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Purpose Hydrogel spacers have been suggested to limit rectal radiation dose with improvements in clinical outcomes in patients undergoing external beam radiation treatment for prostate cancer. No studies to date have assessed the utility and dosimetric effect of SpaceOAR (Augmenix, Inc, Waltham, MA), the only Food and Drug Administration–approved hydrogel rectal spacer, for high-dose-rate (HDR) brachytherapy. Methods Eighteen consecutive patients scheduled for HDR brachytherapy in the treatment of prostate cancer underwent transperineal ultrasound-guided placement of 10 cc of SpaceOAR hydrogel following catheter implantation. Treatment plans were generated using an inverse planning simulated annealing algorithm. Rectal dosimetry for these 18 patients was compared with the 36 preceding patients treated with HDR brachytherapy without SpaceOAR. Results Fifty-four plans were analyzed. There was no difference in age, pretreatment prostate-specific antigen, Gleason score, clinical stage, prostate volume, or contoured rectal volume between those who received SpaceOAR and those who did not. Patients who received SpaceOAR hydrogel had significantly lower dose to the rectum as measured by percent of contoured organ at risk (median, V80 Conclusions Transperineal insertion of SpaceOAR hydrogel at the time of HDR brachytherapy is feasible and decreases rectal radiation dose. Further investigation is needed to assess the clinical impact of this dosimetric improvement and potential toxicity reduction.

Purpose New technologies were integrated into a novel treatment platform combining electromagnetically (EM) tracked catheters, a 3D ultrasound (3DUS) imaging device, and a new treatment planning system to provide a real-time prostate high-dose-rate (HDR) brachytherapy treatment system. This work defines workflows for offline CT and online 3DUS planning scenarios and preclinical end-to-end validation of the platform. Methods and Materials The platform is composed of an EM-tracked stylet, a EM-tracked 3DUS probe, and an EM-tracked template guide, all used with the NDI Aurora field generator (NDI, Ontario, Canada). The treatment planning system performs continuous position and angular readings from all three EM sensors into a streamlined environment that allows for (1) contouring; (2) planning; (3) catheter insertion guidance and reconstruction; (4) QA of catheter path and tip position; and (5) exporting to an afterloader. Data were gathered on the times required for the various key steps of the 3DUS-based workflow. Results The complete 3DUS-based workflow on 16-catheter implant phantoms took approximately 15 min. This time is expected to increase for actual patients. Plan generation is fast (7.6 ± 2.5s) and the initial catheter reconstruction with updated dose distribution is obtained at no (time) cost as part of the insertion process. Subsequent catheter reconstruction takes on average 10.5 ± 3.1s per catheter, representing less than 3 min for a 16-catheter implant. Conclusions This preclinical study suggests that EM technology could help to significantly streamline real-time US-based high-dose-rate prostate brachytherapy.

Purpose High-dose-rate (HDR) brachytherapy as monotherapy is an effective treatment option for localized prostate cancer, but experience with single-fraction brachytherapy is limited by studies with small sample size. We report a large single-institution experience with single-fraction HDR brachytherapy as monotherapy for early-stage prostate cancer. Methods and Materials Retrospective chart review was performed for men treated with HDR brachytherapy as monotherapy for low- to intermediate-risk prostate cancer. Competing risk analyses were performed to estimate subdistribution hazard ratio and cumulative incidence of biochemical recurrence (BCR) and prostate cancer–specific mortality. Results We identified 124 men with a median followup of 2.2 years (interquartile range 25th to 75th percentile: 1.8–3). Overall, 21.0% of patients (n = 26) were low risk, 44.4% (n = 55) were favorable intermediate risk, and 34.7% (n = 43) were unfavorable intermediate risk. At 2 years, the cumulative incidence of BCR was 3.5%: 0% for low risk, 4.0% for favorable intermediate risk patients, and 4.5% for unfavorable intermediate risk patients. In total, 12 BCRs were observed (9.7%) and approximately half occurred after median followup of 2.2 years. Compared with low-risk and favorable intermediate-risk disease, unfavorable intermediate-risk disease was significantly associated with BCR (subdistribution hazard ratio: 3.6, 95% CI: 1.1 to 11.1, p = 0.03). Prostate cancer–specific mortality was 0%. No patient experienced Grade 3 or higher acute or late genitourinary toxicity. Conclusions Single-fraction brachytherapy for early-stage prostate cancer was safe with promising short-term disease control rates, especially for low-risk patients. Longer term followup is needed as we observed an overall BCR rate of 9.7%.

Urethral dose is related to severity of genitourinary toxicity in patients treated with brachytherapy for prostate cancer. This work describes a dose planning method that uses inverse planning to create a low-dose tunnel around the urethra and presents a class solution to achieve this additional dose sparing of the urethra.Fifteen patients on the Radiation Therapy Oncology Group (RTOG) 0321 protocol were treated for prostate cancer with a high-dose-rate brachytherapy dose boost to an external beam radiation treatment regimen. All were treated with 9.5Gy for each of the two fractions after 45Gy of the external beam radiation. The inverse-planning algorithm, inverse planning simulated annealing (IPSA), was used to create both the standard RTOG protocol (SRP) plan for treatment and the a posteriori urethra dose sparing (UDS) plan consisting of a dose tunnel along the urethra. Both plans maintained the protocol parameters: prostate V(100) (volume receiving 100% of prescribed dose)90% and bladder and rectum V(75)1 cm(3). In the SRP plans, the urethra surface was optimized to receive125% of the prescription dose and in the UDS plans100%. Dose-volume histograms for the clinical treatment volume, bladder, rectum, penile bulb, and urethra for both plans are compared using a paired sample t test with significance claimed for probability values0.05.UDS planning reduced the urethra V(100) from 88% to 58% on average (p0.01) and the V(125) from 3.3% to 0.2% (p0.01). Bladder and rectum V(75) were maintained at1 cm(3) and not significantly different between plans. Prostate coverage was maintained per protocol at V(100)90%, with mean for the SRP V(100)=93% versus UDS plan V(100)=90%. Prostate D(90) for SRP was 104% versus UDS plan D(90)=101%. For all patients, the UDS achieved a dose tunnel surrounding the length of the intraprostatic urethra. The class solution for generating UDS is presented.A urethral sparing-focused planning solution using IPSA reduces mean urethral dose by 34%, as compared with IPSA-generated plans based on the RTOG 0321 protocol. This is done while maintaining prostate coverage and critical structure dose. This technique can be applied to all patients in whom urethra toxicity is of particular concern.

Purpose Recent studies have identified that among different available radionuclides, the dose characteristics and shielding properties of ytterbium-169 ( 169 Yb) and thulium-170 ( 170 Tm) may suit high–dose rate (HDR) brachytherapy needs. The purpose of this work was to compare clinically optimized dose distributions using proposed 169 Yb and 170 Tm HDR sources with the clinical dose distribution from a standard microSelectron V2 HDR iridium-192 ( 192 Ir) brachytherapy source (Nucletron B.V., Veenendaal, The Netherlands). Methods and materials CT-based treatment plans of 10 patients having prostate volumes ranging from 17 to 92 cm 3 were studied retrospectively. Clinical treatment of these patients involved 16 catheters and a microSelectron V2 HDR 192 Ir source. All dose plans were generated with inverse planning simulated annealing optimization algorithm. Dose objectives used for the 192 Ir radionuclide source were used for the other two radionuclides. The dose objective parameters were adjusted to obtain the same clinical target (prostate) volume coverage as the original 192 Ir radionuclide plan. A complete set of dosimetric indices was used to compare the plans from different radionuclides. A pairwise statistical analysis was also performed. Results and conclusions All the dose distributions optimized with specific 192 Ir, 169 Yb, and 170 Tm sources satisfied the standard clinical criteria for HDR prostate implants, such as those for the Radiation Therapy Oncology Group clinical trial 0321, for combined HDR and external beam treatment for prostate adenocarcinoma. For equivalent clinical target volume dose coverage, the specific 169 Yb and 170 Tm sources resulted in a statistically significant dose reduction to organs at risk compared with microSelectron V2 HDR 192 Ir source. This study indicates that a 170 Tm or 169 Yb radionuclide source may be an alternative to the 192 Ir radionuclide sources in HDR brachytherapy.

Purpose: To evaluate the use of customized guides for inserting optimized, non-parallel arrangements of high-dose-rate (HDR) brachytherapy needles into prostate gelatin phantoms. Materials and Methods: Four prostate gelatin phantoms were constructed with prostate, urethra, bladder, rectum, penile bulb, and pubic arch anatomical structures. The target volume was the prostate, and the other structures were organs at risk (OAR). The anatomical structures were digitized, and a non-parallel needle arrangement was optimized for each phantom using Needle Planning by Integer Program (NPIP). The optimized needle arrangements contained 13-15 needles, which is less than the standard number currently used in our clinic. None of the optimized needles punctured any non-prostate structures. Inverse Planning by Integer Program (IPIP) was used to compute a dose plan for each optimized needle arrangement that conformed to the guidelines set in the Radiation Therapy Oncology Group (RTOG) 0321 dosimetric protocol. Customized needle guides were digitally created for each phantom to implant the corresponding optimized needle arrangement. The needle guides were 3D-printed in ABS plastic using a uPrint Plus 3D printer (StrataSys). The needle guides were mechanically registered to the phantoms. The needles were inserted into each phantom by a researcher without any clinical brachytherapy experience and without the assistance of trans-rectal ultrasound (TRUS) guidance. The phantoms and implanted needle arrangements were digitized, and another dose plan was computed for each implant. Compliance with the RTOG 0321 protocol, puncturing of OAR, and placement error were evaluated. Results: Three of the needle arrangements were implanted without puncturing any OAR. Due to placement error, one implanted needle arrangement punctured the penile bulb and urethra. We considered this case a failure, and we did not post-process it further. The successfully implanted needle arrangements met all the dose requirements in the RTOG 0321 protocol. The RMS placement error between the dwell positions in the planned and implanted needle arrangements was 3.6 mm, 4.5 mm, and 2.3 mm for the three cases. The majority of the error was along the needle insertion direction (i.e. the z-direction), which is most likely because templates do not restrict motion along this direction, and therefore is where error is the most user-dependent, or because the anatomy was digitized from 3 mm thick CT slices taken in the zdirection, and therefore registration in this direction is the most uncertain. Conclusions: Customized needle guides are a promising method for inserting optimized, non-parallel, brachytherapy needle arrangements. Although NPIP, IPIP, and 3D printers were used to construct the guides in this study, other planning and construction methods could be used without changing our fundamental workflow structure. However, the templatepatient registration and needle insertion workflow must still be improved to reduce placement error. This includes incorporating real-time TRUS guidance to monitor progress and avoid puncturing OAR, which we propose as future work.

Post-implant (PI) V100 & D90 were calculated for each sector and compared with whole prostate as well as intraoperative (IO) parameters. Optimal values were O90% for D90 & O85% for V100. Summary statistics (mean, SD, median, IQR, range) were reported for V100 and D90. The Wilcoxon Rank Sum test was used to compare the percentage drop from intra-op to post-implant, and to compare differences between individual sectors/groups of sectors and the whole prostate. Spearman’s rank correlation was used to examine the association between intra-op and post-implant values. Results: 71 seed implants were performed, mean PI prostate V100 and D90 was 95.5% and 117.1%. 70 had optimal D90 and V100. Only 1 sector (anterior base) had suboptimal PI V100 and D90 (70.3% and 85.9%) which were significantly and clinically lower than corresponding IO values (p! 0.001). This affected PI V100 for the prostate base (88%) and anterior quadrant (86.9%), but not D90 (108% & 106%). Inherent characteristics with the modified peripheral loading approach became evident as the mean IO D90 for the apical sectors (126%) was consistently lower than the base (131%) and midgland (132%), and lateral sectors (134%) had higher D90 than the anterior (123%) and posterior (126%) sectors. There was consistent decrease in the D90 from the IO to the PI plan in the anterior sectors (123% vs 106%, p! 0.001) and base sectors (132% vs 108%, p! 0.001) while an increase was noted in the apical sectors (126% vs 133%, p ! 0.001) as well as posterior sectors (126% vs 131%, p 5 0.006). The lateral sectors and mid sectors had minimal change from the IO plan. Conclusions:Overall dosimetry results to date are very encouraging with 11/12 sectors showing optimal dosimetry in most patients. Sector analysis provides insight into the planning aspects which may have impact in the PI dosimetry and provides useful data for further refinement in practice, further study correlating sector analysis with clinical outcomes is required.