Published by Radformation Survey Team on 12/20/2020
Items of Consensus
How often does a group of physicists agree on something? Let’s put it this way: when over 80% of respondents agree on a survey topic, it’s worth pointing out. Here are the items of consensus for the surveys that fall into this particular category.
LINAC Setup Photos
When using setup photos are used as a reference, over 89.0% of responses indicated the usage of some setup photo display in the linac vault. After using these photos for setup, patients are often imaged to assess patient position, and shifts are applied as necessary.
CT Bore Sizes
With 90% of clinics owning a CT simulator with a bore size of 80cm or greater, it’s clear that clinicians favor a large bore for general purpose simulation. Of those with smaller bores (<80cm) 100% of survey respondents noted issues accommodating all patients during simulation. Indeed, large-bore scanners allow clearance for all body types and enable the use of various (and often bulky) immobilization devices.
Tattoos for Patient Setup
As SGRT becomes a more popular option to verify patient setup, it’s clear that tattoos are still used widely, with 90.6% of all respondents indicating the use of tattoos to mark isocenter, even in IGRT cases. Only 6.3% have stopped using tattoos entirely.
Historically, SRS was performed using a rigid head frame for immobilization. That practice has largely changed over the years. Now 86.9% use frameless immobilization as opposed to framed. Survey responses indicate a steady trend away from frames due to patient comfort and the belief that frameless offers similar or better accuracy (with IGRT) than frames with shorter treatment times. While frames have been falling out of use, frameless users noted frames were still utilized in special cases with small lesions near critical structures.
Patient Treatment Verification Imaging
Treatment uncertainty can be improved via pre-treatment imaging. For static treatments involving MLC, 92.2% verified the shape of MLC’s using portal imaging on the initial treatment, and 74.5% of respondents performed some sort of portal imaging on subsequent treatment fractions. The most common techniques were first fraction check and weekly ports afterward. For IMRT plans, 84.2% forego imaging the individual fields with the patient on the table, opting instead to verify the fields with a 2D array, portal dosimetry, or other IMRT QA.
CT Slice Size & Dose Grid
The choice of CT slice thickness and dose grid size used for simulation varies among departments. Of the free responses, the slice thickness is site-specific and ranged from 1 - 5mm for conventional treatment with 2.5mm being the most common response, while SBRT/SRS treatment had a range of 0.625 - 2mm with a mode of 1mm. The dose grid size was similar to CT thickness since many matched respondents noted matching their grid size to CT slice thickness. For conventional treatment, the grid size ranged from 1 - 5mm with a mode of 2.5mm. SBRT/SRS modalities had a dose grid range of 1 - 2mm and a mode of 1mm.
CT Slice Size (mm)
Dose Grid Size (mm)
Laser Color of Choice
Regarding the color of lasers used for treatment, green lasers are most common, with 65.9% of respondents indicating use of that color. Blue was second most common at 23.5%, and red being the least popular at 9.4%. One survey taker declined to select a color, instead indicating their preferred color is, “whatever is cheapest.”
IGRT Shift Tolerance
Regarding shift limits after imaging, most (67.5%) noted therapists were limited to 1cm shifts shifts without requiring further approval. 15% had a tolerance of 2cm, while 7.5% admitted to having a 3cm shift limitation. 10% responded that they could make, “Any shift deemed necessary.” On the other end of the spectrum, some noted tighter tolerances, as low as 5mm, with some indicating that any shift requires physician approval.
The requirement for physician approval was seen in almost all responses where tolerance was exceeded with 79.5% requiring physician approval, followed by physicist approval (45.5%), dosimetrist approval (15.9%), and chief therapist approval (4.5%).
IMRT and IGRT
SSD verification is the same as non-IMRT
Checking SSDs is another popular form of positioning verification. According to combined data from MedDos and MedPhysUSA surveys, 83.6% of users require some form of SSD check for the first fraction of non-IMRT fields. Fewer clinicians assess ongoing agreement, with 58.9% checking SSDs every week after the first fraction. With regards to IMRT/IGRT plans, 75.0% responded that they verify SSDs in the same manner.
Check SSDs on First Fraction
Check SSDs on a Weekly Basis
A Special Thanks
Thanks to Scott Dube for providing access to over 275 medical physics community surveys for public use. For further reference, a JACMP article by Kisling, et al. provides a complementary analysis of survey results.