It is important to ensure:
- Reproducibility: immobilization and patient comfort
- Homogeneity: leukemic cells anywhere, including skin. Dose variability within the patient +/- 5% excellent and +10% acceptable
- Dose rate :
- has a significant effect on long term toxicity: especially to lung and kidneys. (Dose rate limiting)
- Total Dose: total dose has a significant effect on immunosuppresion and leukemic cell kill
If single dose exceeds 10 Gy, need low dose rate to decrease risk of interstitial pneumonitis
- if high dose rate, need to decrease total dose
- for fractionated TBI, dose rate less important, ex: 1.5 Gy fractions or less, dose rate from 0.05-0.18 Gy/min
Compensators:
- Lung attenuation
- Bolus where it is necessary to compensate for shallower depths
