Feasibility and clinical implementation of MRI-guided surface brachytherapy.

Purpose: Best practices for high-dose-rate surface applicator brachytherapy treatment (SABT) have long relied on computed tomography (CT)-based imaging to visualize diseased sites for treatment planning. Compared with magnetic resonance (MR)-based imaging, CT provides insufficient soft tissue contrast. This work described the feasibility of clinical implementation of MR-based imaging in SABT planning to provide individualized treatment optimization. Material and methods: A 3D-printed phantom was used to fit Freiberg flap-style (Elekta, The Netherlands) applicator. Images were taken using an optimized pointwise encoding time reduction with radial acquisition (PETRA) MR sequence for catheter visualization, and a helical CT scan to generate parallel treatment plans. This clinical study included three patients undergoing SABT for Dupuytren's contracture/palmar fascial fibromatosis imaged with the same modalities.SABT planning was performed in Oncentra Brachy (Elekta Brachytherapy, The Netherlands) treatment planning software. A geometric analysis was conducted by comparing CT-based digitization with MR-based digitization. CT and MR dwell positions underwent a rigid registration, and average Euclidean distances between dwell positions were calculated. A dosimetric comparison was performed, including point-based dose difference calculations and volumetric segmentations with Dice similarity coefficient (DSC) calculations. Results: Euclidean distances between dwell positions from CT-based and MR-based plans were on average 0.68 ±0.05 mm and 1.35 ±0.17 mm for the phantom and patients, respectively. The point dose difference calculations were on average 0.92% for the phantom and 1.98% for the patients. The D95 and D90 DSC calculations were both 97.9% for the phantom, and on average 93.6% and 94.2%, respectively, for the patients. Conclusions: The sub-millimeter accuracy of dwell positions and high DSC's (> 0.95) of the phantom demonstrated that digitization was clinically acceptable, and accurate treatment plans were produced using MR-only imaging. This novel approach, MRI-guided SABT, will lead to individualized prescriptions for potentially improved patient outcomes.

Observer preference of artificial intelligence-generated versus clinical prostate contours for ultrasound-based high dose rate brachytherapy.

BACKGROUND: For trans-rectal ultrasound (TRUS)-based high dose rate (HDR) prostate brachytherapy, prostate contouring can be challenging due to artifacts from implanted needles, bleeding, and calcifications. PURPOSE: To evaluate the geometric accuracy and observer preference of an artificial intelligence (AI) algorithm for generating prostate contours on TRUS images with implanted needles. METHODS: We conducted a retrospective study of 150 patients, who underwent HDR brachytherapy. These patients were randomly divided into training (104), validation (26) and testing (20) sets. An AI algorithm was trained/validated utilizing the TRUS image and reference (clinical) contours. The algorithm then provided contours for the test set. For evaluation, we calculated the Dice coefficient between AI and reference prostate contours. We then presented AI and reference contours to eight clinician observers, and asked observers to select their preference. Observers were blinded to the source of contours. We calculated the percentage of cases in which observers preferred AI contours. Lastly, we evaluate whether the presence of AI contours improved the geometric accuracy of prostate contours provided by five resident observers for a 10-patient subset. RESULTS: The median Dice coefficient between AI and reference contours was 0.92 (IQR: 0.90-0.94). Observers preferred AI contours for a median of 57.5% (IQR: 47.5, 65.0) of the test cases. For resident observers, the presence of AI contours was associated with a 0.107 (95% CI: 0.086, 0.128; p < 0.001) improvement in Dice coefficient for the 10-patient subset. CONCLUSION: The AI algorithm provided high-quality prostate contours on TRUS with implanted needles. Further prospective study is needed to better understand how to incorporate AI prostate contours into the TRUS-based HDR brachytherapy workflow.

AAPM medical physics practice guideline 13.a: HDR brachytherapy, part A.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines (MPPGs) will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: (1) Must and must not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. (2) Should and should not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances. Approved by AAPM's Executive Committee April 28, 2022.

Catheter reconstruction and dosimetric verification of MRI-only treatment planning (MRTP) for interstitial HDR brachytherapy using PETRA sequence.

Objective. The feasibility of MRI-only treatment planning (MRTP) for interstitial high-dose rate (HDR) brachytherapy (BT) was investigated for patients diagnosed with gynecologic cancer.Approach. A clinical MRTP workflow utilizing a 'pointwise encoding time reduction with radial acquisition (PETRA)' sequence was proposed. This is a clinically available MRI sequence optimized to improve interstitial catheter-tissue contrast. Interstitial needles outside the obturator region were reconstructed using MR images only. For catheters penetrating through the obturator, a library-based reconstruction was proposed. In this work, dwell coordinates from the clinical CT-based reconstruction were used as the surrogate for the library-based approach. For MR-only plan, dwell times were activated and assigned as in the clinical plans. The catheter reconstruction was assessed by comparing dwell position coordinates. The dosimetric comparisons between a clinical plan and MR-only plan were assessed for physical and EQD2 dose and volume parameters forD90,D50andD98for clinical target volume (CTV) andD2cc,D0.1ccandD5ccfor OARs.Main results. Catheter reconstruction was possible using the optimized PETRA sequence on MR images. An overall reconstruction difference of 1.7 ± 0.5 mm, attributed to registration-based errors, was found compared to the CT-based reconstruction. The MRTP workflow has the potential to generate a treatment plan with an equivalent dosimetric quality compared to the conventional CT/MRI-based approach. For CTVD90, physical and EQD2 dose and volume parameter differences were 1.5 ± 1.9% and 0.7 ± 1.0 Gy, respectively. ForD2ccOARs, DVH (EQD2) differences were -0.4 ± 1.1% (-0.2 ± 0.5 Gy), 0.5 ± 2.8% (0.2 ± 1.3 Gy) and -0.5 ± 1.4% (-0.2 ± 0.5 Gy) for rectum, bladder, and sigmoid, respectively.Significance. With the proposed MRTP approach, CT imaging may no longer be needed in HDR BT for interstitial gynecologic treatment. A proof-of-concept study was conducted to demonstrated that MRTP using PETRA is feasible, with comparable dosimetric results to the conventional CT/MRI-based approach.

First pointwise encoding time reduction with radial acquisition (PETRA) implementation for catheter detection in interstitial high-dose-rate (HDR) brachytherapy.

PURPOSE: A pointwise encoding time reduction with radial acquisition (PETRA) sequence was optimized to detect empty catheters in interstitial (HDR) brachytherapy with clinically acceptable spatial accuracy for the first time. Image quality and catheter detectability were assessed in phantoms, and the feasibility of PETRA's clinical implementation was assessed on a gynecological cancer patient. METHODS AND RESULTS: Empty catheters embedded in a gelatin phantom displayed positive signal on PETRA and more accurate cross-sections than on clinically employed T2-weighted sequences, differing by 0.4 mm on average from their nominal 2 mm diameter. PETRA presented minimal susceptibility differences and a symmetric metal artifact, contrary to the clinical sequences. The PETRA-CT catheter tip position differences assessed by a treatment planning system (TPS) were < 1 mm. PETRA also detected an interstitial template with empty catheters penetrating a poultry phantom and fused very well with CT. Interstitial catheter positional difference between PETRA and CT images was < 1 mm on average, increasing with distance from isocenter. All interstitial catheters and the employed interstitial template were detected on PETRA images of an endometrial adenocarcinoma patient. Empty needles were traceable using a TPS, with higher spatial resolution and more favorable contrast than on T2-weighted images used for contouring. A treatment plan could be produced by combining information from PETRA for catheter detection and from T2-weighted images for tumor and organs delineation. CONCLUSIONS: PETRA detected successfully and accurately interstitial catheters in phantoms. Its first clinical implementation shows a potential for MR-only treatment planning in interstitial HDR brachytherapy.

Clinical outcomes and dosimetric predictors of toxicity for re-irradiation of vaginal recurrence of endometrial cancer.

OBJECTIVE: To report clinical outcomes and dosimetric predictors of late toxicity for patients with vaginal recurrence of endometrial cancer treated with brachytherapy in the re-irradiation setting. METHODS: On retrospective review, 32 patients with vaginal recurrence of endometrial cancer received salvage brachytherapy with or without pelvic radiotherapy (RT) from 06/2003-12/2017. Prior RT modalities were vaginal brachytherapy (19, 59%), pelvic RT (7, 22%) or both (6, 19%). Image-guided brachytherapy was performed with CT- (25, 78%) or MR-guidance (7, 22%). Vaginal control, recurrence-free survival (RFS) and overall survival (OS) were estimated by Kaplan-Meier method. Late toxicity was graded by Common Toxicity Criteria for Adverse Events. RESULTS: Median time from prior RT to re-irradiation was 22 months (range, 4-140). Salvage RT modalities were pelvic RT and brachytherapy (25, 78%) or brachytherapy alone (7, 22%). With median follow-up of 47 months, 3/5-year vaginal control, RFS and OS rates were 64/56%, 47/41% and 68/42%, respectively. Six patients (19%) had no evidence of disease at 85-155 months. Late grade 2/3 GI, GU and vaginal toxicity rates were 13%/16%, 19%/13%, and 9%/16%. Cumulative D2cc rectum (sum of prior and salvage RT courses) was predictive of grade 2+ and grade 3 GI toxicity. Cumulative D2cc rectum for an estimated 10% risk of late grade 2+ and 3 GI toxicity was 86 Gy and 92 Gy, respectively. CONCLUSIONS: Salvage image-guided brachytherapy in the re-irradiation setting results in modest local control and increased late toxicity for localized recurrent endometrial cancer. With long-term disease control, cumulative D2cc rectum may be used to reduce late GI complication risk.

Interfraction dose deviation and catheter position in cervical interstitial and intracavitary image guided HDR brachytherapy.

Interstitial and intracavitary gynecological HDR brachytherapy involve precise, localized delivery to targets with high dose gradients, sparing adjacent organs at risk (OAR). Due to the proximity of the rectum, bowel and bladder to the target, deviations in the applicator or catheter with respect to patient anatomy can significantly increase dose to OAR. The magnitude and direction of applicator and catheter migration at each fraction was assessed for template interstitial and tandem and ring (T&R) cohorts. The cohort included twelve gynecological patients with intact cervical lesions treated with external beam and brachytherapy. Pre-treatment CT images were registered to the simulation CT with respect to the target. Treatment catheter positions transformed into the planning CT coordinate system to evaluate localized catheter displacement and dose distributions calculated at each fraction. Dose was evaluated on the planning CT with planning contours and dwell locations at treatment position. Absolute deviation, depth and deflection angle for all patients were 4.6 ± 4.2 mm, -1.4 ± 4.0 mm, and 3.1 ± 2.3° respectively (n = 516 catheter positions for all treatment fractions and patients, mean ± SD). Absolute catheter deviation and deflection magnitude for interstitial treatments increased overall with each subsequent fraction with an overall increase of catheter retraction at each fraction (p < 0.005, n = 492 catheters, Kruskal-Wallis). A target EQD2 D90 reduction of 10 ± 10% and 7.7 ± 8.7% of the planned dose for interstitial and T&R cohorts respectively. There was an overall increase in bladder and rectal doses at each fraction. Catheter tracking in interstitial and intracavitary gynecological treatments with CT imaging revealed significant changes in catheter positioning with respect to the target volume. Overall deviations increased in magnitude with each subsequent fraction in the interstitial treatments. This caused patient dosimetry deviations, including target dose reduction and adjacent OAR doses changes.

Feasibility of magnetic resonance-only high-dose-rate surface brachytherapy for clinical application.

PURPOSE: In this article, we investigate the feasibility of magnetic resonance (MR)-only imaging for high-dose-rate (HDR) surface brachytherapy (SABT). We examined whether a standard CT-based planning can be replaced with an MR-only planning. For this purpose, the MRI digitization and plan quality check processes were compared against the standard CT-based processes. A prospective clinical implementation of the MR-only planning was evaluated on a clinical data set. METHODS: A pointwise encoding time reduction with radial acquisition (PETRA) sequence was optimized for visualization of Freiburg flap (FF) on MR images. MR and conventional CT images were acquired with a FF applicator (Elekta, Stockholm, Sweden) placed on the following phantoms: (1) flat styrofoam (FST), FF locked-in placed with supporting structure; (2) cast-made facemask, and (3) porcine leg (PL). Catheters were digitized and activated with 10 mm step size on Oncentra Brachy 4.5.3 Treatment Planning System. The CT-only and MR-only treatment plans were generated by optimizing the dose to the target defined as volume at 3 mm skin depth. To compare the plans, the MRI-to-CT alignment was performed via rigid registration. Positional displacements of dwell positions between CT and MR plans were compared on the FST phantom and the relative percent dose difference in 2210 different points from CT or MR-only plans was compared. For all three phantoms, the comparabilities between CT and MR-only plans were assessed by calculating dice similarity coefficient (DSC) for volumes enclosing 150%, 125%, 100%, 95%, 90%, 80%, and 65% isodose lines (V150  -V65 ). The MR images of FF placed on the forearm of a healthy subject were acquired with this optimized PETRA sequence and used for treatment planning. The relative percent dose was calculated on 140 representative points placed at 3 mm skin depth to evaluate the dose to the skin. RESULTS: Using the optimized PETRA sequence, MRTP digitization accuracy was < 1 mm in each dimension and on three-dimensional (3D) displacement for the FST phantom. In each phantom and clinical data set, it was possible to generate MR-only treatment plans with the 3 mm skin depth prescription. In the FST phantom, the mean relative dose at the points was not significantly different (< 0.1% difference) for CT or MR-based plans. The assessment of similarities in dose profiles between CT and MR-only plans' provided DSC values greater than 0.96, 0.92, and 0.73 for all volumes enclosing up to 100%, 125%, and 150% isodose lines, respectively. CONCLUSION: The feasibility of generating a HDR treatment plan with FF using MR-only has been evaluated in phantoms with varying geometry and for a clinical data set. The optimization of a standard MRI sequence-PETRA-implemented in this study showed that FF-based catheters can be digitized and a plan can be generated using only MRI. The resulting MR-only plans were comparable to the conventional CT-based plans, suggesting that MRI alone can generate clinically acceptable plans for FF in phantoms and on a clinical data set. Reliable MR-only treatment planning could improve treatment prescription through more accurate characterization of soft tissue targets.

Definitive radiotherapy for vaginal recurrence of early-stage endometrial cancer: survival outcomes and effect of mismatch repair status.

OBJECTIVE: To evaluate clinical outcomes, prognostic factors, and toxicity in patients with vaginal recurrence of early-stage endometrial cancer treated with definitive radiotherapy. METHODS: Retrospective review identified 62 patients with stage I-II endometrial cancer and vaginal recurrence treated with external beam radiotherapy and image-guided brachytherapy with definitive intent from November 2004 to July 2017. All patients had prior hysterectomy without adjuvant radiotherapy and >3 months follow-up. Mismatch repair (MMR) status was determined by immunohistochemical staining of the four mismatch repair proteins (MLH1, MSH2, PMS2, and MSH6) when available in the pathology record. Rates of vaginal control, recurrence-free survival, and overall survival were calculated by Kaplan-Meier. Univariate and multivariate analyses were performed by Cox proportional hazards. RESULTS: Most patients had endometrioid histology (55, 89%), grade 1 or 2 tumor (53, 85%), and vaginal-only recurrence (55, 89%). With a median follow-up of 39 months (range, 3-167), 3- and 5-year rates of vaginal control, recurrence-free survival, and overall survival were 86% and 82%, 69% and 55%, and 80% and 61%, respectively. On multivariate analysis, non-endometrioid histology (HR 12.5, P<0.01) was associated with relapse when adjusted for chemotherapy use. Patients with non-endometrioid histology also had a 4.5-fold higher risk of death when adjusted for age (P=0.02). Twenty patients had known MMR status, all with grade 1-2 endometrioid tumors and 10 (50%) with MMR deficiency. The 3-year recurrence-free survival was 100% for MMR-proficient tumors and 52% for MMR-deficient (P=0.03). Late grade 2 and 3 gastrointestinal, genitourinary and vaginal toxicity was reported in 27% and 3%, 15% and 2%, and 16% and 2% of patients, respectively. CONCLUSION: Definitive radiotherapy with image-guided brachytherapy resulted in 5-year local control rates exceeding 80% and late severe toxicity rates were under 3%. Distant recurrence was common and highest for those with grade 3 or non-endometrioid tumors and MMR deficient grade 1-2 disease.

Clinical outcomes following high-dose-rate surface applicator brachytherapy for angiosarcoma of scalp and face.

PURPOSE: Angiosarcoma is a sub-type of soft tissue sarcoma, often presenting as a multifocal or diffuse disease process with poor prognosis. This study presents outcomes of a single institution cohort of patients with angiosarcoma of the scalp and face following treatment with multimodality therapy, including high-dose-rate surface applicator (HDR-SA) brachytherapy, and represents the largest cohort utilizing this therapeutic approach. MATERIAL AND METHODS: Twenty patients with primary or recurrent angiosarcoma of the face or scalp were treated with HDR-SA brachytherapy between 2003-2018, with clinical characteristics and outcomes collected from medical records and used to identify prognostic features. RESULTS: Median follow-up was 45 months. Patients treated with HDR-SA brachytherapy had a 4-year local control rate of 63%, a 4-year progression-free survival (PFS) rate of 20%, and a 4-year overall survival rate of 54%. Disease features associated with worse loco-regional control (LRC) included location on the scalp (vs. face, p = 0.04) and tumor size ≥ 5 cm (p = 0.0099). Outcomes after HDR-SA brachytherapy for salvage therapy vs. HDR-SA brachytherapy as a component of an initial treatment approach were also significantly different, with worse LRC (p = 0.0084) and worse overall survival (OS) (p = 0.0019) in a setting of salvage therapy. CONCLUSIONS: Local control rates following HDR-SA brachytherapy for scalp or face angiosarcoma are moderate and similar to what is described in the literature using a variety of local control treatment modalities. Smaller tumors and those involving the face rather than scalp had better outcomes. PFS rates were poor and there is a pressing need for treatment intensification and novel therapeutic options.

Selection criteria for high-dose-rate surface brachytherapy and electron beam therapy in cutaneous oncology.

PURPOSE: High-dose-rate (HDR) brachytherapy is an alternative treatment to electron external beam radiation therapy (EBRT) of superficial skin lesions. The purpose of this study was to establish the selection criteria for HDR brachytherapy technique (HDR-BT) and EBRT in cutaneous oncology for various clinical scenarios. MATERIAL AND METHODS: The study consists of two parts: a) EBRT and HDR-BT treatment plans comparison analyzing clinical target volumes (CTVs) with different geometries, field sizes, and topologies, and b) development of a prediction model capable of characterization of dose distributions in HDR surface brachytherapy for various geometries of treatment sites. RESULTS: A loss of CTV coverage for the electron plans (D90, D95) was recorded up to 45%, when curvature of the applicator increased over 30°. Values for D2 cm3 for both plans were comparable, and they were in range of ±8% of prescription dose. An increase in higher doses (D0.5 cm3 and D0.1 cm3) was observed in HDR-BT plans, and it was greater for larger lesions. The average increase was 3.8% for D0.5 cm3 and 12.3% for D0.1 cm3. When CTV was approximately flat, electron plans were comparable with HDR-BT plans, having lower average D2 cm3, D0.5 cm3, and D0.1 cm3 of 7.7%. Degradation of quality of electron plans was found to be more dependent on target curvature than on CTV size. CONCLUSIONS: Both EBRT and HDR-BT could be used in treatments of superficial lesions. HDR-BT revealed superior CTV coverage when the surface was very large, complex, curvy, or rounded, and when the topology was complicated. The prediction model can be used for an approximate calculation and quick assessment of radiation dose to organs-at-risk (OARs), at a depth or at a lateral distance from CTV.

Knowledge-based inverse treatment planning for low-dose-rate prostate brachytherapy.

PURPOSE: Permanent low-dose-rate brachytherapy is a widely used treatment modality for managing prostate cancer. In such interventions, treatment planning can be a challenging task and requires experience and skills of the planner. We developed a novel knowledge-based (KB) optimization method based on previous treatment plans. The purpose of this method was to generate clinically acceptable plans that do not require extensive manual adjustments in clinical scenarios. METHODS: Objective functions used in current inverse planning methods are preferably based on spatial invariant dose objectives rather than spatial dose distributions. Therefore, they are prone to return suboptimal plans resulting in time consuming plan adjustments. To overcome this limitation, a KB approach is introduced. The KB model uses the dose distributions of previous clinical plans projected onto a standardized geometry. From those standardized distributions a template plan is generated. The treatment plans were optimized with an in-house developed planning system by solving a constraint inverse optimization problem that mimics the projected template dose plan constraint to DVH metrics. The method is benchmarked under an IRB-approved retrospective study by comparing optimization time, dosimetric performance, and clinical acceptability against current clinical practice. The quality of the KB model is evaluated with a Turing test. RESULTS: The KB model consists of five high-quality treatment plans. Those plans were selected by one of our experts and showed all desired dosimetric features. After generating the model treatment plans were created with one run of the optimizer for the remaining 20 patients. The optimization time including needle optimization ranged from 6 to 29 s. Based on a Wilcoxon signed rank test the new plans are dosimetrically equivalent to current clinical practice. The Turing test showed that the proposed method generates plans that are equivalent to current clinical practice and that the dose prediction drives the optimization to achieve high-quality treatment plans. CONCLUSIONS: This study demonstrated that the proposed KB model was able to capture user-specific features in isodose lines which can be used to generate acceptable treatment plans with a single run of the optimization engine in under a minute. This could potentially reduce the time in the operating room and the time a patient is under anesthesia.

Biopsy Needle System With a Steerable Concentric Tube and Online Monitoring of Electrical Resistivity and Insertion Forces.

OBJECTIVE: Biopsies are the gold standard for clinical diagnosis. However, a discrepancy between the biopsy sample and target tissue because of misplacement of the biopsy spoon can lead to errors in the diagnosis and subsequent treatment. Thus, correctly determining whether the needle tip is in the tumor is crucial for accurate biopsy results. METHODS: A biopsy needle system was designed with a steerable, flexible, and superelastic concentric tube; electrodes to monitor the electrical resistivity; and load cells to monitor the insertion force. The degrees of freedom were analyzed for two working modes: straight-line and deflection. RESULTS: Experimental results showed that the system could perceive the tissue type in online based on the electrical resistivity. In addition, changes in the insertion force indicated transitions between the interfaces of adjacent tissue layers. CONCLUSION: The two monitoring methods guarantee that the biopsy spoon is at the desired position inside the tumor during an operation. SIGNIFICANCE: The proposed biopsy needle system can be integrated into an autonomous robotic biopsy system.

Positional and angular tracking of HDR 192 Ir source for brachytherapy quality assurance using radiochromic film dosimetry.

PURPOSE: To quantify and verify the dosimetric impact of high-dose rate (HDR) source positional uncertainty in brachytherapy, and to introduce a model for three-dimensional (3D) position tracking of the HDR source based on a two-dimensional (2D) measurement. This model has been utilized for the development of a comprehensive source quality assurance (QA) method using radiochromic film (RCF) dosimetry including assessment of different digitization uncertainties. METHODS: An algorithm was developed and verified to generate 2D dose maps of the mHDR-V2 192 Ir source (Elekta, Veenendaal, Netherlands) based on the AAPM TG-43 formalism. The limits of the dosimetric error associated with source (0.9 mm diameter) positional uncertainty were evaluated and experimentally verified with EBT3 film measurements for 6F (2.0 mm diameter) and 4F (1.3 mm diameter) size catheters at the surface (4F, 6F) and 10 mm further (4F only). To quantify this uncertainty, a source tracking model was developed to incorporate the unique geometric features of all isodose lines (IDLs) within any given 2D dose map away from the source. The tracking model normalized the dose map to its maximum, then quantified the IDLs using blob analysis based on features such as area, perimeter, weighted centroid, elliptic orientation, and circularity. The Pearson correlation coefficients (PCCs) between these features and source coordinates (x, y, z, θy , θz ) were calculated. To experimentally verify the accuracy of the tracking model, EBT3 film pieces were positioned within a Solid Water® (SW) phantom above and below the source and they were exposed simultaneously. RESULTS: The maximum measured dosimetric variations on the 6F and 4F catheter surfaces were 39.8% and 36.1%, respectively. At 10 mm further, the variation reduced to 2.6% for the 4F catheter which is in agreement with the calculations. The source center (x, y) was strongly correlated with the low IDL-weighted centroid (PCC = 0.99), while the distance to source (z) was correlated with the IDL areas (PCC = 0.96) and perimeters (PCC = 0.99). The source orientation θy was correlated with the difference between high and low IDL-weighted centroids (PCC = 0.98), while θz was correlated with the elliptic orientation of the 60-90% IDLs (PCC = 0.97) for a maximum distance of z = 5 mm. Beyond 5 mm, IDL circularity was significant, therefore limiting the determination of θz (PCC ≤ 0.48). The measured positional errors from the film sets above and below the source indicated a source position at the bottom of the catheter (-0.24 ± 0.07 mm). CONCLUSIONS: Isodose line features of a 2D dose map away from the HDR source can reveal its spatial coordinates. RCF was shown to be a suitable dosimeter for source tracking and dosimetry. This technique offers a novel source QA method and has the potential to be used for QA of commercial and customized applicators.

Angiosarcoma of the Scalp and Face: A Dosimetric Comparison of HDR Surface Applicator Brachytherapy and VMAT.

PURPOSE: Angiosarcoma of the face and scalp is a rare disease with high rates of recurrence. The optimal treatment approach is not well defined. This study presents a dosimetric comparison of high-dose-rate surface applicator (HDR-SA) brachytherapy to volumetric-modulated arc therapy (VMAT). METHODS: Between 2011 and 2018, 12 patients with primary or recurrent angiosarcoma of the face or scalp were treated with HDR-SA brachytherapy using CT-based planning at our institution. For comparison, deliverable VMAT plans for each patient were generated, and dose distribution was compared to the delivered HDR-SA brachytherapy plans. RESULTS: Both VMAT and HDR-SA brachytherapy plans delivered good coverage of the clinical target. However, the dose distribution of VMAT was significantly different from HDR-SA brachytherapy across a variety of parameters. Mean doses to the lacrimal gland, orbit, lens, and cochlea were significantly higher with HDR-SA brachytherapy vs. VMAT. Brain Dmax, V80%, and V50% were also significantly higher with HDR-SA brachytherapy. CONCLUSIONS: There may be dosimetric advantages to VMAT over HDR-SA brachytherapy for many patients. However, individual tumor location, patient anatomy, and treatment reproducibility may result in HDR-SA brachytherapy being the preferred technique in a subset of patients. Ultimately, a personalized approach is likely to be the optimal treatment plan.

Surface brachytherapy: Joint report of the AAPM and the GEC-ESTRO Task Group No. 253.

The surface brachytherapy Task Group report number 253 discusses the common treatment modalities and applicators typically used to treat lesions on the body surface. Details of commissioning and calibration of the applicators and systems are discussed and examples are given for a risk-based analysis approach to the quality assurance measures that are necessary to consider when establishing a surface brachytherapy program.

Low-dose adjuvant vaginal cylinder brachytherapy for early-stage non-endometrioid endometrial cancer: recurrence risk and survival outcomes.

OBJECTIVE: The aim of this study was to evaluate recurrence patterns and survival outcomes for patients with early-stage non-endometrioid endometrial adenocarcinoma treated with adjuvant high-dose rate vaginal brachytherapy with a low-dose scheme. METHODS: A retrospective review was performed of patients with International Federation of Gynecology and Obstetrics (FIGO) stage I-II non-endometrioid endometrial cancer who received adjuvant vaginal brachytherapy with a low-dose regimen of 24 Gy in six fractions from November 2005 to May 2017. All patients had >6 months of follow-up. Rates of recurrence-free survival, overall survival, vaginal, pelvic, and distant recurrence were calculated by the Kaplan-Meier method. Prognostic factors for recurrence and survival were evaluated by Cox proportional hazards modeling. RESULTS: A total of 106 patients were analyzed. Median follow-up was 49 months (range 9-119). Histologic subtypes were serous (47%, n=50), clear cell (10%, n=11), mixed (27%, n=29), and carcinosarcoma (15%, n=16). Most patients (79%) had stage IA disease, 94% had surgical nodal assessment, and 13% had lymphovascular invasion. Adjuvant chemotherapy was delivered to 75%. The 5-year recurrence-free and overall survival rates were 74% and 83%, respectively. By histology, 5-year recurrence-free/overall survival rates were: serous 73%/78%, clear cell 68%/88%, mixed 88%/100%, and carcinosarcoma 56%/60% (p=0.046 and p<0.01). On multivariate analysis, lymphovascular invasion was significantly associated with recurrence (HR 3.3, p<0.01). The 5-year vaginal, pelvic, and distant recurrence rates were 7%, 8%, and 21%, respectively. Vaginal and pelvic recurrence rates were highest for patients with carcinosarcoma, lymphovascular invasion and/or FIGO stage IB/II disease. At 5 years, vaginal and pelvic recurrence rates for patients with lymphovascular invasion were 33% and 40%, respectively. Patients with stage IA disease or no lymphovascular invasion had 5-year vaginal recurrence rates of 4% and pelvic recurrence rates of 6% and 3%, respectively. CONCLUSIONS: Adjuvant high-dose rate brachytherapy with a low-dose scheme is effective for most patients with early-stage non-endometrioid endometrial cancer, particularly stage IA disease and no lymphovascular invasion. Pelvic radiation therapy should be considered for those with carcinosarcoma, lymphovascular invasion and/or stage IB/II disease.

Combined interstitial and surface high-dose-rate brachytherapy treatment of squamous cell carcinoma of the hand.

PURPOSE: We present a case report of treatment using interstitial and surface high-dose-rate (HDR) brachytherapy for cutaneous squamous cell carcinoma (SCC) involving the interspace of the third and fourth digits. The patient refused two-ray amputation and the lesion was not amenable for external beam radiation therapy (EBRT). This is the first report detailing combined interstitial and surface HDR brachytherapy for a hand SCC. MATERIAL AND METHODS: The patient received 4050 cGy in 9 fractions, twice daily using 6 interstitial catheters and 8 Freiburg flap catheters. The clinical target was defined by MRI and ultrasound as a dorsal mass to the interspace between the heads of the third and fourth metacarpals measuring approximately 7 mm transverse × 5 mm volar-dorsal × 16 mm proximal-distal. RESULTS: The treatment resulted in radiographic and clinical tumor control. The patient retained functional use of her hand. However, there were both acute and late treatment-related side effects. Acutely, inpatient admission for pain control with a nerve block was needed. Long-term toxicity was notable for grade 2 skin necrosis treated with hyperbaric oxygen. CONCLUSIONS: The first interstitial and surface HDR brachytherapy for cutaneous squamous cell carcinoma of a finger interspace for hand function preservation is presented. The initial experience revealed that brachytherapy was tolerated but with notable acute and late side effects. Treatment did result in tumor shrinkage with organ preservation and function of two rays. A larger cohort of patients will be required for additional conclusions related to long-term clinical benefits in patients who refuse ray amputation.