Lynn’s Review
Kevin Brown, MBE, CPhys, FlnstP was Science at Fishbourne’s speaker on the 22nd April. How lucky we are that he joined our group in January!
Kevin’s presentation on MRI guided Radiotherapy reminded us that innovation, passion and dedication are alive and well in England. Particularly in Crawley, where Elekta are in the business of manufacturing Radiotherapy units. They are the world’s second largest maker and exporter, delivering to China and the USA.
Kevin’s position was clear, from his excellent presentation, and his obvious understanding, and demonstration of his desire, to constantly improve upon the MR-Linac unit, of which he has been a part since its inception. His award of the MBE for services to radiotherapy is evidently well deserved.
There is lots of information on the internet, where you can explore in more detail, and I add some links below. Here, I attempt to summarise the main points from Kevin’s talk.
Current Cancer Treatment
There are many predictions and statistics with regards to cancer. I found this on the Cancer Research website: “Nearly 1 in 2 people born in the UK in 1961 will be diagnosed with some form of cancer during their lifetime.”
Currently, treatment for cancer involves, surgery, drugs (chemotherapy and immunotherapy) and radiotherapy. Surgery is local therapy, drugs are systemic, going through the whole body and External Beam Radiotherapy, also a local therapy, where radiation is delivered from outside the patient.
Since around 2005, the management of uncertainty in external beam radiotherapy, is by way of a CT scan. The aim is to target just the cancer wherever it is in the body. The CT scan can give a picture of where a tumor is, then the Clinical Target Volume (CTV) can be determined and a Dose Cloud of radiotherapy administered, so aiming at the tumor, with as little healthy tissue as possible being targeted. Over time, the size of the Dose Cloud has become smaller and less healthy tissue has been affected.
Elekta Unity Potential
The development of the Elekta Unity MR-Linac brings the ability to clearly see a tumor in real time, by using Magnetic Resonance Imaging. A CT scan can acquire a 3D image of the body whereas an MR can show either a 3D data set or continuously acquire a single slice.
The MR has a very strong magnetic field of 1.5 Tesla. The gradient magnet applies a linear change to modify the spin of protons in the body. A radio frequency matched to that of the protons is applied to the target location. The protons line up to the magnet, and the RF pulse they emit as they decay back to their equilibrium state is detected. The timing of the gradient and RF pulses determine what is seen. Quantum spin plays its part here; protons are in hydrogen in water. Hydrogen has a spin of ½ and interacts with electromagnetic fields. Understanding spin is a whole different story! The main point is that MR has a vivid visual impact. It can also be used in real time cine acquisition, so tracking a moving target. I have added a YouTube video explaining MRI below.
The Unity MR-Linac now opens the possibility of knowing exactly the location, shape, size of a tumor each time a patient needs treatment. This means that a more individual, exact way of targeting and dosing can occur. Using a CT scan to locate a tumor, the target area may be marked with small tattoos or metal clips or seeds (fiducial markers), may also be placed inside the body. The patient is then carefully positioned to target the marked area for each treatment. The MR, on the other hand, can give an accurate real-time picture of the daily changes in size and location of a tumor, so enabling more accurate dosing and (in trials) higher doses directly into a tumor with good results so far. The dosing and targeting can therefore be adjusted daily. The ability to target tumors more accurately, may also lead to the need for fewer treatments (for example: 35 visits could potentially be reduced to 2-5 visits) and perhaps eradicate the need for surgery or drug therapy, therefore also reducing side effects.
A team of physicists in the Netherlands pioneered this new technology. A Linear Accelerator was combined with an MR. The magnet used is 30,000 times stronger than Earth’s magnetic field. Once a current is introduced into the superconducting coil and it continues indefinitely therefore no electrical power is needed. The coil is cooled by liquid Helium (about 4K) to make it superconducting.
To prevent the very strong magnet preventing the Linac from working it uses ‘self-shielding’ to create a very low magnetic field where the Linac is.
A beam of X rays provides the treatment, and it is characterized by the energy of electrons used to generate it, in this case about 6 million electron volts of energy. The electrons gain their energy by a Linear Accelerator or ‘Linac’ which has a series of small copper cavities. A Radio Frequency source creates a high electric field in the cavities which accelerates the electrons, which increases their energy as they move down the Linac. The RF signal accelerates the electrons, creating radiation doses, pulsing at 3 million times a second. I have put a link to a YouTube video explaining how a Linac works.
The source of radiation is from a single point at any one time. The radiation source is mounted on a ring and can rotate around the patient in 12 seconds.
Different types of cancers treated with this system offer specific benefits to the patient:
Rectal cancer patients may not require colostomy bags as more accurate treatment and higher dose can avoid the need for surgery.
Prostate Cancer treatment may damage the neurovascular bundle and lead to erectile dysfunction. MR can see the region and deliver less radiation here.
In the treatment of Pancreatic Cancer, the duodenum, which is very sensitive to radiation, can receive lower doses as its location can be seen.
Lymph node Metastasis in the pelvis can be targeted and treated in one day.
In summary: Survival times for cancer patients may not increase greatly if survival is already good under current systems, but treatments can be shortened; side effects diminished and expensive drug therapies reduced or possibly abandoned.
Currently, there are just 3 Unity MR-Linac units in the UK, but perhaps with larger trials NICE may be persuaded to install more of these machines.
The final words; an excellent summary, come from Elekta on the web:
Elekta Unity, the first high field MR/RT system, combines high-field 1.5 Tesla MR imaging, precision radiation therapy and intelligent software, allowing clinicians to see what they treat in real time. Elekta Unity addresses a critical unmet need in cancer therapy. Now clinicians can confidently see and track the tumor and difficult-to-visualize soft tissue anatomies during treatment and adapt the treatment to optimize therapy. This enables personalized therapy for each patient and every treatment session.
Linear Accelerator https://youtu.be/jSgnWfbEx1A?si=O1lIUYbTF3w2dGo6
MRI https://youtu.be/NlYXqRG7lus?si=-1SAAJYIAcKzUusj
https://webinars.elekta.com/watch/aJg73D9JAk8mX39aBPnTs3
https://www.linkedin.com/pulse/why-i-believe-mr-linac-continue-thrive-amid-modern-cost-kevin-brown