Dose tracking in radiation oncology using daily CBCT: effects of physical parameters on dose calculation accuracy.

The availability of cone beam computerized tomography (CBCT) images at the time of treatment has opened possibilities for recalculations and tracking of the delivered dose, becoming an effective tool for adaptive radiotherapy. A significant component in the accuracy of dose recalculation on CBCT images is the calibration of the Hounsfield units (HU) to density. The aim of this thesis, developed at the Policlinic of Modena, is to assert a methodology for the characterization of the HU-to-density calibration curve, and to evaluate the impact of the calibration phantom inserts composition and phantom volume on dose calculation accuracy. The HU-to-density calibration curves from four different phantoms were measured and compared. The HU output of a kV CBCT scan depends on the physical parameters of the phantom density inserts, with particular reference to the atomic number (Z), due to the photoelectric effect which is the main radiation-matter interaction at kV energies. The phantom radial diameter also influences the HU values on the image. The effect of scattering and beam hardening was examined as a function of phantom diameter, founding a high deviation on the HU value of the same density insert when varying the radial diameter of the phantom, especially for high densities. When we are dealing with CBCTs also the acquisition parameters influence the resulting image, that’s why we will show that a protocol-specific calibration curve is needed. The resulting calibration curves were used to compare the calculated doses against planned ones. The percent difference between recalculated and planned dose was obtained for chosen clinically important dose levels and a box plot analysis was conducted. Results show that the best calibration curve for dose recalculation on CBCT images has been obtained when a human-tissue-equivalent inserts are used and when the radial diameter of the phantom is close to the dimensions of the real patient

Fully automated volumetric modulated arc therapy technique for radiation therapy of locally advanced breast cancer

Abstract Background This study aimed to evaluate an a-priori multicriteria plan optimization algorithm (mCycle) for locally advanced breast cancer radiation therapy (RT) by comparing automatically generated VMAT (Volumetric Modulated Arc Therapy) plans (AP-VMAT) with manual clinical Helical Tomotherapy (HT) plans. Methods The study included 25 patients who received postoperative RT using HT. The patient cohort had diverse target selections, including both left and right breast/chest wall (CW) and III-IV node, with or without internal mammary node (IMN) and Simultaneous Integrated Boost (SIB). The Planning Target Volume (PTV) was obtained by applying a 5 mm isotropic expansion to the CTV (Clinical Target Volume), with a 5 mm clip from the skin. Comparisons of dosimetric parameters and delivery/planning times were conducted. Dosimetric verification of the AP-VMAT plans was performed. Results The study showed statistically significant improvements in AP-VMAT plans compared to HT for OARs (Organs At Risk) mean dose, except for the heart and ipsilateral lung. No significant differences in V95% were observed for PTV breast/CW and PTV III-IV, while increased coverage (higher V95%) was seen for PTV IMN in AP-VMAT plans. HT plans exhibited smaller values of PTV V105% for breast/CW and III-IV, with no differences in PTV IMN and boost. HT had an average (± standard deviation) delivery time of (17 ± 8) minutes, while AP-VMAT took (3 ± 1) minutes. The average γ passing rate for AP-VMAT plans was 97%±1%. Planning times reduced from an average of 6 h for HT to about 2 min for AP-VMAT. Conclusions Comparing AP-VMAT plans with clinical HT plans showed similar or improved quality. The implementation of mCycle demonstrated successful automation of the planning process for VMAT treatment of locally advanced breast cancer, significantly reducing workload

A hydrogenated amorphous silicon detector for Space Weather applications

The characteristics of a hydrogenated amorphous silicon (a-Si:H) detector are presented here for monitoring in space solar flares and the evolution of strong to extreme energetic proton events. The importance and the feasibility to extend the proton measurements up to hundreds of MeV is evaluated. The a-Si:H presents an excellent radiation hardness and finds application in harsh radiation environments for medical purposes, for particle beam characterization and, as we propose here, for space weather science applications. The critical flux detection limits for X rays, electrons and protons are discussed