Update of the CLRP Monte Carlo TG-43 parameter database for high-energy brachytherapy sources

Time-resolved clinical dose volume metrics, calculations and predictions based on source tracking measurements and uncertainties to aid treatment verification and error detection for HDR brachytherapy-a proof-of-principle study

Objective.High-dose-rate (HDR) brachytherapy lacks routinely available treatment verification methods. Real-time tracking of the radiation source during HDR brachytherapy can enhance treatment verification capabilities. Recent developments in source tracking allow for measurement of dwell times and source positions with high accuracy. However, more clinically relevant information, such as dose discrepancies, is still needed. To address this, a real-time dose calculation implementation was developed to provide more relevant information from source tracking data. A proof-of-principle of the developed tool was shown using source tracking data obtained from a 3D-printed anthropomorphic phantom.Approach.Software was developed to calculate dose-volume-histograms (DVH) and clinical dose metrics from experimental HDR prostate treatment source tracking data, measured in a realistic pelvic phantom. Uncertainty estimation was performed using repeat measurements to assess the inherent dose measuring uncertainty of thein vivodosimetry (IVD) system. Using a novel approach, the measurement uncertainty can be incorporated in the dose calculation, and used for evaluation of cumulative dose and clinical dose-volume metrics after every dwell position, enabling real-time treatment verification.Main results.The dose calculated from source tracking measurements aligned with the generated uncertainty bands, validating the approach. Simulated shifts of 3 mm in 5/17 needles in a single plan caused DVH deviations beyond the uncertainty bands, indicating errors occurred during treatment. Clinical dose-volume metrics could be monitored in a time-resolved approach, enabling early detection of treatment plan deviations and prediction of their impact on the final dose that will be delivered in real-time.Significance.Integrating dose calculation with source tracking enhances the clinical relevance of IVD methods. Phantom measurements show that the developed tool aids in tracking treatment progress, detecting errors in real-time and post-treatment evaluation. In addition, it could be used to define patient-specific action limits and error thresholds, while taking the uncertainty of the measurement system into consideration.

RapidBrachyTG43: A Geant4-based TG-43 parameter and dose calculation module for brachytherapy dosimetry

BACKGROUND

The AAPM TG-43U1 formalism remains the clinical standard for dosimetry of low- and high-energy γ $\gamma$ -emitting brachytherapy sources. TG-43U1 and related reports provide consensus datasets of TG-43 parameters derived from various published measured data and Monte Carlo simulations. These data are used to perform standardized and fast dose calculations for brachytherapy treatment planning.

PURPOSE

Monte Carlo TG-43 dosimetry parameters are commonly derived to characterize novel brachytherapy sources. RapidBrachyTG43 is a module of RapidBrachyMCTPS, a Monte Carlo-based treatment planning system, designed to automate this process, requiring minimal user input to prepare Geant4-based Monte Carlo simulations for a source. RapidBrachyTG43 may also perform a TG-43 dose to water-in-water calculation for a plan, substantially accelerating the same calculation performed using RapidBrachyMCTPS's Monte Carlo dose calculation engine.

METHODS

TG-43 parametersS K / A $S_K/A$ , Λ $\Lambda$ ,g L ( r ) $g_L(r)$ , andF ( r , θ ) $F(r,\theta)$ were calculated using three commercial source models, one each of125 $^{125}$ I,192 $^{192}$ Ir, and60 $^{60}$ Co, and were benchmarked to published data. TG-43 dose to water was calculated for a clinical breast brachytherapy plan and was compared to a Monte Carlo dose calculation with all patient tissues, air, and catheters set to water.

RESULTS

TG-43 parameters for the three simulated sources agreed with benchmark datasets within tolerances specified by the High Energy Brachytherapy Dosimetry working group. A gamma index comparison between the TG-43 and Monte Carlo dose-to-water calculations with a dose difference and difference to agreement criterion of 1%/1 mm yielded a 98.9% pass rate, with all relevant dose volume histogram metrics for the plan agreeing within 1%. Performing a TG-43-based dose calculation provided an acceleration of dose-to-water calculation by a factor of 165.

CONCLUSIONS

Determination of TG-43 parameter data for novel brachytherapy sources may now be facilitated by RapidBrachyMCTPS. These parameter datasets and existing consensus or published datasets may also be used to determine the TG-43 dose for a plan in RapidBrachyMCTPS.

Interstitial brachytherapy for lip carcinomas: Comparison between Ir-192 low-dose-rate and high-dose-rate treatment

PURPOSE

Low-dose-rate (LDR) and high-dose-rate (HDR) interstitial brachytherapy are known to be effective in the treatment of lip carcinomas. The aim of this study was to retrospectively compare oncologic and toxicity outcomes between the two techniques.

PATIENTS AND METHODS

From 2007 to 2018, patients at the Institut de cancérologie de Lorraine (France) who received exclusive or adjuvant interstitial brachytherapy for lip squamous carcinomas were studied. Two groups were defined: the LDR/PDR group, including patients treated with iridium-192 wires, or pulsed-dose rate technique, and the high-dose-rate group, with patients treated by high-dose-rate technique. The dose ranged between 50Gy and 65Gy (depending on previous surgery) for low-dose-/pulsed-dose rate treatments, and 39Gy for high-dose-rate (twice a day). Early, late toxicity events and oncologic control were reported.

RESULTS

Among the 61 patients whose data were analyzed retrospectively, 36 received the low-dose-/pulsed-dose rate treatment (59%) and 25 the high-dose-rate brachytherapy (41%). The median follow-up time was 44 months. At 36 months, the local control rates were 96.3% for LDR/PDR group and 100% for HDR (P=0.180). The regional control rates were 85.9% and 92% without any difference according to the two groups (P=0.179). The specific overall survival rate was 95.5% with no difference between groups. There were more grade 2 or higher mucositis in the HDR group than in LDR/PDR group (40% versus 16.7%, P=0.042). One case of grade 3 mucositis was recorded in each group. No grade 3 late complications were recorded. High-dose-rate brachytherapy reduced the length of hospitalization by 2 days (P<0.001).

CONCLUSION

High-dose- or low-dose-/pulsed-dose rate brachytherapy seemed to be as effective and well tolerated in our experience of 61 patients.