Real-time dose-rate monitoring with gynecologic brachytherapy: Results of an initial clinical trial

PurposeA nanoscintillator-based fiber-optic dosimeter (nanoFOD) was developed to measure real-time dose rate during high-dose-rate (HDR) brachytherapy. A trial was designed to prospectively test clinical feasibility in gynecologic implants.Methods and MaterialsA clinical trial enrolled women undergoing vaginal cylinder HDR brachytherapy. The nanoFOD was fixed to the cylinder alongside two thermoluminescent dosimeters (TLDs). Treatment was delivered and real-time dose rates captured by the nanoFOD. The nanoFOD and TLD positions were identified in CT images and used to extract the treatment planning system (TPS) calculated dose. The nanoFOD and TLD cumulative doses were compared with the TPS.ResultsNine women were enrolled for 30 fractions, and real-time data were available in 27 treatments. The median ratio of nanoFOD/TPS dose was 1.00 (IQR 0.94–1.02), with a TLD/TPS ratio of 1.01 (IQR 0.98–1.04). Of the nanoFOD dose measurements, 63% were within 5% of the TPS, 26% between 5 and 10% of the TPS, and the remaining 11% between 10 and 20% of the TPS dose. Of the TLD measurements, 70% were within 5% of the TPS, 22% between 5 and 10% of the TPS, and 7% between 10 and 20% of the TPS dose.ConclusionsReal-time dose-rate measurements during HDR brachytherapy were feasible using the nanoFOD and cumulative dose per fraction showed reasonable agreement to TLD and TPS doses. Additional studies to determine dose thresholds that would yield a low false alarm rate and ongoing device development efforts to improve localization of the scintillator in CT images are needed before this detector should be used to inform clinical decisions.     

Time-driven activity-based cost comparison of prostate cancer brachytherapy and intensity-modulated radiation therapy

PurposeTo evaluate the delivery cost of frequently used radiotherapy options offered to patients with intermediate- to high-risk prostate cancer using time-driven activity-based costing and compare the results with Medicare reimbursement and relative value units (RVUs).Methods and MaterialsProcess maps were created to represent each step of prostate radiotherapy treatment at our institution. Salary data, equipment purchase costs, and consumable costs were factored into the cost analysis. The capacity cost rate was determined for each resource and calculated for each treatment option from initial consultation to its completion. Treatment options included low-dose-rate brachytherapy (LDR-BT), combined high-dose-rate brachytherapy single fraction boost with 25-fraction intensity-modulated radiotherapy (HDR-BT-IMRT), moderately hypofractionated 28-fraction IMRT, conventionally fractionated 39-fraction IMRT, and conventionally fractionated (2 Gy/fraction) 23-fraction pelvis irradiation with 16-fraction prostate boost.ResultsThe total cost to deliver LDR-BT, HDR-BT-IMRT, moderately hypofractionated 28-fraction IMRT, conventionally fractionated 39-fraction IMRT, conventionally fractionated 39-fraction IMRT, and conventionally fractionated (2 Gy/fraction) 23-fraction pelvis irradiation with 16-fraction prostate boost was $2719, $6517, $4173, $5507, and $5663, respectively. Total reimbursement for each course was $3123, $10,156, $7862, $9725, and $10,377, respectively. Radiation oncology attending time was 1.5–2 times higher for treatment courses incorporating BT. Attending radiation oncologist’s time consumed per RVU was higher with BT (4.83 and 2.56 minutes per RVU generated for LDR-BT and HDR-BT-IMRT, respectively) compared to without BT (1.41–1.62 minutes per RVU).ConclusionsTime-driven activity-based costing analysis identified higher delivery costs associated with prostate BT compared with IMRT alone. In light of recent guidelines promoting BT for intermediate- to high-risk disease, re-evaluation of payment policies is warranted to encourage BT delivery.     

High-dose-rate prostate brachytherapy appears safe in patients with high baseline International Prostate Symptom Scores

PurposeThe purpose of the study was to report our institutional quality of life data for those undergoing high-dose-rate brachytherapy with an International Prostate Symptom Score (IPSS) ≥15 compared with those with an IPSS <15.Methods and MaterialsThe charts of 95 patients with localized adenocarcinoma of the prostate treated with high-dose-rate as monotherapy or as a boost after external beam radiation therapy at a single institution between 2012 and 2015 were reviewed. All patients completed the IPSS and Expanded Prostate Index for Prostate Cancer–Clinical Practice quality of life assessments before treatment and at least one followup survey. Linear mixed models were performed to test for significant changes and differences in each outcome over time.ResultsMedian followup in the IPSS <15 group was 23 months and 16 months in the IPSS ≥15 group. Median prostate volume was 46.3 cc and 45.4 cc, respectively (p = 0.901). IPSS, incontinence, and urinary irritation/obstruction scores were significantly higher in the IPSS ≥15 group compared with the IPSS <15 group at baseline (all p ≤ 0.05). By the >24 months time point, these scores had decreased below baseline and were not significantly different from those with a baseline IPSS <15 (all p > 0.1). 12.5% in the IPSS ≥15 group developed a new Grade 2 genitourinary toxicity requiring an alpha blocker compared with 26.5% in the IPSS <15 group (p = 0.34). No patients required emergency placement of a foley catheter within 30 days of treatment.ConclusionsGiven the low rates of genitourinary toxicity, this technique appears appropriate even for those with high baseline urinary symptoms.     

Monte Carlo dosimetry of high dose rate gynecologic interstitial brachytherapy

Purpose

To assess the dosimetric effects of the presence of the applicator, air pockets in clinical target volume (CTV) and OARs along with tissue heterogeneities using the Monte Carlo (MC) method in high dose rate (HDR) gynecologic interstitial brachytherapy with a Syed-Neblett template.

Methods and materials

The CT based dosimetry has been achieved with the Geant4 MC toolkit version 9.2. DICOM-RT files of 38 patients were imported into our own platform for MC simulations. The dose distributions were then compared to those obtained with a conventional TG-43 calculation.

Results

Taking account of heterogeneities has effects of the order of 1% on the HDR gynecological dose distributions. However, the exclusion of air pockets and applicator from the DVH calculation can lower the CTV D₉₀ and V₁₀₀ by as much as 8.7% and 5.0% in comparison with TG-43. Rectum dosimetric indices can also be lowered by approximately 3% compared with TG-43 for most cases. Differences for urethra and bladder are for most cases below 1%.

Conclusions

Exclusion of non-biological material such as air pockets and applicator volume from the CTV is important for both TG-43 and MC calculations. It could be easily implemented and automated in treatment planning systems without affecting computation times.     

Analysis of high–dose rate brachytherapy dose distribution resemblance in CyberKnife hypofractionated treatment plans of localized prostate cancer

The present study is to analyze the CyberKnife hypofractionated dose distribution of localized prostate cancer in terms of high–dose rate (HDR) brachytherapy equivalent doses to assess the degree of HDR brachytherapy resemblance of CyberKnife dose distribution. Thirteen randomly selected localized prostate cancer cases treated using CyberKnife with a dose regimen of 36.25 Gy in 5 fractions were considered. HDR equivalent doses were calculated for 30 Gy in 3 fractions of HDR brachytherapy regimen. The D_5% of the target in the CyberKnife hypofractionation was 41.57 ± 2.41 Gy. The corresponding HDR fractionation (3 fractions) equivalent dose was 32.81 ± 1.86 Gy. The mean HDR fractionation equivalent dose, D_98%, was 27.93 ± 0.84 Gy. The V_100% of the prostate target was 95.57% ± 3.47%. The V_100% of the bladder and the rectum were 717.16 and 79.6 mm³, respectively. Analysis of the HDR equivalent dose of CyberKnife dose distribution indicates a comparable resemblance to HDR dose distribution in the peripheral target doses (D_98% to D_80%) reported in the literature. However, there is a substantial difference observed in the core high-dose regions especially in D_10% and D_5%. The dose fall-off within the OAR is also superior in reported HDR dose distribution than the HDR equivalent doses of CyberKnife.     

The emerging role of high-dose-rate (HDR) brachytherapy as monotherapy for prostate cancer

High-dose-rate (HDR) brachytherapy as monotherapy is a comparatively new brachytherapy procedure for prostate cancer. In addition to the intrinsic advantages of brachytherapy, including radiation dose concentration to the tumor and rapid dose fall-off at the surrounding normal tissue, HDR brachytherapy can yield a more homogeneous and conformal dose distribution through image-based decisions for source dwell positions and by optimization of individual source dwell times. Indication can be extended even to T3a/b or a part of T4 tumors because the applicators can be positioned at the extracapsular lesion, into the seminal vesicles, and/or into the bladder, without any risk of source migration or dropping out. Unlike external beam radiotherapy, with HDR brachytherapy inter-/intra-fraction organ motion is not problematic. However, HDR monotherapy requires patients to stay in bed for 1–4 days during hospitalization, even though the actual overall treatment time is short. Recent findings that the α/β value for prostate cancer is less than that for the surrounding late-responding normal tissue has made hypofractionation attractive, and HDR monotherapy can maximize this advantage of hypofractionation. Research on HDR monotherapy is accelerating, with a growing number of publications reporting excellent preliminary clinical results due to the high ‘biologically effective dose (BED)’ of >200 Gy. Moreover, the findings obtained for HDR monotherapy as an early model of extreme hypofractionation tend to be applied to other radiotherapy techniques such as stereotactic radiotherapy. All these developments point to the emerging role of HDR brachytherapy as monotherapy for prostate cancer.     

Long-term outcomes with high-dose-rate brachytherapy for the management of base of tongue cancer

PurposeTo report the long-term results of a prospective, nonrandomized clinical trial using high-dose-rate (HDR) brachytherapy (BT) for the management of base of the tongue (BOT) tumors.Methods and MaterialsBetween January 1992 and June 2011, 60 patients (mean age, 57 years; range, 36–78 years) with T1–T4 and N0-3 carcinoma of BOT were treated. Fifty-six patients (93%) had advanced (Stage III-IV) disease. HDR BT boost (mean dose, 17 Gy; range, 12–30 Gy) was delivered after 50–70 Gy (mean 62 Gy) locoregional external beam irradiation. Seventeen patients (28%) received radiochemotherapy (RCT) with cisplatin.ResultsThe 5-year actuarial rate of local tumor control, locoregional tumor control, overall survival (OS), and cancer-specific survival (CSS) was 57%, 50%, 47%, and 61%, respectively. OS was significantly better in patients (n = 17) receiving RCT (69% vs. 39%; p = 0.005). Delayed soft-tissue ulceration occurred in seven patients (12%). Only one patient (<2%) developed osteoradionecrosis. In univariate analysis, the tumor size (T1–T2–T3 vs. T4) was found to have a significant effect on CSS (p = 0.043), whereas the nodal status (N0 vs. N+) affected locoregional tumor control (p = 0.042), OS (p = 0.002), and CSS (p = 0.015). Low histologic grade (1–2) was associated with better CSS (p = 0.020), whereas RCT significantly improved OS (p = 0.012).ConclusionsExternal beam irradiation combined with interstitial HDR BT boost results in good local tumor control with an acceptable rate of late side effects in patients with BOT carcinoma. RCT improves OS. Our results are similar to those reported with traditional low-dose-rate BT implants.