Clinical Technology

A comprehensive white paper on technology trends explains how and why proton therapy is gaining increasing importance as a cancer treatment option. Part IV explores the measurement tools that help exploit the advantages of proton therapy to the fullest.

Our body is not perfectly stable and the same goes for tumors. Measurement tools contribute in large part to the effi ciency of radiation therapy and refi ning these tools would signifi cantly multiply the power and precision of proton therapy. Cone beam CT (CBCT) and CT-on-rails are candidate technologies to enable imaging directly in the treatment room whereas prompt gamma cameras should allow to verify the beam range.

Improve imagery

Rigorously and regularly measuring the size and shape of the tumor and correctly positioning the patient underneath the beam are paramount. True 3D imaging is used today for tumor localization and patient alignment as in conventional radiation therapy. In proton therapy, we anticipate that it might also be used for proton range accuracy and daily plan correction.

Cone beam CT (CBCT) and CT-on-rails are candidate technologies that have recently emerged in this fi eld, to enable imaging directly in the treatment room. Both have merits and disadvantages. CT imaging gives a better contrast and high spatial resolution: it gives better soft tissue appearance with low imaging doses, in particular due to the option to limit the fi eld of view. In addition, the quick collection of data reduces the possibility of motion artifact.

On the other hand, CBCT offers the possibility of imaging directly in the treatment position, but still faces some challenges arising from the X-ray diffusion, resulting in images with reduced quality and containing some artifacts. CT-on-rails can be seen as a compromise: CT imagery is located within the treatment room. The patient lies on a stationary patient couch that can be brought into the scanner. It provides excellent image quality, opening possibilities for managing changes in inter-fraction patient setup and organ motion, but it requires that the patient be moved from the treatment position to the imaging position. Experience will show the specifi c benefi ts of these two approaches when it comes to proton therapy. The accompanying treatment image manipulation software will play an equally important role, becoming increasingly powerful and indispensable.

Verify beam range

Measuring beam depth is another issue. Because 90% of the body is made up of water, water phantoms are usually used for testing. You can adjust up to onequarter of a millimeter in water, allowing for an exquisitely accurate defi nition of the beam range. However, in an actual patient, there is always the remaining 10% to take into account.

Take for example a brain tumor, generally inoperable and irradiated through the nasal cavities. If these are healthy and clear on the day of treatment planning, but the patient develops a cold by the day the radiation is performed, density in the nasal cavities will have changed. Mucus having a density of 1 whereas air has a density of 10-3, these changed conditions will change the range of the beam. Not reaching the distal part of the tumor will cause treatment failure.

The same goes for irradiation of the prostate or ovaries, going through the intestines, which are generally fi lled with water, but prone to containing bubbles or gases. As treating some unneeded healthy tissue is still better than potentially missing part of the tumor, clinicians today are still opting for a large safety margin, whereas using the sharpest gradient at the distal edge of the tumor, totally sparing e.g. an organ at risk right behind would therefore lead to superior treatment. A tool allowing us to precisely measure radiation depth would as a result multiply the power of proton therapy.

To this purpose, IBA came up with the idea to capture and measure prompt gamma rays emitted from protoninduced nuclear reactions. “We are confident that the prototypes of our prompt gamma cameras will be ready for testing in 2015, after which they can be fine-tuned based on test results. Implementing these will again represent a major asset to our proton therapy installations and cancer treatment in general,” concludes Yves Jongen.

Read the complete white paper on Technology Trends (


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