Clinical Implementation of the Delta 4 Discover Vikren Sarkar, Adam Paxton, Bill Salter
Meet the Discover
Main Topics • Pre-clinical Testing – Does the device influence my treatment beam? – How sensitive is the device in its error detection? • Clinical Usage – Are there any caveats to its use?
How does it influence my beam? • What we checked – Influence on PDDs/Profiles – Attenuation – Superficial Dose – Accounting for it in the TPS • End to end testing
Example PDD and Profile (6X) w/o Discover 120 30x30 1.5cm 100.00 w/ Discover 90.00 100 80.00 w/o 10x10 w/o 30x30 70.00 80 w/ 10x10 60.00 w/ 30x30 50.00 60 40.00 40 30.00 20.00 20 10.00 0.00 0 0 5 10 15 20 25 30 35 ‐ 30.0 ‐ 20.0 ‐ 10.0 0.0 10.0 20.0 30.0
Attenuation • Measured in solid water using a PTW semiflex chamber – 90 SSD, 10 cm depth – 10 x 10 cm 2 and 30 x 30 cm 2 fields Energy Average* Attenuation (%) 6X 1.3 6FFF 1.5 10X 1.0 10FFF 1.2 15X 0.9 18X 0.8 * Averaged over 2 field sizes
Superficial Dose
IMRT QA results with and without Discover • Results from plans delivered to the Phantom+
Conclusions regarding beam influence • The presence of the Discover does not affect the beam spectrum to any clinically significant level. • The beam attenuation from the Discover is very small and can be accounted for within the TPS (through a tray- like accessory). • There is a small increase in superficial dose on the order of 1% relative to Rx dose from the presence of the Discover.
On the ability to catch mistakes • 2 ways to use the Discover: – By itself from the beginning • We get leaf position information (with gantry angle for arc deliveries) but it is not possible to evaluate the dosimetric effect of any leaf position discrepancy – In conjunction with the Phantom+ for at least one fraction • In that case, fluence measured per control point by the Discover can be correlated to dose measured for the same control point in the Phantom+ so that further fluence measurements can be correlated to dose in the Phantom+ (or the patient using additional software)
Leaf motions introduced Shifted Baseline Opened Central Leaf Only
Results from single 3D beam - Gamma
Single 3D field – Other mistakes
Single 3D field – Other mistakes
Single IMRT Field - Shifts
dMLC IMRT Field – Other mistakes
Arc Fields - Shifts
Arc Fields – MLC Gamma
Conclusions on error detection • The Discover detected errors on the order of 1 mm and 2 degrees easily. • The results confirm that the Discover should be used in conjunction with the Phantom+ to take full advantage of its error detection capabilities (wrong energy, wrong jaw position etc) but, by itself, there are still several errors it can catch.
Clinical Implementation • The Discover unit 1. Has low attenuation (which can be accounted for in the TPS) 2. Lies above the detection plane of the LaserGuard II (safety “bubble” still available)
Clinical Implementation • But… the discover is seen as an accessory. – When the discover is “open”, no motion is possible
Clinical Implementation • But… the discover is seen as an accessory. – When the discover is “closed”, no remote motion is possible
Clinical Implementation • Some changes are needed to the workflow to account for this. – Use VMAT instead of static gantry IMRT? – Checking for SSDs – maybe check separations instead? – Put the gantry/collimator at the correct position before leaving the room.
Clinical Implementation • The ideal case to start for our clinic : Prostate SBRT – IGRT is performed in-room (ultrasound) – Only 2-arc VMAT
Clinical Implementation : 1 st Patient • The pre-treatment QA – Gamma (2%,2mm) passrate = 96.4%
Clinical Implementation : 1 st Patient • 5 treatment days - Summary
Clinical Implementation : 1 st Patient • 5 treatment days
Clinical Implementation : 1 st Patient • 5 treatment days
Conclusions • The Discover 1. does not highly impact the beam quality 2. easily detects errors on the order of 1mm in leaf position and 2° in gantry position 3. caught other mistakes introduced in the plan when used in conjunction with the Delta4 phantom 4. will probably require some changes in workflow 5. was sensitive enough to catch small drifts in daily output and raise a flag
Thank you!
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