Sum Of Doses Research Articles

Radiotherapy and radiology: Joint efforts for modern radiation planning and practice

With new irradiation techniques, the dose can be better matched to the contours of the tumour. The corollary is that greater precision is required. Recent intercomparison studies of treatment plans have emphasized the need to harmonise contouring practices. More of a consensus approach is based on using adaptive imaging modalities, expert group recommendations and automatic segmentation atlases, on harmonisation of dosimetric decisions through employing exhaustive nomograms for organs at risk, and on indexes for choosing optimal treatment plans. On another level, quality assurance and data pooling programmes have been set up, making use of DICOM-RT data transfer (image networks). The combination of several irradiation techniques (for example, intensity-modulated conformal radiation therapy plus CyberKnife(®) boost and re-irradiation), making it possible to irradiate tumours better, requires the cumulative doses to be recorded by dose summation software. Real awareness has been achieved in recent years as regards improving the quality of treatment, pooling data and harmonising practices.

Dosimetric quantities in radiological protection and risk assessment

Central to the application of the system of protection recommended by the InternationalCommission on Radiological Protection (ICRP) are the physical quantity, absorbed dose,and the protection quantities, equivalent and effective dose. These protection quantities areused to set dose limits, constraints and reference levels and to test compliance in thevarious activities of occupational and public exposure. They are also used inthe assessment of doses from medical procedures. Effective dose in particularhas proved to be a very valuable quantity that allows the summation of dosesfrom external radiation and internal doses from different radionuclides in a singlerisk-related value. However, while it is possible to measure external radiation exposuresand estimate internal exposures down to very low levels of dose, the associatedrisks, principally of cancer, are much less certain. Equivalent and effective dosesare calculated using simplifying assumptions to apply to reference workers andmembers of the public for the purpose of control of exposures. Risks to individuals orspecific population groups should be calculated not using these quantities butusing best scientific information. The purpose of this note is to provide a shortand readily accessible account of the purpose of the ICRP dosimetric quantities,how they are calculated, how they should be used, and how they relate to riskestimation.

Evaluation of Deformable Image Coregistration in Adaptive Dose Painting by Numbers for Head-and-Neck Cancer

To assess the accuracy of contour deformation and feasibility of dose summation applying deformable image coregistration in adaptive dose painting by numbers (DPBN) for head and neck cancer. Data of 12 head-and-neck-cancer patients treated within a Phase I trial on adaptive (18)F-FDG positron emission tomography (PET)-guided DPBN were used. Each patient had two DPBN treatment plans: the initial plan was based on a pretreatment PET/CT scan; the second adapted plan was based on a PET/CT scan acquired after 8 fractions. The median prescription dose to the dose-painted volume was 30 Gy for both DPBN plans. To obtain deformed contours and dose distributions, pretreatment CT was deformed to per-treatment CT using deformable image coregistration. Deformed contours of regions of interest (ROI(def)) were visually inspected and, if necessary, adjusted (ROI(def_ad)) and both compared with manually redrawn ROIs (ROI(m)) using Jaccard (JI) and overlap indices (OI). Dose summation was done on the ROI(m), ROI(def_ad), or their unions with the ROI(def). Almost all deformed ROIs were adjusted. The largest adjustment was made in patients with substantially regressing tumors: ROI(def) = 11.8 ± 10.9 cm(3) vs. ROI(def_ad) = 5.9 ± 7.8 cm(3) vs. ROI(m) = 7.7 ± 7.2 cm(3) (p = 0.57). The swallowing structures were the most frequently adjusted ROIs with the lowest indices for the upper esophageal sphincter: JI = 0.3 (ROI(def)) and 0.4 (ROI(def_ad)); OI = 0.5 (both ROIs). The mandible needed the least adjustment with the highest indices: JI = 0.8 (both ROIs), OI = 0.9 (ROI(def)), and 1.0 (ROI(def_ad)). Summed doses differed non-significantly. There was a trend of higher doses in the targets and lower doses in the spinal cord when doses were summed on unions. Visual inspection and adjustment were necessary for most ROIs. Fast automatic ROI propagation followed by user-driven adjustment appears to be more efficient than labor-intensive de novo drawing. Dose summation using deformable image coregistration was feasible. Biological uncertainties of dose summation strategies warrant further investigation.

Feasibility of Non-Coplanar Tomotherapy for Lung Cancer Stereotactic Body Radiation Therapy

To quantify the dosimetric gains from non-coplanar helical tomotherapy (HT) arcs for stereotactic body radiation therapy (SBRT) of lung cancer, we created oblique helical arcs by rotating patient's CT images. Ten, 20 and 30 degrees of yaws were introduced in the treatment planning for a patient with a hypothetical lung tumor at the upper, middle and lower portion of the right lung, and the upper and middle left lung. The planning target volume (PTV) was 43 cm(3). 60 Gy was prescribed to the PTV. Dose to organs at risk (OARs), which included the lungs, heart, spinal cord and chest wall, was optimized using a 2.5 cm jaw, 0.287 pitch and modulation factor of 2.5. Composite plans were generated by dose summation of the resultant plans. These plans were evaluated for its conformity index (R(x)) and percentile volume of lung receiving radiation dose of x Gy (V(x)). Conformity index was defined by the ratio of x percent isodose volume and PTV. The results show that combination of non-coplanar arcs reduced R(50) by 4.5%, R(20) by 26% and R(10) by 30% on average. Non-coplanar arcs did not affect V(20) but reduced V(10) and V(5) by 10% and 24% respectively. Composite of the non-coplanar arcs also reduced maximum dose to the spinal cord by 20-39%. Volume of chest wall receiving higher than 30 Gy was reduced by 48% on average. Heart dose reduction was dependent on the location of the PTV and the choice of non-coplanar orientations. Therefore we conclude that non-coplanar HT arcs significantly improve critical organ sparing in lung SBRT without changing the PTV dose coverage.

TH-E-211-02: Estimation of Organ Doses in Reference Pediatric Individuals Undergoing Computed Tomography Using Monte Carlo Simulations

Purpose: To establish an organ dose database for pediatric reference individuals undergoing computed tomography (CT) examinations by using Monte Carlo simulations to readily provide organ doses for patients with different age, gender, examination type, and CT scanner models. Methods and Materials: The Monte Carlo simulation model of Siemens Sensation 16 CT scanner we recently published was employed as base CT scanner model. The CT scanner model was coupled with a series of pediatric hybrid phantoms within MCNPX2.6. Organ doses from helical scans were approximated by the summation of doses from multiple axial slices included in the given scan range of interest which provided flexibility to the CT scan dosimetry calculations. Organ dose calculations were performed for a single axial scan which started from the top of head down to the bottom of the phantoms with an interval of 10 mm for a total of 10 pediatric phantoms: newborn, 1-year, 5-year, 10-year, and 15-year males and females. Results: Absorbed doses (mGy/100mAs-mGy) normalized to 100 mAs and CTDIvol (mGy) were calculated for a total of 30 organs and tissues including active marrow under the tube potentials of 80, 100, and 120 kVp. The normalized organ doses for head, chest, and abdomen/pelvis scans were calculated and compared with the values from CT-Expo. Organ doses based on the hybrid phantom series in this study overall agreed with those from CT-Expo based on two voxel phantoms. Significant dose differences caused by the unrealistic organ locations which were observed for the adult stylized phantoms in the recently published study were not observed. Conclusion: The organ dose matrix established for pediatric individuals will be coupled with the adult version which was recently published and be incorporated into a graphical user interface to provide user-friendly computer program for CT organ dose estimations.

SU‐E‐J‐72: In Vivo Quality Assurance of Head and Neck Cancer IMRT Treatments Using TomoTherapyˈˈs Exit Detector Data

Purpose: The primary objective of this study was to explore the feasibility of utilizing the exit‐detector‐data (EDD) for in vivo quality assurance of head and neck (H&N) cancer patient treatments. Methods: Using TomoTherapyˈs Delivery‐Verification (DVS) software we retrospectively evaluated treatments (53 fractions) of ten H&N cancer patients for dose delivery deviations. MV‐CT scans covering the entire length of treatment volumes and respective EDD files were used for DVS reconstruction and subsequent dose computation on a GPU platform. Differences between planned and reconstructed sinograms were analyzed to evaluate the leaf‐opening time (LOT) differences. Reconstructed dose distributions of fractionated‐deliveries were scaled, convolved to estimate composite dose distributions, and compared against planned dose distributions. The dose summation was strictly based on rigid registrations of the fractionated doses and it did not account for soft‐tissue/dose deformations. Computed DVHs were strictly based on the plannned contours and they did not include anatomical changes, if any. Results: Typical average LOT differences were −3msec‐eq with a standard‐deviation of 8msec‐eq, indicating the integrity of delivered treatments. Although, significant differences were noted for individual reconstructed fraction‐doses, the differences in cumulative reconstructed dose‐distributions were found to be small. Cumulative reconstructed plans show that the minimal dose (D99%) to the PTV was decreased by 1.6±1.4Gy. Average mean doses of the left and right parotids decreased by 1.0±0.6Gy and 0.8±0.7Gy, respectively. The mean dose and volume receiving >60Gy for the upper‐esophagus decreased by 0.7±1.0Gy and 0.6±2.3%, respectively. Overall all the reconstructed doses are lower than the original plans by ∼1.0% and this is consistent with our antropomorphic phantom measurements. Conclusions: The results of study suggest that EDDs are useful for DVS reconstruction and subsequent dose computation and can be a great tool for in vivo quality assurance of clinical H&N cancer treatments. Further studies are needed to account for deformation effects.

SU-E-J-43: Dosimetric Impact of Patient Positioning and Anatomical Changes over the Course of Craniospinal Irradiation Using Helical Tomotherapy

Purpose: To evaluate the impact of patient positioning and anatomical changes over the course of craniospinal irradiation (CSI) using helical tomotherapy. This is done using daily megavoltage computed tomography (MVCT) images and MIM version 5.1, a commercial deformable image registration tool. Methods: A summation of the daily dose delivered to four patients over their treatment courses were calculated using the pre‐treatment MVCT. First, the TomoTherapy Planned Adaptive software was used to calculate the patient dose as treated using the daily MVCT and leaf motion sinogram data. Then, the dose distribution for each fraction was deformed to the dose grid of the planning kilovoltage (kV) CT based on the deformation mapping of the MVCT to the kVCT. The dose to the clinical target volume (CTV) and organs at risk, including the kidneys,lungs, and esophagus, were evaluated. Results: The CTV dose coverage, as indicated by Dn% (n=0, 2, 50, 98, 100), is nearly constant throughout the CSI treatments for all four patients. This consistency is seen despite a weight loss of 4 kg for one patient. The daily CTV dose fluctuations are well within 1%, except for a single fraction where the D0% and D2% are nearly doubled due to a slight overlap of the treatment volume as the dose delivery was restarted after an interruption. The median dose and the volume receiving over 1 Gy for each fraction (V1Gy) for the kidneys and lungs change by <1% from day to day. The esophagus V1Gy and D50% change by <4%. Conclusions: The consistency in dosimetric metrics for the CTV and organs at risk throughout the CSI tomotherapy treatment indicates the advantage of daily imaging verification. Our results suggest that it may not be necessary to create a new CSI treatment plan even when the patient experiences significant weight loss during the treatment.

SU‐E‐T‐654: Calculation of Cumulative Biological Effective Dose Distributions for Multimodality Treatment Regimes

Purpose: Evidence has recently been reported supporting the role of stereotactic body radiotherapy (SBRT) as a supplemental treatment option in the form of a boost or salvage reirradiation following conventional radiotherapy. It may therefore be desirable to augment the process of physical dose summation in the cumulative plan evaluation process by constructing corresponding biological effective dose (BED) distributions that incorporate the biological effects of the different dose fractionation schemes required for multimodality treatments. To that end, we developed a computational process for calculating cumulative BED distributions for patients receiving conventional radiotherapy followed by SBRT. Methods: We developed a program designed to accept two DICOM dose matrices, as calculated in standard treatment planning systems, and calculate the BED at each matrix element obeying the dose per fraction dependence in the BED formalism. It then calculates the cumulative BED distribution for multimodality treatment regimes by matrix summation and outputs the result in DICOM format. Two clinical head and neck IMRT cases (large field (2.13Gy × 33) and small field (2Gy × 32)) were evaluated as part of a pilot study to demonstrate the overall feasibility of the calculation scheme. Following clinical IMRT planning, each case was planned in a mock SBRT scenario (6Gy × 5) where a smaller planning volume was drawn to simulate a boost or salvage reirradiation. The clinical IMRT and mock SBRT dose matrices were then processed to generate cumulative BED distributions. Results: Our computational process was successful in producing cumulative BED distributions. For the large field IMRT case, the overall BED distribution beyond the initial treated volume was dominated by the initial IMRT course, whereas clear additive increase in the BED distribution beyond the initial treated volume was evident in the small field case. Conclusions: Cumulative BED distributions may reveal useful clinical information during plan evaluation.

SU‐E‐T‐392: Using Deformable Registration to Evaluate Combined Biological Effective Dose in Patients Receiving Combination External Beam Radiotherapy and Brachytherapy of Prostate Cancer Patients

Purpose: To determine the feasibility of combining external beam radiotherapy (EBRT) and brachytherapy (BT) in terms of Biological Effective Dose (BED) using deformable image registration to evaluate treatment. Methods: This study analyzed combined EBRT and BT treatments of prostate cancer. Each patient received 45 Gy EBRT IMRT or VMAT technique prescribed to a planning target volume (PTV) followed by a 110 Gy or 100 Gy BT boost using I‐125 or Pd‐103, respectively. EBRT planning CT and post‐implant CT were co‐registered using rigid/deformable registration. The BT dose matrix was mapped via deformable transformation component to the EBRT CT study. The seed dose distribution was combined with the EBRT CT by the re‐sampling of the dose matrix. BED calculations were performed utilizing the linear quadratic model assuming &amp;#945;/&amp;#946; ratio of 2 to convert EBRT and BT dose distributions. This yields evaluable topographical dose volume histogram (DVH) for evaluation of dosage to the PTV and organs at risk (OAR). Results: Twenty seven patient plans were successfully reconstructed to yield combined BED information. The average EBRT BED was found to be 85 Gy and the BT BED average was to be 127 (range 100–155 Gy) for a combined total average dose of 212 (range 185–240 Gy). The combined V0.1cc and V2cc of OAR were evaluated in both conventional and a novel topographical technique. Conclusions: We found it feasible to combine EBRT and BT treatment plans for BED analysis of both target and OAR. This allows for a novel and dynamic evaluation of combined therapy. BED distribution can enable clinicians to identify areas where failure can occur and assess areas of potential toxicity, currently not possible using physical dose summation. It can also be used as a tool for physicians to objectively assess the quality of treatment plans and for multi institutional comparisons.

Second re-irradiation: Efficacy, dose and toxicity in patients who received three courses of radiotherapy with overlapping fields

Purpose To explore the outcome, cumulative dose and toxicity in 23 patients after a third radiation treatment, with a partial or complete overlap of the previous two irradiated regions. Methods and material The dose summation of the three radiation plans was made by the planning system. For patients treated with cyberknife or brachytherapy dose summation was done by dose point calculations. Efficacy and toxicity was scored by looking at the reduction of tumor, pain and bleeding. Results Symptomatic response was observed in 81% and 73% of the patients after, respectively, the third and second radiation. The median cumulative maximum dose to the tumor and its regions was 133 Gy 3 (range: 82–496 Gy 3). The median corrected cumulative dose for the rectum, bowel and bladder resulted in 91 Gy 3, 73 Gy 3 and 79 Gy 3, respectively. Grade 3 acute skin toxicity was only seen in the third radiation course. Conclusion The constraints of 100 Gy 3 for rectum, 90 Gy 3 for bowel and 110 Gy 3 for bladder are safe and can be used as guidelines in the decision for re-irradiation. Symptomatic relieve was seen in 81% of the patients with low grade 3 and no grade 4 acute and late toxicity.

Monte Carlo dose calculation of GZP6 60Co stepping source based on a matrix shift technique

Background As a routine method for stepping source simulation, a Monte Carlo program is run according to the number of steps and then the summation of dose from each run is taken to obtain total dose distribution. This method is time consuming. Aim As an alternative method, a matrix shift based technique was applied to simulate a stepping source for brachytherapy. Materials and methods The stepping source of GZP6 brachytherapy unit was simulated. In a matrix shift method, it is assumed that a radiation source is stationary and instead the data matrix is shifted based on the number of steps. In this study, by running MCNPX program for one point and calculation of the dose matrix using the matrix shift method, the isodose curves for the esophageal cancer tumor lengths of 4 and 6 cm were obtained and compared with the isodose curves obtained by running MCNPX programs in each step position separately (15 and 23 steps for esophageal cancer tumor lengths of 4 and 6 cm, respectively). Results The difference between the two dose matrixes for the stepping and matrix shift methods based on the average dose differences are 3.85 × 10 −4 Gy and 5.19 × 10 −4 Gy for treatment length of 4 cm and 6 cm, respectively. Dose differences are insignificant and these two methods are equally valid. Conclusions The matrix shift method presented in this study can be used for calculation of dose distribution for a brachytherapy stepping source as a quicker tool compared to other routine Monte Carlo based methods.

Clinical feasibility of TBI with helical tomotherapy

Our purpose was to present the clinical feasibility of TBI with helical tomotherapy (HT) in four patients with AML. Treatment planning, delivery, dose verification and summation, toxicity and patient outcomes for each patient are presented. TBI prescription was set in such a manner that 80% of the clinical target volume received 12 Gy in six fractions, at two fractions per day. Dose reconstruction was carried out by recontouring the regions of interest in the daily pretreatment megavoltage computed tomography of each individual fraction and calculating its corresponding dose. A deformable registration model was used for dose summation of all individual fractions. Differences between planned and delivered doses were calculated. Average planned and delivered doses to the regions of interest differed by up to 2.7%. TBI toxicity was limited to radiotherapy oncology group grade 1 dermatitis in all patients and grade 1 headache in one patient. Two patients are alive with no evidence of disease and no GVHD. Two patients died of GVHD, but there was no evidence of disease at the time of death. We conclude that HT simplifies the process of TBI. Dose verification is possible with HT showing small differences between plan and delivered doses.

SU-GG-T-79: Voxel-Based Imaging Analysis for Quantitative Characterization of Post-Implant Prostate Edema in Permanent Prostate Brachytherapy

Purpose: Edema‐induced tissue and source movements can introduce significant deviations in the dose delivered to individual patients. Nonetheless, prostate edema has remained as one of the most unpredictable factors. This work is to develop and test a voxel‐based imaginganalysis approach for quantitative analysis and characterization of prostate edema for patient‐specific post‐implant dosimetry.Method and Materials: Post‐implant serial CTimaging was used to describe the 3D evolution of prostate edema. The CTimages were acquired at approximately 2‐hours, 1‐, 6‐, 11‐, 15‐, 30‐, and 42‐days after the source implantation. The Bioimage Suite software (www.bioimagesuite.org) was used to register and analyze the serial image datasets. Rigid image registrations were performed initially for each consecutive pairs of seven CT datasets so that the prostate in each image dataset was aligned in a common coordinate system. Deformable image registration was then performed for each pair of the re‐aligned consecutive images. The deformation matrices obtained for the consecutive image pairs were used for quantitative analysis of edema evolution characteristics on a voxel‐by‐voxel basis. Results: An imaginganalysis framework for post‐implant serial CTimages has been implemented. The application of this approach was illustrated using real patient datasets. The accuracy of image registration algorithms was tested using simulated datasets with known rigid‐body displacements and tissue deformations. Initial analysis of the deformation matrices obtained from the patient datasets showed that the implanted radioactive sources moved mostly with tissue with little relative migration during edema resolution and the edema resolution was anisotropic. Conclusions: A voxel‐based image registration and analysis approach has been developed for quantitative characterization of patient‐specific post‐implant edema evolution. The spatial correspondence established by the deformation matrices among the voxels sampled at different edema resolution stages would enable accurate calculation and proper summation of radiation doses delivered to each tumor sub‐volume in post‐implant dosimetry.

MO-FF-A4-04: A Method to Construct Synthetic Maps of Spatially Correlated Deformable Image Registration Errors by Random Sampling of De-Correlated Error Modes

Purpose: To develop and test a method for constructing random synthetic maps of spatially correlated deformable image registration errors for estimating uncertainties in daily dose summation. Method and Materials: Two CTs were deformably registered 50 times using a variable region of interest (ROI) as the target of the registration. The displacement vector fields (DVFs) for anatomic motion included spatially correlated errors due to the variable ROI. Maps of the DVF error were created by subtracting the mean DVF from the individual DVFs for the volume shared by all ROIs. These DVF error maps were used as a training set to which principal components analysis was applied, producing spatially de-correlated modes of DVF error. These modes were sampled independently and used to reconstruct new synthetic maps of DVF error that reproduced the characteristics of the training set. Results: We applied three tests to show that a set of our sampled DVF error maps was statistically indistinguishable from a set of validation error maps: (1) the standard deviation of the sampled DVF errors was comparable to that of the validation set; (2) the eigenvalue spectra were the same for the sampled and validation sets; (3) the Kolmogorov-Smirnov test applied to the principal coefficient distributions for the two sets was consistent with their indistinguishability. Conclusion: We have developed a method to construct DVF error maps by sampling probability distributions of the spatially de-correlated error modes. We validated our procedure by demonstrating that maps of DVF error produced by our method were statistically indistinguishable from validation error maps. We propose to use this method to calculate the effect of DVF error on daily dose summation using deformable image registration.

SU-GG-T-256: An Enhanced DICOM-RT Viewer

Purpose: To present an enhanced DICOM-RT viewer for clinical practitioners and R&D scientists and engineers in radiation therapy. Methods and Materials: DICOM-RT is a set of DICOM extensions for radiotherapy. Despite the fact that DICOM-RT was devised in 1997 and has currently been adopted by all major manufacturers, the DICOM-RT viewer is not readily available to many healthcare providers and R&D scientists and engineers in radiation therapy. Triggered by clinical needs, a DICOM/DICOM-RT viewer, DICOMan, was developed on Microsoft Windows XP platform started from scratch three years ago. It supports all kinds of DICOM-RT objects, namely RT Image, RT Structure Set, RT Plan, RT Dose and RT Record. Added to the viewer, a set of built-in tools were also implemented, such as DICOM Decompressor, DICOM Pusher, DICOM Retriever, DICOM editor, DICOM Anonymizer, DICOM Format Converter and so on. Some RT information that is not explicitly expressed in RT objects, such as incident energy fluence and isodose curves, can be reproduced and rendered to facilitate plan review. Results: DICOMan has been tested, routinely used and constantly upgraded for about three years. It has been frequently used to view DICOM CD-ROMs, push DICOM images to treatment planning systems, retrieve images from RT PACS, review treatment plans and help perform dose summation. The anonymizer, format converter and editor are handy tools for R&D scientists and engineers who need to handle DICOM/DICOM-RT objects. Conclusion: DICOM RT extension models radiation therapy practice in many modules related to clinical components of radiation therapy. Many of them are cross-referenced and coexist with the referenced ones in different objects. The regular DICOM viewer can not render RT objects appropriately. A dedicated DICOM RT viewer is needed.

A New Approach to Computing Normal Tissue Complication Probability of an Intensity-Modulated Radiotherapy Treatment with Stereotactic Radiotherapy Boost of Nasopharyngeal Carcinoma: A Case Study

We attempted to develop a method to compute the normal tissue complication probability (NTCP) of various critical organs from combined intensity-modulated radiotherapy (IMRT) and stereotactic radiotherapy (SRT) boost treatment of nasopharyngeal carcinoma (NPC), with the aid of a nonlinear image registration method. The SRT's planning computed tomography (CT) of a NPC patient treated with IMRT was warped to the IMRT's planning CT using a nonlinear image registration. Because CT and dose were inherently in-register, the entire dose distribution could be deformed using the same deformation field derived from the two CT sets. Using the biologically effective dose concept and the linear-quadratic model, physical doses of IMRT and SRT were converted to a 2Gy-per-fraction equivalent dose to facilitate dose summation. The variation of organs' maximum doses of the combined treatments between traditional maximum dose sum and the proposed method was 1.5Gy ± 1.7Gy. After the correction of the effect of fractionation and dose heterogeneity within each organ, NTCP of each organ of interest was computed for the combined treatments. Based on the results of this case study, it is believed that dose registration could be a method for the NTCP computation of various critical organs when different fractionation schemes of radiation therapy treatment are instituted.

Assessment of patient doses in X-ray diagnostics

This paper presents a computer code for the assessment of absorbed effective doses and dose equivalents in X-ray diagnostics. The absorbed doses in a patient's tissues in various X-ray examinations were estimated using the Monte Carlo method. The X-ray spectra generated by the empirical TASMIP model were verified. Further simulations were based on an anthropomorphic phantom of a standard adult. The absorbed doses in voxels in various diagnostic X-ray examinations were calculated using the Monte Carlo method. The result of the calculations was an array of X-ray flux through the surface of every voxel, and a summation of doses on voxels over organ and tissue volumes. Average absorbed doses on organs and tissues of the phantom were determined by further division by the number of voxels inside the respective organ or tissue. Doses in 22 standard organs of the phantom for various standard X-ray examinations were computed. The doses obtained from Monte Carlo simulations were compared with the measured absorbed doses. A comparison was made with the doses calculated by several similar programs for calculating patients' organ doses and the effective dose in medical X-ray examinations.

Generation of Composite Dose and Biological Effective Dose (BED) Over Multiple Treatment Modalities and Multistage Planning Using Deformable Image Registration

Currently there are no commercially available tools to generate composite plans across different treatment modalities and/or different planning image sets. Without a composite plan, it may be difficult to perform a meaningful dosimetric evaluation of the overall treatment course. In this paper, we introduce a method to generate composite biological effective dose (BED) plans over multiple radiotherapy treatment modalities and/or multistage plans, using deformable image registration. Two cases were used to demonstrate the method. Case I was prostate cancer treated with intensity-modulated radiation therapy (IMRT) and a permanent seed implant. Case II involved lung cancer treated with two treatment plans generated on two separate computed tomography image sets. Thin-plate spline or optical flow methods were used as appropriate to generate deformation matrices. The deformation matrices were then applied to the dose matrices and the resulting physical doses were converted to BED and added to yield the composite plan. Cell proliferation and sublethal repair were considered in the BED calculations. The difference in BED between normal tissues and tumor volumes was accounted for by using different BED models, α/β values, and cell potential doubling times. The method to generate composite BED plans presented in this paper provides information not available with the traditional simple dose summation or physical dose summation. With the understanding of limitations and uncertainties of the algorithms involved, it may be valuable for the overall treatment plan evaluation.

SU-FF-T-609: Dose Summation Technology for Radiation Therapy Facilities Equipped with Heterogeneous Planning and Delivery Systems

Purpose: Multi‐modality dose summation is often needed for patients who have been previously treated or are being treated with different systems, but unfortunately, it is rarely available in commercial treatment planning systems. This study presents a technology that sums up 3D dose distributions planned/delivered by different treatment systems to help the radiation therapy team in making optimal plans. Methods and Materials: Ideally, dose summation would be carried out through DICOM RTDOSE import/export, but this option is presently non functional because the import capability is difficult to implement. To remedy the lack of RTDOSE import in our clinic, a software system, DICOMan, was developed to address DICOM issues such as object visualization, system incompatibility, file transfer and format conversion, etc. DICOMan first acts as a DICOM storage server receiving DICOM RTDOSE file that is exported from a planning workstation. It then reads the dose matrix, converts it to another format that is recognizable by the other treatment planning system where dose summation or plan comparison is performed. Results: RTDOSE was exported from the HiArt Tomotherapy Planning System to DICOMan, where it was displayed and converted to the Philips Pinnacle RTPdose format along with specific scripting files that automate the file transfer and the dose summation process. Conclusion: A dose summation function is very useful and sometimes critical in radiation therapy clinics equipped with heterogeneous planning and delivery systems. It reduces uncertainties in the case of multiple treatment systems or patients transferred to other systems. It provides quantitative rather than qualitative dose estimations. Before DICOM RTDOSE import/export becomes widely implemented, the technology described here is helpful in assisting radiation therapy clinics to deliver quality care in the multisystem setting which is so prevalent.

A simplified method of four‐dimensional dose accumulation using the mean patient density representation

The purpose of this work was to demonstrate, both in phantom and patient, the feasibility of using an average 4DCT image set (AVG-CT) for 4D cumulative dose estimation. A series of 4DCT numerical phantoms and corresponding AVG-CTs were generated. For full 4D dose summation, static dose was calculated on each phase and cumulative dose was determined by combining each phase's static dose distribution with known tumor displacement. The AVG-CT cumulative dose was calculated similarly, although the same AVG-CT static dose distribution was used for all phases (i.e., tumor displacements). Four lung cancer cases were also evaluated for stereotactic body radiotherapy and conformal treatments; however, deformable image registration of the 4DCTs was used to generate the displacement vector fields (DVFs) describing patient-specific motion. Dose discrepancy between full 4D summation and AVG-CT approach was calculated and compared. For all phantoms, AVG-CT approximation yielded slightly higher cumulative doses compared to full 4D summation, with dose discrepancy increasing with increased tumor excursion. In vivo, using the AVG-CT coupled with deformable registration yielded clinically insignificant differences for all GTV parameters including the minimum, mean, maximum, dose to 99% of target, and dose to 1% of target. Furthermore, analysis of the spinal cord, esophagus, and heart revealed negligible differences in major dosimetric indices and dose coverage between the two dose calculation techniques. Simplifying 4D dose accumulation via the AVG-CT, while fully accounting for tumor deformation due to respiratory motion, has been validated, thereby, introducing the potential to streamline the use of 4D dose calculations in clinical practice, particularly for adaptive planning purposes.