Toxicity and Dosimetric Analysis of Reirradiation of Head and Neck Cancers with High Dose Rate Brachytherapy

PURPOSE/OBJECTIVE(S)

Reirradiation (reRT) of recurrent or second primary head and neck cancers (HNC) after prior curative-intent external beam radiotherapy (EBRT) has historically achieved local control (LC) rates of 40-50% and been associated with high grade toxicity rates estimated at 25-50%. This study evaluated the hypothesis that patients with small reRT target volumes could be selected for high dose rate brachytherapy (HDR-BT) reRT and achieve similar LC without excess toxicity.

MATERIALS/METHODS

Included were all patients with HNC squamous cell carcinoma treated with HDR-BT after having previously received curative-intent EBRT for primary HNC from 2000-2021. Patients were selected by a multidisciplinary tumor board to be appropriate candidates for HDR-BT reRT without EBRT generally for definitive or adjuvant treatment of small primary tumors without neck nodal metastases. Univariate analysis was performed using the logistic regression model. Survival outcomes were estimated with the Kaplan Meier method.

RESULTS

Twenty-three patients were evaluated. Median follow up time was 19mo. Median age at time of HDR-BT was 64 years. Thirteen patients (57%) were treated for recurrent HNC, of which 7 were in the oral cavity (OC) and 6 were the oropharynx (OPX). Ten patients (43%) were treated for a second primary HNC, of which 5 were in the OC and 5 were in the OPX. Median time from completion of EBRT to HDR-BT was 41 (IQR 14-73) mo. Within their reRT course, 11 patients (48%) were treated with HDR-BT after resection, 9 patients (39%) received concurrent hyperthermia, and 7 patients (30%) received chemotherapy. HDR-BT regimens included 600cGy x5 (N = 11), 600cGy x6 (N = 6), 450cGy x8 (N = 1), 1500cGy x1 (N = 1),1000cGy x1 (N = 1), 500cGy x8 (N = 1), and 700cGy x5 (N = 1). One patient who was treated with two implants received 450cGy x 3 followed by 475cGy x5. A median of 5 brachytherapy catheters were used. Actuarial 2-year LC and overall survival rate was 68% and 62%, respectively. Of the 17 HDR-BT reRT plans available for review, median (IQR) target volume was 15.8 (10.6-34.9) cc. Median (IQR) target V100% was 90.6 (89.4-90.0)%, V150% was 50.5 (49.7-54.4)%, and V200% was 25.4 (23.8-29.0)%. Median (IQR) target D90% was 30.1 (29.8-35.5) Gy, and median D1cc was 116.4 (100.5-171.4) Gy. The mandible dose [median (IQR)] was D2cc:15.1(9.48-18.9) Gy; D1cc:16.9(11.1-21.3) Gy; and D1%:18.8(13.4-22.7) Gy. Nine of the 23 patients (39%) experienced ≥G3 toxicity including fistula, soft tissue necrosis, osteoradionecrosis, ulcer, hemorrhage, and dysphagia requiring a chronic feeding tube. Target D90% was associated with ≥G3 toxicity (p = 0.045). For D90% greater than the median of 30Gy, 45% ≥G3 toxicity was observed.

CONCLUSION

This study suggests that HDR-BT for reRT of small recurrent or second primary HNC can provide similar LC without excess high-grade toxicities as compared to historical outcomes with EBRT reRT. Delivery of equivalent doses higher than 30Gy in 5 fractions should be approached with caution.

A Machine Learning Framework Integrating Electronic Health Records for Survival Prognostication in Cervix Cancer

PURPOSE/OBJECTIVE(S)

Recent advances in Machine learning (ML) have led to promising clinical applications in oncology, such as improved detection on imaging, predicting emergency department visits, and predicting survival. The hypothesis of this study is a machine learning model using features extracted from electronic health records can be created to improve individual prognostication in patients with cervix cancer managed with radiotherapy in a binary higher and lower risk group model.

MATERIALS/METHODS

This study used a single-institution retrospective dataset. Electronic records of patients treated for cervix cancer with definitive radiotherapy from 2003-2014 were queried. Features were selected for model building were based on relevant clinical variables and ease of abstraction from records: age, race, smoking status, parity, self-reported unintentional weight loss, histology, revised 2018 Fédération Internationale de Gynécologie et d'Obstétrique (FIGO) staging, tumor size, number of enlarged lymph nodes, involved node location, presence of metastases, radiotherapy duration, and concurrent chemotherapy. The dataset was split into training and testing cohorts, with multivariable Cox regression with Lasso regularization performed to predict hazard ratios (HR), and internal 5-fold cross-validation (training set) to determine the regularization parameter. For each patient, a partial HR using all variables was predicted. A cut-off value maximally splitting the training dataset into higher and lower risk cohorts was calculated in the training dataset using Kaplan-Meier estimates and log-rank tests, and this predicted cut-off value was evaluated in the test dataset.

RESULTS

A total of 226 patients were included in study, with a median follow-up of 55.1 months; 226 patients in training cohort, and 57 in testing cohort. Feature concordance indices of 0.74 and 0.75 were obtained in the testing and training datasets, respectively, with minimal over-fitting. The three variables that contributed most to the model (with Log HR, 95% CI, p-value) were FIGO stage (0.38, 0.1-0.66, p = 0.01), presence of metastases (0.26, -0.02-0.53, p = 0.07), and unintentional weight loss (-0.34, -0.54-0.14, p<0.01), and FIGO IIB maximally divided the cohort into higher and lower risk stage groupings. A partial HR of 1.15 threshold using all features predicted the largest survival separation between higher and lower risk patients, more so than stage alone (p = 1.18 × 10-3 separated by stage alone vs p = 8.97 × 10-7 separated by partial hazard).

CONCLUSION

A machine learning approach was able to improve prognostication of survival in cervix cancer using additional features from electronic health records. Future work should explore prognostication using large scale datasets and pre-treatment variables for potential incorporation into patient discussions and shared decision making.

Image-Guided High-Dose-Rate Brachytherapy for Definitive Management of Primary Vaginal Cancer: A Single Institutional Experience

PURPOSE/OBJECTIVE(S)

To assess the safety and efficacy of image-guided high-dose-rate brachytherapy (IGBT) alone or in combination with external beam radiation therapy (EBRT) for the treatment of vaginal cancers.

MATERIALS/METHODS

The study analyzed patients diagnosed with primary vaginal cancers from 2004 to 2021 who received definitive radiotherapy at a single institution. Interstitial implants were performed using a freehand technique and transvaginal or transrectal-ultrasound for imaging guidance. IGBT was planned using inverse planning simulated annealing (IPSA) software. Data collected and analyzed included patient and tumor characteristics, dose and fractionation, and treatment outcomes. Complications were assessed using CTCAEv4 scores, and descriptive and survival analyses were performed using R-studio.

RESULTS

Sixty-six patients met inclusion criteria. Patients were staged as I (14), II (23), III (19), and IV (10) based on revised FIGO 2018 staging. 47 (72%) had squamous cell carcinoma histology, and median age was 65 years. The most common regimen was 45 Gy in 25 fractions of EBRT followed by IGBT boost of 18 Gy in 3 fractions with 1 implant (n = 40). For melanoma, an IGBT boost of 19 Gy in 2 fractions with a single implant was used (n = 7). For IGBT monotherapy, the most common regimen was 36 Gy in 6 fractions delivered over 2 implants (n = 3). 41 (66%) of the patients received systemic therapy. Local failures occurred in 8 (12%) patients, while 8 (12%) developed distant metastases. Median overall survival was 64.7 months. Overall survival was 64.3% (95% CI 51.9-79.7%) at 3 years, and 50.9% (95% CI 35.7-72.5%) at 5 years. Grade 3 or 4 toxicities were reported in 4 (6%) patients including vaginal fistula (n = 3) and urethral stricture (n = 1).

CONCLUSION

The results suggest that utilizing IGBT for freehand interstitial implants in combination with EBRT is a safe and effective primary treatment for vaginal cancer, with durable local control and low toxicity. Further research is needed to establish multi-institutional practice patterns and recommendations.

Salvage High-Dose-Rate Brachytherapy for Recurrent Prostate Cancer After Definitive Radiation

PURPOSE

Salvage high-dose-rate brachytherapy (sHDRBT) for locally recurrent prostate cancer after definitive radiation is associated with biochemical control in approximately half of patients at 3 to 5 years. Given potential toxicity, patient selection is critical. We present our institutional experience with sHDRBT and validate a recursive partitioning machines model for biochemical control.

MATERIALS AND METHODS

We performed a retrospective analysis of 129 patients who underwent whole-gland sHDRBT between 1998 and 2016. We evaluated clinical factors associated with biochemical control as well as toxicity.

RESULTS

At diagnosis the median prostate-specific antigen (PSA) was 7.77 ng/mL. A majority of patients had T1-2 (73%) and Gleason 6-7 (82%) disease; 71% received external beam radiation therapy (RT) alone, and 22% received permanent prostate implants. The median disease-free interval (DFI) was 56 months, and median presalvage PSA was 4.95 ng/mL. At sHDRBT, 46% had T3 disease and 51% had Gleason 8 to 10 disease. At a median of 68 months after sHDRBT, 3- and 5-year disease-free survival were 85% (95% CI, 79-91) and 71% (95% CI, 62-79), respectively. Median PSA nadir was 0.18 ng/mL, achieved a median of 10 months after sHDRBT. Patients with ≥35%+ cores and a DFI <4.1 years had worse biochemical control (19% vs 50%, P = .02). Local failure (with or without regional/distant failure) was seen in 11% of patients (14/129), and 14 patients (11%) developed acute urinary obstruction requiring Foley placement and 19 patients (15%) developed strictures requiring dilation.

CONCLUSIONS

sHDRBT is a reasonable option for patients with locally recurrent prostate cancer after definitive RT. Those with <35%+ cores or an initial DFI of ≥4.1 years may be more likely to achieve long-term disease control after sHDRBT.

Evaluating the impact of real-time multicriteria optimizers integrated with interactive plan navigation tools for HDR brachytherapy

PURPOSE

Currently in high-dose-rate (HDR) brachytherapy planning, manual fine-tuning of an objective function is a common practice. Furthermore, automated planning approaches such as multicriteria optimization (MCO) are still limited to the automatic generation of a single treatment plan. This study aims to quantify planning efficiency gains when using a graphics processing unit-based MCO (gMCO) algorithm combined with a novel graphical user interface (gMCO-GUI) that integrates efficient automated and interactive plan navigation tools.

METHODS AND MATERIALS

The gMCO algorithm was used to generate 1000 Pareto optimal plans per case for 379 prostate cases. gMCO-GUI was developed to allow plan navigation through all plans. gMCO-GUI integrates interactive parameter selection tools directly with the optimization algorithm to allow plan navigation. The quality of each plan was evaluated based on the Radiation Treatment Oncology Group 0924 protocol and a more stringent institutional protocol (INSTp). gMCO-GUI allows real-time time display of the dose-volume histogram indices, the dose-volume histogram curves, and the isodose lines during the plan navigation.

RESULTS

Over the 379 cases, the fraction of Radiation Treatment Oncology Group 0924 protocol valid plans with target coverage greater than 95% was 90.8%, compared with 66.0% for clinical plans. The fraction of INSTp valid plans with target coverage greater than 95% was 81.8%, compared with 62.3% for clinical plans. The average time to compute 1000 deliverable plans with gMCO was 12.5 s, including the full computation of the 3D dose distributions.

CONCLUSIONS

Combining the gMCO algorithm with automated and interactive plan navigation tools resulted in simultaneous gains in both plan quality and planning efficiency.

Real-time electromagnetic tracking-based treatment platform for high-dose-rate prostate brachytherapy: Clinical workflows and end-to-end validation

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.

Evaluation of PC-ISO for customized, 3D Printed, gynecologic 192-Ir HDR brachytherapy applicators

The purpose of this study was to evaluate the radiation attenuation properties of PC-ISO, a commercially available, biocompatible, sterilizable 3D printing material, and its suitability for customized, single-use gynecologic (GYN) brachytherapy applicators that have the potential for accurate guiding of seeds through linear and curved internal channels. A custom radiochromic film dosimetry apparatus was 3D-printed in PC-ISO with a single catheter channel and a slit to hold a film segment. The apparatus was designed specifically to test geometry pertinent for use of this material in a clinical setting. A brachytherapy dose plan was computed to deliver a cylindrical dose distribution to the film. The dose plan used an 192Ir source and was normalized to 1500 cGy at 1 cm from the channel. The material was evaluated by comparing the film exposure to an identical test done in water. The Hounsfield unit (HU) distributions were computed from a CT scan of the apparatus and compared to the HU distribution of water and the HU distribution of a commercial GYN cylinder applicator. The dose depth curve of PC-ISO as measured by the radiochromic film was within 1% of water between 1 cm and 6 cm from the channel. The mean HU was -10 for PC-ISO and -1 for water. As expected, the honeycombed structure of the PC-ISO 3D printing process created a moderate spread of HU values, but the mean was comparable to water. PC-ISO is sufficiently water-equivalent to be compatible with our HDR brachytherapy planning system and clinical workflow and, therefore, it is suitable for creating custom GYN brachytherapy applicators. Our current clinical practice includes the use of custom GYN applicators made of commercially available PC-ISO when doing so can improve the patient's treatment. 

Inverse planning optimization for hybrid prostate permanent-seed implant brachytherapy plans using two source strengths

The purpose is to demonstrate the ability to generate clinically acceptable prostate permanent seed implant plans using two seed types which are identical except for their activity. The IPSA inverse planning algorithms were modified to include multiple dose matrices for the calculation of dose from different sources, and a selection algorithm was implemented to allow for the swapping of source type at any given source position. Five previously treated patients with a range of prostate volumes from 20-48 cm3 were re-optimized under two hybrid scenarios: (1) using 0.32 and 0.51 mGy m2 / h 125I, and (2) using 0.64 and 0.76 mGy m2 / h 125I. Isodose lines were generated and dosimetric indices , V150Prostate, D90Prostate, V150Urethra, V125Urethra, V120Urethra,V100Urethra, and D10Urethra were calculated. The algorithm allows for the generation of single-isotope, multi-activity hybrid brachytherapy plans. By dealing with only one radionuclide, but of different activity, the biology is unchanged from a standard plan. All V100Prostate were within 2.3 percentage points for every plan and always above the clinically desirable 95%. All V150Urethra were identically zero, and V120Urethra is always below the clinically acceptable value of 1.0 cm3. Clinical optimization times for the hybrid plans are still under one minute, for most cases. It is possible to generate clinically advantageous brachytherapy plans (i.e. obtain the same quality dose distribution as a standard single-activity plan) while incorporating leftover seeds from a previous patient treatment. This method will allow a clinic to continue to provide excellent patient care, but at a reduced cost. Multi-activity hybrid plans were equal in quality (as measured by the standard dosimetric indices) to plans with seeds of a single activity. Despite the expanded search space, optimization times for these studies were still under two minutes on a modern day laptop and can be reduced to below one minute in a clinical setting. With the typical cost of a set of PPI seeds on the order of thousands of dollars, it is possible to reduce the cost of brachytherapy treatments by allowing for easier use of seeds left over from a previous patient or unused due to a cancelled treatment.

Planning Fireworks Trajectories for Steerable Medical Needles to Reduce Patient Trauma

Accurate insertion of needles to targets in 3D anatomy is required for numerous medical procedures. To reduce patient trauma, a "fireworks" needle insertion approach can be used in which multiple needles are inserted from a single small region on the patient's skin to multiple targets in the tissue. In this paper, we explore motion planning for "fireworks" needle insertion in 3D environments by developing an algorithm based on Rapidly-exploring Random Trees (RRTs). Given a set of targets, we propose an algorithm to quickly explore the configuration space by building a forest of RRTs and to find feasible plans for multiple steerable needles from a single entry region. We present two path selection algorithms with different optimality considerations to optimize the final plan among all feasible outputs. Finally, we demonstrate the performance of the proposed algorithm with a simulation based on a prostate cancer treatment environment.