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SP-0199: Geometrical uncertainties and proton treatment planning
S79
ESTRO 33, 2014 from all disciplines involved in the care for patients with colon and rectal cancer. Diagnostic and treatment algorithms were developed to implement the current evidence and to define core treatment guidance for multidisciplinary team management of colon and rectal cancer throughout Europe. Moreover a paper with highligths on the role of radiotherapy has been published, other documents with the aim to highlight the role of imaging and other single therapeutic strategies, as part of the multidisciplinary approach in rectal cancer, are under submission.
TEACHING LECTURE SP-0197 The role of radiotherapy in modern melanoma treatment L. Bastholt1, R. Bahij1 1 Odense University Hospital, Department of Oncology, Odense, Denmark The role of radiotherapy is well defined in almost all types of cancers However, there has been some reluctance to use radiotherapy in melanoma. Available data have indicated that melanomas are resistant to radiotherapy. However , many findings indicate that melanomas have a wide spectrum of sensitivity to radiotherapy that compares favourably with that of many common epithelial cancer. Therefore radiotherapy must be part of the multidisciplinary management program of melanoma. Currently the success of systemic treatment (immunotherapy, targeted therapies) for melanomas is overwhelming, and this success makes it of utmost importance, to continuously evaluate the role of local treatment strategies (i.e. radiotherapy, surgery). The current role of radiotherapy in the treatment of primary melanoma, regional metastatic melanomas and melanomas with distant metastases well be discussed.
TEACHING LECTURE SP-0198 ICRU guidelines for gynaecological brachytherapy C. Kirisits1, R. Pötter1, On behalf of the Committee2 1 Medical University of Vienna, Dept. of Radiotherapy Comprehensive Cancer Center, Vienna, Austria 2 (B. Erickson C. Haie-Meder J. Lindegaard E. van Limbergen J. Rownd K. Tanderup B. Thomadsen) The current draft forthe new ICRU/GEC-ESTRO report for gynaecological intracavitary brachytherapy has been developed by the committee members together with international consultants and detailed review by the ICRU main commission. It contains 13 chapters. The first four chapters present the essential background, including a clinical introduction, historical and current techniques including the concepts of volumetric imaging for cervix cancer. Chapter 5 contains the key elements for the 4D adaptive target concept, which are based on the Gyn GEC ESTRO recommendations with more detailed definitions. The High, Intermediate and Low Risk Clinical Target Volume (CTVHR, CTVIR, CTVLR)are defined at certain time points during treatment by clinical examination andimaging. The CTVHR represents residual GTV and surrounding are asassumed to carry a high risk for residual cancer cell involvement. A dedicated chapter focus on the main organs at risk which are the rectum, bladder, sigmoid, adjacent bowel and vagina. In addition to contours including the entire organ the report emphasizes the presence of different morbidity endpoints and related substructures within the organ (e.g. bladder neck, anal sphincter). The radiobiology chapter explains the limitations of the linear-quadratic model,but encourages the use of the EQD2 concept as the current best option for treatment planning and overall dose reporting. Dose and volume reporting is following GEC-ESTRO recommendations with a few modifications and extensions. In addition to D90 the D98 as the near minimum dose and theD50 as high dose parameter are recommended. For OAR D2cm³and D0.1cm³ are the main parameters for the 3D volumetric approach. However, it is emphasized to report dose parameters sensitive to the intermediate dose region especially to also take into account the external beam contribution. Dose and volume parameters as e.g. V35Gy, V45Gyor V55Gy are sensitive to the external beam techniques especially also for additional boost techniques. For the vagina a set of dose points are proposed to report the dose close to the brachytherapy applicators, but also at different reproducible positions within the vagina to take into account the external beam fields. The report includes detailed chapters on treatment planning, especially for 3D volumetric approach, but also the underlying concepts of dosimetry which remains essential for volumetric and radiography based planning. The whole report is focussed
on volumetric image based techniques, but contains a full set of methods and parameters for radiographic based treatment planning.
TEACHING LECTURE SP-0199 Geometrical uncertainties and proton treatment planning M. Schwarz1 1 Proton Therapy Centre, Medical Physics, Trento, Italy The interest of applying protons to cancer treatment is based on the finite range of protons in tissue and the sharp fall-off after the dose peak, which in principle allows for an excellent compromise between irradiating the tumor and sparing the neighboring healthy tissues. However, this very same property that make protons appealing for cancer treatment becomes a problem when, due to geometrical uncertainties (e.g. positioning errors, changes in patient anatomy, breathing motion) there is a difference between the expected and the actual proton range in the patient. This difference may be particularly large for diseases sites where there are sharp changes in density (i.e. in proton range) between e.g. the lung and the mediastinal parenchyma, or bone and air in the head and neck region. In photons geometrical uncertainties are handled via the use of a planning target volume (PTV), an approach that implicitly assumes dose invariance after small translations and rotations. However, owing to the finite range of protons, one should start from the assumption that even small positioning errors and changes in patient anatomy between treatment planning and treatment delivery can result in noticeable dose deformation. The proton treatment planning techniques to handle geometrical uncertainties can be divided into two categories, whether or not the beam delivery relies on the use of patient specific hardware. In double scattering (or wobbling/uniform scanning) the dose distribution is shaped by field-specific hardware, i.e.laterally by an aperture (or an MLC) and distally by a range compensator. In this case, the planning technique resembles 3D-CRT with photons, where the planner sets the beam properties via trial and error. The main peculiarities of proton therapy lie in preferring beam directions that avoid (if possible)highly heterogeneous regions of the body, the use of a field-specific PTV and in a procedure called smearing, where the compensator is shaped in such a way to ensure target coverage from range errors produced as consequence of set-up errors. When the treatment is delivered without patient specific hardware, such as in pencil beam scanning (PBS), the planning process is faced on the one hand with a enormously increased number of degrees of freedom, on the other hand with the need of ensuring not only the quality of the nominal dose distribution, but also its ‘robustness’, i.e. a quantification of the difference in quality between planned and delivered dose distribution in presence of uncertainties in the input data (e.g. patient model). As a consequence, the field of ‘robust optimization’ has been developing over the past few years, when methods such as worst case, probabilistic and ‘minimax’ optimization were proposed to explicitly incorporate robustness metrics in the optimization cost function. Unfortunately, these approaches are not yet implemented in commercially available treatment planning systems, so the current clinical practice in proton therapy delivered via PBS is in many respects conservative, i.e. it is mostly addressed at those disease sites where the dosimetric consequences of geometrical uncertainties are small. While robust optimization is not yet available for most clinics, a worthwhile effort is the development of robustness analysis tools, in order to evaluate a posteriori the robustness of a dose distribution for a single patient. Among the advantage of such tools, there is the possibility to accumulate quantitative data on the robustness of existing and past plans, that can then be used as input data for robust optimization.
TEACHING LECTURE SP-0200 Automated multi-criterial treatment planning and Pareto navigation S. Breedveld1 1 Erasmus Medical Center Rotterdam, Radiation Oncology, Rotterdam, The Netherlands Radiation therapy treatment planning has always been a complex task, and with the ongoing technical developments, it is currently possible to achieve much higher plan qualities than ever before. But increased
ESTRO 33, 2014 from all disciplines involved in the care for patients with colon and rectal cancer. Diagnostic and treatment algorithms were developed to implement the current evidence and to define core treatment guidance for multidisciplinary team management of colon and rectal cancer throughout Europe. Moreover a paper with highligths on the role of radiotherapy has been published, other documents with the aim to highlight the role of imaging and other single therapeutic strategies, as part of the multidisciplinary approach in rectal cancer, are under submission.
TEACHING LECTURE SP-0197 The role of radiotherapy in modern melanoma treatment L. Bastholt1, R. Bahij1 1 Odense University Hospital, Department of Oncology, Odense, Denmark The role of radiotherapy is well defined in almost all types of cancers However, there has been some reluctance to use radiotherapy in melanoma. Available data have indicated that melanomas are resistant to radiotherapy. However , many findings indicate that melanomas have a wide spectrum of sensitivity to radiotherapy that compares favourably with that of many common epithelial cancer. Therefore radiotherapy must be part of the multidisciplinary management program of melanoma. Currently the success of systemic treatment (immunotherapy, targeted therapies) for melanomas is overwhelming, and this success makes it of utmost importance, to continuously evaluate the role of local treatment strategies (i.e. radiotherapy, surgery). The current role of radiotherapy in the treatment of primary melanoma, regional metastatic melanomas and melanomas with distant metastases well be discussed.
TEACHING LECTURE SP-0198 ICRU guidelines for gynaecological brachytherapy C. Kirisits1, R. Pötter1, On behalf of the Committee2 1 Medical University of Vienna, Dept. of Radiotherapy Comprehensive Cancer Center, Vienna, Austria 2 (B. Erickson C. Haie-Meder J. Lindegaard E. van Limbergen J. Rownd K. Tanderup B. Thomadsen) The current draft forthe new ICRU/GEC-ESTRO report for gynaecological intracavitary brachytherapy has been developed by the committee members together with international consultants and detailed review by the ICRU main commission. It contains 13 chapters. The first four chapters present the essential background, including a clinical introduction, historical and current techniques including the concepts of volumetric imaging for cervix cancer. Chapter 5 contains the key elements for the 4D adaptive target concept, which are based on the Gyn GEC ESTRO recommendations with more detailed definitions. The High, Intermediate and Low Risk Clinical Target Volume (CTVHR, CTVIR, CTVLR)are defined at certain time points during treatment by clinical examination andimaging. The CTVHR represents residual GTV and surrounding are asassumed to carry a high risk for residual cancer cell involvement. A dedicated chapter focus on the main organs at risk which are the rectum, bladder, sigmoid, adjacent bowel and vagina. In addition to contours including the entire organ the report emphasizes the presence of different morbidity endpoints and related substructures within the organ (e.g. bladder neck, anal sphincter). The radiobiology chapter explains the limitations of the linear-quadratic model,but encourages the use of the EQD2 concept as the current best option for treatment planning and overall dose reporting. Dose and volume reporting is following GEC-ESTRO recommendations with a few modifications and extensions. In addition to D90 the D98 as the near minimum dose and theD50 as high dose parameter are recommended. For OAR D2cm³and D0.1cm³ are the main parameters for the 3D volumetric approach. However, it is emphasized to report dose parameters sensitive to the intermediate dose region especially to also take into account the external beam contribution. Dose and volume parameters as e.g. V35Gy, V45Gyor V55Gy are sensitive to the external beam techniques especially also for additional boost techniques. For the vagina a set of dose points are proposed to report the dose close to the brachytherapy applicators, but also at different reproducible positions within the vagina to take into account the external beam fields. The report includes detailed chapters on treatment planning, especially for 3D volumetric approach, but also the underlying concepts of dosimetry which remains essential for volumetric and radiography based planning. The whole report is focussed
on volumetric image based techniques, but contains a full set of methods and parameters for radiographic based treatment planning.
TEACHING LECTURE SP-0199 Geometrical uncertainties and proton treatment planning M. Schwarz1 1 Proton Therapy Centre, Medical Physics, Trento, Italy The interest of applying protons to cancer treatment is based on the finite range of protons in tissue and the sharp fall-off after the dose peak, which in principle allows for an excellent compromise between irradiating the tumor and sparing the neighboring healthy tissues. However, this very same property that make protons appealing for cancer treatment becomes a problem when, due to geometrical uncertainties (e.g. positioning errors, changes in patient anatomy, breathing motion) there is a difference between the expected and the actual proton range in the patient. This difference may be particularly large for diseases sites where there are sharp changes in density (i.e. in proton range) between e.g. the lung and the mediastinal parenchyma, or bone and air in the head and neck region. In photons geometrical uncertainties are handled via the use of a planning target volume (PTV), an approach that implicitly assumes dose invariance after small translations and rotations. However, owing to the finite range of protons, one should start from the assumption that even small positioning errors and changes in patient anatomy between treatment planning and treatment delivery can result in noticeable dose deformation. The proton treatment planning techniques to handle geometrical uncertainties can be divided into two categories, whether or not the beam delivery relies on the use of patient specific hardware. In double scattering (or wobbling/uniform scanning) the dose distribution is shaped by field-specific hardware, i.e.laterally by an aperture (or an MLC) and distally by a range compensator. In this case, the planning technique resembles 3D-CRT with photons, where the planner sets the beam properties via trial and error. The main peculiarities of proton therapy lie in preferring beam directions that avoid (if possible)highly heterogeneous regions of the body, the use of a field-specific PTV and in a procedure called smearing, where the compensator is shaped in such a way to ensure target coverage from range errors produced as consequence of set-up errors. When the treatment is delivered without patient specific hardware, such as in pencil beam scanning (PBS), the planning process is faced on the one hand with a enormously increased number of degrees of freedom, on the other hand with the need of ensuring not only the quality of the nominal dose distribution, but also its ‘robustness’, i.e. a quantification of the difference in quality between planned and delivered dose distribution in presence of uncertainties in the input data (e.g. patient model). As a consequence, the field of ‘robust optimization’ has been developing over the past few years, when methods such as worst case, probabilistic and ‘minimax’ optimization were proposed to explicitly incorporate robustness metrics in the optimization cost function. Unfortunately, these approaches are not yet implemented in commercially available treatment planning systems, so the current clinical practice in proton therapy delivered via PBS is in many respects conservative, i.e. it is mostly addressed at those disease sites where the dosimetric consequences of geometrical uncertainties are small. While robust optimization is not yet available for most clinics, a worthwhile effort is the development of robustness analysis tools, in order to evaluate a posteriori the robustness of a dose distribution for a single patient. Among the advantage of such tools, there is the possibility to accumulate quantitative data on the robustness of existing and past plans, that can then be used as input data for robust optimization.
TEACHING LECTURE SP-0200 Automated multi-criterial treatment planning and Pareto navigation S. Breedveld1 1 Erasmus Medical Center Rotterdam, Radiation Oncology, Rotterdam, The Netherlands Radiation therapy treatment planning has always been a complex task, and with the ongoing technical developments, it is currently possible to achieve much higher plan qualities than ever before. But increased