Evaluation of interfractional variation of organs and displacement of catheters during high-dose-rate interstitial brachytherapy for gynecologic malignancies

Proton Arc Therapy vs Interstitial HDR Brachytherapy in Gynecologic Cancer with Parametrial/pelvic Side Wall Extension

Purpose

To investigate whether volumetric-modulated proton arc therapy (VPAT) plans generate comparable doses to organs at risk (OARs) compared with interstitial high–dose-rate (iHDR) brachytherapy for patients with gynecologic cancer with disease extension to parametrial/pelvic side wall, who are not eligible for the aggressive procedure.

Materials and Methods

VPAT delivers proton arc beams by modulated energies at the beam nozzle while maintaining the same incident energy to the gantry during the arc rotation. Plans of 10 patients previously treated with iHDR brachytherapy for high-risk clinical treatment volumes (HRCTV; 31.8–110.6 cm³; lateral dimensions, 4.2–5.6 cm) were selected and compared with VPAT plans. VPAT plans for each patient were designed using a 152- to 245-MeV range of energy-modulated proton beams.

Results

HRCTV coverage of the VPAT plans was comparable to that of the iHDR plans, with V150% showing no statistical differences. On average, the V100% and V90% of VPAT plans were higher than those of the iHDR plans, 95.0% vs 91.9% (P = .02) and 98.6% vs 97.5% (P = .02), respectively. D100 was also 17% higher for the VPAT plans (P = .03). On average, the D_2cm³ of bladder, rectum, and small bowels in the VPAT plans were considerably lower than those in iHDR plans (by 17.4%, 35.2%, and 65.6%, respectively; P < .05 for all OARs).

Conclusion

VPAT–generated plans were dosimetrically superior to those with HDR brachytherapy with interstitial needles for locally advanced gynecologic cancer with parametrial/pelvic side wall disease extension. Dosimetrically, VPAT provides a noninvasive alternative to iHDR brachytherapy with a superior dosimetric profile.

Effect of bladder volume on radiation doses to organs at risk and tumor in cervical cancer during image-guided adaptive brachytherapy and treatment outcome analysis

There is no consensus in clinical practice on the optimal bladder volume during brachytherapy. The present study aimed to assess the effect of bladder volume on radiation dose to organs at risk and tumor in cervical cancer during image-guided adaptive brachytherapy and clinical outcome. The retrospective study included patients treated at University of Hong Kong-Shenzhen Hospital between January 2015 and July 2019. Patients with International Federation of Gynecology and Obstetrics (2009) stage IB1-IVB (retroperitoneal lymph nodes metastasis only) cervical cancer treated by external beam radiotherapy with concurrent cisplatin followed by brachytherapy were assessed. A total of 421 brachytherapy insertions were analyzed. Every 83 and 90 cm³ (cc) increase in bladder volume led to an incremental raise of 1 Gy in bladder wall minimum dose received by the most irradiated 1 and 2 cc volumes (D1 and D2cc) of the bladder wall, respectively. An increase in bladder volume was associated with increased D1 and D2cc of bladder (both P<0.001, respectively) and rectal wall (P=0.150 and P=0.084, respectively), and decreased D1cc (P=0.003) and D2cc (P=0.001) of sigmoid wall, the maximum doses to the most minimally exposed 90 (D90) and 95% (D95) of the high risk-clinical target volume (HR-CTV; D90, P=0.010; D95, P=0.006). Patients with cumulative HR-CTV D90≤89.6 Gy had shorter median overall survival (OS) than those with cumulative HR-CTV D90>89.6 Gy (42.1 months vs. not reached, P=0.001). Patients with grade 2 acute urinary toxicity had significantly higher cumulative bladder wall D2cc than those with acute urinary toxicity<grade 2 (86.7±3.7 vs. 78.5±7.9 Gy; P=0.001). As the bladder volume increased, the dose to the bladder and rectal wall increase and dose to the sigmoid colon wall and HR-CTV decrease based on intracavitary brachytherapy. The higher dose of HR-CTV predicted better OS and the higher dose received by the bladder wall was associated with more grade 2 acute urinary toxicity.

Steering a Tendon-Driven Needle in High-Dose-Rate Prostate Brachytherapy for Patients with Pubic Arch Interference

High-dose-rate brachytherapy (HDR BT) is a radiation therapy that places radioactive sources at cancerous tissue using needles. HDR BT offers better dose conformality and sparing of clinical structures, lower operator dependency, and fewer acute irritative symptoms compared to the other form of BT (low-dose-rate (LDR)). However, use of HDR BT is limited for patients with pubic arch interference, where the transperineal path to the prostate is blocked. This study aims to introduce a tendon-driven needle that can bend inside tissue to reach desired positions inside prostate. Initial experiments in a phantom tissue showed the feasibility of the needle to get around the pubic arch for placement at hard-to-reach target positions.

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.

Inter-fractional variation of markers and applicators in single-implant high-dose-rate interstitial brachytherapy for gynecologic malignancies

PURPOSE

Implanted fiducial markers are a commonly used tool in delineating the CTV in high-dose-rate interstitial brachytherapy (HDR-ISBT) for gynecologic malignancy, but their reliability in gynacological sites is not well understood. These markers and interstitial applicators can experience interfractional motion due to organ swelling or other anatomical changes. The purpose of this study was to evaluate the spatial variation of these features.

METHODS AND MATERIALS

The spatial positions of 50 implanted markers and 202 needles were tracked in 15 patients treated over 70 fractions of HDR brachytherapy. Marker and/or needle coordinates were extracted from CT images with contours and dose distributions. Automated analysis determined marker self-consistency and displacements between various elements of the implant.

RESULTS

From start to end fraction, the relative positions of the markers experienced an average magnitude displacement of 4.5 ± 3.0 mm while the average displacement of the applicator tips was 11 ± 8 mm, relative to their respective centers of mass (CM).

CONCLUSIONS

Markers implanted lateral and superior to the CTV experience greater drift than other implant locations.

Design, Fabrication, and Testing of a Flexible Three-Dimensional Printed Percutaneous Needle With Embedded Actuators

Percutaneous needle-based procedures have replaced open surgeries in cancer treatments to perform the tasks with minimal invasiveness to the tissue. Precise placement of the needle at target positions in cancer diagnostic (e.g., breast biopsy) or therapeutic (e.g., prostate brachytherapy) procedures governs the success of such procedures. Also, in many needle insertion applications, it is desired to steer away from critical organs or to maneuver around anatomical obstacles in tissue. This work introduces a flexible three-dimensional (3D) printed percutaneous needle with embedded actuators for improved navigation inside the tissue toward the target. The needle is manipulated via a programmed portable motorized control unit to realize an average angular deflection of about 15 and 14 deg in air and a tissue-mimicking phantom, respectively. We demonstrated the needle's capability to reach the target, while avoiding obstacles. We also demonstrated that the flexible needle can be guided through a desired trajectory by controlling its angular deflection and axial movement. The 3D deflection of the needle is expected to assist in breast cancer lumpectomy for multiple extractions of tissue samples or in prostate brachytherapy via a curvilinear approach. The flexible needle may help reducing the complexity of current path planning algorithms, and thereby improve efficiency of closed-loop control systems in needle steering.

The impact of inter-fraction changes for perineal template-based interstitial gynecologic brachytherapy implants

Purpose

Perineal template-based interstitial gynecologic brachytherapy (ISBT) treatments are evaluated to determine whether adaptive inter-fraction re-planning is beneficial and necessary to meet the treatment aims of the American Brachytherapy Society (ABS) consensus guidelines for interstitial brachytherapy. Adherence to the EMBRACE II protocol is also assessed.

Material and methods

Ten patients receiving radical intent treatment for locally advanced or recurrent gynecologic malignancies underwent a three-fraction ISBT treatment with an ABS-recommended prescription regimen of 21 to 24 Gy. Clinical treatment plans were created according to a computed tomography (CT) acquired immediately post-implant. The first fraction was delivered on the same day as the implant (Day 1). The remaining two fractions were delivered on the next day (Day 2), at least six hours apart. Prior to treating on Day 2, a verification CT was acquired, permitting assessment of over-night changes. The Day 2 CT was used to evaluate deviations in 2-Gy-per-fraction equivalent dose (EQD₂) from the clinically intended dosimetry for clinical target volume (CTV), bladder, rectum, and sigmoid.

Results

For all patients, the median (range) difference between the intended and the delivered dosimetry for the CTV D90% was 1.4 Gy₁₀ (0.3-4.4 Gy₁₀). For all normal tissues, the median (range) difference from the intended normal tissue dose was 2.6 Gy₃ (0.1-15.5 Gy₃). In all cases, the deviation from clinically intended dosimetry did not lead to a violation of recommended normal tissue dose guidelines. For two of 10 patients with large normal tissue differences (> 10 Gy₃ from the intended dose), inter-fraction adaptive planning did improve the plan quality, but was not strictly required to meet the normal tissue dose planning aims.

Conclusions

The implementation of perineal template-based ISBT treatment without inter-fraction adaptive planning can be delivered to comply with the ABS normal tissue dose guidelines and EMBRACE II limits for prescribed dose.

Dosimetric impact of interfractional organs at risk variation during high-dose rate interstitial brachytherapy for gynecologic malignancies

We sought to develop a framework for the identification and management of patients at risk for organs at risk (OARs) overdosing due to interfractional anatomic variation during high-dose rate interstitial brachytherapy for gynecologic malignancies. We analyzed 40 high-dose rate interstitial brachytherapy fractions from 10 patients. Planned OAR doses were compared to delivered doses, which were calculated from computed tomography scans obtained prior to each treatment fraction. Doses were converted to equivalent doses in 2 Gy fractions (EQD2) and doses to the most exposed 2 cm³ (D_2cc) were reviewed. Patients were risk-stratified by identifying dose thresholds corresponding to a 10% or lower risk of receiving an OAR dose exceeding the corresponding planning constraint. For each OAR, 30% to 62.5% of patients received total doses greater than planned, although the magnitude of these differences was <4 Gy in over 75% of cases. Using EMBRACE II guidelines, one patient who had met the planning constraint for bladder and one for small bowel were found to have received doses exceeding the recommended limits. We next calculated thresholds for estimating the risk of OAR overdosing in individual patients and developed a framework based on these thresholds to direct time- and resource-intensive imaging and replanning efforts toward patients who are most likely to derive benefit. In summary, differential OAR dosing due to interfractional anatomic variation is common but likely rarely clinically meaningful. The proposed framework could decrease toxicity and maximize clinical efficiency.