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Children have priority whenever proton therapy is indicated

Children have priority whenever proton therapy is indicated

International experts concur that proton radiation is preferred over X-rays for the treatment of children and teenagers. (see Status Report September 09 "proton therapy for pediatric cancer"). Why is this the case? After all, precise “prospective randomized” comparative clinical trials involving children do not exist – a fact that will never change. Both radiation and pharmacotherapy face the same dilemma involving children: clinical trials in children are prohibited – and not just in Germany. Radiation testing on underaged subjects is even more strictly prohibited. Under § 87 StrlSchV Abs. 1, the test person can only give his consent if he is contractually capable.  
 
Therefore, the preference for proton therapy to treat pediatric cancers, often brain tumors that require irradiation, is justified solely by the computable superiority of the dose distribution of protons compared to X-rays (which is also generally true of adults). The superior dose distribution of proton radiation in the body often allows doctors to increase the dose in the tumor while simultaneously reducing healthy tissue exposure, which is a crucial benefit for a growing adolescent body.  
 
Reduction in irradiated volume with protons. Proton beams can be targeted in three dimensions; they stop in the tumor. Behind the tumor, i.e., the side that is averted from the radiation source, there is no irradiation of healthy tissue, unlike X-rays. The improvement can easily be quantified with the standard protocols for proton scanning (see Status Report April 09):

volume of irrdiated healthy tissue* (normalized to adult person's dimensions)

  X-rays protons
Chordoma 2413 ml 446 ml
Gliom 3330 ml 443 ml
Meningeoma 2756 ml 419 ml
Brain-Metastases 2356 ml 312 ml

*) Tissue volume with more than 0.5 Gy dose accumulation

 

Exposure of child and adolescent tissue to non-lethal doses of radiation as “collateral damage” associated with tumor treatment results in a roughly 1% chance of occurrence in each subsequent year of the child’s life of radiation-induced secondary tumors caused by therapeutic radiation. These secondary tumors are mostly malignant sarcomas. It is well known that these secondary tumors pose a greater risk than the risk of recurrence of the initial tumor, particularly with children, who have most of their lives ahead of them.  
 
Reduced dosing of healthy tissue with proton therapy. As our Internet reports have repeatedly stated, the dose in front of the tumor, i.e., along the path of the radiation from the radiation source to the tumor, is lower, not higher than in the tumor when using the proton scanning method. This physical effect is significant, multiplies the reduction of the irradiated volume, and can once again be quantified using the standard protocols of the RPTC:

 

average dose in healthy brainstem

  X-rays protons
Chordoma 22,7 Gy 7,0 Gy
Gliom 5,6 Gy 0,1 Gy
Meningeoma 36,0 Gy 0,1 Gy
Brain-Metastases 10,5 Gy 0,9 Gy

 

This decreased dose associated with protons is especially effective if applied using the scanning method, which is both precise and nearly free of scattered neutron radiation. The RPTC uses the scanning method, unlike older facilities who still use the scattering method (see Status Report June 09). The decreased dose not only reduces the risk discussed above of subsequent secondary tumors, but also has a positive effect on tissue growth: maturing tissue is particularly sensitive to radiation-induced scarring. For example, girls whose mammary glands are exposed to radiation before puberty experience no further growth in those glands for the rest of their lives.

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