eISSN: 2081-2841
ISSN: 1689-832X
Journal of Contemporary Brachytherapy
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4/2022
vol. 14
 
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abstract:
Original paper

Control charts for evaluation of quality of low-dose-rate brachytherapy for prostate cancer

Nicola J. Nasser
1
,
Elantholi P. Saibishkumar
2
,
Yinkun Wang
3
,
Peter W.M. Chung
4
,
Stephen L. Breen
5

1.
Department of Radiation Oncology, Elmhurst Hospital Center, NYC Health + Hospitals, Queens, NY, USA
2.
British Columbia Cancer Agency, Victoria, British Columbia, Canada
3.
Department of Radiation Physics, Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada
4.
Department of Radiation Oncology, Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada
5.
Odette Cancer Centre – Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
J Contemp Brachytherapy 2022; 14, 4: 354–363
Online publish date: 2022/08/31
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Purpose
Variations in dosimetric outcomes among patients treated with low-dose-rate brachytherapy for prostate cancer exist, even when implants are within dose constraints. Here, we used control charts to investigate reasons for intra-patient dosimetric variability.

Material and methods
Univariate and multivariate control charts for prostate V100 (percentage of prostate volume that received 100% of prescribed radiation dose), D90 (radiation dose to 90% of prostate volume), and RV100 (rectal wall volume that received 100% of prescribed radiation dose) were generated for 212 consecutive prostate cancer patients implanted with iodine-125 (125I) radioactive seeds at the Princess Margaret Cancer Centre. Control limits were calculated based on the first fifty implants. Data points that were out of control were identified, and their pre-treatment and post-treatment dosimetric and clinical parameters were compared to data points that were in-control, using Student’s t-test.

Results
All implants were clinically acceptable. Twelve data points exceeded multivariate control limits. Ten of those points fell below the lower control limit of V100 control chart. Average prostate edema in the 10 out-of-control patients on both multivariate and V100 charts was 8.3%, as compared to 0.4% for in-control patients (p < 0.04). Two patients were observed to be out-of-control on multivariate control chart, but not on V100 control chart, and were found to have a reduction in prostate volume of 19.1% and 20.1% at one month after seed implant, compared to prostate volumes of pre-implantation evaluations.

Conclusions
Control charts helped in identifying cases with out-of-control variability in post-plan prostate dosimetry. Post-treatment prostatic edema and contraction are important factors predicting variability in patients treated with 125I permanent seed brachytherapy.

keywords:

statistical process control, brachytherapy, prostate, quality control, dosimetry

 
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