Dan Scanderbeg, Ph.D.
In January 2009, researchers at UC San Diego published their peer-reviewed article about the clinical implementation of the SAVI® applicator in Radiotherapy and Oncology. Lead author Dan Scanderbeg, Ph.D. discusses the article and the lessons learned while incorporating SAVI into the facility’s HDR program.
Q: What did you learn from your clinical implementation of SAVI?
A: Overall, SAVI was very easy to implement into our existing HDR program. Because you can differentially modulate the dose in each strut, good quality assurance procedures are essential for patient safety. All the new multi-channel devices require pre-fraction QA – so while these devices do an excellent job of sculpting the dose to the patient’s anatomy, it requires you to watch for changes in tissue conformance or device symmetry that can occur during treatment.
Reproducible patient set-up is the key to detecting any inter-fraction movement, as it can prevent you from mistaking patient motion for device motion. Daily CT scout films, prior to each fraction, are what we use to determine if any motion has occurred. If we do notice a change, we will take a full CT scan and compare with the post-insertion CT scan.
Additionally, we have found that if we have any cavity conformance issues or device asymmetry upon insertion, these will usually correct themselves within 24 hours of insertion. If we see one of these issues upon insertion, we will postpone treatment planning for 24 hours to allow the implant to settle.
Q: How can you ensure reproducible patient set-up?
A: We use a breast board and the standard three-point set up typically used with external beam procedures. This ensures the patient is in the same position as the initially scan, preventing us from mistaking the patient’s body rotation as rotation of the device. We also have patients hold their breath during every scan to reduce the possibility of artifact.
Q: What are some other QA considerations physicians should be aware of?
A: Prior to each treatment fraction, there are several things we take into account. We always check for device motion, both in-out motion and rotational motion. Linear motion is measured with a skin-to-hub measurement. Rotational motion can be assessed in multiple ways. You can easily assess gross rotation by examining the alignment of marks on both the skin and the device. The CT scout films will reveal in greater detail if there has been any shift. I there is any question, we will take a full CT scan to confirm.
It is important to have two people present for pre-fraction QA procedures to ensure correct assembly. No matter which HDR afterloader is used with SAVI, the transfer tubes from the machine can be placed interchangeably on the device struts, so it’s essential to have that second check to make sure the guide tubes are connected to the correct strut.
Q: What would you say to other physicians who say treatment planning with multi-channel devices is too complicated?
A: While treatment planning with SAVI takes longer than single catheter devices like the balloon, it’s not a significant difference. Overall, it’s not much more complicated, particularly considering the benefit that comes with the ability to modulate the dose – treating a new patient population that was previously ineligible for APBI. With SAVI, we’ve treated patients with skin bridges as small as 1 or 2 mm, which would not have been possible with single channel devices.
In my opinion, treatment planning with SAVI is actually more enjoyable because it’s more intellectually stimulating than with other devices – I think it’s more of an art.
Q: How does SAVI differ from other single-entry, multi-channel devices?
A: We haven’t been able to sculpt the dose with other devices as much as we can with SAVI. Although the devices also utilize multiple struts, the struts are still close enough to the central lumen so that it limits the ability to control the dose in all directions. With SAVI, the struts are imbedded in the tissue interface and separate enough to allow for extremely precise dose modulation.
Compared to other devices, SAVI comes the closest to interstitial brachytherapy in a single-entry device. Since very few physicians perform interstitial procedures, SAVI offers the ability to treat the widest variety of women. In our patient population, we have found that 40% of the patients we treated with SAVI would have been ineligible for balloon brachytherapy due to skin spacing restrictions alone. There are additional studies that indicate up to 55% percent of women who were previously ineligible for balloon brachytherapy can be treated with SAVI – and that is a significant benefit.
Q: Is there a significance to your article appearing in the Green Journal?
A: Not specifically for this journal, but overall I think it indicates an increasing acceptance of APBI, particularly for newer devices like SAVI. SAVI has a very promising future. Through our patients and studies, we’ve seen how it allows excellent target coverage while minimizing dose to the skin and chest wall. The dose modulation is exceptional, which opens the door to APBI for more women who want a shorter course of treatment.
About Dr. Scanderbeg
Dan Scanderbeg, Ph.D. will be joining UC San Diego as a clinical Medical Physicist and Assistant Professor in July 2009. A graduate of the University of California San Diego, Dr. Scanderbeg was the first Medical Physics Resident at UCSD and will serve as Chief of the Brachytherapy service in the department. For more information, visit http://radonc.ucsd.edu.