A Prospective Comparison of Computed Tomography with Transrectal Ultrasonography Assistance and Magnetic Resonance Imaging-Based Target-Volume Definition During Image Guided Adaptive Brachytherapy for Cervical Cancers.

PURPOSE: Although magnetic resonance imaging (MRI) represents the gold standard for image guided adaptive brachytherapy (IGABT) for cervical cancer, the majority of brachytherapy (BT) continues to be guided by computed tomography (CT). However, CT seems to overestimate the target-volume definition, and the potential of transrectal ultrasonography (TRUS) needs further evaluation. This prospective, comparative study aimed to evaluate CT-based target contouring with the incorporation of TRUS during BT. METHODS AND MATERIALS: Patients with locally advanced cervical cancer undergoing magnetic resonance IGABT between January 2013 and March 2014 were included. During the BT procedure, TRUS imaging with central tandem in situ was acquired at 3 representative levels. Reference points/dimensions (D1-D4) of the hypoechoic region on TRUS images with respect to the central tandem were recorded. CT and magnetic resonance BT planning imaging was performed after BT application. The high-risk clinical target volume (HR-CTV) was contoured on CT scans with incorporation of clinical and TRUS imaging findings and was compared with the gold standard MRI-based target approach. RESULTS: The image sets of 25 patients (International Federation of Gynecology and Obstetrics clinical stage IIB [11; 44%] and IIIB [14; 56%]) were evaluable. The mean (±standard deviation) volumes of HR-CTV on CT and MRI imaging were 39.1 (±20) cm³ and 39 (±19) cm³, respectively (r = 0.92; P < .001). A significant correlation was found between the HR-CTV dimensions (width and thickness) of CT and MRI scans at various levels (r = 0.70-0.80; P < .001). In addition, the absolute differences in target dimensions between CT and MRI were <0.5 cm. A strong correlation was seen between CT and MRI for patients with medial and lateral parametrial invasion (P < .05) compared with no parametrial disease at BT. Furthermore, the mean differences in HR-CTV width between CT and MRI contours at various levels, irrespective of parametrial involvement, was only 0.1 to 0.4 cm. CONCLUSIONS: This study suggests that a CT-based target and organ-at-risk delineation using MRI at diagnosis and real-time TRUS information during BT seems comparable with the gold standard MRI-based approach in IGABT for cervical cancer.

Submandibular function recovery after IMRT in head and neck cancer: A prospective dose modelling study.

PURPOSE: To estimate the dose response relationship for submandibular gland (SMG) recovery using salivary scintigraphy in patients diagnosed with head and neck cancer treated with curative image guided chemoradiation. MATERIAL AND METHODS: Ninety newly diagnosed head and neck cancer patients (T1-3, N0-2c, M0) treated with intensity modulated radiotherapy on a prospective clinical trial were assessed for salivary toxicity at predefined intervals using dynamic salivary scintigraphy. The SMG function was measured using salivary excretion fraction (SEF) ratios at baseline and 6 monthly. Tolerance dose (TD) 50 for submandibular gland was estimated from dose response curves. RESULTS: The mean SEF ratio of 180 SMGs decreased at 6 months with a nadir at 12 months after treatment (SEF ratio 15%) and progressively recovered over time reaching 38% over 24 months. There was significant inverse correlation between SEF ratio and mean SMG dose at 6 months (r = -0.18, p = 0.04); 12-months (r = -0.36, p < 0.001); 18-months (r = -0.48, p < 0.001); 24-months (r = -0.42, p < 0.001); and more than 24-months (r = -0.56, p < 0.001). The estimated TD 50 values at 1 year and 2 year post treatment were 36 Gy and 44 Gy respectively with SEF ratio of ≤45% used to define severe xerostomia. For every 1 Gy reduction in mean dose below 54 Gy, there is 2-2.5% reduction in the probability of severe xerostomia. CONCLUSION: The submandibular gland function declines after radiotherapy with a nadir at 12 months and there is incomplete recovery over time with continued improvement over 24 months. The TD 50 at 1 year and 2 year was 36 Gy and 44 Gy with a 2-2.5% reduction in the probability of severe xerostomia for every 1 Gy reduction in mean dose.

Cardiac Dose Reduction with Deep-Inspiratory Breath Hold Technique of Radiotherapy for Left-Sided Breast Cancer.

INTRODUCTION: Different techniques of radiation therapy have been studied to reduce the cardiac dose in left breast cancer. AIM: In this prospective dosimetric study, the doses to heart as well as other organs at risk (OAR) were compared between free-breathing (FB) and deep inspiratory breath hold (DIBH) techniques in intensity modulated radiotherapy (IMRT) and opposed-tangent three-dimensional radiotherapy (3DCRT) plans. MATERIALS AND METHODS: Fifteen patients with left-sided breast cancer underwent computed tomography simulation and images were obtained in both FB and DIBH. Radiotherapy plans were generated with 3DCRT and IMRT techniques in FB and DIBH images in each patient. Target coverage, conformity index, homogeneity index, and mean dose to heart (Heart Dmean), left lung, left anterior descending artery (LAD) and right breast were compared between the four plans using the Wilcoxon signed rank test. RESULTS: Target coverage was adequate with both 3DCRT and IMRT plans, but IMRT plans showed better conformity and homogeneity. A statistically significant dose reduction of all OARs was found with DIBH. 3DCRTDIBH decreased the Heart Dmean by 53.5% (7.1 vs. 3.3 Gy) and mean dose to LAD by 28% compared to 3DCRTFB. IMRT further lowered mean LAD dose by 18%. Heart Dmean was lower with 3DCRTDIBH over IMRTDIBH (3.3 vs. 10.2 Gy). Mean dose to the contralateral breast was also lower with 3DCRT over IMRT (0.32 vs. 3.35 Gy). Mean dose and the V20 of ipsilateral lung were lower with 3DCRTDIBH over IMRTDIBH (13.78 vs. 18.9 Gy) and (25.16 vs. 32.95%), respectively. CONCLUSIONS: 3DCRTDIBH provided excellent dosimetric results in patients with left-sided breast cancer without the need for IMRT.