for example
if there is a patient planned to treated with 25 fractions with 200 cGy, for 5 days per week (5 weeks), let he absent for 3 days for the first week and absent 2 days for the second and finally absent for 10 days in the last one, how to calculate the actually received dose and the remaining
Dear Dr. Gawad,
Although I have heard of the Ellis NSD-concept, I have more experience with the LQ-model (by Fowler and Barendsen). The literature on missed radiation fractions is extensive; for practical purposes I recommend the papers by Nuran Bese et al. (2007) and by Roger Dale et al (2002) [1,2].
If you do not have access to these two papers, do not hesitate to send me an e-mail, so I can forward them as pdf-attachments.
There are several (more or less freeware) LQ-model software packages, that also have a a module for compensation of missed fractions.
See amongst others: http://www.eyephysics.com/tdf/
Sincerely yours,
Lukas Stalpers, radiation oncologist
AMC - University of Amsterdam, The Netherlands
1. Bese NS, Hendry J, Jeremic B. Effects of prolongation of overall treatment time due to unplanned interruptions during radiotherapy of different tumor sites and practical methods for compensation. Int J Radiat Oncol Biol Phys. 2007;68(3):654-61
2. Dale RG, Hendry JH, Jones B, Robertson AG, Deehan C, Sinclair JA. Practical methods for compensating for missed treatment days in radiotherapy, with particular reference to head and neck schedules. Clin Oncol (R Coll Radiol). 2002; 14: 382–393
Dear Gawad and Lukas
My papers in Red Journal and Clinical Oncology clearly show that for squamous cell carcinomas of the H&N (and may be for Cx, and other sites too), interruptions in the first two weeks are critical, more so when smaller fraction sizes of 2 Gy etc, are used. For sizes 3.5 Gy it was not critical.
What I would have done is change the fraction size, for at least a few fractions, after the interruptions in the first two weeks.
Has the patient completed the treatment? What you can do now is calculate the BED for the critical tissues in the target volume (especially spinal cord and brain) using the equation
BED (in Gy) = nD (1 + (D / (α/β)))
where n is the number of fractions, D is the dose per fraction and α/β is the ratio applicable to the tissues which, for Spinal cord, you can take as 2-3. You are naturally forgetting the effect of time. After calculating the BED received by the critical organs, you can think of how much more dose you can give and give that.
I approached the topic in terms of cumulative interfraction intervas (CIFI)., which I came to by means of Real time cytological examination of cell death markers in tumour cells. All papers published in Top, international peer reviwed journals, but unfortunately not given attention by radiotherapists.
They are available in RG. Dear Gavad and Lukas, please go through when you have the time, and inclination, which I hope you have
Narayanan
Dear Gawad and Lukas
My papers in Red Journal and Clinical Oncology clearly show that for squamous cell carcinomas of the H&N (and may be for Cx, and other sites too), interruptions in the first two weeks are critical, more so when smaller fraction sizes of 2 Gy etc, are used. For sizes 3.5 Gy it was not critical.
What I would have done is change the fraction size, for at least a few fractions, after the interruptions in the first two weeks.
Has the patient completed the treatment? What you can do now is calculate the BED for the critical tissues in the target volume (especially spinal cord and brain) using the equation
BED (in Gy) = nD (1 + (D / (α/β)))
where n is the number of fractions, D is the dose per fraction and α/β is the ratio applicable to the tissues which, for Spinal cord, you can take as 2-3. You are naturally forgetting the effect of time. After calculating the BED received by the critical organs, you can think of how much more dose you can give and give that.
I approached the topic in terms of cumulative interfraction intervas (CIFI)., which I came to by means of Real time cytological examination of cell death markers in tumour cells. All papers published in Top, international peer reviwed journals, but unfortunately not given attention by radiotherapists.
They are available in RG. Dear Gavad and Lukas, please go through when you have the time, and inclination, which I hope you have
Narayanan
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