1. Figure 4 Dosimetric comparison of LDR‑BT versus HDR‑BT
Figure 4 | Dosimetric comparison of LDR‑BT versus HDR‑BT. a | The prostate gland is composed of a peripheral zone, central zone, transitional zone, and an anterior fibromuscular layer. The majority of prostate cancers develop in the peripheral zone. b | Relative dose versus position in tissue. With 3D conformal radiation therapy (3D‑CRT), the maximal point dose is towards the centre of the prostate, near the urethra; the dose decreases gradually toward the periphery of the prostate. Intensity-modulated radiation therapy (IMRT) ensures coverage of the entire prostate gland with dose and minimizes hotspots within the gland. Nonetheless, with IMRT, the prescription dose must be delivered to the planning target volume (PTV), which expands outside of the prostate. With stereotactic body radiation therapy (SBRT), radiotherapy is prescribed to an isodose line to cover the PTV. Furthermore, the hotspot is again in the centre of the prostate toward the urethra; although protocols include a urethra dose constraint101,102, the increased dose toward the centre of the gland with SBRT is sometimes unavoidable74,75. c | Both low-dose-rate brachytherapy (LDR‑BT) and high-dose-rate brachytherapy (HDR‑BT) provide excellent dosimetric coverage of the prostate, particularly because they provide excellent coverage of the peripheral zone with a low dose to the urethra. HDR‑BT might, in some instances, be superior to LDR‑BT because the hotspots assessed by looking at the V150 (volume receiving 150% of the prescribed dose) are typically smaller in a HDR‑BT plan than in a LDR‑BT plan.
Zaorsky, N. G. et al. (2017) The evolution of brachytherapy for prostate cancer
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