Purpose: Developing a method of an HPGe detector precise γ efficiency calibration which is very important for accurate radiation detection during cancer radiotherapy practices. Method and Materials: 24Al radioactive nucleus produced and separated with Momentum Achromat Recoil Spectrometer (MARS) at the K500 superconducting cyclotron of Texas A&M University has positron decays followed by γ transitions up to 8 MeV from 24Mg excited states, which is used for a β‐γ coincidence measurement with a 1‐mm‐thick BC404 plastic scintillator, an HPGe detector and a fast tape‐transport system to calibrate the HPGe detector. Results: By carefully considering the effects of summing, positron annihilation, internal conversion, and β detector efficiency when analyzing 24Al spectrum, we got the efficiency for γ‐ray 7070 keV at 49 mm distance away from the source sample 24Al, which was 0.192(6)%. The Monte Carlo (MC) simulation with CYLTRAN code gave a value of 0.189%, which was in agreement with our measurements. The precise efficiency calibration curve of the HPGe detector up to 7070 KeV at 49 mm distance away from the source sample was obtained. By using the same procedure, we got the efficiency for the 7070 keV γ‐ray at 151 mm distance away from the source sample 24Al, which was 0.0385(8)%. MC simulation value was 0.0399%, which differed from measurement by 4(2)%. This discrepancy led us to assign an uncertainty of 4% to our efficiencies at 151 mm up to 7070 KeV. The Monte Carlo calculations also reproduced the intensity of observed single‐and double‐escape peaks, providing that the effects of positron annihilation‐in‐flight were incorporated. Conclusion: A new method was established. The precise calibration curves obtained from this work are useful for accurate radiation detection and improving quality control to quality assurance (QA) for intensity‐modulated radiation therapy (IMRT). Research sponsored by Department of Energy and Robert Welch Foundation.

Purpose: The purpose of this work is to study the Bragg peak shifts and degradation caused by density and boundary changes in proton beam dose calculation Method and Material: Proton beam delivery provides promising dose characteristics as radiation dose can conform tightly to tumor while sparing surrounding healthy tissues. Proton particles deposit energy in a narrow range around the Bragg peak and as such the dose calculation is more challenging for that the Bragg peak is sensitive to tissue density, tissue composition and organ boundaries along the proton track path. We simulated a few scenarios to study the proton Bragg peak shift due to density and Bragg peak degradation due to change and boundary changes. The calculation of the three dimension dose matrix was performed using a 2 × 2 × 1 mm3 voxels in the depth peak dose range in water phantom after some rough simulation for the dose peak estimation. Results: Bragg peak shift at the iso‐center slice were found to follow a linear relationship with the density of heterogeneity insert based on our simulations with density ranging [0.4 2.0] g/cm∧3 which we studied. Bragg peak degradation and proton dose changed significantly due to low density and small beams size. Proton dose degraded when high energy proton beam irradiated to low density material. Proton dose degraded also when small beam with beam radius at several mm range. Conclusion: Proton dose calculation depends on many factors as Bragg peak is sensitive to tissue density and composition. Besides that, there exist several scenarios causing Bragg peak shift due to density change, causing Bragg peak degradation due to low density and small proton beam. The Monte Carlo simulation is a very accurate solution to provide precise dose distribution in inhomogeneous structures by simulating transport and energy deposition.

Purpose: In this study, we performed dependency study of proton dose on tissue composition using Monte Carlo models of Hounsfield number conversion and cadaver‐based anatomical data Method and Materials: Monte Carlo methods provide the most accurate radiation dose calculation technology as it take into account detailed materials properties, such as materials composition, mass density and interaction cross section. Monte Carlo simulation calculates the energy deposit per mass of each small volume (voxel) after a patient is presented by a large number of voxels. Two methods of building patient‐specified Monte Carlo models have been used in this study: one is to convert patient's CT Hounsfield numbers to materials; the other way is assign anatomical detailed materials using cadavers' segments. Dose distribution and dose volume histogram were compared based on the Monte Carlo models. Results: The dose distribution at the iso‐center slice, the 95% did not cover conformally to the ROI for Hounsfield MC model with shifting 2∼3 mm superior to the ROI. Dose volume history for planning tumor volume (PTV), Brain, Pituitary and Chiasm were used for evaluating the effect of tissue composition. The mean doses difference for PTV was 2.1% for the cadaver‐based MC and Hounsfield conversion MC model. The mean dose difference for Brain, Pituitary and Chiasm was less than 1.0%. Conclusion: Proton radiation dose was calculated and closely compared using two Monte Carlo models: one from CT Hounsfield number conversion and the other from human anatomically detailed Cadaver segments. It is found that the effect of different tissue composition on proton radiation dose calculation is complex involving organs at risk. Our method using cadaver‐based Monte Carlo model for proton dose calculation was shown to be suitable for benchmarking other Monte Carlo dose calculation methods and for providing tissue heterogeneity correction due to the effect of tissue composition.

Purpose: In this work, we aim to build an accurate dose calculation algorithm based on human anatomy‐based model using Monte Carlo simulation for providing basic and benchmarking data for therapeutic protons. Method and Materials: Both phantom‐based and human anatomy‐based models were used. The human anatomy model was developed from VHP® at National Library in Medicine. The human anatomy‐based model was built with 4 mm × 4 mm × 4mm voxel resolution with total over 6 million voxels for describing the whole body. Each voxel was assigned physical properties, including density and isotopic composition. MCNPX was used to simulate the transport and energy deposit to each voxel. An in‐house dosimety software package, Human Anatomy‐based Monte Carlo Dose (HAMD) was developed to analysis the huge dose dataset based on Monte Carlo simulation and the three dimensional dose matrix was super positioned to the CT image correspondingly. Results: The Monte Carlo simulation provided very close agreement to the two widely used proton range‐energy tables with average depth peak difference less than 0.70% and −0.37% to ICRU Report 49 and Janni DNDT respectively from 40 MeV to 250 MeV energy range. HAMD performed well in proton treatment dose calculation. HAMD offers very friendly and familiar interface for physicians to conveniently review a treatment plan. The isodose lines in transverse, sagittal and coronal views provided very conformal coverage to the contours in lung. Conclusion: The simulated proton range‐energy table has been accurately benchmarked compared to measurements. The in‐house developed dose algorithm HAMD performs very well in dose calculation both in phantom‐based and human anatomy‐based heterogeneity. The HAMD needs further validation by using additional human anatomy‐based models and specified beam source configuration. The long‐term and board objective is to provide an extreme accurate dose calculation based on human model for benchmarking clinic treatment planning systems.

Purpose: We aim to provide accurate proton dose calculations for ocular tumors and adjacent critical organs using intensity modulated proton therapy (IMPT) using a human anatomy‐based Monte Carlo model. Dose is simulated using Monte Carlo code MCNPX and compared to standard photon IMRT planning using Pinnacle3® TPS. Method and Materials: The human anatomy model was adapted from the Visible Human Project from the National Library in Medicine. Sectioned images were assigned physical properties. Two independent trials delivering 90% prescription dose to 100% tumor volume were developed using IMRT and IMPT, respectively. Dose profiles for each transverse, sagittal and coronal view of the model were provided for evaluation. Both treatment plans were optimized to deliver maximum dose to the tumor and minimize dose elsewhere. The dose volume histograms for the PTV (tumor), eye, lens, optic nerve, lacrimal gland, brain, chiasm, and pituitary gland were compared between IMRT and IMPT, respectively. Results: IMPT delivered superior isodose coverage to all tissues. Comparing IMRT and IMPT, the mean dose was 4499 cGy and 4750 cGy‐Eq (PTV), 2334 cGy and 1700 cGy‐Eq (eye), 2705 cGy and 1330 cGy‐Eq (lens), 156 cGy and 181 cGy‐Eq (optic nerve), 142 cGy and 23 cGy‐Eq (lacrimal gland), 21 cGy and 0.0 cGy‐Eq (brain), 31 cGy and 0.0 cGy‐Eq (chiasm), and 43 cGy and 0.00 cGy‐Eq (pituitary gland), respectively. The PTV was well covered by 90% isodose to 100% of the tumor volume with an average % prescription dose of 99.9% and 105.6 % for IMRT and IMPT, respectively. Conclusions: IMPT provided conformal dose to the ocular tumor and significantly spared dose to critical organs compared to IMRT. The human‐anatomy dose model performs very well in dose calculation; however, further validation using additional human anatomy‐based models and more specified proton source configuration is needed for optimization purposes.