High Dose Rate Freiburg Flap Applicator for Skin Lesion Treatment

- Alternative to Electron or Photon?

K. Dou, PhD, B. Li, B. Laser, MD, M. Jacobs, MD F. Lerma, PhD, PhD and M. Sarfaraz, PhD

MedStar Health RadAmerica

Mercy Medical Center Radiation Oncology

Nucletron surface applicator

Freiburg Flap Valencia/Leipzig

Varian surface applicator

HDR Freiburg Flap Applicator

Dose Fractionation and Planning

Skin cancer

4 Gy x 10 = 40 Gy

Prescribed to 1 cm depth

Every other day

Skin keloid

4 Gy x 3 = 12 Gy daily

Prescribed to 0.5 cm

Target

V90 > 90% or V95 > 95%

Flap Commissioning

Dose calibration - TLD

Dose distribution – film and MapCheck

Source dwell position – film/Source Pos Simulator

First source dwell position – film/position simulator

CT based Tx planning

Catheter reconstruction

Source activation

Optimization –IPSA –Graphical/Manual - points

Secondary dose check with a spreadsheet

Plan delivery

Freiburg Flap Commission TLD and Film

* TLD for dose calibration within 2%

* Film to check source dwell positions within 1mm

* Film also to check the exposed pattern – dose distribution

Dose distribution for 12x12cm Flap prescribed to 1.5 cm depth

12x12 cm Flap with MapCheck

Head Lesion with Freiburg Flap

Squamous cell carcinoma treated at 1 cm with 4Gy x 10 every other day

Pre-treatment Post 5th treatment

Treatment planning without mask

HDR versus Electron Beam

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 20 40 60 80 100 120 140

Rela

tive d

ose (

%)

Depth (mm)

HDR Source Electron 6e Electron 18e

HDR vs Electron Plan

HDR – Good dose conformality – Hotter skin dose ~ 145%

Electron – Hot area beyond PTV – Less skin dose ~ 100%

HDR

Electron 6 MeV

Flap attached to the mask

HDR Flap- Skin Keloid: bilateral breast

6MeV Electron: bilateral breast

Photon 6MV using Two Arcs

Electron 6 MeV

Scatter Impact - Dose measurement using Ionization Chamber

Freiburg Flap of 7 x 7 cm

w/ 1 cm bead

1cm

1cm Ir-192 HDR source/cable

In-line

Cross-

line

Flap with 1D Array Source

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 3cm 7cm 12cm

Re

lati

ve d

iffe

ren

ce (

%)

1D array size (cm)

Scatter Impact : 1D Array of Freiburg Flap

Flap with 2D Array Source

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

3x3cm 5x5cm 7x7cm 12x12cm

Re

lati

ve d

iffe

ren

ce (

%)

2D array size (cm^2)

Scatter Impact: 2D Array of Freiburg Flap

Scatter Impact on Flap of 2D Array

0.0

2.0

4.0

6.0

8.0

0 2 4 6 8 10

Pe

rce

nta

ge (

%)

Bolus thickness (cm)

Scatter impact on 12x12 Flap

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0.0 2.0 4.0 6.0 8.0 10.0

Pe

rce

nta

ge (

%)

Ion Chamber at depth (cm)

Scatter Impact vs Depth

with vs without a bolus of 2 to 8 cm An 8-cm bolus used and an ion chamber placed at depth 1.5 to 9 cm

Advantages

Convenient, noninvasive tech for skin lesions

Very good cosmetic output

Short treatment time

Easy to implement

Any site: Head, neck, breast, arms, legs,…

Intraoperative option

Reimbursement