Clinical Best Practices for Radiation Safety During Lutetium-177 Therapy.

IMPORTANCE: 177 Lu therapy as part of theranostic treatment for cancer is expanding but it can be a challenge for sites with limited radiation protection staff to implement the radiation safety program required for therapeutic nuclear medicine. OBJECTIVE: To increase the adoption of 177 Lu therapy, especially in smaller centers and clinics, by providing a collection of radiation safety best practices and operational experience. To provide a resource for radiation safety officers supporting the implementation of a 177 Lu therapy program. METHODS: A panel of 11 radiation safety professionals representing sites across Canada and the United States with experience delivering 177 Lu therapy was assembled and discussed their responses to a list of questions focused on the following radiation safety topics: facility layout and design; radiation safety program; and drug management and patient care. RESULTS: A comprehensive set of best practice guidelines for clinical radiation safety during 177 Lu therapy has been developed based on the collective operational experience of a group of radiation safety professionals. Significant findings included that 177 Lu therapy is often safely administered in unshielded rooms, that staff radiation exposure associated with 177 Lu therapy is minimal relative to other nuclear medicine programs, and that some relatively simple preparation in advance including papering of common surfaces and planning for incontinence can effectively control contamination during therapy. CONCLUSION: The guidance contained in this paper will assist radiation safety professionals in the implementation of safe, effective 177 Lu therapy programs, even at smaller sites with limited to no experience in therapeutic nuclear medicine.

Navigation and non-navigation CT scan of the sinuses: comparison of the effective doses of radiation in children and adults.

BACKGROUND: The advent of 3D navigation imaging has opened new borders to the endoscopic surgical approaches of naso-sinusal inflammatory and neoplastic disease. This technology has gained in popularity among otolaryngologists for endoscopic sinus and skull base surgeries in both adults and children. However, the increased tissue radiation required for data acquisition associated with 3D navigation protocols CT scans is a source of concern because of its potential health hazards. We aimed to compare the effective doses of radiation between 3D navigation protocols and standard protocols for sinus computed tomography (CT) scans for both the adult and pediatric population. METHODS: We performed a retrospective cohort study through electronic chart review of patients undergoing sinus CT scans (standard and 3D navigation protocols) from May 2019 to December 2019 using a Siemens Drive (VA62A) CT scanner. The effective dose of radiation was calculated in mSv for all exams. Average irradiation doses were compared using a Student's T-Test or a Kruskall-Wallis test when appropriate. RESULTS: A total of 115 CT scans were selected for analysis, of which 47 were standard protocols and 68 were 3D navigation protocols CT scans. Among these, 31 exams were performed on children and 84 exams on adults. For the total population, mean effective dose in the non-navigation CT scans was 0.37 mSv (SD: 0.16, N = 47) and mean effective dose in the 3D navigation sinus CT group was 2.33 mSv (SD: 0.45, N = 68). The mean difference between the two groups was statistically significant 1.97 mSv (CI 95% - 2.1 to - 1.83; P < 0.0001). There was a sixfold increase in radiation with utilization of 3D navigation protocols. The ratio was identical when the pediatric as well as the adult subset of patients were analyzed. CONCLUSION: In our center, utilization of 3D navigation sinus CT protocols significantly increases radiation exposure. Otolaryngologists should be aware of this significant increase and should attempt to decrease the radiation exposure of their patients by limiting unnecessary scan orders and by evaluating 3D acquisition protocols locally with radiation physicists. LEVEL OF EVIDENCE: Level IV.

A more efficient, radiation-free alternative to systematic chest x-ray for the detection of embolized seeds to the lung.

PURPOSE: To evaluate the efficacy of a seed-migration detector and to compare its performance to fluoroscopy and postoperative chest radiographs. METHODS AND MATERIALS: A gamma scintillation survey meter was converted to a seed-migration detector by adding a shield on the probe detection window. The detector response to three (125)I seed activities was characterized for different source-to-detector distances in water. The detector was used to perform a chest evaluation on 737 patients at their first postoperative visit. When the detector showed positive activity, seed migration was confirmed by taking a chest radiograph and by looking at the region with fluoroscopy. RESULTS: One hundred and three patients (14.0%) presented at least one embolized seed. This accounts for 123 of the 39,887 seeds. Eighty-seven, 12, and 4 patients had respectively one, two, and three seed embolization. Compared with the seed-migration detector, detection based on fluoroscopy would have led to 13 false-negative detections (of 103, or 12.6%), and the radiograph would have resulted in 31 or 30.1%. More important, standard chest X-ray would have required a survey and extra radiation dose to lung to 100% of the patients, rather than the 14% who required it. CONCLUSIONS: The usual recommendation to perform chest radiographs at the first follow-up visit to scan lungs for embolized seeds should be revised because of the high false-negative rate. Scintillator-based gamma counter detector provides superior detection sensitivity and should be adopted as a standard of practice. Chest X-ray could be limited to documenting cases of positive migration.

Commissioning and evaluation of an extended SSD photon model for PINNACLE3: an application to total body irradiation.

Total body irradiations (TBIs) are unusual radiation therapy techniques used to treat specific hematological diseases. Most TBI techniques use extended source to patient distances [source-to-skin distance (SSD)] to provide lateral or anteroposterior irradiations. Those techniques differ from one institution to the other since they need to be customized to accommodate for local material constraints. However, with those unusual techniques come additional challenges for dose calculation. The purpose of this study was to obtain an accurate (better than 4%) dose calculation model for extended source-to-skin distance (eSSD) treatment techniques, which will be used for TBI planning. The studied dynamic TBI technique has special aspects (eSSD, beam spoiler, large field, and out of field dose contribution) that need to be considered in dose calculation. The first part of this study presents an eSSD beam model commissioning in PINNACLE3 and its validation. The second part looks at the comparison between two dose calculation algorithms, the 3D pencil beam and the superposition-convolution algorithms implemented in THERAPLAN PLUS and PINNACLE3, respectively. A regular linac beam was commissioned in each treatment planning system and an additional dedicated TBI beam model was implemented in PINNACLE3. The comparison results indicate that the quality of the TBI treatment greatly depends on the treatment planning system and its beam commissioning. The superposition-convolution algorithm (PINNACLE3) provides a better dose calculation tool for TBI than the 3D pencil beam algorithm (THERAPLAN PLUS) with a maximum mean error of 2.2% on a dynamic treatment. The TBI specific beam model of PINNACLE3 (ESSP-P3) also improves the dose calculation. The maximum difference between calculations and measurements (depth doses and beam profiles) was 2% except for extreme cases (build-up region and depth of 20 cm) where the error was higher. Output factor determination and the dose contribution outside the primary beam weaknesses were found in PINNACLE3. Methods are proposed to overcome these limitations. With the correction method applied, the TBI specific beam model allows a maximum mean error of -0.68% on a dynamic treatment. Accurate TBI dose computation necessitates a good dose calculation algorithm combined with a realistic beam model. Inappropriate dose calculation could lead to an important over- or underdose estimation. No perfect algorithm and beam model were found, but methods are proposed to overcome some of the limitations. Those methods are simple and can be used for other eSSD treatment types.

Attenuator design for organs at risk in total body irradiation using a translation technique.

Total body irradiation (TBI) is an efficient part of the treatment for malignant hematological diseases. Dynamic TBI techniques provide great advantages (e.g., dose homogeneity, patient comfort) while overcoming treatment room space restrictions. However, with dynamic techniques come additional organs at risk (OAR) protection challenges. In most dynamic TBI techniques, lead attenuators are used to diminish the dose received by the OARs. The purpose of this study was to characterize the dose deposition under various shapes of attenuators in static and dynamic treatments. This characterization allows for the development of a correction method to improve attenuator design in dynamic treatments. The dose deposition under attenuators at different depths in dynamic treatment was compared with the static situation based on two definitions: the coverage areas and the penumbra regions. The coverage area decreases with depth in dynamic treatment while it is stable for the static situation. The penumbra increases with depth in both treatment modes, but the increasing rate is higher in the dynamic situation. Since the attenuator coverage is deficient in the dynamic treatment mode, a correction method was developed to modify the attenuator design in order to improve the OAR protection. The correction method is divided in two steps. The first step is based on the use of elongation charts, which provide appropriate attenuator coverage and acceptable penumbra for a specific depth. The second point is a correction method for the thoracic inclination, which can introduce an orientation problem in both static and dynamic treatments. This two steps correction method is simple to use and personalized to each patient's anatomy. It can easily be adapted to any dynamic TBI techniques.

Evaluation of an automatic needle-loading system.

The purpose of this paper is to evaluate the dosimetric capabilities and the radiation protection (RP) performance of a new automatic needle-loading system for permanent prostate implants, the Isoloader (Mentor Corp.). The unit has been used in more than 100 clinical cases at our institution. The Isoloader is a computerized workstation that allows automated seed testing by a solid-state CdZnTe radiation detector and loading in surgical needles. The seeds are received in a shielded and ready-to-use cartridge. Radiation protection measurements were done on a cartridge filled with 67 (125)I seeds and during dosimetric seed verification and needle loading. The reproducibility of the detector was tested and its accuracy was determined by comparison to specified activities of six calibration seeds and to their measurements in a calibrated well-chamber (WC). Finally, the times required to complete dosimetric verification and needle loading were evaluated. The cartridge was found to be adequately shielded, since no significant amount of radiation was detected around it. Radiation during seed assay was found to be worst at the cartridge's bottom, where it has a value of 15.2 microSv/h (1.4 microSv/h at 10 cm). For the needle-loading task, measurements were performed with a typical needle (three seeds) at the shielded needle holder surface yielding 307.2 microSv/h (8.3 microSv/h at 20 cm). Seed dosimetric verification takes an average of 15 s/seed, while it takes a mean time of 50 s/needle to complete the loading task. Measurements of the six seed activities were within 0.65% of the ordered activities and 1.9% higher on average than those from the WC (min = 0.7%; max = 3.5%). The reproducibility of the measurements of the CdZnTe detector was excellent, with an average of 0.01% of deviation from a reference measurement (N = 120; = 1.9%). We therefore conclude that the Isoloader is a safe, fast, and effective needle-loading system.

Early clinical experience with anatomy-based inverse planning dose optimization for high-dose-rate boost of the prostate.

PURPOSE: To present an exhaustive dosimetric comparison between three geometric optimization methods and our inverse-planning simulated annealing (IPSA) algorithm, with two different prescriptions for high-dose-rate (HDR) boost of the prostate. The objective of this analysis was to quantify the dosimetric advantages of the IPSA algorithm compared with more standard geometric optimizations. METHODS AND MATERIALS: Between September 1999 and June 2001, 34 patients were treated to a dose of 40-44 Gy by external pelvic fields, followed by an HDR boost of 18 Gy in 3 fractions. The first 4 patients were treated with HDR using geometric optimization, and anatomy-based inverse-planning dose optimization was used for the remaining 30 patients. We retrospectively used the data from these 30 patients to create HDR dose distributions according to five different dose optimization protocols, including our IPSA algorithm. The various geometric optimization procedures differed in the way the dwell positions were activated and plan normalization was performed. Dose-volume histograms from all these plans were analyzed and multiple implant quality indexes extracted. RESULTS: The IPSA algorithm provided better clinical tumor volume prescription dose coverage than did the geometric optimizations. The average prostate volume receiving 100% of the prescribed dose (V100) was 96.3% and 94.5% for IPSA with two different prescriptions compared with 92.1%, 92.6%, and 88.8% for the three geometric optimization schemes. The average urethra V150 value was 0.0% and 0.7% for IPSA with two different prescriptions, and the three geometric optimization protocols generated average values of 22.9%, 33.9%, and 38.8%. The bladder and rectal dose-volume histograms were similar, although the latest version of the IPSA algorithm slightly decreases the dose to these organs at risk because of organ-specific dose constraints included in the objective function. CONCLUSION: We found that planning an HDR prostate boost could be performed in a fast, secure, and effective manner with the IPSA algorithm. We demonstrated that our inverse-planning algorithm produces superior HDR plans than more conventional geometric optimizations for adenocarcinoma of the prostate. The organs at risk protection included in the objective function is a major feature of the algorithm and should allow us to escalate the HDR dose to the prostate without increasing undesirable side effects.