Frequency of Portal Images Required to Enhance Quality Assurance for Breast Cancer Patients Treated With Radiotherapy
To determine if the verification film (port film) taken and accepted as correct at the
beginning of a course of radiotherapy is adequate to ensure accurate position of treatment
delivery for a 4-5 week course of radiotherapy in breast cancer patients.
- To assess the feasibility of doing on line portal imaging for breast cancer
- To possibly identify a patient population that should be verified daily with on line
Quality assurance is a very important aspect of radiotherapy delivery. There are many
facets of quality assurance but a basic concept is to ensure the radiation is delivered to
the correct target area. At the start of a course of radiotherapy treatment the standard at
the Cross Cancer Institute is to confirm the correct area is being treated. This is done by
taking an x-ray on the treatment unit with the patient in the treatment position (portal
image or verification film). This portal image is examined by the treating oncologist and
compared to the simulation film or a digitally reconstructed radiograph that was generated
when the patient was simulated (set up) for radiotherapy treatment. Some alterations may be
suggested by the oncologist but once a portal film is deemed to reflect the original set-up
- no more routine verifications are performed. It is assumed that the treatment set-up
will be accurate for the remainder or the treatments.
Numerous changes may occur when a patient undergoes a 4-5 week course of RT. The patient
may relax after a few treatments, a patient can lose weight, surgical changes can settle,
all altering the original set up.
There are no data to determine how often a set up should be verified. Ideally it should be
checked daily prior to each treatment initiation. This can be done with on line portal
imaging however resources currently do not allow on line portal imaging for every patient.
By evaluating the impact of weekly portal images the investigators may be able to identify a
population of patients that would benefit from more frequent portal images or patients who
would benefit from daily on line portal images, allowing for appropriate resource
Currently in Canada, and at the Cross Cancer Institute, the treatment of many women with
breast cancer involves radiotherapy. There is a complex process which takes place in order
to plan the radiation therapy before patients commence their treatment. In many
circumstances the investigators use computerized technology to assist in planning their
treatment. This allows more precision in delivering the treatment to the desired areas and
avoiding areas of normal tissue.
Once the planning process is completed, the investigators then place marks with a marker pen
on the skin of the patient to outline the area where the radiation will be delivered. The
investigators confirm that the correct area is being treated with an x-ray taken on the
treatment unit while in the treatment position. This is called a port film or verification
film. The investigators then compare this to what they set up with the computerized data.
If all the information matches, the patient is then treated for the full course of
radiation, with the assumption that all treatments are given in the correct position. No
further checking is done.
The standard at some radiotherapy centers is that the patient treatment position is verified
weekly by a portal film. At the Cross Cancer Institute the investigators only do it once at
the beginning of treatment.
No information is available to confirm the necessity of doing more frequent verification
films, but in view of the very complex nature of the investigators' treatment delivery, it
may be necessary to confirm the accuracy of their treatment more often.
Over the course of a 4-5 week treatment the investigators know that some patients may lose
weight, some become more relaxed after a few days, and some have trouble with the range of
movement in their shoulders; all of these factors influence the positioning of the patient.
Measurements taken on the treatment unit often change during the course of a patients
treatment, but no further verification is performed to ensure that the treated area is still
what was initially intended.
This is a single institute pilot project.
PATIENT CRITERIA/SAMPLE SIZE:
Any breast cancer patients receiving a course of radiotherapy to treat the breast, chest
wall and/or regional lymph nodes.
One-hundred consecutive consenting patients will be analyzed prospectively. Patients will
be stratified as per treatment area: breast only, breast plus regional nodes, chest wall
only and chest wall plus regional nodes. The treatment technique will also be evaluated.
Patients eligible and consenting will be sequentially selected to undergo the standard
radiotherapy planning process and initial verification films. In addition to the standard
initial verification films, all patients will have additional verification films taken
weekly. These will be reviewed by the treating radiation oncologist and a data form will be
completed. The treatment record will also be examined and any changes noted by the
therapists during the course of radiotherapy will be recorded.
No additional amount of radiation is given to the patient. The amount of radiation required
to take the verification films is subtracted from the amount of radiation delivered at the
time of treatment.
The data will be compiled and compared to establish any relationship between target volume
(breast only, breast plus regional nodes, chest wall only and chest wall plus regional
nodes) or technique used to the acceptability rate and accuracy of the verification films.
Susan Chafe, MD
Cross Cancer Institute
Canada: Health Canada