Proton therapy

Fermilab designed and built the proton therapy accelerator as the first proton accelerator specifically for the treatment of cancer. flJ.S. Department of Energy]... 

MeV required in proton-therapy for an effective treatment of deep seated tumors [26]. Fuchs and co-authors have proposed a scaling law [27], allowing the necessary laser parameters to produce proton beams of interest for such applications to be estimated. In their work, best suited to hundreds of fs/some ps duration laser pulses, they use the self-similar fluid model proposed by Mora [28] giving the following estimate for the maximum FWD proton energy ... 

Proton beams bring a significant improvement in the physical selectivity of the treatment. The number of proton therapy centers in operation and in the planning stage increases continuously worldwide. The best clinical results, so far, have been reported for uveal melanoma, tumors of the base of skull, and some brain tumors in children. 

Today, proton beam therapy is applied in more than 20 centers worldwide and new facilities are in preparation (or under discussion). So far, about 30 000 patients have been treated with protons (Tables 5a and 5b). There is a continuously increasing number of proton therapy centers in operation and an impressive number of projects under construction or study. 

On the other hand, proton beams have no radiobiological advantages and a constant relative biological effectiveness (RBE) with respect to photons of 1.0-1.1 is generally assumed. The vast clinical experience accumulated with photons can thus be transferred directly to proton therapy. 

In the past, proton therapy was performed with complex physics machines, adapted to clinical needs, not always available full time, often expensive to maintain, and difficult to tune. Today, several commercial companies offer turn key equipment for proton therapy, adapted to the needs (or to the financial limitations) of the center. It is likely that this trend will develop further. 

The establishment of the Northeast Proton Therapy Center (NPTC) in Boston was obviously the trigger of the movement, but such a fast proliferation was certainly not expected [37]. 

In general, a new radiotherapy technique may be considered to have gained its place among the other ones when the equipment can simply be purchased commercially. This is obviously now the case with proton therapy. 

Local control of the tumor within the treated eye which was 96% and 95% at 60 and 84 months, respectively, was reported. Eye retention probability after proton therapy depends on tumor size, being 97%, 93%, and 78% for patients with small, intermediate, and large tumors, respectively. Survival at 5 years of the patients treated with protons or enucleation is similar (about 80%). 

Figure 16 Proton therapy for uveal melanoma. Dose distribution obtained with a beam of 60-MeV protons with an appropriate spread-out Bragg peak (energy modulated from 14-60 MeV). Transverse section through the center of the eye. The position of the tumor [gross tumor volume (GTV)] is indicated by the posterior hatched area. Protons allow to obtain a homogeneous dose over the whole GTV with effective sparing of the normal structures. This implies a great precision in patient-beam positioning. (Courtesy from PSI, cited in Ref. 3.)...

CNS Tumors in Children. Pediatric tumors located in the CNS are particularly challenging and deserve highly refined techniques of radiation therapy like proton therapy (Fig. 18) [40-42]. The preliminary results from Loma Linda, MGH/HCL, and Centre de Proton Therapie d Orsay are promising and show an excellent immediate and late tolerance. 

The introduction of proton beams aims at further improving the physical selectivity of the irradiation. The clinical results obtained by the pioneers in proton therapy, with machines in physics laboratories, were sufficiently convincing to justify building and buying dedicated hospital-based proton machines. 

Proton therapy equipment is now commercially available from several companies. This is a sign that protons have gained their place in the radiation therapy arsenal. Indeed, the number of proton therapy facilities increases worldwide, both the hospital-based, therapy-dedicated facilities and the facilities in physics laboratories adapted for medical applications. 

Aso T, Kimura A, Tanaka S, Yoshida H, Kanematsu N, Sasaki T, Akagi T. (2005) Verification of the dose distributions with GEANT4 simulation for proton therapy. IEEE Trans on Nuclear Science 52(4) 896-901. 

Ciulla TA, Danis RP, Klein SB, et al. Proton therapy for exudative age-related macular degeneration a randomized, sham-controlled clinical trial. Am J Ophthalmol 2002 134 905-906. 

Within the energy range of importance in proton therapy (from stopping protons to -250 MeV), it is convenient to consider two energy intervals separately (Sjirk Niels Boon, 1998) ... 

Gottschalk, B. 2011.Physics of proton interactions in matter. In Proton Therapy Physics. CRC Press, Boca Raton, FL, Chapter 2, pp. 19-60. 

Lomax AJ (2008) Intensity modulated proton therapy and its sensitivity to treatment uncertainties parts I and II. Phys Med Biol 53 1027-1056... 

Combination of active methods in the longitudinal as well as in the lateral dl rection allows an optimal conformation of the dose distribution to the tumor vol ume. Such a system, called raster scan system (Fig. 31), has been realized for the heavy ion therapy project at GSI [150,151]. Similarly, the proton therapy at PSI is using an active scanning method only a corresponding movement of the patient replaces the magnetic scanning of the beam in the y direction [152,153]. 

Meanwhile there are data indicating a significantly enhanced RBE at least for In-vitro systems also in the case of proton radiation [156] however, since the relevance of this data to the clinical situation Is still under discussion, these data have so far not been considered for treatment planning In proton therapy. 

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