5.Plan Evaluation, DVH Analysis, TPS.pptx

Radiotherapy Plan evaluation, importance of Treatment Planning System, Dose Volume Histogram analysis, types

1. Plan Evaluation, DVH Analysis

2. Treatment Planning Process Step 1: Patient positioning and immobilization Step 2: Image acquisition and input Step 3: Anatomy definition (Define contours for target volume & OAR) Step 4: Dose prescription Step 5: Beam technique Step 6: Dose calculations Step 7: Plan evaluation Step 8: Plan review and documentation Step 9: Plan implementation and verification

3. NEED FOR PLAN EVALUATION SYSTEM Tumor coverage by the prescribed dose Sparing of critical structure Dose homogeneity/ planned inhomogeneity in target volume Various dose parameters

4. Acceptable Criterion Homogenous dose distribution through out the PTV is desirable. At least 95% of tumor volume should receive 95% of Prescribed Dose Inhomogeneity should be within 95 % and 107 % of the prescription dose As Low Dose possible to OAR

5. Evaluation Tools Isodose Curves Dose Statistics

6. Isodose Curves

7. Isodose Curves Isosurface on 3D Display Can be used to assess target coverage, they do not convey a sense of distance between the isosurface and the anatomical volumes

8. Dose Statistics Provide quantitative information on the volume of the target or critical structure, and on the dose received by that volume . Minimum dose to the volume Maximum dose to the volume Mean dose to the volume Dose received by at least 95% of the volume Volume irradiated to at least 95% of the prescribed dose.

9. it summarizes entire 3D dose distribution into a graphical 2D format for each anatomic structure of interest and also provides quantitative information with regard to how much dose is absorbed in how much volume Volume under consideration is divided into a 3-D grid of volume elements ( voxels ) Volume's dose distribution is divided into dose bins , and voxels are grouped according to dose bin without regard to anatomic location. Quantitative evaluation - DVH

10. Types of DVH Differential (or Direct) DVH Cumulative (or Integral) DVH

11. Differential DVH Histogram of frequency with which each dose occurs. Rather than displaying the frequency, usually displayed in the form of “per cent volume of total volume” on the ordinate against the dose on the abscissa.

12. Differential DVH The ideal DVH for a target volume would be a single column indicating that 100% of the volume receives the prescribed dose. For a critical structure, the DVH may contain several peaks indicating that different parts of the organ receive different doses.

13. Cumulative DVH Plot of entire volume of anatomical structure specified dose or higher dose. The computer calculates the volume of the target (or critical structure) that receives at least the given dose and plots this volume (or percentage volume) versus dose. All cumulative DVH plots start at 100% of the volume for 0 Gy, since all of the volume receives at least no dose.

14. Differential or Cumulative? “How much of the target is covered by the 95% isodose line?” The answer cannot be extracted directly from the direct DVH, since it would be necessary to determine the area under the curve for all dose levels above 95% of the prescription dose. For this reason, cumulative DVH displays are more popular.

15. Maximum dose ( Dmax ): Maximum dose to the PTV and to the tissues outside the PTV and to OAR should be identified. For smaller organs like eye, optic nerve and larynx smaller diameter should be considered. Minimum dose ( Dmin ) It is the smallest dose in the defined clinical volume. There is no recommendation for volume limit for reporting minimum dose.

16. Disadvantages Exact location of dose in-homogeneity not displayed. Dose is only a surrogate of biological consequences. Conclusion : Plan evaluation requires not only DVH analysis but it also include dose distribution analysis.

17. Evaluation Tools: Summary Qualitative methods Isodose Curves Quantitative methods Dose Statistics

18. OAR

19. Plan Evaluation: Example Plan1 Plan2 95%

20. Plan Evaluation: Example Plan1 Plan2 95%

21. Plan Evaluation: Example Plan1 Plan2 PTV

22. Plan Evaluation: Example Plan1 Plan2 Eye Lt

23. Plan Evaluation: Example Plan1 Plan2 Eye Rt

24. Plan Evaluation: Example Plan1 Plan2 Spinal Cord