Estimation of maternal and foetal risk of radiation-induced cancer from a survey of computed tomography pulmonary angiography and ventilation/perfusion lung scanning for diagnosing pulmonary embolism during pregnancy.

INTRODUCTION: While there are many papers on maternal and foetal radiation doses from computed tomography pulmonary angiography (CTPA) and ventilation/perfusion (V/Q) lung scanning examinations for diagnosing pulmonary embolism in pregnant patients, few have used clinical data to examine the patient lifetime attributable risk (LAR) of different cancer types. This paper aims to estimate the cancer risk from maternal radiation doses from CTPA and V/Q examinations and associated foetal doses. METHODS: Dosimetric data were determined for 267 pregnant patients who received CTPA and/or V/Q examinations over 8 years. Organ and foetal doses were determined using software allowing patient size variations for CTPA and using two different activity-to-organ dose conversion methods for V/Q scans. The LAR of cancer incidence was estimated using International Commission on Radiological Protection (ICRP) modelling including estimates of detriment. RESULTS: Estimated total cancer incidence was 23 and 22 cases per 100,000 for CTPA and V/Q examinations, respectively, with detriment estimates of 18 and 20 cases. Cancer incidence was evenly divided between lung and breast cancer for CTPA with lung cancer being 80% of all cancer for V/Q. The median foetal doses were 0.03 mSv for CTPA and 0.29 mSv for V/Q. Significant differences in estimated foetal dose for V/Q scans were obtained by the two different methods used. The differences in dose between the modes of CTPA scan acquisition highlight the importance of optimisation. CONCLUSION: Maternal cancer incidence and detriment were remarkably similar for each examination. Optimisation of examinations is critical for low-dose outcomes, particularly for CTPA examination.

Use of deformable image registration techniques to estimate dose to organs at risk following prostate external beam radiation therapy and high-dose-rate brachytherapy.

PURPOSE: The purpose of this investigation was to examine differences in estimates of accumulated rectal dose when using deformable image registration (DIR) compared with rigid image registration (RIR) methods, and parameter addition methods for combined transrectal ultrasound (TRUS)-based high-dose-rate brachytherapy (HDR-BT) and external beam radiation therapy (EBRT) treatments of prostate cancer. MATERIAL AND METHODS: In this retrospective study, data from 10 patients who had previously received HDR-BT in one 15 Gy fraction, followed by 46 Gy EBRT in twenty-three fractions were used. To estimate total combined dose to the rectum, dose accumulation using both DIR and RIR methods were compared with parameter addition methods, which assume the same region of rectal anatomy receives the maximum dose from both treatment modalities. For both rigid and deformable image registration techniques, the quality of image registration was evaluated through metrics, including mean distance to agreement and dice similarity coefficient of prostate contours. Total D1cc and D2cc for the rectum was calculated and compared using each method. RESULTS: The parameter addition methods predicted the highest accumulated dose to the rectum. On average, the predicted D2cc dose was higher than that calculated by the DIR method by 6.59 Gy EQD2 (range, -3.03 to 13.68 Gy EQD2) for partial parameter addition (PPA), and 4.88 Gy EQD2 (range, -3.41 to 11.97 Gy EQD2) for the full parameter addition (FPA) methods. Similarly, RIR predicted higher average doses compared with DIR, with a difference of 3.46 Gy EQD2 (range, -5.50 to 7.90 Gy EQD2). The results showed a significant difference between DIR and parameter addition methods for dose estimation. CONCLUSIONS: This retrospective study demonstrates significant differences in accumulated rectal dose prediction using different image registration methods. Each method has limitations in its application, and when used with real-time HDR-BT dose planning, awareness of these limitations is essential.