The tort of negligence is well understood by most dental practitioners and patients. The aspects of the tort that are perhaps most applicable in the current situation of dosage are causation, reasonable foreseeability and warning of material risk.
The causation of an injury needs to be proven. Alternatively, the injury might well speak for itself in that a dosage of radiation that is high initially, and if repeated, could give rise to a claim for damages. Whilst it would not be easy for a claimant to prove injury and causation from CBVT diagnostic imaging, the likelihood would increase with paediatric patients and repeat exposure patients. Australian courts have been reluctant to give damages where causation is complicated in relation to a loss of a chance.5
The irrefutable fact is that the operation of CBVT without appropriate regulation and guidance will see a higher dosage of radiation delivered to a patient base as a whole but more particularly to certain individuals.
The issue of reasonable foreseeability (and to some extent remoteness of damage) will be one of fact, and will be determined by retrospective studies in the future. Currently, this is hard to determine and makes a successful suit more difficult.
In 1996 Webb et al. found that 50% of patient radiation exposure came from full body CT.6 O’Hare surmised that the availability of multislice CT has almost certainly increased the potential for litigation, particularly in paediatric patients who have a two to three times greater likelihood of radiation induced cancer than adults.7 Moss and Maclean surveyed 53 scanners and found the effective dose varied by up to 36 fold.8 O’Hare cites the lifetime mortality risk from a single CT to a one-year-old child has been held to be as high as 1:550.9
As to material risk and warnings, the wider question of ionizing radiation dosages across a person’s circumstances would be critical in discussing risk and this would include, but not be limited to, occupation and environmental considerations (long haul airline crew or radiographers would have a different risk profile to that of a city office worker), diagnostic and therapeutic radiation history, and patient age and gender.
In cases of general CT radiology, the risks are greater and the duty to inform is clearer. Cardinal et al. explored the issue of informing patients of risks and benefits of radiological examinations: “In addition to the need to educate patients, studies have underscored the need to better educate referring physicians, demonstrating that referring physicians often have limited knowledge of the radiation dose and associated risks for common radiologic examinations. This is unfortunate, for two reasons. First, this knowledge is relevant for appropriate medical decision making in ordering radiologic examinations. Second, referring physicians are well positioned to initiate patient education on the risks associated with these examinations. Referring physicians often have good pre-existing relationships and well-developed lines of communication. They also should understand the benefits of the radiology examination they are ordering for particular patients and have the opportunity to involve the patients in the decision-making process further upstream. By the time patient education can occur in the radiology department, a patient may have taken time off work and made a long trip to the radiology department, and completing the examination may be a foregone conclusion.”10
This is a practical application of the principle that responsibility for the damages that flow from such a referral do not necessarily sit singularly with the radiologist or the dentist. If a dentist refers a patient for radiology for the investigation of pathology, the more serious the suspected pathology, the higher the duty there is to follow up and check that the patient did have the referred investigation performed. There is Australian authority that the duty of care to a patient extends much wider to the referral and even follow up of patients.11
Failure to diagnose
The issue of failure to diagnose in radiology can be characterized as a loss of chance. However, that loss of chance must be a matter of a determination of probability. In a case about failure to diagnose a breast cancer, it was held that: “A mere material increase in the risk of injury followed by the eventuation of the risk in question is insufficient to establish causation. The plaintiff must establish that it was probable that the risk created by the tortfeasor came home.”12
In other words, for a loss of a chance, an increase in the risk of a death from, for example, pathology which was undiagnosed from a CBVT, will not of itself be enough to prove that the failure to diagnose caused the patient death. It must be more likely than not that the failure to diagnose substantially caused the death.
However, does a dental practitioner have a responsibility to diagnose other pathology from a CT scan? Does the dentist take on that responsibility by ordering a CT scan that has a volume that is larger than the area of interest?
Friedland’s paper contemplates most of these issues – albeit from a US perspective.13 It is of guidance and the section on field of view, reproduced below, is apposite to questions of appropriate ordering and selection of field of view.
“One of the issues raised by CBCT is just which anatomical area of the jaws and head or neck should be included in a study. For example, assume one takes a CBCT scan of the fully edentulous maxilla for purposes of evaluating the feasibility of placing implants. Does the image provide sufficient coverage if the beam is collimated (in the vertical) to include just the alveolar bone and only 2 to 3 mm superior to the sinus floor? Or is it necessary to include more of or perhaps even the entire sinus? The general principles of radiology dictate that the taking of films be based on clinical indications and that examinations not be done as part of ‘a fishing expedition’.”
“The rationale for this is to protect both the individual patient’s and the public health from unnecessary radiation. Thus, in the example above, if the patient has no sinus symptoms and no sinus pathology is suspected on clinical examination, there is not a strong argument for including the whole sinus. The answer to how large an area to cover also includes, however, the desires of the treating clinician, although this should not generally override well-accepted principles of radiation hygiene. In the above example, some clinicians may insist on seeing all the way to the orbital floor. Further, some software programs require that certain anatomic landmarks be included since the program uses them as (anatomical) fiduciary markers.”
“It is also possible to collimate too narrowly, either accidentally or by design, and thus to exclude structures that reasonably ought to be included. The issue of purposely collimating too narrowly is closely related to the reading or interpretation of the films, an issue discussed in depth below. CBCT machines are increasingly being marketed to private practitioners who are not oral and maxillofacial radiologists. Companies’ target market is especially orthodontists and practitioners who place dental implants. These practitioners typically do not have sufficient training to interpret the films beyond the confines of their specialty or daily area of practice. Some practitioners believe that one way to overcome the issue of interpretation is to collimate down to the smallest area possible. For example, if an orthodontist does a CT to evaluate an impacted maxillary canine, the idea would be to collimate the beam to include just the tooth and nothing superior or inferior to it. The danger with this approach, however, is that one may miss pathology that is contributing to the noneruption or impaction of the tooth. Similarly, when radiographing the temporomandibular joint (TMJ), if one were to collimate too narrowly, one could potentially miss pathology that is not located directly on or in the condyle or glenoid fossa, but that is contributing to the TMJ problem. In principle, the anatomical area covered by a CT scan should be no different than would have been covered by a plain-film examination. The extent of the examination should be based on the patient’s symptoms and the findings on clinical examination.”
Friedland also addressed the issue of responsibility for interpretation: “While there are no legal cases specifically concerning the matter of the scope of interpreting a CBCT scan, the issue can fairly be regarded as settled. A CT is no different than any other image—a dentist cannot read only part of a panoramic film, or only part of a lateral cephalogram. For example, should an orthodontist miss an enlarged sella turcica resulting from a tumor on a lateral cephalogram, the dentist reading the cephalogram cannot offer as an excuse in any legal proceeding that ‘I read only part of the film’ or ‘I read the film only as it relates to the orthodontic diagnosis and treatment’. The dentist is obligated to read all of the film … Moreover, in determining the standard of care, courts look to what the practice in the profession is, and as is evident from the editorial referenced above, the practice is to read all of the film. Courts are not likely to allow a lower standard of care than the profession demands of itself.”
Whilst this is no doubt a fair assessment of the law in the USA, it is by no means certain to be applied in Australia. However, it would be likely to be of significant influence and guidance. The issue of whether patient choice can be involved was also addressed.13
“While patients may make treatment decisions, their choices are limited by the bounds of accepted standards of care. No dentist would permit a patient to agree to fill only two canals on a molar tooth undergoing endodontic treatment and then to place a crown because the dentist is unable to navigate the third canal or because the patient can only afford to have two canals filled. Such a scenario would call for a referral to an endodontist or foregoing the crown. The same principles apply to the interpretation of films.”
If it is accepted that dentists must ensure that after a wide-area survey the patient has a complete diagnosis, and the dentist lacks the skills and experience to provide this, it is logical that it be referred to an oral or medical radiologist. In the USA, no national dental regulations mean that radiology telemedicine is quite difficult. No such barriers exist in Australia.
It has been established in the High Court case of Chappel v. Hart,14 that when making treatment decisions, there is a responsibility on the treating practitioner to advert as to whether the procedure (in the present case, reading of a radiology image) in the particular circumstances could not be better performed by a more experienced practitioner. As oral radiologists become more prevalent, the onus to refer becomes somewhat stronger. It may be the case that whether one orders a CBVT survey for dental treatment or not, the patient might well have a reasonable expectation to have interpretation (of all the data available) performed as a matter of right – to reinforce the view of Friedland.
It would seem that if one refers a patient (and/or their image) to an oral radiologist, the responsibility for the expertise in reading and interpreting that radiograph resides with the radiologist. Of course, the wording of the referral will be determinative of where the responsibility lies for which structures and the interpretation of the image in relation to those structures.