In vitro quality assurance of three-dimensional conformal radiotherapy mono-isocentric plan for simultaneous treatment of two targets.

OBJECTIVE: The purpose of this study was to check the in vitro efficacy of a radiotherapy plan generated for the treatment of two femoral targets simultaneously in the pelvis. METHODS: The target positions for conformal radiotherapy were simulated by joining two identical water phantoms (approximating the patient dimensions), and a treatment plan to treat the two targets simultaneously with a common isocenter was planned. Calculations were made with a dose prescription of 300cGy to each lesion. The plan was executed on a medical linear accelerator and verified for point doses for individual targets with two ion chambers. Two-dimensional dose verification for fluence was also performed using an array detector of ion chambers (I'mRTMatriXX) to further validate the technique. RESULTS: The minimum, mean and maximum dose in centiGray(cGy) covered by both Ionization Chamber-1 (IC-1) and Ionization Chamber-2 (IC-2) was 295, 303 and 307 as per dose statistics from the treatment plan. The global dose max obtained from the plan was 307 cGy. Measured point doses to both the targets were within ±2%. Dose Difference and Distance to agreement (3%, 3 mm criteria) criteria also passed for 2Dfluence verification. CONCLUSIONS: Radiotherapy of two or multiple targets using monoisocentric technique can appreciably reduce the scatter dose to the normal surrounding tissue around the target/s and also the required setup and treatment time is reduced significantly. Therefore, the technique can be efficiently used to save time without compromising the radio therapeutic ratio and quality treatment, for both palliative and curative intent.

In vivo Dosimetry for Dose Verification of Total Skin Electron Beam Therapy Using Gafchromic® EBT3 Film Dosimetry.

Background and Purpose: Total skin electron beam therapy (TSEBT) is an important skin-directed radiotherapeutic procedure done in the treatment of cutaneous T-cell lymphomas, namely, mycosis fungoides (MF). This procedure is usually done at larger source-to-surface distances with the patient standing on a rotatory platform. As the patient has to stand in different positions without any rigid immobilization devices, there are chances that the total skin may not get uniformly irradiated which could lead to nonuniform dose distributions. Therefore, all the necessary arrangements should be made to evaluate the dose for different regions of the skin using suitable in vivo dosimeters at the radiotherapy centers offering these treatments. This study aimed to evaluate the consistency between the delivered and planned doses in vivo during TSEBT using Gafchromic EBT3 film dosimetry. Materials and Methods: The surface dose for the six MF patients treated for TSEBT at our hospital from 2018 to 2022 was measured and evaluated. 2 cm × 2 cm Gafchromic® EBT3 films were used to measure skin dose at reference body positions of clinical interest. All the patients were treated with the modified Stanford technique. The irradiated film strips were analyzed for the dose using the IMRT OmniPro software. The doses at respective positions were expressed as mean dose ± standard deviation and the deviation was calculated as the percentage of the prescribed dose. Results: One hundred and fifty-four Gafchromic® EBT3 film strips irradiated on six TSEBT patients showed a maximum dose variation of 2.00 ± 0.14 Gy, in the central body regions. The dose variation in the peripheral areas such as hands and ears was larger. A variation of 2 ± 0.32 Gy was observed on the hands and ears. The uniformity of the dose delivered to maximum body parts was within -7% and +16% for the peripheral areas like hands. The American Association of Physicists in Medicine recommends a dose uniformity of 8% and 4% in the vertical and horizontal patient plane for direct incident beam; however, for oblique incidences like in the modified Stanford technique, the dose variation is about 15%. Conclusion: In vivo dosimetry using Gafchromic EBT3 film dosimetry for TSEBT yields objective data to find the under or overdose regions. That can be useful to provide quality treatment, especially when treatments tend to be as complex as TSEBT.

Magnetic Resonance Imaging Image-Based Segmentation of Brain Tumor Using the Modified Transfer Learning Method.

Purpose: The goal of this study was to improve overall brain tumor segmentation (BraTS) accuracy. In this study, a form of convolutional neural network called three-dimensional (3D) U-Net was utilized to segment various tumor regions on brain 3D magnetic resonance imaging images using a transfer learning technique. Materials and Methods: The dataset used for this study was obtained from the multimodal BraTS challenge. The total number of studies was 2240, obtained from BraTS 2018, BraTS 2019, BraTS 2020, and BraTS 2021 challenges, and each study had five series: T1, contrast-enhanced-T1, Flair, T2, and segmented mask file (seg), all in Neuroimaging Informatics Technology Initiative (NIFTI) format. The proposed method employs a 3D U-Net that was trained separately on each of the four datasets by transferring weights across them. Results: The overall training accuracy, validation accuracy, mean dice coefficient, and mean intersection over union achieved were 99.35%, 98.93%, 0.9875%, and 0.8738%, respectively. Conclusion: The proposed method for tumor segmentation outperforms the existing method.