Global Maximum Dose Research Articles

Lung SBRT: Dose gradient optimization based on target size

This study investigated optimization settings that steepen the dose gradient as a function of target size for lung stereotactic body radiation therapy (SBRT). Sixty-eight lung SBRT patients with planning target volumes (PTVs) ranging from 2-203 cc were categorized into small (<20 cc), medium (20-50 cc), and large (>50 cc) groups. VMAT plans were generated using the normal tissue objective (NTO) to penalize the dose gradient at progressively steeper NTO fall-off values (0.1, 0.2, 0.3, 0.4, 0.5 mm-1). Dose was calculated using the AcurosXB algorithm and was normalized so the prescription dose covered 95% of the PTV. Mann-Whitney, Kruskal-Wallis and ANOVA tests were used to assess for statistical differences in the Conformity Index at the 50% isodose level (CI50%), global maximum dose (Dmax), and monitor units (MU) across the various NTO settings. All plans adhered to institutional criteria and met the guidelines of the Radiation Therapy Oncology Group 0813. Steeper NTO fall-off values significantly increased Dmax and MUs across all groups (p < 0.05). CI50% significantly differed with fall-off values in small (0.3 mm-1) and medium (0.2 mm-1) targets, indicating steeper NTO fall-off values improve CI50% for small and medium targets (p < 0.05). Large targets showed no significant CI50% difference across these fall-off values. As target size increases, the importance of fall-off values in achieving an acceptable CI50% diminishes. Smaller targets benefit from steeper fall-off values despite increased Dmax and MUs. Consideration of fall-off value relative to target size is crucial to limit dose spillage outside the target.

A lung SBRT treatment planning technique to focus high dose on gross disease

This study investigated a straightforward treatment planning technique for definitive stereotactic body radiation therapy (SBRT) for patients with early-stage lung cancer aimed at increasing dose to gross disease by strategically penalizing the normal tissue objective (NTO) in the EclipseTM treatment planning system. Twenty-five SBRT cases were replanned to 50 Gy in 5 fractions using static and dynamic NTO methods (50 plans total). The NTO had a start dose of 100% at the target border, end dose of 20%, fall-off rate of 0.4/mm, and a priority of 150. For the static NTO plans, a lower planning target volume (PTV) objective was placed at 52 Gy with a priority of 100. Maximum dose was not penalized. Optimization was performed without user interaction. In contrast, the planner incrementally increased the priority of the NTO on the dynamic NTO plans until 95% of the target volume was covered by the prescription dose. Further, the dynamic NTO plans used both PTV lower and upper objectives at 63-64 Gy with priorities of 50. Maximum dose was penalized to ensure that the hot spot was within ± 2% of the static NTO global maximum dose. Following optimization, all plans were normalized so that the prescription dose covered 95% of the PTV. Plans were scored based on RTOG 0813 criteria, and dose to the internal target volume (ITV) and PTV was evaluated. The Wilcoxon signed-rank test (threshold = 0.05) was used to evaluate differences between the static and dynamic NTO plans. All plans met RTOG 0813 planning guidelines. In comparison to the static NTO plans, the dynamic NTO plans exhibited statistically significant increases in PTV mean dose, ITV mean dose, and PTV-ITV mean dose. Notably, the dynamic NTO plans more effectively concentrated the high dose on gross disease at the center of the PTV. As compared to the static NTO plans, the mean dose was 4.6 Gy higher in the ITV while only 1.3 Gy higher in the PTV-ITV rind of the dynamic NTO plans. Global maximum doses were similar. There were some small yet statistically significant differences in dose conformity between plan types. Furthermore, the dynamic NTO plans demonstrated a significant reduction in total monitor units (MU). This study demonstrated an efficient optimization strategy for lung SBRT plans that concentrates the highest dose in the gross disease, which may improve local control.

A structure-based gamma evaluation method for identifying clinically relevant dose differences in organs at risk.

Gamma evaluation is currently the most widely used dose comparison method for patient specific quality assurance (PSQA). However, existing methods for normalising the dose difference, using either the dose at the global maximum dose point or at each local point, can respectively lead to under- and over-sensitivity to dose differences in organ-at-risk structures. This may be of concern for plan evaluation from clinical perspectives. This study has explored and proposed a new method called structural gamma, which takes structural dose tolerances into consideration while performing gamma analysis for PSQA. As a demonstration of the structural gamma method, a total of 78 retrospective plans on four treatment sites were re-calculated on an in-house Monte Carlo system and compared with doses calculated from the treatment planning system. Structural gamma evaluations were performed using both QUANTEC dose tolerances and radiation oncologist specified dose tolerances, then compared with conventional global and local gamma evaluations. Results demonstrated that structural gamma evaluation is especially sensitive to errors in structures with restrictive dose constraints. The structural gamma map provides both geometric and dosimetric information on PSQA results, allowing straightforward clinical interpretation. The proposed structure-based gamma method accounts for dose tolerances for specific anatomical structures. This method can provide a clinically useful method to assess and communicate PSQA results, offering radiation oncologists a more intuitive way of examining agreement in surrounding critical normal structures.

Investigating a correlation between MLC positional errors and IMRT QA passing rate

Patient-specific quality assurance (QA) using measurement-based techniques has been the standard method used in many institutions as an essential step to ensure the accuracy of the actual treatment. In this work, we studied the use of the trajectory log files in specifying the influence of the linear accelerator multi-leaf collimators (MLC) positional errors in the passing rates of our measurement-based QA. In the study, we analyzed sixty-five QA treatment plan results including plans for head and neck, lungs, pelvises, craniospinal, and total body irradiation. Eclipse treatment planning system with Anisotropic Analytical Algorithm (AAA) dose calculation engine was the system used to generate all of our treatment plans. All plans were delivered on Varian® linear accelerator UNIQUE which is equipped with 120 Millennium MLC. Trajectory log files generated during treatment delivery were analyzed by a software developed using MATLAB. We compared the planned versus the actual delivered fluence from the recorded log files. Direct subtraction of both fluences allowed us to calculate the degree of match between both fluences. We called it the MLC matching percentage. Measurement-based QAs for all IMRT patients were done using Octavius 4D -PTW dosimetry that incorporates 729 chamber array. The gamma analysis passing rates were calculated by verisoft software using criteria of 3% for dose and 3 mm for distance to agreement and based on the global maximum dose of calculation volume and suppressing the dose blow of 5% of maximum dose of the calculated volume. Then we tested the correlation between the QA passing rate with the related MLC matching percentage. The gamma analysis passing rate was in the range of 90%–99.1% and the matching percentage ranged from 89% to 98.8%. The assessment of the correlation between the gamma passing rate and the matching percentage showed 0.45 correlation coefficient. The p-value was less than 0.05 which indicates a statistically significant correlation. The effect size was on the order of 0.7. Trajectory log file analysis combined with the measurement-based patient specific QA is beneficial to our IMRT QA process and it could be an aid to detect the actual delivery error and hence could improve our passing rates in the future.

Hippocampal-sparing whole-brain radiotherapy under coplanar or noncoplanar VMAT.

Whole-brain radiotherapy (WBRT) can alleviate symptoms in patients with brain metastases. However, WBRT may damage the hippocampus. Volumetric modulated arc therapy (VMAT) can achieve a suitable coverage of the target region and a more conforming dose distribution whereas decreasing the dose to organs-at-risk (OARs). Herein, we aimed to compare the differences between treatment plans utilizing coplanar VMAT and noncoplanar VMAT in hippocampal-sparing WBRT (HS-WBRT). Ten patients were included in this study. For each patient, the Eclipse A10 treatment planning system was used to generate 1 coplanar VMAT (C-VMAT) and 2 noncoplanar VMAT treatment plans with various beam angles (noncoplanar VMAT A [NC-A] and noncoplanar VMAT B [NC-B]) for HS-WBRT. The prescribed dose was 30 Gy in 12 fractions. Treatment plans were established based on the OAR dose constraints of the Radiation Therapy Oncology Group 0933 (RTOG 0933). Parameters such as the global maximum dose, dose conformity, dose homogeneity of plans, and OAR doses were evaluated. The maximum biologically equivalent doses in 2-Gy fractions (EQD2) of OARs in C-VMAT were 9.17 ± 0.61, 42.79 ± 2.00, and 42.84 ± 3.52 Gy in the hippocampus, brain stem, and optic chiasm, respectively, which were the lowest among the 3 treatment plans. There was no significant difference in dose conformity among the 3 treatment plans. However, NC-A had a slightly better conformity than C-VMAT and NC-B. NC-A had the best homogeneity, and NC-B had the worst homogeneity (p = 0.042). NC-A and NC-B had the lowest and highest global dose maximum, respectively. Therefore, NC-A, which had an intermediate performance in terms of OAR doses, had the best quality parameters. We used the quality score table based on the p-value to evaluate the significant difference between each treatment technique from the multiparameter results. In terms of treatment plan parameters, only NC-A received a score of 2; for OAR doses, C-VMAT, NC-A, and NC-B received a score of 6, 3, and 5, respectively. For the overall evaluation, C-VMAT, NC-A, and NC-B received a total score of 6, 5, and 5, respectively. Rather than noncoplanar VMAT, 3 full-arc C-VMATs should be utilized in HS-WBRT. C-VMAT can simultaneously maintain treatment plan quality and decrease patient alignment time and total treatment time.

Doses delivered to small and large breasts and adjacent organs in left breast cancer patients utilizing 3D and IM radiotherapy

BackgroundRadiotherapy is still the most facilitated modality for treatment of malignant tumors, including breast cancer, with or without chemotherapy and after surgery or when surgery is impossible. AimThe present article concerns a number of parameters used in radiation therapy techniques, involving the minimum, maximum, mean dose, volume covered with 95% of dose, and global maximum dose delivered to planning target volume (PTV), and the organs at risk, including left lung, heart, thyroid gland, spinal cord, humerus, super clavicle lymph node, and the right breast using the constraints of Radiation Therapy Oncology Group (RTOG). Patients and MethodsTwenty patients with breast tumors, females only, were enrolled in the study. A LINAC with a 6 MV photon beam was used to deliver the prescribed dose. The whole breast irradiation was applied to each patient using two planning techniques: 3D conformal and intensity modulated radiotherapy, and the planning was constructed within 95%–107% of the prescribed dose to the planning target volume as recommended by the RTOG. ResultsThe results showed a significant difference (at the level of P < 0.05) between the two planning techniques based on the doses received by PTV and the OARs. The results were discussed. ConclusionWe concluded that inverse intensity modulation radiation therapy (IMRT) for breast cancer does not improve late toxicity or oncologic outcomes. So, inverse IMRT is not yet the norm, and health insurance usually doesn't pay for treatment unless it's absolutely necessary, like to stop a heart attack. .

Novel VMAT Planning Technique Improves Dosimetry for Head and Neck Cancer Patients Undergoing Definitive Chemoradiotherapy

<h3>Purpose/Objective(s)</h3> Intensity modulated radiotherapy (IMRT) allows for substantial sparing of organs-at-risk (OARs) without compromising delivery of curative-intent doses in patients with head and neck cancers. Volumetric modulated arc therapy (VMAT) allows for rapid treatment delivery and minimizes fractional treatment time. Given the intrinsic complexity of VMAT planning, standard two-arc techniques often fail to achieve planning objectives. We hypothesize that a simple, institutional approach improves OAR dosimetry compared to a standard two-arc technique. <h3>Materials/Methods</h3> Head and neck cancer patients who received definitive chemoradiotherapy were included in this single institution study. VMAT plans were generated per institutional protocol using 6 MV photon beams. Briefly, three single arcs were employed with assigned collimator angles of (C) 0°, (C) 90°, and (C) 90°. The maximum jaw extension of the (C) 0° field encompassed the entirety of the treatment volume. The inferior jaw on the first collimated arc was set with a maximum extension of 1 cm beyond the isocenter, while the superior jaw of the second collimated arc was set with a maximum extension of 1 cm beyond the isocenter. Comparison plans were generated for each patient using the manufacturer's recommended beam arrangement, comprising two collimated arcs - (C) 30° and a reciprocal (C) 330° - with jaw tracking enabled. Mean differences in target volume and OAR dosimetry between planning approaches were calculated. A two-tailed, paired Student's t-test was employed to determine statistically significant differences in dosimetry between standard and institutional plans. <h3>Results</h3> Ten patients were planned using institutional and standard two-arc protocols. Statistically significant mean improvements were observed in ipsilateral parotid mean dose (∆314.7 cGy, p = 0.007) and V30Gy (∆6.62%, p = 0.004), contralateral parotid mean dose (∆292.6 cGy, p = 0.006) and V30Gy (∆5.36%, p = 0.004), parotid volume receiving less than 20 Gy (∆7.36 cc, p = 0.010), pharyngeal constrictor mean dose (∆269.3 cGy, p = 0.003), ipsilateral brachial plexus maximum dose (∆96.0 cGy, p = 0.036), and global maximum dose (∆1.73%, p = 0.047) with the three-arc technique. No significant differences in PTV, spinal cord, mandible, cricopharyngeus, cochlear, or contralateral brachial plexus dosimetry were identified. Subjectively, dosimetrists reported shorter planning time and easier achievement of objectives with the three-arc approach. <h3>Conclusion</h3> Our institutional approach to head and neck VMAT conveys significant dosimetric improvements compared to a standard VMAT beam arrangement. This approach represents a simple and reproducible solution to planning for head and neck cancer patients which may reduce planning time. Additional research is warranted to further optimize this technique and quantify reductions in planning time.

Automated Plan Checking Software Demonstrates Continuous and Sustained Improvements in Safety and Quality: A 3-year Longitudinal Analysis

PurposeThis study aimed to perform a longitudinal analysis of the performance of our automated plan checking software by retrospectively evaluating the number of errors identified in plans delivered to patients in 3, month-long, data collection periods between 2017 and 2020. Methods and MaterialsEleven automated checks were retrospectively run on 1169 external beam radiation therapy treatment plans identified as meeting the following criteria: planning target volume–based multifield photon plans receiving a status of treatment approved in March 2017, March 2018, or March 2020. The number of passes (true positives) and flags were recorded. Flags were subcategorized into false negatives, false negatives due to naming conventions, and true negatives. In addition, 2 × 2 contingency tables using a 2-tailed Fisher's exact test were used to determine whether there were nonrandom associations between the output of the automated plan checking software and whether the check was manual or automated at the original time of treatment approval. ResultsA statistically significant decrease in flags between the pre- and postautomation data sets was observed for 4 contour-based checks, namely adjacent structures overlap, empty structures and missing slices, overlap between body and couch, and laterality, as well as a check that determined whether the plan's global maximum dose was within the planning target volume. A review of the origins of false negatives was fed back into the design of the checks to improve the reliability of the system and help avoid warning fatigue. ConclusionsPeriodic and longitudinal review of the performance of automated software was essential for monitoring and understanding its impact on error rates, as well as for optimization of the tool to adapt to regular changes of clinical practice. The automated plan checking software has demonstrated continuous contributions to the safe and effective delivery of external beam radiation therapy to our patient population, an impact that extends beyond its initial implementation and deployment.

Clinical Implementation of Automated Treatment Planning for Rectum Intensity-Modulated Radiotherapy Using Voxel-Based Dose Prediction and Post-Optimization Strategies.

PurposeThis study aims to demonstrate the feasibility of clinical implementation of automated treatment planning (ATP) using voxel-based dose prediction and post-optimization strategies for rectal cancer on uRT (United Imaging Healthcare, Shanghai, China) treatment planning system.MethodsA total of 180 previously treated rectal cancer cases were enrolled in this study, including 160 cases for training, 10 for validation and 10 for testing. Using CT image data, planning target volumes (PTVs) and contour delineation of the organs at risk (OARs) as input and three-dimensional (3D) dose distribution as output, a 3D-Uet DL model was developed. Based on the voxel-wise prediction dose distribution, intensity-modulated radiation therapy (IMRT) plans were then generated automatedly using post-optimization strategies, including a complex clinical dose target metrics homogeneity index (HI) and conformation index (CI). To evaluate the performance of the proposed ATP approach, the dose-volume histogram (DVH) parameters of OARs and PTV and the 3D dose distributions of the plan were compared with those of manual plans.ResultsBy combining clinical post-optimization strategies, the automatically generated treatment plan can achieve better homogeneous PTV coverage and dose sparing for OARs except the mean dose for femoral-head compared with the use of the mean square error objective function alone. Compared with the manual plan, no statistically significant differences in HI, CI or global maximum dose were found. The manual plans perform slightly better than plans with post-optimization strategies in other dosimetric indexes, but these plans are still within clinical requirements.ConclusionsWith the help of clinical post-optimization strategies, the proposed new ATP solution can generate IMRT plans that are within clinically acceptable levels and comparable to plans manually generated by dosimetrists.

Dosimetric Quality of Online Adapted Pancreatic Cancer Treatment Plans on an MRI-Guided Radiation Therapy System

PurposeStereotactic magnetic resonance image–guided adaptive radiation therapy (SMART) is an emerging technique that shows promise in the treatment of pancreatic cancer and other abdominopelvic malignancies. However, it is unknown whether the time-limited nature of on-table adaptive planning may result in dosimetrically suboptimal plans. The purpose of this study was to quantitatively address that question through systemic retrospective replanning of treated on-table adaptive pancreatic cancer cases. Methods and MaterialsOf 74 consecutive adapted fractions, 30 were retrospectively replanned based on deficiencies in planning target volume (PTV) and gross tumor volume (GTV) coverage or doses to organs-at-risk (OARs) that exceeded ideal constraints. Retrospective plans were created by adjusting dose-volume objectives in an iterative fashion until deemed optimized. The goal of replanning was to improve PTV/GTV coverage while keeping the dose to gastrointestinal OARs the same or lower or to reduce OAR doses while keeping PTV coverage the same or higher. The global maximum dose was required to be maintained within 2% of that of the treated adaptive plan to eliminate it as a confounding factor. A threshold of 5% improvement in PTV coverage or 5% decrease in OAR dose was used to define a clinically significant improvement. ResultsOf the 30 replans, 7 obtained at least 5% PTV coverage improvement. The average increase in PTV coverage for these plans was 11%. No plans were clinically significantly improved in terms of OAR sparing. Changes in beam-on time did not show any correlation. Statistical analysis via a linear mixed-effects model with a nested random effect suggested that both GTV and PTV coverage were improved over SMART process plans by 0.91 cc (P = .02) and 2.03 cc (P < .001), respectively. ConclusionsDosimetric plan quality of at least 10% of SMART fractions may be improved through more extensive replanning than is currently performed on-table. Further work is needed to develop an automated replanning workflow to streamline the in-depth replanning process to better fit into an on-table adaptive workflow.

Using patient-specific bolus for pencil beam scanning proton treatment of periorbital disease.

PurposeA unique mantle cell lymphoma case with bilateral periorbital disease unresponsive to chemotherapy and with dosimetry not conducive to electron therapy was treated with pencil beam scanning (PBS) proton therapy. This patient presented treatment planning challenges due to the thin target, immediately adjacent organs at risk (OAR), and nonconformal orbital surface anatomy. Therefore, we developed a patient‐specific bolus and hypothesized that it would provide superior setup robustness, dose uniformity and dose conformity.Materials/MethodsA blue‐wax patient‐specific bolus was generated from the patient's face contour to conform to his face and eliminate air gaps. A relative stopping power ratio (RSP) of 0.972 was measured for the blue‐wax, and the HUs were overridden accordingly in the treatment planning system (TPS). Orthogonal kV images were used for bony alignment and then to ensure positioning of the bolus through fiducial markers attached to the bolus and their contours in TPS. Daily CBCT was used to confirm the position of the bolus in relation to the patient's surface. Dosimetric characteristics were compared between (a) nonbolus, (b) conventional gel bolus and (c) patient‐specific bolus plans. An in‐house developed workflow for assessment of daily treatment dose based on CBCT images was used to evaluate inter‐fraction dose accumulation.ResultsThe patient was treated to 24 cobalt gray equivalent (CGE) in 2 CGE daily fractions to the bilateral periorbital skin, constraining at least 50% of each lacrimal gland to under 20 Gy. The bolus increased proton beam range by adding 2–3 energy layers of different fields to help achieve better dose uniformity and adequate dose coverage. In contrast to the plan with conventional gel bolus, dose uniformity was significantly improved with patient‐specific bolus. The global maximum dose was reduced by 7% (from 116% to 109%). The max and mean doses were reduced by 6.0% and 7.7%, respectively, for bilateral retinas, and 3.0% and 13.9% for bilateral lacrimal glands. The max dose of the lens was reduced by 2.1%. The rigid shape, along with lightweight, and smooth fit to the patient face was well tolerated and reported as “very comfortable” by the patient. The daily position accuracy of the bolus was within 1 mm based on IGRT marker alignment. The daily dose accumulation indicates that the target coverage and OAR doses were highly consistent with the planning intention.ConclusionOur patient‐specific blue‐wax bolus significantly increased dose uniformity, reduced OAR doses, and maintained consistent setup accuracy compared to conventional bolus. Quality PBS proton treatment for periorbital tumors and similar challenging thin and shallow targets can be achieved using such patient‐specific bolus with robustness on both setup and dosimetry.

Clinical Monte Carlo versus Pencil Beam Treatment Planning in Nasopharyngeal Patients Receiving IMPT.

Pencil beam (PB) analytical algorithms have been the standard of care for proton therapy dose calculations. The introduction of Monte Carlo (MC) algorithms may provide more robust and accurate planning and can improve therapeutic benefit. We conducted a dosimetric analysis to quantify the differences between MC and PB algorithms in the clinical setting of dose-painted nasopharyngeal cancer intensity-modulated proton radiotherapy. Plans of 14 patients treated with PB analytical algorithm optimized and calculated (PBPB) were retrospectively analyzed. The PBPB plans were recalculated using MC to generate PBMC plans and, finally, reoptimized and recalculated with MC to generate MCMC plans. The plans were compared across several dosimetric endpoints and correlated with documented toxicity. Robustness of the planning scenarios (PBPB, PBMC, MCMC) in the presence of setup and range uncertainties was compared. A median decrease of up to 5 Gy (P < .05) was observed in coverage of planning target volume high-risk, intermediate-risk, and low-risk volumes when PB plans were recalculated using the MC algorithm. This loss in coverage was regained by reoptimizing with MC, albeit with a slightly higher dose to normal tissues but within the standard tolerance limits. The robustness of both PB and MC plans remained similar in the presence of setup and range uncertainties. The MC-calculated mean dose to the oral avoidance structure, along with changes in global maximum dose between PB and MC dosimetry, may be associated with acute toxicity-related events. Retrospective analyses of plan dosimetry quantified a loss of coverage with PB that could be recovered under MC optimization. MC optimization should be performed for the complex dosimetry in patients with nasopharyngeal carcinoma before plan acceptance and should also be used in correlative studies of proton dosimetry with clinical endpoints.

Advanced proton beam dosimetry part II: Monte Carlo vs. pencil beam-based planning for lung cancer.

Proton pencil beam (PB) dose calculation algorithms have limited accuracy within heterogeneous tissues of lung cancer patients, which may be addressed by modern commercial Monte Carlo (MC) algorithms. We investigated clinical pencil beam scanning (PBS) dose differences between PB and MC-based treatment planning for lung cancer patients. With IRB approval, a comparative dosimetric analysis between RayStation MC and PB dose engines was performed on ten patient plans. PBS gantry plans were generated using single-field optimization technique to maintain target coverage under range and setup uncertainties. Dose differences between PB-optimized (PBopt), MC-recalculated (MCrecalc), and MC-optimized (MCopt) plans were recorded for the following region-of-interest metrics: clinical target volume (CTV) V95, CTV homogeneity index (HI), total lung V20, total lung VRX (relative lung volume receiving prescribed dose or higher), and global maximum dose. The impact of PB-based and MC-based planning on robustness to systematic perturbation of range (±3% density) and setup (±3 mm isotropic) was assessed. Pairwise differences in dose parameters were evaluated through non-parametric Friedman and Wilcoxon sign-rank testing. In this ten-patient sample, CTV V95 decreased significantly from 99-100% for PBopt to 77-94% for MCrecalc and recovered to 99-100% for MCopt (P<10-5). The median CTV HI (D95/D5) decreased from 0.98 for PBopt to 0.91 for MCrecalc and increased to 0.95 for MCopt (P<10-3). CTV D95 robustness to range and setup errors improved under MCopt (ΔD95 =-1%) compared to MCrecalc (ΔD95 =-6%, P=0.006). No changes in lung dosimetry were observed for large volumes receiving low to intermediate doses (e.g., V20), while differences between PB-based and MC-based planning were noted for small volumes receiving high doses (e.g., VRX). Global maximum patient dose increased from 106% for PBopt to 109% for MCrecalc and 112% for MCopt (P<10-3). MC dosimetry revealed a reduction in target dose coverage under PB-based planning that was regained under MC-based planning along with improved plan robustness. MC-based optimization and dose calculation should be integrated into clinical planning workflows of lung cancer patients receiving actively scanned proton therapy.

The effect of beam interruption during FFF-VMAT plans for SBRT.

To investigate the dosimetric effect of intended beam interruption during volumetric modulated arc therapy (VMAT) with flattening filter free (FFF) beam for exploring the possibility of deep inspiration breath hold stereotactic body radiation therapy (SBRT). A total of ten SBRT plans with 6 and 10 MV FFF beams were retrospectively selected. All plans consisted of four partial arcs, except one plan with six partial arcs. We delivered the plans using a Varian Truebeam™ with three different scenarios; without interruption (0int), with one intentional interruption (1int), or with two intentional interruptions (2int), per each partial arc. The treatment log files were exported from the treatment console, and the variations in delivered MU were evaluated at the beam interruption angles. The dose distributions were also measured using a 3D cylindrical diode array detector, ArcCHECK™. The 2D global gamma evaluations were performed, compared to the planned dose distribution, with 3%/3 and 4%/2mm passing criterion. The dose difference (DD) was also determined between uninterrupted and interrupted data with 3, 2, 1, and 0.5% of global maximum dose. The interruption caused a total increase of 0.14 ± 0.05% and 0.25 ± 0.08% of the total planned MU, ranging from 1746 to 3261 MU, at the interrupted angles in 1int and 2int, respectively. All global gamma passing rates satisfied our clinical threshold of 90%, and the differences of passing rates were less than 0.3% on average with both criterions. All measured 1int and 2int data were within 3% DD from 0int measured data. For 6 MV FFF beams, the average passing rate with 2, 1, and 0.5% DD were 99.9 ± 0.2%, 92.3 ± 12.0%, and 81.9 ± 24.9%, respectively, between 0int and 1int, and 99.8 ± 0.4%, 92.1%12.4%, and 80.7 ± 26.5%, respectively, between 0int and 2int. For 10 MV FFF beams, the average passing rate with 2, 1, and 0.5% DD were 100.0 ± 0.2%, 95.4 ± 9.4% and 87.0 ± 19.8%, respectively, between 0int and 1int, and 99.9 ± 0.3%, 95.4 ± 9.7%, and 87.2 ± 21.3% between 0int and 2int. The dosimetric impact of beam interruption was investigated with small field and high dose rate FFF-VMAT SBRT plans. The delivered dose distributions with up to 12 interruptions per plan were still clinically acceptable. Only minimal changes were observed in Gamma, DD, and log file analysis.

Dose Comparison between Proton Pencil Beam and Monte Carlo Dose Calculation Algorithm in Lung Cancer Patients

Proton pencil beam dose calculation algorithms (PBA) have limitations in modeling proton scatter dose and its impact on depth dose properties through heterogeneous tissues present when treating lung cancer patients. Monte Carlo dose calculations (MC) may provide more accurate dose calculations when compared with the current algorithms that are in clinical use. This study investigates clinical pencil beam scanning (PBS) planned dose differences between PB and MC in lung cancer patients. With IRB approval, a comparative dosimetric analysis between RaystationTM Monte Carlo v4.0 (pending FDA 510 clearance) and RaystationTM pencil beam v4.0 dose algorithms was performed on 10 patient plans. PBS gantry plans were generated using single-field optimization technique to maintain target coverage under 3% range and 3 mm setup uncertainty. Dose prescriptions ranged from 60 Gy(RBE) to 66.6 Gy(RBE). Dose differences between PBA and MC were recorded for the following plan metrics: CTV V95, CTV homogeneity index (HI), total lung V20, total lung VRX (relative volume of lung receiving the prescribed dose or higher), and global maximum dose. Non-parametric Wilcoxon signed-rank testing was carried out to evaluate pairwise differences in planned dose and dose-volume parameters between PBA and MC. In this 10 patient sample, CTV V95 ranged from 99% to 100% with a median of 100% for PBA. When recalculated with MC, CTV V95 ranged from 77% to 94% with a median of 90% (p=0.002). MC treatment plans showed a reduction of dose homogeneity within the target volume. The median CTV HI (D95/D5) was 0.98 for PBA and 0.91 for MC (p = 0.002). Total lung V20 distributions were statistically identical to within 1% between dose calculation algorithms (p=1.0). Median lung VRX was 7% and 1% for PBA and MC, respectively (p = 0.002), indicating a reduction in lung volume receiving high dose when using MC. Lastly, the global maximum patient dose increased from a median value of 106% for PBA (range 101-113%) to 109% for MC (range 104-122%, p = 0.002). A retrospective analysis of 10 lung cancer PBS plans revealed a planned dose reduction in coverage to the CTV when recalculated using MC. This suggests that the use of PBA dose calculation in this disease site may lead to underdosing of the target volume and may support the clinical integration of MC dose calculation during treatment planning.Abstract 3654Pencil BeamMonte CarloMedianRangeMedianRangeSign Rank pCTV V95100%99% - 100%90%77% - 94%0.002CTV HI0.980.95 - 1.000.910.87-0.940.002Lung V2025%15% - 35%25%16% - 34%1.000Lung VRX7%2% - 11%1%0% - 6%0.002Max Dose106%101% - 113%109%104% - 122%0.002 Open table in a new tab

Superiority in Robustness of Multifield Optimization Over Single-Field Optimization for Pencil-Beam Proton Therapy for Oropharynx Carcinoma: An Enhanced Robustness Analysis

To compare the difference in robustness of single-field optimized (SFO) and robust multifield optimized (rMFO) proton plans for oropharynx carcinoma patients by an improved robustness analysis. We generated rMFO proton plans for 11 patients with oropharynx carcinoma treated with SFO intensity modulated proton therapy with simultaneous integrated boost prescription.Doses from both planning approaches were compared for the initial plans and the worst cases from 20 optimization scenarios of setup errors and range uncertainties. Expected average dose distributions per range uncertainty were obtained by weighting the contributions from the respective scenarios with their expected setup error probability, and the spread of dose parameters for different range uncertainties were quantified. Using boundary dose distributions created from 56 combined setup error and range uncertainty scenarios and considering the vanishing influence of setup errors after 30 fractions, we approximated realistic worst-case values for the total treatment course. Error bar metrics derived from these boundary doses are reported for the clinical target volumes (CTVs) and organs at risk (OARs). The rMFO plans showed improved CTV coverage and homogeneity while simultaneously reducing the average mean dose to the constrictor muscles, larynx, and ipsilateral middle ear by 5.6Gy, 2.0Gy, and 3.9Gy, respectively. We observed slightly larger differences during robustness evaluation, as well as a significantly higher average brainstem maximum and ipsilateral parotid mean dose for SFO plans. For rMFO plans, the range uncertainty-related spread in OAR dose parameters and many error bar metrics were found to be superior. The SFO plans showed a lower global maximum dose for single-scenario worst cases and a slightly lower mean oral cavity dose throughout. An enhanced robustness analysis has been proposed and implemented into clinical systems. The benefit of better CTV coverage and OAR dose sparing in oropharynx carcinoma patients by rMFO compared with SFO proton plans is preserved in a robustness analysis with consideration of setup error and range uncertainty.

Using a handheld stereo depth camera to overcome limited field-of-view in simulation imaging for radiation therapy treatment planning.

A correct body contour is essential for reliable treatment planning in radiation therapy. While modern medical imaging technologies provide highly accurate patient modeling, there are times when a patient's anatomy cannot be fully captured or there is a lack of easy access to computed tomography (CT) simulation. Here, we provide a practical solution to the surface contour truncation problem by using a handheld stereo depth camera (HSDC) to obtain the missing surface anatomy and a surface-surface image registration to stich the surface data into the CT dataset for treatment planning. For a subject with truncated simulation CT images, a HSDC is used to capture the surface information of the truncated anatomy. A mesh surface model is created using a software tool provided by the camera manufacturer. A surface-to-surface registration technique is used to merge the mesh model with the CT and fill in the missing surface information thereby obtaining a complete surface model of the subject. To evaluate the accuracy of the proposed approach, experiments were performed with the following steps. First, we selected three previously treated patients and fabricated a phantom mimicking each patient using the corresponding CT images and a 3D printer. Second, we removed part of the CT images of each patient to create hypothetical cases with image truncations. Next, a HSDC was used to image the 3D-printed phantoms and the HSDC-derived surface models were registered with the hypothetically truncated CT images. The contours obtained using the approach were then compared with the ground truth contours derived from the original simulation CT without image truncation. The distance between the two contours was calculated in order to evaluate the accuracy of the method. Finally, the dosimetric impact of the approach is assessed by comparing the volume within the 95% isodose line and global maximum dose (Dmax ) computed based on the two surface contours for the breast case that exhibited the largest contour variation in the treated breast. A systematic strategy of using a 3D HSDC to compensate for missing surface information caused by the truncation of CT images was established. Our study showed that the proposed technique was able to reliably provide the full contours for treatment planning in the case of severe CT image truncation(s). The root-mean-square error for the registration between the aligned HDSC surface model and the ground truth data was found to be 2.1 mm. The average distance between the two models was 0.4 ± 1.7 mm (mean ± SD). Maximum deviations occurred in areas of high concavity or when the skin was close to the couch. The breast tissue covered by 95% isodose line decreased by 3% and Dmax increased by 0.2% with the use of the HSDC model. The use of HSDC for obtaining missing surface data during simulation has a number of advantages, such as, ease of use, low cost, and no additional ionizing radiation. It may provide a clinically practical solution to deal with the longstanding problem of CT image truncations in radiation therapy treatment planning.

Applying a RapidPlan model trained on a technique and orientation to another: a feasibility and dosimetric evaluation.

BackgroundThe development of a dose-volume-histogram (DVH) estimation model for knowledge-based planning is very time-consuming and it could be inefficient if it was only used for similar upcoming cases as supposed. It is clinically desirable to explore and validate other potential applications for a configured model. This study tests the hypothesis that a supine volumetric modulated arc therapy (VMAT) model can optimize intensity modulated radiotherapy (IMRT) plans of other patient setup orientations.MethodsBased on RapidPlan, a DVH estimation model was trained using 81 supine VMAT rectal plans and validated on 10 similar cases to ensure the robustness of its designed purpose. Attempts were then made to apply the model to re-optimize the dynamic MLC-sequences of the duplicated IMRT plans from 30 historical patients (20 prone and 10 supine) that were treated with the same prescription as for the model (50.6 and 41.8 Gy to 95 % of PGTV and PTV simultaneously/22 fractions). The performance of knowledge-based re-optimization and the impact of setup orientations were evaluated dosimetrically.ResultsThe VMAT model validation on similar cases showed comparable target dose distribution and significantly improved organ sparing (by 10.77 ~ 18.65 %) than the original plans. IMRT plans of either setup can be re-optimized using the supine VMAT model, which significantly reduced the dose to the bladder (by 25.88 % from 33.85 ± 2.96 to 25.09 ± 1.32 Gy for D50 %; by 22.77 % from 33.99 ± 2.77 to 26.25 ± 1.22 Gy for mean dose) and femoral head (by 12.27 % from 15.65 ± 3.33 to 13.73 ± 1.43 Gy for D50 %; by 10.09 % from 16.26 ± 2.74 to 14.62 ± 1.10 Gy for mean dose), all P < 0.01. Although the dose homogeneity and PGTV conformity index (CI_PGTV) changed slightly (≤0.01), CI_PTV of IMRT plans was significantly increased (Δ = 0.17, P < 0.01) by the manually defined target-objectives in the VMAT optimizer. The semi-automated IMRT planning increased the global maximum dose and V107 % due to the missing of hot spot suppression by specific manual optimizing or fluence map editing.ConclusionsThe Varian RapidPlan model trained on a technique and orientation can be used for another. Knowledge-based planning improves organ sparing and quality consistency, yet the target-objectives defined for VMAT-optimizer should be readapted to IMRT planning, followed by manual hot spot processing.

Dose distributions verification for High dose rate brachytherapy plans by using ionization chambers 2D array

The purpose of this paper is to perform dosimetric verification (in-phantom) of dose distributions calculated with treatment planning system (TPS) by using 2D chamber array device in HDR brachytherapy. HDR brachytherapy treatment plans’dose distribution verification is performed using the two-dimensional (2D) ionization chamber array MatriXX Evolution developed by IBA Dosimetry (IBA Dosimetry, Germany) whose detector area is covered with the Nucletron Freiburg Flap Applicator Set (Nucletron BV,Veenendaal, the Netherlands) with catheters such that the detector plane was set to 0.86 cm from the catheter plane. Fixed slabs of RW3 (Perspex) were added below the 2D-ARRAY to provide full scattering conditions. The phantom was scanned on computed tomography (CT) for treatment planning with 2.5-mm slice thickness. Based on the CT data of the phantom, three different plans were calculated by the planning system (Oncentrabrachy version 4.3, Nucletron BV) and then are exported to the VERISOFT software for comparison with measured data. For comparison of dose distributions, both dose planes – measured &amp; calculated – were normalized  to the global maximum dose of the reference matrix (measured data set) and compared using the Gamma index method. Gamma indexes were evaluated using a dose-difference criterion of 3% and a distance criterion of 3 mm (γ≤1).The total number of evaluated dose points for the vault test case is 9755, 98.6 % of them (9623 point) passed the criteria of acceptability (3% delta dose and 3-mm distance criteria) and 1.4% of them (132 point) failed it. The total number of evaluated dose points for the full test case is 19964, 93.6 % of them (18683 point) passed  the criteria of acceptability and 6.4% of them (1281 point) failed it. And the total number of evaluated dose points for the cylinder test case is 19871, 96.9 % of them (19258 point) passed the criteria of acceptability and 3.1% of them (613 point) failed it. By thisThe use of the two-dimensional (2D) ionization chamber array MatriXX Evolution for brachytherapy applications has been successfully demonstrated. The array measurements in these planes have shown acceptable agreement with the TPS, generally within 3% delta dose and 3-mm distance agreement criteria within each plane. The comparisons made led to make a relation between the passing percentage values to the number of the evaluated dose points for each test case and it was found that as the number of these pixels increases the possibility of having more failing points increases.

SU‐E‐T‐106: An Institutional Review of Using Commercially Available Software to Evaluate Treatment Plan Quality for Various Treatment Sites and Beam Deliveries

Purpose:Use Sun Nuclear Quality Reports™ with PlanIQ™ to evaluate different treatment delivery techniques for various treatment sites.Methods:Fifteen random patients with different treatment sites were evaluated. These include the Head/Neck, prostate, pelvis, lung, esophagus, axilla, bladder and abdomen. Initially, these sites were planned on the Pinnacle 3 V9.6 treatment planning system and utilized nine 6MV step‐n‐shoot IMRT fields. The RT plan, dose and structure sets were sent to Quality Reports™ where a DVH was recreated and the plans were compared to a unique Plan Algorithm for each treatment site. Each algorithm has its own plan quality metrics and objectives, which include the PTV coverage, PTV maximum dose, the prescription dose outside the target, doses to the critical structures, and the global maximum dose and its location. Each plan was scored base on meeting each objective. Plans may have been reoptimized and reevaluated with Quality Reports™ based on the initial score. PlanIQ™ was used to evaluate if any objective not met was achievable or difficult to obtain. A second plan using VMAT delivery was created for each patient and scored with Quality Reports™.Results:There were a wide range of scores for the different treatment sites with some scoring better for IMRT plans and some better for the VMAT deliveries. The variation in the scores could be attributed to the treatment site, location, and shape of the target. Most deliveries were chosen for the VMAT due to the short treatment times and quick patient throughput with acceptable plan scores.Conclusion:The tools are provided for both physician and dosimetrist to objectively evaluate the use of VMAT delivery versus the step‐n‐shoot IMRT delivery for various sites. PlanIQ validates if objectives can be met. For the physicist, a concise pass/fail report is created for plan evaluation.