The document discusses standards for precision in radiation oncology, including definitions of target volumes and dose reporting levels according to International Commission on Radiation Units and Measurements (ICRU) reports. It notes unresolved issues for 3D conformal radiation therapy and intensity-modulated radiation therapy, such as margins between gross tumor and clinical target volumes. The document recommends that a new ICRU report is needed to address these modern radiotherapy techniques and provide common guidelines.

1. Precision in Radiation Oncology: what are the standards and how could it apply to IORT Vincent GREGOIRE, MD, PhD, hon. FRCP Radiation Oncology Dept., & Center for Molecular Imaging and Experimental Radiotherapy, Université Catholique de Louvain, St-Luc University Hospital, Brussels, Belgium

2. Bataini et al, 1982 , 4 5 5 5 6 5 7 5 8 5 9 5 T o t a l d o s e ( G y ) 0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 Tumor control (%) Dose-response curve for neck nodes ≤ 3 cm Tumor Control Probability (TCP)

3.  Human  Monkey Baumann et al., Strahlenther Onkol 170: 131-139, 1994 Normal Tissue Control Probability (NTCP)

4. Target J. John, 1974

6. Target volumes in EBRT Before Rx-CH 46 Gy (Rx-CH) Right piriform sinus (ICDO-10: C12.9) SCC grade 2 TNM 6 th ed: T4N0M0 Fiberoptic examination CT MRI T2 FS FDG-PET

8. Clinical Target Volume (CTV) Target volumes in EBRT

9. Mesorectal subsite Lymph node regions Posterior PS Selection and delineation of Target Volume Haustermans et al., 2005

10. The Planning Target Volume is a geometrical concept, introduced for treatment planning and evaluation. It is the recommended tool to shape dose distributions that ensure with a clinically acceptable probability that an adequate dose will actually be delivered to all parts of the CTV… Planning Target Volume (PTV) ICRU IMRT report Target volumes in EBRT

11. CTV 2 = GTV 2 ICRU IMRT report Target volumes in EBRT PTV 1 : dose 1 CTV 1 GTV 1 (pre-RxTh CT+ iv contrast) PTV 2 : dose 2 GTV 2 (FDG-PET @ 46 Gy)

12. Target volumes in IORT + EBRT CTV 1 = “tumor bed” PTV 1 = PTV 1 : dose 1 IORT PTV 2 : dose 2 CTV 2 (clinical knowledge) EBRT

16. The Human Condition. R. Magritte, 1935

19. ICRU Reference Point Not A “Typical Point” for IMRT Segments 4-7, 9-13 13 segment IM Field From Jatinder Palta, University of Florida Absorbed dose in EBRT Segment 1 Segment 2 Segment 3 Segment 8

22. Homogeneity and Conformity Low Homogenenity – High Conformity High Homogeneity – Low Conformity Dose Dose Dose Dose Vol Vol Vol Vol Absorbed dose in EBRT ICRU IMRT report Vol Dose Vol Dose Vol Dose Vol Dose High Homogeneity – High Conformity Low Homogeneity – Low Conformity

29. CTV to PTV margin recipe Target volumes in Radiation Oncology Van Herk, 2003

30. Effect Dose Uncomplicated tumor control: Therapeutic Ratio Unacceptable normal tissue damage Tumour control Uncomplicated tumour control

31. ICRU committee on volume and dose specification for prescribing, reporting and recording special techniques in external photon beam therapy: conformal and IMRT. Vincent GREGOIRE, M.D., Ph.D. and Thomas R. MACKIE, Ph.D.* Radiation Oncology Dept., & Center for Molecular Imaging and Experimental Radiotherapy, Université Catholique de Louvain, St-Luc University Hospital, Brussels, Belgium and * Dept. of Medical Physics, University of Wisconsin, Madison, WI, USA.

32. The stone of Rosette (Champolion)

36. Organ At Risk (OAR) PTV Rectal wall Rectum ICRU IMRT report Normal tissues in EBRT

37. Parotid sparing with IMRT ICRU IMRT report Normal tissues in EBRT Superficial lobe Superficial and deep lobe

41. Dose-Volume Reporting D 95 D 2 0 10 20 30 40 50 60 70 80 90 100 50 55 60 65 70 Dose (Gy) Percent Volume D98=60Gy D50=60Gy D v with v≠50 may require a change in prescription value D 98 D 50 is close to ICRU Reference Dose at a Point Absorbed dose in EBRT

45. ICRU committee for 3D-CRT and IMRT ICRU IMRT report GTV 1 CTV 1 PTV 1 CTV 2 PTV 2 CTV 3 PTV 3 Microscopic Extension Regional Involvement

46. Example 1 ICRU IMRT report Target volumes in EBRT PTV 1 : dose 1 CTV 1 PTV 2 : dose 2 GTV 1 (pre-RxTh CT+ iv contrast) CTV 2 = GTV 1

47. Dose-Volume Reporting D 50 best corresponds to the level at D ICRU-point Absorbed dose in EBRT 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Dose (Gy) Percent Volume Differential Cumulative D 95 D 98 D 50 D 2 D 50 = 60 Gy