Process

On this page

1. Introduction
2. Pre-treatment imaging and simulation
3. Treatment planning - External Beam RT
4. Treatment planning - IMRT
5. Treatment planning - Special techniques
6. Treatment planning - Brachytherapy
7. Treatment delivery - External beam radiotherapy (3D-CRT, IMRT/VMAT, SRT)
8. Treatment delivery - Brachytherapy
9. Treatment delivery - IGRT and respiratory/organ motion management
10. Total body irradiation (TBI)
11. Management of non-standard situations - Fetal dose
12. Management of non-standard situations - Pacemakers and ICDs
13. Management of non-standard situations - Hip prostheses

Pre-treatment imaging and simulation

Patient data acquisition is an important part of the RT process, since reliable data are required for treatment planning purposes and allow for a treatment plan to be properly carried out. Patient data acquisition includes identification of the target volumes and OARs, determination of patient treatment position, determination and verification of treatment field geometry, and the generation of radiographs or DRRs for each treatment beam for comparison with portal images. For this purpose dedicated equipment for radiotherapy simulation has been developed. Conventional simulation systems are based on treatment unit geometry in conjunction with diagnostic radiography and fluoroscopy systems. Modern CT simulation systems are based on CT images using special software, often available in a 3D treatment planning system.

Important principles

Patient data requirements for treatment planning include outlining the external shape of the patient for all areas where the beams enter and exit, and in adjacent areas. Targets and internal structures must be outlined in order to determine their shape and volume for dose calculation. Electron densities for each volume element in the dose calculation matrix must be determined if a correction for heterogeneities is to be applied. Transverse CT scans contain all information required for complex treatment planning and form the basis of CT-simulation in modern radiotherapy treatment. Immobilization devices serve not only to immobilize the patient during treatment, but also provide a reliable means of reproducing the patient position from treatment planning and simulation to treatment, and from one treatment to another.

Introduction to references

A general discussion of the various aspects of treatment preparation including patient data acquisition, simulation and immobilization is presented in Chapter 7 of the IAEA Radiation Oncology Physics Handbook.

Treatment planning - External Beam RT

The process of radiation treatment for cancer patients involves many steps. One crucial step in this process is the preparation of  the optimal treatment plan that will deliver a high dose to the diseased volume and an acceptable dose to  healthy tissues which may be at risk for complications. Treatment planning includes the use of 3-dimensional imaging to determine the precise location of the malignant disease as well is the critical structures to be avoided. Usually this involves CT scanning but other imaging modalities such as magnetic resonance imaging (MRI), positron emission tomography (PET), single photon emission tomography (SPECT), or ultrasound may aid this process as well. Once the target volume and normal tissues have been delineated, the optimum beam arrangement is determined using a treatment planning computer with sophisticated radiation dose calculation software.

Important principles

An important aspect of treatment planning includes accurate patient positioning such that the treatment set-up is reproducible from the imaging device to the therapy machine and then for each daily treatment fraction. In the treatment planning computer, the dose calculation algorithm must be able to predict the dose delivered to the tumour and different normal tissues accurately. Furthermore, with modern therapy machines that are capable of beam intensity modulation, the beam directions need to be determined and automated optimization routines must be capable of providing the best multileaf collimator configurations. Plan evaluation is usually performed with the use of dose-volume histograms (DVH).

Introduction to references

Chapter 7 of the IAEA Handbook for Teachers and Students gives a good summary of the various activities involved in the treatment planning process. IAEA TRS-430 and in AAPM TG-53 have treatment planning process summaries and contain the details of the acceptance, commissioning and quality assurance of radiation treatment planning systems.

Treatment planning - IMRT

Intensity modulated radiation therapy (IMRT) involves the use of radiation beams in which the intensity of parts of the beam are varied during the patient irradiation procedure. The intensity can be varied by the use of beam modifying filters, or the shapes of a multileaf collimator (MLC) are changed during the irradiation.  The result is a highly conformal dose distribution which covers the target volume with a relatively tight margin. The net effect is that less normal tissue gets irradiated allowing for the possibility of increasing the tumour dose and thereby increasing the probability of tumour control.

Important principles

IMRT requires the use of a treatment planning system that has inverse planning capabilities. Because of the very high number of beam shapes that may be used for IMRT delivery with an MLC, it is impractical to perform manual optimization. By giving specific dose-volume constraints for the target volume and critical tissues, the inverse planning system automatically determines the best dose delivery configuration. In addition, because of the complexity of the treatment techniques, individualized dose verification is required for each patient. This can be done by recalculating the patient dose delivery technique for a phantom of known composition and shape and performing measurements in that phantom for that specific patient dose delivery technique. It can also be done by using verification software that is totally independent of the software used by the treatment planning system.

Introduction to references

Chapter 15 of the IAEA Radiation Oncology Physics Handbook gives a brief summary of the use of MLC and IMRT. The report by the AAPM IMRT subcommittee gives guidance to the medical physicist in developing and implementing a viable and safe IMRT program.

Treatment planning - Special techniques

Computerized radiation treatment planning systems are generally generic in nature in that they are capable of handling multiple treatment techniques for both external beam therapy and brachytherapy. However, complex procedures have evolved that require the use of specialized, stand-alone treatment planning computers. In addition, there are various clinical procedures that also require special consideration. Examples include:  total body irradiation (TBI) with photons; stereotactic radiosurgery with a linac or Gamma Knife; tomotherapy; intraoperative radiation therapy; electron beam arc therapy; and total skin electron irradiation (TSEI).

Important principles

If a generic treatment planning system is to be used for a special technique then a unique commissioning program must be employed. Special measurements are required and an evaluation of the capabilities and limitations of that technique must be performed. For example, a total body irradiation procedure should be evaluated under the extended distance treatment that is used clinically to generate the appropriate large-field radiation data. Similarly, small field dosimetry must be performed with appropriately sized radiation detectors and evaluated for stereotactic radiosurgery. For techniques requiring specialized computer systems, a unique acceptance, commissioning and QA process will be required.

Introduction to references

The IAEA Radiation Oncology Physics Handbook provides a summary of special procedures in radiation therapy. Several AAPM reports provide guidance on total and half body photon irradiation, total skin electron therapy, stereotactic radiosurgery and stereotactic body radiation therapy.

Radiation Knowledge: International Radiotherapy Plan Competition

https://humanhealth.iaea.org/HHW/MedicalPhysics/Training_Events/Othertra...

Treatment planning - Brachytherapy

Brachytherapy involves the placement of radioactive sources in or near tissue, usually for the treatment of cancer. The sources can be placed on top of the tissue (surface or mould), in the tissue (interstitial), in a lumen (intraluminal), in a cavity (intracavitary). They can be used  during an operation (intraoperative) that involves surgical removal of diseased tissue with subsequent irradiation of tissues at risk, or in a blood vessel (intravascular) with the source being placed in or close to the lesion. Some sources could be left in for a specified length of time (temporary implants) while others are applied as a permanent implant. The sources could be loaded manually or using a remote control afterloading device. The irradiation could be given by high dose rate (HDR) or a low dose rate (LDR) sources.

Important principles

Computerized treatment planning for brachytherapy is done by specialized systems designed for HDR treatments or using more generalized radiation treatment planning systems. Brachytherapy treatment planning always involves some form of source localization with respect to the tissues to be irradiated, either using 90 degree or oblique radiographs or using 3-D  image data sets. The dose calculation algorithms tend to be less sophisticated than those used for external beam planning since the geometrical dispersion of photons is the predominate cause of the shape of the dose distribution.

Introduction to references

Chapter 13 of the IAEA Handbook for Teachers and Students gives a good overview the physical and clinical aspects of brachytherapy. The report by the AAPM Task Group 56 provides a brachytherapy code of practice.The IAEA Human Health Reports No. 12 provides guidance on 3-D image based brachytherapy.

Treatment delivery - External beam radiotherapy (3D-CRT, IMRT/VMAT, SRT)

Intensity-modulated radiotherapy (IMRT)

IMRT is a 3D conformal radiotherapy technique, which applies multiple beams with optimized intensity-modulated fluence distributions. The optimal modulated intensity for each beam is determined through the dose optimization process, referred to as inverse planning, incorporating dose criteria not only for the target volume but also for the neighboring organs at risk. IMRT is generally delivered with MLC-equipped linacs using either a static or a dynamic approach with moving leaves. In the latter approach the beams can be delivered without, or concurrently with gantry rotation (intensity-modulated arc therapy, IMAT). A set of commissioning and QA tests specific to the IMRT planning and delivery equipment, as well as treatment techniques applied in a particular institute, must be implemented before its clinical routine use.

Important principles

The routine clinical application of IMRT requires detailed knowledge of the software used for inverse treatment planning, the equipment used for dose delivery, quality assurance issues related to the dose distribution optimization process and the dose delivery process. It is recommended to carry out a verification of all IMRT plans; at least until the entire IMRT team is comfortable with the planning and treatment delivery process. Such a QA programme must include verification of linac radiation output as well as tests of the MLC positioning and movement.

Introduction to references

A large number of publications on IMRT are available dealing with the various aspects of IMRT. An introduction to and overview of the topic can be found in the AAPM document , the IAEA Handbook, J. Van Dyk's Compendium, and the Handbook of Radiotherapy Physics. A comprehensive discussion of both physical and clinical aspects of IMRT is provided in the books edited by Bortfeld et al. and Meyer, and in the IPEM Report. QA of IMRT is discussed extensively in the ESTRO booklet and the recent AAPM Report.

Treatment delivery - Brachytherapy

A treatment protocol has to be established for each individual tumour site to be treated by brachytherapy, which should include information on the applicators and specific equipment needed for the procedure. Before a brachytherapy treatment starts a number of checks have to be performed, which concern the treatment plan, the sources and the delivery equipment used for that particular patient treatment. The mechanical integrity of the system should also be checked regularly.

Important principles

After creating the treatment plan the radiation oncologist has to check that the correct source-applicator combination has been chosen, and that the dose distribution is in accordance with the prescription. The total irradiation time should also be checked to ensure that it is reasonable for the proposed insertion. Subsequent to transfer of the planning data to the brachytherapy unit, they have to be checked for consistency and validity. Following the connection of the applicators to the afterloading unit, the correspondence of the applicators with the treatment plan has to be verified. It is especially important to ensure that the actual source to be loaded (type, strength) has the correct parameters in the treatment planning system. The dose per fraction and the step length have to be verified and the correct values of dwell locations and dwell times have to be checked for each channel.

Introduction to references

Many patient-related QA aspects of brachytherapy are described in reports of national and international organizations as reviewed in the ESTRO Booklet. More general information can be found in the IAEA Radiation Oncology Physics Handbook.

Treatment delivery - IGRT and respiratory/organ motion management

IGRT is the process of using images after the initial plan has been established, and making decisions based on these images with respect to the remainder of the treatment process. IGRT is generally applied within the treatment room during a course of radiotherapy, and can be 2D, 3D or 4D. IGRT reduces the chance of geographical miss of the target and allows reduced treatment margins in the planning target volume (PTV), which may result in fewer treatment complications, and permits dose escalation.

Respiratory motion has a significant effect on the dose delivery to targets in the chest and upper abdominal cavities. To compensate for these effects relatively large margins are added to a clinical target volume (CTV), thus limiting the maximum dose delivery to these patients. Respiratory motion management may reduce the margin around a moving CTV, but is also appropriate when the procedure will increase normal tissue sparing. To account for organ motion 4D imaging technology was developed, which allows viewing of volumetric CT images changing over the fourth dimension: time. The next step is creating a 4D plan from a 4D CT set in which the tumour motion is taken into account using one of the strategies that is available to compensate for respiratory motion. The technologies mostly applied are motion-encompassing methods, respiratory gated techniques, breath-hold techniques, forced shallow-breathing methods, and respiration-synchronized techniques.

Important principles

IGRT solutions can be categorized by beam quality, i.e., whether they are based on MV or kV beams, and by beam collimation, i.e., whether they are cone-beam or fan-beam solutions. 2D IGRT systems are available based on integration of a linac with paired orthogonal planar imagers. 3D kV-imaging of the patient in treatment position directly prior to treatment is one of the most common 3D IGRT procedures currently performed in clinical practice. As the actual treatment beam is used for imaging, 3D MV-based solutions provide the most direct geometric information concerning the alignment of treatment beam and the target volume. On the other hand, MV-based solutions will inherently be inferior to kV-based solutions as the latter provides better soft-tissue contrast. Other approaches include 2D or 3D ultrasound systems.

Firstly, tumour motion should be measured for each patient for whom respiratory motion is a concern. Then a choice has to be made between one of the interventional strategies taking into account the tolerance of the patient to a specific approach and the resources available in the department. Respiratory motion management generally involves advanced equipment, education and training in the use of complex technology, and the implementation of a dedicated QA programme.

Introduction to references

IGRT has been discussed in detail in the Report of the Consultant’s meeting and in the ESTRO-EIR Report. More information on IGRT techniques can be found in J. Van Dyk's Compendium, in the IAEA Handbook, and in the books edited by Bortfeld et al. and Meyer. The IPEM Report describes a number of evidence-based practices for geometric verification, and provides guidelines how individual centres may implement geometric verification processes locally. In 2009, the American College of Radiology published practice guidelines and technical standard for IGRT. The IAEA has prepared a short questionnaire to assist radiotherapy departments in gauging their readiness to undertake IGRT

An introduction to and overview of 4D treatment planning and 4D IMRT delivery are provided in the textbook on Image-Guided IMRT by Bortfeld et al. Management of respiratory motion in RT has been discussed in detail in the AAPM Report and in J. Van Dyk's Compendium, and briefly in the IAEA Handbook.

Total body irradiation (TBI)

Total body irradiation (TBI) is a special radiotherapeutic technique that delivers to a patient’s whole body a uniform dose using megavoltage photon beams. Such large field techniques encompass irradiation of the whole body, half body irradiation and total nodal irradiation. TBI is used primarily as part of a preparatory cytoreductive conditioning regimen prior to bone marrow transplantation. TBI is a complex treatment modality requiring strict adherence to specific quality assurance protocols, and often includes in vivo dosimetry at several locations on the patient’s body.

Total Skin Electron Irradiation (TSEI) is a special radiotherapeutic technique that aims to irradiate the patient’s whole skin while sparing all other organs from any appreciable radiation dose. Since the skin is a superficial organ, the choice of electron beams for treatment of generalized skin malignancies (most often mycosis fungoides) is obvious. The patient population requiring TSEI is relatively small and the TSEI techniques are relatively complex and cumbersome, therefore the TSEI technique is available only in specialised radiotherapy centres. All contemporary TSEI procedures are based on linacs which are used for conventional radiotherapy and modified for delivery of the large and uniform electron fields required for the TSEI.

Important principles

Cobalt-60 gamma rays or megavoltage x rays are used for TBI, applying either stationary beams with field sizes encompassing the whole patient, or moving beams with smaller field sizes in translational or rotational motion to cover the whole patient. Usually parallel-opposed irradiations are used and the patient’s position is switched between the two irradiations. TBI treatment techniques are carried out with treatment machines specially designed for total body irradiation, or by using conventional megavoltage radiotherapy equipment at large SSD. The TBI dose is generally prescribed to the midpoint at the level of the umbilicus. Uniformity of dose throughout the body is achieved with the use of bolus, partial attenuators, and compensators. Because the lung is an organ at risk, often additional lung shielding is applied during TBI.

Patients are generally treated with multiple large electron beams by rotating them in a large electron field. Various techniques involving beam spoilers or special filters are used to produce the large, clinical electron beam at an extended SSD. Bremsstrahlung contamination of the electron beam, a potential detriment to the patient, must be known for each TSEI technique to ensure that the total prescribed electron dose is not accompanied by an unacceptably high total body photon dose. Certain areas of the patient’s skin as well as some organs (such as nails and eyes) may have to be shielded in order to avoid treatment morbidity.

Introduction to references

Various aspects of early techniques of TBI, including requirements for a QA programme, were summarised in the initial AAPM Report. More recent developments in the field of TBI can be found in J. Van Dyk’s Compendium, the Practical Radiotherapy Planning Textbook, the IAEA Handbook, and the Handbook of Radiotherapy Physics.

The various aspects of the early types of TSEI, including requirements for a QA programme, were summarised in the initial AAPM report. More recent developments in the field of SRT can be found in J. Van Dyk's Compendium, the IAEA Handbook, and the Handbook of Radiotherapy Physics.

Management of non-standard situations - Fetal dose

Radiation is a known teratogen, i.e. causes birth defects, and may induce cancer. The effects of radiation on the fetus depend on the dose to the fetus and the stage of development at the time of exposure. Pregnancy is generally not a contraindication to radiation therapy in patients with cancer remote from the pelvis because appropriate shielding can reduce the fetal dose sufficiently.

Important principles

A crude estimate of the dose to the fetus can be obtained from published data. Because of approximations in these data, discrepancies between calculated estimates and actual measurements may occur. Often a considerable reduction in fetal dose can be obtained by designing a special shield. Shielding material can either be placed on the couch, on a special construction that can be placed over the patient, or positioned on the blocking tray of the linac. It is important to measure in vivo the fetal dose, e.g. at the top of the fundus, the umbilicus, and the symphysis, throughout the expected range of fetal growth. When applying IMRT, an additional step to reduce the fetal dose is to optimize the IMRT treatment plan with as few monitor units as possible.

Introduction to references

The ICRP Report describes the biological effects of radiation on the fetus in detail. The AAPM Report presents data and techniques to estimate the radiation dose the fetus will receive when women are treated with radiotherapy during pregnancy. Designs for simple to more complex types of shielding equipment are also described to reduce the fetal dose with appropriate shielding. The publication of Kry et al. gives practical information complimentary to the AAPM Report, while the paper of Josipović. et al. elucidates the specific problems when applying IMRT treatment techniques.

Management of non-standard situations - Pacemakers and ICDs

Radiotherapy can influence the functioning of pacemakers and implantable cardioverter-defibrillators (ICDs). ICDs offer the same functionality as pacemakers but are also able to deliver a high-voltage shock to the heart if needed. The risk of potentially life-threatening malfunctioning of these devices when exposed to electromagnetic interference or ionizing radiation is well recognized. Modern ICDs show a large variation in their sensitivity to radiation, and seem to be more sensitive to radiation than pacemakers. Electromagnetic effects are usually not considered to be a source of concern.

Important principles

Current management guidelines are mostly based on in vitro studies due to lack of in vivo data. Theses studies showed that most cardiac devices had some kind of malfunction related to RT, some of which could have lead to serious consequences and require reprogramming. Factors determining the impact of RT on implanted devices include: type of device, proximity of the device to the beam, type and energy of the beam, total dose received, and shielding of the device. Clinical recommendations concern to monitor the ECG and have pacemaker/ICD-qualified personnel stand by at every fraction, to have standard cardiopulmonary resuscitation equipment directly available and intensive device follow-up during and/or RT.

Introduction to references

Guidelines for ICDs are provided in the AAPM report 203 and publications of Hurkmans et al. and Gelblum et al.

Management of non-standard situations - Hip prostheses

For patients with metallic hip prosthesis, treatment planning for tumours in the pelvic region (prostate, bladder, rectum, and anus) has to consider the prosthesis material as well as its position and form, if photon beams are administered through the prosthesis. However, knowledge about the prosthesis material may be missing, or the actual geometry may deviate from the assumed one, so that serious under- or over-dosage of the tumour, or an increase in dose in organs at risk, may occur. In order to avoid this risk, it is recommended to design a treatment technique using fields which are not administered through the prosthesis. If such a solution is not possible, then a good estimate has to be made of the influence of the prosthesis on the resulting dose distribution. When the prosthesis is bilateral, treatment planning is further complicated because only a limited number of beam angles can be used to avoid the prostheses. IMRT using either coplanar or non-coplanar beams may produce favorable results in the treatment of patients with bilateral prostheses.

Important principles

Treatment planning systems currently available are not always able to predict accurately the dose distribution around metallic prosthesis. Firstly, when implanted objects of high atomic number (Z) material are present, severe image artefacts are generated in conventional CT, strongly hindering the ability to delineate some organs. Megavoltage imaging is therefore often used to complement CT information and will show, for instance, if a prosthesis is solid or hollow, and can also be used for exit dose measurements. Furthermore, the presence of high-Z material in a photon beam causes a dose enhancement and reduction at the proximal and distal prosthesis interfaces, respectively. Only Monte Carlo simulation has the ability to calculate precisely the impact of a hip prosthesis on the dose distribution, whereas superposition and pencil beam algorithms do not. However, further from the prosthesis, the difference between these dose calculation algorithms diminishes.

Introduction to references

The AAPM Report is intended to reflect the scientific understanding and technical methodology in clinical dosimetry for radiation oncology patients with high-Z hip prostheses. Its purpose is to make the radiation oncology community aware of the problems arising from the presence of these devices in the radiation beam, to quantify the dose perturbations they cause, and to provide recommendations for treatment planning and delivery.