Multimodality Dosimetric Evaluation for the Treatment of Recurrent Brain Tumors

PURPOSE/OBJECTIVE(S)

GammaTile Surgically Targeted Radiation Therapy (STaRT) are bioresorbable collagen tiles containing four Cesium-131 radioactive seeds which are permanently implanted into the operative bed immediately following the surgical resection of a brain tumor. Alternative radiation treatment approaches for recurrent brain tumors include external beam radiation therapy (EBRT) with either proton or photon (volumetric modulated arc therapy, or VMAT) radiation. The purpose of this study is to perform a comparative dosimetric study of these three modalities for cases of recurrent brain tumors. We hypothesize that GammaTile would be dosimetrically superior at sparing radiation dose to surrounding organs at risk.

MATERIALS/METHODS

A total of 5 patients have received GammaTile StaRT therapy at our institute for recurrent brain tumors in 2021-2022. Out of these 5 patients, 3 were recurrent glioblastoma (GBM) and 2 were brain metastasis (brain-met) cases. All patients were previously treated with radiation. Typical prescription for GammaTile therapy is 60 Gy to the High Risk CTV (HR_CTV), specified by 5mm depth from the plane of the seeds. For recurrent GBM cases, the alternative methods of radiation are proton therapy and photon therapy using VMAT. The standard re-irradiation dose for proton and photon therapy is 35 Gy in 10 fractions prescribed to PTV (3 mm expansion of EBRT CTV). For brain-met cases, an alternate method is hypo-fractionation radiation therapy with Linac-based SBRT. Linac-based SBRT prescription depends on the volume of EBRT CTV. For one of the brain-met cases, the SBRT prescription was 30 Gy in 5 fractions, and for the other case it was 27 Gy in 3 fractions to PTV (2 mm expansion from EBRT CTV). Proton and photon plans were generated in a treatment planning system using a double scattering Mevion system and a VersaHD with agility head, respectively. All the physical doses were converted to biological effective dose (BED) for evaluation.

RESULTS

The dosimetric quantities are summarized in table 1. These quantities were evaluated using HR_CTV and EBRT_CTV for GammaTile therapy and EBRT (proton/photon), respectively. GammaTile therapy reduces dose to normal brain tissue considerably. However, it may have more uncertainty in the dose delivered compared to proton and photon EBRT.

CONCLUSION

It appears that all three treatment modalities are adequate for treating recurrent brain tumors. However, GammaTile therapy may allow to deliver higher dose to the targets while reducing the irradiation to adjacent normal tissue.

Improving Complex Brachytherapy Efficiency in the Current Financial Climate

PURPOSE/OBJECTIVE(S)

To optimize multidisciplinary collaboration in the setting of limited resources to increase the efficiency of complex brachytherapy workflow for patients with locally advanced cervical cancer.

MATERIALS/METHODS

High Dose Rate (HDR) brachytherapy is a critical component in the treatment of women with locally advanced cervical cancer. The completion of HDR brachytherapy to provide a complete treatment of concurrent chemoradiation and brachytherapy of <56 days has been well established. A quality improvement (QI) initiative was born out of the need to accommodate an increasing volume of patients with locally advanced cervical cancer. The challenges addressed were: different location of the operating room (OR), HDR brachytherapy suite, MR scanner; Inconsistent OR days; Post-Anesthesia Care Unit (PACU)/transportation delays; Anesthesiology staffing constraints. The QI initiative required multidisciplinary collaboration. A new protocol was finalized which provided protected OR time, and changed analgesia from general anesthesia requiring prolonged monitoring in PACU, to a pre-procedural epidural with moderate sedation. Additionally, a dedicated anesthesiologist was assigned to discuss process improvement, and the medical history for these complex patients as it relates to anesthesia safety. The streamlined process allows the patients' physical time in PACU to be bypassed; a dedicated brachytherapy nurse competent in moderate sedation recovery accompanies the patient to CT simulation. An MR protocol was established with tentative slots secured. The primary metric was the change in the number of interstitial cases performed. Additional metrics included: total case time, anesthesiology delay, MR delay, and number of OR days where 2 complex cases are performed.

RESULTS

Prior to initiation of QI initiative, from 01/2022-09/2022 there were 27 cases, average 3.0/month. After implementation of QI project, from 10/2022-02/2023 there were 32 cases, average 6.4/month, a 113.3% increase. Total case time decreased from baseline 9.3 hours to average 6 hours (Range: 3.8-10.6). Anesthesiology related delays were on average 18.5 minutes (Range: -15-35). MR related delays were on average 87.6 minutes (Range: 35-275). These changes now permit the flexibility of performing 2 complex interstitial cases per day, instead of one. The average days per month where two interstitial cases are performed increased from 0.4 to 1.4.

CONCLUSION

As hospital systems continue to face economic constraints, it is critical that we leverage our existing resources in order to provide timely care to our patients. This QI initiative shows that despite the limitation in brachytherapy operations, systems can be changed through multidisciplinary collaboration to improve efficiencies and increase capacities while working within financial workforce constraints to provide optimal patient care.

Efficacy of Curvilinear Needle Implantation for Prostate HDR Brachytherapy

PURPOSE/OBJECTIVE(S)

High-dose-rate (HDR) brachytherapy is gaining popularity due to better dose distribution, good clinical outcomes, and convenience of the procedure. Conventionally, Rectilinear (straight needle) Method (RLM) is utilized for HDR procedure. However, the efficacy of a newly developed technique, the Curvilinear (curved needle conforming the prostate shape) Method (CLM), for HDR brachytherapy has not yet been explored. In this study, efficacy of the CLM is evaluated. The CLM technique is expected to significantly improve the radiation dose distribution with small number of needles that will potentially improve the clinical outcomes.

MATERIALS/METHODS

Randomly 16 prostate cancer patients were selected (median age: 68.3 yrs, Stage: T1-T2a) from an IRB approved pool of patients. Prostate and OARs (urethra, rectum and bladder) were contoured on T2-weigthed MRI for all the patients. Thirty-two HDR plans, 16 for RLM and 16 for CLM, were prepared using Oncentra treatment planning software with Ir-192 isotope and were optimized using Hybrid Inverse treatment Planning Optimization (HIPO) tool. Prescription dose was 15 Gy in single fraction. Data for relevant parameters (V100, V200, D90, D10, Dmax, etc.) for prostate and OARs were collected using the dose-volume histogram. P-value less than equal to 0.05 was considered statistically significant.

RESULTS

Average prostate volume was 33.1cc (range 17.7-51.3cc, median 30.6cc). In CLM technique the target coverage and dose constraints for OARs were improved by 0.3%-6.4% and 1.6%-34.2%, respectively (see Table below). Certain dose constraints were difficult to meet for some cases with RLM (prostate V100 (4 pts) and V200 (5 pts); rectum Dmax (5 pts) and D12 Gy (10 pts). On average, over 44.6% (average 17.5 vs 9.7 needles) reduction of needles was achieved with CLM (p-value < 0.001).

CONCLUSION

The CLM technique generated significantly improved dosimetric plans using less number of needles. Reduction in number of needles would be associated with potential decrease in toxicity and improved clinical outcomes. Future plan includes clinical implementation of the CLM technique.

Prognostic value of SUVmax on FDG-PET/CT before and after stereotactic body radiotherapy (SBRT) on recurrence and survival in early-stage non-small cell lung cancer (NSCLC)

8539

Background: Stereotactic body radiotherapy (SBRT) is the standard of care in medically inoperable early-stage non-small cell lung cancer (NSCLC). Assessment of FDG-PET/CT before and after SBRT may stratify risk of disease recurrence and survival outcomes. Methods: Patients with T1-2N0M0 NSCLC who underwent PET/CT prior to SBRT (50-60 Gy over 3-5 fractions) between 2012 and 2019 were retrospectively identified. Pre-SBRT SUVmax and change in SUVmax at 3 and 6 months after SBRT were assessed as predictors of local control (LC), progression-free survival (PFS), and overall survival (OS). Optimal cutoff points for comparison were determined by receiver operator characteristic (ROC) analysis. Survival analyses were performed with Kaplan-Meier estimates with log rank testing, and Cox proportional hazards models including age, sex, T stage, histology, and performance status. Results: Out of 163 patients identified, 71 (43.6%) underwent repeat PET/CT within 6 months of SBRT completion. Median follow-up was 19 months (range 1 – 94 months). For the whole cohort, 1-year and 2-year LC, PFS, and OS were 95.0% and 80.3%, 75.9% and 47.7%, and 87.1% and 67.0%, respectively. Pre-SBRT SUVmax greater than 12.3 had an aHR of 2.80 (95% CI 1.3 – 6.2, p = 0.011) for PFS. A cutpoint of 12.6 for pre-SBRT SUVmax had an aHR of 3.00 (95% CI 1.6 – 5.8, p = 0.003) for OS. Pre-SBRT SUVmax did not significantly predict LC. A 3-month SUVmax decrease of at least 45% was associated with improved LC (aHR = 0.15, 95% CI 0.02 – 0.91, p = 0.018). At 6 months following SBRT, a cutoff point of a 53% decrease in SUVmax was associated with better LC (p = 0.038). Change in SUVmax was not significantly associated with PFS or OS at either time point. Performance status significantly predicted PFS and OS in all models. No other factors were significant. Conclusions: Pre-treatment SUVmax cutoffs can predict PFS and OS in early-stage NSCLC. At both the 3- and 6-month time points following SBRT, cutoff values for change in SUVmax can stratify risk of local recurrence.[Table: see text]

Use of surgery and stereotactic body radiotherapy (SBRT) in very elderly patients with early-stage non-small cell lung cancer (NSCLC): A national cancer database (NCDB) analysis

e20058

Background: SBRT treatment for very elderly ( > 80 years) patients with early stage NSCLC has been reported to be well tolerated with good short term efficacy. Using a large hospital based registry, we report a comparison of patterns of practice, outcomes, and prognostic factors for very elderly patients undergoing any treatment for early-stage NSCLC. Methods: The NCDB was queried for patients with clinical Stage I-IIA NSCLC with age ≥ 80 years diagnosed from 2001-2015 treated with surgery or SBRT alone. Patients were excluded if they received chemotherapy /immunotherapy or non-standard SBRT doses (i.e. > 5 fractions of RT, < 30 Gy or > 70 Gy total dose). Survival analyses were performed with propensity-matching, Kaplan-Meier estimates, Cox proportional hazards regression, and log rank testing. Results: 26039 patients met search criteria, median age 83 (80-90) years. 17141 (65.8%) patients underwent surgery, and 8898 (34.2%) underwent SBRT. Median follow up was 31 months. Median survival was 52 and 35 months for surgery and SBRT. Of patients receiving SBRT, 2044 (23%) had a contraindication to primary surgery due to patient risk factors. Age, clinical stage, tumor size, surgery type, CDCC score, BED, bronchial involvement, and type of treatment facility were predictive of median survival. BED > 154 Gy was associated with greater median survival (p < 0.01). Lobectomy was associated with greater median survival vs sub-lobar resection/pneumonectomy (p < 0.0001). For stage I tumors, surgery was associated with better median survival (56 vs. 35 months, p < 0.0001), but for stage IIA patients both modalities had similar median survival (30 vs 29 months, p = 0.04). Conclusions: Surgery remains the predominant treatment modality for early stage NSCLC in this very elderly population, and is associated with good outcomes for patients with stage I tumors. For elderly patients who are poor surgical candidates due to medical co-morbidities SBRT is associated with reasonable median survival. With limited information on patient comorbidities, more robust studies are needed to determine the effects of patient selection on treatment outcomes in this population.

Implementation and experimental results of 4D tumor tracking using robotic couch

PURPOSE

This study presents the implementation and experimental results of a novel technique for 4D tumor tracking using a commercially available and commonly used treatment couch and evaluates the tumor tracking accuracy in clinical settings.

METHODS

Commercially available couch is capable of positioning the patient accurately; however, currently there is no provision for compensating physiological movement using the treatment couch in real-time. In this paper, a real-time couch tracking control technique is presented together with experimental results in tumor motion compensation in four dimensions (superior-inferior, lateral, anterior-posterior, and time). To implement real-time couch motion for tracking, a novel control system for the treatment couch was developed. The primary functional requirements for this novel technique were: (a) the treatment couch should maintain all previous∕normal features for patient setup and positioning, (b) the new control system should be used as a parallel system when tumor tracking would be deployed, and (c) tracking could be performed in a single direction and∕or concurrently in all three directions of the couch motion (longitudinal, lateral, and vertical). To the authors' best knowledge, the implementation of such technique to a regular treatment couch for tumor tracking has not been reported so far. To evaluate the performance of the tracking couch, we investigated the mechanical characteristics of the system such as system positioning resolution, repeatability, accuracy, and tracking performance. Performance of the tracking system was evaluated using dosimetric test as an endpoint. To investigate the accuracy of real-time tracking in the clinical setting, the existing clinical treatment couch was replaced with our experimental couch and the linear accelerator was used to deliver 3D conformal radiation therapy (3D-CRT) and intensity modulated radiation therapy (IMRT) treatment plans with and without tracking. The results of radiation dose distribution from these two sets of experiments were compared and presented here.

RESULTS

The mechanical accuracies were 0.12, 0.14, and 0.18 mm in X, Y, and Z directions. The repeatability of the desired motion was within ±0.2 mm. The differences of central axis dose between the 3D-CRT stationary plan and two tracking plans with different motion trajectories were 0.21% and 1.19%. The absolute dose differences of both 3D tracking plans comparing to the stationary plan were 1.09% and 1.20%. Comparing the stationary IMRT plan with the tracking IMRT plan, it was observed that the central axis dose difference was -0.87% and the absolute difference of both IMRT plans was 0.55%.

CONCLUSIONS

The experimental results revealed that the treatment couch could be successfully used for real-time tumor tracking with a high level of accuracy. It was demonstrated that 4D tumor tracking was feasible using existing couch with implementation of appropriate tracking methodology and with modifications in the control system.

Robotic system for prostate brachytherapy

In contemporary brachytherapy procedures, needle placement at the desired target is challenging for a variety of reasons. A robot-assisted brachytherapy system can potentially improve needle placement and seed delivery, resulting in enhanced therapeutic outcome. In this paper we present a robotic system with 16 degrees of freedom (DOF) (9 DOF for the positioning module and 7 DOF for the surgery module) that has been developed and fabricated for prostate brachytherapy. Strategies to reduce needle deflection and target movement were incorporated after extensive experimental validation. Provision for needle motion and force feedback was included in the system to improve robot control and seed delivery. Preliminary experimental results reveal that the prototype system is sufficiently accurate in placing brachytherapy needles.

Needle insertion force estimation model using procedure-specific and patient-specific criteria

Placement accuracy of different types of surgical needles in soft biological tissues depends on a variety of factors. The needles used for prostate brachytherapy procedures are typically about 200 mm in length and 1.27-1.47 mm in diameter. These needles are prone to deflection and thereby depositing the seeds at a location other than the planned one. Thus tumorous tissues may not receive the planned dose whereas the critical organs may be over-dosed. A significant amount of needle deflection and target movement is related to some procedure-specific criteria and some patient-specific criteria. In this paper we have developed needle insertion force models taking both procedure-specific criteria and patient-specific criteria. These statistical models can be used to estimate the force that the needle will experience during insertion and thereby control the needle to reduce the needle deflection and enhance seed delivery accuracy.

Effects of velocity modulation during surgical needle insertion

Precise interstitial intervention is essential for many medical diagnostic and therapeutic procedures. But accurate insertion and placement of surgical needle in soft tissue is quite challenging. The understanding of the interaction between surgical needle and soft tissue is very important to develop new devices and systems to achieve better accuracy and to deliver quality treatment. In this paper we present the effects of velocity (linear, rotational, and oscillatory) modulation on needle force and target deflection. We have experimentally verified our hypothesis that needle insertion with continuous rotation reduces target movement and needle force significantly. We have observed little changes in force and target deflection in rotational oscillation (at least at lower frequency) of the needle.

Efficacy of prostate stabilizing techniques during brachytherapy procedure

During the prostate brachytherapy procedure, multiple needles are inserted into the prostate and radioactive seeds are deposited. Stabilizing needles are first inserted to provide some rigidity and support to the prostate, ideally this will provide better seed placement and an overall improved treatment. However, there is much speculation regarding the effectiveness of using regular brachytherapy needles as stabilizers. In this study, we explored the efficacy of (1) two types of needles--18 gauge brachytherapy needle vs. 18 gauge hooked needle; and (2) parallel vs. angulated needle configurations to stabilize the prostate. Prostate phantom movement and needle insertion progression were imaged using ultrasound (US). The recorded images were analyzed and prostate displacement was computed from images using implanted artifacts. Experimentation allowed us to further understand the mechanics behind prostate stabilization. We observed superior stabilization by the hooked needles compared to the regular brachytherapy needles (more than 40% for parallel stabilization). Prostate movement was also reduced significantly when regular brachytherapy needles were in an angulated configuration as compared to the parallel configuration (approximately 40%). When the hooked needles were angled for stabilization, further improvement in decreased displacement was observed. In general, for convenience of dosimetric planning, all needles are desired to be in parallel and in this case, hooked needles are better suited to improve stabilization of the prostate. On the other hand, both regular and hooked needles appear to be equally effective in reducing prostate movement when they are in angulated configurations, which will be useful in robotic permanent seed implantation (PSI).

In-vivo measurement of surgical needle intervention parameters: a pilot study

Percutaneous intervention is essential in numerous medical diagnostic and therapeutic procedures. In these procedures, accurate insertion of the surgical needle is very important. But precise interstitial intervention is quite challenging. Robot-assisted needle intervention can significantly improve accuracy and consistency of various medical procedures. To design and control any robotic system, the design and control engineers must know the forces that will be encountered by the system and the motion trajectories that the needling mechanism will have to follow. Several researchers have reported needle insertion forces encountered while steering through soft tissue and soft material phantoms, but hardly any in-vivo force measurement data is available in the literature. In this paper, we present needle insertion forces and motion trajectories measured during actual brachytherapy needle insertion while implanting radioactive seeds in the prostate glands of twenty five patients.