To the Editor
I have read with interest the Editorial by Glimelius Citation[1], commenting on the paper by Brooks et al. Citation[2] about fractionation in rectal cancer. There are some mistakes as well as some uncertainties in Table I.
1. The title of the table is “Biological equivalent doses”. Values given in the table are BED, that is “Biologically effective dose”, not biologically equivalent doses. Biologically equivalent doses are doses equivalent to classical fractionation given with 2 Gy per fraction. The same remark applies to Brooks paper, Table I. Readers may tend to be confused between the two terms.
An example is given below for late effects, derived from Table I.
2. In the same table, the column head is figuring “Tumour control/acute normal tissue complication probability”, and “Late normal tissue complication probability”. Probability values, as for TCP and NTCP vary between 0 and 1. However, the values given below are BED not TCP or NTCP.
3. In the footnote of the same table, γ/α is cited as the repair factor. Repair factor concerns multiple fractions per day, whereas γ/α is the repopulation factor, which addresses the overall treatment time.
4. It has been assumed that the α/β ratio for rectal cancer is 10 Gy. This value has been derived from head and neck carcinoma where much data has been available. No values for α/β ratio have been reported for rectal cancer. Emerging data for prostate cancer Citation[3–5] and breast cancer Citation[6], Citation[7] tend to show that these tumours have low α/β values, therefore not contraindicating hypofractionation. Rectal cancer, being an adenocarcinoma, would behave more like breast or prostate cancer, rather than squamous cell head and neck carcinoma.
5. Similarly, the repopulation factor has been established gathering the long literature about the time factor in head and neck cancer. Applying the same repopulation factor, with even a short proliferation delay (Tk) of 7 days rather than the commonly assumed 28 days, has to be taken with caution when addressing rectal cancer.
References
- Glimelius B. Rectal cancer irradiation. Long course, short course or something else?. Acta Oncol 2006; 45: 1013–7
- Brooks S, Glynn-Jones R, Novell R, Harrison M, Brown K, Makris A. Short course continuous, hyperfractionated, accelerated radiation therapy (CHART) as preoperative treatment for rectal cancer. Acta Oncol 2006; 45: 1079–85
- Brenner DJ, Martinez AA, Edmundson GK, Mitchell C, Thames HD, Armour EP. Direct evidence that prostate tumors have high sensitivity to fractionation (low α/β ratio), similar to late-responding normal tissue. Int J Radiat Oncol Biol Phys 2002; 52: 6–13
- Wang JZ, Li XA, Yu CX, DiBiase SJ. The low alpha/beta ratio for prostate cancer: What does the clinical outcome of HDR brachytherapy tell us. Int J Radiat Oncol Biol Phys 2003; 57: 1101–8
- Fowler JF. The radiobiology of prostate cancer including new aspects of fractionated radiotherapy. Acta Oncol 2005; 44: 265–76
- Whelan T, Mackenzie R, Julian J, Levine M, Shelley W, Grimard L, et al. Randomized trial of breast irradiation schedules after lumpectomy for women with lymph node-negative breast cancer. J Natl Cancer Inst 2002; 94: 1143–50
- Courdi A, Ortholan C, Hannoun-Lévi JM, Ferrero JM, Largillier R, Balu-Maestro C, et al. Long-term results of hypofractionated radiotherapy and hormonal therapy without surgery for breast cancer in elderly patients. Radiother Oncol 2006; 79: 156–61