Intraoperative implantation of a mesh of directional palladium sources (CivaSheet): Dosimetry verification, clinical commissioning, dose specification, and preliminary experience

Abstract

PURPOSE To present the clinical commissioning of a novel 103Pd directional brachytherapy device (CivaSheet™) for intraoperative radiation therapy. METHODS AND MATERIALS Clinical commissioning for the CivaSheet™ consisted of establishing: (i) source strength calibration capabilities, (ii) experimental verification of TG-43 dosimetry parameters, (iii) treatment planning system validation, and (iv) departmental practice for dose specification and source ordering. Experimental verification was performed in water with radiochromic film calibrated with a 37kVp x-ray beam. Percentage difference ([measurements – calculation] / calculation) and distance to agreement (difference between film-to-source distance and distance that minimized the percentage difference) were calculated. Nomogram values (in U/100 Gy) for all configuration (up to 20 × 20 sheets) were calculated for seed ordering. Clinical commissioning was used on patients enrolled in an ongoing IRB-approved protocol. Results A source calibration procedure was established and the treatment planning system was commissioned within standard clinical uncertainties. Percentage dose differences (distances to agreement) between measured and calculated doses were 8.6% (−0.12mm), 0.6% (−0.01mm), −6.4% (0.22mm), and −15.8% (0.72mm) at depths of 2.3mm, 5.1mm, 8.0mm, and 11.1mm respectively. All differences were within the experimental uncertainties. Nomogram values depended on sheet size and spatial extent. A value of 2.4U/100 Gy per CivaDot™ was found to satisfy most cases, ranging from 2.3 to 3.3U/100 Gy. Nomogram results depended on elongation of the treatment area with a higher variation observed for smaller treatment areas. Post-implantation dose evaluation was feasible. CONCLUSIONS Commissioning and clinical deployment of CivaSheet™ was feasible using BrachyVision™ for post-operative dose evaluation. Experimental verification confirmed that the available TG-43 dosimetry parameters are accurate for clinical use.

Systematic Review of Intensity-Modulated Brachytherapy (IMBT): Static and Dynamic Techniques

“…Static-shielded LDR sources such as eye plaques are commercially available, and the CivaSheet (CivaTech Oncology, Inc, Durham, NC) ( Fig. 1A) 58,63,133 are in ongoing clinical trials.…”

“…"Static" techniques included any shielded technique in which the shield did not move relative to the source or regions of interest during treatment. The shield could be associated with the applicator or the source directly (subcategories "static-shielded applicators" [46][47][48][49] and "static-shielded sources," [53][54][55][56][57][58][59][60][61][62][63][64] respectively), but a given approach was not included if a static shield was solely associated with an OAR for its sparing and not with the source or applicator (eg, mandibular shields in head and neck BT). Techniques were considered "dynamic" if the shield was translated or rotated during treatment relative to the source or regions of interest as part of the treatment plan.…”

“…1B), 53,56,57,59,61,64 or intraoperative BT for pancreatic, abdominopelvic, and colorectal cancer. 54,55,58,62,63 Lin et al introduced directional D-shaped 125 I sources with a 0.2 mm-thick gold shield for interstitial LDR-BT to achieve an angular uniform dose over a 180-degree sector around the axis of the source in the transverse plane. 60 They reported dosimetric validation results for breast cancer when compared with 192 Irbased high-dose-rate (HDR)-BT plans, and the treatmentplanning technique for the directional, D-shaped LDR source (Fig.…”

“…36,38,40,46,48,49,[84][85][86][87][88]95,96 Studies have demonstrated favorable incidence rates for 3-year local recurrence (6%-16.9%), clinical complete response (63.8%-96%), organ preservation (62%-96%), grade 3 acute toxicity (constipation/diarrhea or incontinence, 6.7%-9%) and late toxicity (bleeding, 9%-28%), and good-excellent bowel function (85%) at 2.5 to 3 years of median followup. 38,40,48,49 Other, multiple, or no specific disease site Studies of IMBT have also included other sites such as the pancreas, 63 multiple malignant sites (an ongoing clinical trial of any solid tumor of the abdomen or pelvis), 58 no specific disease sites, 55,62 and nonmalignant applications, such as intravascular BT for coronary artery disease. 72,81 None of these studies performed systematic comparisons between conventional BT and IMBT plans for target coverage, OAR sparing, or both or inverse planning optimization and delivery times.…”

“…More studies of feasibility in computed tomography/magnetic resonance imaging compatibility, optimal shield/ source materials, planning algorithms, and applicator design are warranted. Especially in the case of dynamic IMBT techniques in prototype and early clinical phases, more studies of feasibility in workflow and commissioning 5,12,58,97,98 are needed to address practical barriers to clinical implementation. The increased degrees of freedom and mechanical complexity require studies addressing potential sources of error in dosimetry and treatment errors resulting from shield mispositioning.…”