I would like to have a better understanding of the medical, biological, physical and economical factors that are taken into account when deciding on what dose is delivered per fraction of radiotherapy for any given tumor.
Good question, the answer is not unequivocal. I am attaching an interesting paper - Thames. On the Origin of Dose Fractionation. Still 2Gy/fraction is widely used. In SBRT the doses per fractions may differ considerably from one institution to another. The dose-painting approach prescribes a dose distribution not a dose per fraction, in order to deliver higher dose to more resistant part of the tumor, but how one determines which are the more sensitive parts is still debatable. Nowadays due to the great technological improvements one should try to deliver as high doses as the surrounding tissue can tolerate. One can calculate the NTCP for a given plan and see if it is low enough. Clinical data represent a population response, and when the clinical observations are applied for a given case one can say only that in such % of the cases one gets tumor control, while the concrete individual the probability for control might be close to 0 or 1:
https://www.researchgate.net/publication/334130824_Modelling_the_effect_of_spread_in_radiosensitivity_parameters_and_repopulation_rate_on_the_probability_of_tumour_control
In general the principle should be – The higher dose the better as long as the normal tissue stays intact or sufficiently intact and if the clinical protocol allows it :).
Thank you Dr Stavrev, so from your answer i take it that one of the main dose limiting factors is the tolerance (radiation sensitivity) of the surrounding healthy tissue.
Thanks also for the interesting links!
The German school is very interesting:
In 1904, Perthes recommended treatment in one session or at most a few fractions, with close monitoring of the dose.
1900 to ~1920: the German school
Although radiotherapy was being developed in many places during the early part of the
twentieth century, German research dominated. The German approach was characterized by the use of a few large ‘caustic’ doses of radiation. Such treatments frequently led to impressive responses, but few long-term ‘cures’, for reasons of biology that we now understand, but that were not appreciated at the time. The start of this period might date from the report of Freund in 1903 of the disappearance of a hairy mole after treatment with X-rays.
This guy Perthes, who is a surgeon obviously envisions the radiation as an invisible surgical knife – thus why not use it in one treatment or few, something that nowadays we do with SBRT, VMAT and similar treatments, because now we know where and what type of dose we can deliver, while unfortunately 100 years ago this was not so. I am attaching another interesting paper too.
We must find the best cost-efficiency relation with the best survival.
We have a median 13.9 fractions per patient with more than one thousand patients per year. Each tumor and patient we must study the best treatment.
As a result of massive RT overdoses, several deaths and severe side effects resulted, but also some cases of unexpected good results or cure.
Why unexpected!? The knowledge that such results should be expected is available at least from 1990s.
The trial put all compensations to be paid by machine producer.
To me this is a great injustice! The financial burden must have been put mainly on the hospital and the medical physicists put in jail. After each maintenance the medical physicists must perform the appropriate QA and assure that the LA is in adequate condition to treat patients. On the other hand the phrase “the people driving the LA“ is puzzling, pointing probably towards the lack of medical physicist there. If this is so – the director of the hospital and the minister of health must have been put on trial as well. That’s my verdict :).
The age of the patient. The site of the tumour. The histological type. The presence of co-morbidity.
The type of treatment machine used its also important in deciding the dose per fraction if radiotherapy.
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