Clinical Implementation of the Delta 4 Discover Vikren Sarkar, Adam - - PowerPoint PPT Presentation

Clinical Implementation of the Delta4 Discover

Vikren Sarkar, Adam Paxton, Bill Salter

Meet the Discover

• 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?

Main Topics

• What we checked

– Influence on PDDs/Profiles – Attenuation – Superficial Dose – Accounting for it in the TPS

• End to end testing

How does it influence my beam?

Example PDD and Profile (6X)

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 5 10 15 20 25 30 35 w/o 10x10 w/o 30x30 w/ 10x10 w/ 30x30 20 40 60 80 100 120 ‐30.0 ‐20.0 ‐10.0 0.0 10.0 20.0 30.0

30x30 1.5cm

w/o Discover w/ Discover

• Measured in solid water using a PTW semiflex chamber

– 90 SSD, 10 cm depth – 10 x 10 cm2 and 30 x 30 cm2 fields

Attenuation

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

• Results from plans delivered to the Phantom+

IMRT QA results with and without Discover

• 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
• f 1% relative to Rx dose from the presence of the

Discover.

Conclusions regarding beam influence

• 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)

On the ability to catch mistakes

Leaf motions introduced

Baseline Central Leaf Only Opened Shifted

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

• 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.

Conclusions on error detection

• 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

• The pre-treatment QA

– Gamma (2%,2mm) passrate = 96.4%

Clinical Implementation : 1st Patient

• 5 treatment days - Summary

Clinical Implementation : 1st Patient

• 5 treatment days

Clinical Implementation : 1st Patient

• 5 treatment days

Clinical Implementation : 1st Patient

• 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

Conclusions

Thank you!