Optimized penile surface mold brachytherapy using latest stereolithography techniques: A single-institution experience.

PURPOSE: To describe a technique of penile surface mold high-dose-rate (HDR) brachytherapy and early outcomes. METHODS AND MATERIALS: Five patients diagnosed with a T1aN0 squamous cell carcinoma of the penis were treated using a penile surface mold HDR brachytherapy technique. A negative impression of the penis was obtained using dental alginate. CT images were acquired of the penile impression; subsequently, a virtual model of the patient's penis was generated. The positive model was imported into a computer-assisted design program where catheter paths were planned such that an optimized offset of 5 mm from the penile surface was achieved. The virtual model was converted into a custom applicator. A total dose of 40 Gy was delivered in 10 fractions. Patients were followed at 1, 3, 6, and 12 months after treatment and then every 6 months thereafter. Toxicities were reported using Common Terminology Criteria for Adverse Events v4.0. RESULTS: All patients tolerated treatment well. Acute Grade 2 skin reactions were observed within the first month after treatment. Median followup was 35 months. Late Grade 1 skin toxicities were observed. One patient experienced a urethral stricture requiring dilatation. Two patients developed local recurrence. CONCLUSION: This technique allows the delivery of penile HDR brachytherapy as an outpatient procedure with minimal discomfort to the patient during each application and is a repeatable and accurate setup. This technique warrants validation in larger series with longer followup.

Technical Note: On EM reconstruction of a multi channel shielded applicator for cervical cancer brachytherapy: A feasibility study.

PURPOSE: Electromagnetic tracking (EMT) is a promising technology for automated catheter and applicator reconstructions in brachytherapy. In this work, a proof-of-concept is presented for reconstruction of the individual channels of a new shielded tandem (140 mm long shield) dedicated to intensity-modulated brachytherapy. METHODS: All six channels of a straight prototype were reconstructed using an electromagnetic (EM) system from Aurora (NDI, Waterloo, ON, Canada). The influence of the shield on the EMT system was characterized by taking measurements at nine different positions with and without the shielded part of the applicator next to the probe. A Student t-test was used to analyze the data. RESULTS: For registration purposes, the center-to-center distance (4 mm) was taken from the computed-assisted design (CAD) structure. The computed interchannel distances from the three opposite pairs were 4.33 ± 0.40 mm, 4.14 ± 0.35 mm, and 3.88 ± 0.26 mm. All interchannel distances were within the geometrical tolerance in the shielded portion of the applicator (±0.6 mm) and account for the fact that the sensor (0.8 mm diameter) was smaller than the channel diameter. According to the paired Student t-test, the data given by the EM system with and without the shielded applicator tip are not significantly different. CONCLUSION: This study shows that the reconstruction of channel path is possible within the mechanical accuracy of the applicator.

Quantitative MRI assessment of a novel direction modulated brachytherapy tandem applicator for cervical cancer at 1.5T.

BACKGROUND AND PURPOSE: The purpose of this work is to quantitatively investigate the artifacts and image distortions induced in the MR images by a recently proposed direction modulated brachytherapy (DMBT) tandem applicator prototype. This new MRI-compatible applicator allows better sparing of organs-at-risk (OAR) for cervical cancer patients, while providing conformal dose distributions to target volumes. MATERIALS AND METHODS: Specific phantom and tools were designed and manufactured for this study. The phantom was filled with a tissue-like solution and MR images were acquired with clinical protocols as per GEC-ESTRO recommendations. Images were obtained at 6 different orientations that mimic possible clinical settings and full-width-at-half-maximum (FWHM) was recorded at multiple locations/angles. The accuracy of detecting the centerline of the tandem was assessed using a novel radial-fiducials mount. RESULTS: FWHM from all line profiles at all angles and all orientations was 6.14±0.7mm (compared to 6mm of the actual DMBT tandem diameter). The in-plane spatial-shift observed at para-axial and para-sagittal views was less than 0.5mm. CONCLUSIONS: This work demonstrated that the novel DMBT tandem applicator prototype has minimal artifact in T2-weighted images employed in clinical practice, suggesting the applicator might be a good candidate for MRI-guided adaptive brachytherapy.

Clinical evaluation of an endorectal immobilization system for use in prostate hypofractionated Stereotactic Ablative Body Radiotherapy (SABR).

BACKGROUND: The objective of this study was to evaluate a novel prostate endorectal immobilization system (EIS) for improving the delivery of hypofractionated Stereotactic Ablative Body Radiotherapy (SABR) for prostate cancer. METHODS: Twenty patients (n = 20) with low- or intermediate-risk prostate cancer (T1-T2b, Gleason Score < 7, PSA ≤ 20 ng/mL), were treated with an EIS in place using Volumetric Modulated Arc Therapy (VMAT), to a prescription dose of 26 Gy delivered in 2 fractions once per week; the intent of the institutional clinical trial was an attempt to replicate brachytherapy-like dosimetry using SABR. EBT3 radiochromic film embedded within the EIS was used as a quality assurance measure of the delivered dose; additionally, prostate intrafraction motion captured using pre- and post-treatment conebeam computed tomography (CBCT) scans was evaluated. Treatment plans were generated for patients with- and without the EIS to evaluate its effects on target and rectal dosimetry. RESULTS: None of the observed 3-dimensional prostate displacements were ≥ 3 mm over the elapsed treatment time. A Gamma passing rate of 95.64 ± 4.28 % was observed between planned and delivered dose profiles on EBT3 film analysis in the low-dose region. No statistically significant differences between treatment plans with- and without-EIS were observed for rectal, bladder, clinical target volume (CTV), and PTV contours (p = 0.477, 0.484, 0.487, and 0.487, respectively). A mean rectal V80% of 1.07 cc was achieved for plans using the EIS. CONCLUSIONS: The EIS enables the safe delivery of brachytherapy-like SABR plans to the prostate while having minimal impact on treatment planning and rectal dosimetry. Consistent and reproducible immobilization of the prostate is possible throughout the duration of these treatments using such a device.

Customized vaginal vault brachytherapy with computed tomography imaging-derived applicator prototyping.

PURPOSE: A novel customized vaginal brachytherapy mould technique has been developed for clinical use. This image-guided technique provides a brachytherapy applicator solution for irregular vaginal vault configuration and/or a wide vaginal apex relative to the vaginal introitus that would be sub-optimally treated with standard cylinders. METHODS: The customized vaginal applicator is generated by the following process: CT images are obtained with contrast-soaked vaginal packing in situ to highlight unique anatomical detail. A 3-dimensional digital model is developed from the images and subsequently converted into a custom applicator with the use of stereolithography, which is an additive manufacturing technique whereby layers 50-100 µm thick of resin are deposited and polymerized using a laser to create intricate 3-dimensional objects. The density of the applicator and the dose delivered using the custom applicator were both measured to ensure accurate dosimetry. RESULTS: The CT-based densities of a clinical vaginal cylinder and the cylinder generated using stereolithography were 1.29 ± 0.06 g/cm(3) vs 1.28 ± 0.01 g/cm(3), respectively. The mean measured dose from a representative stereolithographed applicator normalized to dose measured for a single plastic catheter was 99.8 ± 4.2%. In patient dosimetric results indicate improved coverage of the lateral aspect of vaginal vault with the custom cylinder relative to the standard cylinder; 700 cGy vs 328 cGy, respectively, at a representative lateral vaginal dose point, while simultaneously achieving relatively narrow dose distribution in the anterior/posterior direction. CONCLUSIONS: Stereolithographic applicator production was available within a clinically acceptable timeframe, and its clinical feasibility and utility has been demonstrated.

Design and construction of a quality control phantom for SPECT and PET imaging.

In this article, the authors present a method for quickly and easily constructing test phantoms for PET and SPECT quality assurance. As a demonstration, they constructed a complex prototype test phantom, showing the strengths of the construction method. Images taken using a PET/CT and a SPECT scanner are presented, along with a qualitative evaluation of PET/CT using the test phantom. The construction technique provides a quick, easy, and cost effective means of constructing a phantom for use in nuclear medicine imaging.

First report of a permanent breast 103Pd seed implant as adjuvant radiation treatment for early-stage breast cancer.

PURPOSE: A new technique of adjuvant partial breast irradiation using 103Pd permanent breast seed implants (PBSI) is presented. The procedure is performed in a single 1-hour session under local anesthesia. METHODS AND MATERIALS: Patients referred to a single institution for adjuvant radiotherapy after lumpectomy for an infiltrating ductal carcinoma < or = 3 cm in diameter, surgical margin > or = 2 mm, no extensive in situ carcinoma, no lymphovascular invasion, and minimal or negative lymph node involvement were offered a PBSI. RESULTS: Between May and December 2004, 31 eligible patients underwent CT scan and ultrasound simulations assessing PBSI feasibility. Fifteen were excluded because of feasibility issues, and 16 received PBSI. A minimal peripheral dose of 90 Gy was prescribed to the planning target volume corresponding to the clinical target volume identified on the CT scan plus a margin of 1 cm. The procedure was well tolerated; 56% of the patients reported no pain during the procedure, and 46% of the patients developed National Cancer Institute Common Toxicity Criteria Grade 1 acute reaction. None experienced toxicity Grade 2 or 3. CONCLUSIONS: Permanent breast seed implantation seems feasible and well tolerated on these preliminary clinical data and represents an ultimate step in the reduction of treatment fraction for partial breast irradiation.