## Radiation oncology physics

**Автор:** E. B. Podgorsak

**Год:** 2005

**Страницы:** 696

**Язык:** Английский

**Издательство:** IAEA

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**Описание: **

In the late 1990s the IAF.A initiated for its Member
States a systematic and comprehensive plan to support the development of
teaching programmes in medical radiation physics. Multiple projects were
initiated at various levels that, together with the well known short term
training courses and specialization fellowships funded by the IAEA Technical
Cooperation programme, aimed at supporting countries to develop their own
university based master of science programmes in medical radiation physics.

Chapter 1. Basic radiation physics. 1

Introduction. 1

Fundamental physical constants (rounded off to four significant figures). 1

Important derived physical constants and relationships. 1

Physical quantities and units. 3

Classification of forces in nature. 4

Classification of fundamental particles. 4

Classification of radiation. 5

Classification of ionizing photon radiation. 6

Einstein's relativistic mass, energy and momentum relationships. 6

Radiation quantities and units. 7

Atomic and Nuclear Structure. 7

Basic definitions for atomic structure. 7

Rutherford's model of the atom. 9

Bohr's model of the hydrogen atom. 10

Multielectron atoms. 12

Nuclear structure. 14

Nuclear reactions. 15

Radioactivity. 16

Activation of nuclides. 19

Modes of radioactive decay. 20

Electron Interactions. 22

Electron-orbital electron interactions. 23

Electron-nucleus interactions. 23

Stopping power. 24

Mass scattering power. 25

Photon Interactions. 26

Types of indirectly ionizing photon radiation. 26

Photon beam attenuation. 26

Types of photon interaction. 28

Photoelectric effect. 28

Coherent (Rayleigh) scattering. 29

Compton effect (incoherent scattering). 30

Pair production. 32

Photonuclear reactions. 34

Contributions to attenuation coefficients. 34

Relative predominance of individual effects. 36

Effects following photon interactions. 37

Summary of photon interactions. 38

Example of photon attenuation. 40

Production of vacancies in atomic shells. 41

Bibliography 43

Chapter 2. Dosimetric Principles, Quantities and Units. 45

Introduction. 45

Photon fluence and energy fluence. 45

Kerma. 48

Сема. 48

Absorbed dose. 49

Stopping power. 49

Relationships between various dosimetric quantities. 54

Energy fluence and kerma (photons). 54

Fluence and dose (electrons). 56

Kerma and dose (charged particle equilibrium). 57

Collision kerma and exposure. 60

Cavity Theory. 61

Bragg-Gray cavity theory. 61

Spencer-Attix cavity theory. 62

Considerations in the application of cavity theory to ionization chamber calibration and dosimetry protocols. 64

Large cavities in photon beams. 66

Burlin cavity theory for photon beams. 66

Stopping power ratios. 68

Bibliography. 70

Chapter 3. Radiation Dosimeters. 71

Introduction. 71

Properties of Dosimeters. 72

Accuracy and precision. 72

Type A standard uncertainties. 72

Type В standard uncertainties. 73

Combined and expanded uncertainties. 73

Linearity. 74

Dose rate dependence. 74

Energy dependence. 75

Directional dependence. 76

Spatial resolution and physical size. 76

Readout convenience. 76

Convenience of use. 76

Ionization Chamber Dosimetry Systems. 77

Chambers and electrometers. 77

Cylindrical (thimble type) ionization chambers. 78

Parallel-plate (plane-parallel) ionization chambers. 79

Brachytherapy chambers. 79

Extrapolation chambers. 79

film Dosimetry. 81

Radiographic film. 81

Radiochromic film. 84

Luminescence Dosimetry. 84

Thermoluminescence. 85

Thermoluminescent dosimeter systems. 86

Optically stimulated luminescence systems. 88

Semiconductor Dosimetry. 89

Silicon diode dosimetry systems. 89

Mosfet dosimetry systems. 90

Other Dosimetry systems. 91

Alanine/electron paramagnetic resonance dosimetry system. 91

Plastic scintillator dosimetry system. 92

Diamond dosimeters 92

Gel dosimetry systems. 93

Primary Standards. 94

Primary standard for air kerma in air. 95

Primary standards for absorbed dose to water. 95

Ionometric standard for absorbed dose to water. 96

Chemical dosimetry standard for absorbed dose to water. 96

Calorimetric standard for absorbed dose to water. 97

Summary of some commonly used Dosimetric systems. 97

Bibliography. 99

Chapter 4. Radiation monitoring instruments. 101

Introduction. 101

Operational quantities for Radiation monitoring. 102

Area Survey meters. 103

Ionization chambers. 105

Proportional counters. 105

Neutron area survey meters. 105

Geiger-Muller counters. 106

Scintillator detectors. 107

Semiconductor detectors. 107

Commonly available features of area survey meters. 108

Calibration of survey meters. 108

Properties of survey meters. 110

Sensitivity. 110

Energy dependence. 110

Directional dependence. 111

Dose equivalent range. 111

Response time. 111

Overload characteristics. 111

Long term stability. 112

Discrimination between different types of radiation. 112

Uncertainties in area survey measurements. 112

Individual monitoring. 113

Film badge. 113

Thermoluminescence dosimetry badge. 115

Radiophotoluminescent glass dosimetry systems. 116

Optically stimulated luminescence systems. 116

Direct reading personal monitors. 117

Calibration of personal dosimeters. 118

Properties of personal monitors. 118

Sensitivity. 118

Energy dependence. 119

Uncertainties in personal monitoring measurements. 119

Equivalent dose range. 119

Directional dependence. 120

Discrimination between different types of radiation. 120

Bibliography 120

Chapter 5. Treatment machines for external beam Radiotherapy. 123

Introduction. 123

X Ray beams and X Ray units. 124

Characteristic X rays. 124

Bremsstrahlung (continuous) X rays. 124

X ray targets. 125

Clinical X ray beams. 126

X ray beam quality specifiers. 127

X ray machines for radiotherapy. 127

Gamma Ray beams and Gamma Ray units. 129

Basic properties of gamma rays. 129

Teletherapy machines. 130

Teletherapy sources. 130

Teletherapy source housing. 131

Dose delivery with teletherapy machines. 132

Collimator and penumbra. 132

Particle Accelerators. 132

Betatron. 134

Cyclotron. 134

Microtron. 135

LINACS. 136

Linac generations. 137

Safety of linac installations. 137

Components of modern linacs. 138

Configuration of modern linacs. 138

Injection system. 140

Radiofrequency power generation system. 143

Accelerating waveguide. 143

Microwave power transmission. 144

Auxiliary system. 145

Electron beam transport. 146

Linac treatment head. 146

Production of clinical photon beams in a linac. 147

Beam collimation. 148

Production of clinical electron beams in a linac. 149

Dose monitoring system. 149

Radiotherapy with protons, neutrons and heavy ions. 151

Shielding Considerations. 152

Cobalt-60 Teletherapy units versus Linacs. 153

Simulators and Computed Tomography Simulators. 156

Radiotherapy simulator. 157

Computed tomography simulator. 158

Training Requirements. 159

Bibliography. 160

Chapter 6. External photon beams physical aspects. 161

Introduction. 161

Quantities Used in Describing a Photon Beam. 161

Photon fluence and photon fluence rate. 162

Energy fluence and energy fluence rate. 162

Air kerma in air. 163

Exposure in air. 164

Dose to small mass of medium in air. 164

Photon beam sources. 166

Inverse Square Law. 167

Penetration of Photon beams into a Phantom or patient. 169

Surface dose. 171

Buildup region. 171

Depth of dose maximum zmax. 172

Exit dose. 172

Radiation treatment parameters. 172

Radiation beam field size. 173

Collimator factor. 174

Peak scatter factor. 175

Relative dose factor. 177

Central axis depth doses in water source to surface distance set-up. 179

Percentage depth dose. 179

Scatter function. 181

Central Axis Depth Doses in Water: Source to Axis Distance Set-up. 183

Tissue-air ratio. 184

Relationship between TAR(d, AQ, hv) andPDD (d,A,f,hv). 185

Scatter-air ratio. 189

Relationship between SAR(d, AQ, hv) and S(z, A,f,hv). 190

Tissue-phantom ratio and tissue-maximum ratio. 190

Relationship between TMR(z, AQ, hv) and PDD (z,A,f,hv). 192

Scatter-maximum ratio. 193

Off-Axis ratios and beam profiles. 194

Beam flatness. 196

Beam symmetry. 197

Isodose distributions in water phantoms. 197

Single field isodose distributions in patients. 199

Corrections for irregular contours and oblique beam incidence. 200

Effective source to surface distance method. 201

Tissue-air ratio or tissue-maximum ratio method. 202

Isodose shift method. 202

Missing tissue compensation. 202

Wedge filters. 203

Bolus. 203

Compensators. 203

Corrections for tissue inhomogeneities. 204

Model based algorithms. 205

Clarkson segmental integration. 206

Relative dose measurements withionization chambers. 209

Delivery of dose with a single external beam. 212

Example of dose calculation. 213

Shutter correction time. 215

Bibliography. 216

Chapter 7. Clinical treatment planning in external photon beam radiotherapy. 219

Introduction. 219

Volume Definition. 219

Gross tumour volume. 220

Clinical target volume. 220

Internal target volume. 221

Planning target volume. 221

Organ at risk. 222

Dose Specification. 222

Patient data Acquisition and Simulation. 223

Need for patient data. 223

Nature of patient data. 223

Two dimensional treatment planning. 223

Three dimensional treatment planning. 224

Treatment simulation. 225

Patient treatment position and immobilization devices. 226

Patient data requirements. 228

Conventional treatment simulation. 229

Simulators. 229

Localization of the target volume and organs at risk. 230

Determination of the treatment beam geometry. 230

Acquisition of patient data. 230

Computed tomography based conventional treatment simulation. 230

Computed tomography based patient data acquisition. 230

Determination of the treatment beam geometry. 232

Computed tomography based virtual simulation. 233

Computed tomography simulator. 233

Virtual simulation. 233

Digitally reconstructed radiographs. 234

Beam's eye view. 234

Virtual simulation procedure. 235

Conventional simulator versus computed tomography simulator. 237

Magnetic resonance imaging for treatment planning. 238

Summary of simulation procedures. 240

Clinical Considerations for Photon Beams. 241

Isodose curves. 241

Wedge filters. 241

Bolus. 244

Compensating filters. 245

Corrections for contour irregularities. 246

Isodose shift method. 246

Effective attenuation coefficient method. 248

Tissue-air ratio method. 248

Corrections for tissue inhomogeneities. 248

Tissue-air ratio method. 249

Batho power law method. 250

Equivalent tissue-air ratio method. 250

Isodose shift method. 250

Beam combinations and clinical application. 251

Weighting and normalization. 251

Fixed source to surface distance versus isocentric techniques. 251

Parallel opposed beams. 252

Multiple coplanar beams. 253

Rotational techniques. 254

Multiple non-coplanar beams. 255

Field matching. 255

Treatment plan Evaluation. 256

Isodose curves. 257

Orthogonal planes and isodose surfaces. 257

Dose statistics. 257

Dose-volume histograms. 258

Direct dose-volume histogram. 259

Cumulative dose-volume histogram. 259

Treatment evaluation. 260

Port films. 261

On-line portal imaging. 262

Treatment time and monitor unit calculations. 264

Treatment time and monitor unit calculations for a fixed source to surface distance set-up. 265

Monitor unit and treatment time calculations for isocentric set-ups. 267

Normalization of dose distributions. 270

Inclusion of output parameters in the dose distribution. 270

Treatment time calculation for orthovoltage and cobalt-60 units. 271

Bibliography. 271

Chapter 8. Electron beams physical and clinical aspects. 273

Central Axis Depth dose Distributions in water. 273

General shape of the depth dose curve. 273

Electron interactions with an absorbing medium. 274

Inverse square law (virtual source position). 276

Range concept. 277

Buildup region (depths between the surface and zmax (i.e.0 279

Dose distribution beyond zmax (z>zmax). 279

Dosimetric parameters of Electron beams. 281

Electron beam energy specification. 281

Typical depth dose parameters as a function of energy. 281

Percentage depth dose. 282

Percentage depth doses for small electron field sizes. 282

Percentage depth doses for oblique beam incidence. 283

Output factors. 284

Therapeutic range Rw. 285

Profiles and off-axis ratios. 285

Flatness and symmetry. 285

Clinical considerations in electron beam therapy. 286

Dose specification and reporting. 286

Small field sizes. 287

Isodose curves. 287

Field shaping. 289

Electron applicators. 289

Shielding and cut-outs. 289

Internal shielding. 290

Extended source to surface distance treatments. 290

Irregular surface correction. 291

Bolus. 291

Inhomogeneity corrections. 292

Coefficient of equivalent thickness. 292

Scatter perturbation (edge) effects. 293

Electron beam combinations. 295

Matched (abutted) electron fields. 295

Matched photon and electron fields. 295

Electron arc therapy. 295

Electron therapy treatment planning. 298

Bibliography. 299

Chapter 9. Calibration of photon and electron beams. 301

Introduction. 301

Calorimetry. 302

Fricke dosimetry. 303

Ionization chamber dosimetry. 304

Mean energy expended in air per ion pair formed. 304

Reference dosimetry with ionization chambers. 305

Standard free air ionization chambers. 305

Cavity ionization chambers. 306

Phantom embedded extrapolation chambers. 306

Clinical beam calibration and measurement chain. 307

Dosimetry protocols. 307

Ionization chamber based dosimetry systems. 308

Ionization chambers. 308

Electrometer and power supply. 309

Phantoms. 310

Chamber signal correction for influence quantities. 312

Air temperature, pressure and humidity effects: Ktp. 312

Chamber polarity effects: polarity correction factor Кpol. 313

Chamber voltage effects: recombination correction factor Ksat. 314

Chamber leakage currents. 318

Chamber stem effects. 319

Determination of absorbed dose using calibrated ionization chambers. 319

Air kerma based protocols. 320

Absorbed dose to water based protocols. 323

Stopping Power Ratios. 326

Stopping power ratios for electron beams. 326

Stopping power ratios for photon beams. 327

Mass-energy absorption coefficient ratios. 328

Perturbation correction factors. 329

Displacement perturbation factor Pdis and effective point of measurement. 330

Chamber wall perturbation factor Pwall 331

Central electrode perturbation Pcel. 333

Cavity or fluence perturbation correction Pcav. 334

Beam quality specification. 335

Beam quality specification for kilovoltage photon beams. 336

Beam quality specification for megavoltage photon beams. 337

Beam quality specification for megavoltage electron beams. 339

Calibration of megavoltage photon and electron beams: practical aspects. 342

Calibration of megavoltage photon beams based on the air kerma in air calibration coefficient Nk,Co. 342

Calibration of megavoltage photon beams based on the dose to water calibration coefficient Nd,w,Co. 343

Calibration of megavoltage electron beams based on the air kerma in air calibration coefficient Nk,Co. 345

Calibration of high energy electron beams based on the dose to water calibration coefficient Nd,w,Co. 346

Kilovoltage Dosimetry. 347

Specific features of kilovoltage beams. 347

Air kerma based in-phantom calibration method (medium energies). 348

Air kerma based backscatter method (low and medium photon energies). 349

Air kerma in air based calibration method for very low energies. 351

Absorbed dose to water based calibration method. 351

Error and uncertainty analysis for ionization chamber measurements. 352

Errors and uncertainties. 352

Classification of uncertainties. 352

Uncertainties in the calibration chain. 352

Bibliography. 353

Chapter 10. Acceptance tests and commissioning measurements. 355

Introduction. 355

Measurement Equipment. 355

Radiation survey equipment. 355

Ionometric dosimetry equipment. 356

Film. 356

Diodes. 356

Phantoms. 357

Radiation field analyser and water phantom. 357

Plastic phantoms. 357

Acceptance tests. 358

Safety checks. 359

Interlocks, warning lights and patient monitoring equipment. 359

Radiation survey. 359

Collimator and head leakage. 360

Mechanical checks. 361

Collimator axis of rotation. 361

Photon collimator jaw motion. 361

Congruence of light and radiation field. 362

Gantry axis of rotation. 363

Patient treatment table axis of rotation. 363

Radiation isocentre. 364

Optical distance indicator. 364

Gantry angle indicators. 365

Collimator field size indicators. 365

Patient treatment table motions. 365

Dosimetry measurements. 365

Photon energy. 366

Photon beam uniformity. 366

Photon penumbra. 366

Electron energy. 367

Electron beam bremsstrahlung contamination. 367

Electron beam uniformity. 368

Electron penumbra. 368

Monitor characteristics. 368

Arc therapy. 370

Commissioning. 370

Photon beam measurements. 370

Central axis percentage depth doses. 370

Output factors. 371

Blocking tray factors. 373

Multileaf collimators. 373

Central axis wedge transmission factors. 374

Dynamic wedge. 375

Transverse beam profiles/off-axis energy changes. 376

Entrance dose and interface dosimetry. 376

Virtual source position. 377

Electron beam measurements. 378

Central axis percentage depth dose. 378

Output factors. 380

Transverse beam profiles. 383

Virtual source position. 383

Time required for commissioning. 384

Bibliography. 385

Chapter 11. Computerized treatment planning systems for external photon beam. 386

Radiotherapy. 387

Introduction. 387

System hardware. 388

Treatment planning system hardware. 388

Treatment planning system configurations. 389

System software and calculation algorithms. 390

Calculation algorithms. 390

Beam modifiers. 393

Photon beam modifiers. 393

Electron beam modifiers. 394

Heterogeneity corrections. 395

Image display and dose-volume histograms. 395

Optimization and monitor unit calculations. 396

Record and verify systems. 396

Biological modeling. 397

Data acquisition and entry. 397

Machine data. 397

Beam data acquisition and entry. 398

Patient data. 399

Commissioning and quality assurance. 400

Errors. 400

Verification. 401

Spot checks. 402

Normalization and beam weighting. 402

Dose-volume histograms and optimization. 403

Training and documentation. 403

Scheduled quality assurance. 403

Special considerations. 404

Bibliography. 405

Chapter 12. Quality assurance of external beam radiotherapy. 407

Introduction. 407

Definitions. 407

Quality assurance. 407

Quality assurance in radiotherapy. 407

Quality control. 408

Quality standards. 408

Need for quality assurance in radiotherapy. 408

Requirements on accuracy in radiotherapy. 409

Accidents in radiotherapy. 411

Managing a quality assurance programme. 414

Multidisciplinary radiotherapy team. 414

Quality system/comprehensive quality assurance programme. 416

Quality assurance programme for equipment. 418

Structure of an equipment quality assurance programme. 418

Equipment specification. 419

Acceptance. .419

Commissioning. 420

Quality control. 420

Uncertainties, tolerances and action levels. 421

Quality assurance programme for cobalt-60 teletherapy machines. 423

Quality assurance programme for linacs. 425

Quality assurance programme for treatment simulators. 425

Quality assurance programme for computed tomography scanners and computed tomography simulation. 429

Quality assurance programme for treatment planning systems. 430

Quality assurance programme for test equipment. 431

Treatment delivery. 433

Patient charts. 433

Portal imaging. 434

Portal imaging techniques. 436

Future developments in portal imaging. 439

In vivo dose measurements. 439

In vivo dose measurement techniques. 440

Use of electronic portal imaging systems for in vivo dosimetry. 443

Record and verify systems. 443

Quality audit. 445

Definition. 445

Practical quality audit modalities. 446

Postal audit with mailed dosimeters. 446

Quality audit visits. 446

What should be reviewed in a quality audit visit? 447

Bibliography. 448

Chapter 13. Brachytherapy: physical and clinical aspects. 451

Introduction. 451

Photon source characteristics. 455

13.2.1. Practical considerations 455

Physical characteristics of some photon emitting brachytherapy sources. 456

Mechanical source characteristics. 456

Source specification. 457

Specification of у ray sources. 457

Specification of Xray sources. 459

Clinical use and dosimetry systems. 460

Gynaecology. 460

Types of source. 460

Dose specification. 460

Source arrangement. 460

Applicators. 461

Rectal and bladder dose monitoring. 461

Interstitial brachytherapy. 461

Patterson-Parker system. 461

Quimby system. 462

Paris system. 462

Remote afterloading systems. 463

Permanent prostate implants. 464

Choice of radionuclide for prostate implants. 465

Planning technique: ultrasound or computed tomography. 465

Preplanning, seed placement and dose distributions. 465

Post-implant dose distributions and evaluation. 465

Eye plaques. 466

Intravascular brachytherapy. 466

Dose specification and reporting. 467

Intracavitary treatments. 467

Interstitial treatments. 467

Dose distributions around sources. 468

AAPM TG 43 algorithm. 468

Other calculation methods for point sources. 471

Linear sources. 473

Unfiltered line source in air. 473

Filtered line source in air. 474

Filtered line source in water. 475

Dose calculation procedures. 475

Manual dose calculations. 475

Manual summation of doses. 475

Precalculated dose distributions (atlases). 475

Computerized treatment planning. 476

Source localization. 476

Dose calculation. 476

Dose distribution display. 476

Optimization of dose distribution. 477

Calculation of treatment time. 477

Use of Patterson-Parker tables. 477

Choice of reference points. 478

Decay corrections. 478

Commissioning of brachytherapy computer treatment planning systems. 479

Check of the reconstruction procedure. 479

Check of consistency between quantities and units. 479

Computer versus manual dose calculation for a single source. 479

Check of decay corrections. 479

Source commissioning. 480

Wipe tests. 480

Autoradiography and uniformity checks of activity. 480

Calibration chain. 480

Quality assurance. 481

Constancy check of a calibrated dosimeter. 481

Regular checks of sources and applicators. 481

Mechanical properties. 481

Source strength. 481

Wipe tests. 482

Checks of source positioning with afterloading devices. 482

Radiation monitoring around patients. 482

Quality management programme. 482

Brachytherapy versus External beam radiotherapy. 483

Bibliography. 483

Chapter 14. Basic radiobiology. 485

Introduction. 485

Classification of radiations in radiobiology. 486

Cell cycle and cell death. 487

Irradiation of cells. 488

Direct action in cell damage by radiation. 488

Indirect action in cell damage by radiation. 488

Fate of irradiated cells. 489

Type of radiation damage. 489

Timescale. 489

Classification of radiation damage. 490

Somatic and genetic effects. 490

Stochastic and deterministic (non-stochastic) effects. 491

Acute versus late tissue or organ effects. 491

Total body radiation response. 491

Foetal irradiation. 492

Cell survival curves. 492

Dose response curves. 494

Measurement of radiation damage in tissue. 496

Normal and tumour cells: therapeutic ratio. 497

Oxygen effect. 498

Relative biological effectiveness. 500

Dose rate and fractionation. 501

Radioprotectors and r adiosensitizers. 503

Bibliography. 504

Chapter 15. Special procedures and techniques in radiotherapy. 505

Introduction. 505

Stereotactic irradiation. 506

Physical and clinical requirements for radiosurgery. 506

Diseases treated with stereotactic irradiation. 507

Equipment used for stereotactic radiosurgery. 507

Historical development. 508

Radiosurgical techniques. 509

Gamma Knife. 509

Linac based radiosurgery. 509

Miniature linac on robotic arm. 511

Uncertainty in radiosurgical dose delivery. 512

Dose prescription and dose fractionation. 513

Commissioning of radiosurgical equipment. 514

Quality assurance in radiosurgery. 514

Gamma Knife versus linac based radiosurgery. 515

Frameless stereotaxy. 516

total body irradiation. 516

Clinical total body irradiation categories. 516

Diseases treated with total body irradiation. 517

Technical aspects of total body irradiation. 517

Total body irradiation techniques. 518

Dose prescription point. 519

Commissioning of total body irradiation procedure. 519

Test of total body irradiation dosimetry protocol. 521

Quality assurance in total body irradiation. 521