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230 poster Use of THERAPLAN plus treatment planning system in endovascular brachytherapy
$80
Posers
effects. The healthy tissues - involved in the tissue destructing irradiation growth of length proportional to the irradiated length might be the possible reason of these side- effects. The time of irradiation and the side- effects show the following inherence: In case of 11 min. or more, the number of intestinal and urinary side- effects declines significantly. A possible reason for this phenomena is, that the protrahation of irradiation, the irradiation similar to MDR (middle dose rate) is advantageous for the repair mechanism of the healthy tissues. 230
poster
Use of THERAPLAN Plus treatment planning system in endovascular brachytherapy J.E. Cveler 1, C. Angers2 L. L.Eapen 1, M. Labinaz3, J.F. Marquis3 1Ottawa Regional Cancer Centre, Ottawa, Canada, 2MDS Nordion, Ottawa, Canada, 3Ottawa Heart Institute, Ottawa, Canada Purpose: The purpose of this work was to evaluate the THERAPLAN Plus Image Based Brachytherapy System for calculating dose distributions for intravascular radiotherapy. Materials and Methods: THERAPLAN Plus Image Based Brachytherapy software was used to capture IVUS images of the coronary arteries and to perform 3D dose calculations. The software had to be modified to allow dose calculation and display at distances closer to the source than fo standard brachytherapy applications. A Sr-90 source from BetaCath device (Novoste) was used. It was modeled in THERAPLAN Plus as a linear source with the anisotropy function calculated by Wang and Li using Monte Carlo (Med. Phys. 27, 2528., 2000). Results: The overall agreement between the dose rate matrix calculated by THERAPLAN Plus for a single Sr-90 source and Wang and Li data was within 5% at distances greater than 0.5 mm from the source. Larger disagreements were observed at distances less than 0.5 mm from the source. Treatment plans for a train of 16 sources were generated. The dose delivered to various parts of the arterial wall was evaluated in terms of isodose distribution on transverse ultrasound images as well as in 3D. Dose volume histograms, DVH, Were generated to evaluate the dose coverage for different parts of arterial wall. Using a standard prescription distance of 2 mm from the source for all patients does not provide adequate dose coverage to all parts of the artery if highly non-concentric plaque is present. This study indicates a possible need for custom treatment planning based on individual vessel anatomy.
CONFORMAL RADIOTHERAPY 231
poster
Conformal radiotherapy on prostatic lesions: dosimetric comparison between static and dynamic treatment geometries E. Madon 1, E. Trevisiol1, A. Urgesi 1, S. Gribaudo1, M. Donetti2-, F. Marchetto3, R. Cirio3, C. Sanz Freire3 1AO S.Anna OIRM, Radiotherapy, Turin, Italy, 2TERA foundation, Novara, Italy, 3University of Turin, INFN, Turin, Italy Since september 1998, in our department we employ a dynamic multileaf collimator system for conformal treatments in particular in pelvic region for prostate lesions. This secondary collimation system is made by 20 tungsten couples of leaves and it is mounted on the linac's top. Every single leaf is independent and its movement can be planned for each static field or can be related to the linac rotation during dynamic arcs, so we can use this system in static or dynamic way. The TPS are different but they are both investigated with a pixel ionization chamber. Dose distributions obtained with different conformal techniques have been compared in terms of target, rectum and bladder dose, conformality number. The dynamic multileaf collimator (DMLC) is attached to a Philips SL75/5 linear accelerator. The 20 couples of leaves are geometrically focused and positioned by motors. Each leaf is driven by a DC motor-encoder unit. Dimensions of leaves are 6.2 mm of width, so minimal allowed square field is 12.4x12.4 mm 2 and maximal is 124 x 124 mm 2. The maximun leaf speed is about 5 mm/s for each bank; the maximum overtravel is 10 mm. Leaves leakage is from 7.4 % at the central axis to 3.4 % at 40 mm far from beam central axis. Interleaves leakage is always before 2%. Mean penumbra is
2.7168 /- 0.52 mm. The pixel ionization chamber used to test calculation algorithm of TPS is a dosimeter with a large sensitive volume that have a segmented electrode of 1024 square pixels of 7.5 mm: every single pixel is connected to a current-frequence converter in a 64 channels electronic circuit of high integration scale (VLSI). Chips are read with fast input/output modules, connected with microprocessor VxWorks that allows data in real time (50 microsecond to read 1024 channels). Different geometries of treatment have been performed and then compared: 6 static coplanar fields all around the treatment couch, 5/7 static coplanar fields over the treatment couch and different coplanar dynamic arcs over the treatments couch with the anthropomorphyc phantom in prone position. The dynamic arcs are simply conformed to target volume, or also conformed to OAR; we tested also dynamic arcs in wich we modulate the dose-rate during the arc rotation also shaping part of target. The TPS calculation algorithm for static fields have been tested comparing 2D dose ditribution at definite depth with pixel chamber counts ditribution: it has been found a good agreement (<2%) between calculations and measurements even if algorithm doesn't take care of the double focalization of leaves. The TPS calculation algorithm for dynamic fields introduces some limitations that we have tested: the treatment arc is a sequence of static fields of a definite step and it doesn't take care of leaves movements during irradiation. Moreover, during real treatment the homogeneity of irradiation can be influenced by interruption of gantry movement due to an unbalance of the accelerator head, become heavier by DMLC that causes a different dose-rate during an arc. The first limitation does't influence dose distribution (<3%), also becouse the leaves speed is not so high to let great difference in leves position from one step to next. The irradiation inhomogeneity due to real possible gantry stop, measured with the pixel chamber, reaches also 5%. Among all the different geometries of treatment under study, the dynamic modulated ones are much more better than static ones, in terms of conformality number, even if it doesn't mean that we surely have the best target dose homogeneity or the lower OAR preservation. A statistical analysis on patients treated from the beginning of 1999 to the end of 2000 with static and dynamic geometries are under study, but doesn't deny dosimetric results. 232
poster
The effect of having one mulUleaf collimator in a department where it is used for conformal fields, M.E. Welch, S. Harlow Royal Free Hospital, Radiotherapy, London, England The Multileaf Collimator (MLC) is now a universal tool for field shaping in Radiotherapy. A department can become reliant on the device with serious repercussions if it fails unexpectedly. This effect is enhanced if only one MLC has been purchased. The impact of an MLC on a department is immense. Assuming that a full field device is purchased typically 40x40cm it is capable of conforming the field to almost any treatment shape. It is flexible in that a field may be created while a patient is waiting or modified on a daily basis. There are no heavy shielding blocks to manage and the field is reproducible on a daily basis to 1mm. Most large field MLCs are now integral in the head and whilst this gives the advantage of no treatment limitations ie distance of treatment head to the patient it does have one major disadvantage. If the MLC should fail for what ever reason the machine cannot be used clinically. This puts incredible pressure on all personnel in the department. If the machine cannot be salvaged quickly patients will need to replanned. Many departments do this automatically when a patient is originally planned. Not all patients can have a directly compatible backup plan. An example is that MLCs are usually fitted to a dual mode (Electrons/Photons) and multi energy machine. An example would be two machines one a 6MV Photon only the other a 6/15MV Photon and 6 Electron energies. Obviously although the MLC may not be used for Electron treatments these treatments cannot proceed and cannot be transferred to the backup machine. The 6Mv patients can be transferred but may require a shaped field which will therefore entail blocks being manufactured. The 15Mv patients may be transferrable but with an increase in the number of applied fields, and again blocks may be required. A possible compromise would be to use non diverging blocks temporarily but this is an inferior treatment. Obviously blocks could be manufactured at the original planning but then why purchase an MLC. The stress on a department during such an MLC fault situation is unacceptable. The long hours and the risk due to haste of an error occurring is great. Perhaps more time should be spent on the reason for purchasing an MLC. Would the department especially if small ie 2-3 machines be better off electing for basic machines and enhancing their block cutting methods. At least that way patients could be rotated around machines as required. Due to the
Posers
effects. The healthy tissues - involved in the tissue destructing irradiation growth of length proportional to the irradiated length might be the possible reason of these side- effects. The time of irradiation and the side- effects show the following inherence: In case of 11 min. or more, the number of intestinal and urinary side- effects declines significantly. A possible reason for this phenomena is, that the protrahation of irradiation, the irradiation similar to MDR (middle dose rate) is advantageous for the repair mechanism of the healthy tissues. 230
poster
Use of THERAPLAN Plus treatment planning system in endovascular brachytherapy J.E. Cveler 1, C. Angers2 L. L.Eapen 1, M. Labinaz3, J.F. Marquis3 1Ottawa Regional Cancer Centre, Ottawa, Canada, 2MDS Nordion, Ottawa, Canada, 3Ottawa Heart Institute, Ottawa, Canada Purpose: The purpose of this work was to evaluate the THERAPLAN Plus Image Based Brachytherapy System for calculating dose distributions for intravascular radiotherapy. Materials and Methods: THERAPLAN Plus Image Based Brachytherapy software was used to capture IVUS images of the coronary arteries and to perform 3D dose calculations. The software had to be modified to allow dose calculation and display at distances closer to the source than fo standard brachytherapy applications. A Sr-90 source from BetaCath device (Novoste) was used. It was modeled in THERAPLAN Plus as a linear source with the anisotropy function calculated by Wang and Li using Monte Carlo (Med. Phys. 27, 2528., 2000). Results: The overall agreement between the dose rate matrix calculated by THERAPLAN Plus for a single Sr-90 source and Wang and Li data was within 5% at distances greater than 0.5 mm from the source. Larger disagreements were observed at distances less than 0.5 mm from the source. Treatment plans for a train of 16 sources were generated. The dose delivered to various parts of the arterial wall was evaluated in terms of isodose distribution on transverse ultrasound images as well as in 3D. Dose volume histograms, DVH, Were generated to evaluate the dose coverage for different parts of arterial wall. Using a standard prescription distance of 2 mm from the source for all patients does not provide adequate dose coverage to all parts of the artery if highly non-concentric plaque is present. This study indicates a possible need for custom treatment planning based on individual vessel anatomy.
CONFORMAL RADIOTHERAPY 231
poster
Conformal radiotherapy on prostatic lesions: dosimetric comparison between static and dynamic treatment geometries E. Madon 1, E. Trevisiol1, A. Urgesi 1, S. Gribaudo1, M. Donetti2-, F. Marchetto3, R. Cirio3, C. Sanz Freire3 1AO S.Anna OIRM, Radiotherapy, Turin, Italy, 2TERA foundation, Novara, Italy, 3University of Turin, INFN, Turin, Italy Since september 1998, in our department we employ a dynamic multileaf collimator system for conformal treatments in particular in pelvic region for prostate lesions. This secondary collimation system is made by 20 tungsten couples of leaves and it is mounted on the linac's top. Every single leaf is independent and its movement can be planned for each static field or can be related to the linac rotation during dynamic arcs, so we can use this system in static or dynamic way. The TPS are different but they are both investigated with a pixel ionization chamber. Dose distributions obtained with different conformal techniques have been compared in terms of target, rectum and bladder dose, conformality number. The dynamic multileaf collimator (DMLC) is attached to a Philips SL75/5 linear accelerator. The 20 couples of leaves are geometrically focused and positioned by motors. Each leaf is driven by a DC motor-encoder unit. Dimensions of leaves are 6.2 mm of width, so minimal allowed square field is 12.4x12.4 mm 2 and maximal is 124 x 124 mm 2. The maximun leaf speed is about 5 mm/s for each bank; the maximum overtravel is 10 mm. Leaves leakage is from 7.4 % at the central axis to 3.4 % at 40 mm far from beam central axis. Interleaves leakage is always before 2%. Mean penumbra is
2.7168 /- 0.52 mm. The pixel ionization chamber used to test calculation algorithm of TPS is a dosimeter with a large sensitive volume that have a segmented electrode of 1024 square pixels of 7.5 mm: every single pixel is connected to a current-frequence converter in a 64 channels electronic circuit of high integration scale (VLSI). Chips are read with fast input/output modules, connected with microprocessor VxWorks that allows data in real time (50 microsecond to read 1024 channels). Different geometries of treatment have been performed and then compared: 6 static coplanar fields all around the treatment couch, 5/7 static coplanar fields over the treatment couch and different coplanar dynamic arcs over the treatments couch with the anthropomorphyc phantom in prone position. The dynamic arcs are simply conformed to target volume, or also conformed to OAR; we tested also dynamic arcs in wich we modulate the dose-rate during the arc rotation also shaping part of target. The TPS calculation algorithm for static fields have been tested comparing 2D dose ditribution at definite depth with pixel chamber counts ditribution: it has been found a good agreement (<2%) between calculations and measurements even if algorithm doesn't take care of the double focalization of leaves. The TPS calculation algorithm for dynamic fields introduces some limitations that we have tested: the treatment arc is a sequence of static fields of a definite step and it doesn't take care of leaves movements during irradiation. Moreover, during real treatment the homogeneity of irradiation can be influenced by interruption of gantry movement due to an unbalance of the accelerator head, become heavier by DMLC that causes a different dose-rate during an arc. The first limitation does't influence dose distribution (<3%), also becouse the leaves speed is not so high to let great difference in leves position from one step to next. The irradiation inhomogeneity due to real possible gantry stop, measured with the pixel chamber, reaches also 5%. Among all the different geometries of treatment under study, the dynamic modulated ones are much more better than static ones, in terms of conformality number, even if it doesn't mean that we surely have the best target dose homogeneity or the lower OAR preservation. A statistical analysis on patients treated from the beginning of 1999 to the end of 2000 with static and dynamic geometries are under study, but doesn't deny dosimetric results. 232
poster
The effect of having one mulUleaf collimator in a department where it is used for conformal fields, M.E. Welch, S. Harlow Royal Free Hospital, Radiotherapy, London, England The Multileaf Collimator (MLC) is now a universal tool for field shaping in Radiotherapy. A department can become reliant on the device with serious repercussions if it fails unexpectedly. This effect is enhanced if only one MLC has been purchased. The impact of an MLC on a department is immense. Assuming that a full field device is purchased typically 40x40cm it is capable of conforming the field to almost any treatment shape. It is flexible in that a field may be created while a patient is waiting or modified on a daily basis. There are no heavy shielding blocks to manage and the field is reproducible on a daily basis to 1mm. Most large field MLCs are now integral in the head and whilst this gives the advantage of no treatment limitations ie distance of treatment head to the patient it does have one major disadvantage. If the MLC should fail for what ever reason the machine cannot be used clinically. This puts incredible pressure on all personnel in the department. If the machine cannot be salvaged quickly patients will need to replanned. Many departments do this automatically when a patient is originally planned. Not all patients can have a directly compatible backup plan. An example is that MLCs are usually fitted to a dual mode (Electrons/Photons) and multi energy machine. An example would be two machines one a 6MV Photon only the other a 6/15MV Photon and 6 Electron energies. Obviously although the MLC may not be used for Electron treatments these treatments cannot proceed and cannot be transferred to the backup machine. The 6Mv patients can be transferred but may require a shaped field which will therefore entail blocks being manufactured. The 15Mv patients may be transferrable but with an increase in the number of applied fields, and again blocks may be required. A possible compromise would be to use non diverging blocks temporarily but this is an inferior treatment. Obviously blocks could be manufactured at the original planning but then why purchase an MLC. The stress on a department during such an MLC fault situation is unacceptable. The long hours and the risk due to haste of an error occurring is great. Perhaps more time should be spent on the reason for purchasing an MLC. Would the department especially if small ie 2-3 machines be better off electing for basic machines and enhancing their block cutting methods. At least that way patients could be rotated around machines as required. Due to the