Journal of the ICRU Vol 10 No 1 (2010) Report 83 Oxford University Press
doi:10.1093/jicru/ndq005
Executive Summary isocentric delivery of multiple small beams (beamlets) of non-uniform intensity. Hence, effective treatment planning for IMRT is quite demanding and is performed in 3D in an iterative manner based on 3D images of the volume to be treated. Such approaches require that traditional ICRU recommendations for prescribing, recording, and reporting of treatments be adapted and expanded. This Report discusses such recommendations in detail. A special emphasis is placed upon the use of dose –volume histograms (DVHs) in reporting and recording. This Report recommends that a CTV should always be associated with the GTV for malignant tumors. In postoperative irradiation, often only a CTV is delineated. The selection of the CTV should be based on the knowledge of the probability of microscopic tumor infiltration into the surrounding normal tissues and/or nodes; the delineation of the CTV should result from the knowledge of the anatomical pathways for tumor infiltration and dissemination. In IMRT, organs or structures that are not delineated can receive significant radiation absorbed doses. Contouring organs at risk (OAR) is the first step to control the dose in normal tissues, which might cause unacceptable complications. For so-called “parallel-like organs,” the whole organ should be entirely delineated. For so-called “seriallike organs,” those parts of the organ that could receive a high dose should be delineated in a consistent way. For tubular types of organ (e.g., the rectum), delineation of the wall is preferred to whole-organ delineation. Especially for a serial-like organ, a planning organ at risk volume (PRV) should be delineated around the OAR. Tissues not included in the CTV or not delineated as doselimiting OARs should still be specifically delineated and named the remaining volume at risk (RVR). Dose –volume constraints applied to the RVR avoid unsuspected regions of high dose. In addition, the absorbed dose to the RVR can be useful in estimating the risk of late effects, such as carcinogenesis. Numerous recent publications note that the PTV and PRV margins should be based on clinical measurements. Not surprisingly, these results indicate
# International Commission on Radiation Units and Measurements 2010
Downloaded from http://jicru.oxfordjournals.org/ at East Carolina University on April 25, 2015
The advent of intensity-modulated radiation therapy (IMRT) is rapidly changing the field of external-beam radiation therapy. Using computerbased optimization techniques to allow IMRT to comply with user-specified absorbed-dose and dose – volume constraints in specified target volumes as well as in normal tissues, IMRT allows a dramatic customization of the three-dimensional (3D) dose distribution. Quite often reductions of absorbed dose in critical organs at risk means that the targeted region can be exposed to escalated levels of radiation for the same level of normaltissue toxicity. The advantages for curative treatment and even for some palliative treatments are readily apparent. Historical evidence generally indicates improved tumor control and decreased morbidity whenever an improvement of the ratio tumor-to-normal-tissue dose was achieved. Intensity-modulated radiation therapy requires the precise selection and delineation of the various anatomic volumes based on 3D volume imaging. Moreover, treatment-planning systems must now integrate various imaging modalities, including functional imaging for planning, not only before the start of treatment, but also during treatment to allow the adaptation of the absorbed-dose distribution to the desired and possibly changing target volumes. The concepts of gross tumor volume (GTV) and clinical target volume (CTV) remain of critical importance. Gross tumor volumes are delineated on a 3D basis using clinical (e.g., physical examination), anatomical (e.g., CT, MRI), and/or functional-imaging modalities (e.g., PET, functional MRI). Intensitymodulated radiation therapy easily accommodates the delineation and treatment of multiple GTVs. The GTVs can be delineated before the start of treatment and at various times during treatment. However, the nomenclature used should clearly reflect the possibility of having various GTVs by using unambiguous annotations. The use of terminology such as biological target volume, proliferative target volume, and hypoxic target volume is not recommended and is not discussed in this Report. For indirectly ionizing beams such as photons, IMRT is implemented most commonly by the
PRESCRIBING, RECORDING, AND REPORTING PHOTON-BEAM IMRT
straightforward manner. The minimum and maximum absorbed doses are not recommended for reporting, but are replaced by the near-minimum, D98 %, and near-maximum, D2 %, values. The report recommends that the median absorbed dose, specified by D50 %, should be reported, as it is considered to correspond best with the previously defined dose at the ICRU reference point. Three clinical examples included in the Report illustrate the use of recommendations contained within this Report. Intensity-modulated radiation therapy places significant demands on all aspects of quality assurance, from the acquisition of appropriate 3D images, through the absorbed-dose optimization process, to beamlet delivery and verification. Appropriate quality assurance should be performed to ensure that the planning and treatment equipment is functioning within the tolerances required for IMRT. Quality assurance in IMRT is demanding and relates to or involves all aspects of the clinical situation, the clinical experience, and the goals of the treatment. Appropriate patient-specific quality control is necessary to ensure that the patient receives the prescribed dose as accurately as possible. These criteria do not replace visual inspection of the calculated dose distribution to determine if there is significantly higher or lower dose to a small fraction of the volume irradiated. Several methods of obtaining comparative absorbed-dose samples are recommended, but a clinic should employ a variety of methods and not rely on a single system of patient-specific quality control. Finally, the previous ICRU recommendation of 5 % absorbed-dose accuracy is replaced by a statistical measure. This Report recommends that in lowgradient situations, defined as a relative change of absorbed dose that is less than 20 %/cm in any direction, that 85 % of target-volume absorbed-dose samples should be within 5 %. For high gradients, defined to be relative changes of absorbed dose that are greater than or equal to 20 %/cm, the use of distance to agreement is recommended instead of absorbed-dose accuracy. In high-gradient regions, the dose distribution should have 85 % of absorbeddose samples within 5 mm of the intended position. As cancer is a disease that will be a major health factor for the remaining life of the patient, it is recommended to record and retain the parameters to describe the absorbed-dose distribution in the patient for at least the life of the patient plus a minimum of 5 years or in accordance with local regulatory requirements. In addition to the requirements relevant to patient care, for clinical trials all of the parameters describing the absorbed-dose distribution in the patient should be retained as long as scientifically needed. 6
Downloaded from http://jicru.oxfordjournals.org/ at East Carolina University on April 25, 2015
that systematic uncertainties have more impact on the accuracy of absorbed dose delivered to the patient than do random uncertainties. This Report strongly recommends that the margins not be compromised when delineating the PTV or PRV, even in those situations in which these volumes might encroach on an OAR or CTV. Moreover, the report describes optimization techniques, which can control the compromise of absorbed-dose homogeneity in the PTV with dose reduction in the PRV. The IMRT treatment-planning process uses a complex iterative computer-based optimization process. The so-called optimizer serves to convert the radiation oncologist’s treatment goals into a set of beamlets of specified intensities and directions for delivery of the planned treatment. This Report designates the set of treatment goals as the “planning aims” to differentiate them from the “prescription.” A detailed example is used to guide this discussion. Unlike three-dimensional conformal therapy (3D-CRT), IMRT does not deliver absorbed dose in all of the target volume concurrently. Hence, IMRT delivered to organs in motion, such as lungs, or to organs that change volume or location between fractions can generate regions of high and low absorbed dose in the CTV, even though a generous PTV margin has been established. Such challenges are more important for IMRT than for conventional irradiation techniques due to the very high dose gradients IMRT can achieve. In addition, sparing of OARs might also introduce regions of non-uniformity in the PTV. Intensity-modulated radiation therapy has gained prominence because it allows a lower dose to neighboring sensitive normal tissues even though it can sometimes result in less dose homogeneity to the tumor. Although the absorbed dose in normal tissue might be lower than in 3D-CRT, it can be distributed over larger volumes. In this Report, recommendations concerning absorbed-dose reporting evolved from previous ICRU recommendations while attempting to retain a relationship with the previous recommendations. Dose-reporting recommendations are adapted to IMRT and to the changing technological advances, such as DVHs, and thus allow the decades of clinical experience in conventional therapy to be interpreted in the context of IMRT. The move from single-point to volume-based absorbed-dose specification is possible because of modern imaging and computer technology, and is essential for IMRT. This Report therefore recommends dose – volume-based specification of absorbed dose. This is most easily accomplished by employing the concept of DVHs. By a logical and careful choice of these reporting parameters, the connection with previous ICRU recommendations can be maintained in a fairly
doi:10.1093/jicru/ndq005
Executive Summary isocentric delivery of multiple small beams (beamlets) of non-uniform intensity. Hence, effective treatment planning for IMRT is quite demanding and is performed in 3D in an iterative manner based on 3D images of the volume to be treated. Such approaches require that traditional ICRU recommendations for prescribing, recording, and reporting of treatments be adapted and expanded. This Report discusses such recommendations in detail. A special emphasis is placed upon the use of dose –volume histograms (DVHs) in reporting and recording. This Report recommends that a CTV should always be associated with the GTV for malignant tumors. In postoperative irradiation, often only a CTV is delineated. The selection of the CTV should be based on the knowledge of the probability of microscopic tumor infiltration into the surrounding normal tissues and/or nodes; the delineation of the CTV should result from the knowledge of the anatomical pathways for tumor infiltration and dissemination. In IMRT, organs or structures that are not delineated can receive significant radiation absorbed doses. Contouring organs at risk (OAR) is the first step to control the dose in normal tissues, which might cause unacceptable complications. For so-called “parallel-like organs,” the whole organ should be entirely delineated. For so-called “seriallike organs,” those parts of the organ that could receive a high dose should be delineated in a consistent way. For tubular types of organ (e.g., the rectum), delineation of the wall is preferred to whole-organ delineation. Especially for a serial-like organ, a planning organ at risk volume (PRV) should be delineated around the OAR. Tissues not included in the CTV or not delineated as doselimiting OARs should still be specifically delineated and named the remaining volume at risk (RVR). Dose –volume constraints applied to the RVR avoid unsuspected regions of high dose. In addition, the absorbed dose to the RVR can be useful in estimating the risk of late effects, such as carcinogenesis. Numerous recent publications note that the PTV and PRV margins should be based on clinical measurements. Not surprisingly, these results indicate
# International Commission on Radiation Units and Measurements 2010
Downloaded from http://jicru.oxfordjournals.org/ at East Carolina University on April 25, 2015
The advent of intensity-modulated radiation therapy (IMRT) is rapidly changing the field of external-beam radiation therapy. Using computerbased optimization techniques to allow IMRT to comply with user-specified absorbed-dose and dose – volume constraints in specified target volumes as well as in normal tissues, IMRT allows a dramatic customization of the three-dimensional (3D) dose distribution. Quite often reductions of absorbed dose in critical organs at risk means that the targeted region can be exposed to escalated levels of radiation for the same level of normaltissue toxicity. The advantages for curative treatment and even for some palliative treatments are readily apparent. Historical evidence generally indicates improved tumor control and decreased morbidity whenever an improvement of the ratio tumor-to-normal-tissue dose was achieved. Intensity-modulated radiation therapy requires the precise selection and delineation of the various anatomic volumes based on 3D volume imaging. Moreover, treatment-planning systems must now integrate various imaging modalities, including functional imaging for planning, not only before the start of treatment, but also during treatment to allow the adaptation of the absorbed-dose distribution to the desired and possibly changing target volumes. The concepts of gross tumor volume (GTV) and clinical target volume (CTV) remain of critical importance. Gross tumor volumes are delineated on a 3D basis using clinical (e.g., physical examination), anatomical (e.g., CT, MRI), and/or functional-imaging modalities (e.g., PET, functional MRI). Intensitymodulated radiation therapy easily accommodates the delineation and treatment of multiple GTVs. The GTVs can be delineated before the start of treatment and at various times during treatment. However, the nomenclature used should clearly reflect the possibility of having various GTVs by using unambiguous annotations. The use of terminology such as biological target volume, proliferative target volume, and hypoxic target volume is not recommended and is not discussed in this Report. For indirectly ionizing beams such as photons, IMRT is implemented most commonly by the
PRESCRIBING, RECORDING, AND REPORTING PHOTON-BEAM IMRT
straightforward manner. The minimum and maximum absorbed doses are not recommended for reporting, but are replaced by the near-minimum, D98 %, and near-maximum, D2 %, values. The report recommends that the median absorbed dose, specified by D50 %, should be reported, as it is considered to correspond best with the previously defined dose at the ICRU reference point. Three clinical examples included in the Report illustrate the use of recommendations contained within this Report. Intensity-modulated radiation therapy places significant demands on all aspects of quality assurance, from the acquisition of appropriate 3D images, through the absorbed-dose optimization process, to beamlet delivery and verification. Appropriate quality assurance should be performed to ensure that the planning and treatment equipment is functioning within the tolerances required for IMRT. Quality assurance in IMRT is demanding and relates to or involves all aspects of the clinical situation, the clinical experience, and the goals of the treatment. Appropriate patient-specific quality control is necessary to ensure that the patient receives the prescribed dose as accurately as possible. These criteria do not replace visual inspection of the calculated dose distribution to determine if there is significantly higher or lower dose to a small fraction of the volume irradiated. Several methods of obtaining comparative absorbed-dose samples are recommended, but a clinic should employ a variety of methods and not rely on a single system of patient-specific quality control. Finally, the previous ICRU recommendation of 5 % absorbed-dose accuracy is replaced by a statistical measure. This Report recommends that in lowgradient situations, defined as a relative change of absorbed dose that is less than 20 %/cm in any direction, that 85 % of target-volume absorbed-dose samples should be within 5 %. For high gradients, defined to be relative changes of absorbed dose that are greater than or equal to 20 %/cm, the use of distance to agreement is recommended instead of absorbed-dose accuracy. In high-gradient regions, the dose distribution should have 85 % of absorbeddose samples within 5 mm of the intended position. As cancer is a disease that will be a major health factor for the remaining life of the patient, it is recommended to record and retain the parameters to describe the absorbed-dose distribution in the patient for at least the life of the patient plus a minimum of 5 years or in accordance with local regulatory requirements. In addition to the requirements relevant to patient care, for clinical trials all of the parameters describing the absorbed-dose distribution in the patient should be retained as long as scientifically needed. 6
Downloaded from http://jicru.oxfordjournals.org/ at East Carolina University on April 25, 2015
that systematic uncertainties have more impact on the accuracy of absorbed dose delivered to the patient than do random uncertainties. This Report strongly recommends that the margins not be compromised when delineating the PTV or PRV, even in those situations in which these volumes might encroach on an OAR or CTV. Moreover, the report describes optimization techniques, which can control the compromise of absorbed-dose homogeneity in the PTV with dose reduction in the PRV. The IMRT treatment-planning process uses a complex iterative computer-based optimization process. The so-called optimizer serves to convert the radiation oncologist’s treatment goals into a set of beamlets of specified intensities and directions for delivery of the planned treatment. This Report designates the set of treatment goals as the “planning aims” to differentiate them from the “prescription.” A detailed example is used to guide this discussion. Unlike three-dimensional conformal therapy (3D-CRT), IMRT does not deliver absorbed dose in all of the target volume concurrently. Hence, IMRT delivered to organs in motion, such as lungs, or to organs that change volume or location between fractions can generate regions of high and low absorbed dose in the CTV, even though a generous PTV margin has been established. Such challenges are more important for IMRT than for conventional irradiation techniques due to the very high dose gradients IMRT can achieve. In addition, sparing of OARs might also introduce regions of non-uniformity in the PTV. Intensity-modulated radiation therapy has gained prominence because it allows a lower dose to neighboring sensitive normal tissues even though it can sometimes result in less dose homogeneity to the tumor. Although the absorbed dose in normal tissue might be lower than in 3D-CRT, it can be distributed over larger volumes. In this Report, recommendations concerning absorbed-dose reporting evolved from previous ICRU recommendations while attempting to retain a relationship with the previous recommendations. Dose-reporting recommendations are adapted to IMRT and to the changing technological advances, such as DVHs, and thus allow the decades of clinical experience in conventional therapy to be interpreted in the context of IMRT. The move from single-point to volume-based absorbed-dose specification is possible because of modern imaging and computer technology, and is essential for IMRT. This Report therefore recommends dose – volume-based specification of absorbed dose. This is most easily accomplished by employing the concept of DVHs. By a logical and careful choice of these reporting parameters, the connection with previous ICRU recommendations can be maintained in a fairly
