Relationship of irradiated bone marrow volume and neutropenia in patients undergoing concurrent chemoradiation therapy for cervical cancer.

Introduction: Concurrent chemoradiation therapy (CCRT) is the standard of care in the management of cervical cancer (International Federation of Gynecology and Obstetrics [FIGO] 2008 Stages IB2-IVA). Apart from the myelotoxic effects of chemotherapy, irradiation of pelvic bone marrow (BM) in the radiation field, can also contribute to hematological toxicity. Objectives: We examined the relationship of irradiated BM volume and neutropenia in cervical cancer patients undergoing CCRT. Materials and Methods: This prospective study was conducted in a tertiary cancer center with a longitudinal study design. A total of 43 patients undergoing CCRT for cervical cancer were included. Using auto bone segmentation, the external contour of pelvic bones from L4 vertebral body to ischial tuberosities were delineated as BM. The volume of BM receiving 10, 20, 40, 50 Gy was calculated. Complete blood counts were done weekly to evaluate the neutropenia and were graded according to Common Terminology Criteria for Adverse Events, version 3.0. The risk of developing neutropenia was analyzed using logistic regression. Results: Twenty-seven patients (62.8%) received 5 cycles of chemotherapy, 14 patients (32.6%) received 4 cycles of chemotherapy and 2 patients (4.7%) received 3 cycles of chemotherapy. Overall, 22 patients (51.2%) experienced acute neutropenia. On multivariate analysis increased BM V50Gy had a statistically significantly odds of developing any grade of neutropenia (odds ratio [OR] =1.43; 95% confidence interval [CI], 1.03-1.97; P = 0.028). When comparing patients receiving BM V40Gy ≥40% with BM V40Gy <40% odds of any grade of neutropenia was increased (OR = 2.03; 95% CI, 0.55-7.42; P = 0.28). Moreover, when comparing patients receiving BM V50Gy ≥15% with BM V50Gy <15% odds of any grade of neutropenia was increased (OR = 2.13; 95% CI, 0.57-7.97; P = 0.26). Conclusions: High-dose irradiation to the larger volume of BM prevents compensatory hyperplasia which leads to neutropenia in patients undergoing CCRT for cervical cancer.

Study of Variation in Dose Calculation Accuracy Between kV Cone-Beam Computed Tomography and kV fan-Beam Computed Tomography.

Cone-beam computed tomography (CBCT) images are presently used for geometric verification for daily patient positioning. In this work, we have compared the images of CBCT with the images of conventional fan beam CT (FBCT) in terms of image quality and Hounsfield units (HUs). We also compared the dose calculated using CBCT with that of FBCT. Homogenous RW3 plates and Catphan phantom were scanned by FBCT and CBCT. In RW3 and Catphan phantom, percentage depth dose (PDD), profiles, isodose distributions (for intensity modulated radiotherapy plans), and calculated dose volume histograms were compared. The HU difference was within ± 20 HU (central region) and ± 30 HU (peripheral region) for homogeneous RW3 plates. In the Catphan phantom, the difference in HU was ± 20 HU in the central area and peripheral areas. The HU differences were within ± 30 HU for all HU ranges starting from -1000 to 990 in phantom and patient images. In treatment plans done with simple symmetric and asymmetric fields, dose difference (DD) between CBCT plan and FBCT plan was within 1.2% for both phantoms. In intensity modulated radiotherapy (IMRT) treatment plans, for different target volumes, the difference was <2%. This feasibility study investigated HU variation and dose calculation accuracy between FBCT and CBCT based planning and has validated inverse planning algorithms with CBCT. In our study, we observed a larger deviation of HU values in the peripheral region compared to the central region. This is due to the ring artifact and scatter contribution which may prevent the use of CBCT as the primary imaging modality for radiotherapy treatment planning. The reconstruction algorithm needs to be modified further for improving the image quality and accuracy in HU values. However, our study with TG-119 and intensity modulated radiotherapy test targets shows that CBCT can be used for adaptive replanning as the recalculation of dose with the anisotropic analytical algorithm is in full accord with conventional planning CT except in the build-up regions. Patient images with CBCT have to be carefully analyzed for any artifacts before using them for such dose calculations.