Tumor size and dose?

[producer]

Hi, a question to the radiation 'experts' of our crew..

Is a 1cm tumor treated with the same  dose as a 2.5cm tumor? It sound like a smaller tumor would require less  beams or overall energy to kill or am i mistaken?



cheers

chris

[PaulW]

The dose is typically 13 Gray to the tumour margin, if done in a single fraction regardless of tumour size.
This is how much radiation is absorbed by the tumour, not how much is transmitted through your head.

The total amount of radiation travelling through you is related to the tumour volume.

Think of how long it takes to heat a small cup of water in the microwave, versus a large bowl of water.

The radiosurgeon needs to boil the water if you like!
Small tumour = short time in the microwave.
Big tumour = Long time in the microwave.
Desired effect get the water to boiling point.

The boiling of the water is the 13 Gray bit...
The time in the microwave and the total amount of radiation you receive is not generally reported.
But its directly related to tumour volume.

Hope that makes sense?


 

[mk]

Paul explained it well. To add to his explanation, I would add that the definition of one Gray is 1 Joule of energy/kg. Thus the larger the mass of the tumor, the more "energy" (i.e. joules) are absorbed.

Nowadays typical doses for single-session radiation are 12-13Gy. It has been shown that this provides optimum tumor control. However in the case of larger tumors the radiation oncologists may opt to deliver a lower dose, 11 or even 10 Gy, in an effort to avoid tumor swelling. In my case they used a dose of 11 Gy for a 2.8 cm tumor.

Marianna

[Suu]

I don't know the answer to your question but want to wish you all the best of luck.

Cheers,
Suu

[producer]

Thank you all.  Yes I think Paul really helped me understand with his great analogy!


I have today completed my 2nd of 3 CK session..   Both sessions have only lasted 20 mins each and my total dose will be 18Gy.

I have heard some people's fractionated sessions lasting up to 45 mins each so trying to understand why mine is such a short period.

thanks again


chris

[chloes mema]

Loved PaulW's explanation.

Read this post to my husband.  When done reading, I said to him, "So why don't I just put my head in the microwave?"   

Have to have some humor....

Karen

[producer]

Microwave wont start unless door is closed Karen.. wouldve beat you to it!   


chris

[PaulW]

The bigger the tumour the more radiation it needs so the longer the treatment.
Just like the water in the Microwave.
Also I believe Stanford have recently installed the latest Cyberknife??
Treatment times have been reduced through the use of a variable iris collimator, which means the cyberknife can now change beam sizes without the robot having to change the piece of metal with a hole in it, that lets the xrays through.
Also improved programming has sped up treatment times.

[MaryBKAriz]

Such an interesting set of posts. Thank you for the question and answers.

Mary 

[Suu]

Loved PaulW's explanation.

Read this post to my husband.  When done reading, I said to him, "So why don't I just put my head in the microwave?"   

Have to have some humor....

Karen

I laughed till tears ran out of my good eye and then again when I read Chris' answer!  At my age it isn't good to laugh that hard without nearly wetting myself! 
Thanks. 

[producer]

Glad to have put a smile on your face Suu..and a happy tear


chris

[chloes mema]

Glad to have put a smile on your face Suu..and a happy tear


chris

Me, too Suu!

I still think I could've got the microwave to work, Chris.   

Karen

[MDemisay]

You guys are a laugh a minute!

I thought I was special at my inability to cry with both eyes, only crying with one. Guess I'm not as strange as I once thought, that's a good thing ain't it?

Mike

[producer]

I guess where there is will there is a way Karen!  lol

Surely youre not as strange as you thought prior to joining the forum Mike


chris