Intensity-Modulated Radiation Therapy PDF

PREFACE

CONFORMAL AND INTENSITY-MODULATED RADIOTHERAPY—WHY AND HOW?

Scientific rationale

Whilst drug development plays an important but expensive role in the treatment of some cancers, it is estimated that, at a time when 2% of patients are cured by drugs, some 30% are cured by a combination of surgery and radiotherapy. Radiotherapy may be the ‘sticking plaster of cancer' but it is likely to be necessary for many decades to come and it merits continual development. The development of 3D conformal radiotherapy (CFRT), in which the high-dose volume matches the target volume and avoids normal tissues, has been a major theme for improving the physical basis of radiotherapy. Intensity-modulated radiation therapy (IMRT) is the most advanced form of CFRT. As with medical imaging, its development requires the professional activity of physicists and engineers. In the next ten years, it will be routinely possible to automatically geometrically shape radiation fields, modulate the intensity of such radiation under computer control, verify that radiotherapy is being accurately delivered, predict the clinical outcome via biological models and, if not eliminate uncertainties, quantify them. It may be possible to customize radiotherapy to the individual radiosensitivity of individual patients. Robotic radiotherapy is in its infancy but deserves more attention (Schweikard et al 1995, 1996, Gilio et al 1998, Delpy et al 1998, Shiomi et al 1998, Webb 1999a,b,d, 2000a,b, Brahme and Lind 1999). It may solve the problem of accurately irradiating the moving patient and moving target.

Since ‘missing the tumour'is the most serious possible CFRT mistake, CFRT is ‘driven' by 3D multimodality medical imaging. It is thus evident, given that 3D CFRT is the only way to improve the dose-based estimate of tumour control probability, that a Centre of Excellence in 3D CFRT must have either the same level of capability in medical imaging or at least have telematic access to registered 3D images. The role of ultrasound has, to date, been more diagnostic than therapeutic but may, in future, not only provide a means to monitor tumour regression but also, more importantly, monitor target position fraction-by-fraction. The daily alignment of the high-dose volume with the target, by ultrasound guidance, has been achieved in a research setting, but requires translating to the clinic. This may provide the solution to the ultimate doubts expressed by the critics of CFRT that, whilst the weapon is excellent, it may not hit all of the moving target . Bel et al (2000) describe a computer-driven couch which could be used for patient repositioning.