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40 HIPO: A hybrid inverse treatment planning optimization algorithm in HDR brachytherapy
Proffered Papers
Monday, September 26
variations between prostates these TCP values are averaged whereas for variations within one prostate these TCP values are multiplied, yielding an averaged TCP value for that dose. This is repeated for several dose levels. This is also done for all other parameters. Finally all parameters are varied simultaneously. This provided TCP-dose curves for inter- and intra-patient variations and their combinations. The homogeneous dose for which the TCP=50% (DTcP=50%) and the slope of the TCP-dose curve at that point (slope50%) have been determined.
Results: The tool has been tested by different users and appears to be user-friendly and to work conveniently on both Linux and MS Windows PCs.
48 14
56
4&
The table shows the values for DTCP=50 % and slope50 % for the individual parameter variations and the combination. The values found by variations in [3, T1/2 and Pcell are similar and given in the row 'rest'. Probably, the most realistic assumption is that both interand intra-paUent variations play a role. If both variations have the values as indicated above, the slope50 % is a rather low 1.5%/Gy. However, this would also imply that the DTCP=50 % would be a rather high 155Gy. Note, however, that the latter value can be tuned by adjusting e.g. Pcell" Conclusion: We have developed a convenient tool for TCP computations in brachytherapy treatments for permanent prostate implants with Iodine seeds. Variations in the modelling parameters o and Tpo t are found to have the
defined as the weighted sum of the individual objective functions for the different structures, PTV, Boost volumes and OARs, and is given by:
OARs f
~"PTV
= w]} L
z" PTV
+w2JH
NT
+w3f ~
~
j=l
(3) The new hybrid algorithm, starts from an initial set of catheters placed at random or user specified positions, uses an SA algorithm design to select and adjust catheter positions where the standard LBFGS algorithm is utilized for 3D dose optimization for each catheter combination. The number of SA annealing steps, the final temperature or the difference between the last 2-3 most promising solutions can be used as stopping criterion. This HIPO algorithm was tested for a number of clinical prostate HDR monotherapy implants [3] and its results were compared to the manually created pre-plans. A good quality of plans was achieved in clinically reasonable time (3-5min on a P4 3.6GHz, 2GB RAM). An advanced robust algorithm for inverse treatment planning optimization was introduced and tested for the case of HDR prostate cancer treatment. The comparison with the clinical data was satisfactory. References 1. M. Lahanas, D. Baltas, N. Zamboglou, A hybrid evolutionary algorithm for multi-objective anatomy-based dose optimization in high-dose-rate brachytherapy, Phys. Med. Biol. 48 (2003) 399-415. 2. Milickovic N, Lahanas M, Papagiannopoulou M, Zambogiou N and Baltas D 2002 Multiobjective anatomy-based dose optimization for HDR brachytherapy with constraint free deterministic algorithms Phys. Med. Biol. 47 2263-80. 3. Martin T., Baltas D., et al. 3-D Conformal HDR Brachytherapy as Monotherapy for Iocalised prostate cancer - A pilot study, Strahlenther Onkol 4, 225-231, 2004.
Breast and radiobiology
40 HIPO: A hybrid inverse treatment planning optimization algorithm in HDR brachytherapy A. Karabis I, S. Giannouli 1, D. Baltas 2 1Pi-Medical Ltd., Athens, Greece 2Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, Offenbach, Germany
41 Technical and practical aspects of M R I / C T brachytherapy treatment planning N. Bauer, C. Kirisits, ]. Dimopoulos, R. POtter Department of Radiotherapy and Radiobiology, Medical University of Vienna, Vienna, Austria
1
N
1
X
(1)
(2) where (~ is a transition function. The objective function that is used for the HIPO engine is
r jOAR
+ __LWj+3}~'
largest impact on the computed TCP value.
An advanced hybrid, inverse treatment planning optimization algorithm is introduced based on a stochastic method, Simulated Annealing (SA), for searching for the catheter placement and a deterministic method, LBFGS, for 3D dose distribution optimization. The objective functions used [1].[2], have a common characteristic in that they penalize dose values above and/or below the specified upper and lower dose limits for the anatomical structures:
$29
in
During the last decade CT and MRI based brachytherapy treatment planning has become "state of the art" at the University Hospital Vienna - especially for the treatment of gynaecoiogical malignancies: since 1998 more than 270 patients with approximately 800 brachytherapy applications have been planned and treated based on X-rays and dedicated CT or MRI sequences transferred to the treatment planning systems (TPS). Directly after insertion or implantation of the applicators, semiorthogonal X-rays are taken. Afterwards the patient is transferred to the imaging device. In case of complex anatomy the implantation is performed directly in the MRI or CT room, where each step of the application can be verified immediately on-site. A standard MRI protocol for gynaecologic T2 images consists of transverse images transferred directly to the TPS and para-sagittal and para-coronal views orthogonal to the applicator. The experience of our department is based on an open MRI scanner with 0.2 T. In case of intracavitary treatments with tandem ring applicator, the orientation of the ring can not be determined accurately on MRI images: the applicator has to be reconstructed based on X-rays while the patient undergoes MRI imaging.
Monday, September 26
variations between prostates these TCP values are averaged whereas for variations within one prostate these TCP values are multiplied, yielding an averaged TCP value for that dose. This is repeated for several dose levels. This is also done for all other parameters. Finally all parameters are varied simultaneously. This provided TCP-dose curves for inter- and intra-patient variations and their combinations. The homogeneous dose for which the TCP=50% (DTcP=50%) and the slope of the TCP-dose curve at that point (slope50%) have been determined.
Results: The tool has been tested by different users and appears to be user-friendly and to work conveniently on both Linux and MS Windows PCs.
48 14
56
4&
The table shows the values for DTCP=50 % and slope50 % for the individual parameter variations and the combination. The values found by variations in [3, T1/2 and Pcell are similar and given in the row 'rest'. Probably, the most realistic assumption is that both interand intra-paUent variations play a role. If both variations have the values as indicated above, the slope50 % is a rather low 1.5%/Gy. However, this would also imply that the DTCP=50 % would be a rather high 155Gy. Note, however, that the latter value can be tuned by adjusting e.g. Pcell" Conclusion: We have developed a convenient tool for TCP computations in brachytherapy treatments for permanent prostate implants with Iodine seeds. Variations in the modelling parameters o and Tpo t are found to have the
defined as the weighted sum of the individual objective functions for the different structures, PTV, Boost volumes and OARs, and is given by:
OARs f
~"PTV
= w]} L
z" PTV
+w2JH
NT
+w3f ~
~
j=l
(3) The new hybrid algorithm, starts from an initial set of catheters placed at random or user specified positions, uses an SA algorithm design to select and adjust catheter positions where the standard LBFGS algorithm is utilized for 3D dose optimization for each catheter combination. The number of SA annealing steps, the final temperature or the difference between the last 2-3 most promising solutions can be used as stopping criterion. This HIPO algorithm was tested for a number of clinical prostate HDR monotherapy implants [3] and its results were compared to the manually created pre-plans. A good quality of plans was achieved in clinically reasonable time (3-5min on a P4 3.6GHz, 2GB RAM). An advanced robust algorithm for inverse treatment planning optimization was introduced and tested for the case of HDR prostate cancer treatment. The comparison with the clinical data was satisfactory. References 1. M. Lahanas, D. Baltas, N. Zamboglou, A hybrid evolutionary algorithm for multi-objective anatomy-based dose optimization in high-dose-rate brachytherapy, Phys. Med. Biol. 48 (2003) 399-415. 2. Milickovic N, Lahanas M, Papagiannopoulou M, Zambogiou N and Baltas D 2002 Multiobjective anatomy-based dose optimization for HDR brachytherapy with constraint free deterministic algorithms Phys. Med. Biol. 47 2263-80. 3. Martin T., Baltas D., et al. 3-D Conformal HDR Brachytherapy as Monotherapy for Iocalised prostate cancer - A pilot study, Strahlenther Onkol 4, 225-231, 2004.
Breast and radiobiology
40 HIPO: A hybrid inverse treatment planning optimization algorithm in HDR brachytherapy A. Karabis I, S. Giannouli 1, D. Baltas 2 1Pi-Medical Ltd., Athens, Greece 2Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach, Offenbach, Germany
41 Technical and practical aspects of M R I / C T brachytherapy treatment planning N. Bauer, C. Kirisits, ]. Dimopoulos, R. POtter Department of Radiotherapy and Radiobiology, Medical University of Vienna, Vienna, Austria
1
N
1
X
(1)
(2) where (~ is a transition function. The objective function that is used for the HIPO engine is
r jOAR
+ __LWj+3}~'
largest impact on the computed TCP value.
An advanced hybrid, inverse treatment planning optimization algorithm is introduced based on a stochastic method, Simulated Annealing (SA), for searching for the catheter placement and a deterministic method, LBFGS, for 3D dose distribution optimization. The objective functions used [1].[2], have a common characteristic in that they penalize dose values above and/or below the specified upper and lower dose limits for the anatomical structures:
$29
in
During the last decade CT and MRI based brachytherapy treatment planning has become "state of the art" at the University Hospital Vienna - especially for the treatment of gynaecoiogical malignancies: since 1998 more than 270 patients with approximately 800 brachytherapy applications have been planned and treated based on X-rays and dedicated CT or MRI sequences transferred to the treatment planning systems (TPS). Directly after insertion or implantation of the applicators, semiorthogonal X-rays are taken. Afterwards the patient is transferred to the imaging device. In case of complex anatomy the implantation is performed directly in the MRI or CT room, where each step of the application can be verified immediately on-site. A standard MRI protocol for gynaecologic T2 images consists of transverse images transferred directly to the TPS and para-sagittal and para-coronal views orthogonal to the applicator. The experience of our department is based on an open MRI scanner with 0.2 T. In case of intracavitary treatments with tandem ring applicator, the orientation of the ring can not be determined accurately on MRI images: the applicator has to be reconstructed based on X-rays while the patient undergoes MRI imaging.