TT showed to be able of a much more efficient sparing: the mean dose to the mucosa decreased from 36.2 Gy (IMRT) to 23.4 Gy (l-r) while V30Gy decreased from 47 cc (IMRT) to 18 cc (-I-I). Large gains using 1-I were also found for larynx (mean dose: IMRT: 48.8 Gy; -I-I-: 26.4 Gy), esophagous (mean dose: IMRT: 43.4 Gy; Fr: 29.1 Gy), thyroid (mean dose: IMRT: 48.2 Gy; -i-i-: 41.4 Gy). Conclusions: -I-Ihas the potential to significantly improve the therapeutic ratio with respect to a conventional IMRT delivery method due to its ability in largely better sparing OARs. The careful definition of "new" structures/organs (like "mucosae") is very useful in maximizing the potentials of l-I- with a consequent potential reduction of toxicity. 247 C R I T I C A L APPRAISAL OF THE MANAGEMENT PARASELLAR M E N I N G O T H E L I A L M E N I N G I O M A
OF
A
M. Motta 1, A. Bolognesi~, N. Di Muzio ~, S. Broggi2, G.M. Cattaneo 2, M. Pasetti I, L. S. Politi3, F. Fazio 1,4,s ~Dep.t of Radiation Oncology; 2Dep.t of Medical Physics, and 3Dept of Neuroradiology, Scientific Institute H.S. Raffaele, Milano, Italy; 4INB- CNR, 5University of Milano Bicocca, Institute HS Raffaele, Milano, Italy Objective: to evaluate the feasibility of radicat radiation treatment for a meningioma located around the optic chiasm, avoiding complete blindness for the patient. Material and methods: a 50 years old woman affected by meningothelial meningioma located around the optic chiasm and the left optic nerve was treated in our Institution. She could not be submitted to radiosurgical treatment with y-knife because of the location and the extension of the lesion. GTV was drawn joined by a radiation oncologist and a neuro -radiologist , and dose
March 1 2 -
15
Poster Presentations
connecting the corresponding feature points between the images. The feature point tracking was carried out using point pattern matching with a probabilistic relaxation method. This quantification technique enables us to track the realistic local motion of any positions inside the whole lung without any burden on a patient. Gridding interpolation of the obtained vectors into all voxels inside the lung volume was carried out. The deformed CTV was estimated from a CTV defined at an initial CT image. Dynamic 3D-CT images were scanned with synchronization of conventional respiratory waveform, and the motion-quantification technique was verified. Results: More than 2000 bifurcations were derived from each lung 3D-CT image. The feature point tracking process made them correspond and more than 1000 displacement vectors were obtained. The probabilistic reaxation method was found to be effective in preventing mismatched point tracking. The averaged error distance of the displacement vectors was estimated to be N0.2 mm, where the voxel size was 0.625 m m x 0.625 mm x 1 ram. Taking account of the thinning algorithm etc., this motion-evaluation technique includes an uncertainty of ~1 voxel in all directions. However, it is expected that the accuracy of this technique is sufficiently high for radiation therapy. The occupied volume per vector was estimated as 2.2 cc/vector. This vector density seems to be enough for gridding interpolation. The CTV deformation using the interpolated motion data was correctly confirmed. Synchronization of the conventional respiratory waveform enables to estimate the motion at any respiratory phase. Clinical verification of the technique using dynamic 3D-CT (4DCT) data is in progress. Conclusions: This 3D motionquantification technique enables us to track the lung motion at each position in the lung without any fiducial markers. The accuracy is expected to be within 1-voxel. The method can automatically estimate the deformation of the target volume. This technique is expected to be a powerful tool for radiotherapy, such as motion quantification for actual 4D-CT images, dose estimation in moving targets and normal tissues, and 4D treatment planning. 3D lung motion, Anatomical feature, Topology 243 V I S U A L I Z A T I O N OF DOSE D I S T R I B U T I O N ENDOBRONCHIAL SURFACE USING BRONCHOSCOPY
ON THE VIRTUAL
S. Minohara, M. Baba, 7-. Yashiro, K. Kagei, N. Hirasawa, T. Miyamoto, S. Kandatsu Research Center for Charged Particle Therapy, National Institute of Radiological Sciences Objective: To estimate effects of irradiation on lung tumor around bronchi, we developed the visualizing application of planning dose distribution on virtual bronchoscopic images. In the treatment planning, the calculated dose distribution is displayed on axial CT images, or sagittal and coronal reconstruction images. However the real dose distribution in the patient would be affected with respiratory motion and reproducibility of target position, and in generally it is difficult to directly observe the tissue response by irradiation except for the skin surface. Especially in particle radiotherapy, dose at boundary of planning target volume is important to clinical result because the lateral shape and the depth end of particle beam are very sharp. Actual bronchoscopy can be advanced to peripheral bronchi under direct vision, and is useful for the radiotherapy to evaluate effects of the irradiation on tumor and normal tissues. Therefore the comparison of tissue responses by actual bronchoscopic findings and planning dose distribution on virtual bronchoscopy would be important to evaluate the accuracy of irradiation and the dose response. So we developed the software to superimpose the color map of planning dose distribution on virtual bronchoscopic images. Material and methods: Respiratory gated CT images using multi-detector CT scanner (GEYMS Ltd. Light Speed Ultar16, 0.5 seconds/rotation) is taken for the patient of lung cancer. Treatment planning is performed to a set of gated CT image using a HIPLAN which is treatment planning system for carbon-ion radiotherapy developed our institute. Then the isocenter information file, dose distribution files at each filed and a set of CT volume file are inputted to application software
of virtual bronchoscopy. We developed this application based on commercial software of virtual bronchoscopy (AZE Ltd. Virtual Place Advance Plus. Ver.2). After the geometrical adjustment and interpolation with CT images and dose distribution, the 3-dimensional voxel data set is reconstructed. Each voxel is defined as x, y, z, CT value, and dose at each field. Using volume rendering technique, virtual bronchoscopic images are reconstructed. The pixel of image at endobronchial surface on virtual bronchoscopy has the value of dose where the pixel intersects the voxel. In proportion as the dose, pixels at endobronchial surface are visualized by color map. Results: Planning dose distribution at each filed or total filed was visualized on the endobronchial surface of virtual bronchoscopy, and was simultaneously displayed on axial, sagittal and coronal multiplanar reconstruction CT images, too. It is easy to change the dose distribution of total filed to each filed. When the observing point on virtual bronchoscopy is moved on the 3-dimensional bronchoschopic image by interactive exploration, the bronchoschopic image with dose map was obtained in real-time. On each cross-sectional CT image, the location and the direction of the observing point were simultaneously displayed and moved in association with the bronchoschopic image. In addition, the value of dose at any point on virtual endobronchial surface is possible to search by computer-mouse operation. Thus we can observe the dose distribution at any point with any angle on virtual endobronchial surface. Conclusions: We developed the unique dose distribution display system on virtual bronchoscopic images. This system is emerging as a useful approach for evaluation of pulmonary dose response in comparison of actual bronchoscopic images. 244 FLUCTUATION I N SPEED AND A M P L I T U D E OF LUNG TUMOR M O T I O N DETECTED BY REAL-TIME T U M O R TRACKING RADIOTHERAPY SYSTEM S. Onodeara, M. Fujino, K. Fujita, R. Onimaru, H. Aoyama, G. Sharp, H. Shirato Department of Radiology, Hokkaido University School of Medicine, Japan Objective: Accurate knowledge about lung tumor motion is a key step in four-dimensional radiotherapy (4DRT). We describe what we have found about inter-fractional and intrafractional changes in the amplitude and speed of internal tumor motion using a real-time tumor-tracking radiotherapy (RTRT) system which records the trajectory of the internal fiducial marker near the tumor. One of the most important steps is the accurate registration of the tumor position at the right phase of internal tumor motion. 4D setup method--that is, a method for setting up tumors in motion at the right time and with the right coordinates--is also reported. M a t e r i a l and Methods: A fiducial marker was implanted into or near the lung tumor. During treatment planning and daily setup in the treatment room, the trajectory of the internal fiducial marker was recorded for 1 to 2 minutes at the rate of 30 times per second by the RTRT system. To maximize gating efficiency, the patient's position on the treatment couch was adjusted using the 4D setup system. Inter-fractional and intra-fractional changes in the absolute amplitude and speed of the fiducial marker were analyzed using the data for 21 patients with lung tumors. In total, 60 treatment days, or 3 treatment days for each patient in average, were used for the analysis. Results: The trajectory of the marker detected in the 4D setup system was well visualized and used for daily setup. Various degrees of inter-fractional and intra-fractional changes in the absolute amplitude and speed of the internal marker were detected. The achievable efficiency varied considerably among patients. Even in the same patient, the achievable efficiency of the irradiation varied considerably among treatment days. Thirtythree percent (20/60) of average absolute amplitudes were longer than 10 mm along the RL, CC, and AP directions in 21 patients. The standard deviation of the absolute amplitude was larger than 5 mm in 23% (14/60). The maximum speed of the marker exceeded 20 mm/s in 33% of the treatment days, with the highest speed at 94 mm/s. The estimated achievable efficiency of the gated radiotherapy was 62.4% +19.0% with the use of a 4-2 mm gating window. The actual treatment
Poster P r e s e n t a t i o n s
time was 25 4- 13 (mean 4- standard deviation) minutes for 10.5 4- 1.7 Gy. The number of readjustments necessary per irradiation treatment day was 4.1 4- 4.1, prompted by baseline shifting of the tumor position in most patients. The actual efficiency was grossly estimated as 28%. Conclusion: Interfractional and intra-fractional changes in the absolute amplitude and speed of lung tumors were detected. The present findings showed that the variation of the absolute amplitude of the trajectory among patients was remarkable not only in the cranio-caudal direction but also in the lateral and antero-dorsal directions. Even with real-time tracking technology, it will be difficult to make pursuing radiotherapy clinically feasible. The 4D setup using tumor motion trajectories with fine on-line remote control of the treatment couch was shown to be useful for reducing the uncertainty of tumor motion and to increase the efficiency of gated irradiation. 245 I O N I Z I N G R A D I A T I O N AS AN EXPERIMENTAL TOOL I N STUDIES OF ADULT NEUROGENESIS I N M A M M A L I A N BRAIN
J.M. Wojtowicz Department of Physiology, University of Toronto, Canada Objective: Ionizing radiation has been the method of choice in experiments requiring a blockade of cell division in adult brain. Specifically, the phenomenon under investigation is the adult neurogenesis that occurs in all mammals, including humans. Neurogenesis results in the production of thousands of new neurons per day in young individuals. This rate tapers off to very low levels by middle-age. The prime objective of the current studies on neurogenesis is to determine the functional role of young neurons as opposed to the mature pre-existing neurons. Material and Methods: We have used gamma irradiation at 1-10 Gy directed to the head of experimental animals (Long Evans or Sprague-Dawley adult rats). In most experiments we used two fractions repeated at 24hr interval. Animals were anaesthetised prior to irradiation with pentobarbital (60mg/kg) i.p. Control animals were also anesthetized but not irradiated. Results: The main experimental approach was to abolish the neuronal production and study the consequences on physiology and behaviour. In using the gamma irradiation we aimed to achieve a selective blockade of cell division of neuronal stem cells or precursor cells in the brain without significant effects on mature neuronal population. We verified the effectiveness of irradiation on cell division using selective histological markers of cell division (bromodeoxyuridine and Ki-67). We further showed that young neuronal production is blocked by using markers of immature neurons (doublecortin and PSA-NCAM). For example, irradiation by 7.5Gy resulted in the reduction of cell division by 77% and reduction of the number of immature neurons by 90%. In this and previous experiments the effects of irradiation on neurons were more pronounced than the effects on non-neuronal proliferating cells such as gila cells. The effects of irradiation were irreversible i.e. cell proliferation did not recover at 3 months after irradiation. We did not observe any evidence of prolonged inflammation after the irradiation. Behavioral tests comparing learning in control vs. irradiated rats show specific deficits that can be attributed to the missing young neurons. For example, the learning of the contextual fear conditioning task that depends on the hippocampus, part of the brain that contains a large number of dividing neurons, was impaired in the irradiated group. A cued fear conditioning task that is known to be hippocampus independent was not impaired. Physiological tests show that synaptic plasticity attributed to the young neurons was selectively blocked by irradiation. Conclusion: Ionizing radiation is a surprisingly effective and flexible tool in inhibiting production of new neurons in the adult brain of experimental animals. However, these results suggest that whole head irradiation of human patients at the clinically relevant doses may result in strong inhibition of ongoing neurogenesis in the hippocampus and perhaps other brain regions that may contain the dividing stem cells. Avoidance of normal functional targets related to cognition such as the
March 12 - 15
$87
hippocampus would appear to be essential in future clinical strategies involving irradiation. 246 THE POTENTIALS OF TOMOTHERAPY I N S I M U L T A N E O U S INTEGRATED BOOST (SIB) "MUCOSA-SPARING" I R R A D I A T I O N OF N A S O P H A R I N X CANCERS
C. Fiorino, I. Dell'Oca*, A. Pierelli, G.M. Cattaneo, E. De Martin, S. Broggi, N. Di Muzio*, F. Fazio °*, R. Calandrino. Medical Physics, Institute H. S. Raffaele, Milano, Italy; *Radiotherapy, Institute H. S. Raffaele, Milano, Italy; °IBFM CNR, University of Milano Bicocca, Institute H. S. Raffaele, Milano, Italy Purpose: A Tomotherapy unit (HiArt 2) was recently installed at our Institute and clinically activated. In order to explore the potentials of -I-i- in the field of HNC, a number of planning studies comparing Linac-IMRT technique (Varian 600CD Linac, inversely optimised by the Helios/Eclipse system) vs l-iplanning were activated. In current investigation four nasopharinx patients (stage IIb-IVb) were considered for the comparison. Materials and methods: A SIB technique delivering 54 Gy, 61.5 and 64.5 Gy in 30 fractions respectively to non-positive nodes (PTVl), positive nodes (PTV2) and tumour (PTV3) was planned with IMRT and -FI. In both situations (i.e. IMRT and -FI-) the same "minimum" constraints for PTV coverage and for parotids, spinal cord, brain stem, mandible and optical pathways (OARsetl) were used for planning optimization. Moreover, a number of other structures were defined for planning purposes: mucosae outside PTV (including oral cavity and tongue), larynx, thyroid, esophagous, inner ear, sub-mental connective tissue, brain, lungs apex (OARset2). The planner was asked to spare as much as possible these additional structures without compromising PTV coverage and the sparing of OARsetl. The comparison was performed considering a number of dose-volume parameters, like mean and maximum dose, or fraction of volume V receiving at least a certain dose d (Vd). Results: Excellent PTV coverage was obtained with both techniques with a better homogeneity of the dose distribution within each PTV together with a better coverage with TT (for instance: V50 Gy for PTVl: 98.2 % for IMRT; 99.7 % for q-I). Concerning OARsetl, both techniques were generally able to satisfy our constraints; however, -FI- was able to reduce the mean parotid dose (from 31.3 Gy of IMRT to 30.0 Gy) and the spinal cord Dmax (from 41.2 Gy to 37.8 Gy). Concerning OARset2, TT showed to be able of a much more efficient sparing: the mean dose to the mucosa decreased from 36.2 Gy (IMRT) to 23.4 Gy (l-r) while V30Gy decreased from 47 cc (IMRT) to 18 cc (-I-I). Large gains using 1-I were also found for larynx (mean dose: IMRT: 48.8 Gy; -I-I-: 26.4 Gy), esophagous (mean dose: IMRT: 43.4 Gy; Fr: 29.1 Gy), thyroid (mean dose: IMRT: 48.2 Gy; -i-i-: 41.4 Gy). Conclusions: -I-Ihas the potential to significantly improve the therapeutic ratio with respect to a conventional IMRT delivery method due to its ability in largely better sparing OARs. The careful definition of "new" structures/organs (like "mucosae") is very useful in maximizing the potentials of l-I- with a consequent potential reduction of toxicity. 247 C R I T I C A L APPRAISAL OF THE MANAGEMENT PARASELLAR M E N I N G O T H E L I A L M E N I N G I O M A
OF
A
M. Motta 1, A. Bolognesi~, N. Di Muzio ~, S. Broggi2, G.M. Cattaneo 2, M. Pasetti I, L. S. Politi3, F. Fazio 1,4,s ~Dep.t of Radiation Oncology; 2Dep.t of Medical Physics, and 3Dept of Neuroradiology, Scientific Institute H.S. Raffaele, Milano, Italy; 4INB- CNR, 5University of Milano Bicocca, Institute HS Raffaele, Milano, Italy Objective: to evaluate the feasibility of radicat radiation treatment for a meningioma located around the optic chiasm, avoiding complete blindness for the patient. Material and methods: a 50 years old woman affected by meningothelial meningioma located around the optic chiasm and the left optic nerve was treated in our Institution. She could not be submitted to radiosurgical treatment with y-knife because of the location and the extension of the lesion. GTV was drawn joined by a radiation oncologist and a neuro -radiologist , and dose