1. Dose distribution in matter: Multiple and wedge field technique Dr. Dipanjan Majumder MD PGT Dept. of radiotherapy Medical college,kolkata

7. Co- 60 4-6 MV beam thickness  15 cm dose uniform if  20 cm 10 MV or higher energy needed.

10. Unit of intgral dose is gram-rad or kilogram-gray Or simply joule. 1000 rad delivered at midpoint of a 25 cm thick pt. Field size 10 cm d ; SSD = 100 cm.

15. Isocentric technique: Point of intersection of collimator axis and gantry axis - isocenter Stationary beam: Isocenter placed within patient beams directed from different direction. SSD=SAD-d if SSD  SAD isocentric method can be used Advantage: setup accuracy Machine isocentricity dependence rather skin marks

17. Calculations: D iso = D o ×S c ×S p ×TMR Diso=dose rate at isocenter Do=Dmax dose rate for 10,10 field at the SAD Sc=collimator scater factor Sp=phantom scater factor.(for given field size at isocenter) TMR=average TMR over all deapths.

21. HOW TO TREAT SUPERFICIAL TUMOR BY MULTIPLE FIELDS?

26. Separation of adjacent fields

28. Lance & Morgan angled beam technique.

29. Split beam technique:

30. Field separation methods : Geometric: Two adjacent beams are considered.joined at given depth d. L1&L2 be the lengths, SSD1&SSD2 are source to surface distance.then S=S1+S2=½.L1.d/SSD1+½.L2.d/SSD2

31. WHAT THE PROBLEM IN JUCTIONAL REGION: THREE FIELD OVERLAP

33. Calculations: Three-field overlap dS=S1-S2 dS=0 then L1/L2=SSD1/SSD2 If field sizes different SSD s to be adjusted accordingly. If S1+S2 increased by dS three field overlap eliminated but cold spot at mid line. Practically dS* used; dS*=dS.[(d*-d)/d] d* =distance of critical organ from surface ; d= midline distance

34. Dosimetric: Separation of the fields can be determined by optimizing placement of the fields on contour so that composite isodose uniform. Hot and cold spots are acceptable .

36. S=½.L.d/SSD

37. CSI field matching technique:

39. θ coll =arc tan(½.L 1 .1/SSD) Θ couch =arc tan(½.L 2 .1/SAD) L1=length of posterior spinal field. L2=length of lateral cranial field SSD=for spinal field SAD=for cranial field

41. Thank youss Thank you