α/β, alpha/beta ratio

The ratio of “intrinsic radiosensitivity” to “repair capability” of a specified tissue (in units of Gy). This ratio is large (>8 Gy) for rapidly proliferating tissues and most tumors. It is small (<6 Gy) for slowly proliferating tissues, including late normal-tissue complications. This difference is vital for the success of radiotherapy. When beta (β) is large, both mis-repair and good-repair are high. It is the mis-repair that causes the cell survival curve to bend downward [1]. It is the "dose for which the number of acutely responding cell deaths is equal to the number of late-responding cell deaths (the dose for which the linear and quadratic components of cell death are equal). (...) The α/β ratio may differ among tumor types" [2]. It is the fractionation factor [13]. For skin tumors, the α/β for 90% control rate is 13.8 Gy [3].

	List of α/β (Gy)
Heart	3 [3]
Spinal cord (radiation myelopathy)	0,87 [12], 2 [4,5]
Lung	3 [4], 4 (fibrosis), 5 (pneumonitis) [5], 2.7-4 (late reactions) [6]
Liver (fibrosis)	1 [4,5]
Kidney (nephropathy)	2 [5], 3 [4], 2-2.4 (late reactions) [6]
Parotid gland	2 [4]
Salivary glands (permantent xerostomia)	3 [5]
Lachrymal system (dry eye, ulceration)	3 [5]
Nervous system	3 [4]
Central nervous system (brain, spinal cord) (late reactions)	1.8-2.2 [6]
Eye lens (cataract)	1-2 [5]
Optic nerve (neuropathy)	2 [5]
Chiasma opticum (loss of vision)	2 [5]
Testicle	1 [4]
Testis (early reactions)	12-13 [6]
Ovary	1 [4]
Eye	1 [4]
Bone	3 [4]
Bone marrow	10 (transient hypoplasia), 5 (lethal aplasia [1 year]) [5]
Cartilage	1 [4], 6 [5]
Larynx (chronic oedema, necrosis)	2-4 [5]
Rectum (chronic inflammation, ulcer)	5 [4,5], 2.5-5 (late reactions) [6]
Urinary bladder	2 [4], 10 (acute cystitis), 5-10 (shrinkage, ulceration) [5], 3-7 (late reactions) [6]
Skin (acute erythema, dry radiodermatitis)	8.8 (erytema) (confidence interval: 6.9; 11.6) [14], 9-10 [5], 9-12 (early reactions) [6], 11,2 (desquamation) (confidence interval: 8.5; 17.6) [14], 12.3 (erytema) (confidence interval: 1.8; 22.8) [15]
Hair follicles (hair loss)	7 [5]
Mucosa (early reactions)	9-10 [6]
Oral mucosa (acute ulcerative mucositis)	10 [5]
Stomach (ulcer)	4 [5]
Small intestine (acute malabsorption)	8 [5]
Jejunum (early rections)	6-10 [6]
Small intestine (ulcer/obstruction)	4 [5]
Colon (early reactions)	9-11 [6]
Breast, adult (fibrosis/atrophy)	2-3 [5]

Human tumors	List of α/β (Gy)
Malign melanoma	0.57 [7], 1.5 [2]
Prostate adenocarcinoma	1.2 [8], 1.49 [9], 1.5-3.5 [2,10]
Bladder cancer (transitional cell carcinoma)	13 (for external beam radiotherapy [EBRT]) and 24 (for EBRT and brachytherapy) [16]
Rhabdomyosarcoma	2.8 [11]
Skin	13.8 [3]
Vocal cord	9.9 (Harrison et al., 1988, cited in [6])
Oropharynx	13-19 (Rezvani et al., 1993, cited in [6])
Larynx	25-35 (Maciejewski et al., 1988, cited in [6]), 50-infinity (Chappell et al., 1995, and Roberts et al., 1998, cited in [6])

Bibliographic references:
[1] Fowler, J. (2006). Part I: Basic Concepts in Treatment Planning, 1. Practical Time-Dose Evaluations, or How to Stop Worrying and Learn to Love Linear Quadratics. In: S. Levitt, J. Purdy, C. Perez and S. Vijayakumar, ed., Technical Basis of Radiation Therapy, Practical Clinical Applications, 4th ed. Springer-Verlag Berlin Heidelberg, pp.3-31.
[2] Beyzadeoglu, M., Ozyigit, G. and Ebnuli, C. ed., (2010). 2.6.2. Linear-Quadratic Model (LQ Model). In: Basic Radiation Oncology, 1st ed. Berlin: Springer Berlin Heidelberg, p.104.
[3] Maia MAC, Oliveira SC. Radioterapia nos tumores de pele. In: Âmbito Editores Ltda, 3.ª ed. Manual de condutas diagnósticas e terapêuticas em oncologia [Portuguese]. São Paulo, Brazil: Kowalski LP, Guimarães GC, Salvajoli JV, Feher O, Antoneli CBG (eds.); 2006; 327-330.
[4] Sfjro.fr. (2010). eLQ - Radiation Therapy Equivalent Dose Calculator. [online] Available at: http://www.sfjro.fr/ilq/en/biblio.html [Accessed 25 Jul. 2016].
[5] Dörr, W. (2009). 13 - Pathogenesis of normal-tissue side-effects. In: M. Joiner and A. van der Kogel, ed., Basic Clinical Radiobiology, 4th ed. London, United Kingdom: Hodder Arnold, an Hachette UK Company, pp.179-181.
[6] Fowler JF. The radiobiology of prostate cancer including new aspects of fractionated radiotherapy. Acta Oncol. 2005;44(3):265-76. Available at: http://dx.doi.org/10.1080/02841860410002824.
[7] Bentzen SM, Overgaard J, Thames HD, Overgaard M, Vejby Hansen P, von der Maase H, et al. Clinical radiobiology of malignant melanoma. Radiother Oncol. 1989 Nov;16(3):168-82. Available at: http://dx.doi.org/10.1016/0167-8140(89)90017-0.
[8] Brenner DJ, Martinez AA, Edmundson GK, Mitchell C, Thames HD, Armour EP. Direct evidence that prostate tumors show high sensitivity to fractionation (low alpha/beta ratio) comparable to late-responding normal tissue. Int J Radiat Oncol Biol Phys. 2002 Jan 1;52(1):6-13. Available at: http://dx.doi.org/10.1016/s0360-3016(01)02664-5.
[9] Fowler JF. Biological factors influencing optimum fractionation in radiation therapy. Acta Oncol. 2001;40(6):712-7. Available at: http://dx.doi.org/10.1080/02841860152619124.
[10] Brenner DJ, Hall EJ. Fractionation and protraction for radiotherapy of prostate carcinoma. Int J Radiat Oncol Biol Phys. 1999 Mar 15;43(5):1095-101. Available at: http://dx.doi.org/10.1016/S0360-3016(98)00438-6.
[11] Timmerman RD, Mendonca M. In regard to Donaldson et al: results from the IRS-IV randomized trial of hyperfractionated radiotherapy in children with rhabdomyosarcoma-a report from the IRSG. IJROBP 2001;51:718-728. Int J Radiat Oncol Biol Phys. 2002 Dec 1;54(5):1579-80; author reply 1580. Available at: http://dx.doi.org/10.1016/S0360-3016(02)03015-8.
[12] Schultheiss TE. The radiation dose-response of the human spinal cord. Int J Radiat Oncol Biol Phys. 2008 Aug 1;71(5):1455-9. Available at: http://dx.doi.org/10.1016/j.ijrobp.2007.11.075.
[13] Dale RG, Hendry JH, Jones B, et al. Practical methods for compensating for missed treatment days in radiotherapy, with particular reference to head and neck schedules. Clin Oncol (R Coll Radiol). 2002 Oct;14(5):382-93. Available at: http://dx.doi.org/10.1053/clon.2002.0111.
[14] Turesson I, Thames HD. Repair capacity and kinetics of human skin during fractionated radiotherapy: erytema, dequamation, and telangiectasia after 3 and 5 year's follow-up. Radiother Oncol. 1989 Jun;15(2):169-88. Available at: https://doi.org/10.1016/0167-8140(89)90131-x.
[15] Bentzen SM, Christensen JJ, Overgaard J, Overgaard M. Some methodological problems in estimating radiobiological parameters from clinical data. Alpha/beta ratios and electron RBE for cutaneous reactions in patients treated with postmastectomy radiotherapy. Acta Oncol. 1988;27(2):105-16. Available at: https://doi.org/10.1016/0167-8140(89)90131-x.
[16] Pos FJ, Hart G, Schneider C, Sminia P. Radical radiotherapy for invasive bladder cancer: What dose and fractionation schedule to choose? Int J Radiat Oncol Biol Phys. 2006 Mar 15;64(4):1168-73. Available at: https://doi.org/10.1016/j.ijrobp.2005.09.023.