| Ch 8 | Page 9 / 25 | |
| Cancer radiotherapy |
Goals of radiotherapy | |
Goal: To definitively sterilise the cancer cells within the irradiated volume in order to obtain total cure of the cancer.
Neccessary conditions: absence of remote metastases.
In these conditions, treatment will often last several weeks since it is necessary to use high tolerated dose, whilst respecting healthy tissue and precisely targeting the tumour.
Radiotherapy is a major weapon for fighting against cancer. The following indications are those for which it is the most efficient and often replaces mutilating and inefficient surgical procedures.
In order to be curative, the necessary dose to control the tumour should be inferior to the tolerated dose of the critical neighbouring organs. These doses are defined to within an accuracy of 5 to 10% and vary from one individual to another, more or less according to a Gauss curve. The margin between success and failure is relatively narrow, and a rigourous technique is therefore mandatory: we alternate between the risk of local relapse and, for a few supplementary Grays, the risk of necrosis.
Generally speaking, vegetating tumours are more radiosensitive than infiltrating
tumours due to the oxygen effect.
The following table, borrowed from Pr Jean-Pierre Gérard, shows the sensitivity of various tumours:
| Histological tumours | Median dose
for 90% of definitive sterilisation |
Leukaemia |
15
- 25 Gy |
Seminoma |
25
- 35 Gy |
Dysgerminoma |
25
- 35 Gy |
Wilms tumour |
25
- 40 Gy |
Hodgkin's disease |
30
- 45 Gy |
Non Hodgkin's Lymphoma |
35
- 55 Gy |
Malpighian
carcinoma |
55
- 75 Gy |
Adenocarcinoma |
55
- 80 Gy |
Urothelial
carcinoma |
60
- 75 Gy |
Sarcoma |
60
- 90 Gy |
Glioblastoma |
60
- 80 Gy |
Melanoma |
70
- 85 Gy |
This second table, also borrowed from Pr Jean-Pierre Gérard, shows the importance of tumour volume among malpighian tumours in order to obtain tumour sterilisation.
| Tumour volume | Necessary dose |
| Infraclinical disease | 45 - 60 Gy |
| Tumour < 2 cm diameter | 60 - 64 Gy |
| Tumour > 2 cm - < 4 cm | 65 - 70 Gy |
| Tumour > 4 cm | 75 - 85 Gy |
The greater the volume, the higher the necessary dose. Generally speaking, cutaneous and conjunctive tissue does not regularly tolerate a dose above 65-70 Gy, except in the case of a very small volume.
In order to be efficient, radiotherapy should be able to irradiate the whole tumour (and in particular its microscopic extensions to neighbouring healthy tissue).
Goal: to slow down the progression of already advanced local tumours or those with remote metastases which cannot be cured using local treatment.
The treatment should be short and relativey non-aggressive, like, for instance, split-course irradiation allowing the patient to recover between two radiotherapy treatment sessions.
Goal: to relieve the patient from a major symptom, for instance:
- pain from bone metastases. The effect can generally be rapid, appearing after a few fractions (with an occasional transitory outbreak of the symptoms in relation to radiotherapy-induced inflammation or oedema). It is estimated that 75% of patients are partially or totally relieved from their pain at the end of treatment or in the following weeks;
- haemorrhage syndrome,
- compression such as spinal cord or radicular compression. Spinal cord compression is an emergency in radiotherapy: in order to be truly efficient (full patient recovery), this treatment should be administered as soon as the first symptoms appear (immediately following confirmation by RMI). It is relatively efficient if the patient still has leg sensitivity. The treatment consists of a few fractions in order to obtain a powerful effect. An emergency meeting should be organised between the physician, the surgeon and the radiotherapist at the patient's bedside in order to discuss and rapidly decide on the most appropriate treatment modality (surgery or radiotherapy).
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