A technical question on Radiation

[Sushupthi]

A technical question:

The radiation oncologist tells me that I received 19.5 Gy via Cyberknife over 3 days, a high biologic dose, and 42Gy via conventional (IMRT) radiation over 21 days. He says these are not linearly additive ( ie., not just for a total of 61.5Gy) but that the effective biologic dosage is over 80Gy. I was asking him why not more days of IMRT to doubly ensure that all/any cancer cells are killed. The following study seems to indicate that high dosage is better with ADT. It says that 80Gy is better than 70 Gy, leading to the survival rate improving from 65% to 77%

See this study: ( you may have to copy paste the link)

ascopost.com/issues/februar...

It talks about alpha and beta rays and gets technical. Question is did I get enough or should I insist on more? He says I got plenty !

[Tall_Allen]

In fact, the prostate dose you receive is biologically equivalent to an 8% higher dose than the 80Gy dose you were reading about. That kind of high dose is only achievable with a hypofractionated boost like the one you received.

[Sushupthi in reply to Tall_Allen]

Thank you Tall-Allen! This answers my question and addresses my concerns.

That said, what I am curious about is, is there a formula that takes the raw dose numbers as input and calculates the total resulting biologic dose? Is there an algorithm for that? Or is that too complex for a layman to comprehend and better left alone by me (the “layest” of all possible laymen!)

Thx

[Tall_Allen in reply to Sushupthi]

Your RO went to school for years to master the concepts of radiobiology.There is software that you can buy that computes it based on the alpha/beta ratio - it's not for the layman. Just trust me and your RO.

[Sushupthi in reply to Tall_Allen]

Ok. That closes that question. Thx

[janebob99]

I agree with everything Tall_Allen said. (I have a Ph.D in Nuclear Engineering).

The irradiation you received consists of extremely high energy (6 MeV) X-rays (photons). You were not irradiated with alpha rays (ionized energetic helium nuclei), or beta rays (high energy electrons), or neutrons. Only photons (X-rays) irradiated you.

There is a thing called the 'alpha/beta ratio", which means:

"Alpha/Beta ratio relates to the relative importance of single and double strand DNA breaks in causing cell death. In effect, alpha/beta ratio indicates how resistant a cell is to radiation damage."

The "alpha" parameter refers to the probability of cell death arising from a single "double hit" producing a double strand break in the DNA. The 'beta" parameter refers to the probability of cell death arising from multiple "single hits," each generating single strand breaks, close enough together to cause a double strand break in the DNA.

The Alpha/beta ratio is about 1.5 for prostate cancer. It can be as high as 10 in other cancers.

oncologymedicalphysics.com/...

Bob in New Mexico

[Sushupthi in reply to janebob99]

Thank you. Thanks for the link. The science behind this is fascinating! The electronics engineer in me is endlessly fascinated by the sophistication of the equipment- the Cyberknife and the IMRT; the technicians showed me what they do and how the machine works; the array of screens they monitor to ensure that the beams fall with millimeter precision; the manner in which the arms go around me whirring and clicking - how it scans and makes precision adjustments - it is like magic! In my penultimate session, the IMRT machine stopped (before I went on the table), and a technician arrived to diagnose it - turned out to be a loose screw - he told me about the redundancies and fail-safe mechanisms built in the machines. Explained to me diagnostics and checks they run to keep the machines in top shape- I asked him about 6-Sigma level of fault prevention in manufacturing processes - he said this has to beat that - not one patient has been given an erroneous dose in the years of operation at the Hospital. It is just a marvel to see the degree to which they to go deliver top-notch care.

[janebob99 in reply to Sushupthi]

Yes, I agree.

I've had 2 sessions of SBRT using a Versa HD X-Ray machine. Not as sophisticated as the Cyberknife, but still a marvel of engineering.

My local cancer center is building a new vault to house a combined MRI + X-ray Linac machine. But, I will have completed my RT before that machine comes on line.

Are you a HAM radio operator, by the way? I just became one!

Bob in New Mexico

[Sushupthi in reply to janebob99]

Congrats on becoming a Ham operator! No, I am not one, yet. A Nuclear Engineer cum Ham operator - a unique combination !

Thanks again for the Radiobiology link - exactly what I was looking for - fascinating - I am coding the equations in a macro.

[janebob99 in reply to Sushupthi]

Oohh...I love it.

Where do you live?

I'm in Albuquerque, NM, and I'm almost 70 y.o.

I worked at Sandia National Laboratories for 30 years doing research on magnetic fusion energy reactors, and then as a registered Patent Agent writing patent applications for other scientists at SNL. I work at home now writing patent applications remotely for GM, Boeing, and NASA, for an IP law firm in Detroit, MI.

[Sushupthi in reply to janebob99]

I have been to Albuquerque- went on a hot air balloon ride. I live in Maryland. 68yrs. From South India (Madras); Math major; then electronics engg; then MBA from Kellogg; joined the IMF/World Bank in the 80’s. Retired. My adult son has autism; so, spend most of my time with him, hiking locally, traveling to NP’s and generally taking life easy. The PCr diagnosis last year was a jolt; did not want to go thru surgery-so, radiation. Happy with that decision. Hoping to enjoy life and nature for a long, long time!

[janebob99 in reply to Sushupthi]

Thanks for sharing. You'd make a great HAM amateur radio operator, with your electronics background. It's a fun hobby, and you'll meet lots of very nice, smart people. A little bit like the Health Unlocked community. The license tests are very easy to pass. You can spend a little money, or a lot...depending on how deep you want to go.

[Mgtd in reply to janebob99]

see the post below

[Mgtd in reply to Sushupthi]

For you and Bob. I can not tell you how much I appreciate Ham operators.

During Vietnam I would sit for 12 hours or so waiting my turn to use the MARS network. Ham guys would patch me through and thanks to then Senator Barry Goldwater who picked up the bill for the telephone call from Arizona to New York I was able to spend 3 to 5 minutes talking to my wife. “Over”.

Took us a while to remember that “over.” How the world has changed.

Thanks for keeping the tradition alive.

[janebob99 in reply to Mgtd]

Very cool!!

73,

Bob

KJ5GMA

[Justfor_ in reply to janebob99]

73 de SV1___

[j-o-h-n in reply to Sushupthi]

"a loose screw" Are you sure the technician didn't mean you?

Good Luck, Good Health and Good Humor.

j-o-h-n

[Sushupthi in reply to j-o-h-n]

No😅😅😅oo! I as teasing them whether they forgot to pay the PEPCO electricity bill - that is when they said what happened. A minor peripheral area - but still the safety protocol kicked in and stopped the machine .

[j-o-h-n in reply to Sushupthi]

Good.......... didn't want any phillips heads hanging around with us slotted flat heads...or technicians that don't know how to turn on the power switch.

Good Luck, Good Health and Good Humor.

j-o-h-n

[j-o-h-n in reply to janebob99]

Anyway you can turn my ex-wife into glowing green (a Mexican Habanero tint) since she's already a big junk of lead?

Good Luck, Good Health and Good Humor.

j-o-h-n