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SRS treatment planning: where automation yields precision, speed, workflow efficiency

22 Feb 2021 Sponsored by Elekta

Elekta’s dose optimization software Leksell Gamma Knife Lightning is transforming the treatment planning of intracranial stereotactic radiosurgery

Leksell Gamma Knife Lightning
Workflow efficiency Leksell Gamma Knife Lightning enables fast-track comparison of SRS treatment plan options followed by selection of the optimal plan for each patient. (Courtesy: Elekta)

It’s one of the fundamental challenges facing radiotherapy equipment manufacturers: how to balance the relentless clinical demand for automation and enhanced workflow efficiency versus the desire of care providers to customize treatment planning and radiation delivery to meet the personalized needs of every cancer patient. Back in May last year, Elekta, a specialist equipment provider in precision radiation medicine, went some way towards squaring this circle with the market introduction of Leksell Gamma Knife Lightning, an automated treatment planning system that integrates with Leksell Gamma Knife, the manufacturer’s flagship stereotactic radiosurgery (SRS) platform for the treatment of benign and malignant intracranial tumours as well as vascular and functional disorders in the brain.

For context, the Gamma Knife SRS system exploits multiple narrow beams from different directions to deliver conformal, high-dose radiation to the disease target in one or a few fractions while minimizing collateral damage to surrounding healthy tissue and organs at risk (OARs). Despite widespread deployment in cancer centres worldwide, it’s fair to say that the precision targeting inherent to SRS remains a non-trivial dose optimization challenge for the medical physics team – and not least when it comes to focusing “high-payload” radiation onto metastatic small lesions (as small as 2 mm3 in extent) and having it fall off as quickly as possible.

If that’s the problem, Leksell Gamma Knife Lightning is shaping up a lot like the solution. This next-generation treatment planning system enables medical physicists, radiation oncologists and neurosurgeons to automatically create multiple SRS treatment plans in less than a minute, with optimization based on dose constraints to one or more lesions and OARs. The result: fast-track comparison of treatment plan options followed by selection of the optimal plan for each patient (in terms of conformality and tissue sparing). In some cases, that can include a reduction in “beam-on” time by as much as 50% compared with manual forward planning.

The view from the clinic

As part of the network of alpha test sites for Lightning, Prague Na Homolce Hospital (Czech Republic) was ideally positioned last summer to become one of the first Elekta customers to deploy the software clinically for SRS patient treatments. The department of stereotactic and radiation neurosurgery at Na Homolce handles around 1200 patients annually in its Leksell Gamma Knife centre, with Lightning now used to plan all but the most straightforward single-shot SRS treatments on its Icon device. (Worth noting, though, that Lightning is also fully compatible with Perfexion, Elekta’s other commercial Gamma Knife system.)

Josef Novotný

“The benefits of Lightning are especially evident in complex cases when very high dose conformity and protection of critical structures like the optic nerve are required,” explains Josef Novotný, head of medical physics at Na Homolce. Novotný should know: he has notched up more than 20 years of clinical experience with Leksell Gamma Knife, having participated in the development of the Perfexion and Icon systems while also supporting clinical roll-out at over 150 Leksell Gamma Knife centres around the world.

Equally instructive, says Novotný, is the impact of Lightning on Na Homolce’s SRS clinical workflow and patient throughput. “Lightning streamlines the overall treatment planning process for SRS, such that the typical calculation time per plan is less than one minute,” he adds. “We also see a reduction in beam-on time by almost 15% owing to efficient planning and use of a very high number of isocentres – akin to ‘dose painting’ of the tumour targets.”

An initial study by the Na Homolce team, the results of which are to be formally presented at the Third European Congress on Medical Physics (ECMP) in Turin this summer, provides quantitative evidence of Lightning’s clinical benefits. Novotný and colleagues report that Lightning improves both selectivity (i.e. dose reduction outside the target) and Shaw conformity index (a measure of targeting accuracy) by about 9%, while reducing the 12 Gy volume (which is often used as a predictor for complication rate) by about 5%. In selected cases, the researchers also observe enhanced sparing of critical structures by about 12% (optic nerve), 9% (cochlea) and 5% (pituitary).

“It can be generally said that Lightning is superior to previous methods used for treatment planning on Leksell Gamma Knife,” notes Novotný. “That means better treatment plans versus multiple metrics – whether in terms of dosimetry characteristics, lower doses to critical structures, as well as reduced beam-on time.”

Collective progression

Another enthusiastic early-adopter of Lightning is Ian Paddick, chief medical physicist at the Queen Square Radiosurgery Centre in London and immediate past-president of the International Stereotactic Radiosurgery Society (ISRS). For the past two decades, Paddick has provided training, mentorship and consultancy to more than 100 Gamma Knife centres around the world. It’s within this wider frame of reference that he sees Lightning as a catalyst for community-wide progression and innovation in SRS treatment planning. Put another way: a “rising tide lifts all boats” scenario that will ultimately promote convergence towards clinical best practice and enhanced patient outcomes across the Gamma Knife user base.

The upsides are already evident at a more granular level. For starters, claims Paddick, Lightning will do a better job on the majority of tumour targets than an expert treatment planner – in terms of enhanced conformality, selectivity and dose gradient. What’s more, Lightning is also incredibly fast. “I could not believe it when I first used the software,” he adds. “In fact, I’ve just used Lightning for a case with six complex metastases and it took about 35 seconds to produce an optimized treatment plan. Generating the same plan manually took me around 40 minutes.”

Of course, the treatment plans generated by Lightning still need to be reviewed and signed off, with the opportunity to manually adjust dose distribution ahead of treatment delivery (allowing further optimization, for example, if the dose is spilling out of the target in the vicinity of a cranial nerve). “In this way,” adds Paddick, “Lightning can be used to do most of the heavy-lifting, with the final ‘sculpting’ and optimization of the dose distribution being hand-crafted by the medical physicist, neurosurgeon or radiation oncologist.”

Herein lies another opportunity: the use of Lightning to fast-track learning and development among inexperienced SRS planners at new Gamma Knife centres. “If you want to master the art of manual SRS planning, you really need to pit yourself against Lightning,” Paddick argues. “Used in the right way for performance benchmarking, Lightning will always show you what can be achieved in terms of dose optimization and plan quality.”

Novotný, for his part, believes that Lightning will simultaneously drive improvements within established Gamma Knife centres while helping new SRS users to achieve consistent, high-quality treatment planning sooner – i.e. without the lengthy learning curve and accumulated experience from planning many stereotactic cases. “It’s clear that Lightning lowers the barriers to entry in SRS,” he concludes. “Once the target volume and critical anatomical volumes are defined, the operator just has to specify prescription dose to the target volume and dose constraints to any adjacent structures. The rest is handled automatically by Lightning.”

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