Linear Accelerators

[1]     What are the differences (disadvantages and advantages) between LINACS and Cobalt-60 machines e.g. doserate?

[2]     Sketch the main components of a linear accelerator.

[3]     Describe the theory of beam production and the part each component plays in the production of a clincally useful beam:

·         Modulator

·         Klystrons & Magnetron

·         Electron Gun

·         Accelerator Waveguide

·         Bending Magnet

·         Target

·         Flattening Filter

·         Collimation (primary & secondary)

·         Monitor Ionisation Chambers

·         Wedges (physical/flying/dynamic)

[4]     What changes are made to change the Linac from photon to electron mode?

[5]     What are the differences between the Varian 600C and the Siemens KD2?



Orthovoltage (Conventional) X-ray Machines

[6]     Describe the operation of a standard therapy x-ray machine.

[7]     What is the purpose of the beryllium window (how thick)?

[8]     How is most of the energy lost?

[9]     Describe how and why full wave rectification of the high voltage supply is necessary.

[10] Sketch the radiation spectrum seen, with and without the effect of target filtration and additional filtration.

[11] Explain the need for external filters.

[12] What materials are used?

[13] Why do applicators for x-rays (>150kVp) have a closed perspex end?

[14] What is the ‘Heel Effect’?

[15] Sketch depth dose curves for 300, 100 and 50kV x-rays.

[16] What are the approximate 90% depths for low and medium energies?



Ionisation Chambers

[17] Sketch a free air ionisation chamber set-up.

[18] What is the definition of exposure?

[19] How does this affect the design of the free-air ionisation chamber?

[20] What thickness of surrounding air is required at 200kV? 300kV?

[21] Sketch a simple thimble chamber.

[22] What is the air equivalent wall?

[23] What is the calibration chain for ionisation chambers at your training hospital?

[24] Describe the consistency checks using Strontium-90.



Photon/Electron Interactions & Depth Dose Characteristics

[25] Describe the main photon interaction processes, their energy and atomic number dependence and threshold for domination using a graph.

[26] Describe the main electron interaction processes.

[27] Sketch depth dose curves and isodose distributions for kilovoltage, megavoltage and electron beams.

[28] What is the ‘rule of thumb’ describing the relationship between dMAX and the photon/electron energy?

[29] What are the advantages in terms of treatment planning of each of these types of radiation?





Exposure, Absorbed Dose and Air Kerma

[30] Give the definitions and units of each of the above quantities.

[31] How are the three related?

[32] What calculations must be made to change dose in air to dose in water?

[33] Sketch graphs indicating the differences at increasing energy for bone and tissue.

[34] Under what conditions can air kerma and dose be considered identical, when not?



Brachytherapy: Intracavity

[35] What is intracavity brachytherapy?

[36] What are the advantages of this type of treatment?

[37] Describe the properties of an ideal source and relate to currently used Cs-137 & Ra-226.

[38] What are the advantages of afterloading brachytherapy devices?

[39] What are the approximate dose rates for LDR, MDR & HDR afterloading systems?

[40] What are biological effects of using a LDR or MDR machine?

[41] Describe the Selectron suite and afterloading machine (plus applicators) at your training hospital.

[42] What radiation protection devices are in place?

[43] What is the purpose of catheterisation?

[44] What are the anatomical origins and geometrical positions of points A & B in the Manchester system?

[45] What are the dose limits to the rectal and bladder points?



Brachytherapy: Interstitial

[46] What are the major features of the Paris system of dosimetry (9 Rules)?

[47] How does this differ from the Manchester system?

[48] What are the properties of Ir-192?

[49] In dose calculations what are the basal doserate, the reference doserate and the treatment volume.

[50] What is the effective length of the hairpin taken to be?



Unsealed Source Therapy

[51] What are the properties of I-131?

[52] How is it used therapeutically?

[53] What are the administered activities for ablation and overactive thyroid treatment?

[54] Describe the procedure in each case.



QA Procedures (Megavoltage)

[55] List the daily checks performed and the tolerances for each result.

[56] What additional checks are performed weekly?

[57] List the checks performed monthly on the Linac (8).

[58] What codes of practice are used?

[59] Describe the experimental set-up including the field size, MU, build-up material, tolerances, etc. for each check.

[60] What is the definition of TMR?



QA Procedures (Kilovoltage)

[61] What is the code of practice relating to kilovoltage output measurements?

[62] How has this changed since the previous document?

[63] How are the three energy ranges categorised?

[64] Describe the procedure for checking the output reading.

[65] What is the backscatter factor?

[66] What corrections must be applied to the instrument reading? After multiplication by chamber calibration factor, mass absorption coefficient, ratio water/air, etc.

[67] What are the differences between the measurement/calculation made for outputs at 90, 135 and 300kV?

[68] What other QC procedures might be carried out on the kilovoltage unit (5)?

[69] Describe the calibration chain for ionisation chambers & dosemeters.

[70] Describe the procedure for consistency checks with Sr-90.

[71] Briefly describe QC checks performed on the Selectron.