Transcript No Slide Title

Targeting Issues For Proton Treatments
Of The Prostate
SJ Rosenthal Ph.D., JA Wolfgang Ph.D., Sashi Kollipara
Department of Radiation Oncology
Massachusetts General Hospital, Boston MA
TARGETING ISSUES FOR PROTON TREATMENTS OF THE PROSTATE
S. J. ROSENTHAL, PH.D. AND J.A.WOLFGANG, PH.D.
Massachusetts General Hospital, Boston MA,
USA
E-mail: [email protected]
Prostate cancer is one of the most common malignancies for which high dose radiation offers the promise of
definitive treatment. The last decade has seen conventional treatments become more complex in an attempt
to escalate prostate dose while preserving adjacent tissues. Proton treatments to high doses are possible with
simpler field arrangements but present unique problems for the requisite high precision targeting of the
prostate.
We have begun a series of prostate treatments at the new Northeast Proton Therapy Center at the
Massachusetts General Hospital in Boston. Based on these patients we have studied issues of patient setup, prostate motion, dose modeling, and range compensator design.
In this presentation, we describe our experience using digital radiography to set up prostate patients.
The analysis of set up radiographs is seen as essential in accurate patient alignment and the determination of
prostate motion, indicated by implanted gold seeds. We also have modeled the lateral beams used in our
protocol with a pencil beam model that indicates the range adjustments needed to account for beam scatter
effects of traversing the femoral heads and bony pelvis.
High precision particle beam prostate therapy presents a complex targeting challenge. The range
compensating devices, designed to limit dose distal to the target, need to be aligned to bony anatomy, while
lateral shaping of the beam must move relative to bony anatomy as the prostate moves. We will discuss
ways to accomplish both high precision lateral targeting and acceptable distal dose to critical structures.
History of Proton Prostate Therapy
Issue of Proton Scatter
Issue of Organ Motion
Setting Compensator Smear
Patient/Organ Set Up Technique
Early Patient Study
Range Compensator Strategy
History of Proton Prostate Therapy
1982
-1992
Perineal Proton Boost for Prostate Protocol Up to 75.6 CGE
Used 160 MeV Beam at Harvard Cyclotron Laboratory
Rectal Probe to Immobilize Prostate
Radiographic Set Up
1995
-2000
Perineal Boost Increased to 79CGE At HCL
Boost with Probe Delivered First to Reduce Toxicity
1991
- 2002
LLUMC Proton Only with Lateral Fields
Retained Probe for Alignment
2002
NPTC Study of Proton Treatments of the Prostate
Lateral Fields Plan Optimized with Pencil Beam Calculation
Organ Motion Adjustments - No Probe
Digital Radiography for Rapid Set Up and Seed Tracking
2002
Prostate Dose Escalation Protocol Up to 84.6 CGE
Pencil Beam vs. Broad Beam
Pencil Beam Calculation Needed
to Insure Distal Coverage
Cold Target when Broad
Beam Calculation is
Used
Add 1 cm to Range and Modulation for
Good Coverage with Pencil Beam
Calculation
Broad Beam
Calculation
Pencil Beam
Calculation
Gold Seeds in
Prostate
Prostate Seed Daily Motion First Three Patients
Patient 1
Patient 3
Patient 2
10
10
S-I (mm)
S-I (mm)
S-I (mm)
10
5
5
5
0
0
-10 A-P (mm)-5
0
5
10
-10 A-P (mm) -5
0
0
-5
5
10
-10
A-P (mm) -5
-10
10
5
5
5
0
0
-5
-10
A-P RADIOGRAPH
5
10
-10 L-R (mm)-5
5
10
S-I (mm)
S-I (mm)
S-I (mm)
10
0
10
-10
LATERAL RADIOGRAPH
-10
LATERAL RADIOGRAPH
10
-10 L-R (mm) -5
5
-5
-5
LATERAL RADIOGRAPH
0
0
0
-5
-10
A-P RADIOGRAPH
5
10
-10
L-R (mm) -5
0
-5
-10
A-P RADIOGRAPH
Daily Treatment Set Up
6 Prostate Patients
• Monitored position of prostate by marking
position of seeds relative to original setup
simulation position
• Perform statistical analysis of observed
setup error for six patients
• Take average setup error after N (total
fractions) treatments and apply it to
remaining treatments
Setup Error Analysis
Standard Deviation averaged about 2 mm per patient
Setup error could be as large as 0.5 – 1.0 cm
Increasing the Compensator Smear From 5 to 10 mm
5 mm Smear
10 mm Smear
Actually Improves Femoral Head Sparing and Prostate Coverage
Increasing the Compensator Smear From 5 to 10 mm
Prostate 5 m
Smear
Prostate 10 mm
Smear
Anterior Rectum
10 mm Smear
Anterior Rectum
5 mm Smear
Allows for prostate to bony anatomy mis-registration up to 1 cm
Consequences of Prostate
Motion and Re -Targeting
Create Shifted Prostate Target to Simulate
Movement in Treatment Plan
GTV Draw by MD
GTV with 1cm
Shift Inferior
GTV Draw by MD
GTV with 1cm
Shift Inferior
Target Beam to Shifted Prostate but Retain Aperture
and Compensator designed to Original Target
Minimum Dose To Prostate
As Planned No Shift
Shifted Prostate With Tracking
100
99
95
90
75
50
Maximum Dose To Femoral Heads
As Planned No Shift
With Prostate Tracking
99
95
90
75
50
43
40 % Isodose
40
43 % Isodose
Dose to Femoral Heads and Prostate in Fixed and Shifted Plans
Femoral Heads Fixed Plan
Prostate
Fixed Plan
Shifted Prostate
Shifted Plan
Femoral Heads
Shifted Plan