First Experiences with Dynamic
Interactive Realtime Dose Verification
during Transperineal Permanent Seedimplantation (TPSI) of Patients
with “Low Risk” Prostate Cancer in an Outpatient Setting
Block,
T.1; Zimmermann, F.2; Czempiel, H.1
1Urologische Praxis und Medizinphysik Vaterstetten,
2Klinik für Strahlentherapie und Radioonkologie, Technische Universität
München
Introduction:
This study evaluates the recently introduced dynamic interactive realtime
verification of dose distribution during TPSI of patients with “low
risk” prostate cancer (PCa cT1-2 Gleason Score 2-6 iPSA <10
ng/ml) in order to analyse if realtime calculation can improve postimplant
dose distribution. It is well known from other series that D90 >140
Gy results in a high percentage of patients with long time PSA recurrence
free survival.
Patients/Method:
62 patients (66.4 ± 7.1 years) were treated with TPSI (125-I-RAPID
Strands® 0.552-0.737 mCi) because of low risk prostate cancer according
to the recommendations of ABS, ESTRO and EORTC. Planning procedures
were performed as: Online-Planning (prescription dose 145 Gy, D90 >180
Gy, V100 >98%, minimal dose at the surface of the prostate >120
Gy, D1 and D30 urethra <230 Gy and <215 Gy respectively, D10 anterior
rectal wall ?145 Gy, dosimetry software: VariSeed 7.0 (n=45) and PSID
3.5 (n=17)). During realtime dose verification the TRUS-shown position
image of each needle was transferred immediately into the planning system
before releasing the seeds.
Interactive dynamic dose verification
The
needle position could be corrected according to the virtually overlapped
position. The dose distribution was recalculated before the next needle
with seeds were implanted. Consecutively the critical dose criteria
were calculated real time. Each patient underwent a CT based postplanning
procedure 30 days after TPSI.
Virtual
Overlapping of Implantation Needle and Seeds with immediate Dose Calculation
Results:
Conclusion:
Dynamic interactive realtime dose verification allows excellent quality
control during the complete TPSI. If necessary, additional seeds can
be added in order to improve the dose distribution. In the CT postplanning
procedure this technique lead to D90 and V100 of >150 Gy and >90%
respectively.
