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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Assessing the feasibility of volumetric-modulated arc therapy using simultaneous integrated boost (SIB-VMAT): An analysis for complex head-neck, high-risk prostate and rectal cancer cases

Intensity-modulated radiotherapy (IMRT) allowed the simultaneous delivery of different doses to different target volumes within a single fraction, an approach called simultaneous integrated boost (SIB). As consequence, the fraction dose to the boost volume can be increased while keeping low doses to the elective volumes, and the number of fractions and overall treatment time will be reduced, translating into better radiobiological effectiveness. In recent years, volumetric-modulated arc therapy (VMAT) has been shown to provide similar plan quality with respect to fixed-field IMRT but with large reduction in treatment time and monitor units (MUs) number. However, the feasibility of VMAT when used with SIB strategy has few investigations to date. We explored the potential of VMAT in a SIB strategy for complex cancer sites. A total of 15 patients were selected, including 5 head-and-neck, 5 high-risk prostate, and 5 rectal cancer cases. Both a double-arc VMAT and a 7-field IMRT plan were generated for each case using Oncentra MasterPlan treatment planning system for an Elekta Precise linac. Dosimetric indexes for targets and organs at risk (OARs) were compared based on dose-volume histograms. Conformity index, homogeneity index, and dose-contrast index were used for target analyses. The equivalent uniform doses and the normal tissue complication probabilities were calculated for main OARs. MUs number and treatment time were analyzed to score treatment efficiency. Pretreatment dosimetry was performed using 2-dimensional (2D)-array dosimeter. SIB-VMAT plans showed a high level of fluence modulation needed for SIB treatments, high conformal dose distribution, similar target coverage, and a tendency to improve OARs sparing compared with the benchmark SIB-IMRT plans. The median treatment times reduced from 13 to 20 minutes to approximately 5 minutes for all cases with SIB-VMAT, with a MUs reduction up to 22.5%. The 2D-array ion-chambers' measurements reported an agreement of more than 95% for a criterion of 3% to 3 mm. SIB-VMAT was able to combine the advantages of conventional SIB-IMRT with its highly conformal dose distribution and OARs sparing and the advantages of 3D-conformal radiotherapy with its fast delivery.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Dosimetric evaluation of MapCHECK 2 and 3DVH in the IMRT delivery quality assurance process

Based on per-field data, 3 dose-volume histogram (DVH) is designed to calculate 3-dimensional (3D) dose using patient-computed tomography (CT) for an intensity-modulated radiation therapy (IMRT) delivery quality assurance (DQA) process measured with diode detector arrays. In this study, the characteristics and suitability of 3DVH for an IMRT DQA process were evaluated by assessment of clinically applied results. The DQA plans were prepared with a 2D diode detector array (MapCHECK 2) for 20 IMRT patients (10 with head and neck cancer and 10 with prostate cancer), and the matching rate between the calculated dose and the measured dose was analyzed. The relative dose differences between the original IMRT plan and the recalculated plan by 3DVH were evaluated for tumor target and organs at risk (OARs). Confidence limits (CLs) were determined for quantification of the degree of agreement that should be expected in each DQA method. The individual CLs for DQA accuracy of 3D dosimetric evaluation in the tumor target and OARs were also calculated to evaluate the differences compared with conventional 2D-based DQA results. The matching rates were sufficient to validate the accuracy of IMRT DQA analyses and the calculated CL values were reasonable values considering the normal criteria of our institution. The 3DVH analysis generally had better matching rate than per-field measurement analysis and the CL values for OARs were better than those for the planning target volume (PTV). The usefulness of the 3DVH tool was verified for IMRT DQA from the point of view of dose evaluation in the corresponding patient's CT data. It also enables dosimetric evaluation in each important structure (PTV and OARs), which can promote more effective evaluation of DQA error in terms of tumor treatment and side effects.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Dosimetric comparison of 3D conformal, IMRT, and V-MAT techniques for accelerated partial-breast irradiation (APBI)

The purpose is to dosimetrically compare the following 3 delivery techniques: 3-dimensional conformal radiation therapy (3D-CRT), intensity-modulated arc therapy (IMRT), and volumetric-modulated arc therapy (V-MAT) in the treatment of accelerated partial-breast irradiation (APBI). Overall, 16 patients with T1/2N0 breast cancer were treated with 3D-CRT (multiple, noncoplanar photon fields) on the RTOG 0413 partial-breast trial. These cases were subsequently replanned using static gantry IMRT and V-MAT technology to understand dosimetric differences among these 3 techniques. Several dosimetric parameters were used in plan quality evaluation, including dose conformity index (CI) and dose-volume histogram analysis of normal tissue coverage. Quality assurance studies including gamma analysis were performed to compare the measured and calculated dose distributions. The IMRT and V-MAT plans gave more conformal target dose distributions than the 3D-CRT plans (p < 0.05 in CI). The volume of ipsilateral breast receiving 5 and 10 Gy was significantly less using the V-MAT technique than with either 3D-CRT or IMRT (p < 0.05). The maximum lung dose and the ipsilateral lung volume receiving 10 (V{sub 10}) or 20 Gy (V{sub 20}) were significantly less with both V-MAT and IMRT (p < 0.05). The IMRT technique was superior to 3D-CRT and V-MAT of low dose distributions in ipsilateral lung (p < 0.05 in V{sub 5} and D{sub 5}). The total mean monitor units (MUs) for V-MAT (621.0 ± 111.9) were 12.2% less than those for 3D-CRT (707.3 ± 130.9) and 46.5% less than those for IMRT (1161.4 ± 315.6) (p < 0.05). The average machine delivery time was 1.5 ± 0.2 minutes for the V-MAT plans, 7.0 ± 1.6 minutes for the 3D-CRT plans, and 11.5 ± 1.9 minutes for the IMRT plans, demonstrating much less delivery time for V-MAT. Based on this preliminary study, V-MAT and IMRT techniques offer improved dose conformity as compared with 3D-CRT techniques without increasing dose to the ipsilateral lung. In terms of MU and delivery time, V-MAT is significantly more efficient for APBI than for conventional 3D-CRT and static-beam IMRT.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Dosimetric effect of Elekta Beam Modulator micromultileaf in three-dimensional conformal radiotherapy and intensity-modulated radiotherapy for prostate cancer

The purpose of this study is to analyze the dosimetric effect of Elekta Beam Modulator in 3-dimensional conformal radiation therapy (3DCRT) and in intensity-modulated radiation therapy (IMRT) for localized prostate cancer. We compared treatment plans developed with 2 different Elekta multileaf collimators (MLC): Beam Modulator micro-MLC (mMLC) (4-mm leaf width at the isocenter) and standard MLC (10-mm leaf width at the isocenter). The comparison was performed for 15 patients with localized prostate cancer in 3DCRT and IMRT delivery; a total of 60 treatment plans were processed. The dose-volume histograms were used to provide the quantitative comparison between plans. In particular, we analyzed differences between rectum and bladder sparing in terms of a set of appropriate Vx (percentage of organ at risk [OAR] volume receiving the x dose) and differences between target conformity and coverage in terms of coverage factor and conformation number. Our analysis demonstrates that in 3DCRT there is an advantage in the use of Elekta Beam Modulator mMLC in terms of organ sparing; in particular, a significant decrease in rectal V{sub 60} and V{sub 50} (p = 0.001) and in bladder V{sub 70} and V{sub 65} (p = 0.007 and 0.002, respectively) was found. Moreover, a better target dose conformity was obtained (p = 0.002). IMRT plans comparison demonstrated no significant differences between the use of the 4 or 10-mm MLCs. Our analysis shows that in 3DCRT the use of the Elekta Beam Modulator mMLC gives a gain in target conformity and in OARs dose sparing whereas in IMRT plans there is no advantage.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

A treatment planning approach to spatially fractionated megavoltage grid therapy for bulky lung cancer

The purpose of this study was to explore the treatment planning methods of spatially fractionated megavoltage grid therapy for treating bulky lung tumors using multileaf collimator (MLC). A total of 5 patients with lung cancer who had gross tumor volumes ranging from 277 to 635 cm{sup 3} were retrospectively chosen for this study. The tumors were from 6.5 to 9.6 cm at shortest dimension. Several techniques using either electronic compensation or intensity-modulated radiation therapy (IMRT) were used to create a variety of grid therapy plans on the Eclipse treatment planning system. The dose prescription point was calculated to the volume, and a dose of 20 Gy with 6-MV/15-MV beams was used in each plan. The dose-volume histogram (DVH) curves were obtained to evaluate dosimetric characteristics. In addition, DVH curves from a commercially available cerrobend grid collimator were also used for comparison. The linear-quadratic radiobiological response model was used to assess therapeutic ratios (TRs) and equivalent uniform doses (EUD) for all generated plans. A total of 6 different grid therapy plans were created for each patient. Overall, 4 plans had different electronic compensation techniques: Ecomps-Tubes, Ecomps-Circles, Ecomps-Squares, and Ecomps-Weave; the other 2 plans used IMRT and IMRT-Weave techniques. The DVH curves and TRs demonstrated that these MLC-based grid therapy plans can achieve dosimetric properties very similar to those of the cerrobend grid collimator. However, the MLC-based plans have larger EUDs than those with the cerrobend grid collimator. In addition, the field shaping can be performed for targets of any shape in MLC-based plans. Thus, they can deliver a more conformal dose to the targets and spare normal structures better than the cerrobend grid collimator can. The plans generated by the MLC technique demonstrated the advantage over the standard cerrobend grid collimator on accommodating targets and sparing normal structures. Overall, 6 different plans showed 6 different dosimetric parameters. However, an optimal grid therapy plan selection from among these 6 types requires more information from clinical trials and radiobiological studies.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Left-sided breast cancer irradiation using rotational and fixed-field radiotherapy

The 3-dimensional conformal radiotherapy (3DCRT) technique is the standard for breast cancer radiotherapy. During treatment planning, not only the coverage of the planning target volume (PTV) but also the minimization of the dose to critical structures, such as the lung, heart, and contralateral breast tissue, need to be considered. Because of the complexity and variations of patient anatomy, more advanced radiotherapy techniques are sometimes desired to better meet the planning goals. In this study, we evaluated external-beam radiation treatment techniques for left breast cancer using various delivery platforms: fixed-field including TomoDirect (TD), static intensity-modulated radiotherapy (sIMRT), and rotational radiotherapy including Elekta volumetric-modulated arc therapy (VMAT) and tomotherapy helical (TH). A total of 10 patients with left-sided breast cancer who did or did not have positive lymph nodes and were previously treated with 3DCRT/sIMRT to the entire breast were selected, their treatment was planned with Monaco VMAT, TD, and TH. Dosimetric parameters including PTV coverage, organ-at-risk (OAR) sparing, dose-volume histograms, and target minimum/maximum/mean doses were evaluated. It is found that for plans providing comparable PTV coverage, the Elekta VMAT plans were generally more inhomogeneous than the TH and TD plans. For the cases with regional node involvement, the average mean doses administered to the heart were 9.2 (± 5.2) and 8.8 (± 3.0) Gy in the VMAT and TH plans compared with 11.9 (± 6.4) and 11.8 (± 9.2) Gy for the 3DCRT and TD plans, respectively, with slightly higher doses given to the contralateral lung or breast or both. On average, the total monitor units for VMAT plans are 11.6% of those TH plans. Our studies have shown that VMAT and TH plans offer certain dosimetric advantages over fixed-field IMRT plans for advanced breast cancer requiring regional nodal treatment. However, for early-stage breast cancer fixed-field radiotherapy is potentially more beneficial in terms of OAR sparing.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Initial experience of ArcCHECK and 3DVH software for RapidArc treatment plan verification

The purpose of this study was to perform delivery quality assurance with ArcCHECK and 3DVH system (Sun Nuclear, FL) and to evaluate the suitability of this system for volumetric-modulated arc therapy (VMAT) (RapidArc [RA]) verification. This software calculates the delivered dose distributions in patients by perturbing the calculated dose using errors detected in fluence or planar dose measurements. The device is tested to correlate the gamma passing rate (%GP) and the composite dose predicted by 3DVH software. A total of 28 patients with prostate cancer who were treated with RA were analyzed. RA treatments were delivered to a diode array phantom (ArcCHECK), which was used to create a planned dose perturbation (PDP) file. The 3DVH analysis used the dose differences derived from comparing the measured dose with the treatment planning system (TPS)-calculated doses to perturb the initial TPS-calculated dose. The 3DVH then overlays the resultant dose on the patient's structures using the resultant “PDP” beams. Measured dose distributions were compared with the calculated ones using the gamma index (GI) method by applying the global (Van Dyk) normalization and acceptance criteria, i.e., 3%/3 mm. Paired differences tests were used to estimate statistical significance of the differences between the composite dose calculated using 3DVH and %GP. Also, statistical correlation by means of logistic regression analysis has been analyzed. Dose-volume histogram (DVH) analysis for patient plans revealed small differences between treatment plan calculations and 3DVH results for organ at risk (OAR), whereas planning target volume (PTV) of the measured plan was systematically higher than that predicted by the TPS. The t-test results between the planned and the estimated DVH values showed that mean values were incomparable (p < 0.05). The quality assurance (QA) gamma analysis 3%/3 mm showed that in all cases there were only weak-to-moderate correlations (Pearson r: 0.12 to 0.74). Moreover, clinically relevant differences increased with increasing QA passing rate, indicating that some of the largest dose differences occurred in the cases of high QA passing rates, which may be called “false negatives.” The clinical importance of any disagreement between the measured and the calculated dose is often difficult to interpret; however, beam errors (either in delivery or in TPS calculation) can affect the effectiveness of the patient dose. Further research is needed to determinate the role of a PDP-type algorithm to accurately estimate patient dose effect.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Dosimetric comparison of IMRT rectal and anal canal plans generated using an anterior dose avoidance structure

To describe a dosimetric method using an anterior dose avoidance structure (ADAS) during the treatment planning process for intensity-modulated radiation therapy (IMRT) for patients with anal canal and rectal carcinomas. A total of 20 patients were planned on the Elekta/CMS XiO treatment planning system, version 4.5.1 (Maryland Heights MO) with a superposition algorithm. For each patient, 2 plans were created: one employing an ADAS (ADAS plan) and the other replanned without an ADAS (non-ADAS plan). The ADAS was defined to occupy the volume between the inguinal nodes and primary target providing a single organ at risk that is completely outside of the target volume. Each plan used the same beam parameters and was analyzed by comparing target coverage, overall plan dose conformity using a conformity number (CN) equation, bowel dose-volume histograms, and the number of segments, daily treatment duration, and global maximum dose. The ADAS and non-ADAS plans were equivalent in target coverage, mean global maximum dose, and sparing of small bowel in low-dose regions (5, 10, 15, and 20 Gy). The mean difference between the CN value for the non-ADAS plans and ADAS plans was 0.04 ± 0.03 (p < 0.001). The mean difference in the number of segments was 15.7 ± 12.7 (p < 0.001) in favor of ADAS plans. The ADAS plan delivery time was shorter by 2.0 ± 1.5 minutes (p < 0.001) than the non-ADAS one. The ADAS has proven to be a powerful tool when planning rectal and anal canal IMRT cases with critical structures partially contained inside the target volume.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Radiobiologic comparison of helical tomotherapy, intensity modulated radiotherapy, and conformal radiotherapy in treating lung cancer accounting for secondary malignancy risks

The aim of the present study is to examine the importance of using measures to predict the risk of inducing secondary malignancies in association with the clinical effectiveness of treatment plans in terms of tumor control and normal tissue complication probabilities. This is achieved by using radiobiologic parameters and measures, which may provide a closer association between clinical outcome and treatment delivery. Overall, 4 patients having been treated for lung cancer were examined. For each of them, 3 treatment plans were developed based on the helical tomotherapy (HT), multileaf collimator-based intensity modulated radiation therapy (IMRT), and 3-dimensional conformal radiation therapy (CRT) modalities. The different plans were evaluated using the complication-free tumor control probability (p{sub +}), the overall probability of injury (p{sub I}), the overall probability of control/benefit (p{sub B}), and the biologically effective uniform dose (D{sup ¯¯}). These radiobiologic measures were used to develop dose-response curves (p-D{sup ¯¯} diagram), which can help to evaluate different treatment plans when used in conjunction with standard dosimetric criteria. The risks for secondary malignancies in the heart and the contralateral lung were calculated for the 3 radiation modalities based on the corresponding dose-volume histograms (DVHs) of each patient. Regarding the overall evaluation of the different radiation modalities based on the p{sub +} index, the average values of the HT, IMRT, and CRT are 67.3%, 61.2%, and 68.2%, respectively. The corresponding average values of p{sub B} are 75.6%, 70.5%, and 71.0%, respectively, whereas the average values of p{sub I} are 8.3%, 9.3%, and 2.8%, respectively. Among the organs at risk (OARs), lungs show the highest probabilities for complications, which are 7.1%, 8.0%, and 1.3% for the HT, IMRT, and CRT modalities, respectively. Similarly, the biologically effective prescription doses (D{sub B}{sup ¯¯}) for the HT, IMRT, and CRT modalities are 64.0, 60.9, and 60.8 Gy, respectively. Regarding the risk for secondary cancer, for the heart, the lowest average risk is produced by IMRT (0.10%) compared with the HT (0.17%) and CRT (0.12%) modalities, whereas the 3 radiation modalities show almost equivalent results regarding the contralateral lung (0.8% for HT, 0.9% for IMRT, and 0.9% for CRT). The use of radiobiologic parameters in the evaluation of different treatment plans and estimation of their expected clinical outcome is shown to provide very useful clinical information. The radiobiologic analysis of the response probabilities showed that different radiation modalities appear to be more effective in different patient geometries and target sizes and locations. Furthermore, there is not a clear pattern between the plans that appear to be more effective for the treatment and the risk of secondary malignancy. It seems that radiobiologically based treatment planning taking into account the risk of secondary cancer can be established as an effective clinical tool for a more clinically relevant treatment optimization.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

Tumor control probability and the utility of 4D vs 3D dose calculations for stereotactic body radiotherapy for lung cancer

Four-dimensional (4D) dose calculations for lung cancer radiotherapy have been technically feasible for a number of years but have not become standard clinical practice. The purpose of this study was to determine if clinically significant differences in tumor control probability (TCP) exist between 3D and 4D dose calculations so as to inform the decision whether 4D dose calculations should be used routinely for treatment planning. Radiotherapy plans for Stage I-II lung cancer were created for 8 patients. Clinically acceptable treatment plans were created with dose calculated on the end-exhale 4D computed tomography (CT) phase using a Monte Carlo algorithm. Dose was then projected onto the remaining 9 phases of 4D-CT using the Monte Carlo algorithm and accumulated onto the end-exhale phase using commercially available deformable registration software. The resulting dose-volume histograms (DVH) of the gross tumor volume (GTV), planning tumor volume (PTV), and PTV{sub setup} were compared according to target coverage and dose. The PTV{sub setup} was defined as a volume including the GTV and a margin for setup uncertainties but not for respiratory motion. TCPs resulting from these DVHs were estimated using a wide range of alphas, betas, and tumor cell densities. Differences of up to 5 Gy were observed between 3D and 4D calculations for a PTV with highly irregular shape. When the TCP was calculated using the resulting DVHs for fractionation schedules typically used in stereotactic body radiation therapy (SBRT), the TCP differed at most by 5% between 4D and 3D cases, and in most cases, it was by less than 1%. We conclude that 4D dose calculations are not necessary for most cases treated with SBRT, but they might be valuable for irregularly shaped target volumes. If 4D calculations are used, 4D DVHs should be evaluated on volumes that include margin for setup uncertainty but not respiratory motion.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Evaluations of secondary cancer risk in spine radiotherapy using 3DCRT, IMRT, and VMAT: A phantom study

This study evaluated the secondary cancer risk from volumetric-modulated arc therapy (VMAT) for spine radiotherapy compared with intensity-modulated radiotherapy (IMRT) and 3-dimensional conformal radiotherapy (3DCRT). Computed tomography images of an Radiological Physics Center spine anthropomorphic phantom were exported to a treatment planning system (Pinnacle{sup 3}, version 9.4). Radiation treatment plans for spine were prepared using VMAT (dual-arc), 7-field IMRT (beam angles: 110°, 130°, 150°, 180°, 210°, 230°, and 250°), and 4-field 3DCRT technique. The mean and maximum doses, dose-volume histograms, and volumes receiving more than 2 and 4 Gy to organs at risk (OARs) were calculated and compared. The lifetime risk for secondary cancers was estimated according to the National Cancer Registry Programme Report 116. VMAT delivered the lowest maximum dose to the esophagus (4.03 Gy), bone (8.11 Gy), heart (2.11 Gy), spinal cord (6.45 Gy), and whole lung (5.66 Gy) as compared with other techniques (IMRT and 3DCRT). The volumes of OAR (esophagus) receiving more than 4 Gy were 0% for VMAT, 27.06% for IMRT, and up to 32.35% for 3DCRT. The estimated risk for secondary cancer in the respective OAR is considerably lower in VMAT compared with other techniques. The results of maximum doses and volumes of OARs suggest that the risk of secondary cancer induction for the spine in VMAT is lower than IMRT and 3DCRT, whereas VMAT has the best target coverage compared with the other techniques.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

Patient performance–based plan parameter optimization for prostate cancer in tomotherapy

The purpose of this study is to evaluate the influence of treatment-planning parameters on the quality of treatment plans in tomotherapy and to find the optimized planning parameter combinations when treating patients with prostate cancer under different performances. A total of 3 patients with prostate cancer with Eastern Cooperative Oncology Group (ECOG) performance status of 2 or 3 were included in this study. For each patient, 27 treatment plans were created using a combination of planning parameters (field width of 1, 2.5, and 5 cm; pitch of 0.172, 0.287, and 0.43; and modulation factor of 1.8, 3, and 3.5). Then, plans were analyzed using several dosimetrical indices: the prescription isodose to target volume (PITV) ratio, homogeneity index (HI), conformity index (CI), target coverage index (TCI), modified dose HI (MHI), conformity number (CN), and quality factor (QF). Furthermore, dose-volume histogram of critical structures and critical organ scoring index (COSI) were used to analyze organs at risk (OAR) sparing. Interestingly, treatment plans with a field width of 1 cm showed more favorable results than others in the planning target volume (PTV) and OAR indices. However, the treatment time of the 1-cm field width was 3 times longer than that of plans with a field width of 5 cm. There was no substantial decrease in treatment time when the pitch was increased from 0.172 to 0.43, but the PTV indices were slightly compromised. As expected, field width had the most significant influence on all of the indices including PTV, OAR, and treatment time. For the patients with good performance who can tolerate a longer treatment time, we suggest a field width of 1 cm, pitch of 0.172, and modulation factor of 1.8; for the patients with poor performance status, field width of 5 cm, pitch of 0.287, and a modulation factor of 3.5 should be considered.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

Comparison of doses received by the hippocampus in patients treated with single isocenter– vs multiple isocenter–based stereotactic radiation therapy to the brain for multiple brain metastases

To investigate the doses received by the hippocampus and normal brain tissue during a course of stereotactic radiation therapy using a single isocenter (SI)–based or multiple isocenter (MI)–based treatment planning in patients with less than 4 brain metastases. In total, 10 patients with magnetic resonance imaging (MRI) demonstrating 2-3 brain metastases were included in this retrospective study, and 2 sets of stereotactic intensity-modulated radiation therapy (IMRT) treatment plans (SI vs MI) were generated. The hippocampus was contoured on SPGR sequences, and doses received by the hippocampus and the brain were calculated and compared between the 2 treatment techniques. A total of 23 lesions in 10 patients were evaluated. The median tumor volume, the right hippocampus volume, and the left hippocampus volume were 3.15, 3.24, and 2.63 mL, respectively. In comparing the 2 treatment plans, there was no difference in the planning target volume (PTV) coverage except in the tail for the dose-volume histogram (DVH) curve. The only statistically significant dosimetric parameter was the V{sub 100}. All of the other measured dosimetric parameters including the V{sub 95}, V{sub 99}, and D{sub 100} were not significantly different between the 2 treatment planning techniques. None of the dosimetric parameters evaluated for the hippocampus revealed any statistically significant difference between the MI and SI plans. The total brain doses were slightly higher in the SI plans, especially in the lower dose region, although this difference was not statistically different. The use of SI-based treatment plan resulted in a 35% reduction in beam-on time. The use of SI treatments for patients with up to 3 brain metastases produces similar PTV coverage and similar normal tissue doses to the hippocampus and the brain when compared with MI plans. SI treatment planning should be considered in patients with multiple brain metastases undergoing stereotactic treatment.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Clinical and dosimetric implications of intensity-modulated radiotherapy for early-stage glottic carcinoma

Conventional parallel-opposed radiotherapy (PORT) is the established standard technique for early-stage glottic carcinoma. However, case reports have reported the utility of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) with or without image guidance (image-guided radiotherapy, IGRT) in select patients. The proposed advantages of IMRT/VMAT include sparing of the carotid artery, thyroid gland, and the remaining functional larynx, although these benefits remain unclear. The following case study presents a patient with multiple vascular comorbidities treated with VMAT for early-stage glottic carcinoma. A detailed explanation of the corresponding treatment details, dose-volume histogram (DVH) analysis, and a review of the relevant literature are provided. Conventional PORT remains the standard of care for early-stage glottic carcinoma. IMRT or VMAT may be beneficial for select patients, although great care is necessary to avoid a geographical miss. Clinical data supporting the benefit of CRT are lacking. Therefore, these techniques should be used with caution and only in selected patients.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Using individual patient anatomy to predict protocol compliance for prostate intensity-modulated radiotherapy

If a prostate intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT) plan has protocol violations, it is often a challenge knowing whether this is due to unfavorable anatomy or suboptimal planning. This study aimed to create a model to predict protocol violations based on patient anatomical variables and their potential relationship to target and organ at risk (OAR) end points in the setting of definitive, dose-escalated IMRT/VMAT prostate planning. Radiotherapy plans from 200 consecutive patients treated with definitive radiation for prostate cancer using IMRT or VMAT were analyzed. The first 100 patient plans (hypothesis-generating cohort) were examined to identify anatomical variables that predict for dosimetric outcome, in particular OAR end points. Variables that scored significance were further assessed for their ability to predict protocol violations using a Classification and Regression Tree (CART) analysis. These results were then validated in a second group of 100 patients (validation cohort). In the initial analysis of the hypothesis-generating cohort, percentage of rectum overlap in the planning target volume (PTV) (%OR) and percentage of bladder overlap in the PTV (%OB) were highlighted as significant predictors of rectal and bladder dosimetry. Lymph node treatment was also significant for bladder outcomes. For the validation cohort, CART analysis showed that %OR of < 6%, 6% to 9% and > 9% predicted a 13%, 63%, and 100% rate of rectal protocol violations respectively. For the bladder, %OB of < 9% vs > 9% is associated with 13% vs 88% rate of bladder constraint violations when lymph nodes were not treated. If nodal irradiation was delivered, plans with a %OB of < 9% had a 59% risk of violations. Percentage of rectum and bladder within the PTV can be used to identify individual plan potential to achieve dose-volume histogram (DVH) constraints. A model based on these factors could be used to reduce planning time, improve work flow, and strengthen plan quality and consistency.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Pancreatic cancer planning: Complex conformal vs modulated therapies

To compare the roles of intensity-modulated radiation therapy (IMRT) and volumetric- modulated arc therapy (VMAT) therapy as compared to simple and complex 3-dimensional chemoradiotherpy (3DCRT) planning for resectable and borderline resectable pancreatic cancer. In all, 12 patients who received postoperative radiotherapy (8) or neoadjuvant concurrent chemoradiotherapy (4) were evaluated retrospectively. Radiotherapy planning was performed for 4 treatment techniques: simple 4-field box, complex 5-field 3DCRT, 5 to 6-field IMRT, and single-arc VMAT. All volumes were approved by a single observer in accordance with Radiation Therapy Oncology Group (RTOG) Pancreas Contouring Atlas. Plans included tumor/tumor bed and regional lymph nodes to 45 Gy; with tumor/tumor bed boosted to 50.4 Gy, at least 95% of planning target volume (PTV) received the prescription dose. Dose-volume histograms (DVH) for multiple end points, treatment planning, and delivery time were assessed. Complex 3DCRT, IMRT, and VMAT plans significantly (p < 0.05) decreased mean kidney dose, mean liver dose, liver (V{sub 30}, V{sub 35}), stomach (D{sub 10}%), stomach (V{sub 45}), mean right kidney dose, and right kidney (V{sub 15}) as compared with the simple 4-field plans that are most commonly reported in the literature. IMRT plans resulted in decreased mean liver dose, liver (V{sub 35}), and left kidney (V{sub 15}, V{sub 18}, V{sub 20}). VMAT plans decreased small bowel (D{sub 10}%, D{sub 15}%), small bowel (V{sub 35}, V{sub 45}), stomach (D{sub 10}%, D{sub 15}%), stomach (V{sub 35}, V{sub 45}), mean liver dose, liver (V{sub 35}), left kidney (V{sub 15}, V{sub 18}, V{sub 20}), and right kidney (V{sub 18}, V{sub 20}). VMAT plans significantly decreased small bowel (D{sub 10}%, D{sub 15}%), left kidney (V{sub 20}), and stomach (V{sub 45}) as compared with IMRT plans. Treatment planning and delivery times were most efficient for simple 4-field box and VMAT. Excluding patient setup and imaging, average treatment delivery was within 10 minutes for simple and complex 3DCRT, IMRT, and VMAT treatments. This article shows significant improvements in 3D plan performance with complex planning over the more frequently compared 3- or 4-field simple 3D planning techniques. VMAT plans continue to demonstrate potential for the most organ sparing. However, further studies are required to identify if dosimetric benefits associated with inverse optimized planning can be translated into clinical benefits and if these treatment techniques are value-added therapies for this group of patients with cancer.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Technical solutions to reduce mediastinal irradiation in young patients undergoing treatment for lymphomas: Preliminary experience

This study aims at optimizing treatment planning in young patients affected by lymphoma (Stage II to III) by using an inclined board (IB) that allows reducing doses to the organs at risk. We evaluated 19 young patients affected by stage I to III lymphomas, referred to our Department for consolidation radiotherapy (RT) treatment on the mediastinum. Patients underwent 2 planning computed tomography (CT) scans performed in different positions: flat standard position and inclined position. A direct comparison between the different treatment plans was carried out analyzing dosimetric parameters obtained from dose-volume histograms generated for each plan. Comparison was performed to evaluate the sparing obtained on breast and heart. Dosimetric evaluation was performed for the following organs at risk (OARs): mammary glands, lungs, and heart. A statistically significant advantage was reported for V{sub 5}, V{sub 20}, and V{sub 30} for the breast when using the inclined board. A similar result was obtained for V{sub 5} and V{sub 10} on the heart. No advantage was observed in lung doses. The use of a simple device, such as an inclined board, allows the optimization of treatment plan, especially in young female patients, by ensuring a significant reduction of the dose delivered to breast and heart.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

The comparison of 5-field conformal radiotherapy techniques for the treatment of prostate cancer: The best for femoral head sparing

External radiotherapy is a standard treatment procedure for localized prostate cancer. Given the relatively high long term survival treatment complications have been brought in center of attention. In this planning study, between 2012 and 2014, CT simulation data of 90 consecutive high-risk prostate cancer patients were collected. In the first phase, all were planned for whole pelvis irradiation up to 46Gy in 23 daily fractions. In the second phase, only the prostate gland was the target of radiation. Next, the subjects were divided randomly into three groups and each received a unique 5field conformal radiation plan including Plan A (Gantry angle: 0, 60, 120, 240, and 300), Plan B (Gantry angles: 0, 90, 120, 240, and 270) and Plan C (Gantry angles: 0, 60, 90, 270, and 300). The total dose was 70Gy. For each patient, the rectum, bladder, and both femoral heads were contoured as the at risk organs (OAR). From dose volume histograms, the proportional dose of PTV V100, the bladder and rectum V80 and V90 and femoral head V50 and V100 were calculated in all subjects and compared across plans. A statistically significant difference in the femoral head V50 and V100 was found between our studied 5field plans so that in Plan A (beam angles: 0, 60, 120, 240 and 300) less dose was received by both heads of femur. This study suggests that 5 field treatment planning including an anterior, two anterior oblique and two posterior oblique portals to be more proper for 3D conformal radiotherapy in order to spare femoral head with acceptable PTV coverage, and bladder and rectal doses.

61 RADIATION PROTECTION AND DOSIMETRY↗