Spinal Cord Dmax Research Articles

Evaluating Utility of 4D PET-CT Motion Freeze Imaging for Lung SABR

In Lung stereotactic ablative radiotherapy (SABR), 4D PET-CT gives an edge over static 3D PET-CT in target volume delineation given its ability to reduce motion artifacts. Motion Freeze (MF) PET imaging combines the quantitative benefits of 100% counts of 4D phase-matched PET-CT imaging into a single static image by collecting CT & PET data at each phase of the breathing cycle, then matching the data for attenuation consistency. This provides further robustness of biologic target volume delineation with reduced image noise. The authors evaluated the utility of 4D PET-CT MF imaging in lung SABR treatments & the consequent dosimetric impact when either motion inclusive (retrospective imaging) technique or gating technique were to be used. Five patients of lung SABR were included for purpose of this dosimetric study (1 Ca lung and 4 lung oligo-metastasis). All patients underwent 4D CT /PET scan with the RPM system on 16 slice PET-CT scanner. The 4D CT and 4D PET data were binned in 10 phases of respiratory cycle. The Motion match software was utilized to create a MF image of all the 10 PET bins (MF-10) and 3 bins corresponding to end expiratory phase 40%,50%,60% (MF-3) in which tumor position was relatively stable. For study purpose we analyzed 3 clinical scenarios for target delineation (a) target volume generated using 4D CT alone (b) 4D CT all bins deformably registered with MF-10 (c) 4D-CT 3 bins deformably registered with corresponding MF-3, using gradient based intensity based registration algorithm. Three VMAT 6 MV FFF plans were generated for all the above all 3 volumes. The dosimetric parameters analysed included Target volume coverage, dose spillage (high, intermediate and low dose) & OAR doses as per RTOG protocol. Statistical comparison was done using paired sample t test in statistical analysis software. The target volume was reduced using 4D PET MF 10 & MF 3 as compared to 4D CT alone though the values were statistically insignificant [P=0.75(MF10), P=0.68 (MF3)]. There was statistically insignificant difference in target volume coverage parameters i.e. Conformity index, Heterogeneity index, dose spillage (high, intermediate and low dose) among all the plans. However the trend towards reduced OAR doses was seen in MF 10 plan & MF 3 plan as compared to 4D CT plan {Lungs V20 [P=0.06(MF10), P=0.08(MF3)], Heart Dmax [P=0.02(MF10), P=0.03(MF3)], Spinal cord Dmax [P=0.08(MF10), P=0.07(MF3)], Chest wall Dmax [P=0.001(MF10), P=0.037(MF3)], Great Vessel Dmax [P=0.03(MF10), P=0.045 (MF3)]}. Inclusion of 4D PET-CT MF scan 10 bins (non gated delivery) or 3 bins (gated delivery) can improvise the robustness of Lung SABR in terms of better target volume delineation, OAR doses & estimation of SUV values helping in better treatment response evaluation in follow up. While this study, first of its kind for Lung SABR, gives proof-of-concept & integration into workflow, a larger sample size evaluating 4D PET-CT MF would address the target delineation issue.

Assessment of DVH Prediction Model and Auto-Planning Module for Head and Neck VMAT Planning

The Auto-Planning module on a treatment planning system (TPS) can efficiently produce clinically acceptable VMAT plans with consistent quality. However, the initial optimization objectives of organs at risk (OARs) in Auto-Planning module need to be manually pre-set, with the result that plan quality and planning time are planner dependent. In this study, a dose volume histogram (DVH) prediction model was implemented for predicting reasonable initial optimization objectives to the Auto-Planning module. The advantage of this combination method was investigated for head and neck VMAT planning. 20 patients with head and neck cancer were selected randomly. 70 Gy in 35 fractions was given to PGTV (planning target volume expanded form gross tumor volume) and 63 Gy in 35 fractions was given to PCTV1 (covering adjacent high-risk structures and bilateral retropharyngeal lymph nodes), with (11 cases) or without (9 cases) 56 Gy in 35 fractions to PCTV2 (for prophylactic lymph nodes if clinically indicated). A DVH prediction model, which uses the geometry of targets and OARs to predict the DVH for OARs in PlanIQ software, was implemented for predicting the initial optimization objectives to the Auto-Planning module. To evaluate the advantage of this combination method, two types VMAT plans were generated as followed: VMATap plans were optimized by the Auto-Planning module with initial objectives from the Auto-Planning template with manually pre-setting objectives, and VMATpre plans were optimized by the Auto-Planning module with initial objectives predicted from the DVH prediction model in PlanIQ. Then, the dosimetric indices between VMATap and VMATpre plans were compared. There were no significant differences of V70Gy, V63 Gy, and V56 Gy between VMATap plans and VMATpre plans for PGTV, PCTV1, and PCTV2, respectively. Additionally, there were no significant differences of Dmax between VMATap plans and VMATpre plans for eye-L, lens-L and optic nerve-L. In some extent, VMATpre plans were more sparing eye-R and len-R than VMATap plans, while VMATap plans produced lower optic nerve-R dose than VMATpre plans. Furthermore, Dmax of brainstem and spinal-cord were both dramatically reduced in VMATpre plans than VMATap plans with significant differences (p < 0.01). Especially for brainstem, Dmax of VMATpre plans were well consistent with the predicted values by the DVH prediction model. For Dmean of parotids, no significant differences were found between these VMAT plans. The reason maybe that the predicted values, initial objectives in VMATpre plans, were around the manually pre-setting initial objectives in VMATap plans. DVH prediction model can generate reasonable initial objectives for the Auto-Planning module in a treatment planning system. The combination method has the potential advantage to further reduce radiation dose received by OARs.

A comparative study of identical VMAT about two adjacent targets with and without fixed-jaw technique

BackgroundThe radiation transmission through the multileaf collimators is undesired in modern techniques such as volumetric modulated arc therapy (VMAT). According to identical plans, in this study, we aim to investigate the dosimetric impact of jaw tracking on the VMAT plans on two adjacent targets.MethodsTwo treatment plans were designed for eight pelvic (cervical) patients with two targets using the same optimization parameters. The original plan (O-plan) used automatically selected jaw positions. In the new plan (F-plan), the jaws were fixed to block two targets in two beams. The dosimetric parameters of the two plans were compared to evaluate the improvement of dose sparing for the body volume between two targets (named interOAR) in F-VMAT.ResultsThe mean dose of interOAR reduced significantly from 654.96 ± 113.38 cGy for O-VMAT, to 490.84 ± 80.26 cGy for F-VMAT (p = 0.018). The monitor units (MUs) in the F-plans were 1.49-fold higher than that in the O-plan. The F and O-plan performed similarly in target dose homogeneity. The differences in Dmax of spinal cord, Dmax of spinal cord planning organ at risk volume, and V20, V30, and V40 of the intestine were insignificant.ConclusionsVMAT plans with the fixed-jaw method can reduce the volume between two targets effectively. However, despite the plan quality, the method can only be used when the regular methods cannot reach the clinical requirements for critical organs because of additional MUs.

Combining deep-inspiration breath hold and intensity-modulated radiotherapy for gastric mucosa-associated lymphoid tissue lymphoma: Dosimetric evaluation using comprehensive plan quality indices

BackgroundAlthough there have been many attempts to increase the therapeutic ratio of radiotherapy for gastric mucosa-associated lymphoid tissue lymphoma (MALToma), only a few planning studies have reported the efficacy of the modern radiotherapy technique till date. Therefore, we performed the dosimetric comparison among 3-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) plans, using deep-inspiration breath hold (DIBH) or free-breathing (FB) techniques, to determine the most optimal plan for gastric MALToma.MethodsWe evaluated 9 patients with gastric MALToma for whom 3D-CRT, step-and-shoot IMRT (SIMRT), volumetric-modulated arc therapy (VMAT), and tomotherapy plans with identical prescribed doses were generated using DIBH or FB computed tomography (CT). Planning target volume (PTV) coverage and non-target doses were calculated for each plan and compared with plan quality metric (PQM) scores.ResultsAll 72 plans of 9 patients satisfied our dosimetric goals, and the IMRT plans and 3D-CRT plans had similarly good conformity index values with no differences related to respiratory movement. IMRT plans yielded significantly better doses to the organs-at-risk, and DIBH plans yielded significantly lower liver, heart, and lung Dmean and spinal cord Dmax with smaller irradiated volumes compared to FB plans. For the mean PQM scores, VMAT-DIBH and SIMRT-DIBH yielded the best scores, whereas 3D plans provided reduced beam monitor unit values.ConclusionOur findings demonstrate that modern RT technologies (DIBH with VMAT or SIMRT) could potentially provide excellent target coverage for gastric MALToma while reducing doses to organs-at-risk. However, the relevance of the most optimal plan considering clinical outcomes should be confirmed further in a larger patient cohort.

Influence of 3D-CRT and conformal IMRT on thyroid function of patients with cervical and upper thoracic esophageal cancer and comparison of clinical efficacy.

Clinical efficacy in patients with cervical and upper thoracic esophageal cancer was compared between three-dimensional conformal radiotherapy (3D-CRT) and conformal intensity-modulated radiotherapy (IMRT). Medical data of 120 esophageal cancer patients undergoing RT in the Radiology Department in Xiaogan Hospital Affiliated to Wuhan University of Science and Technology (Xiaogan, China) from March 2015 to March 2018 were retrospectively analyzed. Patients were divided into 3D-CRT group (treated with 3D-CRT, n=60) and IMRT group (treated with IMRT, n=60). The target conformal index (CI), PTV maximum dose (Dmax), PTV Dmin and PTV Dmean in both groups were observed. Changes in double-lung V5, double-lung V20, double-lung V30 and spinal cord Dmax in both groups were also observed. The serum free triiodothyronine (FT3), free tetraiodothyronine (FT4) and thyroid-stimulating hormone (TSH) concentrations were detected via chemiluminescence assay. Moreover, the short-term efficacy and radiation injury were observed. CI in IMRT group was significantly higher than that in 3D-CRT group (P<0.001). The organ-at-risk dose parameter V20 in IMRT group was obviously lower than that in 3D-CRT group (P<0.001). Serum FT3 and FT4 concentrations in both groups before RT were significantly higher than those after RT (P<0.05), but the TSH concentration was significantly lower than that after RT (P<0.05). Serum FT3 and FT4 concentrations in IMRT group after RT were obviously higher than those in 3D-CRT group (P<0.05). The incidence rates of radiation esophagitis and radiation pneumonitis in IMRT group were remarkably lower than those in 3D-CRT group (P<0.05). IMRT can reduce the double-lung V20 in patients, improve the target conformal degree, better protect the normal tissues, cause less damage to thyroid function, and reduce radiation injury during and after RT of esophageal cancer.

Dosimetric Impact of Automated Non-Coplanar Treatment Planning Using Stereotactic Radiosurgery for Multiple Cranial Metastases: Comparison between Hyperarc and Cyberknife Dose Distributions

The purpose of this study was to clarify the dosimetric impact of automated non-coplanar treatment planning, HyperArc-based stereotactic radiosurgery (SRS) for multiple cranial metastases by comparing with Robotic Radiosurgery System, Cyberknife planning. Eleven cancer patients with multiple cranial metastases (range of the number of tumors: 3 to 5) treated by CyberKnife M6 (Accuray Inc, Sunnyvale, USA) in the period from January 2016 to December 2017 were selected for this study. MultiPlan (Accuray Inc, Sunnyvale, USA) with Ray-tracking dose calculation algorithm was used as a radiation treatment planning system. The GTV was defined as the area of contrast enhancement on MRI and PTV was equal to GTV. The treatment dose of 23 Gy per single fraction was prescribed to the 70%-80% isodose line covering 95% of PTV. The dose to the surrounding healthy brain and organs at risk (e.g., brain stem) were optimized to minimize complications for all plans generated using our institutional protocol; PTV Dmin > 20 Gy, brainstem Dmax < 15 Gy, spinal cord Dmax < 14 Gy, optic nerve Dmax < 10 Gy, and optic chiasm Dmax < 10 Gy. These plans were replanned with an automated non-coplanar treatment planning solution implemented in a treatment planning system, named HyperArc. HyperArc plan were designed using four non-coplanar arc single-isocenter VMAT in 6MV flattening filter free mode for simulated delivery with the True beam STx (Varian) in high intensity with HD-MLC. One isocenter was used for all targets and was placed at the center of mass of all targets. Dose calculation algorithm was Acuros XB. Dosimetric differences were evaluated using target conformity/homogeneity (Paddick CI and HI), dose fall-off (gradient index) and radiation necrosis indicator (total brain V12-GTV). Summary of DVH paramters for two plans are shown in table 1. PTV CI, HI and GI were 0.60±0.11, 1.72±0.22, and 3.94±0.74, respectively, for Cyberknife plan, whereas they were 0.87±0.08, 1.44±0.05, and 5.31±1.42, respectively, for HyperArc plan (p <0.05). Total brain V12-GTV for Cyberknife and HyperArc were 5.26±2.83 cm3 and 4.02±1.71, respectively. These results showed that HyperArc plan had better CI, HI and total lung V12-GTV, although Cyberknife had better GI.Abstract TU_31_3204; Table 1DVH parameterHyperArcCyberknifePTV maximum29.78±0.9233.60±2.61 minimum20.73±0.2719.71±1.34 mean25.88±0.2727.53±1.01 HI1.44±0.051.72±0.22 CI0.87±0.080.60±0.11 GI5.31±1.423.94±0.74Total brain mean1.15±0.290.97±0.35 V12-GTV4.02±1.715.26±2.83 V2163.00±78.84151.20±89.73 Open table in a new tab We compared HyperArc and Cyberknife plans for brain multiple metastases SRS for the first time. Our results demonstrated that HyperArc-based SRS planning had the great potential for being suitable tool for brain multiple metastases SRS.

Palliative two-dimensional radiotherapy of pancreatic carcinoma: a feasibility study.

The aim of the study was to analyze the dose to be administered with two-dimensional involved-field palliative radiotherapy in advanced pancreatic carcinoma with respect to current dose-volume constraints (QUANTEC). The following standard regimens were evaluated: 30 Gy at 3 Gy/fraction (regimen A), 36 Gy at 2.4 Gy/fraction (regimen B), 45 Gy at 1.8 Gy/fraction (regimen C), and 50 Gy at 2 Gy /fraction (regimen D). The following constraints were considered: spinal cord Dmax <50 Gy, duodenum Dmax <55 Gy, liver Dmean <30 Gy, kidneys Dmean <15 Gy. For dose/fraction different from 1.8-2 Gy, the correction of constraints using a value of alpha/beta = 3 for late effects was considered. The calculation of dose/volume constraints was repeated for three different radiation beams: cobalt unit, 6 MV photons, and 15 MV photons. Standard field sizes were used and adapted according to the different beam types, using the parameters of our previous study. Respect of dose-volume constraints was assessed for each type of beam and treatment (dose per fractionation) in all patients. Treatments were considered acceptable in case of: 1) respect of the constraints for spinal cord and duodenum in all patients; 2) respect in >10/15 patients of constraints for kidneys and liver. Therefore, minor violations (<10%) of the constraints for these organs were accepted (in less than 5/15 patients), in consideration of the palliative aim of treatment. In regimen A (30 Gy, 3 Gy/fraction), evaluated constraints were respected in all patients, regardless of the type of energy. In regimen B (36 Gy, 2.4 Gy/fraction), constraints were met in all patients undergoing irradiation with 6 and 15 MV photons. However, using the cobalt unit, kidney constraint was respected only in 5 of 15 patients. In regimens C and D (45 Gy, 1.8 Gy/fraction and 50 Gy, 2 Gy/fraction, respectively), the constraint for the kidney was respected only in 2-5 patients, depending on the energy used. Furthermore, using 50 Gy, the spinal cord constraint was not respected in 2-3 patients, depending on the beam used. Therefore, only the following treatments were considered acceptable: 1) 30 Gy, 3 Gy/fraction, regardless of the energy used; 2) 36 Gy, 2.4 Gy/fraction, only for treatments performed with linear accelerator (6-15 MV). The clinical benefits of radiotherapy in pancreatic tumors should not be withheld from patients treated in centers only with two-dimensional technology. Prospective trials, particularly in developing countries, would be useful to evaluate the efficacy in this setting of involved-field two-dimensional treatments using the dose and fractionation defined in this analysis.

Dosimetric impact of induction chemotherapy on intensity-modulated radiotherapy for locally advanced nasopharyngeal carcinoma and dosimetric characteristics of replanning

Objective To investigate the benefits of replanning after induction chemotherapy (IC) by analyzing the dosimetric impact of IC on intensity-modulated radiotherapy (IMRT) for locally advanced nasopharyngeal carcinoma (NPC) and the dosimetric characteristics of replanning after IC, and to provide data for the rational design of clinical radiotherapy plans. Methods 16 NPC patients underwent contrast-enhanced CT scan once before and after IC. Target volumes were delineated and the chemotherapy plans were created, defined as Plan-1 and Plan-2, respectively. Then the target structure after IC was copied to Plan-1, generating the third plan, defined as Plan-1-2. The paired t-test was used to compare the dosimetric parameters between Plan-1 and Plan-1-2 and between Plan-2 and Plan-1-2. Results Plan-1 vs. Plan-1-2: Plan-1-2 showed significantly reduced Dmean of target volume compared with Plan-1(P<0.05). Plan-1-2 significantly increased Dmean and Dmax of the spinal cord (P<0.05), although significantly reduced Dmean of the brain stem and Dmax of the temporal lobes compared with Plan-1. Plan-1-2 also had significantly reduced conformity index (CI) and significantly increased homogeneity index (HI) for the target volume compared with Plan-1(P<0.05). Plan-2 vs. Plan-1-2: Compared with Plan-1-2, Plan-2 significantly increased Dmean and Dmin of gross tumor volume (GTV) and primary GTV (P<0.05) and significantly reduced Dmean of the temporal lobes and Dmax and Dmean of the spinal cord (P<0.05), with Dmax decreased to 430.48 cGy; Plan-2 had significantly increased CI and significantly reduced HI for the target volume compared with Plan-1-2(all P<0.05). Conclusions IMRT plan-1 after IC has worse dosimetric distribution, while replanning after IC has more dosimetric benefits. Key words: Nasopharyngeal neoplasms/induction chemotherapy; Nasopharyngeal neoplasms/intensity modulated radiotherapy; Target delineation; Dosimetry

Evaluating the Feasibility of Applying Deformable Registration Into Adaptive Therapy for NRG Oncology RTOG 1106

Adaptive radiotherapy has been introduced to reduce normal tissue toxicities and escalate tumor dose and is evaluated in clinical trials. The purpose of our study is to evaluate the feasibility and efficacy of deformable registration, as compared with rigid registration, for adaptive planning of RTOG 1106 Randomized Phase II Trial of Individualized Adaptive Radiotherapy Using During-Treatment FDG-PET/CT and Modern Technology in Locally Advanced Non-Small Cell Lung Cancer (NSCLC). Thirteen patients from RTOG 1106 trial with both primary planning CTs and re-scanned CTs were included in this study. An experienced radiation oncologist contoured the tumor volumes (TVs) and organs at risk (OARs) on the re-scanned CTs, and treatment plans were made on these CTs. Backward deformable registration (from adaptive image to initial image) and Forward deformable registration (from initial images to adaptive images) were performed upon these patients. The deformed contours were compared with the original contours for geometry and dosimetry. The geometry comparison was performed using the Dice Similarity Coefficient (DSC) and Mean Distance to Agreement (MDA). The dosimetry differences were evaluated by the deviation of dose between deformed contours and original. Five different contours were studied that included Heart, Lungs-GTV, Esophagus, Spinal Cord, and PTV. The performance of backward deformable registration and forward deformable registration were also compared. The average DSC of all contours for forward deformable registration is 84.83±15.48%, while the average DSC for backward deformable registration is 85.12±16.01%. The DSC for Heart, Lung_L, Lung_R, and GTV are 86.69±5.70%, 95.17±2.06%, 96.17±1.83%, and 61.88±13.24% respectively. The relatively low DSC value for GTV is due to the volume change of GTVs from the primary CTs to the re-scanned CTs. The MDA for Esophagus and Spinal Cord are 1.89±0.56mm and 2.19±1.59mm respectively. For the dosimetric comparison, the average deviation of V30Gy, V40Gy, Dmax, and Dmean of Heart, V5, V20, and Dmean of Lungs, Dmax and Dmean of Esophagus, Dmax of Spinal Cord, and Dmin, Dmax, and D95 of PTV are 7.08±7.97%, 5.86±6.95%, 1.38±2.65Gy, 3.46±4.35Gy, 1.45±1.20%, 0.95±0.76%, 0.55±0.46Gy, 0.62±0.53Gy, 3.22±2.93Gy, 0.72±0.73Gy, 10.39±11.13Gy, 0.59±1.15Gy, 4.30±5.90Gy Respectively. Deformable registration is highly desirable for accurate dosimetry of adaptive planning. Detailed workflow of the implementation needs to be optimized.

Anatomical and Dosimetric Changes during IMRT for Oropharyngeal Cancer Detected by Weekly Cone-Beam CT With Deformable Image Registration

Re-planning is often necessary during IMRT for head and neck cancer due to tumor regression and changes of body contour. CBCT was obtained for patients with OPC once a week to confirm anatomical and dosimetric changes of tumor and organs at risk (OAR). Ten patients with OPC treated by a two-step IMRT method were included. For all patients, treatment-planning computed tomography (CT) was done twice before and at the fourth week for initial and boost IMRT, respectively. All 10 patients were given 70 Gy/35 fractions with concurrent chemotherapy (CDDP; 5, Cetuximab; 4, CBDCA 1). On board CBCTs were obtained on days 1, 8, 15, 22, and 29 of IMRT. Deformed volumes of tumor and OARs in the CBCT were compared with those in the planning CT. Dose distribution at the isocenter level was recalculated based on weekly CBCT image and compared with the initial planned dose distribution. Area of body surface, PTV D2, D50 and D98, and Dmax of the spinal cord on the isocenter level were selected for analysis. After volumes on initial treatment-planning CT were deformed into CBCT images on days 1-29, change rates from CBCT images on day1 were determined for CBCT images from day 8 to day 29. Change rates of more than 5% in area or dose were regarded as significant change. Results: Average change rates and number of patients with significant change were shown in Table 1. Area of body surface decreased gradually. After day 22, five of the 10 patients showed decrease of body area of more than 5%. Area of body surface and Dmax of the spinal cord were inversely correlated (r = -0.47). After day 22, Dmax of the spinal cord increased more than 5% for eight patients (80%). Notably, PTV D2, D50 and D98 were not changed during the period from day 1 to day 29. In patients with OPC treated by a two-step IMRT method, weekly CBCT demonstrated decrease of body surface and increase of Dmax of the spinal cord after 22-29 days of treatment. Although changes in PTV doses were minimal, re-planning may be necessary to protect spinal cord toxicity when significant decrease of body area was noted.Abstract 2812; Table 1Average change rate and number of patients with significant changeAverage change rateNumber of patients with significant changeDay1Day8Day15Day22Day29Day1Day8Day15Day22Day29Body surface(cm2)100%97%97%96%96%Body surface(cm2)03356PTV D98 (Gy)100%99%99%99%98%PTV D98 (Gy)00001PTV D50100%100%100%100%100%PTV D5000000PTV D2100%100%100%100%100%PTV D200001Spinal cordDmax (Gy)100%101%102%101%104%Spinal cordDmax (Gy)02589 Open table in a new tab

Knowledge Engineering-Based Quality Evaluation of NRG Oncology RTOG 0522 Treatment Plans

To evaluate radiotherapy treatment plan quality of IMRT plans submitted for RTOG 0522 clinical trial (A Randomized Phase III Trial of Concurrent Accelerated Radiation and Cisplatin versus Concurrent Accelerated Radiation, Cisplatin, and Cetuximab (C225) [Followed by Surgery for Selected Patients] for Stage III and IV Head and Neck Carcinomas). To use knowledge engineering based models from RapidPlan (built from HN002) for the quality study, and to re-optimize the plans by the model with the aim of further sparing the organs at risk and improve the quality of these plans in general. A head and neck RapidPlan model was initially built in Varian Eclipse treatment planning system (Version 13.6.15) using treatment plans from the NRGHN002 clinical trial (A Randomized Phase II Trial for patients with p16 positive, non-smoking-associated, locoregionally advanced oropharyngeal cancer). The model was duplicated and tuned to be used for QA and re-optimizing treatment plans from RTOG 0522. The modified model was then used to QA and re-optimize plans with deviation unacceptable scores (i.e., failed to pass the dosimetric compliance criteria of RTOG 0522). Initial quality review of 748 IMRT plans submitted to RTOG0522 show that 21 plans did not meet the spinal cord dose constraint (D0.03 cc <= 48 Gy), and 323 plans did not meet the dose constraint for parotid glands (one of the gland has mean dose less than 26 Gy). All the 21 plans that did not meet spinal cord constraint were pick for further analysis using the HN002 model, the results show that 15 of them has submitted plan dose volume histogram (DVH) fell above the predicted band. All the 21 plans were further optimized using model generated line objectives for organ at risks (OARs) (spinal cord, parotid glans, larynx, and NonPTV). All of plans achieved better scores after re-optimization (per-protocol or deviation acceptable). Average spinal cord Dmax [Gy] was decreased from 48.9 ± 2 Gy to 41.4 ± 4.8 Gy. Average parotids gland Dmean [Gy] were decreased from 34.1 ± 12 Gy to 29.5 ± 12 Gy. PTV coverage for re-optimized plans is comparable with original plans. PTV_7000 V65 Gy[%], D95%[Gy] and V80 Gy[%] for original plans are 98.7 ± 2.7%, 70 ± 2.3 Gy, 1.2 ± 4.5 Gy; and those for the re-optimized plans are 99.9 ± 0.1%, 70.8 ± 0.6 Gy, and 0.05 ± 0.1%, respectively. Knowledge-engineering based models predicted IMRT plans of better target coverage and OAR sparing as compared with submitted 0522 cases. All of IMRT plans with the worst score of deviation unacceptable from RTOG 0522 were improved to scores of variation acceptable or better with Knowledge based planning (KBP) re-optimization. These models will be used as part of the clinical trial quality assurance program to improve the quality of treatment plans submitted for clinical trials.

The dosimetric effects of limited elective nodal irradiation in volumetric modulated arc therapy treatment planning for locally advanced non-small cell lung cancer.

Contemporary radiotherapy guidelines for locally advanced non-small cell lung carcinoma (LA-NSCLC) recommend omitting elective nodal irradiation, despite the fact that evidence supporting this came primarily from older reports assessing comprehensive nodal coverage using 3D conformal techniques. Herein, we evaluated the dosimetric implications of the addition of limited elective nodal irradiation (LENI) to standard involved field irradiation (IFI) using volumetric modulated arc therapy (VMAT) planning. Target volumes and organs-at-risk (OARs) were delineated on CT simulation images of 20 patients with LA-NSCLC. Two VMAT plans (IFI and LENI) were generated for each patient. Involved sites were treated to 60 Gy in 30 fractions for both IFI and LENI plans. Adjacent uninvolved nodal regions, considered high risk based on the primary tumor site and extent of nodal involvement, were treated to 51 Gy in 30 fractions in LENI plans using a simultaneous integrated boost approach. All planning objectives for PTVs and OARs were achieved for both IFI and LENI plans. LENI resulted in significantly higher esophagus Dmean (15.3 vs. 22.5 Gy, p < 0.01), spinal cord Dmax (34.9 vs. 42.4 Gy, p = 0.02) and lung Dmean (13.5 vs. 15.9 Gy, p = 0.02), V20 (23.0 vs. 27.9%, p = 0.03), and V5 (52.6 vs. 59.4%, p = 0.02). No differences were observed in heart parameters. On average, only 32.2% of the high-risk nodal volume received an incidental dose of 51 Gy when untargeted in IFI plans. The addition of LENI to VMAT plans for LA-NSCLC is feasible, with only modestly increased doses to OARs and marginal expected increase in associated toxicity.

Feasibility of dynamic adaptive passive scattering proton therapy with computed tomography image guidance in the lung.

Hypo-fractionated proton beam therapy (PBT) is an approach that has been increasingly explored over the past decade. It requires high geometric accuracy for targeting of the PBT beams. However, image-guided PBT is currently commonly performed with kV X-ray images of bony anatomy. A dynamic adaptive passive scattering PBT system using computed tomography-based three-dimensional image guidance was developed, and its effectiveness was then evaluated retrospectively in patients with nonsmall cell lung cancer (NSCLC). The dynamic adaptive PBT system consisted of computed tomography-based image registration and proton dose calculation using a simplified Monte Carlo algorithm, with a range adaptation system that could adjust the range shifter thickness to alter the dose distribution. Three patients were retrospectively analyzed. All plans, which each had a total dose of 60 Gy (relative biological effectiveness; RBE), were generated using two fields (Gantry angles: 270 degree and 180 degree) in a passive scattering method. Three dose distributions were generated for each patient according to the following different registrations: bone registration, tumor registration, and tumor registration with range adaptation. The following dosimetric parameters were compared with the original plan: target dose coverage at D95% for the clinical target volume (CTV), homogeneity of D5% to D95% for the CTV, and dose distributions in normal tissue (Dmax of Spinal cord and V20 Gy of lung). For the bone registration method, the average D95% and D5% to D95% for the CTV showed average differences from the original plan of -3.7 ± 4.1 Gy (mean ± 1SD; RBE) and 3.6 ± 3.9 Gy (RBE) respectively. The tumor registration method achieved better coverage than the bone registration method, although the dosimetric parameters for coverage and homogeneity still showed average differences in -2.0 ± 2.3 Gy (RBE) and 1.9 ± 2.2 Gy (RBE) respectively. The range adaptive plan showed comparable coverage and homogeneity [D95%: -1.0 ± 1.3 Gy (RBE) and D5% to D95%: 0.9 ± 1.0 Gy (RBE) on average] to the original plan, as well as demonstrating similar normal tissue sparing. The approach could be completed in less than 10 min, including CT acquisition, image registration, dose recalculation with range optimization, and the operator's visual verification. The tumor dose coverage in patients with NSCLC may deteriorate as a result of respiratory or body movement if daily proton range adaptation is not performed. Our approach may provide higher geometric accuracy for localization of the tumor, and the dynamic range adaptation enables us to achieve the planned dose distribution for hypo-fractionated PBT in the lung.

Dose escalation by image-guided intensity-modulated radiotherapy leads to an increase in pain relief for spinal metastases: a comparison study with a regimen of 30 Gy in 10 fractions.

PurposeUnder the existing condition that the optimum radiotherapy regimen for spinal metastases is controversial, this study investigates the benefits of dose escalation by image-guided intensity-modulated radiotherapy (IG-IMRT) with 60–66 Gy in 20–30 fractions for spinal metastases.ResultsIn the dose-escalation group, each D50 of planning gross tumor volume (PGTV) was above 60 Gy and each Dmax of spinal cord planning organ at risk volume (PRV) was below 48 Gy. The median biological effective dose (BED) of Dmax of spinal cord was lower in the dose-escalation group compared with that in the 30-Gy group (69.70 Gy vs. 83.16 Gy, p < 0.001). After one month and three months of the radiotherapy, pain responses were better in the dose-escalation group than those in the 30-Gy group (p = 0.005 and p = 0.024), and the complete pain relief rates were respectively 73.69% and 34.29% (p = 0.006), 73.69% and 41.38% (p = 0.028) in two compared groups. In the dose-escalation group, there is a trend of a longer duration of pain relief, a longer overall survival and a lower incidence of acute radiation toxicities. No late radiation toxicities were observed in both groups.Materials and MethodsDosimetric parameters and clinical outcomes, including pain response, duration of pain relief, radiation toxicities and overall survival, were compared among twenty-five metastatic spinal lesions irradiated with the dose-escalation regimen and among forty-four lesions treated with the 30-Gy regimen.ConclusionsConventionally-fractionated IG-IMRT for spinal metastases could escalate dose to the vertebral lesions while sparing the spinal cord, achieving a better pain relief without increasing radiation complications.

Dosimetric comparison between automatic three-dimensional conformal radiotherapy, inverse three-dimensional conformal radiotherapy, and inverse intensity-modulated radiotherapy

Objective To compare dosimetric parameters between automatic three-dimensional conformal radiotherapy (a3DCRT), inverse three-dimensional conformal radiotherapy (i3DRT), inverse intensity-modulated radiotherapy (iIMRT). Methods Ten lung cancer patients with a single target and 10 intracranial tumor patients also with a single target, who were treated in our radiotherapy center from 2014 to 2015, were included in the study. Their image data were transferred to RayStation 4.5 via network, and then the treatment plans for a3DCRT, i3DCRT, and iIMRT were designed for the 20 patients. The dosimetric parameters for planning target volume (PTV) and organs at risk (OAR) were compared between the three plans using multiple dependent variables and two dependent variables. Results For lung cancer patients, iIMRT achieved better results in D98%, D50%, D2%, conformity index (CI), and homogeneity index (HI) than i3DCRT and a3DCRT (P=0.007, 0.001, 0.002, 0.000, and 0.000), and the CI of a3DCRT was superior to that of i3DCRT (P=0.000); there were no significant differences in heart D33, spinal cord Dmax and D1 cm3, and both lungs between the three plans (P=0.702, 0.237, 0.163, 0.739, 0.908, 0.832, 0.886, 0.722, 0.429, 0.840, and 0.702). For intracranial tumor patients, there were no significant differences in dosimetric parameters between the three plans, except that the CI of iIMRT and a3DCRT was superior to that of i3DCRT (P=0.648, 0.783, 0.256, 0.931, 0.002, and 0.034); there were no significant differences in whole brain irradiation dose between the three plans (P=0.446, 0.755, 0.772, 0.0266, 0.440, 0.290, and 0.939). Conclusions For the single target in patients with lung cancer and intracranial tumors, a3DCRT can improve the CI of PTV compared with i3DCRT, and shows no significant dosimetric disadvantage for OARs compared with iIMRT. Considering the simplicity and low cost of 3DCRT, a3DCRT holds promise as a novel radiotherapy technique. Key words: Beamset’s orientation auto-optimization; Inverse three-dementional conformal radiotherapy; Automatic three-dementional conformal radiotherapy; Inverse intensity-modulated radiotherapy

Phantom-to-clinic development of hypofractionated stereotactic body radiotherapy for early-stage glottic laryngeal cancer

The purpose of this study was to commission and clinically test a robotic stereotactic delivery system (CyberKnife, Sunnyvale, CA) to treat early-stage glottic laryngeal cancer. We enrolled 15 patients with cTis-T2N0M0 carcinoma of the glottic larynx onto an institutional review board (IRB)-approved clinical trial. Stereotactic body radiotherapy (SBRT) plans prescribed 45 Gy/10 fractions to the involved hemilarynx. SBRT dosimetry was compared with (1) standard carotid-sparing laryngeal intensity-modulated radiation therapy (IMRT) and (2) selective hemilaryngeal IMRT. Our results demonstrate that SBRT plans improved sparing of the contralateral arytenoid (mean 20.0 Gy reduction, p < 0.001), ipsilateral carotid Dmax (mean 20.6 Gy reduction, p < 0.001), contralateral carotid Dmax (mean 28.1 Gy reduction, p < 0.001), and thyroid Dmean (mean 15.0 Gy reduction, p < 0.001) relative to carotid-sparing IMRT. SBRT also modestly improved dose sparing to the contralateral arytenoid (mean 4.8 Gy reduction, p = 0.13) and spinal cord Dmax (mean 4.9 Gy reduction, p = 0.015) relative to selective hemilaryngeal IMRT plans. This “phantom-to-clinic” feasibility study confirmed that hypofractionated SBRT treatment for early-stage laryngeal cancer can potentially spare dose to adjacent normal tissues relative to current IMRT standards. Clinical efficacy and toxicity correlates continue to be collected through an ongoing prospective trial.

Dosimetric benefits of automation in the treatment of lower thoracic esophageal cancer: Is manual planning still an alternative option?

This study aimed to design automated volumetric-modulated arc therapy (VMAT) plans in Pinnacle auto-planning and compare it with manual plans for patients with lower thoracic esophageal cancer (EC). Thirty patients with lower thoracic EC were randomly selected for replanning VMAT plans using auto-planning in Pinnacle treatment planning system (TPS) version 9.10. Historical plans of these patients were then compared. Dose-volume histogram (DVH) statistics, dose uniformity, and dose homogeneity were analyzed to evaluate treatment plans. Auto-planning was superior in terms of conformity index (CI) and homogeneity index (HI) for planning target volume (PTV), significantly improving 8.2% (p = 0.013) and 25% (p = 0.007) compared with manual planning, respectively, and decreasing dose of heart and liver irradiated by 20 to 40 Gy and 5 to 30 Gy, respectively (p < 0.05). Meanwhile, auto-planning further reduced the maximum dose (Dmax) of spinal cord by 6.9 Gy compared with manual planning (p = 0.000). Additionally, manual planning showed the significantly lower low-dose volume (V5) for the lung (p = 0.005). For auto-planning, the V5 of the lung was significantly associated with the relative volume index (the volume ratio of PTV to the lung), and the correlation coefficient (R) and p-value were 0.994 and 0.000. Pinnacle auto-planning achieved superior target conformity and homogeneity and similar target coverage compared with historical manual planning. Most of organs at risk (OARs) sparing was significantly improved by auto-planning except for the V5 of the lung, and the low dose distribution was highly associated with PTV volume and lung volume in auto-planning.

Does Motion Assessment With 4-Dimensional Computed Tomographic Imaging for Non-Small Cell Lung Cancer Radiotherapy Improve Target Volume Coverage?

Introduction:Modern radiotherapy with 4-dimensional computed tomographic (4D-CT) image acquisition for non–small cell lung cancer (NSCLC) captures respiratory-mediated tumor motion to provide more accurate target delineation. This study compares conventional 3-dimensional (3D) conformal radiotherapy (3DCRT) plans generated with standard helical free-breathing CT (FBCT) with plans generated on 4D-CT contoured volumes to determine whether target volume coverage is affected.Materials and methods:Fifteen patients with stage I to IV NSCLC were enrolled in the study. Free-breathing CT and 4D-CT data sets were acquired at the same simulation session and with the same immobilization. Gross tumor volume (GTV) for primary and/or nodal disease was contoured on FBCT (GTV_3D). The 3DCRT plans were obtained, and the patients were treated according to our institution’s standard protocol using FBCT imaging. Gross tumor volume was contoured on 4D-CT for primary and/or nodal disease on all 10 respiratory phases and merged to create internal gross tumor volume (IGTV)_4D. Clinical target volume margin was 5 mm in both plans, whereas planning tumor volume (PTV) expansion was 1 cm axially and 1.5 cm superior/inferior for FBCT-based plans to incorporate setup errors and an estimate of respiratory-mediated tumor motion vs 8 mm isotropic margin for setup error only in all 4D-CT plans. The 3DCRT plans generated from the FBCT scan were copied on the 4D-CT data set with the same beam parameters. GTV_3D, IGTV_4D, PTV, and dose volume histogram from both data sets were analyzed and compared. Dice coefficient evaluated PTV similarity between FBCT and 4D-CT data sets.Results:In total, 14 of the 15 patients were analyzed. One patient was excluded as there was no measurable GTV. Mean GTV_3D was 115.3 cm3 and mean IGTV_4D was 152.5 cm3 (P = .001). Mean PTV_3D was 530.0 cm3 and PTV_4D was 499.8 cm3 (P = .40). Both gross primary and nodal disease analyzed separately were larger on 4D compared with FBCT. D95 (95% isodose line) covered 98% of PTV_3D and 88% of PTV_4D (P = .003). Mean dice coefficient of PTV_3D and PTV_4D was 84%. Mean lung V20 was 24.0% for the 3D-based plans and 22.7% for the 4D-based plans (P = .057). Mean heart V40 was 12.1% for the 3D-based plans and 12.7% for the 4D-based plans (P = .53). Mean spinal cord Dmax was 2517 and 2435 cGy for 3D-based and 4D-based plans, respectively (P = .019). Mean esophageal dose was 1580 and 1435 cGy for 3D and 4D plans, respectively (P = .13).Conclusions:IGTV_4D was significantly larger than GTV_3D for both primary and nodal disease combined or separately. Mean PTV_3D was larger than PTV_4D, but the difference was not statistically significant. The PTV_4D coverage with 95% isodose line was inferior, indicating the importance of incorporating the true size and shape of the target volume. Relatively less dose was delivered to spinal cord and esophagus with plans based on 4D data set. Dice coefficient analysis for degree of similarity revealed that 16% of PTVs from both data sets did not overlap, indicating different anatomical positions of the PTV due to tumor/nodal motion during a respiratory cycle. All patients with lung cancer planned for radical radiotherapy should have 4D-CT simulation to ensure accurate coverage of the target volumes.

Effect of atelectasis changes on tissue mass and dose during lung radiotherapy.

Purpose:To characterize mass and density changes of lung parenchyma in non-small cell lung cancer (NSCLC) patients following midtreatment resolution of atelectasis and to quantify the impact this large geometric change has on normal tissue dose.Methods:Baseline and midtreatment CT images and contours were obtained for 18 NSCLC patients with atelectasis. Patients were classified based on atelectasis volume reduction between the two scans as having either full, partial, or no resolution. Relative mass and density changes from baseline to midtreatment were calculated based on voxel intensity and volume for each lung lobe. Patients also had clinical treatment plans available which were used to assess changes in normal tissue dose constraints from baseline to midtreatment. The midtreatment image was rigidly aligned with the baseline scan in two ways: (1) bony anatomy and (2) carina. Treatment parameters (beam apertures, weights, angles, monitor units, etc.) were transferred to each image. Then, dose was recalculated. Typical IMRT dose constraints were evaluated on all images, and the changes from baseline to each midtreatment image were investigated.Results:Atelectatic lobes experienced mean (stdev) mass changes of −2.8% (36.6%), −24.4% (33.0%), and −9.2% (17.5%) and density changes of −66.0% (6.4%), −25.6% (13.6%), and −17.0% (21.1%) for full, partial, and no resolution, respectively. Means (stdev) of dose changes to spinal cord Dmax, esophagus Dmean, and lungs Dmean were 0.67 (2.99), 0.99 (2.69), and 0.50 Gy (2.05 Gy), respectively, for bone alignment and 0.14 (1.80), 0.77 (2.95), and 0.06 Gy (1.71 Gy) for carina alignment. Dose increases with bone alignment up to 10.93, 7.92, and 5.69 Gy were found for maximum spinal cord, mean esophagus, and mean lung doses, respectively, with carina alignment yielding similar values. 44% and 22% of patients had at least one metric change by at least 5 Gy (dose metrics) or 5% (volume metrics) for bone and carina alignments, respectively. Investigation of GTV coverage showed mean (stdev) changes in VRx, Dmax, and Dmin of −5.5% (13.5%), 2.5% (4.2%), and 0.8% (8.9%), respectively, for bone alignment with similar results for carina alignment.Conclusions:Resolution of atelectasis caused mass and density decreases, on average, and introduced substantial changes in normal tissue dose metrics in a subset of the patient cohort.

Preliminary analysis of the sequential simultaneous integrated boost technique for intensity-modulated radiotherapy for head and neck cancers.

The aim of this study was to compare three strategies for intensity-modulated radiotherapy (IMRT) for 20 head-and-neck cancer patients. For simultaneous integrated boost (SIB), doses were 66 and 54 Gy in 30 fractions for PTVboost and PTVelective, respectively. Two-phase IMRT delivered 50 Gy in 25 fractions to PTVelective in the First Plan, and 20 Gy in 10 fractions to PTVboost in the Second Plan. Sequential SIB (SEQ-SIB) delivered 55 Gy and 50 Gy in 25 fractions, respectively, to PTVboost and PTVelective using SIB in the First Plan and 11 Gy in 5 fractions to PTVboost in the Second Plan. Conformity indexes (CIs) (mean ± SD) for PTVboost and PTVelective were 1.09 ± 0.05 and 1.34 ± 0.12 for SIB, 1.39 ± 0.14 and 1.80 ± 0.28 for two-phase IMRT, and 1.14 ± 0.07 and 1.60 ± 0.18 for SEQ-SIB, respectively. CI was significantly highest for two-phase IMRT. Maximum doses (Dmax) to the spinal cord were 42.1 ± 1.5 Gy for SIB, 43.9 ± 1.0 Gy for two-phase IMRT and 40.3 ± 1.8 Gy for SEQ-SIB. Brainstem Dmax were 50.1 ± 2.2 Gy for SIB, 50.5 ± 4.6 Gy for two-phase IMRT and 47.4 ± 3.6 Gy for SEQ-SIB. Spinal cord Dmax for the three techniques was significantly different, and brainstem Dmax was significantly lower for SEQ-SIB. The compromised conformity of two-phase IMRT can result in higher doses to organs at risk (OARs). Lower OAR doses in SEQ-SIB made SEQ-SIB an alternative to SIB, which applies unconventional doses per fraction.