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  1. Usually • / is assumed to be 10 for early reacting tissues (including tumours ) and 3 for late reacting tissues • T1/2 is assumed to be 1.5 hours for both early and late reacting tissues • Using these values the therapeutic gain will be less using HDR compared to LDR (~0.5 Gy/h) (unless a lot of fractions are used in the HDR schedule ~ 33) BIR/IPEM, London, June 23rd

  2. However…. Randomized prospective and retrospective studies show overall statistically equivalent local control, overall survival, and complication rates between HDR and LDR. Review: Stewart and Viswanathan, Cancer 2007 BIR/IPEM, London, June 23rd

  3. Published half time of repair BIR/IPEM, London, June 23rd

  4. HDR: 7Gy in 7 fractions HDR: 12.5Gy in 3 fractions HDR: 5Gy in 10 fractions HDR: 2Gy in 33 fractions Different half time for tumour and OAR BEDtumour,LDR= BEDtumour,HDR= 80Gy BEDOAR,LDR= BEDOAR,HDR /tumour=10 Gy /OAR=3 Gy t1/2,tumour = 1.5 h C. Orton, IJROBP, 2001 BIR/IPEM, London, June 23rd