Are weekly port films or daily cone beams considered standard of care for 3D breast treatment?

It doesn't have to be either/or. But...

As Don Rumsfeld said, "You go to war with the army you have, not the army you want." Some practices, and they are rare admittedly (think: a site with only a Tomotherapy machine) can't really do "port films" per se and they're wont to do daily IGRT/CBCT. If "MRI linacs" ever supplant the traditional linacs of today (doubtful!) you could make the same argument: the standard of care is daily MRI on an MRI linac. (As an aside, weekly port films are a form of IGRT in the scientific sense but not in a "billing sense.")

In the very early days of IGRT (Exactrac with optical surface tracking and isometric automated kV plain film/DRR matching... that was my first modern IGRT experience) and kV CBCT, I'm talking ...

We were using plain MV films (1. modality), every 5 fractions (2. frequency), aligned to bony anatomy (3. alignment criteria), with instructions for iso shifts if discrepancies were greater than 1 cm (4. threshold for shifts). The same principles apply with volumetric imaging (see previous discussion on "What do you do for physician approval of IGRT images?" posted in 2014).

The use of portal imaging was a means of internally aligning the patient after DAILY external landmarks (ie, tattoos) were referenced during patient setup. If port films were off, adjustments were made, and another port film was obtained to verify that the shift was appropriate. So we are not necessarily flying blind by doing port films every 5 treatments. Port films h...

We have not been doing daily imaging for tangential beam RT unless set up and reproducibility is a challenge or pt treated with DIBH ( we do daily MV imaging for these pts)

This is a great conversation and points to a much bigger issue: just because we have the technology, does it mean we have to use it on every patient (eg: 2-field breast), even if there is no documented clinical benefit (and potentially increases a patient's radiation exposure)? Healthcare spending in the U.S. was $3.3 trillion in 2016, which translates to $10,348 per person, or 17.9% of the GDP. As radiation oncologists, are we contributing to the problem? I'm conflicted about doing cone beam every day for a simple tangent breast treatment - I can see some benefit to it, but is the cost worth it and the extra radiation exposure to the patient? Are we doing it for the right reasons? I like @Dr. First Last's comment "what would be a very inte...

A survey of IGRT practice patterns by Nabavizadeh et al., revealed that for breast treatments, the majority of respondents used port films, with the assumption that the vast majority of respondents were using tangents (67.4% used portal imaging, and only 10.4% using CBCT or MVCT). In terms of frequency, 62% obtained images weekly, while 24% obtained images daily (likely in those cases using DIBH). The study showed a "large decline in the utilization of portal imaging, ... except for breast."

So it appears that in the age of volumetric imaging (CT and MRI), weekly port films are still widely used as a standard of care, unless the criteria outlined by @Dr. First Last are met.

~EPILOGUE

This month in the Red Journal an article from Royce et al appears detailing medical malpractice outcomes in regards to radiation oncology. A very good article and enlightening. One point among many it highlights is that wrong-site treatment is a significant medical malpractice issue in radiation oncology. Makes sense. I have always held the opinion (it's an opinion as there is no data) that IGRT, CBCT especially, makes it essentially impossible to treat the wrong site in a patient. (That is to say, CBCT is an effective "screening tool" for wrong-site treatment.) One might argue this needs to be studied; perhaps so. However, let's assume wrong-site treatment takes place in 1 out of 500 patient treatment cases (0.2% incidence). If IG...

@Dr. First Last raises an excellent point regarding long term risk from daily CBCT for breast radiotherapy, i.e., risk from excessive imaging dose. Consider: breast cancer patients often survive for decades, many are young, the opposite breast, lungs, heart will receive daily CT levels of dose. Integrating these variables is the work of physics and radiobiology. A detailed paper estimating such risks from those communities would be welcomed by all of us.