Compute for Additional Dose for Delay Treatment

[akimcm2017]

Hello. Would like to get advice on how to compute for additional MU/fraction for treatment in case of 2-3 weeks non-treatment due to machine problems. And how do you compute for additional MU/fractio for patient who was was supposed to be treated for only about 2 months (35 fractions all in all) but was extended for 4 months since patient has many absence. How do you compensate for this?

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[deleted18755]

Hello. Would like to get advice on how to compute for additional MU/fraction for treatment in case of 2-3 weeks non-treatment due to machine problems. And how do you compute for additional MU/fractio for patient who was was supposed to be treated for only about 2 months (35 fractions all in all) but was extended for 4 months since patient has many absence. How do you compensate for this?

No good answers here but if a patient is so no compliant that it would take 4 months for a 35 fraction treatment after all else failed and the writing was on the wall with regard to that degree of noncompliance I would have just discontinued treatment after a few weeks (if they are missing that many treatments then I would imagine that the RT is not effective and/or the risk/benefit is in favor of no RT ... just getting side effects with no benefit?)

If a patient missed 3 weeks of treatment because of “machine issues” I would honestly be trying to calculate how much I owe them for malpractice (a few days or even a week is one thing but 3 weeks is simply not acceptable in the US)

 

[medgator]

Most pts would leave my practice if my machine was down more than a few days in a row outside of a major natural disaster

 

[Neuronix]

akimcm2017 is not posting from a country with a high human development index. Please take the post in context and be constructive if possible.

 

[deleted18755]

First do no harm, especially when RT is administred in an adjuvant setting and you don’t have the most advanced technology to spare normal toxicity to begin with.

 

[scarbrtj]

First, it will depend on disease site and extent of disease and a few other factors. Willing to provide an exact clinical scenario or two?

 

[seper]

I do try to make up lost time in classic H&N cancer (p16 negative and smokers). I add 3-5 Gy per week when the overall treatment time becomes > 8 weeks

 

[evilbooyaa]

Honestly, if a patient misses 2-3 weeks for an adjuvant treatment, I'd just stop.

Definitive, I'd do something conservative like one additional fraction per 3-5 days missed, assuming that critical OARs could still be met with the cumulative dose. No good data behind that, although I've seen some stuff about adding a fraction (or a single day of BID fractionation) to make up one or two missed days in H&N.

Palliative, I'd try to get the treatment done faster than a 2-3 week time frame.

 

[seper]

Effect of radiotherapy delay in overall treatment time on local control and survival in head and neck cancer: Review of the literature

Effect of radiotherapy delay in overall treatment time on local control and survival in head and neck cancer: Review of the literature

 

[scarbrtj]

For postop early stage breast, long break equals no more XRT for you IMHO. So disease site matters, treatment goal matters, etc. That said...

Would like to get advice on how to compute for additional MU/fraction for treatment in case of 2-3 weeks non-treatment due to machine problems.

At the outset, note that as you have to add more BED to make up for lost time, the BED for late effects does not decrease (on account of the break; ie with short breaks late effect BEDs don't go down). The time factor decreases the BED-Gy10 by 0.5/day. There is no time factor for late BED-Gy3 effects. For a head/neck case to 70/35:

Tumor control no break = 70*(1+2/10)-(49/2) = 59.5
Tumor control w 3 week break, no Rx change = 70*(1+2/10)-((49+21)/2)=49

This suggests you need to increase the dose by ~20% to make up for the 3 week break, which would equal 84 Gy/42 fractions. That means about 7 treatment days, or 9 elapsed days; but you will need to add some dose on top because the extra treatment takes time too. So let's just say 86 Gy/43 fractions: Regis' final answer.

86/70 = 23% dose increase

Late effects no break = 70*(1+2/3) = 117
Late effects to make up for break = 86*(1+2/3) = 143

This means late effect risks will (intuitively) go up by ~23% as well if you try to account for the time break. One assumes in a HN case the cord max would go from 45 Gy to 55 Gy if you just run the Rx ahead 8 more fractions than planned. Is that OK? Probably. Only you can decide!