1. Above and below the diaphragm
Hodgkin’s Lymphoma
Treatment Planning
Above and below the diaphragm
Why is it so complex?
Patty Sponseller, CMD

3. It’s just AP/PA right?
Mantle
Para-aortics

4. Although AP/PA a lot going on here!

5. Radiation Fields Mantle covers chin and just below diaphragm
Laterally “flash” skin to include both axilla
Involved field radiation
Inverted Y covers paraaortic, pelvic and inguinal lymph nodes

6. Mantle RT Radiation to a large area of the neck, Chest and axilla
Cover all the main lymph node areas above the diaphragm
Shielding to part of the lungs, heart and shoulders
Mantle is derived from the name of a garment much like a cloak in medieval times

7. Variation with the DD throughout the fields
PATIENT THICKNESS CHANGES
PATIENT CONTOUR IRREGULARITIES
DIFFERENT HETEROGENITIES
MISSING TISSUE
BEAM CHARACTERISTICS
GEOMETRIC MATCH

8. Basic dose distribution data is obtained under standard conditions
Homogenous density in a water phantom
Perpendicular beam incidence
Flat surface
Why is this?

9. During Treatment
The beam may be obliquely incident with respect to the surface
Surface may be curved or irregular in shape
Under these conditions, standard DD are not applicable without corrections

10. Corrected in Pinnacle

11. Beam data includes profile scans across the beam, depth doses and output factors (ratio of the dose measured for a specific F S standard to a 10 cm2) measured for every machine energy and many square field sizes. This measured data is used to determine the many, many free parameters in the Pinnacle model for EACH linear accelerator.
In Pinnacle we are then modeling the energy that comes from the head of the Tx unit including all the scatter within the head that affects the energy spectrum.

12. Modeling – Convolution Algorithm
An integral that calculates at every point within the dose grid. That dose calculation includes the attenuation of the beam as it travels through tissue times the energy fluence of energy spectrum times the energy kernel.

13. Convolution Algorithm

14. Want to know more?

15. Imaging Conventional X rays Ultrasound CT scan PET (FDG)
Ability to screen for distant Dz
Uptake in nodal areas that
look normal on CT
False positives
Not good at detecting
marrow involvelment

16. Simulation for Adjacent Fields
Maintain patient position when all fields are treated
Proper immobilization for entire torso
Clam shell used if pelvis RT for males
Consider oophoropexy for females
Supine position with arms akimbo
Immobilization indexed to treatment couch

17. Matching new fields with previously TX
Tattoo documentation cannot be overemphasized
Compare prior DRR’s and portal images
Examine the chart carefully for possible changes during prior RT
Reproduce prior RT with new scan to ensure which segment of spinal cord was irradiated

18. Goal is a Homogenous Dose Distribution Adjacent fields have the same divergence

19. Adjacent Fields Adjacent fields do not match divergence
Dose discrepancies over spinal cord

20. Inverted Y
May need to split up inverted Y into 2 fields for adult or tall adolescent
Otherwise-

21. Paraortics/Spleen

22. You have this problem
The larger inverted Y does not match the divergence of the mantle field
Hot and cold spots

23. Blocking
Spleen/Paraortic Fields or Inverted Y usually can accommodate MLC
Mantle Fields typically are a combination of MLC and Cerrobend blocking
Lung Block shapes are usually too complex for MLC
May consider a larynx block on AP field

24. Combination of MLC’s and custom blocks

25. Portal Imaging
See the
combination
here

26. Field Blocks
Blocks are shaped or tapered to match the divergence of the beam
This minimizes block transmission pneumbra (partial transmission of the beam at the edges of the block)
Do we do this for all our photon blocking at UWMC?

27. Custom Blocking Lipowitz Metal Cerrobend (brand name)
Approx 83% of Pb density
Low melting point
Materials making up Cerrobend are
Bismuth
Lead
Tim
Cadmium

28. How thick are the blocks?
Half Value layer
The thickness of the material required to attenuate the intensity of the beam to half its original value
How many HVL’s in MV photon blocking?

29. Original Value
100%
50%
25%
12.5%
6.25%
3.12%
1.56%
5 HVL’s

30. How thick are the blocks?
5 HVL’s of Cerrobend needed
What is the HVL thickness of Cerrobend?
1 HVL of Cerrobend is 1.5 cm thick
In the megavoltage range of photons the most common used thickness is 7.5 cm
Which is equivalent to about 6 cm of pure lead

31. Mantle Fields Dose Distribution is calculated with cerrobend blocking
Pinnacle will not allow Step N Shoot with custom blocking
Here we use a “Poor Man” Technique
Treat more than one field, close jaws and adjust weighting

32. Other Techniques Use wedge on AP field if FS allows Compensators
Decimal

33. Para/Spleen or Inverted Y
Usually MLC’s can be used for blocking on all fields
May require Step N shoot for hot spots

34. Point under a block
17 cm
4.5 cm
6.25 cm
17 cm

35. Fields 17 X 17 cm = 17 cm 2 4.5 x 17 cm= 7 cm 2 6.25 x 17 cm= 9 cm 2
Calculate the dose under a block at 10 cm depth

36. Which blocks are bettter?