WHY RADIATION AFFECTS CANCER CELLS MORE THAN NORMAL CELLS – GREATER PROPORTION OF DIVIDING CELLS (PART 2)
It is important to realise how long the delay between treatment and cell death can be. Very rapidly growing tumours may start to shrink within a week or so of starting treatment because their cells divide every few days. On the other hand, the cells of slowly growing tumours only divide every few months. This means that a slowly growing tumour can keep shrinking for some months after radiation is finished.
A delay before radiation damage becomes obvious also occurs with normal cells. For example, the cells lining the mouth divide every day or so, cells on the skin surface every week or so. When radiation is stopped, a reaction in the mouth will quickly start getting better but a skin reaction can keep getting worse for a week or more. The longest delay is seen in the case of tissues whose cells very rarely divide other than when the tissue is injured. These tissues may look fairly normal and function fairly normally for years, but heal very slowly or not at all if they are injured or infected. This poor healing is only partly due to the fact that some of the cells die when they try to divide. Another reason is that blood and lymph vessels are also damaged by radiation leaving tissues with a poor blood supply and sluggish drainage.
Radiation damage to the reproductive ability of cells has one other possible serious consequence. This one is only of concern to those of you who are lucky enough to be cured, or at least to live many years after your treatment. People who have had radiation treatment have a higher than normal, but still small, risk of developing a completely new cancer within the irradiated areas. I am not referring here to a recurrence of the original cancer but to a completely new cancer caused by the radiation. Radiation-caused leukaemia typically develops about five years after radiation. Other types of cancer take twenty or more years. The risk is small but definite. When weighing up your cost/benefit balance, do try to keep this one in perspective. I stress that it will only concern you if your treatment is successful in controlling your original cancer.
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