INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION Preventing accidental exposures from new...

INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION ——————————————————————————————————————

Preventing accidental exposures Preventing accidental exposures from new external beam radiation from new external beam radiation

therapy technologiestherapy technologies

ICRP Publication 112Task Group:

P. Ortiz López (chairman), J.M. Cosset, O. Holmberg, J.C. Rosenwald, P.

Dunscombe, J.J. Vilaragut, L. Pinillos, S. Vatnitsky


Lessons from accidental Lessons from accidental exposures with conventional exposures with conventional

techniques are availabletechniques are available

They have been useful in They have been useful in improving safetyimproving safety



The key questions are:The key questions are:

1. Are lessons from conventionallessons from conventional techniques applicable to newer technologies?

2. Are there new lessonsnew lessons from new technologies?

3. Can we anticipate “what elsewhat else can go wrong?”


1st question1st question

Are lessons from lessons from conventionalconventional techniques applicable to newer technologies?

Applicable to new Applicable to new technologies?technologies?


Overall lesson from conventional Overall lesson from conventional techniquestechniques

• “…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, indeedYes, indeed


115 patients severely affected


Lessons from conventionalLessons from conventional techniques valid for new technologies?

Beam calibration: independent verification of absorbed dose at the reference point


Lessons from conventionalfrom 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

28 patients severely 28 patients severely overdosed in Panamaoverdosed in Panama

1045 patients 1045 patients underdosed in the UK underdosed in the UK


Lessons from conventionalLessons from conventional techniques valid for new technologies?

Clear notification of maintenance and Clear notification of maintenance and repairs repairs to the person responsible for radiotherapy physics, before resuming patient treatments

27 patients severely

affected in Spain


All these lessons from All these lessons from conventional techniques conventional techniques are are valid for new technologiesvalid for new technologies

They should be part of training They should be part of training programmes, and incorporated programmes, and incorporated

into procedures in into procedures in radiotherapy departmentsradiotherapy departments



2nd question Are there new lessonsnew lessons from

new technologies?

Yes, the followingYes, the following


New lessonsNew lessons::Software control of accelerator

functions data integrity may be lost after computer “crash” or “frozencomputer “crash” or “frozen””



Loss of data integrityLoss 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 Checking procedures are required for computer “crashes”. Irradiation parameters may be wrong “crashes”. Irradiation parameters may be wrong uponupon


Interlock misadjustmentInterlock understanding

Test of interlocks at equipment acceptance



Tolerances and interlocks Tolerances and interlocks • Misadjustment of the tolerance limits of a dose-

rate interlock occurred on a tomotherapy unit• Important: understanding interlocks and Important: understanding interlocks and

ensuring their testing at equipment acceptanceensuring their testing at equipment acceptance


Wrong calibration files for an Wrong calibration files for an applicator were supplied by the applicator were supplied by the

manufacturermanufacturer



Intraoperative radiotherapy• 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!


Errors from imaging: Wrong site treatment

(right-left)Image distortion



Multiple imaging modalities: problem with consistency in identification and

labelling

• 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



Image reconstruction

• 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


Confusion of different coordinate systems

???



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

(B)

(A)


Significant radiation dose from daily imaging for verification



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


Several events due to poor Several events due to poor understanding of new techniques and understanding of new techniques and

poor communication and recordingpoor communication and recording



Calibration of very small beams (micro multileaf collimators)

• Partial volume irradiation of the chamber. Wrong absorbed dose determination

• Knowledge needs to be sharper, as well as the level of awareness Knowledge needs to be sharper, as well as the level of awareness of the task at hand of the task at hand

• Education and specific training essential for new technologiesEducation and specific training essential for new technologies



Record and verify systems

• 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



Dynamic wedges• 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



Small fields in stereotactic treatment with applicator



Confusion 40 mm - 40 cmPatient died from the accidental

exposure

40 (mm)

40 (cm)


Avoid poor understanding of new techniques and poor communication

and recordingLesson Lesson No “quick” training…No “quick” training…

… … but solid trainingbut solid training



All these new lessons are useful in All these new lessons are useful in preventing reported types of risks, butpreventing reported types of risks, but



3rd question: Can we anticipate

what elsewhat else can go wrong?



The unknown or unreported 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 Do we need to wait until they occur, to

learn the lesson?learn the lesson? ¿What should be done about increasing

equipment complexity and thus ever larger lists of double checks and verifications?



There are proactive methods of There are proactive methods of safety assessmentsafety assessment

• 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


Example No. 1 of major finding from Example No. 1 of major finding from probabilistic safety assessmentprobabilistic 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



• 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;



• 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


Take-home messagesTake-home messages


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.


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.


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.


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.


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 re-commissioned after equipment modifications including software upgrades and updates.


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.


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 Without these features, target dose escalation could lead to severe patient complicationscould lead to severe patient complications


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.


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.


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.


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.


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.



RecapRecap• Most lessons from conventionallessons from conventional

techniques are applicable to new technologies

• Additional lessons for new technologiesAdditional lessons for new technologies have become available (ICRP 112)(ICRP 112)

• Anticipative approachesAnticipative approaches provide a risk-informed and rational choice of safety provisions


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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