Inguinal radiotherapy delivery is many a times a complex dosimetric uncertainty and we need to judiciously choose the technique for best patient outcome

1. Inguinal Radiotherapy
Treatment techniques
Dr Ajeet Kumar Gandhi
MD (AIIMS), DNB (Gold Medalist), ECMO
UICCF (MSKCC,USA)
Assistant professor, Radiation oncology
Dr RMLIMS, Lucknow

2. Inguinal Radiotherapy
Treatment techniques
Thunderbird” is used for many
techniques because they all
attempt to produce a pattern of
dose deposition where the shape
of the prescription isodose
volume resembles that of a bird
with outstretched wings, similar
to the symbolic representation of
the huge bird of thunder,
lightening, and rain of Native
North American myth.

3. Radiation techniques
1. Photon through-and-through
2. Photon pelvis with electron tags
3. Photon pelvis with electron boost fields
4. Partial transmission block
5. Segmental boost
6. Modified segmental boost
7. IMRT

4. Radiation techniques 1
I. Photon through-and-through
• Simplest technique to irradiate pelvis
and inguinal nodes
• Opposed AP-PA fields
• Lateral field borders just lateral to
greater trochanter of femur
• Field weightage A:P=3:2
• Ant Field 6 MV; Post Field 15 MV
• Does not require field match lines
• No risk of underdosage or overdosage
• Larger field of treatment
• High dose to OAR

5. Radiation technique 2
II. Photon pelvis with electron tags
• Standard isocentric AP-PA fields with
enface right & left electron inguinal
fields abutting lateral margin of
pelvic field
• Ease of setup
• Relatively lower doses to femoral
heads
• Significantly greater doses along
match lines
• Variability in daily setup
• Inhomogeneity across match line
• Severe skin reactions due to
requirement of high energy electrons

6. Radiation technique 3
III.Photon pelvis with electron boost fields
[Electron thunderbird]
• Isocentric extended large AP pelvic field
to include inguinal and femoral nodes
with narrow PA pelvis field and enface
right and left electron boost fields
(abutting the posterior exit beam )

7. Radiation technique 4
IV.Partial transmission block
• Extended AP pelvic field to include inguinal and femoral nodes with
partial transmission blocks and PA pelvic field
• Open inguinal “winged” and partial transmission pelvic AP field and
standard PA field
• Decreased field numbers
• Simple treatment planning
• Easy setup
• Minimizes dose inhomogeneity
• Slightly higher femoral head dose

8. Radiation technique 4
Partial transmission block
• Posterior field size c and a wing field width w, so
that the size of the anterior extended field is c +
2w.
• In the wing field at groin area, the prescription
depth is denoted d;. The parameter ‘s’ is defined at
the skin level entrance of the anterior central ray;
s measures the extent of the posterior field exiting
into the wing field.
• The parameter t is the central thickness of the
transmission block. From the geometry in Figure
1, it is evident that a triangular portion of the
posterior beam exits into the wing portion of the
anterior field at the patient’s groin.

9. Radiation technique 5
V. Segmental boost [photon thunderbird with skin/Superficial
match]
• Extended AP pelvic field to include inguinal and femoral nodes. PA field
matched at depth of inguinal nodes and right and left anterior inguinal
photon boost fields
• Uses multileaf collimators (MLCs)
• Produces excessively high doses above the field match plane

10. Beam arrangements
• Beam arrangements for two techniques: (a) segmental boost technique and (b)
modified segmental boost technique. RA right anterior; LA left anterior; RAO
right anterior oblique; LAO left anterior oblique.

11. Radiation techniques
VI. Modified segmental boost [photon thunderbird with deep match
]
• Extended AP pelvic field to include inguinal and femoral nodes. PA field
matched at midline and right and left AP inguinal photon boost fields to
match divergence of PA field
• Uniform dose distribution to pelvis and inguinal nodes
• Dose can be prescribed at different depths for right and left inguinal areas
• Ease of simulation, treatment planning, treatment delivery, daily
reproducibility and acceptable femoral head doses

12. Modified Segmental Boost

13. Dosimetric comparison of different
techniques

14. Dosimetric comparison of different techniques

15. Inguinal boost field: Clinical marking
• Inguinal nodes are situated 3-4 cm below ant
skin surface
• use CT scan images for verification of depth
• Patient supine
• Energy –Electrons
• Portals – Single anterior (direct incident )
• Superior border- 2 cm above ing lig
• Inferior border – 5 cm below ing lig
• Lateral borders- up to ASIS
• Medial- pubic tubercle

16. Thank you