Radiotherapy Treatment Planning

Radiotherapy Treatment Planning
Part No...., Module No....Lesson No Module title Radiotherapy Treatment Planning Part X: Optimisation in External Beam Radiotherapy Lesson 4: Treatment Planning Learning objectives: Upon completion of this lesson, the students will be able to: Understand the general principles of radiotherapy treatment planning Appreciate different dose calculation algorithms Understand the need for testing the treatment plan against a set of measurements Be able to apply the concepts of optimization of medical exposure throughout the treatment planning process Appreciate the need for quality assurance in radiotherapy treatment planning Activity: Lecture - 2 practical sessions: 1 Hand planning using isodose plots, 2 Monitor unit calculations Duration: 2 hours References: J van Dyk et al Commissioning and QA of treatment planning computers. Int. J. Radiat. Oncol. Biol. Phys. 26: J van Dyk et al, 1999 Computerised radiation treatment planning systems. In: Modern Technology of Radiation Oncology (Ed.: J Van Dyk) Chapter 8. Medical Physics Publishing, Wisconsin, ISBN , pp M Millar et al 1997 ACPSEM position paper. Australas. Phys. Eng. Sci. Med. 20 Supplement B Fraass et al 1998 AAPM Task Group 53: QA for clinical RT planning. Med. Phys. 25: IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Part No...., Module No....Lesson No
Module title Treatment planning is the task to make sure a prescription is put into practice in an optimized way Prescription Planning Planning is the most important link between clinical intention and the practical treatment. The lecturer shall also point out that this optimization process should take into account the circumstances of the patient and the radiotherapy centre. Optimization is within ‘prevailing conditions’ Treatment Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Objectives Understand the general principles of radiotherapy treatment planning Appreciate different dose calculation algorithms Understand the need for testing the treatment plan against a set of measurements Be able to apply the concepts of optimization of medical exposure throughout the treatment planning process Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Contents of the lecture
Part No...., Module No....Lesson No Module title Contents of the lecture A. Radiotherapy treatment planning concepts B. Computerized treatment planning This is a rather complex lecture which features both basic and high tech topics. It is assumed that the lecturer has to make some selections from the material to make it suitable for the audience. In total, there are three hours of lecturing time allocated for this part of the course. The last part of the lecture is concerned with quality assurance, a topic which will be more elaborated on in part XII of the course. However, it is felt that the QA specific to treatment planning would be best discussed in connection with the planning process. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

The need to understand treatment planning
Part No...., Module No....Lesson No Module title The need to understand treatment planning IAEA Safety Report Series 17 “Lessons learned from accidental exposures in radiotherapy “ (Vienna 2000): About 1/3 of problems directly related to treatment planning! May affect individual patient or cohort of patients Participants should have a copy of SRS17 - they can have a look for typical accidents relating to planning themselves. In any case, this emphasizes the need to be aware of treatment planning processes and understand the basics. Section B of the lecture will put this then into the context of computerized treatment planning. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

A. Basic Radiotherapy Treatment Planning Concepts
Part No...., Module No....Lesson No Module title A. Basic Radiotherapy Treatment Planning Concepts i. Planning process overview ii. Patient data required for planning iii. Machine data required for planning iv. Basic dose calculation Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

i. Planning process overview
Part No...., Module No....Lesson No Module title i. Planning process overview Combine machine parameters and individual patient data to customize and optimize treatment Requires machine data, input of patient data, calculation algorithm Produces output of data in a form which can be used for treatment (the ‘treatment plan’) Patient information Treatment unit data This slide should make participants think about what they want to achieve with treatment planning - one wants to optimise the treatment for an individual patient using the treatment choices available at a particular centre. Planning Treatment plan Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

The treatment planning process
Part No...., Module No....Lesson No Module title The treatment planning process Individual patient Radiotherapy treatment units Patient data: CT scan, outlines Beam data: radiation quality, PDD, profiles, ... Localization of tumor and critical structures Optimization of source or beam placement Treatment planning aims to combine information of individual patients (eg outlines and disease site and size with data for the treatment units available in a particular department. This involves the optimization of the treatment approach for each individual patient.The present and the following slide are a more complex version of the previous one - it is currently hidden but can be made visible if appropriate for the audience. Simulation Dose calculation Preparation of treatment sheet and record and verify data Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

ii. Patient information required
Part No...., Module No....Lesson No Module title ii. Patient information required Radiotherapy is a localized treatment of cancer - one needs to know not only the dose but also the accurate volume where it has been delivered to. This applies to tumor as well as normal structures - the irradiation of the latter can cause intolerable complications. Again, both volume and dose are important. For the second point, the lecturer can point out that volume is indeed a very important issue in predicting the probability of normal tissue complications. NTCP = normal tissue complication probability. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

One needs to know Target location Target volume and shape
Secondary targets - potential tumor spread Location of critical structures Volume and shape of critical structures Radiobiology of structures Anwar

Target delineation ICRU 50 & 62
Gross Tumor Volume (GTV) = clinically demonstrated tumor Clinical Target Volume = GTV + area at risk (eg. potentially involved lymph nodes) Anwar

It all comes down to the correct dose to the correct volume
Part No...., Module No....Lesson No It all comes down to the correct dose to the correct volume Module title Comparison of three different treatment techniques (red, blue and green) in terms of dose to the target and a critical structure Target dose Critical organ Dose Volume histograms are introduced here not primarily as a tool to understand and characterize dose distributions, but a tool to describe the desired dose distribution. Dose Volume Histograms are a way to summarize this information IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title The ideal DVH Tumor: High dose to all Homogenous dose Critical organ Low dose to most of the structure 100% 100% dose dose Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Dose Volume Histograms
Part No...., Module No....Lesson No Module title Dose Volume Histograms Comparison of three different treatment techniques (red, blue and green) in terms of dose to the target and a critical structure Critical organ The lecturer can switch back to this DVH slide after the explanation of the previous slide - at present it is hidden. Target dose Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Need to keep in mind Always a 3D problem Different organs may respond differently to different dose patterns. Question: Is a bit of dose to all the organ better than a high dose to a small part of the organ? The last question can be partially answered by distinguishing organs as shown on the next slides, a repeat form part III of the course. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

In practice not always that clear cut
Part No...., Module No....Lesson No Module title In practice not always that clear cut ICRU report 62 Need to understand anatomy and physiology A clinical decision The different structures shown on the right are just a small selection of all possible ones. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title In many organs, dose and volume effects are linked - eg. Boersma* et al., classified the following (Dose,Volume) regions to be regions of high risk for developing rectal bleeding: This is just an example for the probability of complications increasing with both dose and volume. The lecturer can point out that even this data is only useful for a whole patient population. It does not allow to predict the complication probability in a particular patient. *Int. J. Radiat. Oncol. Biol. Phys., 1998; 41:84-92. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title In EBT practice Need to know where to direct beam to, and how large the beam must be and how it should be shaped The picture shows a simulator film which outline the radiation field (rectangular) for a prostate treatment. The question which should be in everyone's mind by now is: Is this rectangle really a good choice of treatment field… this leads to the next section. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Target design and reference images
Part No...., Module No....Lesson No Module title Target design and reference images In radiotherapy practice the target is localized using diagnostic tools: Diagnostic procedures - palpation, X-ray, ultrasound Diagnostic procedures - MRI, PET, SPECT Diagnostic procedures - CT scan, simulator radiograph Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Selection of treatment approach
Part No...., Module No....Lesson No Module title Selection of treatment approach Requires training and experience May differ from patient to patient Requires good diagnostic tools Requires accurate spatial information May require information obtained from different modalities The last point can be interpreted in different ways: Different modalities may be palpation and a cell biopsy and it could be different imaging modalities as illustrate in the next slides. The lecturer can omit much of the following if it is too far removed from the participants reality. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Minimum patient data required for external beam planning
Part No...., Module No....Lesson No Module title Minimum patient data required for external beam planning Target location Patient outline The picture shows a device which allows to draw an axial outline of a patient. This outline can replace a CT scan for treatment planning. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Diagnostic tools which could be used for patient data acquisition
Part No...., Module No....Lesson No Module title Diagnostic tools which could be used for patient data acquisition CT scanner, MRI, PET scanner, US,… Simulator including laser system, optical distance indicator (ODI) Many functions of the simulator are also available on treatment units as an alternative - simulator needs the same QA! Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Note on the role of simulation
Part No...., Module No....Lesson No Module title Note on the role of simulation Simulator is often used twice in the radiotherapy process Patient data acquisition - target localization, contours, outlines Verification - can the plan be put into practice? Acquisition of reference images for verification. Simulator may be replaced by other diagnostic equipment or virtual simulation Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Virtual simulation All aspects of simulator work are performed on a 3D data set of the patient This requires high quality 3D CT data of the patient in treatment position Verification can be performed using digitally reconstructed radiographs (DRRs) This and the following slides introduces a technique which is currently finding its way into many radiotherapy practices in the developed world. As such the lecturer can choose to omit this and the next 4 slides. However, in practice, virtual simulation can be cheaper than buying a simulator if a CT scan of the patient is available. As such it may be of interest also for others in the future. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Virtual Simulation 3D Model of the patient and the Treatment Devices Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Simulator Rotating gantry Diagnostic X-ray tube Radiation beam defining system This slide is a repeat from part V of the course. Here the lecturer should emphasis the diagnostic tools included. Simulator couch Image intensifier and X-ray film holder Nucletron/Oldelft Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Radiotherapy simulator
Part No...., Module No....Lesson No Module title Radiotherapy simulator Obtain images and mark beam entry points on the patient Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title CT Simulation (Thanks to ADAC) Marking the Patient already during CT Moveable Lasers Isocenter Position This complex slide illustrates the ‘high form’ of virtual simulation. The patient undergoes a CT scan and the clinician identifies the target while the patient is still on the couch. The target localisation is then fed back to a movable laser system which will indicate on the patient where the centre of the target is. These points can be marked on the patient in situ and the beams positioned accordingly. CT images Isocenter Projection Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Patient marking Marks on shell Create relation between patient coordinates and beam coordinates The lecturer can point out that the marks must be easily visible on treatment set-up and stay on the patient for the required number of fractions. If deletable skin marks are used, it is good practice to redraw the marks in regular intervals (eg every week). Tattoos Skin markers Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

There may be a need to combine images from different modalities
Part No...., Module No....Lesson No Module title There may be a need to combine images from different modalities Look at them next to each other... MR angiogram MR image The next 9 slides are an ‘excursion’ into image matching. This is an important tool in radiotherapy for: optimization of the target volume and therefore the beam design comparison of reference and treatment images for verification follow up of patients - compare diagnostic scans prior and post treatment… The information could be included anywhere in part X of the course - if time is pressing and the participants have different information needs, the slides can be omitted. In the present version of the lecture the slides are hidden - they do not appear in a presentation but can be un-hidden by the lecturer if desired. In any case they provide a glimpse of modern radiotherapy approaches. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Fusion of images = Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Fusion of images “overlay” adjust: scale, location, orientation Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Registration Identify identical points/lines on each image - these features could either be part of the patient (eg bones) or external reference frames Computer ‘registers’ these points/lines -thereby changing scale, location and orientation of one image Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Image registration external frames stereotactic procedures Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Image registration with external markers
Part No...., Module No....Lesson No Module title Image registration with external markers CT scan MRI Leksell fiducial markers on both Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Combination of images Look at them next to each other… Fusion Registration Matching/molding The computer automatically finds structures of interest and combines two images Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Image matching using internal reference points
Part No...., Module No....Lesson No Module title Image matching using internal reference points Complex computing problem Still in its infancy Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Combination of images Useful for optimization of the target volume and therefore the beam design Important for comparison of reference and treatment images for verification Useful for follow up of patients - compare diagnostic scans prior and post treatment... Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Beam placement and shaping
Part No...., Module No....Lesson No Module title Beam placement and shaping DRR with conformal shielding This slide is part of the original sequence of the course and should be shown. Blocks are essential in beam shaping and avoidance of irradiation of normal tissues. In both cases shown above, a clinician has decided what areas in a rectangular radiation field should be shielded to reduce the dose to normal tissues. simulator film with block Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Tools for optimization of the radiotherapy approach
Part No...., Module No....Lesson No Module title Tools for optimization of the radiotherapy approach Choice of radiation quality Entry point Number of beams Field size Blocks Wedges Compensators From a general point of view, the higher the number of beams, the more sparing of tissue in the individual beam. The tumor is in the focus of all the beams. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Optimization approaches
Part No...., Module No....Lesson No Module title Optimization approaches Choice of best beam angle beam beam target patient target patient wedge In the context of the wedge, the lecturer can spend some time pointing out why the thick end is in a location where there is less tissue overlaying the target. target Use of a beam modifier patient Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Beam number and weighting
Part No...., Module No....Lesson No Module title Beam number and weighting Beam 1 beam 50% 100% 50% target patient Beam 2 patient The lecturer can point out that beam weighting is a very important tool - it is often found that the beam closest to the target has the highest weighting 40% 30% 10% 20% Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

A note on weighting of beams
Part No...., Module No....Lesson No Module title A note on weighting of beams Different approaches are possible: 1. Weighting of beams as to how much they contribute to the dose at the target 2. Weighting of beams as to how much dose is incident on the patient These are NOT the same 25% 40% 25% 25% 30% 10% The lecturer should point out that these are only different ways to specify weighting (and there are others possible). The resultant optimum plan is the same with the same beam on time - however, the specified weighting is different. The lecturer can ask the participants which of the two weighting schemes are indicated in the two color codes 1 = blue 2 = orange This is an approximation only. 20% 25% Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Use of wedges Wedged pair Three field techniques Isodose lines patient The lecturer can point out that these are just two techniques possible with wedges - in addition to this there is typically a choice of wedge angel which can be optimised. patient Typical isodose lines Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Part No...., Module No....Lesson No Module title Beam placement and shaping Entry point Field size Blocks Wedges Compensators a two-dimensional approach? Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Part No...., Module No....Lesson No Module title Beam placement and shaping Entry point Field size Blocks Wedges Compensators Multiple beams Dynamic delivery Non-coplanar Dose compensation (IMRT) not just missing tissue Biological planning This is actually a 3D approach Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Target Localization Diagnostic procedures - palpation, X-ray, ultrasound Diagnostic procedures - MRI, PET, SPECT Diagnostic procedures - CT scan, simulator radiograph The lecturer can point out that the three levels of diagnostic procedures reflect increasing customisation for RT. The first is more a qualitative localization which the oncologist must in their experience and mind transfer to the patient coordinate frame within the treatment set-up. The second set of images are - at least in principle transferable to an image based patient RT coordinate system using image fusion. The third allows the direct combination of the diagnostic information with radiotherapy beam data - and the creation of reference images for treatment verification (see next slide) Allows the creation of Reference Images for Treatment Verification: Simulator Film, Digitally Reconstructed Radiograph Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Simulator image During ‘verification session’ the treatment is set-up on the simulator exactly like it would be on the treatment unit. A verification film is taken in ‘treatment’ geometry Anwar

Simulator Film Shows relevant anatomy
Indicates field placement and size Indicates shielding Can be used as reference image for treatment verification Field defining wires Anwar

An alternative reference image
Part No...., Module No....Lesson No Module title An alternative reference image Simulator image - a real image of the patient Computer generated ‘digitally reconstructed radiograph’ (DRR) - shows what the planning computer thinks the portal image should look like This and the three following slides are currently hidden - the concept of a digitally reconstructed radiograph is important for state of the art radiotherapy - it will be revisited later in the lecture when computerised treatment planning is discussed. It can be omitted here, in particular if its relevance is limited for the participants. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Digitally reconstructed radiographs (DRRs)
Part No...., Module No....Lesson No Module title Digitally reconstructed radiographs (DRRs) Computer generated virtual images Requires patient CT dataset Choice of image quality - diagnostic or therapy type image Depends significantly on the number of CT slices available Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

DRRs can mimic any geometry
Part No...., Module No....Lesson No Module title DRRs can mimic any geometry Divergent beams 3D Dose pictures Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

An alternative reference image
Part No...., Module No....Lesson No Module title An alternative reference image Simulator image - a real image of the patient Computer generated ‘digitally reconstructed radiograph’ (DRR) - shows what the planning computer thinks the portal image should look like Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

iii. Machine data requirements for treatment planning
Part No...., Module No....Lesson No Module title iii. Machine data requirements for treatment planning Beam description (quality, energy) Beam geometry (isocentre, gantry, table) Field definition (source collimator distance, applicators, collimators, blocks, MLC) Physical beam modifiers (wedges, compensator) Dynamic beam modifiers (dynamic wedge, arcs, MLC IMRT) Normalization of dose Most of this has been discussed in part V and earlier sections of part X of the course. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Machine data required for planning
Depends on complexity of treatment approaches resources available for data acquisition May be from published data or can be acquired MUST be verified... Anwar

Module title Quick Question: The answer could vary and will make participants aware of their situation. It could be: Staff medical physicists Consulting medical physicists Data provided by manufacturer Data provided once by outside consultant (eg. IAEA expert) Who is responsible for the preparation of beam data for the planning process? IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Acquisition of machine data
Part No...., Module No....Lesson No Module title Acquisition of machine data …from vendor or publications (eg BJR 17 and 25) - this requires verification!!! Done by physicist Some dosimetric equipment must be available (water phantom, ion chambers, film, phantoms,…) Documentation essential The slide shows a Wellhoefer scanning beam data acquisition under a Varian linear accelerator. The lecturer can point out that much simpler systems may be sufficient to verify data for treatment planning used eg for a 60-Co unit. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Machine data availability
Part No...., Module No....Lesson No Module title Machine data availability Hardcopy (isodose charts, output factor tables, wedge factors,…) - for emergencies and computer break downs Treatment planning computer (as above or beam model) - as standard planning data Independent checking device (eg. mu checks) - should be a completely independent set of data It is important to point out that the machine data should be kept in duplicate and preferably in different formats. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Machine data availability
Part No...., Module No....Lesson No Module title Machine data availability Hardcopy (isodose charts, output factor tables, wedge factors,…) Treatment planning computer (as above or beam model) Independent checking device (eg. mu checks) The data must be dated, verified in regular intervals and the source (including the person responsible for it) must be documented Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Machine data summary Need to include all beams and options (internal consistencyالقوام، اللزوجة, conventions, collisionتصادم protection, physical limitations) Data can be made available for planning in installments as required Some data may be required for individual patients only (eg. special treatments) Only make available data which is verified Anwar

Module title Quick Question: What data is available for physical wedges in your center? This should include at least: Wedge angle - and how it is defined Wedge output modification factor - and to which depth and field sizes it applies The field sizes for which the wedge can be used Beam hardening? Maybe a new beam must be defined by TMRs or percentage depth dose Profiles in both directions (wedged and un-wedged - the latter is affected by divergence related profile changes) Weight (eg for OHS restrictions on lifting) This should include at least: Wedge angle - and how it is defined Wedge output modification factor - and to which depth and field sizes it applies The field sizes for which the wedge can be used Beam hardening? Maybe a new beam must be defined by TMRs or percentage depth dose Profiles in both directions (wedged and un-wedged - the latter is affected by divergence related profile changes) Weight (eg for OHS restrictions on lifting) IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

From single to multiple beams
Part No...., Module No....Lesson No Module title From single to multiple beams Mainly an issue for megavoltage photons where we have significant contribution of dose to the target from many beams 1 4 3 2 60 Gy If multiple beams are used to treat the same volume, one must take the weighting of the beams into account. A useful way to make sure that the normalization is correct is to ensure the weighting of all beams together equals 1. However other options exist and normalisation must take them into consideration. Beam weighting must be factored in !!! Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Compensators Physical compensators lead sheets brass blocks customized milling Intensity modulation multiple static fields arcs dynamic MLC The aim of all compensators is to modulate the photon fluence in different parts of the beam. This is a two dimensional map rather than a one dimensional one as in the case of the wedge. Similarly to the wedge there is also a physical version of compensators shown here and one created by moving jaws (or better the MLC) on a megavoltage photon unit. This is called Intensity Modulated Radiation Therapy (IMRT) and illustrated in the next slides. It is currently the topic of a lot of research and holds great promise for improved dose distributions in the target. Depending on the participants, the lecturer can decide to omit the following two slides. Similar information is also provided in the next lecture and in part X of the course. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Intensity modulation Can be shown to allow optimization of the dose distribution Make dose in the target homogenous Minimize dose out of the target Different techniques physical compensators intensity modulation using multi leaf collimators Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Module title Intensity Modulation MLC pattern 1 MLC pattern 2 Achieved using a Multi Leaf Collimator (MLC) The field shape can be altered either step-by-step or dynamically while dose is delivered MLC pattern 3 The lecturer can take participants through the right part of the slide step by step, adding up the fluence distribution in all three fields shown. In practice, there will be often more than 50 subfields or segments. Intensity map Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

iv. Basic dose calculation
Part No...., Module No....Lesson No Module title iv. Basic dose calculation Once one has the target volume, the beam orientation and shape one has to calculate how long a beam must be on (60-Co or kV X-ray units) or how many monitor units must be given (linear accelerator) to deliver the desired dose at the target. Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

3D display of beam placement may help to identify the structures in the field.
Anwar

Module title Dose calculation The lecturer can ask what the difference between the two dose pictures may be... Anwar IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

Dose display options Isodose lines Color wash Anwar

Isodose display - can be complex and 3D
Anwar

مع أطيب الأمنيات بالتوفيق والنجاح
Anwar

Radiotherapy Treatment Planning

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Radiotherapy Treatment Planning

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