Use of dynamic contrast-enhanced MRI for the early assessment of outcome of CyberKnife stereotactic radiosurgery for patients with spinal metastases.

AIM: To explore the value of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) for evaluating early outcomes of CyberKnife radiosurgery for spinal metastases. MATERIALS AND METHODS: Patients with spinal metastases who were treated with CyberKnife radiosurgery from July 2018 to December 2020 were enrolled. Conventional MRI and DCE-MRI were performed before treatment and at 3 months after treatment. Patients showing disease progression were defined as the progressive disease (PD) group and those showing complete response, partial response, and stable disease were defined as the non-PD group. The haemodynamic parameters (volume transfer constant [Ktrans], rate constant [Kep], and extravascular space [Ve]) before and after treatment between the groups were analysed. Area under the curve (AUC) values were calculated. RESULTS: A total of 27 patients with 39 independent spinal lesions were included. The median follow-up time was 18.6 months (6.2-36.4 months). There were 27 lesions in the non-PD group and 12 lesions in the PD group. Post-treatment Kep, ΔKtrans and ΔKep in the non-PD group (0.959/min, - 32.6% and -41.1%, respectively) were significantly lower than the corresponding values in PD group (1.429/min, 20.4% and -6%; p<0.05). Post-treatment Ve and ΔVe (0.223 and 27.8%, respectively) in the non-PD group were significantly higher than that of the PD group (0.165 and -13.5%, p<0.05). ΔKtrans showed the highest diagnostic efficiency, with an AUC of 0.821. CONCLUSIONS: DCE-MRI parameters change significantly at an early stage after CyberKnife stereotactic radiosurgery for spinal metastases. DCE-MRI may be of value in determining the early treatment response.

Assessment of the results and hematological side effects of 3D conformal and IMRT/ARC therapies delivered during craniospinal irradiation of childhood tumors with a follow-up period of five years.

BACKGROUND: Craniospinal irradiation (CSI) of childhood tumors with the RapidArc technique is a new method of treatment. Our objective was to compare the acute hematological toxicity pattern during 3D conformal radiotherapy with the application of the novel technique. METHODS: Data from patients treated between 2007 and 2014 were collected, and seven patients were identified in both treatment groups. After establishing a general linear model, acute blood toxicity results were obtained using SPSS software. Furthermore, the exposure dose of the organs at risk was compared. Patients were followed for a minimum of 5 years, and progression-free survival and overall survival data were assessed. RESULTS: After assessment of the laboratory parameters in the two groups, it may be concluded that no significant differences were detected in terms of the mean dose exposures of the normal tissues or the acute hematological side effects during the IMRT/ARC and 3D conformal treatments. Laboratory parameters decreased significantly compared to the baseline values during the treatment weeks. Nevertheless, no significant differences were detected between the two groups. No remarkable differences were confirmed between the two groups regarding the five-year progression-free survival or overall survival, and no signs of serious organ toxicity due to irradiation were observed during the follow-up period in either of the groups. CONCLUSION: The RapidArc technique can be used safely even in the treatment of childhood tumors, as the extent of the exposure dose in normal tissues and the amount of acute hematological side effects are not higher with this technique.

A Monte Carlo model for organ dose reconstruction of patients in pencil beam scanning (PBS) proton therapy for epidemiologic studies of late effects.

Significant efforts such as the Pediatric Proton/Photon Consortium Registry (PPCR) involving multiple proton therapy centers have been made to conduct collaborative studies evaluating outcomes following proton therapy. As a groundwork dosimetry effort for the late effect investigation, we developed a Monte Carlo (MC) model of proton pencil beam scanning (PBS) to estimate organ/tissue doses of pediatric patients at the Maryland Proton Treatment Center (MPTC), one of the proton centers involved in the PPCR. The MC beam modeling was performed using the TOPAS (TOol for PArticle Simulation) MC code and commissioned to match measurement data within 1% for range, and 0.3 mm for spot sizes. The established MC model was then tested by calculating organ/tissue doses for sample intracranial and craniospinal irradiations on whole-body pediatric computational human phantoms. The simulated dose distributions were compared with the treatment planning system dose distributions, showing the 3 mm/3% gamma index passing rates of 94%-99%, validating our simulations with the MC model. The calculated organ/tissue doses per prescribed doses for the craniospinal irradiations (1 mGy Gy-1 to 1 Gy Gy-1) were generally much higher than those for the intracranial irradiations (2.1 µGy Gy-1 to 0.1 Gy Gy-1), which is due to the larger field coverage of the craniospinal irradiations. The largest difference was observed at the adrenal dose, i.e. ∼3000 times. In addition, the calculated organ/tissue doses were compared with those calculated with a simplified MC model, showing that the beam properties (i.e. spot size, spot divergence, mean energy, and energy spread) do not significantly influence dose calculations despite the limited irradiation cases. This implies that the use of the MC model commissioned to the MPTC measurement data might be dosimetrically acceptable for patient dose reconstructions at other proton centers particularly when their measurement data are unavailable. The developed MC model will be used to reconstruct organ/tissue doses for MPTC pediatric patients collected in the PPCR.

An assessment of bone-seeking radionuclides for palliation of metastatic bone pain in a vertebral model.

OBJECTIVE: Bone-seeking radiopharmaceuticals have the main role in the treatment of painful bone metastases. The aim of this study was to dosimetrically compare radiopharmaceuticals in use for bone pain palliation therapy and bone scan. METHODS: The MCNPX code was used to simulate the radiation transport in a vertebral phantom. Absorbed fractions were calculated for monoenergetic electrons, photons and alpha particles. S values were obtained for radionuclides 32P, 33P, 89Sr, 90Y, 99mTc, 117mSn, 153Sm, 166Ho, 169Er, 177Lu, 186Re, 188Re, 223Ra, 224Ra and their progenies for target regions including the active marrow and the bone endosteum. RESULTS: The results demonstrated the dependence of dosimetric parameters on the source or target size, particle energy and location of the source. The electron emitters including 33P, 117mSn, 169Er and 177Lu and 223Ra as an α-emitter gave the lower absorbed dose to the active marrow. These radionuclides gave the highest values of the Relative Advantage Factor (RAF). CONCLUSIONS: According to the results, 33P, 117mSn, 169Er, 177Lu and 223Ra have fewer side effects on the active marrow than other investigated radionuclides. Therefore, these radionuclides may be a better choice for use in palliative radiotherapy.

External beam accelerated partial breast irradiation: dosimetric assessment of conformal and three different intensity modulated techniques.

Background The aim of the study was to evaluate and compare four different external beam radiotherapy techniques of accelerated partial breast irradiation (APBI) considering target coverage, dose to organs at risk and overall plan quality. The investigated techniques were three dimensional conformal radiotherapy (3D-CRT), "step and shoot" (SS) and "sliding window" (SW) intensity-modulated radiotherapy (IMRT), intensity-modulated arc therapy (RA). Patients and methods CT scans of 40 APBI patients were selected for the study. The planning objectives were set up according to the international recommendations. Homogeneity, conformity and plan quality indices were calculated from volumetric and dosimetric parameters of target volumes and organs at risk. The total monitor units and feasibility were also investigated. Results There were no significant differences in the coverage of the target volume between the techniques. The homogeneity indices of 3D-CRT, SS, SW and RA plans were 0.068, 0.074, 0.058 and 0.081, respectively. The conformation numbers were 0.60, 0.80, 0.82 and 0.89, respectively. The V50% values of the ipsilateral breast for 3D-CRT, SS, SW and RA were 47.5%, 40.2%, 39.9% and 31.6%, respectively. The average V10% and V40% values of ipsilateral lung were 13.1%, 28.1%, 28%, 36% and 2.6%, 1.9%, 1.9%, 3%, respectively. The 3D-CRT technique provided the best heart protection, especially in the low dose region. All contralateral organs received low doses. The SW technique achieved the best plan quality index (PQI). Conclusions Good target volume coverage and tolerable dose to the organs at risk are achievable with all four techniques. Taking into account all aspects, we recommend the SW IMRT technique for APBI.

Early response assessment of re-ossification after palliative conventional radiotherapy for vertebral bone metastases.

BACKGROUND: To evaluate the therapeutic outcomes in patients with bone metastases receiving radiotherapy (RT), it is important to use objective radiological response criteria. The aim of this study was to investigate the changes in pain and re-ossification after RT for painful vertebral bone metastases without paralysis by malignant spinal cord compression. METHODS: The participants included 55 patients who received RT for painful vertebral bone metastases without paralysis in our institution between 2012 and 2016. Bone modifying agents (BMAs) were administered in all patients. Follow-up assessments were done just before the start of RT and at 1, 2, 3, 4, and 6 months after RT. Radiological responses of irradiated vertebrae by RT were assessed by computed tomography (CT) using MD Anderson response classification criteria (MDA criteria) and the pain response was assessed by Numeric Rating Scale (NRS). Response was classified as complete response (CR), partial response (PR), progressive disease (PD), and stable disease (SD). RESULTS: The rates of CR were 2%, 7%, 20%, 30%, and 56% at 1, 2, 3, 4, and 6 months, respectively. The rates of CR or PR were 15%, 49%, 77%, 91%, and 91% at 1, 2, 3, 4, and 6 months, respectively. The rates of CR or PR were significantly higher in patients with breast cancer than in patients with lung cancer (p = 0.043). At one month, there was an association between the NRS and radiological response assessed by MDA criteria. There was a significant trend that, with a better response, there were more patients without pain (p = 0.021). CONCLUSIONS: Under BMAs administration, successful RT for vertebral bone metastases decreased pain and caused re-ossification. The MD Anderson criteria could be useful for assessment of radiological responses of irradiated vertebrae.

Radiation dose for pediatric scoliosis patients undergoing whole spine radiography: Effect of the radiographic length in an auto-stitching digital radiography system.

OBJECTIVE: This study investigated the influence of spatial overlap and radiographic length (RL) on the effective dose (ED) and organ dose for pediatric patients undergoing whole spine radiography using an auto-stitching digital radiography (DR) system. METHODS: First, the system parameters were tested on a 10-year-old pediatric anthropomorphic phantom with a Shimadzu DR system, and the effects of the spatial overlap and RL on radiation doses were validated. The ED and organ dose were calculated on the basis of a Monte Carlo simulation program. Subsequently, 82 patients with adolescent idiopathic scoliosis were recruited. The spatial overlap and RL for each patient were modified to further investigate the dose reduction feasibility. RESULTS: RL and ED were appropriately correlated on the basis of patients' height. For a patient measuring 158 cm, the Shimadzu DR system was equipped with a 17-inch detector with a cut-off RL of 75 cm. The phantom simulations indicated that ED was reduced to a minimum value of 0.188 ± 0.001 mSv with a high RL for RL < 75 cm. The minimum value increased to 0.300 ± 0.002 mSv for an RL of 75 cm and dropped to 0.222 ± 0.001 mSv for the maximum RL. By employing optimized RLs for patients, EDs were significantly reduced (p < 0.05). Moreover, ED reductions were higher when longer RLs were employed. CONCLUSION: A decrease in the spatial overlap and number of radiographic acquisitions by adjusting RLs when possible could reduce ED and almost all organ doses. This study emphasized the effects of RL on the radiation dose and provided useful guidance for modifying the RL for patients to reduce the whole spine radiography dose using a modern auto-stitching DR system.

Influence of monte carlo variance with fluence smoothing in VMAT treatment planning with Monaco TPS.

INTRODUCTION: The study aimed to investigate the interplay between Monte Carlo Variance (MCV) and fluence smoothing factor (FSF) in volumetric modulated arc therapy treatment planning by using a sample set of complex treatment planning cases and a X-ray Voxel Monte Carlo-based treatment planning system equipped with tools to tune fluence smoothness as well as MCV. MATERIALS AND METHODS: The dosimetric (dose to tumor volume, and organ at risk) and physical characteristic (treatment time, number of segments, and so on) of a set 45 treatment plans for all combinations of 1%, 3%, 5% MCV and 1, 3, 5 FSF were evaluated for five carcinoma esophagus cases under the study. RESULT: Increase in FSF reduce the treatment time. Variation of MCV and FSF gives a highest planning target volume (PTV), heart and lung dose variation of 3.6%, 12.8% and 4.3%, respectively. The heart dose variation was highest among all organs at risk. Highest variation of spinal cord dose was 0.6 Gy. CONCLUSION: Variation of MCV and FSF influences the organ at risk (OAR) doses significantly but not PTV coverage and dose homogeneity. Variation in FSF causes difference in dosimetric and physical parameters for the treatment plans but variation of MCV does not. MCV 3% or less do not improve the plan quality significantly (physical and clinical) compared with MCV greater than 3%. The use of MCV between 3% and 5% gives similar results as 1% with lesser calculation time. Minimally detected differences in plan quality suggest that the optimum FSF can be set between 3 and 5.

Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography organ-based tube current modulation technique.

PURPOSE: This technical note quantifies the dose and image quality performance of a clinically available organ-dose-based tube current modulation (ODM) technique, using experimental and simulation phantom studies. The investigated ODM implementation reduces the tube current for the anterior source positions, without increasing current for posterior positions, although such an approach was also evaluated for comparison. METHODS: Axial CT scans at 120 kV were performed on head and chest phantoms on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St. Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens, and brain regions for ODM and 3D-modulation (SmartmA) settings. Monte Carlo simulations, validated with experimental data, were performed on 28 voxelized head phantoms and 10 chest phantoms to quantify organ dose and noise standard deviation. The dose and noise effects of increasing the posterior tube current were also investigated. RESULTS: ODM reduced the dose for all experimental dosimeters with respect to SmartmA, with average dose reductions across dosimeters of 31% (breast), 21% (lung), 24% (heart), 6% (spine), 19% (eye lens), and 11% (brain), with similar results for the simulation validation study. In the phantom library study, the average dose reduction across all phantoms was 34% (breast), 20% (lung), 8% (spine), 20% (eye lens), and 8% (brain). ODM increased the noise standard deviation in reconstructed images by 6%-20%, with generally greater noise increases in anterior regions. Increasing the posterior tube current provided similar dose reduction as ODM for breast and eye lens, increased dose to the spine, with noise effects ranging from 2% noise reduction to 16% noise increase. At noise equal to SmartmA, ODM increased the estimated effective dose by 4% and 8% for chest and head scans, respectively. Increasing the posterior tube current further increased the effective dose by 15% (chest) and 18% (head) relative to SmartmA. CONCLUSIONS: ODM reduced dose in all experimental and simulation studies over a range of phantoms, while increasing noise. The results suggest a net dose/noise benefit for breast and eye lens for all studied phantoms, negligible lung dose effects for two phantoms, increased lung dose and/or noise for eight phantoms, and increased dose and/or noise for brain and spine for all studied phantoms compared to the reference protocol.

An anthropomorphic spine phantom for proton beam approval in NCI-funded trials.

As part of the approval process for the use of scattered or uniform scanning proton therapy in National Cancer Institute (NCI)-sponsored clinical trials, the Radiological Physics Center (RPC) mandates irradiation of two RPC anthropomorphic proton phantoms (prostate and spine). The RPC evaluates these irradiations to ensure that they agree with the institutions' treatment plans within criteria of the NCI-funded cooperative study groups. The purpose of this study was to evaluate the use of an anthropomorphic spine phantom for proton matched-field irradiation, and to assess its use as a credentialing tool for proton therapy beams. We used an anthropomorphic spine phantom made of human vertebral bodies embedded in a tissue substitute material called Muscle Substitute/Solid Rigid Number 4 (MS/SR4) comprising three sections: a posterior section containing the posterior surface and the spinous processes, and left and right (L/R) sections containing the vertebral bodies and the transverse processes. After feasibility studies at three institutions, the phantom, containing two thermoluminescent dosimeters (TLDs) for absolute dose measurements and two sheets of radiochromic film for relative dosimetry, was shipped consecutively to eight proton therapy centers participating in the approval study. At each center, the phantom was placed in a supine or prone position (according to the institution's spine treatment protocol) and imaged with computed tomography (CT). The images then were used with the institution's treatment planning system (TPS) to generate two matched fields, and the phantom was irradiated accordingly. The irradiated phantom was shipped to the RPC for analysis, and the measured values were compared with the institution's TPS dose and profiles using criteria of ± 7% for dose agreement and 5 mm for profile distance to agreement. All proton centers passed the dose criterion with a mean agreement of 3% (maximum observed agreement, 7%). One center failed the profile distance-to-agreement criterion on its initial irradiation, but its second irradiation passed the criterion. Another center failed the profile distance-to-agreement criterion, but no repeat irradiation was performed. Thus, seven of the eight institutions passed the film profile distance-to-agreement criterion with a mean agreement of 1.2 mm (maximum observed agreement 5 mm). We conclude that an anthropomorphic spine phantom using TLD and radiochromic film adequately verified dose delivery and field placement for matched-field treatments.

Monte Carlo calculations of lung dose in ORNL phantom for boron neutron capture therapy.

Monte Carlo simulations were performed to evaluate dose for possible treatment of cancers by boron neutron capture therapy (BNCT). The computational model of male Oak Ridge National Laboratory (ORNL) phantom was used to simulate tumours in the lung. Calculations have been performed by means of the MCNP5/X code. In this simulation, two opposite neutron beams were considered, in order to obtain uniform neutron flux distribution inside the lung. The obtained results indicate that the lung cancer could be treated by BNCT under the assumptions of calculations.

Effective dose for scoliosis patients undergoing full spine radiography.

Scoliotic patients underwent many radiological examinations during their control and treatment periods. Nowadays, few studies have calculated effective dose which is the primary indicator of radiation risk. In this study, the PCXMC program is used to calculate the effective doses associated with scoliosis radiography. Five age groups of patients, proposed by the National Radiological Protection Board, have been chosen: <1, 1-4, 5-9, 10-15 and ≥16 y (adult patients). Patient and radiographic data were collected from 99 patient examinations for both anteroposterior and lateral full spine X-ray projections. Results showed the effective dose ranged from 118 to 1596 µSv for the frontal projection and from 97 to 1370 µSv for the lateral projection, with patient age varying from 3 months to 22 y. This study presents the effective dose against patient age and demonstrates the necessity to optimise patient protection for this type of examination.

Predicted risks of second malignant neoplasm incidence and mortality due to secondary neutrons in a girl and boy receiving proton craniospinal irradiation.

The purpose of this study was to compare the predicted risks of second malignant neoplasm (SMN) incidence and mortality from secondary neutrons for a 9-year-old girl and a 10-year-old boy who received proton craniospinal irradiation (CSI). SMN incidence and mortality from neutrons were predicted from equivalent doses to radiosensitive organs for cranial, spinal and intracranial boost fields. Therapeutic proton absorbed dose and equivalent dose from neutrons were calculated using Monte Carlo simulations. Risks of SMN incidence and mortality in most organs and tissues were predicted by applying risks models from the National Research Council of the National Academies to the equivalent dose from neutrons; for non-melanoma skin cancer, risk models from the International Commission on Radiological Protection were applied. The lifetime absolute risks of SMN incidence due to neutrons were 14.8% and 8.5%, for the girl and boy, respectively. The risks of a fatal SMN were 5.3% and 3.4% for the girl and boy, respectively. The girl had a greater risk for any SMN except colon and liver cancers, indicating that the girl's higher risks were not attributable solely to greater susceptibility to breast cancer. Lung cancer predominated the risk of SMN mortality for both patients. This study suggests that the risks of SMN incidence and mortality from neutrons may be greater for girls than for boys treated with proton CSI.

A deterministic partial differential equation model for dose calculation in electron radiotherapy.

High-energy ionizing radiation is a prominent modality for the treatment of many cancers. The approaches to electron dose calculation can be categorized into semi-empirical models (e.g. Fermi-Eyges, convolution-superposition) and probabilistic methods (e.g.Monte Carlo). A third approach to dose calculation has only recently attracted attention in the medical physics community. This approach is based on the deterministic kinetic equations of radiative transfer. We derive a macroscopic partial differential equation model for electron transport in tissue. This model involves an angular closure in the phase space. It is exact for the free streaming and the isotropic regime. We solve it numerically by a newly developed HLLC scheme based on Berthon et al (2007 J. Sci. Comput. 31 347-89) that exactly preserves the key properties of the analytical solution on the discrete level. We discuss several test cases taken from the medical physics literature. A test case with an academic Henyey-Greenstein scattering kernel is considered. We compare our model to a benchmark discrete ordinate solution. A simplified model of electron interactions with tissue is employed to compute the dose of an electron beam in a water phantom, and a case of irradiation of the vertebral column. Here our model is compared to the PENELOPE Monte Carlo code. In the academic example, the fluences computed with the new model and a benchmark result differ by less than 1%. The depths at half maximum differ by less than 0.6%. In the two comparisons with Monte Carlo, our model gives qualitatively reasonable dose distributions. Due to the crude interaction model, these so far do not have the accuracy needed in clinical practice. However, the new model has a computational cost that is less than one-tenth of the cost of a Monte Carlo simulation. In addition, simulations can be set up in a similar way as a Monte Carlo simulation. If more detailed effects such as coupled electron-photon transport, bremsstrahlung, Compton scattering and the production of delta electrons are added to our model, the computation time will only slightly increase. Its margin of error, on the other hand, will decrease and should be within a few per cent of the actual dose. Therefore, the new model has the potential to become useful for dose calculations in clinical practice.

The risk of developing a second cancer after receiving craniospinal proton irradiation.

The purpose of this work was to compare the risk of developing a second cancer after craniospinal irradiation using photon versus proton radiotherapy by means of simulation studies designed to account for the effects of neutron exposures. Craniospinal irradiation of a male phantom was calculated for passively-scattered and scanned-beam proton treatment units. Organ doses were estimated from treatment plans; for the proton treatments, the amount of stray radiation was calculated separately using the Monte Carlo method. The organ doses were converted to risk of cancer incidence using a standard formalism developed for radiation protection purposes. The total lifetime risk of second cancer due exclusively to stray radiation was 1.5% for the passively scattered treatment versus 0.8% for the scanned proton beam treatment. Taking into account the therapeutic and stray radiation fields, the risk of second cancer from intensity-modulated radiation therapy and conventional radiotherapy photon treatments were 7 and 12 times higher than the risk associated with scanned-beam proton therapy, respectively, and 6 and 11 times higher than with passively scattered proton therapy, respectively. Simulations revealed that both passively scattered and scanned-beam proton therapies confer significantly lower risks of second cancers than 6 MV conventional and intensity-modulated photon therapies.

Stray radiation dose and second cancer risk for a pediatric patient receiving craniospinal irradiation with proton beams.

Proton beam radiotherapy unavoidably exposes healthy tissue to stray radiation emanating from the treatment unit and secondary radiation produced within the patient. These exposures provide no known benefit and may increase a patient's risk of developing a radiogenic cancer. The aims of this study were to calculate doses to major organs and tissues and to estimate second cancer risk from stray radiation following craniospinal irradiation (CSI) with proton therapy. This was accomplished using detailed Monte Carlo simulations of a passive-scattering proton treatment unit and a voxelized phantom to represent the patient. Equivalent doses, effective dose and corresponding risk for developing a fatal second cancer were calculated for a 10-year-old boy who received proton therapy. The proton treatment comprised CSI at 30.6 Gy plus a boost of 23.4 Gy to the clinical target volume. The predicted effective dose from stray radiation was 418 mSv, of which 344 mSv was from neutrons originating outside the patient; the remaining 74 mSv was caused by neutrons originating within the patient. This effective dose corresponds to an attributable lifetime risk of a fatal second cancer of 3.4%. The equivalent doses that predominated the effective dose from stray radiation were in the lungs, stomach and colon. These results establish a baseline estimate of the stray radiation dose and corresponding risk for a pediatric patient undergoing proton CSI and support the suitability of passively-scattered proton beams for the treatment of central nervous system tumors in pediatric patients.

Skeletal dosimetry in the MAX06 and the FAX06 phantoms for external exposure to photons based on vertebral 3D-microCT images.

3D-microCT images of vertebral bodies from three different individuals have been segmented into trabecular bone, bone marrow and bone surface cells (BSC), and then introduced into the spongiosa voxels of the MAX06 and the FAX06 phantoms, in order to calculate the equivalent dose to the red bone marrow (RBM) and the BSC in the marrow cavities of trabecular bone with the EGSnrc Monte Carlo code from whole-body exposure to external photon radiation. The MAX06 and the FAX06 phantoms consist of about 150 million 1.2 mm cubic voxels each, a part of which are spongiosa voxels surrounded by cortical bone. In order to use the segmented 3D-microCT images for skeletal dosimetry, spongiosa voxels in the MAX06 and the FAX06 phantom were replaced at runtime by so-called micro matrices representing segmented trabecular bone, marrow and BSC in 17.65, 30 and 60 microm cubic voxels. The 3D-microCT image-based RBM and BSC equivalent doses for external exposure to photons presented here for the first time for complete human skeletons are in agreement with the results calculated with the three correction factor method and the fluence-to-dose response functions for the same phantoms taking into account the conceptual differences between the different methods. Additionally the microCT image-based results have been compared with corresponding data from earlier studies for other human phantoms.

Evaluation of a commercial three-dimensional electron beam treatment planning system.

We evaluated a commercial three-dimensional (3D) electron beam treatment planning system (CADPLAN V.2.7.9) using both experimentally measured and Monte Carlo calculated dose distributions to compare with those predicted by CADPLAN calculations. Tests were carried out at various field sizes and electron beam energies from 6 to 20 MeV. For a homogeneous water phantom the agreement between measured and CADPLAN calculated dose distributions is very good except at the phantom surface. CADPLAN is able to predict hot and cold spots caused by a simple 3D inhomogeneity but unable to predict dose distributions for a more complex geometry where CADPLAN underestimates dose changes caused by inhomogeneity. We discussed possible causes for the inaccuracy in the CADPLAN dose calculations. In addition, we have tested CADPLAN treatment monitor unit and electron cut-out factor calculations and found that CADPLAN predictions generally agree with manual calculations.