Average Gross Tumor Volume Research Articles

Role of adaptive radiotherapy during concomitant chemoradiotherapy for limited-stage small-cell lung cancer.

Tumor shrinkage is frequently observed during conventionally fractionated chemoradiotherapy for limited-stage small-cell lung cancer (SCLC). The specific goals of this study are to evaluate the gross tumor volume (GTV) changes due to treatment-induced tumor reduction during the course of radiotherapy (RT) and to examine its potential use in adaptive radiotherapy (ART) for tumor dose escalation or normal tissue sparing in patients with SCLC. A total of 10 patients with SCLC eligible for chemoradiotherapy underwent computed tomography (CT) scan after Fractions 13 and 23 (at nominal doses of 23.4 Gy and 41.4 Gy, respectively). The GTV was delineated on the repeat CT scans, and two treatment plans were generated with or without adaptation to tumor shrinkage during RT for each patient. Dosimetric and volumetric analyses were performed. The average GTV reduction observed over 13 fractions was 58.5% (range: 13.2%-92.3%; P < 0.001) and over 23 fractions was 70% (range: 36.9%-84.5%; P < 0.001). Compared with the plan without adaptation, ART resulted in mean lung dose relative decreases of 8.7%, mean lung volume receiving ≥20 Gy relative decreases of 5%, mean lung volume receiving ≥5Gy relative decreases of 10%, mean medulla spinalis dose relative decreases of 21 cGy, mean esophagus volume receiving ≥50 Gy relative decreases of 19%, and mean heart volume receiving ≥42 Gy relative decreases of 13%. The benefits of ART were the greatest for tumor volumes ≥30 cm3 and are directly dependent on GTV reduction during treatment. ART for SCLC achieved a significant benefit in terms of organ at risk (OAR) and dose escalation.

Evaluating the Necessity of Adaptive RT and the Role of Deformable Image Registration in Lung Cancer with Different Pathologic Classifications.

This study aimed to analyze differential radiotherapy (RT) responses according to the pathological type of lung cancer to see the possibility of applying adaptive radiotherapy (ART). ART planning with resampled-computed tomography was conducted for a total of 30 patients (20 non-small-cell lung cancer patients and 10 small-cell lung cancer patients) using a deformable image registration technique to reveal gross tumor volume (GTV) changes according to the duration of RT. The small-cell lung cancer group demonstrated an average GTV reduction of 20.95% after the first week of initial treatment (p = 0.001), whereas the adenocarcinoma and squamous cell carcinoma groups showed an average volume reduction of 20.47% (p = 0.015) and 12.68% in the second week. The application of ART according to the timing of GTV reduction has been shown to affect changes in radiation dose irradiated to normal tissues. This suggests that ART applications may have to be different depending on pathological differences in lung cancer. Through these results, the present study proposes the possibility of personalized treatment options for individual patients by individualizing ART based on specific radiation responses by pathologic types of lung cancer.

Feasibility of a simultaneously integrated boost concept for hypofractionated stereotactic radiotherapy of unresected brain metastases

BackgroundIn stereotactic radiotherapy, dose is prescribed to an isodose surrounding the planning target volume (PTV). However, the desired dose inhomogeneity inside the PTV leaves the specific dose distribution to the gross tumor volume (GTV) unspecified. A simultaneously integrated boost (SIB) to the GTV could solve this shortcoming. In a retrospective planning study with 20 unresected brain metastases, a SIB approach was tested against the classical prescription.MethodsFor all metastases, the GTV was isotropically enlarged by 3 mm to a PTV. Two plans were generated, one according to the classical 80% concept with 5 times 7 Gy prescribed (on D2%) to the 80% PTV surrounding isodose (with D98%(PTV) ≥ 35 Gy), and the other one following a SIB concept with 5 times 8.5 Gy average GTV dose and with D98%(PTV) ≥ 35 Gy as additional requirement. Plan pairs were compared in terms of homogeneity inside GTV, high dose in PTV rim around GTV, and dose conformity and gradients around PTV using Wilcoxon matched pairs signed rank test.ResultsThe SIB concept was superior to the classical 80% concept concerning dose homogeneity inside GTV: Heterogeneity index of GTV was in the SIB concept (median 0.0513, range 0.0397–0.0757) significantly (p = 0.001) lower than in the 80% concept (median 0.0894, range 0.0447–0.1872). Dose gradients around PTV were not inferior. The other examined measures were comparable.ConclusionOur stereotactic SIB concept better defines the dose distribution inside PTV and can be considered for clinical use.

Initial tumor volume as an important predictor for indication of intra-cavitary brachytherapy, intra-cavitary/interstitial brachytherapy, and multi-catheter sole interstitial brachytherapy in cervical cancer patients treated with chemoradiotherapy.

Advances in three-dimensional image-guided brachytherapy technique allow for using intra-cavitary and interstitial brachytherapy (ICIS-BT), and sole interstitial brachytherapy (ISBT) in addition to conventional intra-cavitary brachytherapy (ICBT). However, no consensus has been reached regarding the choice of these techniques. The aim of this study was to propose the size criteria for indication of interstitial techniques. We examined initial gross tumor volume (GTV) at presentation and at each brachytherapy session. Also, dose volume histogram parameters for each modality were compared in 112 patients with cervical cancer treated with brachytherapy (ICBT, 54; ICIS-BT, 11; and ISBT, 47). The average GTV at diagnosis was 80.9 cm3 (range, 4.4-343.2 cm3), which shrank to 20.6 cm3 (25.5% of initial volume, range, 0.0-124.8 cm3) at initial brachytherapy. GTV > 30 cm3 at brachytherapy and high-risk clinical target volume > 40 cm3 were good threshold values for indication of interstitial technique, and tumors with initial GTV > 150 cm3 could be candidates for ISBT. An ISBT dose of 89.10 Gy can be prescribed in equivalent dose in 2 Gy fractions (range, 65.5-107.6 Gy), which was higher than those of ICIS (73.94 Gy, range, 71.44-82.50 Gy) and ICBT (72.83 Gy, range, 62.50-82.27 Gy) (p < 0.0001). Initial tumor volume is an important predictor for indication of ICBT and ICIS-BT. ISBT or at least an interstitial technique is recommended for initial GTV > 150 cm3.

Developing a CBCT-Guided Online Adaptive Radiotherapy Approach for Isotoxic Delivery of Ultra-High Dose to Oligometastatic Disease in Combination with Immunotherapy

<h3>Purpose/Objective(s)</h3> A Phase I trial combining stereotactic body radiotherapy (SBRT), 45Gy in 3 fractions(fx), with pembrolizumab was safe (9% grade 3 toxicity) with promising local control and overall survival. Whether SBRT dose escalation can improve outcomes is uncertain. A subsequent planning study showed feasibility of ultra-high SBRT dose, 90Gy in 3fx, while respecting organ at risk (OAR) tolerances. However, due to patient anatomy interfractional uncertainty, online adaptation may enhance safety/efficacy. This work develops a CBCT-guided adaptive radiotherapy approach for isotoxic treatment with ultra-high doses using retrospective data and simulated online adaptation. <h3>Materials/Methods</h3> Patient data from 15 subjects of the original Phase I trial were used (gross tumor volume (GTV) mean volume 177cc; range 67-390cc). Disease sites were liver(n=8), pelvis(n=4), abdomen(n=2), lung(n=1). Clinical prescriptions were to 65cc subvolumes of the GTV (SubGTV). In the adaptive setting, rather than define a specific sub volume, OAR expansions based on tolerance and achievable dose gradients were cropped from GTV so that the SubGTV receiving ultra-high dose adapts to changing anatomy. Initial 6 arc VMAT plans used a clinical goal based automated plan optimization platform. High priority was given to critical OAR Dmax goals, medium priority was given to GTV coverage (V90Gy) and OAR volumetric constraints. SubGTV core was defined with further contraction away from OARs with low priority goals to ensure a centralized GTV hot spot. For a subset of patients (8 total: 3 liver, 2 abdomen, 2 pelvis, 1 lung), an online adaptive session using clinical CBCTs was simulated with anatomy recontoured for plan reoptimization/evaluation and comparison of adapted (ADP) vs. scheduled (SCH) plans. <h3>Results</h3> For initial plans, all OAR goals were satisfied. The average GTV V90Gy was 80.8cc/57.3% (range: 53.8-144.5cc/24.4-99.1%). In online adaptive sessions, the ADP plan was preferred over the SCH plan in 7 of 8 cases. ADP plans generally had superior coverage (average GTV V90Gy of 86.3cc (ADP) vs. 77.9cc (SCH)). ADP plans nearly always met OAR tolerances (one minor exception: skin D0.03cc (tolerance of 11.0Gy/fx) was 11.5Gy (ADP) vs. 11.9Gy (SCH)). In contrast, SCH plans often did not meet OAR constraints, with critical violations to bowel (n=2), stomach(n=3), duodenum(n=1), inferior vena cava(n=1) as well as violations to skin(n=3) and bone(n=2). <h3>Conclusion</h3> This work develops a paradigm for true isotoxic radiotherapy treatment maximizing ablative target doses using CBCT-guided online adaptive SBRT. A forthcoming phase I trial will investigate potential clinical benefit from escalation to ultra-high doses. As adaptive technologies evolve, the OAR-guided isotoxic approach developed here may be an important future direction for radiation oncology. NCT02608385

Computed Tomography-Based Evaluation of Volume and Position Changes of the Target Region and Organs at Risk During Radiotherapy for Esophageal Cancer: A Pilot Study.

ObjectiveTo analyze changes in volume and position of target regions and organs at risk (OARs) during radiotherapy for esophageal cancer patients.MethodsOverall, 16 esophageal cancer patients who underwent radiotherapy, including 10 cases of intensity-modulated radiation therapy (IMRT) and six of three-dimensional conformal radiotherapy (3D-CRT), were enrolled. The prescription doses for the planning target volumes (PTVs) were as follows: PTV1, 64 Gy/32 fractions; and PTV2, 46 Gy/23 fractions. Repeat computed tomography (CT) was performed for patients after the 5th, 10th, 15th, 20th, and 25th fractions. Delineation of the gross tumor volume (GTV) and OAR volume was determined using five repeat CTs performed by the same physician. The target and OAR volumes and centroid positions were recorded and used to analyze volume change ratio (VCR), center displacement (ΔD), and changes in the distance from the OAR centroid positions to the planned radiotherapy isocenter (distance to isocenter, DTI) during treatment.ResultsNo patient showed significant changes in target volume (TV) after the first week of radiotherapy (five fractions). However, TV gradually decreased over the following weeks, with the rate slowing after the fourth week (40 Gy). The comparison of TV from baseline to 40 Gy (20 fractions) showed that average GTVs decreased from 130.7 ± 63.1 cc to 92.1 ± 47.2 cc, with a VCR of −29.21 ± 13.96% (p<0.01), while the clinical target volume (CTV1) decreased from 276.7 ± 98.2 cc to 246.7 ± 87.2 cc, with a VCR of −10.34 ± 7.58% (p<0.01). As TVs decreased, ΔD increased and DTI decreased. After the fourth week of radiotherapy (40 Gy), centroids of GTV, CTV1, and prophylactic CTV (CTV2) showed average deviations in ΔD of 7.6 ± 4.0, 6.9 ± 3.4, and 6.0 ± 3.0 mm, respectively. The average DTI of the heart decreased by 4.53 mm (from 15.61 ± 2.96 cm to 15.16 ± 2.27 cm).ConclusionDuring radiotherapy for esophageal cancer, Targets and OARs change significantly in volume and position during the 2nd–4th weeks. Image-guidance and evaluation of dosimetric changes are recommended for these fractions of treatment to appropriate adjust treatment plans.

Proton Beam Therapy For Large Hepatocellular Carcinomas In Western Patients

High rates of local control with low risk of hepatotoxicity have been reported in Eastern patients with large hepatocellular carcinomas (HCCs) treated with proton beam therapy (PBT). How generalizable these data are to Western patients is unclear. We present a retrospective study on the clinical outcomes of Western patients with large HCCs treated with PBT at a single institution. Forty-four HCC patients with tumors ≥ 5 cm and ineligible for other liver-directed therapies were treated with PBT between 2014-2019 with a 15-fraction regimen of 45.0-67.5 Gy (RBE). Radiation-induced liver disease (RILD) was defined by a Child-Pugh (CP) score increase of 2 or greater and/or RTOG grade 3 enzyme elevation. Overall survival (OS), progression-free survival (PFS), and local control (LC) were calculated using the Kaplan-Meier method and univariate predictors of OS by Cox regression analysis. Patients represented a high-risk cohort: 50% with BCLC stage C, 27% with CP-B/C cirrhosis, 34% with gross vascular invasion, and a median gross tumor volume (GTV) size and volume of 11.1 cm (5.6-21.5 cm) and 364 cc (48-2439 cc), respectively. The target lesion(s) received prior liver-directed therapies in 39% of patients. Pencil beam scanning was used in the majority of patients (64%), and a simultaneous integrated boost/protection technique was employed in 75% to deliver moderate tumor dose escalation to an average GTV mean BED of 87.0 Gy(RBE) (see table for average dosimetric parameters). Median follow-up for all patients and survivors was 8.5 months and 11 months, respectively. 1-year OS and PFS were 53% (95% CI 33-66%) and 19% (95% CI 10-35%), respectively. Median OS and PFS were 12 months (95% CI 7-25) and 4 months (95% CI 2-9), respectively. 1-yr LC was 93% (95% CI 74-98%), and crude local failure (LF) rate was 14% (n = 6) with one isolated LF. Median time to local failure was 43 months (95% CI 14-not reached). Tumor size and GTV dose were not statistically different between patients with LC and LF. Out of field liver recurrences were the dominant pattern of failure occurring in 61% of patients with disease progression. On univariate analysis, only tumor size was prognostic for OS (HR 1.27, p<0.001). Two (4.5%) grade 3 non-GI toxicities occurred: 1 chest wall pain syndrome/rib fracture and 1 pneumonitis. One acute GI grade ≥2 toxicity (nausea) occurred. Six patients (14%) experienced RILD; all but one patient had baseline CP-B liver function. In this largest series to date of Western HCC patients with high-risk large tumors, moderate dose escalated PBT results in excellent local control rates and acceptable toxicities. Out of field and distant failures remain problematic, which warrant improved systemic therapies in these patients.Abstract 3408; TableParameter Gy (RBE)GTV MeanGTV DmaxGTV D95GTV DminGTV % > 90Gy BEDLiver-GTV MeanAverage61.664.85448.252%15.5Range45.8-69.947.6-71.537.5-69.417.9-68.62.93-21.0 Open table in a new tab

MR imaging as a precise technique to evaluate skull-base tumor volume: Comparison of CT, MR imaging and FDG PET from murine and clinical data

In spite of the many imaging modalities used in clinics, the one that best reflects the true delineation of skull-base (infratemporal fossa, ITF) malignancies is still unknown. In order to compare the tumor recognition capabilities of different imaging modalities, established murine models and patients with skull-base tumors were evaluated by computer tomography (CT), magnetic resonance (MR) imaging, and fluorine-18 fluorodeoxyglucose (18FDG) positron emission tomography (PET) for delineation of gross tumor volume (GTV).PET, MR imaging, and CT enhanced by iodine staining were all sensitive to, and able to recognize, the skull-base tumor in the murine model. No significant difference (p > 0.9999) was observed between average GTV according to MR imaging (176.67 ± 19.6 mm3) and the histological measurement result (170.23 ± 22.24 mm3) for the murine model. In contrast, the GTVs according to CT (88.77 ± 13.03 mm3, p < 0.0001) and 18FDG PET (35.67 ± 6.56 mm3, p < 0.0001) were much smaller.In nine patients for whom the three modalities were available, tumor volume comparisons tended to be consistent with the murine model data. According to both the established murine model and clinical patient data, MR imaging possessed the optimal ability to recognize tumor contours.

Breathing-motion-compensated robotic guided stereotactic body radiation therapy : Patterns of failure analysis.

We retrospectively evaluated the patterns of failure for robotic guided real-time breathing-motion-compensated (BMC) stereotactic body radiation therapy (SBRT) in the treatment of tumors in moving organs. Between 2011 and 2016, atotal of 198 patients with 280 lung, liver, and abdominal tumors were treated with BMC-SBRT. The median gross tumor volume (GTV) was 12.3 cc (0.1-372.0 cc). Medians of mean GTV BEDα/β=10 Gy (BED= biological effective dose) was 148.5 Gy10 (31.5-233.3 Gy10) and prescribed planning target volume (PTV) BEDα/β=10 Gy was 89.7 Gy10 (28.8-151.2 Gy10), respectively. We analyzed overall survival (OS) and local control (LC) based on various factors, including BEDs with α/β ratios of 15 Gy (lung metastases), 21 Gy (primary lung tumors), and 27 Gy (liver metastases). Median follow-up was 10.4months (2.0-59.0 months). The 2‑year actuarial LC was 100 and 86.4% for primary early and advanced stage lung tumors, respectively, 100% for lung metastases, 82.2% for liver metastases, and 90% for extrapulmonary extrahepatic metastases. The 2‑year OS rate was 47.9% for all patients. In uni- and multivariate analysis, comparatively lower PTV prescription dose (equivalence of 3× 12-13 Gy) and higher average GTV dose (equivalence of 3× 18 Gy) to current practice were significantly associated with LC. For OS, Karnofsky performance score (100%), gender (female), and SBRT without simultaneous chemotherapy were significant prognostic factors. Grade3 side effects were rare (0.5%). Robotic guided BMC-SBRT can be considered asafe and effective treatment for solid tumors in moving organs. To reach sufficient local control rates, high average GTV doses are necessary. Further prospective studies are warranted to evaluate these points.

Hypertrophic adenoids in patients with nasopharyngeal carcinoma: appearance at magnetic resonance imaging before and after treatment.

IntroductionPatients with nasopharyngeal carcinoma (NPC) sporadically develop abnormal adenoids. Nasopharyngeal adenoids are usually included in the gross tumor volume (GTV) but may have different therapeutic responses than tumor tissue. Therefore, distinguishing adenoids from tumor tissue may be required for precise and efficient chemoradiotherapy and radiotherapy. We characterized nasopharyngeal adenoids and investigated the therapeutic responses of NPC and nasopharyngeal adenoids using magnetic resonance imaging (MRI).MethodsMRI data from 40 NPC patients with a coexisting adenoid mass before and after treatment were analyzed. The features of the adenoid masses, including location, striped appearance, size, interface, symmetry/asymmetry, and cysts, were evaluated. Treatment response were scored according to the World Health Organization guidelines.ResultsA striped appearance was observed in 36 cases before treatment and in all cases after treatment. In these 36 cases, the average GTVs including and excluding the uninvolved adenoids were 19.8 cm3 and 14.8 cm3, respectively. The average percentage change after excluding the uninvolved adenoids from the GTV was 31.0%. Stable disease in the adenoids was identified in 27 (96.4%) of 28 patients after neoadjuvant chemotherapy, while NPC clearly regressed. Partial adenoid responses were identified in 33 (82.5%) of 40 patients at 3 months after chemoradiotherapy or radiotherapy, whereas complete tumor responses were achieved in all patients. Six months after treatment, the adenoids continued to atrophy but did not disappear, and tumor recurrence was not found.ConclusionsNasopharyngeal adenoids and carcinoma tissue in NPC patients can be distinguished by using MRI and have different responses to chemoradiotherapy and radiotherapy. These findings contribute to better delineating the GTV of NPC, based on which spatially optimized strategies can be developed to render precise and efficient chemoradiotherapy and radiotherapy. Additionally, we observed a clear difference in the responses of these two tissue types to current therapies. This finding may reduce or avoid unnecessary biopsies or overtreatment.

Determination of Internal Target Volume for Radiation Treatment Planning of Esophageal Cancer by Using 4-Dimensional Computed Tomography (4DCT)

To determine an efficient strategy for the generation of the internal target volume (ITV) for radiation treatment planning for esophageal cancer using 4-dimensional computed tomography (4DCT). 4DCT sets acquired for 20 patients with esophageal carcinoma were analyzed. Each of the 4DCT sets was binned into 10 respiratory phases. For each patient, the gross tumor volume (GTV) was delineated on the 4DCT set at each phase. Various strategies to derive ITV were explored, including the volume from the maximum intensity projection (MIP; ITV_MIP), unions of the GTVs from selected multiple phases ITV2 (0% and 50% phases), ITV3 (ITV2 plus 80%), and ITV4 (ITV3 plus 60%), as well as the volumes expanded from ITV2 and ITV3 with a uniform margin. These ITVs were compared to ITV10 (the union of the GTVs for all 10 phases) and the differences were measured with the overlap ratio (OR) and relative volume ratio (RVR) relative to ITV10 (ITVx/ITV10). For all patients studied, the average GTV from a single phase was 84.9% of ITV10. The average ORs were 91.2%, 91.3%, 94.5%, and 96.4% for ITV_MIP, ITV2, ITV3, and ITV4, respectively. Low ORs were associated with irregular breathing patterns. ITV3s plus 1 mm uniform margins (ITV3+1) led to an average OR of 98.1% and an average RVR of 106.4%. The ITV generated directly from MIP underestimates the range of the respiration motion for esophageal cancer. The ITV generated from 3 phases (ITV3) may be used for regular breathers, whereas the ITV generated from 4 phases (ITV4) or ITV3 plus a 1-mm uniform margin may be applied for irregular breathers.

A Clinical Process for Imaging, Planning, and Delivery of Dose Escalation for Intraprostatic Gross Tumor Volumes

Conventional prostate cancer radiation therapy uniformly irradiates the entire prostate gland. This practice ignores evidence that the gross tumor volume (GTV) within the gland impacts local recurrence and metastatic spread. We have developed a clinical process to image, plan and deliver an escalated dose to an intraprostatic GTV. Patients undergo an MRI study with endorectal coil, MRI guided biopsy, and fiducial marker insertion, followed by CT/MRI simulation. The coil causes anatomical distortions that necessitate deformable registration. Images are imported into the treatment planning system. The prostate and GTV are contoured on T2 and ADC images and exported to a biomechanical-based deformable registration program. Deformable registration is performed and the resulting GTV contours are exported to the planning system. Volumetric modulated arc therapy plans are developed to deliver 95 Gy in 38 fractions to the GTV, while delivering 76 Gy to the remaining prostate. Planning criteria include PTV D99 of at least 95% of the prescription, and no more than 90 Gy to 0.5 cc of rectum or bladder. Six patients to date have been enrolled on a prospective research ethics board approved study and planned as described above. Patients has 1-3 GTVs with a median GTV volume of 1.8 cc (range, 0.1 - 4.4 cc). The accuracy of the deformable registration was assessed to be systematically better than 0.5 mm, with a standard deviation of 1.6 mm or less in any direction. The deformation vector field was available for four of the patients. The average maximum GTV deformation (3D vector) was 5 mm (range, 3 - 9 mm). Four patients met all target and normal tissue criteria, while 2 patients required compromise of the high dose PTV (D99 reduced to 86 and 87 Gy) to spare rectum. The median dose to 0.5 cc of rectum and bladder were 83 Gy and 79 Gy, and the median rectum D30 was 37 Gy. A clinical process that images intraprostatic GTVs, applies a deformable registration, and develops a treatment plan to deliver escalated dose to the GTV while minimizing normal tissue doses is feasible. Deformation caused by the endorectal coil is substantial for these small GTVs, demonstrating the necessity of deformable registration. Further investigations will attempt to incorporate MRI-based image guidance for daily target localization.

Preliminary study of the internal margin of the gross tumor volume in thoracic esophageal cancer

PurposeTo measure the displacement of the tumor of the gross tumor volume (GTV) of thoracic esophageal cancer in the calm states of end-inspiration and end-expiration for determining the internal margin of the GTV (IGTV). MethodsTwenty-two patients with thoracic esophageal cancer who were unable to undergo surgery were identified in our hospital. The patients received radiotherapy. By using 16-slice spiral computed tomography (CT), we acquired the calm states of end-inspiration and end-expiration. The displacement and volume changes in tumor target volume were measured, and the changes were analyzed to determine if these were associated with the tidal volume and the location and length of the target volume V. In the end, we analyzed the displacement of tumor target volume and calculated the internal margin of the GTV by empirical formula. ResultsThe average tidal volume was 463.6ml. The average GTV at end-inspiration was 33.3ml and at end-expiration was 33.35ml. Three was not any significant between two groups (T=−0.034, P>0.05). The IGTV (X-axis direction) was 3.09mm for the right sector and 4.08mm for the left border; the IGTV (Z-axis direction) was 3.96mm for the anterior border and 2.83mm for the posterior border; and the IGTV (Y-axis direction) was 7.31mm for the upper boundary (head direction) and 10.16mm for the lower boundary (feet direction). The motion of the GTV showed no significant correlation with the tidal volume of patients and the length of the tumor, but in relation to the tumor location, the displacement of the lower thoracic and the middle thoracic target volumes occurred in the direction of the anterior and right, which were not significantly different (T=0.859, 0.229, P>0.05) The significant differences were observed for the other directions (P<0.05). ConclusionsBecause of respiratory and organ movements, the displacement of the tumor target volume was different in all directions. Therefore, we recommend that expansion of the planning target volume during clinical radiation treatment needs to include the displacement of the tumor target volume caused by respiratory and organ movements during each radiotherapy session.

Respiratory gated [18F]FDG PET/CT for target volume delineation in stereotactic radiation treatment of liver metastases

The use of 4D-[(18)F]fluorodeoxyglucose (FDG) PET/CT in combination with respiratory gated magnet resonance imaging (MRI) in target volume definition for stereotactic radiation of liver metastases was investigated. A total of 18patients received respiration gated FDG-PET/CT and MRI. Data were fused using a rigid co-registration algorithm. The quality of the co-registration was rated on a scale from 1 (excellent) to 5 (poor) for co-registration of MRI with gated PET and ungated PET. Gross tumor volume (GTV) was delineated in CT (GTV (CT)), MRI (GTV(MRI)), and PET (GTV(PET)). MRI- and PET-based GTVs were defined by three observers each. Interobserver variability was calculated for all patients as well as for subgroups with and without previous treatment of liver metastases. All GTVs were compared for all patients and separately for patients with previous local therapy. In addition, a semiautomatic segmentation algorithm was applied on the PET images. Co-registration between MR and PET images was rated with 3.3 in average when non-gated PET was used and improved significantly (p < 0.01) to 2.1 using gated PET. The average GTV(CT) was 51.5ml, GTV(MRI) 51.8ml, and the average GTV(PET) 48.1ml. Volumes delineated in MRI were 9.9% larger compared to those delineated in CT. Volumes delineated in PET were 13.8% larger than in MRI. The differences between the GTVs were more pronounced in patients with previous treatment. The GTVs defined in MRI showed an interobserver variability of 47.9% (84.1% with previous treatment and 26.2% without previous treatment). The PET-defined GTVs showed an interobserver variability of 21% regardless of previous treatment. Semiautomatic segmentation did not provide satisfying results. FDG-PET can distinguish vital tumor tissue and scar tissue, and therefore alters the GTV especially in patients with previous local treatment. In addition, it reduces the interobserver variability significantly compared to MRI. However, respiratory gated PET is necessary for good co-registration of PET and MRI.

A New Brain Positron Emission Tomography Scanner With Semiconductor Detectors for Target Volume Delineation and Radiotherapy Treatment Planning in Patients With Nasopharyngeal Carcinoma

We compared two treatment planning methods for stereotactic boost for treating nasopharyngeal carcinoma (NPC): the use of conventional whole-body bismuth germanate (BGO) scintillator positron emission tomography (PET(CONV)WB) versus the new brain (BR) PET system using semiconductor detectors (PET(NEW)BR). Twelve patients with NPC were enrolled in this study. [(18)F]Fluorodeoxyglucose-PET images were acquired using both the PET(NEW)BR and the PET(CONV)WB system on the same day. Computed tomography (CT) and two PET data sets were transferred to a treatment planning system, and the PET(CONV)WB and PET(NEW)BR images were coregistered with the same set of CT images. Window width and level values for all PET images were fixed at 3000 and 300, respectively. The gross tumor volume (GTV) was visually delineated on PET images by using either PET(CONV)WB (GTV(CONV)) images or PET(NEW)BR (GTV(NEW)) images. Assuming a stereotactic radiotherapy boost of 7 ports, the prescribed dose delivered to 95% of the planning target volume (PTV) was set to 2000 cGy in 4 fractions. The average absolute volume (±standard deviation [SD]) of GTV(NEW) was 15.7 ml (±9.9) ml, and that of GTV(CONV) was 34.0 (±20.5) ml. The average GTV(NEW) was significantly smaller than that of GTV(CONV) (p = 0.0006). There was no statistically significant difference between the maximum dose (p = 0.0585) and the mean dose (p = 0.2748) of PTV. The radiotherapy treatment plan based on the new gross tumor volume (PLAN(NEW)) significantly reduced maximum doses to the cerebrum and cerebellum (p = 0.0418) and to brain stem (p = 0.0041). Results of the present study suggest that the new brain PET system using semiconductor detectors can provide more accurate tumor delineation than the conventional whole-body BGO PET system and may be an important tool for functional and molecular radiotherapy treatment planning.

Correlation of Respiratory Motion of Pancreatic Tumors with Biliary Stent or Intra-Tumoral Fiducials: Consequences for ITV and Respiratory Gating

Correlation of Respiratory Motion of Pancreatic Tumors with Biliary Stent or Intra-Tumoral Fiducials: Consequences for ITV and Respiratory Gating

Tumor Volume as a Potential Imaging-Based Risk-Stratification Factor in Trimodality Therapy for Locally Advanced Non-small Cell Lung Cancer

The role of trimodality therapy for locally advanced non-small cell lung cancer (NSCLC) continues to be defined. We hypothesized that imaging parameters on pre- and postradiation positron emission tomography (PET)-computed tomography (CT) imaging are prognostic for outcome after preoperative chemoradiotherapy (CRT)/resection/consolidation chemotherapy and could help risk-stratify patients in clinical trials. We enrolled 13 patients on a prospective clinical trial of trimodality therapy for resectable locally advanced NSCLC. PET-CT was acquired for radiation planning and after 45 Gy. Gross tumor volume (GTV) and standardized uptake value were measured at pre- and post-CRT time points and correlated with nodal pathologic complete response, loco-regional and/or distant progression, and overall survival. In addition, we evaluated the performance of automatic deformable image registration (ADIR) software for volumetric response assessment. All patients responded with average total GTV reductions after 45 Gy of 43% (range: 27-64%). Pre- and post-CRT GTVs were highly correlated (R² = 0.9), and their respective median values divided the patients into the same two groups. ADIR measurements agreed closely with manually segmented post-CRT GTVs. Patients with GTV ≥ median (137 ml pre-CRT and 67 ml post-CRT) had 3-year progression-free survival (PFS) of 14% versus 75% for GTV less than median, a significant difference (p = 0.049). Pre- and post-CRT PET-standardized uptake value did not correlate significantly with pathologic complete response, PFS, or overall survival. Preoperative CRT with carboplatin/docetaxel/45 Gy resulted in excellent response rates. In this exploratory analysis, pre- and post-CRT GTV predicted PFS in trimodality therapy, consistent with our earlier studies in a broader cohort of NSCLC. ADIR seems robust enough for volumetric response assessment in clinical trials.

Four-dimensional measurement of intrafractional respiratory motion of pancreatic tumors using a 256 multi-slice CT scanner

Purpose To quantify pancreas and pancreatic tumor movement due to respiratory motion using volumetric cine CT images. Materials and methods Six patients with pancreatic tumors were scanned in cine mode with a 256 multi-slice CT scanner under free breathing conditions. Gross tumor volume (GTV) and pancreas were manually contoured on the CT data set by a radiation oncologist. Intrafractional respiratory movement of the GTV and pancreas was calculated, and the results were compared between the respiratory ungated and gated phases, which is a 30% duty cycle around exhalation. Results Respiratory-induced organ motion was observed mainly in the anterior abdominal side than the posterior side. Average GTV displacement (ungated/gated phases) was 0.7 mm/0.2 mm in both the left and right directions, and 2.5 mm/0.9 mm in the anterior, 0.1 mm/0 mm in the posterior, and 8.9 mm/2.6 mm in the inferior directions. Average pancreas center of mass displacement relative to that at peak exhalation was mainly in the inferior direction, at 9.6 mm in the ungated phase and 2.3 mm in the gated phase. Conclusions By allowing accurate determination of the margin, quantitative analysis of tumor and pancreas displacement provides useful information in treatment planning in all radiation approaches for pancreatic tumors.

Sci-Thurs PM: Delivery-07: Evaluation of prospects to use daily megavoltage CT studies for adaptive radiotherapy

To evaluate gross tumor volume (GTV) changes for non-small cell lung cancer (NSCLC) patients using daily megavoltage CT (MVCT) studies acquired before each treatment fraction on helical tomotherapy, and to relate the potential benefit of adaptive image-guided radiotherapy to changes in GTV. 17 patients were prescribed 30 fractions of radiotherapy on helical tomotherapy for NSCLC at London Regional Cancer Program from December 2005 to March 2007. The GTV was contoured on the daily MVCT studies of each patient. Adapted plans were created using merged MVCT-kVCT image sets to investigate the advantages of replanning for patients with differing GTV regression characteristics. The average GTV change observed over 30 fractions was -38%, ranging from -12 to -87%. No significant correlation was observed between GTV change and patient's physical or tumor features. The pattern of GTV changes of the 17 patients could be broadly divided into 3 groups with distinctive potential for benefit from adaptive planning. GTV changes are difficult to predict quantitatively based on patient or tumor characteristics. If changes do occur, there are points in time during the treatment course when it may be appropriate to adapt the plan to improve sparing of normal tissues. If the GTV decreases by greater than 30% at any point in the first twenty fractions of treatment, adaptive planning is appropriate to further improve the therapeutic ratio.

Adaptive Radiotherapy Planning on Decreasing Gross Tumor Volumes as Seen on Megavoltage Computed Tomography Images

To evaluate gross tumor volume (GTV) changes for patients with non-small-cell lung cancer by using daily megavoltage (MV) computed tomography (CT) studies acquired before each treatment fraction on helical tomotherapy and to relate the potential benefit of adaptive image-guided radiotherapy to changes in GTV. Seventeen patients were prescribed 30 fractions of radiotherapy on helical tomotherapy for non-small-cell lung cancer at London Regional Cancer Program from Dec 2005 to March 2007. The GTV was contoured on the daily MVCT studies of each patient. Adapted plans were created using merged MVCT-kilovoltage CT image sets to investigate the advantages of replanning for patients with differing GTV regression characteristics. Average GTV change observed over 30 fractions was -38%, ranging from -12 to -87%. No significant correlation was observed between GTV change and patient's physical or tumor features. Patterns of GTV changes in the 17 patients could be divided broadly into three groups with distinctive potential for benefit from adaptive planning. Changes in GTV are difficult to predict quantitatively based on patient or tumor characteristics. If changes occur, there are points in time during the treatment course when it may be appropriate to adapt the plan to improve sparing of normal tissues. If GTV decreases by greater than 30% at any point in the first 20 fractions of treatment, adaptive planning is appropriate to further improve the therapeutic ratio.