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ADAPTIVE RADIOTHERAPY TO ACCOUNT FOR GEOMETRIC DISCREPANCIES
S 20
S YMPOSIUM
Adaptive treatment strategies: managing workflow and QA 46 speaker ADAPTIVE RADIOTHERAPY CONCEPT, WORKFLOW AND QA M. Sharpe1 1
M ONDAY, AUGUST 31, 2009
48 speaker ADAPTIVE RADIOTHERAPY CHANGES G. Sanguineti1
TO
PROGRESSIVE
ANATOMICAL
1
J OHN H OPKINS U NIVERSITY, Dept of Radiation Oncology and Molecular Radiation Changes, Baltimore, MD, USA
P RINCESS M ARGARET H OSPITAL AND U NIVERSITY OF TORONTO, Radiation Medicine Program, Toronto, Canada
Image-guidance for radiation therapy (IGRT) has emerged as a vital means of controlling the accuracy and precision of target localization in treatment delivery. In the case of imaging modalities that assess soft-tissues, the ability to direct radiation therapy by frequent imaging also opens the door to assess anatomical changes over the course of treatment. Anatomical changes can include, for example, tumour response to radiation and chemotherapy, variations in organ filling, deformation of the skeleton, weight loss/gain, all of which can alter the relative position and shape of targets and normal tissues and affect the delivery of the dose distribution with the accumulation of each treatment fraction.An "adaptive" treatment would respond, to at least some of this information, by guiding alterations to the treatment plan. The term "Adaptive Radiation Therapy" (ART) has been used to embody strategies that respond to patient setup uncertainties and organ movement, gross anatomical changes, and even physiological changes observed by MRI/MRS and PET. Changes to the treatment plan can mitigate uncertainties that compromise the dose to the target and critical structures or, should it arise, exploit an opportunity to improve normal tissue sparing. It is important to weight the benefit of these opportunities against the risks of introducing errors, reducing treatment efficiency, and increasing workload. The costs and benefits and approach to adaptation can be expected to be highly dependent on the disease site and the overall duration of treatment. The developing concepts of adaptive intervention have broad implications for radiotherapy treatment and the assessment of response. This presentation will review ART concepts, considerations for workflow, and its implications for error management, quality control and quality assurance. The role of imaging and image registration in the assessment of geometric variations and uncertainties will be reviewed, and some of the methods of quantifying uncertainties will be presented. The status of tools for supporting clinical workflow and appropriate quality assurance will be discussed.
Adaptive radiotherapy aims at maintaining the planned dose distribution throughout the whole treatment course. It implies the presence of a planned dose distribution tightly conformed around the target(s) while ‘sparing‘ the surrounding normal structures, the occurrence of significant changes in either the organs at risk (OAR) or the target(s) during the course of radiotherapy to the point that this may translate in a significant deviation of the cumulative delivered dose and the availability of imaging during treatment. The head and neck seems to satisfy the above conditions and therefore it represents a reasonable model.The dose to both the tumor and the OAR may change during a course of fractionated RT as a result of direct or indirect anatomical changes: it has been shown, for example, that the dose to the parotid may increase due their shrinkage and their ‘collapse‘ in the high dose region, or that the dose to the spinal cord may increase after a dramatic reduction in tumor volume. However, while these data prove that tissue modifications take place during RT and may actually impact patient care, several issues still need to be clarified, including a more precise and widespread knowledge of tissue changes during RT, the proper timing for re-planning and the prediction of which patients/regions of interest need to be monitored for changes.At JHU, as part of a quality assurance protocol, we have been collecting weekly KV (planning) CT scans for all oropharyngeal cancer patients treated with dose painting IMRT since early 2008. So far, we have acquired serial scans for 49 patients. The purpose of the present lecture is to critically discuss the topic, summarize the available data on progressive changes of OAR during treatment along with our own data in terms of volumetric and dosimetric changes. 49 speaker 4D ADAPTIVE MANAGEMENT FOR PATIENT RESPIRATORY MOTION D. Yan1 1 W ILLIAM B EAUMONT H OSPITAL, Radiation Oncology, Royal Oak MI, USA
47 speaker ADAPTIVE RADIOTHERAPY TO ACCOUNT FOR GEOMETRIC DISCREPANCIES J. Nijkamp1 1
A NTONI VAN L EEUWENHOEK H OSPITAL , N ETHERLANDS C ANCER I NSTI Radiation Oncology, Amsterdam, Netherlands
TUTE,
With more and more availability of volumetric in-room imaging equipment like cone-beam CT, tomotherapy and in future the incorporated MR systems a large amount of data is available during the course of treatment. The images can be used for online correction of patients, minimizing both systematic and random errors. This is, however, only reducing the simplest geometric discrepancies, shifts.For more complex discrepancies, such as rotations and deformations, adaptive radiotherapy (ART) strategies can be used to estimate and minimize systematic errors during the course of treatment, allowing for margin reduction or coverage increase.The concept of ART has been around for more than 8 years, but the use of it in clinics around the world is, however, limited. On one hand it is time consuming because re-contouring and replanning is almost always involved. On the other side the lack of widely available clinical software for the entire ART chain is also not really helping. The main condition for the use of adaptive strategies is that residual systematic errors after the procedure are significantly smaller than the initial systematic error and that still a relative large portion of the treatment needs to be given after the procedure. The margin reduction should always be balanced with the effort and imaging dose involved.Examples in which ART strategies have an added value are prostate cancer and rectal cancer. During prostate treatment systematic rotations around the LR axis in the order of 6 dg can occur. Estimating and correcting this error after 1 week of treatment can result in residual errors in the order of 2 dg. During treatment of rectal cancer systematic CTV shape change in the order of 7 mm SD are found at the border with the bladder/uterus/small bowel. Proper treatment margins should therefore be in the order of 20 mm. Estimating an average CTV shape after 5 of the 25 fractions results in a reduction of the needed margin of approximately 5 mm. With the small bowel being the main organ at risk, major improvement in the treatment can be appreciated. Auto-contouring of target volumes, faster plan optimizers and good cooperation with vendors is needed to further develop ART strategies and improve treatment of patients.
Patient/organ geometrical and morphological variations during the course of lung cancer radiotherapy have been well understood. Among all variations, the most significant one is organ position baseline variation. Study has shown that inter-treatment target baseline variation can be minimized efficiently using daily free breathing cone beam CT imaging location and patient repositioning. However, the relative position variation between target and normal organs, the dose response related organ volume variation, as well as intra-treatment motion pattern variations, cannot be easily corrected by repositioning the patient. Therefore, treatment feedback and adaptive planning modification become necessary in the motion management of lung cancer radiotherapy. Clinical process of 4D adaptive radiotherapy contains four major components. These are treatment dose construction, motion verification/identification, treatment position correction/planning modification decisions, and 4D adaptive planning. The first two components assess treatment dose and patient geometric variation, and provide feedbacks to the modification decisions and 4D adaptive planning. The sub-process of modification decisions contains a set of pre-design decision rules or control laws. These control laws are triggered by the outputs of the verification/identification, and used to determine if the ongoing treatment needs to be modified and what type of modification needs to take place. Two methodologies have been used for 4D adaptive planning, which are patient-specific planning target construction and 4D inverse planning. Internal target volume (ITV) is probably the earliest technique in constructing patient-specific target volume to compensate for target motion. However, this method only includes motion geometric information in the construction without considering patient specific dose distribution, therefore the target margin has not been optimized. In contrast, a recent development in patient-specific target margin construction includes motion probability density function (pdf) directly in the 4D dose evaluation; therefore individual dose distribution is considered in the target margin design. Utilizing a pre-estimated patient motion pdf, treatment plan can also be optimized by modulating beam intensity with respect to 4D cumulative dose distribution. Concept of utilizing non-uniform beam intensity to compensate for temporal displacements of target position has been pointed out long time ago, however it has not been implemented until recent years. Process of designing beam intensity by including patient motion pdf in the dose calculation and inverse planning has been called 4D inverse planning. The principle of 4D inverse planning is to include the frequency information of organ displacement, instead of the instant spatial information used for the gating and tracking techniques, into planning optimization. One advantage of this implementation is the improvement in reliability of treatment delivery, however this needs to be carefully evaluated. Current study shows the standard deviation of motion pdf observed during the treatment delivery can be used to determine if a ongoing 4D adaptive treatment plan needs to be modified. In addition, the interplay effect caused by relative motion of MLC and target can
S YMPOSIUM
Adaptive treatment strategies: managing workflow and QA 46 speaker ADAPTIVE RADIOTHERAPY CONCEPT, WORKFLOW AND QA M. Sharpe1 1
M ONDAY, AUGUST 31, 2009
48 speaker ADAPTIVE RADIOTHERAPY CHANGES G. Sanguineti1
TO
PROGRESSIVE
ANATOMICAL
1
J OHN H OPKINS U NIVERSITY, Dept of Radiation Oncology and Molecular Radiation Changes, Baltimore, MD, USA
P RINCESS M ARGARET H OSPITAL AND U NIVERSITY OF TORONTO, Radiation Medicine Program, Toronto, Canada
Image-guidance for radiation therapy (IGRT) has emerged as a vital means of controlling the accuracy and precision of target localization in treatment delivery. In the case of imaging modalities that assess soft-tissues, the ability to direct radiation therapy by frequent imaging also opens the door to assess anatomical changes over the course of treatment. Anatomical changes can include, for example, tumour response to radiation and chemotherapy, variations in organ filling, deformation of the skeleton, weight loss/gain, all of which can alter the relative position and shape of targets and normal tissues and affect the delivery of the dose distribution with the accumulation of each treatment fraction.An "adaptive" treatment would respond, to at least some of this information, by guiding alterations to the treatment plan. The term "Adaptive Radiation Therapy" (ART) has been used to embody strategies that respond to patient setup uncertainties and organ movement, gross anatomical changes, and even physiological changes observed by MRI/MRS and PET. Changes to the treatment plan can mitigate uncertainties that compromise the dose to the target and critical structures or, should it arise, exploit an opportunity to improve normal tissue sparing. It is important to weight the benefit of these opportunities against the risks of introducing errors, reducing treatment efficiency, and increasing workload. The costs and benefits and approach to adaptation can be expected to be highly dependent on the disease site and the overall duration of treatment. The developing concepts of adaptive intervention have broad implications for radiotherapy treatment and the assessment of response. This presentation will review ART concepts, considerations for workflow, and its implications for error management, quality control and quality assurance. The role of imaging and image registration in the assessment of geometric variations and uncertainties will be reviewed, and some of the methods of quantifying uncertainties will be presented. The status of tools for supporting clinical workflow and appropriate quality assurance will be discussed.
Adaptive radiotherapy aims at maintaining the planned dose distribution throughout the whole treatment course. It implies the presence of a planned dose distribution tightly conformed around the target(s) while ‘sparing‘ the surrounding normal structures, the occurrence of significant changes in either the organs at risk (OAR) or the target(s) during the course of radiotherapy to the point that this may translate in a significant deviation of the cumulative delivered dose and the availability of imaging during treatment. The head and neck seems to satisfy the above conditions and therefore it represents a reasonable model.The dose to both the tumor and the OAR may change during a course of fractionated RT as a result of direct or indirect anatomical changes: it has been shown, for example, that the dose to the parotid may increase due their shrinkage and their ‘collapse‘ in the high dose region, or that the dose to the spinal cord may increase after a dramatic reduction in tumor volume. However, while these data prove that tissue modifications take place during RT and may actually impact patient care, several issues still need to be clarified, including a more precise and widespread knowledge of tissue changes during RT, the proper timing for re-planning and the prediction of which patients/regions of interest need to be monitored for changes.At JHU, as part of a quality assurance protocol, we have been collecting weekly KV (planning) CT scans for all oropharyngeal cancer patients treated with dose painting IMRT since early 2008. So far, we have acquired serial scans for 49 patients. The purpose of the present lecture is to critically discuss the topic, summarize the available data on progressive changes of OAR during treatment along with our own data in terms of volumetric and dosimetric changes. 49 speaker 4D ADAPTIVE MANAGEMENT FOR PATIENT RESPIRATORY MOTION D. Yan1 1 W ILLIAM B EAUMONT H OSPITAL, Radiation Oncology, Royal Oak MI, USA
47 speaker ADAPTIVE RADIOTHERAPY TO ACCOUNT FOR GEOMETRIC DISCREPANCIES J. Nijkamp1 1
A NTONI VAN L EEUWENHOEK H OSPITAL , N ETHERLANDS C ANCER I NSTI Radiation Oncology, Amsterdam, Netherlands
TUTE,
With more and more availability of volumetric in-room imaging equipment like cone-beam CT, tomotherapy and in future the incorporated MR systems a large amount of data is available during the course of treatment. The images can be used for online correction of patients, minimizing both systematic and random errors. This is, however, only reducing the simplest geometric discrepancies, shifts.For more complex discrepancies, such as rotations and deformations, adaptive radiotherapy (ART) strategies can be used to estimate and minimize systematic errors during the course of treatment, allowing for margin reduction or coverage increase.The concept of ART has been around for more than 8 years, but the use of it in clinics around the world is, however, limited. On one hand it is time consuming because re-contouring and replanning is almost always involved. On the other side the lack of widely available clinical software for the entire ART chain is also not really helping. The main condition for the use of adaptive strategies is that residual systematic errors after the procedure are significantly smaller than the initial systematic error and that still a relative large portion of the treatment needs to be given after the procedure. The margin reduction should always be balanced with the effort and imaging dose involved.Examples in which ART strategies have an added value are prostate cancer and rectal cancer. During prostate treatment systematic rotations around the LR axis in the order of 6 dg can occur. Estimating and correcting this error after 1 week of treatment can result in residual errors in the order of 2 dg. During treatment of rectal cancer systematic CTV shape change in the order of 7 mm SD are found at the border with the bladder/uterus/small bowel. Proper treatment margins should therefore be in the order of 20 mm. Estimating an average CTV shape after 5 of the 25 fractions results in a reduction of the needed margin of approximately 5 mm. With the small bowel being the main organ at risk, major improvement in the treatment can be appreciated. Auto-contouring of target volumes, faster plan optimizers and good cooperation with vendors is needed to further develop ART strategies and improve treatment of patients.
Patient/organ geometrical and morphological variations during the course of lung cancer radiotherapy have been well understood. Among all variations, the most significant one is organ position baseline variation. Study has shown that inter-treatment target baseline variation can be minimized efficiently using daily free breathing cone beam CT imaging location and patient repositioning. However, the relative position variation between target and normal organs, the dose response related organ volume variation, as well as intra-treatment motion pattern variations, cannot be easily corrected by repositioning the patient. Therefore, treatment feedback and adaptive planning modification become necessary in the motion management of lung cancer radiotherapy. Clinical process of 4D adaptive radiotherapy contains four major components. These are treatment dose construction, motion verification/identification, treatment position correction/planning modification decisions, and 4D adaptive planning. The first two components assess treatment dose and patient geometric variation, and provide feedbacks to the modification decisions and 4D adaptive planning. The sub-process of modification decisions contains a set of pre-design decision rules or control laws. These control laws are triggered by the outputs of the verification/identification, and used to determine if the ongoing treatment needs to be modified and what type of modification needs to take place. Two methodologies have been used for 4D adaptive planning, which are patient-specific planning target construction and 4D inverse planning. Internal target volume (ITV) is probably the earliest technique in constructing patient-specific target volume to compensate for target motion. However, this method only includes motion geometric information in the construction without considering patient specific dose distribution, therefore the target margin has not been optimized. In contrast, a recent development in patient-specific target margin construction includes motion probability density function (pdf) directly in the 4D dose evaluation; therefore individual dose distribution is considered in the target margin design. Utilizing a pre-estimated patient motion pdf, treatment plan can also be optimized by modulating beam intensity with respect to 4D cumulative dose distribution. Concept of utilizing non-uniform beam intensity to compensate for temporal displacements of target position has been pointed out long time ago, however it has not been implemented until recent years. Process of designing beam intensity by including patient motion pdf in the dose calculation and inverse planning has been called 4D inverse planning. The principle of 4D inverse planning is to include the frequency information of organ displacement, instead of the instant spatial information used for the gating and tracking techniques, into planning optimization. One advantage of this implementation is the improvement in reliability of treatment delivery, however this needs to be carefully evaluated. Current study shows the standard deviation of motion pdf observed during the treatment delivery can be used to determine if a ongoing 4D adaptive treatment plan needs to be modified. In addition, the interplay effect caused by relative motion of MLC and target can