1PhD Scholar, Department of Physics, Government Postgraduate College, Kotdwar, Uttarakhand
2Scietific Officer, Department of Medical Physics, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India, mishrasp05@gmail.com
3Associate Professor, Department of Physics, Government Postgraduate College, Kotdwar, Uttarakhand, rajkumar.tyagi@gmail.com
4Assistant Professor, Department of Medical Physics, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India, Anoopsrivastava78@gmail.com
*Corresponding author email id: jyoti797bisht@gmail.com
Online published on 31 August, 2018.
This study is focused to evaluate volumetrically the target coverage and organ at risk doses in high dose rate intracavitary brachytherapy (ICBT) application.
Twenty one ICBT applications have been selected for this study. Seven patients have been treated with external beam radiotherapy for 46 Gy/23# and ICBT with 7 Gy/3 sessions. Patient magnetic resonance imaging (MRI) (3 T General Electric USA) has been taken for delineation of gross tumour volume before radiotherapy started, then patients underwent computed tomography (CT) simulation (16 slices, Siemens-Somatom, Germany) procedure for external beam radiotherapy planning followed by ICBT after 1 week. For first insertion, MRI and CT simulation scan both were acquired to locate the target volume and organ at risk. Only CT scan images were acquired for subsequent brachytherapy session. The patient data was transferred to treatment-planning system (Oncentra master plan Ver.4.3) through (Digital Imaging and Communications in Medicine) DICOM. clinical target volume CTV, rectum, bladder, sigmoid colon and bowel loops were contoured as per Radiation Therapy Oncology Group RTOG criteria. For CTV D90, D95, D100, D150 and D200, volumes were evaluated from dose-volume histogram. For Organ at risk OARs D0.1cc, D1cc, D2cc, D5cc and D10cc were evaluated from dose volume hiostogram DVH.
Dose was prescribed at point A for all patients. The mean target volume evaluated was 76.3 cm3. For patients having target volume greater than 80 cm3, point A needs to be shifted to acquire the desired target coverage. Mean 90% CTV coverage was 89.47%, 95% coverage was 87.12%, 100% coverage was 79.98%, 150% coverage was 48.17% and 200% isodose line covers 26.97% target volume. The mean International Commission on Radiotherapy Units and Measurements (ICRU) rectal, bladder doses was 4.64 Gy and 5.3 Gy. Volumetric doses 0.1cc, 1cc, 2cc, 5cc and 10cc were measured for rectum and bladder, and D2cc was compared with ICRU point doses. For sigmoid colon and bowel loops, D2cc, D5cc and D10cc were analysed.
Three-dimensional CT scan image-based dosimetry facilitates the evaluation of dose of bowel loop and sigmoid colon, and 2D radiograph-based point dosimetry cannot provide this critical information as often these organs may be in high-dose-gradient.
Brachytherapy, Volumetric dosimetry, Clinical target-volume, Organ at risk, Dose volume histogram, Computed tomography (CT), Magnetic resonance imaging (MRI)
