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FROM 2D TO 3D: ONLY BENEFITS OR ALSO PITFALS? Primo Strojan - PowerPoint PPT Presentation

Sep 12, 2022 •133 likes •426 views

FROM 2D TO 3D: ONLY BENEFITS OR ALSO PITFALS? Primo Strojan Conformity: High-dose volume is shaped to closely conform to the designed target volumes & Dose to critical normal tissues is minimal (as much as possible) 2D RT:

  1. FROM 2D TO 3D: ONLY BENEFITS OR ALSO PITFALS? Primož Strojan

  2. Conformity: High-dose volume is shaped to closely “conform” to the designed target volumes & Dose to critical normal tissues is minimal (as much as possible)

  3. “2D” RT: Targets defined & dose calculated in 1. 2-dimensions Simple beam arrangements 2. Beams are not shaped or simple 3. beam-shaping devices are used - pre-manufactured blocks - individual shielding blocks Forward treatment planning 4. (trial-and-error process: field/beam weights are modified iteratively & manually)

  4. 2-D PLANNING

  6. Computer based planning, calculation & visiualization distribution of dose

  7. Missing tissue compensators Pre-manufactured (standard) blocks Custom-made alloy blocks

  8. “Conformal” RT: Targets defined & dose calculated in 3- 1. dimensions Multiple beam directions 2. Beams are shaped (or intensity 3. modulated) Forward (or inverse*) treatment planning 4. *Computer-assisted optimization: definition of objectives and constrains determination of optimal beam arrangement & weighting

  9. 2-D PLANNING 3-D PLANNING

  10. Anatomical data acquisitation

  14. 2D-RT 3D-RT IMRT 5 1 2 3 4

  15. TARGET(S) NORMAL TISSUES more conformal dose as low dose as distribution possible TU NT CONFORMITY

  16. TARGET(S) NORMAL TISSUES more conformal dose as low dose as distribution possible TU NT CONFORMITY STEEP DOSE GRADIENTS

  17. “Conformal” RT: Targets defined / dose calculated in 3- 1. dimensions Multiple beam directions 2. Beams are shaped (or intensity 3. modulated) Forward (or inverse) treatment planning 4. PROBLEMS ?!

  18. 1. Increased risk of a marginal miss Tumor is not eradicated • Accurat identification of target(s) and OAR • Movements patient target beams

  19. Identification of target and AORs

  20. CT PET CT + PET

  21. Movements ICRU Report 62, 1999

  22. TARGET(S) NORMAL TISSUES more conformal as low dose as distribution possible TU TU NT NT CONFORMITY + STEEP DOSE GRADIENTS

  23. Tumor reduction & weight loss Mayer JL. Karger: Basel, 2007. p.8.

  24. 2. Less homogenous dose distribution • Radiobiology – “double – trouble” effect late-responding tissues, large treatment volumes • Interpretation & verification of resulted dose distribution ICRU reference point, min, max, mean dose Dose distribution Dose Volume Histograms – DVHs to predict NTCP to assess quality of treatment plan

  25. DVHs = 2D presentation of 3D dose distribution (what % of volume is raised to a defined dose)

  26. DVHs • quantitative description of dose distribution - no information on spatia distribution - all regions of an organ are eaqually important - as good as is the anatomic information provided how accurately routine imaging reflect underlying anatomy marked inter-physician differences in image segmentation - interactions between organs are not considered - no information on functional status of nonirradiated organ volume

  27. 3. Larger total body dose Risk of radiation-induced malignancies • increased beam-on time ( MUs 2-3x) leakage through the collimator • more fields volume of NT exposed to lower RT doses 1% 1.75% for IMRT (Hall E & Wuu CS IJROBP 2003; Hall E. IJROBP, 2006)

  28. 4. Increase in costs More labour intensive and expensive

  29. CONCLUSIONS “3D”: Targets defined in 3-dimensions using CT More complex beam arrangements and shaping More conformal dose distribution Steep dose gradients Identification of target(s) Patient immobilization and setup - risk of marginal miss - homogenous dose distribution - total body dose - in costs

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