hdr planning principles for prostate brachytherapy

UNIVERSITÄTSKLINIKUM Schleswig-Holstein UNIVERSITÄTSKLINIKUM Schleswig-Holstein

Campus Kiel, Clinic of Radiotherapy

HDR Planning Principles

Frank-André Siebert



HDR Planning Principles

Equipment Imaging Dose calculation and planning Workflow Specials



Basics

HDR Afterloading device

Source cable

moveable Implant needle



Basics

Iridium-192 T1/2 = 73.81 days Effective energy = 0.3719 MeV Length: 3.5 - 5 mm Diameter: about 1 mm

Source

HDR: High Dose Rate > 12 Gy/h



Basics

• Parallel implant geometry • Dwell positions (1), discrete • Dwell times (2)

Step size, e.g. 5 mm

Dwell positions with dwell times

⇒ Two variables for treatment planning

⇒ IMBT Intensity Modulated Brachytherapy



5s 5s

5s

5s

5s

5s

5s

5s

5s

4s

4s

2.7s

5s

Dwell times and dwell positions



Basics

Rivard et al. Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys 2004

TG-43 Formalismus

Sk: Air-Kerma-Strength Λ: Dose-Rate constant GL: Geometry function gL: Radial Dose function F: Anisotropy function



The evolution of brachytherapy treatment planning Rivard et al. Med Phys 36(6), 2009

Recommendations of the AAPM/ESTRO/ABS TG-186 (just submitted)



How / when do we perform the treatment planning ?

Preplanning

Intra-operative planning

some days before implantation

in the operation theatre

CT-based postimplant procedure

• Different timing • Different images • Same treatment planning

techniques



Basics

Treatment planning techniques:

1. Forward planning 2. Geometrical optimization 3. Inverse planning (volume optimization) 4. Combinations 1.-3.

How can I persuade the planning computer to calculate a proper plan?



Forward planning

• User biased • Needs experience • Fast



Forward planning, shaping tools

Good tools, but check the dwell times!



Geometrical optimization

Ti

Pref

• Relative dwell times are inversely proportional to the distance to other dwell positions

• Can be normalized to reference point • Very fast • Not based on anatomy



Geometrical optimization

• Easy to use • Not anatomy based



Inverse Planning

Dose constraints for individual organs needed



Inverse planning

Convert dose distribution Di to penalty value wi (dij: dose rate matrix)

8.5 Gy

Ene

rgy

E.g. Dprostate ≥ 8.5Gy

(Summation over all dose points)

(Summation over clinical criteria)



Inverse planning

E

Iterations

Dwell times tj change until global minimum EMin is reached.

EMin



Inverse Planning

No one-click solution

Constraints must be adapted

User-independant solution

Can save time

Check the results

Optimal result

Inverse planning

?


Campus Kiel, Clinic of Radiotherapy B. Lachange et al. IJROBP 2002 (54) 86-100

IPSA better than geometrical optimization


Comparison of Conventional and Inverse Planning


Conventional Planning

(CP)

Inverse Planning

(IP)

p-Value

D90 CTV1 [Gy] 5.62 5.63 0.67

D90 CTV2 [Gy] 11.03 10.89 0.38

V200 CTV1 [%] 29.83 29.87 0.80

V200 CTV2 [%] 5.76 8.14 <0.01

COIN CTV1 0.26 0.30 0.17

COIN CTV2 0.54 0.52 0.86

D2cc Rectum [Gy] 6.04 6.12 0.09

D0.1cc Urethra [Gy] 9.57 9.52 0.34

Dosimetric and quantitative parameters used for analysis. The means of 38 plans considered are shown. Statistically significant is only the difference in V200 for CTV2. The inverse planning still tends to so-called hot spots, although dwell smooth function had been set to 100%.

Wolf et al. Radiother Oncol 103: S134 (Supplement 2).


Campus Kiel, Clinic of Radiotherapy Med Phys 2011 Milickovic et al.

The observed average displacement of needles (1 mm) and of prostate (0.57 mm) is quite small as compared with the average displacement noted in several other reports


Campus Kiel, Clinic of Radiotherapy Med Phys 2011 Milickovic et al.



Kiel method for HDR prostate (boost) : Setup

Preparation of patient: enema the evening before or Glycilax® in the morning before treatment

Patient positioning in lithotomy position (spinal / global anesthesia)

Transrectal ultrasound (TRUS)

Stepper unit

Parallel needle guidance by template



Kiel concept of HDR-Brachytherapy for prostate cancer

Prostate volume < 60 ml

Staging: T1-T3

Distance rectum to prostate > 5 mm

BT: 2 x 15 Gy plus EBRT:

50 Gy (pelvis), 40 Gy (prostate)

BT 15 Gy Finish Start BT 15 Gy

EBRT 20 Gy 2 weeks

EBRT 20 Gy 2 weeks

EBRT of pelvis 10 Gy 1 week

Prostate block in 0° and 180°



Kiel concept of HDR-Brachytherapy for prostate cancer

Hardware: B&K TRUS Profocus 2202 scanner, transducer type 8848

AccuSeed DSTM floor mounted stepper

3.33 mm template

Trocar point steel needles

Philips C-arm

GammaMedPlusTM afterloader



AccuSeed DS stepper with BK 8656 transducer



Biplane TRUS

Transversal image acquisition (2D)

∆z=2.5mm

Longitudinal image acquisition (2D)

∆Θ

3D dataset



at z=1 cm

Transversal image acquisition (2D) Longitudinal image acquisition (2D) and reconstruction



Teamwork is essential

Urologist

Technician, nurse, …

Radiotherapist Physicist

Anesthetist



Kiel: U-shape form of needles Needle positions are set by experience

dist.: 5-10 mm Use information of biopsy report

Needle implantation

Geometry is essential



Ultrasound Acquisition

Definition of reference plane

VitesseTM 2.0



Needle detection in transversal plane



Needle tip detection in longitudinal plane

Stepper with encoder is sending dΘ and dz to planning system

dz

dΘ



Contouring



Needle curvature



Dose calculation:

Source stepping distance: 5 mm

Maximum dwell times: 12 s

Dwell time resolution 1/10 s

Dose prescription

CTV1: 15 Gy (Periphery)

CTV2: 8-9 Gy (Prostate gland)

Urethra dose: < 10 Gy

Rectum dose: < 8 Gy



Dose calculation in BrachyVision

1. Step: 4s dwell time at each position (336s)

1. Step in dose calculation: Set all dwell times constant to 4 s (336 s)



Dose calculation in BrachyVision

2. Step: manual optimization of dwell times (331s)

2. Step in dose calculation: Manual optimization (313 s)



Time schematic for operation room (OR)

Time

0‘ 5‘ 15‘ 30‘ 40‘ 50‘ 51‘ 60‘ 65‘ 70‘ 75‘ 90‘



Transfer to afterloader console



Practical hints

Correct connection of Transfer tubes


Campus Kiel, Clinic of Radiotherapy Check channel numbers !



„Crossed“ needles



Practical hints

Good US image quality necessary Patient must be well prepared Avoid patient movements US balloon without air bubbles Enhanced urethra visibility by foamy gel in catheter

Insert needles with speed and force Tilt needle if possible and necessary



Practical hints

Ultrasound set-up Very important Check proper fixation probe on stepper Few pressure on prostate



Practical hints

Needle tip not clearly visible Compare needle ends to known needle positions

?



Deflating the balloon from 30ml to 0ml


Needle tip reconstruction

Siebert et al. Med Phys 2009 Frequency: 9 MHz

15 dB

-15 dB



Implant needle tip

Tip End of hollow part

First dwell position



Intra-operative HDR planning

Disadvantages Working under pressure of time. Whole team must be present.

Advantages: We know with high accuracy

where the dose will be delivered. Situation of treatment plan is

close to reality. Whole team is present.



Checklist: HDR program (new / improvement)

Literature research, courses (e.g. ESTRO) Patient selection Equipment: hardware, software, imaging Radiation protection Configure TPS Prescription dose, dose constraints Training Dummy run (phantom) Establish QA program …


Thank you for your attention !


hdr planning principles for prostate brachytherapy

Health & Medicine