Background and Purpose
The purpose of this study was to investigate the dependence of departmental catheter implant strategies and planning guidelines on derivation of appropriate in-vivo source tracking error thresholds during high dose rate (HDR) prostate brachytherapy (pBT).
Thirteen radiotherapy departments from around the world participated in the study. Each department was sent an anonymised trans-rectal ultrasound (TRUS) image dataset of a single patient. The prostate, urethra, and rectum contoured by an experienced radiation oncologist. Departments were asked to create a treatment plan on the patient dataset (and using the same contours) according to their own local protocols and return to the DICOM datasets (DICOM RT plan, and dose files) to the investigators. Errors in source position were then simulated artificially by modifying the dwell position coordinates in the DICOM plan files using a custom Python code. The effect of these source position errors on dose volume histogram (DVH) indices was investigated, and the magnitude of this effect compared across all 13 departmental plans. Appropriate in-vivo source tracking error thresholds were then derived for each department. The effect of the number of catheters, dwell positions, total reference air kerma (TRAK), and plan modulation on the derived in-vivo source tracking error threshold was examined.
The derived in-vivo source tracking error threshold was found to vary across departments, indicating that a universal in-vivo source tracking error threshold for HDR pBT would not be appropriate. Factors such as number of catheters, plan modulation, and proximity of catheters to organs at risk were found to most strongly affect the derived source tracking error threshold.
Universal in-vivo source tracking error thresholds for HDR pBT cannot be confidently applied due to inter-departmental variation in planning techniques. Plan robustness to source position displacements may be improved by limiting the number of highly weighted dwell positions in the proximity of organs at risk. Due to the complexity in deriving these in-vivo source tracking error thresholds, it would be beneficial to utilise online adaptive HDR pBT treatments facilitated by in-vivo source tracking devices. This could compensate for any errors in treatment delivery, minimising the risk of mistreatment.
Joel Poder – Radiation Oncology Medical Physicist St George Hospital Cancer Care CentreJoel is employed at the St George Hospital Cancer Care Centre in the Radiation Oncology department as a Medical Physics Specialist, where he is the lead of the brachytherapy and stereotactic radiosurgery portfolios. He is an ABG executive committee member, and represents the ABG on the AAPM brachytherapy scientific committee. He has an active research interest in brachytherapy in-vivo treatment verification, stereotactic treatment verification and deformable image registration.
Andrew Howie – Senior Radiation Oncology Medical Physicist St George Hospital Cancer Care CentreAndrew is currently employed at St George Hospital Cancer Care Centre as a Senior Radiation Oncology Medical Physicist. He has many years of experience in the field of brachytherapy and is responsible for establishing the HDR brachytherapy program at the centre.
Dean Cutajar – Research Fellow Centre for Medical Radiation Physics, University of WollongongDr. Cutajar is employed as a Research fellow with the Centre for Medical Radiation Physics, and works as a research physicist part time at the St George Hospital Cancer Care Centre. He has many years experience in the field of brachytherapy dosimetry.
Joseph Bucci – Senior Staff Specialist St George Hospital Cancer Care CentreDr Joseph Bucci has trained in Medical and Radiation Oncology. He has over 17 years’ experience in the treatment of cancer and focuses on research related to Quality Assurance in Brachytherapy. He has a particular interest in the management of urological malignancies. Dr Bucci trained in prostate brachytherapy at the British Columbia Cancer Agency in 2000-01 in Vancouver. He has held senior positions at the St. George Hospital Cancer Centre and the St. George Private Hospital. Dr Bucci was part of the team that established the first publicly funded prostate seed brachytherapy program in Sydney.
Anatoly Rosenfeld – Distinguished Professor Centre for Medical Radiation Physics, University of WollongongProfessor Anatoly Rozenfeld is the Director and founder of CMRP, and is world renowned for his research work on semiconductor radiation detectors and their application for mini- and micro- dosimetry in radiation therapy, radiation protection, nuclear medicine and space sciences. Professor Rozenfeld has published more than 240 articles, 3 chapters in books, holds 18 ex- Soviet, USA, Canadian, Chinese and Australian patents, and also delivered many invited talks and seminars around the world. He is recipient of 2014 UOW Vice Chancellor Excellence Awards for Researcher of the Year and Award for Outstanding Achievements in Research Commercialization.