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ReasonablyBadass t1_ivnskp7 wrote

I never quite got why we don't use multiple radiation beams from multiple angles?

Low powered in the tissue they pass, but overlapping in the tumor.

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TheFram t1_ivo5wkf wrote

We do. There are various techniques used to deliver modern radiation treatments and they rarely use only a single beam to treat a tumor. That only really happens for skin lesions. Otherwise, multiple-beam radiation therapy techniques include 3D conformal , IMRT (intensity modulated radiation therapy), DCA (dynamic conformal arcs), VMAT (volumetric modulated arc therapy), SBRT (stereotactic body radiation therapy)….the list goes on.

There are many factors involved in choosing a technique such as exit dose (radiation dose to tissue beyond the target), skin dose, (maximum dose is not at the point of beam entry on skin but rather at a calculated depth), treatment site, treatment intent (palliative patients typically get insurance approval for less-conformal treatment plans since the dose to surrounding areas is lower than a curative dose which is much more aggressive), etc.

Source: I am a radiation therapist, AKA the person who delivers the treatments.

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Egoy t1_ivohqvy wrote

Already answered but I wanted to put it in layman’s terms in case anybody was wondering. When they do even and ‘old school’ x-ray rad treatment the beam is rotated around multiple axis centred on the treatment location. The tech line up your markings to put the treatment location at the correct spot the.n the machine rotates With another rotating head on it as well so the beam path hits different tissue during the treatment except at the treatment location. Surrounding tissue gets a significantly lower dose than the target location.

I did 25 rounds in 2021, it’s crazy how sophisticated even the outdated treatment methods are.

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ptjunkie t1_ivnstho wrote

They do, but typically the delivery nozzle of the machine rotates around the patient to get other angles.

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ReasonablyBadass t1_ivnt9d7 wrote

I meant at the same time, so that you get higher energy in the tumor tissue.

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ptjunkie t1_ivntufc wrote

I don’t think there is a benefit from doing it all at once. You can just rotate and dynamically collimate the beam to hit it over a longer period of time with the same effect.

Not to mention that multiple angles would require multiple beams, or complicated beam splitters to change the energy levels for the changing depth of tumor from different angles.

In practice, most treatment plans are delivered in fractions anyway, to synchronize the radiation delivery with the cancer cell life cycle.

They aren’t trying to burn the tumor out, they are trying to snuff out the tumor cells as the body heals around it.

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st4nkyFatTirebluntz t1_ivnxe2o wrote

Listen, I'm high, tired, and didn't even slightly read the underlying study. But, wasn't that the whole point? That they tried maximizing the rate of delivery to the affected area, and that it seems to improve the ratio of therapeutic benefit to harmful side effect?

Spitballing wildly, I'd imagine there's some sort of optimal rate for tumor destruction (obviously dependent on the type of tumor and other specific details), and optimal rates for non-tumor preservation, and you'd be able to optimize between the two by utilizing multiple beams from multiple directions in certain scenarios.

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Mounta1nK1ng t1_ivpfm3h wrote

You are correct. The whole point is delivering it all at once so you get the FLASH effect. Different radiobiological mechanism than traditional fractionated radiotherapy.

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Mounta1nK1ng t1_ivpcbmz wrote

The FLASH studies have shown the lower side effects by using a single pulse, so the idea when putting this into clinical practice would be a single shot. Obviously no fractionation, as this isn't relying on the 5 R's. It's relying on a transient radiation-induced hypoxia that affects tumor cells more as they're already hypoxic.

For clinical treatment they would be looking at multiple treatment head gantries so the tumor could be shot from multiple angles at once in a single pulse so that you get the benefit of the FLASH effect that this treatment relies on.

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Xist3nce t1_ivntq00 wrote

Interesting point. Now I wonder that too. It’s so simple so there’s got to be a reason, maybe it’s just not effective? Any cancer researchers wanna chime in to sate this curiosity?

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TheAero1221 t1_ivo99i1 wrote

REFER TO GUY BELOW

Not a researcher, but I know that traditionally there has been a concerted effort to deliver radiation to the cancer site via small angles of attack that vary over time. They do this because even though the radiation is not at its maximum concentration when traveling through the noncancerous tissue, there is still some chance of causing undesired damage if those areas are repeatedly exposed. Subsequent treatments change the angle of attack so that they can minimize the radiation exposure to any given area of tissue that they do not wish to damage. Attacking from a wider angle may mean less total safe treatments are possible since fewer viable attack angles will remain after each treatment. Idk. Again not a researcher, just guessing. Could be totally wrong.

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Mounta1nK1ng t1_ivpj6t8 wrote

You are correct that you're totally wrong. We don't vary the angles over time, we just select a large number of angles. Basic idea, if you shot from just one angle, all the tissue on the entrance path would be getting more dose than the tumor. If you shot through 10 different angles for a single treatment, than each entrance path through normal tissue would be getting only 10% of the dose, but where they all overlap at the tumor, it's getting 100% of the dose. This treatment with the 10 angles (usually actually only 5, 7, or 9 for static IMRT) would be given every day for 5-8 weeks in conventional radiotherapy using those same angles for each daily treatment.

The evolution of this is having the gantry rotate constantly through the treatment, varying the dose rate and shape of the beam during the rotation to avoid dose to especially sensitive tissues, while making sure you completely cover the target. So instead of 10 (or 5 or 7) discrete angles you have the maximal spread of the entrance dose. It's called VMAT, volumetric modulated arc therapy.

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