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Techniques for Inguinal/Groin Irradiation

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

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Techniques for Inguinal/Groin Irradiation

  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 12. Modified Segmental Boost
  13. 13. Dosimetric comparison of different techniques
  14. 14. Dosimetric comparison of different techniques
  15. 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. 16. Thank you
  • ssuser1a1aed

    Aug. 15, 2021
  • AasthaShah15

    Jul. 26, 2020

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

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