Dose selection

Numerous studies have confirmed D90 (the minimum dose received by 90% of the prostate volume) and V100 (percentage of the prostate volume receiving 100% of the prescribed dose) are correlated with outcome [54-56].

Prescription doses for I-125 or palladium-103 (103Pd) are typically 140 to 160 Gy or 110 to 130 Gy, respectively. In practice, many brachytherapists plan a dose higher than the above mentioned doses to compensate for edema, seed misplacement, and so on. Merrick et al. [57] examined variability in permanent prostate brachytherapy preimplant dosimetry among eight experienced brachytherapy teams. A range of D90 values from 112% to 151% of the prescription dose was planned. Several investigations suggest that an acceptable dose range for postimplant D90 for I-125 may be 130 to 180 Gy as long as normal structures are not overdosed. Zelefsky et al. [58] reported that D90 < 130 Gy was associated with and increased risk of failure. Meanwhile, Gomez-Iturriaga Pina et al. [59] reported that D90 from 180 Gy to 200 Gy was associated with excellent biochemical disease-free survival and acceptable toxicity.

When combined EBRT and brachytherapy, a wide variety of implant and beam radiation dose combinations are used. Implant prescription doses area generally dropped to approximately 70% to 80% of monotherapy doses, ranging from 110 to 120 Gy with I-125 and 90 to 100 Gy with Pd-103. External beam doses of 40 to 50 Gy area typically used. No studies have investigated either the sequencing of EBRT and brachytherapy, or the time interval between the two.

A wide variety of seed activities, seed numbers, or total activities have been used because of no clinical evidence of any effect outcome. Seed activities typically vary from 0.3 to 0.6 mCi for I-125 and 1.2 to 2.2 mCi for Pd-103.

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