• Three-dimensional conformal radiation therapy (3D-CRT)

Two-dimensional Conventional radiation therapy refers to the old techniques where treatments were planned with a limited number of beams delineated by orthogonal x-rays plan. Beam shapings were limited to simple square or rectangular beams. Due to the low conformity of these treatments, adjacent tissues/organs often fall into the high dose region resulting in treatment side effects. Conversely three-dimensional conformal radiation therapy (3D-CRT) is based on 3D anatomic information provided most of the time by CT-scan using treatment fields that conforms far better to the target volume avoiding as much as possible the surrounding normal tissue. Target volumes are defined in 3 dimensions using contours drawn on many slices from a CT-imaging study (picture 43). It is a multiple stages procedure including patient positioning, a strict immobilization, image acquisition, defining target volume, field shaping as well as dose calculation. The main advantage of the 3D-CRT is the possibility of a dose escalation without increase in normal tissue toxicity. However this technique is still slow and labor intensive.

• Intensity modulated radiation therapy (IMRT)

The intensity modulated radiation therapy (IMRT) is an advanced form of 3D-CRT and represents the most common type of EBRT. An innovative technology is used to produce more uniform dose distribution with the same main goals : to intensify the irradiation on the tumour target and to alleviate the surrounding toxicity. Fluence files are electronically transmitted to the computer controlled linear accelerator to deliver the intensity-modulated beams. By using more than 9 angles beams and thousands of segments, it allows a higher dose escalation to the most aggressive cancer cells (picture 44). The principal IMRT modalities are the image guided radiation therapy (IGRT) with the use of realtime imaging during the procedure instead of pre-radiation imaging acquisition and volumetric modulated arc therapy (VMAT) based on a 360° complete arc of radiation units.

• Stereotaxic body radiation therapy (SBRT)

A technological step further is more based on biological knowledges than technological improvement. The rationale stands on the relationship between radiation dose and cytotoxicity effect where a few large individual doses have more cell-killing effect than the same dose given gradually. In that perspective a whole cure of EBRT will last 1 to 5 days instead of weeks. SBRT is also the fruit of technological progresses with the development of the Gamma Knife®, X-Knife®, CyberKnife®, and Clinac® (picture 45).

EBRT as a whole are validated prostate cancer therapies with permanent improvement the last one being hypofractioning. Indeed the initial standard fractionation of 1.8-2 Grays needed 5 sessions per week during 6-7 weeks. Then the conventional hypofractionation of 3-5 Grays was performed also 5 days per week but only in 2 weeks. Eventually with the SBRT and an hypofractionation of 15-25 Grays only 1 to 5 radiation sessions are needed.

• Proton or neutron beam radiation therapy

Proton beam therapy focuses beams of protons instead of x-rays on the cancer. Unlike x-rays, which release energy both before and after they hit their target, protons cause little damage to tissues they pass through. Although in theory proton beam therapy might be more effective than using x-rays, so far studies have not shown if this is true. Very few centers in the world are able to deliver these very expensive therapies. Unlike the others EBRTs, proton and neutron beam radiation therapies have not been studied on large populations and additional scientific data are needed.