Sammer, M.* ; Zahnbrecher, E. ; Dobiasch, S. ; Girst, S.* ; Greubel, C.* ; Ilicic, K. ; Reindl, J.* ; Schwarz, B.* ; Siebenwirth, C.* ; Walsh, D.W.M.* ; Combs, S.E. ; Dollinger, G.* ; Schmid, T.E.
     
 
    
        
Proton pencil minibeam irradiation of an in-vivo mouse ear model spares healthy tissue dependent on beam size.
    
    
        
    
    
        
        PLoS ONE 14:e0224873 (2019)
    
    
    
		
		
			
				Proton radiotherapy using minibeams of sub-millimeter dimensions reduces side effects in comparison to conventional proton therapy due to spatial fractionation. Since the proton minibeams widen with depth, the homogeneous irradiation of a tumor can be ensured by adjusting the beam distances to tumor size and depth to maintain tumor control as in conventional proton therapy. The inherent advantages of protons in comparison to photons like a limited range that prevents a dosage of distal tissues are maintained by proton minibeams and can even be exploited for interlacing from different beam directions. A first animal study was conducted to systematically investigate and quantify the tissue-sparing effects of proton pencil minibeams as a function of beam size and dose distributions, using beam widths between s = 95, 199, 306, 411, 561 and 883 mu m (standard deviation) at a defined center-to-center beam distance (ctc) of 1.8 mm. The average dose of 60 Gy was distributed in 4x4 minibeams using 20 MeV protons (LET similar to 2.7 keV/mu m). The induced radiation toxicities were measured by visible skin reactions and ear swelling for 90 days after irradiation. The largest applied beam size to ctc ratio (s/ctc = 0.49) is similar to a homogeneous irradiation and leads to a significant 3-fold ear thickness increase compared to the control group. Erythema and desquamation was also increased significantly 3-4 weeks after irradiation. With decreasing beam sizes and thus decreasing s/ctc, the maximum skin reactions are strongly reduced until no ear swelling or other visible skin reactions should occur for s/ctc < 0.032 (extrapolated from data). These results demonstrate that proton pencil minibeam radiotherapy has better tissue-sparing for smaller s/ctc, corresponding to larger peak-to-valley dose ratios PVDR, with the best effect for s/ctc < 0.032. However, even quite large s/ctc (e.g. s/ctc = 0.23 or 0.31, i.e. PVDR = 10 or 2.7) show less acute side effects than a homogeneous dose distribution. This suggests that proton minibeam therapy spares healthy tissue not only in the skin but even for dose distributions appearing in deeper layers close to the tumor enhancing its benefits for clinical proton therapy.
			
			
				
			
		 
		
			
				
					
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        Publikationstyp
        Artikel: Journalartikel
    
 
    
        Dokumenttyp
        Wissenschaftlicher Artikel
    
 
    
        Typ der Hochschulschrift
        
    
 
    
        Herausgeber
        
    
    
        Schlagwörter
        Radiation-therapy; Radiotherapy; Optimization; Skin
    
 
    
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        Sprache
        englisch
    
 
    
        Veröffentlichungsjahr
        2019
    
 
    
        Prepublished im Jahr 
        
    
 
    
        HGF-Berichtsjahr
        2019
    
 
    
    
        ISSN (print) / ISBN
        1932-6203
    
 
    
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	    Band: 14,  
	    Heft: 11,  
	    Seiten: ,  
	    Artikelnummer: e0224873 
	    Supplement: ,  
	
    
 
  
        
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            Verlag
            Public Library of Science (PLoS)
        
 
        
            Verlagsort
            Lawrence, Kan.
        
 
	
        
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        Begutachtungsstatus
        Peer reviewed
    
 
     
    
        POF Topic(s)
        30203 - Molecular Targets and Therapies
    
 
    
        Forschungsfeld(er)
        Radiation Sciences
    
 
    
        PSP-Element(e)
        G-501300-001
    
 
    
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        Erfassungsdatum
        2019-12-02