Preventing accidental exposures
from new external beam
radiation therapy technologies
ICRP Publication 112
Task Group:
P. Ortiz López (chairman), J.M. Cosset,
O.
Holmberg, J.C. Rosenwald, P. Dunscombe,
J.J. Vilaragut, L. Pinillos,
S. Vatnitsky
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Lessons from accidental
exposures with conventional
techniques are available
They have been useful in
improving safety
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The key questions are:
1. Are lessons from conventional
techniques applicable to newer
technologies?
2. Are there new lessons from new
technologies?
3. Can we anticipate “what else can go
wrong?”
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1st question
Are lessons from
conventional
techniques
applicable to
newer
technologies?
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Applicable to new
technologies?
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Overall lesson from conventional
techniques
• “…purchasing new equipment without a
concomitant effort on education and training
and on a programme of quality assurance is
dangerous”.
Valid for new
technologies?
Yes, indeed
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Lessons from conventional techniques
valid for new technologies?

Beam calibration:
independent
verification of absorbed
dose at the reference
point
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115
patients
severely
affected
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Lessons from conventional techniques
valid for new technologies?



Need for commissioning of
treatment planning systems
(TPS)
Validation of procedures and
of their modifications,
particularly TPS
For individual patients:
check of the dose to a point,
independently fromTPS
calculations
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28 patients severely
overdosed in Panama
1045 patients
underdosed in the UK
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Lessons from conventional techniques
valid for new technologies?

Clear notification of maintenance and
repairs to the person responsible for
radiotherapy physics, before resuming
patient treatments
27
patients
severely
affected in
Spain
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All these lessons from
conventional techniques are
valid for new technologies
They should be part of training
programmes, and incorporated
into procedures in
radiotherapy departments
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2nd question
Are there new lessons from
new technologies?
Yes, the following
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New lessons:
Software control of accelerator
functions
data integrity may be lost after
computer “crash” or “frozen”
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Loss of data integrity
•
•
•
•
When saving data on treatment plan, the computer
got “frozen”. After restarting, data on collimator
setting was “lost” from the data file
As a result, open fields instead of small fields were
applied
Consequences: one patient received 39 Gy in the
first three sessions
Checking procedures are required for computer
“crashes”. Irradiation parameters may be wrong
upon
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Interlock misadjustment
Interlock understanding
Test of interlocks at
equipment acceptance
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Tolerances and interlocks
•
•
Misadjustment of the tolerance limits of a doserate interlock occurred on a tomotherapy unit
Important: understanding interlocks and
ensuring their testing at equipment acceptance
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Wrong calibration files for an
applicator were supplied by the
manufacturer
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Intraoperative radiotherapy
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•
•
•
Supply of wrong calibration file for a given applicator
Measurements revealed a discrepancy, the physicist
asked the installation engineer and received an erroneous
advice
The radiotherapy department accepted the advice,
assuming that the maintenance engineer was right and
the measurements by the physicist may be wrong
The problem was discovered later at a survey
Avoid “believes or assumptions” and base the treatment on
proper understanding and verification!
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Errors from imaging:
Wrong site treatment
(right-left)
Image distortion
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Multiple imaging modalities: problem
with consistency in identification and
labelling
•
•
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Left-right error
Distorsion of images when transferring them from the
TPS to the “record and verify”
Potential problems of image artefacts and wrong tissue
density
Wiith increased use of different imaging modalities,
consistency in imaging identification and image labelling
becomes more critical
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Image reconstruction
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•
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Geometric distorsion of CT images,
when being uploaded in the graphics
memory of the TPS
Misplacement of the field coordinates
Attention to image data transfer:
Specific verifications required
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Confusion of different
coordinate systems
???
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Reference markers in virtual
simulation
•
•
The tatoo for the initial plane of virtual simulation
(A) was taken as the isocenter plane (B).
Understanding and becoming fully familiar with
details of new techniques
(A)
(B)
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Significant radiation dose from
daily imaging for verification
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Daily imaging for localization
•
•
Significant radiation dose was given from daily
localization images
Need to integrate significant imaging doses into
the therapy dose planned by the TPS
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Several events due to poor
understanding of new techniques and
poor communication and recording
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Calibration of very small beams (micro
multileaf collimators)
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•
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Partial volume irradiation of the chamber. Wrong absorbed dose
determination
Knowledge needs to be sharper, as well as the level of awareness of
the task at hand
Education and specific training essential for new technologies
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Record and verify systems
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•
•
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Old system: TPS calculation for
normalized dose (1Gy) followed
by manual scaling up to the
prescribed dose when
transferring the plan to the record
and verify system
New system: direct scaling up by
the TPS and automatic transfer
Unusual treatment modality.
Scaling up was done twice.
A check procedure was not
followed. About 67% overdose
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Dynamic wedges
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•
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Erroneous selection of the type of wedges with
the result of excessive monitor units
Monitor units for physical wedges, treatment with
dynamic wedge
Misunderstanding of the acronym (enhanced
wedges, EW)
23 patients overdosed, four of them died in the
first year
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Small fields in stereotactic
treatment with applicator
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Confusion 40 mm - 40 cm
Patient died from the accidental
exposure
40 (cm)
40 (mm)
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Avoid poor understanding of new
techniques and poor communication
and recording
Lesson No “quick” training…
… but solid training
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All these new lessons are useful in
preventing reported types of risks, but
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3rd question:
Can we anticipate
what else can go wrong?
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The unknown or unreported
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What about possible unreported events?
What about other types of potential events,
which have not happened yet?
Do we need to wait until they occur, to learn
the lesson?
¿What should be done about increasing
equipment complexity and thus ever larger
lists of double checks and verifications?
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There are proactive methods of
safety assessment
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•
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Failure mode and effect analysis (FMEA)
Probabilistic Safety Assessment (PSA)
Risk Matrix Approach
Examples: work done by the Ibero American FORO of Nuclear
and Radiation Safety Regulatory Agencies and by the
American Association of Physicists in Medicine, briefly
described in ICRP 112
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Example No. 1 of major finding from
probabilistic safety assessment
• Much attention has been focused on
major catastrophic, multiple-patient
events with very low probability, but
• Other types of events with much higher
probability, involving single patients, can
also be severe, may more easily go
unreported
• They deserve increased attention and
preventive measures
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Example No. 2 of major finding from
probabilistic safety assessment
• Increased software control (control of linear
accelerator functions, treatment planning,
virtual simulation, image guided radiotherapy,
record and verify control, radiotherapy
information systems, electronic charts) confers
software safety a paramount importance
• Software deserves increased attention in
standards and by regulatory bodies and
professional bodies;
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Example No. 3 of major finding from
probabilistic safety assessment
• Safety aspects related to the approval
of the treatment plan by the radiation
oncology and measures on the patient
directly such as in vivo dosimetry or its
equivalent measures, daily observation
of the patient and periodic medical
control bear an important part in risk
reduction, in terms of prevention and
mitigation of accidental exposures
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Take-home messages
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Introducing new technologies
• Decision to implement a new technology
should be based on an evaluation of the
expected benefit, rather than being driven
by technology itself
• A step-by-step approach should be
followed to ensure a safe implementation.
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Staff training, availability and
dedication
• Replacement of proper training with a short
briefing or demonstration should be avoided,
because important safety implications of new
techniques cannot be fully appreciated from a
short briefing.
• Certain safety-critical tasks, such as
calibration, beam characterization, complex
treatment planning and pretreatment
verification, require a substantial increase in
staff allocation.
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Safety awareness of responsible
persons for radiotherapy
• Independent verification of beam calibration
remains essential.
• Investigating discrepancies in dose
measurements before applying the beam to
patient treatments.
• Hospital administrators of radiation therapy
departments should provide a work
environment that encourages working with
awareness, facilitates concentration and
avoids distraction.
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Manufacturers
• Manufacturers should be aware of their
responsibility for delivering the correct
equipment with the correct calibration files
and accompanying documents.
• They also have a responsibility to provide
correct information and advice, upon request,
from users.
• Procedures to meet these responsibilities
should be developed and quality controlled.
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Programme of purchasing,
acceptance and commissioning
• Programmes for purchasing, acceptance
testing and commissioning should not only
address treatment machines but also
treatment planning systems, radiation therapy
information systems, imaging equipment
used for radiation therapy, software,
procedures and entire clinical processes.
• Devices and processes should be recommissioned after equipment modifications
including software upgrades and updates.
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Need for new protocols for
treatment prescription and
dosimetry
• Protocols for treatment prescription, reporting
and recording, such as found in ICRU
reports, should be revised to accommodate
new technologies.
• They should be adopted at a national level
with the support of professional bodies.
Similarly, dosimetry protocols should be
developed for small and non-standard
radiation fields.
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Dose escalation
• Dose escalation without a concomitant
increase in normal tissue complication
probability generally implies a reduction of
geometrical margins.
• Such a reduction is only possible with
conformal therapy accompanied by precise,
image-guided patient positioning and effective
immobilization together with a clear
understanding of the accuracy achieved in
clinical practice.
• Without these features, target dose escalation
could lead to severe patient complications
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Safety-critical communication
and notifications
• Unambiguous, well structured communication
is essential, considering the complexity of
radiation therapy and the multidisciplinary
nature of the health care environment.
• In particular, procedures to notify physicists of
maintenance and repair activities, identified
as crucial in conventional technology, are
even more necessary with new technologies.
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Computers and data integrity
• Procedures should be in place to deal
with situations created by computer
“crashes”, which may cause loss of data
integrity and lead to severe accidental
exposures.
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Updating of quality control tests
• When conventional tests and checks
are not applicable or not effective for
new technologies, the safety philosophy
should aim at finding measures to
maintain the required level of safety.
• This may require the design of new
tests or the modification and validation
of the old ones.
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Using lessons from experience
• Lessons learned from past accidental
exposure should be incorporated into
training. Radiation therapy facilities are
encouraged to share their experiences of
actual and potential safety incidents
through participation in databases such as
Radiation Oncology Safety Information
System (ROSIS), often referred to in this
report.
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Overcoming the lack of experience
when introducing new technologies
• Prior to the introduction of new techniques and
technologies, there is little or no operational
experience to share. Two complementary
measures are recommended:
– Prospective safety assessments should be undertaken
in order to develop risk-informed and cost-effective
quality assurance programmes.
– Moderated electronic networks and panels of experts
supported by professional bodies should be established
in order to expedite knowledge sharing at the early
phase of introducing a new technology.
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Recap
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•
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Most lessons from conventional
techniques are applicable to new
technologies
Additional lessons for new technologies
have become available (ICRP 112)
Anticipative approaches provide a riskinformed and rational choice of safety
provisions
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Thank you
• You are invited to use these lessons for
training and to apply them in practice
• More details in ICRP publication 112
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