Michael Sia

Dosimetric variations in permanent breast seed implant due to patient arm position.

PURPOSE Planning and delivery for permanent breast seed implant (PBSI) are performed with the ipsilateral arm raised; however, changes in implant geometry can be expected because of healing and anatomical motion as the patient resumes her daily activities. The purpose of this study is to quantify the effect of ipsilateral arm position on postplan dosimetry. METHODS AND MATERIALS Twelve patients treated at the Tom Baker Cancer Centre were included in this study. Patients underwent two postimplant CT scans on the day of implant (Day 0) and two scans approximately 8 weeks later (Day 60). One scan at each time was taken with the ipsilateral arm raised, recreating the planning scan position, and the other with both arms down in a relaxed position beside the body, recreating a more realistic postimplant arm position. Postplans were completed on all four scans using deformable image registration (MIM Maestro). RESULTS On the Day 0 scan, the V200 for the evaluation planning target volume was significantly increased in the arm-down position compared with the arm-up position. Lung, rib, and chest wall dose were significantly reduced at both time points. Left anterior descending coronary artery, heart, and skin dose showed no significant differences at either time point. CONCLUSIONS Although some dosimetric indices show significant differences between the arm-up and arm-down positions, the magnitude of these differences is small and the values remain indicative of implant quality. Despite the delivery of the majority of dose with the arm down, it is reasonable to use CT scans taken in the arm-up position for postplanning.

Parameters predicting for prostate specific antigen response rates at one year post low-dose-rate intraoperative prostate brachytherapy

Purpose To develop a model for prostate specific antigen (PSA) values at one year among patients treated with intraoperatively planned 125I prostate brachytherapy (IOPB). Material and methods Four hundred and deven patients treated with IOPB for prostate adenocarcinoma were divided into four groups: those with PSA values ≥ 3 ng/ml; < 3 and ≥ 2; < 2 and ≥ 1 or PSA < 1 between 10.5 and 14.5 months post implantation (1yPSA). Ordinal regression analysis was then performed between patient, tumor, and treatment characteristics. 1yPSA values were also compared with toxicity outcomes. Results Median 1yPSA was 0.77 (0.04-17.36). Thirty-two patients (8%) had a PSA ≥ 3; 35 (9%) had PSA < 3, ≥ 2; 87 (21%) had PSA < 2, ≥ 1, and most patients 254 (62%) had PSA < 1. PSA response was independent of gland volume, Gleason score, clinical stage, seed activity, V90, V200, D90, or number of needles and seeds used. Older patients had significantly lower 1yPSA; median ages 65.1 (46.5-81.0), 62.1 (50.4-79.5), 60.5 (47.1-80.3), and 58.1 (45.1-74.2) years for each of the 1yPSA groups respectively (p < 0.001). Also, both implant V150 (p < 0.001) and initial PSA values (p = 0.04) were predictive of 1yPSA values. There was no correlation between 1yPSA values and toxicity encountered. Conclusions PSA response at 1 year post IOPB appears to be dependent on patient age, initial PSA, and implant V150. Our results provide reassurance that parameters other than biochemical failure influence 1yPSA values.

Sci—Sat AM: Brachy — 09: Permanent seed re‐implantation using image guidance for composite dose planning

Treatment outcome has been associated with dosimetric implant quality assessed in a postplan. Uncertainties during the implant and in the period before postplan evaluation lead to dosimetric deviations from the original treatment plan. The observed range of postplan results can include patients with dosimetry below recommended levels. Further treatment options may be considered to boost the delivered dose and a second seed implant is one way to accomplish this. This work describes the development of a procedure to plan and deliver a second seed implant and an evaluation of the dosimetric improvement. A patient with a post-plan D90 of 124 Gy was offered a second seed implant 21 weeks after the initial implant. A total dose of 163 Gy was prescribed due to radiobiological considerations for the time between implants. A volume study was performed 2 weeks before the implant and variable angle images of the seeds from the first implant were obtained to reconstruct the original seed coordinates. The second implant was planned considering the total composite physical dose distribution by forward planning additional seeds onto the original implant coordinates. The additional seeds were manually added to a new plan on the volume study images at the planned coordinates and delivered as a typical preplanned implant. Post-plan evaluation four weeks after the second implant showed a D90 of 177 Gy and a V100 of 92.7%. These results demonstrate the effective use of a second seed implant with image guided composite planning to improve dosimetric implant quality.