Geraldine Workman

UK & Ireland Prostate Brachytherapy Practice Survey 2014-2016

Purpose To document the current prostate brachytherapy practice across the UK and Ireland and compare with previously published audit results. Material and methods Participants from 25 centers attending the annual UK & Ireland Prostate Brachytherapy Conference were invited to complete an online survey. Sixty-three questions assessed the center’s experience and staffing, clinician’s experience, clinical selection criteria and scheduling, number of cases per modality in the preceding three years, low-dose-rate (LDR) pre- and post-implant technique and high-dose-rate (HDR) implant technique. Responses were collated, and descriptive statistical analysis performed. Results Eighteen (72%) centers responded with 17 performing LDR only, 1 performing HDR only, and 6 performing both LDR and HDR. Seventy-one percent of centers have > 10 years of LDR brachytherapy experience, whereas 71% centers that perform HDR brachytherapy have > 5 years of experience. Thirteen centers have 2 or more clinicians performing brachytherapy with 61% of lead consultants performing > 25 cases (LDR + HDR) in 2016. The number of implants (range), that includes LDR and HDR, performed by individual practitioners in 2016 was > 50 by 21%, 25-50 by 38%, and < 25 by 41%. Eight centers reported a decline in LDR monotherapy case numbers in 2016. Number of center’s performing HDR brachytherapy increased in last five years. Relative uniformity in patient selection is noted, and LDR pre- and post-implant dosimetry adheres to published quality guidelines, with an average post-implant D90 of > 145 Gy in 69% of centers in 2014 and 2015 compared to 63% in 2016. The median CT/US volume ratios were > 0.9 ≤ 1.0 (n = 4), > 1.0 ≤ 1.1 (n = 7), and > 1.1 (n = 2). Conclusion There is considerable prostate brachytherapy experience in the UK and Ireland. An apparent fall in LDR case numbers is noted. Maintenance of case numbers and ongoing compliance with published quality guidelines is important to sustain high quality outcomes.

Verification of high-dose-rate brachytherapy treatment planning dose distribution using liquid-filled ionization chamber array

Purpose This study aims to investigate the dosimetric performance of a liquid-filled ionization chamber array in high-dose-rate (HDR) brachytherapy dosimetry. A comparative study was carried out with air-filled ionization chamber array and EBT3 Gafchromic films to demonstrate its suitability in brachytherapy. Material and methods The PTW OCTAVIUS detector 1000 SRS (IA 2.5-5 mm) is a liquid-filled ionization chamber array of area 11 x 11 cm2 and chamber spacing of 2.5-5 mm, whereas the PTW OCTAVIUS detector 729 (IA 10 mm) is an air vented ionization chamber array of area 27 x 27 cm2 and chamber spacing of 10 mm. EBT3 films were exposed to doses up to a maximum of 6 Gy and evaluated using multi-channel analysis. The detectors were evaluated using test plans to mimic a HDR intracavitary gynecological treatment. The plan was calculated and delivered with the applicator plane placed 20 mm from the detector plane. The acquired measurements were compared to the treatment plan. In addition to point dose measurement, profile/isodose, gamma analysis, and uncertainty analysis were performed. Detector sensitivity was evaluated by introducing simulated errors to the test plans. Results The mean point dose differences between measured and calculated plans were 0.2% ± 1.6%, 1.8% ± 1.0%, and 1.5% ± 0.81% for film, IA 10 mm, and IA 2.5-5 mm, respectively. The average percentage of passed gamma (global/local) values using 3%/3 mm criteria was above 99.8% for all three detectors on the original plan. For IA 2.5-5 mm, local gamma criteria of 2%/1 mm with a passing rate of at least 95% was found to be sensitive when simulated positional errors of 1 mm was introduced. Conclusion The dosimetric properties of IA 2.5-5 mm showed the applicability of liquid-filled ionization chamber array as a potential QA device for HDR brachytherapy treatment planning systems.

A sector-based postimplant dosimetric comparison of sagittal and axial ultrasound-guided source placement during I-125 permanent prostate brachytherapy

262 Background: To use sector based pre- and postimplant dosimetric analysis to evaluate the effect of changes in implant technique in a developing I-125 permanent prostate brachytherapy program (PPB). Methods: 109 men treated with PPB were divided into two groups by implant technique. The first 50 patients (group 1) had needle-by-needle seed deposition under axial ultrasound (USS) guidance and subsequent 59 patients (group 2) having needle placement row-by-row then seed deposition under sagittal USS guidance. Twelve sector dose volume analysis of pre-implant ultrasound (USpre) and postimplant CT (CTpost) study was performed in all cases. Individual sectors were created by dividing the cranio-caudal prostate into three equal lengths creating prostate base, midgland and apex. Each of these volumes was then divided into four axial sectors (right and left anterior, right and left posterior). The difference in the minimum dose delivered to 90% of prostate volume (D90) and the prostate volume receiving 100%, 1...

Use of sector analysis of I-125 permanent prostate brachytherapy to evaluate and compare pre- and postimplant dosimetry.

242 Background: To evaluate 12 sector analysis in the assessment and comparison of pre- and post- implant dosimetric parameters during the development of an I-125 prostate brachytherapy (PPB) service. METHODS 50 consecutive men being treated with PPB had dose volume analysis in 12 sectors of their pre implant ultrasound (PIUS) and post implant CT (PICT) data using a Variseed 8.0 treatment planning system. PIUS dosimetry was performed 2 weeks prior to implantation and PICT dosimetry 4 weeks post implant. Individual sectors were created by dividing the cranio-caudal prostate length into 3 equal lengths creating prostate base (PB), midgland (PM) and apex (PA). Each of these volumes was then divided into four axial sectors (right and left anterior, right and left posterior). The planning target volume (PTV), dose to 90% of prostate (D90), prostate volume enclosed by 100% (V100), 150% (V150) and 200% (V200) dose were recorded in each sector on PIUS and PICT. Adjacent sectors on PIUS were assessed for dose-volume homogeneity as were adjacent sectors on PICT. Differences in individual sectors on PIUS and PICT were evaluated. RESULTS Adjacent sector analysis demonstrated dose homogeneity in all sectors of PIUS and the majority of sectors on PICT. Statistically significant differences between PIUS and PICT were noted in target volume, particularly in PB with PICT >PIUS. When individual sectors on PIUS and PICT were compared, statistically significant differences were noted in the majority of dosimetric parameters. The anterior PB and PM were significantly lower on PICT (p value < 0.001) and significantly higher at the posterior PM and PA (p value < 0.05). These changes were consistent across all analysed parameters. In particular, significant absolute differences in D90 in equivalent sectors on PIUS and PICT were seen. CONCLUSIONS 12 sector analysis allows rapid assessment of PIUS and PICT dose and volume homogeneity. It offers a scientific method of identifying areas of relative over and under dosing on PICT when compared with PIUS providing both clinicians and physicists with a learning tool to refine dosimetric analysis and highlight sectors where implant quality could be improved.