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Particle therapy

Particle therapy

Painting with protons: treatment beams recreate works of art

27 Sep 2023 Tami Freeman
Proton beams recreate works of art

Intensity-modulated proton therapy (IMPT) is an advanced cancer treatment technique that uses narrow pencil-like beams of protons – painted spot-by-spot and layer-by-layer within the patient – to deliver radiation in highly complex dose patterns. Combined with sophisticated treatment planning techniques, IMPT can shape the proton dose to match the targeted tumour with unprecedented accuracy, maximizing the destruction of cancer cells while minimizing damage to nearby healthy tissue.

Looking to showcase the impressive power of IMPT to create intricate dose distributions, medical physicist Lee Xu from the New York Proton Center came up with an unusual approach – he used proton pencil beams to recreate a series of well-known paintings as treatment plans, effectively using the protons as a paintbrush.

“When I first entered this field, I remember looking at treatment plans and being amazed at how beautiful they were. They really looked like works of art to me,” Xu tells Physics World. “As I spent more and more time observing treatment planning, I realized how similar dosimetrists were to artists. The only difference really, was in the medium they used and the canvas they applied the medium onto.”

Xu chose five well-known paintings – Girl with a Pearl Earring by Johannes Vermeer, The Starry Night by Vincent van Gogh, The Scream by Edvard Munch, Composition with Red, Blue and Yellow by Piet Mondrian, and Son of Man by René Magritte – to recreate in the Eclipse v16.1 treatment planning system, sharing the resulting images in Medical Dosimetry.

To generate each “painting”, the planning system used clinical protons with energies of 70–250 MeV to deposit “paint” (radiation dose) onto a “canvas” (a water phantom), with a total prescription of 100 Gy in 50 fractions. Each treatment plan employed between one and six proton fields directed onto the front of the canvas, with the isocentre placed at a depth of 10 cm.

The process begins in a similar manner to a traditional artwork – by creating a preliminary sketch on the canvas to determine the overall layout, in this case using the 2D brush tool in Eclipse’s contouring workspace. Next, key elements such as the sky and the ground are delineated as contours and divided into separate structures to represent different colours, tones and textures. In some cases, Xu used a final subdivision into even smaller structures (up to 65 for the most complex painting) to reflect more intricate details.

Xu assigned different colours to various isodose levels between 0 and 100 Gy in intervals of roughly 300 cGy. He then optimized the treatment plans to deposit doses within the canvas that achieved the desired colour in each region. Xu notes that the final dose distribution was calculated using the same proton convolution-superposition algorithm employed in his clinic.

“After I became acquainted with pencil-beam scanning proton therapy, I realized the possibilities for dose painting using protons were near limitless,” says Xu. “I really wanted to see how far I could push it, and what better way than to recreate some of my favourite paintings using proton beams. While I’ve had this idea for almost five years now, I only recently had the time and patience to bring it to fruition.”

The final recreations exhibited a marked resemblance to the original artworks with sufficient resolution to elucidate fine details. Xu notes that each painting is actually a three-dimensional work of art and can be viewed at multiple depths within the water phantom.

As well as being an impressive demonstration of cutting-edge medical technology, the paintings serve an additional purpose. Xu envisages that they could act as an educational tool, to help patients undergoing treatment understand the general principles of proton therapy, or even to help medical and medical physics students better understand proton physics and dosimetry by using a series of annotated paintings.

“I hope this paper showcases how far we’ve come since the days of 2D planning and how modern technology has allowed us to provide highly targeted care that is specific to each patient,” Xu adds. “I also hope this work serves as a reminder to all of us within the fields of radiation oncology and medical physics that while we often consider ourselves scientists or clinicians, deep down we are also artists; and without art, our field wouldn’t be the same.”

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