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Moving from Gap Corrections to Gap Management in Radiotherapy
In Welcome to the Forum
Moving from Gap Corrections to Gap Management in Radiotherapy
In Welcome to the Forum
sptgnadar
Aug 15, 2020
We are doing gap correction at present only if more than 2 week delay. is it OK? with tdf, upto 7 days break, it will tell no more extra # needed. can we have a copy of the presentation please? No, it is not OK...especially for rapidly proliferating tumors like SCC, even if the gap is couple of days, we need to address it & manage it... Please note that copy of the presentation & all other files, including Excel files, are available in RESOURCES section (navigate through MORE--> RESOURCES) What is the full form of tdf? For those of you who are not familiar with TDF, it is Time-Dose-Fractionation. Dr. Orton in 1973 published what are called as TDF tables (see the ref given in my presentation) to compare different fractionation regimes. In India, it is the most often used method to account for treatment interruptions! Some head and neck patients , due to reaction treatment interrupted. so managing the gap by giving 2 fractions daily on few days. so how to consider the incomplete repair effects? Of course the fractions would be separated out by at least 6 hours, preferably 8 hours. If gap occurs btw EXBT and Brachy then what are the options? Well, the document doesn't explain how the dose can be adjusted in the brachytherapy part...if the OTT is extended more than the originally planned one, well, dose has to be adjusted in brachy...but the methodology, I am not clear. In the examples, treating 5 days, two fractions daily, biological effect must be different. How can it be takes into consideration? This question has been asked in different formats. Well, my answer is: we are NOT delivering the ENTIRE treatment by altered fractionation. It is only in those special circumstances, when patients skip part of the treatment, we are altering PART OF THE TREATMENT COURSE...as far as only a small portion of the treatment is affected this way, I do not think we need to bother much.... Can I know about the validity of LQ model for higher dose per fraction? WHAT ABOUT THE GAP INCASE OF SRT OF BRAIN CONTAINING HIGH DOSE? Please go through the RCR document...see page 18 When dose per fraction is higher, the repopulation would not have begun....like for example, in SBRT treatment course where number of fractions are only 5....the repopulations starts occurring after 28 days, by which time such treatment courses would have completed... In situations where treatment is started and in the first week it is interrupted by the pandemic? As I told in the first few slides of my presentation, the POSITION of the treatment interruption in the course of the treatment (whether it occurs early or late during the course) does not appear to be important... How do we manage months long gaps? I mentioned that such months long gaps would be EXTREMELY DIFFICULT to manage! This document's methodology is not meant for managing such long gaps. Still, you can use the Excel sheet to see the results for yourselves. What is the acceptable tumour dose per fraction in altered or hyper fraction. E.g head & neck cancer I think this question can only be best answered by the treating consultant. It all depends on the consultant's views and preferences about the fraction size. In the times of IMRT what normal tissue do we consider. Also , normal tissue recovery should be considered or not? As I told during the Q&A session, the equation doesn't look at the technique or the actual doses received by the normal tissue. When you are calculating the BEDs, you HAVE TO USE only the d,N as per the dose prescription to the tumor in BOTH THE EQUATIONS. What is the effect of increasing dose per fraction on the normal tissue tolerance ? As I have stated above, we do not need to bother too much about dose per fraction since this is going to be only for few fractions & that too occurring after a gap. However ultimately the treating consultant has to take a call based on case-to-case bases, taking into account all relevant factors. Having said this, I must add here cautious notes. When you are trying to account for treatment interruptions of LONGER DURATIONS happening toward the end of the originally planned OTT, it would result in TOO HIGH A DOSE PER FRACTION which may not be acceptable. That is why I state that the treating physician has to take a call on case-to-case basis considering all factors. If the solution yields a dose per # that is too high, then try a balanced approach! Bottom line: Do not feel satisfied with the TDF based correction / solution! Is there any difference in the calculation for photon and proton ? Please see RCR document's page number 18. RCR considerations on accommodating adaptive planning and it's implication in this? Adaptive planning does not matter here as far as it does not alter the OTT. If adaptive planning leads to extending OTT (even if it is by few days), due to imaging, contouring and subsequent planning, then you need to account for the gap by the methods explained. Hence, if you are planning for adaptive RT, do it in such a way that you do not end up extending the OTT. One of the solutions in the presentation was to alter the dose per fraction, does that mean to replan? It depends on your TPS...if the dose per fraction is significantly altered and if you are doing VMAT/IMRT, then, yes, it would involve replanning....
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