Contamination Resulting From a Broken 125I Seed During a Brachytherapy Procedure.

ABSTRACT: Brachytherapy programs within radiation therapy departments are subject to stringent radiation safety requirements in order to ensure the safety of the staff and patients. Training programs often include brachytherapy-specific radiation safety training modules that address the specific risks associated with radioactive sources, emergency procedures, and regulatory requirements specific to the use of radioisotopes. Unlike other uses of radioactive materials, brachytherapy uses sealed sources and therefore under routine operations does not encounter radioactive contaminants. This article presents an unusual clinical situation in which an 125I brachytherapy seed was damaged during routine clinical workflow, resulting in radioactive contamination within the clinical environment. Decisions made at the time of the incident resulted in contamination that spread beyond the initial location. The incident highlighted a shortcoming of the radiation safety program in preparing staff for the possibility of having to deal with unsealed radioactivity. Brachytherapy programs would be strengthened by including training specific to radioactive contamination in their emergency training to equip staff to respond to unexpected damage to the sealed sources.

Dosimetric consequences of misalignment and realignment in prostate 3DCRT using intramodality ultrasound image guidance.

PURPOSE: It is common practice to correct for interfraction motion by shifting the patient from reference skin marks to better align the internal target at the linear accelerator's isocenter. Shifting the patient away from skin mark alignment causes the radiation beams to pass through a patient geometry different from that planned. Yet, dose calculations on the new geometry are not commonly performed. The intention of this work was to compare the dosimetric consequences of treating the patient with and without setup correction for the common clinical scenario of prostate interfraction motion. METHODS: In order to account for prostate motion, 32 patients initially aligned to the room lasers via skin marks were realigned under the treatment beams by shifting the treatment couch based on ultrasound image guidance. An intramodality 3D ultrasound image guidance system was used to determine the setup correction, so that errors stemming from different tissue representations on different imaging modalities were eliminated. Two scenarios were compared to the reference static treatment plan: (1) Uncorrected patient alignment and (2) corrected patient alignment. Prostate displacement statistics and the dose to the clinical target volume (CTV), bladder, and rectum are reported. Monte Carlo dose calculation methods were employed. RESULTS: Comparing the uncorrected and corrected scenarios using the static treatment plan as the reference, the average percent difference in D95 for the CTV improved from -5.1% (range -40%, 1.3%) to 0.0% (-3.5%, 2.0%) and the average percent difference in V90 for the bladder and rectum changed from -11% (-84%, 232%) to -8.3% (-61%, 5.2%) and from -47% (-100%, 108%) to 0.9% (-62%, 102%), respectively. There was no simple correlation between displacement and dose discrepancy before correction. After patient realignment, the prescribed dose to the CTV was achieved within 1% for 75% (24/32) of the patients. After patient realignment, 50% of the patients had doses that differed from the static treatment plan by 25% for the bladder and 8% for the rectum. CONCLUSIONS: The dose degradation due to prostate motion (before correction) is not accurately predicted from the average trends for all patients. Outliers included smaller displacements that lead to larger dosimetric differences in the corrected scenario, especially for the bladder and rectum, which exhibited doses substantially different from that planned.

Dosimetric evolution of the breast electron boost target using 3D ultrasound imaging.

PURPOSE: To investigate the effect of treatment planning, patient setup, and interfraction motion errors on the delivered dose for external beam electron boosts for postoperative early stage breast cancer patients. METHODS AND MATERIALS: For 5 patients, 10-15 Gy was prescribed and administered via a conventionally defined electron boost treatment field - no dose distribution was calculated. Two computed tomography (CT) data sets were acquired on an average of 47 days apart. Using Monte Carlo techniques the clinically defined electron beams were reconstructed on CT1 and CT2, and a dosimetric comparison between the two data sets was made. Additionally, 3D ultrasound (US) imaging was performed to monitor interfraction motion. 3D US images were acquired concurrently with the CT images, as well as prior to each boost fraction in the treatment room. Taking into account interfraction motion, the dose to the clinical target volume (CTV) was calculated. RESULTS: Based on conventionally determined treatment fields the CT1-based CTV D95 averaged 49% (range 12-89%) of the prescribed dose. Representing setup errors, the CT2-based CTV D95 averaged 47% (range 16-91%) of the prescribed dose. Considering interfraction motion, the average radial displacement was 11 mm, and the resulting CTV D95 was further reduced in 2/5 patients. CONCLUSIONS: Poor initial coverage at the time of planning is exacerbated by breast mobility and interfraction tumour bed motion, increasing the uncertainty in the delivered dose.