Webinar Session 1 – Q&A

What proportion of your patients do you find DIBH is acceptable for?

Over time we have been using DIBH in more and more of our left sided cases. I would say that when become comfortable with the technique, well over half of the left sided cases are reasonable candidates. – Dr. Marks

We treat essentially all of our left sided breast cancer patients with DIBH. – David Gierga

More than 80% of our left-sided patients are qualified. – Lily Tang

Do you use this technique for right sided breast treatments?

We have started to do this occasionally for right sided patients in order to reduce the lung dose.  As one gets more comfortable with the technique it becomes hard to argue against using it.  When you do not use DIBH, and if you block the heart, you will under-dose a small portion of the medial inferior breast.  In settings where that is clinicially acceptable, I skip the DIBH.

How many years after radiation therapy does cardiac disease occur?

Conventional wisdom has been that it takes many years for cardiac injury to occur. However, there is increasing data to suggest that cardiac injury can occur sooner, perhaps within the first few years following radiation. We just published commentary on this exact topic in the red journal within the last month or two. That is easy to search under my name.  I will try to find the reference and post it.   In the Sarah Darby New England Journal paper she reported cardiac injury within the first year or two of radiation as well.

Are CBCT’s/KV match done daily to check setup prior to tx/Vision RT?

No, we do weekly KV to verify AlignRT setup. -Lily Tang

Is there any concern about more lung volume being tx during breath hold?

No. The chest moves anterior with DIBH, and the field borders need to be adjusted accordingly.  If these borders are positioned per the anatomy, there should NOT be any increase in lung volume.  Indeed, the percent of lung in the field will be reduced with DIBH as the total lung volume will increase with DIBH.

If DIBH technique is not available, do you prefer prone position tx?

No. I am not a fan of prone treatment. With prone the heart moves anteriorly, so if you are going to block the heart, you are actually reducing coverage of the deep chest wall tissues. This is probably OK for patients with DCIS, or where the deep breast/chest is not target. But in patients with invasive cancer, I worry that we are skimping on target coverage when we do prone and block the heart. This is all well outlined in a paper in the Red J about 8 years ago by Junzo Chino and me. – Dr. Marks

What tests should be included in SGRT commissioning per TG 147?

Hidden target end to end test, localization displacement accuracy and spatial reproducibility.

Does radiation heart damage only occur at high doses?

This is a challenging question.   Darby reported no threshold.  I am not sure I believe that.  The effects seen at apparently very low doses might be an artifact of variations in patient set up.  In other words a patient planned to get a low dose to the heart may have occasionally gotten a higher dose due to set up errors.  I beleive that doses maybe in excess of about 10 Gy can cause injury, but that is opinion and not based on too much data.   There is data to implicate cardiac injury after craniospinal RT, and that is low dose exit to the heart, and for Hodgkins disease, again with modest doses.   It is thus best to minimize dose to minimize risk.  I hope that that helps.

What is a typical/recommended translational threshold value in AlignRT for DIBH treatments?

We use 3mm. -Lily Tang

How do you do the gated functioning test at commissioning?

Two things you would need to test. 1) whether the gating function works–you can move the monitoring object to see if it can turn off/on the beam. There are many other ways of doing it.  2) the output. Per AAPM TG 142, the gated beam output needs to be within 2% of the non-gated output. -Lily Tang

Dr. Marks, please give me the reference to the time course of radiation injury.

See:
Reassessing the Time Course for Radiation-Induced Cardiac Mortality in Patients With Breast Cancer
Cited in Scopus: 0
Lawrence B. Marks, Timothy M. Zagar, Orit Kaidar-Person
International Journal of Radiation Oncology • Biology • Physics, Vol. 97, Issue 2, p303–305

Would you use electrons for a reconstructed chestwall with implants?

Generally not as the chest wall thickness is too variable for electrons.  We do use a separate electron IMN field in some cases.   It can be challenging to use the DIBH with matching fields, so for years we did not use DIBH with electron INM fields.  But over time, we have become comfortable with that and have been doing that some.  I have a patient under tx now where I am doing 4 fields DIBH; tangents; SC and IMN.

Has there ever been a head to head comparison of DIBH using RPM gating versus AlignRT with respect to reproducibility and planning? Are there any clinically significant differences?

I’m aware of at least one study: Rong et al PLOS One 2014 9:5. They noted superior correlation with AlignRT vs RPM. Certainly imaging the entire surface may be more advantageous than a single point. Also surface images can be used for both initial patient positioning and DIBH monitoring.

Is there much value in DIBH treatments for cancers other than Breast?

Both MSKCC and UNC have treated lung, live, and pancreas in DIBH as well. -Lily Tang

Do you use and verify with SGRT any integrated boost technique? What are your experiences?

We have treated one patient in electron boost. It’s more challenging but doable.

Have you used Electronic Compensators for tangents?

Yes. In fact we have treated one electron boost patient with AlignRT in DIBH. -Lily Tang

Is there an AlignRT system in the CT/Simulator room?

GateCT is available in the CT/sim room. It is utilized for marker-less 4DCT acquisition and reconstruction.