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195 speaker VOLUMETRIC IMAGING: ADAPTIVE RADIOTHERAPY STRATEGIES FOR CLINICAL IMPLEMENTATION
T UESDAY, M AY 10, 2011
Teaching lecture 195 speaker VOLUMETRIC IMAGING: ADAPTIVE RADIOTHERAPY STRATEGIES FOR CLINICAL IMPLEMENTATION V. Khoo1 1 R OYAL M ARSDEN H OSPITAL T RUST & I NSTITUTE OF C ANCER R ESEARCH, Clinical Oncology, London, United Kingdom
The methodology for precision radiotherapy remains appropriate target volume delineation and treatment planning followed by reliable and accurate dose delivery over the entire course of radiotherapy. It is well recognised that one of the limitations for precision radiotherapy whether it is delivered by conformal or intensity modulated external beam radiotherapy is the presence of internal organ and target motion. This lecture will focus mainly on external beam therapies rather than on brachytherapy but accurate definition of implanted volumes is also a crucial element of quality brachytherapy. Amongst the recent strategic developments to account for temporal spatial variations noted during radiotherapy delivery is the use of adaptive therapy. The adaptive strategy uses repeated cross sectional imaging to determine the magnitude of systematic and random components of target variability for the individual patient. This imaging process often involves several feedback loops that may be either on-line or off-line to reduce the spatial positional uncertainty inherent in the initial radiotherapy treatment planning scan. Once the magnitude of the temporal spatial variations is quantified, the modifications to the treatment plan can be initiated and implemented. This process will still require verification and may need further optimisation where appropriate. Initially proposed and utilised in prostate radiotherapy, it was reported to significantly reduce the mean systematic error from 4 mm to 0.5 mm. It has since been investigated for other tumour subsites such as bladder, cervical as well as liver and other deformable target sites. In bladder radiotherapy where the target organ is the bladder, there can be substantial variation in both the position and size of the organ of up t. there is good evidence to define individual patterns of bladder filling reliably. Using this information, it is possible to predict the size of the bladder at the time of irradiation subsequent to the use of daily volumetric imaging on the LINAC. This strategy termed predictive organ localisation (POLO) has been tested and can be implemented clinically using a library of predefined plans based on the a-priori knowledge of the deformed bladder. Further refinement on this strategy Adaptive-POLO (APOLO) uses a wider range of library plans for daily on-line adaptive therapy. This has been implemented in routine clinical practice and can be utilised within a standard radiotherapy treatment slot. There will need to be education and training needs for radiotherapy staff. Other important issues include resource allocation. The potential clinical benefits for these adaptive strategies will need to be fully assessed in clinical trials to quantify the magnitude of benefit for our patients. 196 speaker A CRITICAL OVERVIEW OF ARC THERAPY TECHNIQUES T. Bortfeld1 , S. Webb2 1 M ASSACHUSETTS G ENERAL H OSPITAL & H ARVARD M EDICAL S CHOOL, Radiation Oncology, Boston, USA 2 I NSTITUTE OF C ANCER R ESEARCH & R OYAL M ARSDEN NHS T RUST, Joint Department of Physics, Sutton, United Kingdom
Purpose/Objectives: Two years ago we published an article on single-arc IMRT (Rapidarc, VMAT), in which we concluded that single-arc IMRT is a promising technique but that it may compromise the quality of the dose distribution in complex cases if one limits the delivery time to 2 minutes (PMB 54:N9-N20, 2009). We also warned against too high expectations because some of the initial studies were driven by commercial as opposed to scientific interests, and suggested that more research work needs to be done to better understand the potential and limitations of single-arc IMRT. In the past two years, many planning studies comparing arc IMRT with several other delivery techniques have been published, as well as relatively few algorithmic advances of arc IMRT. The main objective of this teaching lecture is to review the recent publications and thus the state of the art in arc IMRT. We will also provide some more theoretical insights into the potential dosimetric efficiency benefits of rotating the gantry during IMRT delivery. Materials/Methods: We will begin with a brief historic review of arc IMRT. Interestingly, IMRT has its roots in arc therapy but the fixed field IMRT approach using multiple static gantry positions has become more prevalent in the clinical implementation of IMRT. More recently, arc and single-arc IMRT delivery have gained more interest again. We will focus in particular on publications on arc IMRT from the past two years. Results: The results presented in recent papers on arc-IMRT do not always agree. However, a few common themes have emerged: the dose distributions with arc IMRT are as good or sometimes better than with fixed field IMRT. For complex cases, the use of multiple arcs provides a dosimetric advantage compared with single-arc IMRT, and Tomotherapy plans are better still. The delivery times with arc IMRT, especially with single-arc IMRT, are generally shorter, though not by as much as indicated in the initial studies. Treatment
T EACHING LECTURE
S 77
planning for arc IMRT is more involved and takes substantially more time than for fixed field IMRT. These results represent a snapshot in time as far as both the planning and delivery technologies are concerned. From a more fundamental theoretical point of view, arc and fixed field IMRT are dosimetrically equivalent if "enough" time is provided for the delivery of the arc treatment, and "enough" beams (of the order of 10-20, i.e., more than the typical number) are used in the case of fixed field IMRT. "Cutting corners" will tip the balance in either direction. Conclusions: Overall, the debate about arc vs. fixed field IMRT reminds one of the discussion of step-and-shoot vs. dynamic IMRT from 15 years ago. Both techniques have certain pros and cons, but both can yield excellent results and they therefore have been and will be in clinical use in parallel. 197 speaker IMAGE-GUIDED ADAPTIVE RADIATION THERAPY - MORE THAN A VERIFICATION TOOL J. J. Sonke1 1 T HE N ETHERLANDS C ANCER I NSTITUTE - A NTONI VAN L EEUWENHOEK H OSPITAL, Radiation Oncology, Amsterdam, Netherlands
Considerable geometrical uncertainties such as setup error, organ motion, shape change and treatment response limit the precision and accuracy of radiation therapy (RT). Consequently, the actually delivered dose does not equal the planned dose (what you see is not what you get). Image guided radiotherapy (IGRT) is the process of 1) acquiring an image of the patients anatomy, generally in the treatment room with the patient in treatment position, 2) comparing the treatment position with planned position of the tumor, organs at risk or some surrogate and 3) correcting the treatment position, generally with a couch correction. A large variety of imaging modalities are available for in-room imaging producing 2D, 3D, and/or 4D datasets. Adaptive radiotherapy (ART) is the process where the patient’s treatment plan is customized to patient-specific variation by evaluating and characterizing the systematic and/or random variations through image feedback and including them in adaptive planning [1]. Where IGRT is generally limited to the reduction of locally rigid variations, ART has the potential to reduce more complex variations such as differential motion, shape changes and treatment response. An important component of ART is deformable image registration to bring the repeat imaging series into the same reference system for analysis and dose accumulation. Additionally, early response assessment on the functional aspects of the tumor and normal tissue’s can be incorporated in a re-plan once these have been proven to correlate with outcome. Image guided and adapted RT (IGART) provides a powerful patient specific quality assurance (QA) platform verifying the patient’s position relative to planning and making corrections if needed to better approximate to the original treatment intent of the planning stage. Consequently, proving the efficacy of IGART in a clinical trial has ethical objections (in the standard arm, the available technology to avoid geographic misses is not used). On the other hand, the increased precision and accuracy of IGART might be utilized to reduce safety margins and personalize the treatment plan based on geometric and possibly functional characterizations. The efficacy of such changes to the treatment plan relies on additional assumptions of disease spread distributions and dose-effect relationships. Such changes are therefore good candidates for clinical trials, where IGART is the enabling technology. It is important to realize that despite the implementation of advanced correction strategies, treatment uncertainties will never be completely eliminated and consequently safety margins will never be zero. D. Yan et al. Computed tomography guided management of interfractional patient variation, Seminars in radiation oncology 2005;15(3):168-79.
Teaching lecture 195 speaker VOLUMETRIC IMAGING: ADAPTIVE RADIOTHERAPY STRATEGIES FOR CLINICAL IMPLEMENTATION V. Khoo1 1 R OYAL M ARSDEN H OSPITAL T RUST & I NSTITUTE OF C ANCER R ESEARCH, Clinical Oncology, London, United Kingdom
The methodology for precision radiotherapy remains appropriate target volume delineation and treatment planning followed by reliable and accurate dose delivery over the entire course of radiotherapy. It is well recognised that one of the limitations for precision radiotherapy whether it is delivered by conformal or intensity modulated external beam radiotherapy is the presence of internal organ and target motion. This lecture will focus mainly on external beam therapies rather than on brachytherapy but accurate definition of implanted volumes is also a crucial element of quality brachytherapy. Amongst the recent strategic developments to account for temporal spatial variations noted during radiotherapy delivery is the use of adaptive therapy. The adaptive strategy uses repeated cross sectional imaging to determine the magnitude of systematic and random components of target variability for the individual patient. This imaging process often involves several feedback loops that may be either on-line or off-line to reduce the spatial positional uncertainty inherent in the initial radiotherapy treatment planning scan. Once the magnitude of the temporal spatial variations is quantified, the modifications to the treatment plan can be initiated and implemented. This process will still require verification and may need further optimisation where appropriate. Initially proposed and utilised in prostate radiotherapy, it was reported to significantly reduce the mean systematic error from 4 mm to 0.5 mm. It has since been investigated for other tumour subsites such as bladder, cervical as well as liver and other deformable target sites. In bladder radiotherapy where the target organ is the bladder, there can be substantial variation in both the position and size of the organ of up t. there is good evidence to define individual patterns of bladder filling reliably. Using this information, it is possible to predict the size of the bladder at the time of irradiation subsequent to the use of daily volumetric imaging on the LINAC. This strategy termed predictive organ localisation (POLO) has been tested and can be implemented clinically using a library of predefined plans based on the a-priori knowledge of the deformed bladder. Further refinement on this strategy Adaptive-POLO (APOLO) uses a wider range of library plans for daily on-line adaptive therapy. This has been implemented in routine clinical practice and can be utilised within a standard radiotherapy treatment slot. There will need to be education and training needs for radiotherapy staff. Other important issues include resource allocation. The potential clinical benefits for these adaptive strategies will need to be fully assessed in clinical trials to quantify the magnitude of benefit for our patients. 196 speaker A CRITICAL OVERVIEW OF ARC THERAPY TECHNIQUES T. Bortfeld1 , S. Webb2 1 M ASSACHUSETTS G ENERAL H OSPITAL & H ARVARD M EDICAL S CHOOL, Radiation Oncology, Boston, USA 2 I NSTITUTE OF C ANCER R ESEARCH & R OYAL M ARSDEN NHS T RUST, Joint Department of Physics, Sutton, United Kingdom
Purpose/Objectives: Two years ago we published an article on single-arc IMRT (Rapidarc, VMAT), in which we concluded that single-arc IMRT is a promising technique but that it may compromise the quality of the dose distribution in complex cases if one limits the delivery time to 2 minutes (PMB 54:N9-N20, 2009). We also warned against too high expectations because some of the initial studies were driven by commercial as opposed to scientific interests, and suggested that more research work needs to be done to better understand the potential and limitations of single-arc IMRT. In the past two years, many planning studies comparing arc IMRT with several other delivery techniques have been published, as well as relatively few algorithmic advances of arc IMRT. The main objective of this teaching lecture is to review the recent publications and thus the state of the art in arc IMRT. We will also provide some more theoretical insights into the potential dosimetric efficiency benefits of rotating the gantry during IMRT delivery. Materials/Methods: We will begin with a brief historic review of arc IMRT. Interestingly, IMRT has its roots in arc therapy but the fixed field IMRT approach using multiple static gantry positions has become more prevalent in the clinical implementation of IMRT. More recently, arc and single-arc IMRT delivery have gained more interest again. We will focus in particular on publications on arc IMRT from the past two years. Results: The results presented in recent papers on arc-IMRT do not always agree. However, a few common themes have emerged: the dose distributions with arc IMRT are as good or sometimes better than with fixed field IMRT. For complex cases, the use of multiple arcs provides a dosimetric advantage compared with single-arc IMRT, and Tomotherapy plans are better still. The delivery times with arc IMRT, especially with single-arc IMRT, are generally shorter, though not by as much as indicated in the initial studies. Treatment
T EACHING LECTURE
S 77
planning for arc IMRT is more involved and takes substantially more time than for fixed field IMRT. These results represent a snapshot in time as far as both the planning and delivery technologies are concerned. From a more fundamental theoretical point of view, arc and fixed field IMRT are dosimetrically equivalent if "enough" time is provided for the delivery of the arc treatment, and "enough" beams (of the order of 10-20, i.e., more than the typical number) are used in the case of fixed field IMRT. "Cutting corners" will tip the balance in either direction. Conclusions: Overall, the debate about arc vs. fixed field IMRT reminds one of the discussion of step-and-shoot vs. dynamic IMRT from 15 years ago. Both techniques have certain pros and cons, but both can yield excellent results and they therefore have been and will be in clinical use in parallel. 197 speaker IMAGE-GUIDED ADAPTIVE RADIATION THERAPY - MORE THAN A VERIFICATION TOOL J. J. Sonke1 1 T HE N ETHERLANDS C ANCER I NSTITUTE - A NTONI VAN L EEUWENHOEK H OSPITAL, Radiation Oncology, Amsterdam, Netherlands
Considerable geometrical uncertainties such as setup error, organ motion, shape change and treatment response limit the precision and accuracy of radiation therapy (RT). Consequently, the actually delivered dose does not equal the planned dose (what you see is not what you get). Image guided radiotherapy (IGRT) is the process of 1) acquiring an image of the patients anatomy, generally in the treatment room with the patient in treatment position, 2) comparing the treatment position with planned position of the tumor, organs at risk or some surrogate and 3) correcting the treatment position, generally with a couch correction. A large variety of imaging modalities are available for in-room imaging producing 2D, 3D, and/or 4D datasets. Adaptive radiotherapy (ART) is the process where the patient’s treatment plan is customized to patient-specific variation by evaluating and characterizing the systematic and/or random variations through image feedback and including them in adaptive planning [1]. Where IGRT is generally limited to the reduction of locally rigid variations, ART has the potential to reduce more complex variations such as differential motion, shape changes and treatment response. An important component of ART is deformable image registration to bring the repeat imaging series into the same reference system for analysis and dose accumulation. Additionally, early response assessment on the functional aspects of the tumor and normal tissue’s can be incorporated in a re-plan once these have been proven to correlate with outcome. Image guided and adapted RT (IGART) provides a powerful patient specific quality assurance (QA) platform verifying the patient’s position relative to planning and making corrections if needed to better approximate to the original treatment intent of the planning stage. Consequently, proving the efficacy of IGART in a clinical trial has ethical objections (in the standard arm, the available technology to avoid geographic misses is not used). On the other hand, the increased precision and accuracy of IGART might be utilized to reduce safety margins and personalize the treatment plan based on geometric and possibly functional characterizations. The efficacy of such changes to the treatment plan relies on additional assumptions of disease spread distributions and dose-effect relationships. Such changes are therefore good candidates for clinical trials, where IGART is the enabling technology. It is important to realize that despite the implementation of advanced correction strategies, treatment uncertainties will never be completely eliminated and consequently safety margins will never be zero. D. Yan et al. Computed tomography guided management of interfractional patient variation, Seminars in radiation oncology 2005;15(3):168-79.