VMAT: An Emerging Technology in Radiation Therapy
VMAT is being touted as an innovation to optimise IMRT with
low-dose volumetric image guidance and targeting, active leakage control,
single digital controller, tight dynamic tolerance with enhanced patient safety.
Rita Dutta checks out the potential of the technology
VMAT room at Fortis, Mulund
Recently, Fortis Hospital at Mulund in Mumbai acquired Volumetric
Modulated ARC Therapy (VMAT) to augment its radiation therapy department. It
proudly declared that it is the first hospital in India to acquire the most
sophisticated radiation therapy equipment -Elekta Synergy LINEAC with Volumetric
VMAT which can treat tumours and small lesions in the brain and other parts
of the body quickly with precision. Not known to many, recently Medanta Cancer
Institute of Medanta Medicity, Gurgaon and Mazumdar Shaw Cancer Centre of Narayana
Hrudayalaya, Bangaluru have started using VMAT.
VMAT from Elekta Medical Systems India Pvt Ltd is an advanced radiotherapy
optimisation which allows the radiation dose to be delivered accurately and
efficiently in significantly shorter treatment time. VMAT is being touted as
the next generation arc therapy technique that establishes new standards for
radiation therapy treatment speed and dose reduction to the patient. VMAT treatment
is specially recommended for patients who cannot lie still for long time and
the movement can impair the delivery of radiation. It is also beneficial for
patients undergoing re-irradiation as the sharp fall off of dose in the proximity
of previous treated fields can be achieved. Elekta VMAT also offers flexibility
of using single arc or where clinically indicated, multiple arcs to optimise
target dose delivery for different patients and pathologies.
With VMAT, single or multiple radiation beams sweep in uninterrupted
arc(s) around the patient, speeding treatment delivery. The Linac gantry sweeps
around the patient delivering uninterrupted, highly conformal beams of radiation
in single or multiple arcs. Different machine parameters such as the doserate,
multi leaf collimeter (MLC) and back-up diaphragms, collimator angle and gantry
angle and speed are dynamically modulated to best conform and cover tumours
while protecting healthy tissue and organs at risk. Doctors can use VMAT with
complete or partial arc(s) to reduce treatment times from 8-12 minutes required
for conventional radiation therapy to 80 seconds for simple cases and three
to eight minutes for more complex cases
Elekta VMAT planning for a head and neck cancer case
Different trials and studies (see box) indicate that VMAT
has been thoroughly tested for different indications for the prostate, lung,
head and neck, pancreas, colon and rectum, etc. VMAT can cut delivery doses
by as much as 40-50 per cent and treatment time by as much as 70 per cent.
According to Dr Rupal Chheda, Consultant Radiation Oncologist, Fortis Cancer
Institute, Mumbai, VMAT is an innovation to optimise Intensity Modulated
Radiotherapy (IMRT) and maximises the treatment flexibility with variable delivery
parameters. VMAT consists of treating patients by means of one or more gantry
arcs with continuously varying beam aperture, gantry speed and dose rate. This
trio helps improve sparing of critical structures and normal tissues, without
compromising on target coverage and patient safety.
Says Dr Swarupa Mitra, Consultant, Radiation Oncology, Artemis
Health Institute, Gurgaon, VMAT combines the digital linear accelerator,
3D volumetric imaging, and advanced treatment planning expertise. Due to the
use of multiple arcs, and flexibility in using digital controls for all the
parameters, the treatment time has shortened remarkably.
Modified Version of IMRT
Asked in what ways is VMAT a modified version of IMRT, Arindam Gupta, Director-Sales
& Marketing, Elekta Medical Systems India Pvt Ltd, Gurgaon, says, The
more Linac parameters we can modulate, the better the conformance and treatment
quality we get. Elektas VMAT is a more advanced form of IMRT as we are
now able to dynamically modulate more treatment-critical parameters such as
the dose rate, gantry-angle, gantry rotation speed and MLC leaves. According
to him, compared to 3D-Conformal and IMRT, the advantages of VMAT is better
conformance (better coverage of tumour targets and better sparing of critical
structures), less doses to the patient and faster treatment time. Better sparing
of critical structures means less side-effects, better tumour coverage means
better local control and less potential for recurrence.
VMAT also delivers lower integral dose to the patient. Firstly, our beam
shaping (MLC) system design ensures that leakage radiation is kept to minimum.
Our system has a secondary X and Y back-up jaws that auto-track with the MLC
leaves to ensure that the gaps in between the MLC leaves are closed so radiation
leakage through these gaps are minimised. It is important that we close these
gaps as much as possible as these are usually where adjacent critical structures
lie. As important as covering and conforming to the tumour is, the quality and
efficacy of treatment equally depends on how well critical structures are protected,
Secondly, since it is delivering radiation while the gantry is dynamically moving,
it is able to better distribute or spread out the dose instead of concentrating
on depositing it to the tumour from fixed angles. This superior dose distribution
is the reason why we can deliver the desired dose to the tumour target with
less radiation. To explain this in a more layman's term, think of the tumour
as a bucket and radiation as rainfall and the critical structures as a piece
of paper under the bucket. The objective is to fill the bucket with rainfall
while keeping the piece of paper under the bucket as dry as possible,
Less dose means less peripheral exposure and also lessening
the potential for causing secondary malignancies caused by excessive stray radiation.
And faster treatment time means more patient comfort and less potential for
patients to move during the treatment which makes the treatment more efficient
and accurate, adds Gupta.
May 2010: Single Arc Volumetric Modulated
Arc Therapy of head and neck cancer;
Radiotherapy and Oncology, Volume 95, Issue 2.
November 2009: Single Arc VMAT of H&N
Cancer; International Journal of Radiation Oncology Biology Physics, Volume
75, Issue 3.
November 2009: Evaluation of Arc-based Intensity
Modulated Radiotherapy for Head and Neck Cancer International Journal
of Radiation Oncology Biology Physics, Volume 75, Issue 3.
November 2009: VMAT Compared with Gated Highly Conformal Optimisation
for Dose Escalation in Partial Liver Radiotherapy International Journal
of Radiat ion Oncology Biology Physics, Volume 75, Issue 3, Supplement
October 2009: A fast radiotherapy paradigm for anal cancer with
volumetric modulated arc therapy (VMAT); Radiat Oncol.
May 2010: Volumetric modulated arc therapy for delivery of hypofractionated
stereotactic lung radiotherapy: A dosimetric and treatment efficiency
analysis; Radiotherapy and Oncology, Volume 95, Issue 2.
November 2009: Image Guided Stereotactic Body Radiotherapy for
Lung Cancer Using 4D Treatment Planning and On-line Cone-beam CT; International
Journal of Radiation Oncology Biology Physics, Volume 75, Issue 3.
June 2010: Continuous Arc Rotation of the Couch Therapy for the
Delivery of Accelerated Partial Breast Irradiation: A Treatment Planning
Analysis; Int J Radiat Oncol Biol Phys.
May 2010: High dose for prostate irradiation with image guided
radiotherapy: Contribution of intensity modulation arctherapy; Cancer
November 2009: VMAT Cs. serial tomotherapy, step-and-shoot IMRT
and 3D-conformal RT for treatment of prostate cancer; Radiotherapy and
Oncology, Volume 93, Issue 2.
Bone and soft tissue
2009: Re-irradiation of Spinal Column Metastases with VMAT International
Journal of Radiation Oncology Biology Physics, Volume 75, Issue 3, Supplement
Asked about what prompted Fortis to go for VMAT, Dr Chheda said, Due
to its higher treatment delivery efficiency and great potential to improve the
treatment quality, Fortis has been prompted to choose this advanced technology.
Also, the fact that a wide range of cases like prostate, head and neck, brain,
lung etc have been treated with VMAT around the world, coupled with publication
of various clinical trials comparing VMAT with other radiotherapy techniques
helped us take the decision. VMAT seems to be a promising approach with
the potential to allow patients to be taken in a timely fashion and thus, make
this comfortable experience available to more number of cancer patients,
says Dr Chheda.
Hence, it delivers a treatment that improves the sparing of critical structures
and healthy tissue in very short treatment time without compromising target
coverage and patient safety. Thus, there is improved dose distribution and high
conformality for optimal sparing of normal tissue in very short time.
According to Dr Tejender Kataria, Chairperson of Radiation Oncology of Medanta
Cancer Institute, Gurgaon, which has treated four patients so far using Elekta
VMAT, With VMAT, the patient comfort is excellent and the anxiety of lying
alone in the room for a long time has been alleviated by the short treatment
times. Quick delivery means technicians can attend to patients with enough
time and care rather than waiting by the console for treatments to get delivered.
Faster treatment time ensures increased throughput, expanding daily capacity
of the Linac and opening up more treatment slots per day on the Linac.
The physics team needs to spend lesser time on planning while using MONACO
system vis a vis XIO-CMS or ERGO++ , although the initial learning curve to
understand and utilise the biological cost functions was there. This gives them
ample time to devote to Quality Assurance of patients and machine care without
compromising the quality of planning. We as physicians are seeing the results
of fine contouring and biological planning translate into minimum side effects
to the patients, while on treatment and lesser need for hospitalisation or treatment
breaks. We do hope to see this translate into better outcomes for patients,
as the overall toxicity can be reduced by more than 60 per cent with the use
of such high end planning and delivery systems, said Dr Kataria.
About VMATs Growing Demand
Being launched during ESTRO 2007, Elekta has sold over 300 VMAT units worldwide
by now. The first commercial clinical treatments started at University
of Vienna and Royal Marsden Hospital and was announced on 21st January 2008,
almost two months earlier than the first commercial clinical Rapid Arc treatments,
informs Gupta. Besides, three Indian hospitals (Medanta Medicity, Naraya Hrudayalaya
and Fortis) using VMAT, some leading international hospitals using Elekta VMAT
are Johns Hopkins, USA, Princess Margaret Hospital, Canada, William Beaumont
Hospital, USA, Thomas Jefferson University, USA, Netherlands Cancer Institute
- Antoni van Leeuwenhoek Hospital, NL, Germany, Royal Marsden Hospital, UK,
etc. There are a number of other hospitals in India that will start treating
patients with VMAT soon like Dharamshila Cancer Hospital in New Delhi, Inlaks
Hospital in Pune, MD Oswal Cancer Hospital in Ludhiana and Government Medical
College Hospital in Aurangabad, says Gupta. VMAT has approvals like FDA
510k and CE Marking. Elektas VMAT is also having type approval from the
Atomic Energy Regulatory Board of India.
What has made Elekta VMAT viable is that the functionality is available as an
upgrade option rather than a separate treatment machine, thereby reducing capital
outlay. Even if hospitals do not order VMAT function when they are ordering
a new Linac, they can always upgrade to VMAT at a later stage, says Gupta.
In the US, VMAT has the same reimbursement code as IMRT which is about $ 350k
per fraction. So a typical 30 fraction treatment would cost around $ 10,000.
In India, the hospitals are charging about Rs 50,000 to Rs 75000 more
for VMAT treatment compared to IMRT-IGRT treatment, informs Gupta.
VAMT Vs RapidArc
overall toxicity can be reduced by more than 60 per cent with the use of
such high end planning and delivery systems"
- Dr Tejender Kataria
Medanta Cancer Institute
the linac accelerator platform, the radiation technologies focus is
to treat tumour only and avoid the normal tissues"
- Dr BS Ajaikumar
HealthCare Global Enterprises Ltd
VMAT is a more advanced form of IMRT. With thiswe can dynamically modulate
various treatment- critical parameters"
- Arindam Gupta,
Director-Sales & Marketing
Elekta Medical Systems India Pvt Ltd
Despite the buzz, some experts point out that VMAT is nothing
new. It is currently being sold by three vendors, namely- Varian, Elekta and
Philips. Varian's Volumetric Modulated Arc Therapy is called RapidArc
(TrueBeam is the latest version), Elekta's Volumetric Modulated Arc Therapy
is called VMAT and Philips technology is called SmartArc. So, is it actually
as 'different' as it is portrayed out to be? Says Dr Srinivas Chilukuri, Consultant
Clinical Oncologist, Yashoda Cancer Institute, Hyderabad, The arc therapy
was out of use since mid 80's, since there were a lot of technical issues, such
as lack of effective beam shaping devices like MLC. In a way, this technology
is revival of an old system. Conceptually, all these technologies are based
on the same fundamentals, but they differ significantly in several technical
issues. Varian's RapidArc is probably the most popular among the three with
largest clinical experience.
So, can VMAT from Elekta be considered a competition to RapidArc from Varian?
According to Dr Chedda, While in Rapid Arc, the focus is on single arc
delivery, in VMAT there is a choice of single as well as multiple arcs to treat
both routine and complex cases. However, Dr Chilukuri differs, RapidArc
also has the facility of single or multiple arcs and hence, this facility
is not exclusive to Elekta's VMAT. In fact 30 per cent of our treatments are
with single arcs and the rest are with two to three arcs.
However, hospitals using RapidArc defend it. Though
as a radiation oncologist, I am excited about this technology, which benefits
the patient due to reduction in treatment - less discomfort to the patient,
less patient movements during treatment, less probability for second cancers,
being the first RapidArc users in India, I am positively biased towards
RapidArc. In fact after Yashoda Cancer Institute became one of the first few
centres in the world with more than 500 patient treatments to use RapidArc,
he is far more confident of this technology. This technology has
benefitted the patients, oncologists as well as hospital administrators
in several ways. The patients are getting benefitted from quick treatments as
well as reduced side-effects. The treating radiation oncologists find it more
patient-friendly and highly efficient, says Dr Chilukuri, adding, As
of now, the literature regarding usefulness of RapidArc is robust, whereas literature
about other VMAT technologies is limited. In fact, as of now, it is difficult
to compare VMAT technology with RapidArc as the literature on the former is
According to Bangaluru-based Dr BS Ajaikumar, Chairman, HealthCare Global Enterprises
Ltd (HCG), which is using Cyberknife, all the radiation technologies are more
or less at the same level currently, under the Linac platform. In the
Linac accelerator platform, the radiation technologies focus is to treat
tumour only and avoid the normal tissues. Various forms of energy can be given
to the tumour which lessens the damage of normal tissue. All the Radiation Technologies
try to achieve this and this is promoted by various vendors, under different
brand names. Finally, the sale of the technology depends on how each one market
or positions themselves. As of now, the literature regarding usefulness
of RapidArc is robust, whereas literature about other VMAT technologies is limited,
point out others. Various options of the same technology have been acquired
by different hospitals under different brand names, says Dr Ajaikumar.
However, Dr Kataria differs, saying, One of the most distinct differentiators
of Elekta VMAT lies in the Elekta Monaco treatment planning software. Monaco
uses the world's most advanced and accurate dose calculation enginethe
XVMC Monte Carlo algorithm. The software takes into account many biological
considerations such as whether the type of organ being treated is a serial (ie
spine) or parallel (ie lung) organ. She further points out that another
differentiator of the Elekta VMAT system is the Linac's digital design. For
complex treatments where many machine parameters are being dynamically modulated
constantly, it is critical that the machine's brain or control system
has full cognisance and pinpoint co-ordination of what its different parts are
doing. The Elekta Linac does exactly that it ensures that all the
parameters being constantly dynamically modulated are interlocked with each
other, thus ensuring a tight dynamic clinical accuracy to ensure that the treatment
is carried out exactly as it was planned to be, she adds.
Elektas VMAT system also features active radiation leakage reduction.
The beam shaping system was designed for optimum shielding ensuring that
the amount of leakage or stray radiation is always kept at a minimum. This feature
very significantly lessens any potential for any secondary malignancies caused
by stray or peripheral radiation. This feature also makes the type of treatments
safer for younger patients, says Gupta. Also, patient safety is also a
key feature of the Elekta VMAT system. Three tiers of Guardian Technology
constantly monitors hundreds of machine parameters in microseconds, ensuring
that the equipment is always running at peak condition. There is after all no
room for error afforded when patients are at stake, says Dr Kataria.
The Road Ahead
With three hospitals going for VMAT and many being in the pipeline, would this
emerging technology become far more popular in the years to come? It is
difficult to predict its use in India, as more than technical reasons, market
forces drive the sale of any technology in India as in other parts of world.
If one vendor sells this technology at much lower cost than the other, then
people would go for it rather than thinking which is better. I am a hard core
physician, so not married to any particular technology. I support whichever
is better for my patients, says Dr Chilukuri.
However, Gupta is upbeat not only about its growing popularity,
but also the fact that it may take over RapidArcs market. We think
with the inherent advantages of the system: low-dose volumetric image guidance
and targeting, active leakage control, single digital controller, tight dynamic
tolerance, XV Monte Carlo Calculation Engine and biological modeling, 3-tiers
of safety (continuous monitoring and verification of machine parameters with
digital monitoring system and Mosaiq V&R), we can surpass RapidArc in terms
of not only the quality of treatment delivery, but equally or even more important
in terms of patient safety, says he.
The widely untapped radiation therapy market in India would
also work in its favour. From the existing 425 radiotherapy units (including
old cobalt units) present in the Indian market, the ever increasing burden of
cancer has boosted the demand for radiotherapy units to nearly 1,500 units.
This would welcome innovative technologies.