Clinical implications of defining the gross tumor volume with combination of CT and 18FDG-positron emission tomography in non-small-cell lung cancer

Stereotactic radiotherapy for lung oligometastases

30-60% of cancer patients develop lung metastases, mostly from primary tumors in the colon-rectum, lung, head and neck area, breast and kidney. Nowadays, stereotactic radiotherapy (SRT ) is considered the ideal modality for treating pulmonary metastases. When lung metastases are suspected, complete disease staging includes a total body computed tomography (CT ) and/or positron emission tomography-computed tomography (PET -CT ) scan. PET -CT has higher specificity and sensitivity than a CT scan when investigating mediastinal lymph nodes, diagnosing a solitary lung lesion and detecting distant metastases. For treatment planning, a multi-detector planning CT scan of the entire chest is usually performed, with or without intravenous contrast media or esophageal lumen opacification, especially when central lesions have to be irradiated. Respiratory management is recommended in lung SRT, taking the breath cycle into account in planning and delivery. For contouring, co-registration and/or matching planning CT and diagnostic images (as provided by contrast enhanced CT or PET-CT ) are useful, particularly for central tumors. Doses and fractionation schedules are heterogeneous, ranging from 33 to 60 Gy in 3-6 fractions. Independently of fractionation schedule, a BED10 > 100 Gy is recommended for high local control rates. Single fraction SRT (ranges 15-30 Gy) is occasionally administered, particularly for small lesions. SRT provides tumor control rates of up to 91% at 3 years, with limited toxicities. The present overview focuses on technical and clinical aspects related to treatment planning, dose constraints, outcome and toxicity of SRT for lung metastases.

Optimal Standardized Uptake Value Threshold for Auto contouring of Gross Tumor Volume using Positron Emission Tomography/Computed Tomography in Patients with Operable Nonsmall-Cell Lung Cancer: Comparison with Pathological Tumor Size

Purpose:

Incorporating ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG-PET/CT) for gross tumor volume (GTV) delineation is challenging due to varying tumor edge based on the set threshold of the standardized uptake value (SUV). This study aims to determine an optimal SUV threshold that correlates best with the pathological tumor size.

Materials and Methods:

From January 2013 to July 2014, 25 consecutive patients of operable nonsmall-cell lung cancer (NSCLC) who underwent staging¹⁸F-FDG-PET/CT before surgical resection were included in the test cohort and 12 patients in the validation cohort. GTVs were delineated on the staging PET/CT by automatic delineation using various percentage threshold of maximum SUV (SUVmax) and absolute SUV. The maximum pathological tumor diameter was then matched with the maximum auto-delineated tumor diameter with varying SUV thresholds. First-order linear regression and Bland–Altman plots were used to obtain an optimal SUV threshold for each patient. Three radiation oncologists with varying degrees of experiences also delineated GTVs with the visual aid of PET/CT to assess interobserver variation in delineation.

Results:

In the test set, the mean optimal percentage threshold for GTV was SUVmax of 35.6%±18.6% and absolute SUV of 4.35 ± 1.7. In the validation set, the mean optimal percentage threshold SUV and absolute SUV were 36.9 ± 16.9 and 4.1 ± 1.6, respectively. After a combined analysis of all 37 patients, the mean optimal threshold was 36% ± 17.9% and 4.27 ± 1.7, respectively. Using Bland–Altman plots, auto-contouring with 40% SUVmax and SUV 4 was in greater agreement with the pathological tumor diameter.

Conclusion:

Automatic GTV delineation on PETCT in NSCLC with percentage threshold SUV of 40% and absolute SUV of 4 correlated best with pathological tumor size. Auto-contouring using these thresholds will increase the precision of radiotherapy contouring of GTV and will save time.

Precision radiotherapy for non-small cell lung cancer

Precision medicine is becoming the standard of care in anti-cancer treatment. The personalized precision management of cancer patients highly relies on the improvement of new technology in next generation sequencing and high-throughput big data processing for biological and radiographic information.

Systemic precision cancer therapy has been developed for years. However, the role of precision medicine in radiotherapy has not yet been fully implemented. Emerging evidence has shown that precision radiotherapy for cancer patients is possible with recent advances in new radiotherapy technologies, panomics, radiomics and dosiomics.

This review focused on the role of precision radiotherapy in non-small cell lung cancer and demonstrated the current landscape.

Comparison of gross target volumes based on four-dimensional CT, positron emission tomography-computed tomography, and magnetic resonance imaging in thoracic esophageal cancer

PURPOSE

The application value of ¹⁸ F-FDG PET-CT combined with MRI in the radiotherapy of esophageal carcinoma was discussed by comparing the differences in position, volume, and the length of GTVs delineated on the end-expiration (EE) phase of 4DCT, ¹⁸ F-FDG PET-CT, and T₂ W-MRI.

METHODS

A total of 26 patients with thoracic esophageal cancer sequentially performed 3DCT, 4DCT, ¹⁸ F-FDG PET-CT, and MRI simulation for thoracic localization. All images were fused with the 3DCT images by deformable registration. GTV_CT and GTV_50% were delineated on 3DCT and the EE phase of 4DCT images, respectively. The GTV based on PET-CT images was determined by thresholds of SUV ≥ 2.5 and designated as GTV_PET2.5 . The images of T₂ -weighted sequence and diffusion-weighted sequence were referred as GTV_MRI and GTV_DWI , respectively. The length of the abnormality seen on the 4DCT, PET-CT, and DWI was compared.

RESULTS

GTV_PET2.5 was significantly larger than GTV_50% and GTV_MRI (P = .000 and 0.008, respectively), and the volume of GTV_MRI was similar to that of GTV_50% (P = .439). Significant differences were observed between the CI of GTV_MRI to GTV_50% and GTV_PET2.5 to GTV_50% (P = .004). The CI of GTV_MRI to GTV_CT and GTV_PET2.5 to GTV_CT were statistically significant (P = .039). The CI of GTV_MRI to GTV_PET2.5 was significantly lower than that of GTV_MRI to GTV_50% , GTV_MRI to GTV_CT , GTV_PET2.5 to GTV_50% , and GTV_PET2.5 to GTV_CT (P = .000-0.021). Tumor length measurements by endoscopy were similar to the tumor length as measured by PET and DWI scan (P > .05), and there was no significant difference between the longitudinal length of GTV_PET2.5 and GTV_DWI (P = .072).

CONCLUSION

The volumes of GTV_MRI and GTV_50% were similar. However, GTV_MRI has different volumes and poor spatial matching compared with GTV_PET2.5 .The MRI imaging could not include entire respiration. It may be a good choice to guide target delineation and construction of esophageal carcinoma by combining 4DCT with MRI imaging. Utilization of DWI in treatment planning for esophageal cancer may provide further information to assist with target delineation. Further studies are needed to determine if this technology will translate into meaningful differences in clinical outcome.

18F-Fluorodeoxyglucose PET in Locally Advanced Non-small Cell Lung Cancer: From Predicting Outcomes to Guiding Therapy

PET using 18-fluorodeoxyglucose (FDG) has become an important part of the work-up for non-small cell lung cancer (NSCLC). This article summarizes advancements in using FDG-PET for patients with locally advanced NSCLC treated with definitive radiation therapy (RT). This article discusses prognostication of outcome based on pretreatment or midtreatment PET metrics, using textural image features to predict treatment outcomes, and using PET to define RT target volumes and inform RT dose modifications. The role of PET is evolving and is moving toward using quantitative image information, with the overarching goal of individualizing therapy to improve outcomes for patients with NSCLC.

Treatment patterns and survival after 18F-fluorodeoxyglucose positron emission tomography/computed tomography-guided local consolidation therapy for oligometastatic non-small cell lung cancer: a two-center propensity score-matched analysis

Purpose

In this retrospective study, we evaluated the treatment patterns and survival after positron emission tomography-computed tomography (PET/CT)-guided local consolidation therapy (LCT) for oligometastatic non-small cell lung cancer (NSCLC).

Methods

We reviewed the medical records of Chinese patients with oligometastatic stage IV non-small cell lung cancer (≤ 5 metastases) who had undergone PET/CT and were eligible for systemic therapy at two centers between May 2005 and August 2019. Propensity score matching (1:1) was used to reduce selection bias and imbalanced distribution of confounding factors.

Results

We identified 84 eligible patients and used propensity scores to create well-matched groups of 35 patients who did or did not undergo LCT. Among all patients, the 1-year overall survival (OS) rate was 47.6% and the 2-year OS rate was 22.6%. Relative to the group that did not receive LCT, the LCT group had a significantly higher OS rate (13 months vs. 7 months, p = 0.002). The two groups had similar incidences and classifications of LCT-related side effects. In multivariable analysis, LCT was found to be strongly associated with a favorable OS (hazard ratio: 0.508, 95% confidence interval: 0.311–0.828, p = 0.001).

Conclusion

We concluded that LCT was significantly associated with improved clinical outcomes among the Chinese patients with oligometastatic NSCLC who were eligible for systemic treatment and could undergo PET/CT evaluation.

Impact of Peer Review in the Radiation Treatment Planning Process: Experience of a Tertiary Care University Hospital in Pakistan

PURPOSE

To evaluate and report the frequency of changes in radiation therapy treatment plans after peer review in a simulation review meeting once a week.

MATERIALS AND METHODS

Between July 1 and August 31, 2016, the radiation plans of 116 patients were discussed in departmental simulation review meetings. All plans were finalized by the primary radiation oncologist before presenting them in the meeting. A team of radiation oncologists reviewed each plan, and their suggestions were documented as no change, major change, minor change, or missing contour. Changes were further classified as changes in clinical target volume, treatment field, or dose. All recommendations were stratified on the basis of treatment intent, site, and technique. Data were analyzed by Statistical Package for the Social Sciences and are presented descriptively.

RESULTS

Out of 116 plans, 26 (22.4%) were recommended for changes. Minor changes were suggested in 15 treatment plans (12.9%) and a major change in 10 (8.6%), and only one plan was suggested for missing contour. The frequency of change recommendations was greater in radical radiation plans than in palliative plans (92.3% v 7.7%). The head and neck was the most common treatment site recommended for any changes (42.3%). Most of the changes were recommended in the technique planned with three-dimensional conformal radiation therapy (50%). Clinical target volume (73.1%) was identified as the most frequent parameter suggested for any change, followed by treatment field (19.2%) and dose (0.08%).

CONCLUSION

Peer review is an important tool that can be used to overcome deficiencies in radiation treatment plans, with a goal of improved and individualized patient care. Our study reports changes in up to a quarter of radiotherapy plans.

Assessment of contour variability in target volumes and organs at risk in lung cancer radiotherapy

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It aimed to examine if there’s any significant differences in TV & OAR contouring in lung trials QA.

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Statistically significant difference in trial protocol compliances of TV & OAR contouring existed.

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Trial protocol compliances of TV & OARs delineation can be identified through trial QA.

Aims

This study aimed to examine whether any significant differences existed in trial protocol compliance in target volumes (TV) and organs at risk (OARs) contouring amongst clinical oncologists specialised in lung cancer radiotherapy.

Materials/methods

Two lung radiotherapy trials that require all prospective investigators to submit pre-trial outlining quality assurance (QA) benchmark cases were selected. The contours from the benchmark cases were compared against a set of reference contours which were defined by the trial management group (TMG). In order to quantify the degree of variation in TV and OARs contouring, the matching index (MI), Dice coefficient (DICE), Jaccard index (JI), Van‘t Riet Index and geographical miss index (GMI) were calculated.

Results

A total of 198 structures contoured by 21 clinicians were collected from the outlining benchmark cases. There were 40 clinical target volumes (CTV), 32 spinal cord, 36 oesophagus, 36 heart and 54 lungs volumes included in the study. Analysis of the pre-trial benchmark cases revealed statistically significant differences (p ≤ 0.05) in trial protocol compliances between clinical oncologists’ target volume and organs at risk contours. Our results demonstrated that the lung contours had the highest level of conformity, followed by heart, CTV, spinal cord and oesophagus respectively.

Conclusions

This study showed that there was a statistically significant difference in trial protocol compliance for lung clinical oncologists’ TV and OARs contouring within the pre-trial QA benchmark cases. Trial protocol compliances of TV and OARs delineation can be identified through assessing outlining QA benchmark cases.

Radiotherapy for Inoperable Non-Small Cell Lung Cancer using Helical Tomotherapy

Aim

To investigate the impact of tomotherapy on the dose delivered to the lungs and other normal tissues.

Material and Methods

From February 2008 to May 2009, 35 patients with stage IIIA/IIIB non-small cell lung cancer were treated with helical tomotherapy at the S. Camillo-Forlanini Hospital. For our study we selected 20 patients who underwent chemotherapy followed by sequential radiotherapy. The planning target volume was delineated using planning CT scan and FDG-PET. The mean prescribed radiation dose was 67.5 Gy delivered in 30 fractions at a dose of 2.25 Gy per fraction.

Results

Median follow-up was 12.3 months. All patients developed acute esophageal toxicity, 15 of RTOG grade 1 and 5 of RTOG grade 2. At first follow-up 15 patients presented stable disease or partial response, 4 patients presented complete response, and 1 patient presented disease progression.

Conclusions

Helical tomotherapy is useful to achieve dose-per-fraction escalation without increasing the treatment-related morbidity. Our results applying dose escalation were encouraging considering that we delivered doses that may be difficult to achieve with 3-dimensional treatments with no excessive complication rates.

Dosimetric Analysis of Microscopic Disease in SBRT for Lung Cancers

Objective:

The objective of this study is to theoretically and experimentally evaluate the dosimetry in the microscopic disease regions surrounding the tumor under stereotactic body radiation therapy of lung cancer.

Methods:

For simplicity, the tumor was considered moving along 1 dimension with a periodic function. The probability distribution function of the tumor position was generated according to the motion pattern and was used to estimate the delivered dose in the microscopic disease region. An experimental measurement was conducted to validate both the estimated dose with a probability function and the calculated dose from 4-dimensional computed tomography data using a dynamic thorax phantom. Four tumor motion patterns were simulated with cos⁴(x) and sin(x), each with 2 different amplitudes: 10 mm and 5 mm. A 7-field conformal plan was created for treatment delivery. Both films (EBT2) and optically stimulated luminescence detectors were inserted in and around the target of the phantom to measure the delivered doses. Dose differences were evaluated using gamma analysis with 3%/3 mm.

Results:

The average gamma index between measured doses using film and calculated doses using average intensity projection simulation computed tomography was 80.8% ± 0.9%. In contrast, between measured doses using film and calculated doses accumulated from 10 sets of 4-dimensional computed tomography data, it was 98.7% ± 0.6%. The measured doses using optically stimulated luminescence detectors matched very well (within 5% of the measurement uncertainty) with the theoretically calculated doses using probability distribution function at the corresponding position. Respiratory movement caused inadvertent irradiation exposure, with 70% to 80% of the dose line wrapped around the 10 mm region outside the target.

Conclusion:

The use of static dose calculation in the treatment planning system could substantially underestimate the actual delivered dose in the microscopic disease region for a moving target. The margin for microscopic disease may be substantially reduced or even eliminated for lung stereotactic body radiation therapy.

Impact of moving target on measurement accuracy in 3D and 4D PET imaging-a phantom study

PURPOSE

The purpose of this study was to evaluate the impact of tumor motion on maximum standardized uptake value (SUV_max) and metabolic tumor volume (MTV) measurements in both 3-dimensional and respiratory-correlated, 4-dimensional positron emission tomography (PET) imaging. We also evaluated the effect of implementing different attenuation correction methods in 4-dimensional PET image reconstruction on SUV_max and MTV.

METHODS AND MATERIALS

An anthropomorphic thorax phantom with a spherical ball as a surrogate for a tumor was used. Different types of motion were imposed on the ball to mimic a patient's breathing motion. Three-dimensional PET imaging of the phantom without tumor motion was performed and used as the reference. The ball was then set in motion with different breathing motion traces and imaged with both 3- and 4-dimensional PET methods. The clinical 4-dimensional PET imaging protocol was modified so that 3 different types of attenuation correction images were used for reconstructions: the same free-breathing computed tomography (CT) for all PET phases, the same average intensity projection CT for all PET phases, and 4-dimensional CT for phase-matched attenuation correction. Tumor SUV_max and MTV values that were measured from the moving phantom were compared with the reference values.

RESULTS

SUV_max that was measured in 3-dimensional PET imaging was different from the reference value by 20.4% on average for the motions that were investigated; this difference decreased to 2.6% with 4-dimensional PET imaging. The measurement of MTV in 4-dimensional PET also showed a similar magnitude of reduction of deviation compared with 3-dimensional PET. Four-dimensional PET with use of phase-matched 4-dimensional CT for attenuation correction showed less variation in SUV_max and MTV among phases compared with 4-dimensional PET with free-breathing CT or average intensity projection CT for attenuation correction.

CONCLUSIONS

Four-dimensional PET imaging reduces the impact of motion on measured SUV_max and MTV when compared with 3-dimensional PET imaging. Clinical 4-dimensional PET imaging protocols should consider phase-matched 4-dimensional CT imaging for attenuation correction to achieve more accurate measurements.

Gradient-based delineation of the primary GTV on FLT PET in squamous cell cancer of the thoracic esophagus and impact on radiotherapy planning

Background

To validate a gradient-based segmentation method for gross tumor volume(GTV) delineation on ⁸F-fluorothymidine (FLT)positron emission tomography (PET)/ computer tomography (CT) in esophageal squamous cell cancer through pathologic specimen, in comparison with standardized uptake values (SUV) threshold-based methods and CT. The corresponding impact of this GTV delineation method on treatment planning was evaluated.

Methods and materials

Ten patients with esophageal squamous cell cancer were enrolled. Before radical surgery, all patients underwent FLT-PET/CT. GTVs were delineated by using four methods. GTV_GRAD, GTV_1.4 and GTV_30%max were segmented on FLT PET using a gradient-based method, a fixed threshold of 1.4 SUV and 30% of SUV_max, respectively. GTV_CT was based on CT data alone. The maximum longitudinal tumor length of each segmented GTV was compared with the measured tumor length of the pathologic gross tumor length (L_Path). GTV_GRAD, GTV_1.4 and GTV_30%max were compared with GTV_CT by overlap index. Two radiotherapy plannings (plan_GRAD) and (plan_CT) were designed for each patient based on GTV_GRAD and GTV_CT. The dose-volume parameters for target volume and normal tissues, CI and HI of plan_GRAD and plan_CT were compared.

Results

The mean ± standard deviation of L_Path was 6.47 ± 2.70 cm. The mean ± standard deviation of L_GRAD,L_1.4, L_30%max and L_CT were 6.22 ± 2.61, 6.23 ± 2.80, 5.95 ± 2.50,7.17 ± 2.28 cm, respectively. The Pearson correlation coefficients between L_Path and each segmentation method were 0.989, 0.920, 0.920 and 0.862, respectively. The overlap indices of GTV_GRAD, GTV_1.4, GTV_30%max when compared with GTV_CT were 0.75 ± 0.12, 0.71 ± 0.12, 0.57 ± 0.10, respectively. The V₅, V₁₀, V₂₀, V₃₀ and mean dose of total-lung,V₃₀ and mean dose of heart of plan_GRAD were significantly lower than plan_CT.

Conclusions

The gradient-based method provided the closest estimation of target length. The radiotherapy plannings based on the gradient-based segmentation method reduced the irradiated volume of lung, heart in comparison to CT.

Geographic miss of lung tumours due to respiratory motion: a comparison of 3D vs 4D PET/CT defined target volumes

Background

PET/CT scans acquired in the radiotherapy treatment position are typically performed without compensating for respiratory motion. The purpose of this study was to investigate geographic miss of lung tumours due to respiratory motion for target volumes defined on a standard 3D-PET/CT.

Methods

29 patients staged for pulmonary malignancy who completed both a 3D-PET/CT and 4D-PET/CT were included. A 3D-Gross Tumour Volume (GTV) was defined on the standard whole body PET/CT scan. Subsequently a 4D-GTV was defined on a 4D-PET/CT MIP. A 5 mm, 10 mm, 15 mm symmetrical and 15×10 mm asymmetrical Planning Target Volume (PTV) was created by expanding the 3D-GTV and 4D-GTV’s. A 3D conformal plan was generated and calculated to cover the 3D-PTV. The 3D plan was transferred to the 4D-PTV and analysed for geographic miss. Three types of miss were measured. Type 1: any part of the 4D-GTV outside the 3D-PTV. Type 2: any part of the 4D-PTV outside the 3D-PTV. Type 3: any part of the 4D-PTV receiving less than 95% of the prescribed dose. The lesion motion was measured to look at the association between lesion motion and geographic miss.

Results

When a standard 15 mm or asymmetrical PTV margin was used there were 1/29 (3%) Type 1 misses. This increased 7/29 (24%) for the 10 mm margin and 23/29 (79%) for a 5 mm margin. All patients for all margins had a Type 2 geographic miss. There was a Type 3 miss in 25 out of 29 cases in the 5, 10, and 15 mm PTV margin groups. The asymmetrical margin had one additional Type 3 miss. Pearson analysis showed a correlation (p < 0.01) between lesion motion and the severity of the different types of geographic miss.

Conclusion

Without any form of motion suppression, the current standard of a 3D- PET/CT and 15 mm PTV margin employed for lung lesions has an increasing risk of significant geographic miss when tumour motion increases. Use of smaller asymmetric margins in the cranio-caudal direction does not comprise tumour coverage. Reducing PTV margins for volumes defined on 3D-PET/CT will greatly increase the chance and severity of a geometric miss due to respiratory motion. 4D-imaging reduces the risk of geographic miss across the population of tumour sizes and magnitude of motion investigated in the study.

Comparison of primary target volumes delineated on four-dimensional CT and 18 F-FDG PET/CT of non-small-cell lung cancer

Background

To determine the optimal threshold of ¹⁸ F-fluorodexyglucose (¹⁸ F-FDG) positron emission tomography CT (PET/CT) images that generates the best volumetric match to internal gross target volume (IGTV) based on four-dimensional CT (4DCT) images.

Methods

Twenty patients with non-small cell lung cancer (NSCLC) underwent enhanced three-dimensional CT (3DCT) scan followed by enhanced 4DCT scan of the thorax under normal free breathing with the administration of intravenous contrast agents. A total of 100 ml of ioversol was injected intravenously, 2 ml/s for 3DCT and 1 ml/s for 4DCT. Then ¹⁸ F-FDG PET/CT scan was performed based on the same positioning parameters (the same immobilization devices and identical position verified by laser localizer as well as skin marks). Gross target volumes (GTVs) of the primary tumor were contoured on the ten phases images of 4DCT to generate IGTV₁₀. GTV_PET were determined with eight different threshold using an auto-contouring function. The differences in the position, volume, concordance index (CI) and degree of inclusion (DI) of the targets between GTV_PET and IGTV₁₀ were compared.

Results

The images from seventeen patients were suitable for further analysis. Significant differences between the centric coordinate positions of GTV_PET (excluding GTV_PET15%) and IGTV₁₀ were observed only in z axes (P < 0.05). GTV_PET15%, GTV_PET25% and GTV_PET2.0 were not statistically different from IGTV₁₀ (P < 0.05). GTV_PET15% approximated closely to IGTV₁₀ with median percentage volume changes of 4.86%. The best CI was between IGTV₁₀ and GTV_PET15% (0.57). The best DI of IGTV₁₀ in GTV_PET was IGTV₁₀ in GTV_PET15% (0.80).

Conclusion

None of the PET-based contours had both close spatial and volumetric approximation to the 4DCT IGTV₁₀. At present 3D-PET/CT should not be used for IGTV generation.

Defining internal target volume using positron emission tomography for radiation therapy planning of moving lung tumors

Substantial disagreement exists over appropriate PET segmentation techniques for non-small cell lung cancer. Currently, no segmentation algorithm explicitly considers tumor motion in determining tumor borders. We developed an automatic PET segmentation model as a function of target volume, motion extent, and source-to-background ratio (the VMSBR model). The purpose of this work was to apply the VMSBR model and six other segmentation algorithms to a sample of lung tumors. PET and 4D CT were performed in the same imaging session for 23 patients (24 tumors) for radiation therapy planning. Internal target volumes (ITVs) were autosegmented on maximum intensity projection (MIP) of cine CT. ITVs were delineated on PET using the following methods: 15%, 35%, and 42% of maximum activity concentration, standardized uptake value (SUV) of 2.5 g/mL, 15% of mean activity concentration plus background, a linear function of mean SUV, and the VMSBR model. Predicted threshold values from each method were compared to measured optimal threshold values, and resulting volume magnitudes were compared to cine-CT-derived ITV. Correlation between predicted and measured threshold values ranged from slopes of 0.29 for the simplest single-threshold techniques to 0.90 for the VMSBR technique. R2 values ranged from 0.07 for the simplest single-threshold techniques to 0.86 for the VMSBR technique. The VMSBR segmentation technique that included volume, motion, and source-to-background ratio, produced accurate ITVs in patients when compared with cine-CT-derived ITV.

Advances in 4D radiation therapy for managing respiration: part II - 4D treatment planning

The development of 4D CT imaging technology made possible the creation of patient models that are reflective of respiration-induced anatomical changes by adding a temporal dimension to the conventional 3D, spatial-only, patient description. This had opened a new venue for treatment planning and radiation delivery, aimed at creating a comprehensive 4D radiation therapy process for moving targets. Unlike other breathing motion compensation strategies (e.g. breath-hold and gating techniques), 4D radiotherapy assumes treatment delivery over the entire respiratory cycle - an added bonus for both patient comfort and treatment time efficiency. The time-dependent positional and volumetric information holds the promise for optimal, highly conformal, radiotherapy for targets experiencing movements caused by respiration, with potentially elevated dose prescriptions and therefore higher cure rates, while avoiding the uninvolved nearby structures. In this paper, the current state of the 4D treatment planning is reviewed, from theory to the established practical routine. While the fundamental principles of 4D radiotherapy are well defined, the development of a complete, robust and clinically feasible process still remains a challenge, imposed by limitations in the available treatment planning and radiation delivery systems.

Real-time 4-D radiotherapy for lung cancer

Respiratory motion considerably influences dose distribution, and thus clinical outcomes in radiotherapy for lung cancer. Breath holding, breath coaching, respiratory gating with external surrogates, and mathematical predicting models all have inevitable uncertainty due to the unpredictable variations of internal tumor motion. The amplitude of the same tumor can vary with standard deviations > 5 mm occurring in 23% of T1-2N0M0 non-small cell lung cancers. Residual motion varied 1-6 mm (95th percentile) for the 40% duty cycle of respiratory gating with external surrogates. The 4-D computed tomography is vulnerable to problems relating to the external surrogates. Real-time 4-D radiotherapy (4DRT), where the temporal changes in anatomy during the delivery of radiotherapy are explicitly considered in real time, is emerging as a new method to reduce these known sources of uncertainty. Fluoroscopic, real-time tumor-tracking technology using internal fiducial markers near the tumor has ± 2 mm accuracy, and has achieved promising clinical results when used with X-ray therapy. Instantaneous irradiation based on real-time verification of internal fiducial markers is considered the minimal requisite for real-time 4DRT of lung cancers at present. Real-time tracking radiotherapy using gamma rays from positron emitters in tumors is in the preclinical research stage, but has been successful in experiments in small animals. Real-time tumor tracking via spot-scanning proton beam therapy has the capability to cure large lung cancers in motion, and is expected to be the next-generation real-time 4DRT.

Diagnostic and staging impact of radiotherapy planning FDG-PET-CT in non-small-cell lung cancer

BACKGROUND AND PURPOSE

To evaluate whether FDG-PET performed for radiotherapy (RT) planning can detect disease progression, compared with staging PET.

MATERIALS AND METHODS

Twenty-six patients with newly-diagnosed non-small-cell lung cancer underwent planning PET-CT for curative RT within 8 weeks (mean: 33±14days) of staging PET-CT. Progressive disease (PD) was defined as >25% increase in tumour size (transaxial) or volume, as delineated by SUV threshold of 2.5, or new sites (SUV>2.5).

RESULTS

The planning PET detected PD in 16 patients (61%), compared to four patients (15%) by CT component of PET-CT. The mean scan interval was longer in patients with progression: 40±12days, compared to 22±11days without progression. Planning PET detected PD in 13/17 (76%), 12/14 (86%) and 7/7 patients if the interval was ≥4, 5 and 6 weeks, respectively, compared with 3/9 patients if interval <4 weeks. Planning PET detected PD in primary metabolic volume in seven patients, 20 new nodal sites in 12 new nodal stations and nine patients, five extra-nodal sites in five patients. This resulted in upstaging in nine patients (35%): stage IIIA in three, IIIB in three and IV in three.

CONCLUSIONS

RT-planning FDG-PET can provide incremental diagnostic information and may impact on staging in a significant number of patients.

Functional and molecular image guidance in radiotherapy treatment planning optimization

Functional and molecular imaging techniques are increasingly being developed and used to quantitatively map the spatial distribution of parameters, such as metabolism, proliferation, hypoxia, perfusion, and ventilation, onto anatomically imaged normal organs and tumor. In radiotherapy optimization, these imaging modalities offer the promise of increased dose sparing to high-functioning subregions of normal organs or dose escalation to selected subregions of the tumor as well as the potential to adapt radiotherapy to functional changes that occur during the course of treatment. The practical use of functional/molecular imaging in radiotherapy optimization must take into cautious consideration several factors whose influences are still not clearly quantified or well understood including patient positioning differences between the planning computed tomography and functional/molecular imaging sessions, image reconstruction parameters and techniques, image registration, target/normal organ functional segmentation, the relationship governing the dose escalation/sparing warranted by the functional/molecular image intensity map, and radiotherapy-induced changes in the image intensity map over the course of treatment. The clinical benefit of functional/molecular image guidance in the form of improved local control or decreased normal organ toxicity has yet to be shown and awaits prospective clinical trials addressing this issue.

F-18-FDG-PET confined radiotherapy of locally advanced NSCLC with concomitant chemotherapy: results of the PET-PLAN pilot trial

PURPOSE

The integration of fluoro-deoxy-D-glucose positron emission tomography (FDG-PET) in the process of radiotherapy (RT) planning of locally advanced non-small-cell lung cancer (NSCLC) may improve diagnostic accuracy and minimize interobserver variability compared with target volume definition solely based on computed tomography. Furthermore, irradiating only FDG-PET-positive findings and omitting elective nodal regions may allow dose escalation by treating smaller volumes. The aim of this prospective pilot trial was to evaluate the therapeutic safety of FDG-PET-based RT treatment planning with an autocontour-derived delineation of the primary tumor.

METHODS AND MATERIALS

Eligible patients had Stages II-III inoperable NSCLC, and simultaneous, platinum-based radiochemotherapy was indicated. FDG-PET and computed tomography acquisitions in RT treatment planning position were coregistered. The clinical target volume (CTV) included the FDG-PET-defined primary tumor, which was autodelineated with a source-to-background algorithm, plus FDG-PET-positive lymph node stations. Limited by dose restrictions for normal tissues, prescribed total doses were in the range of 66.6 to 73.8 Gy. The primary endpoint was the rate of out-of-field isolated nodal recurrences (INR).

RESULTS

As per intent to treat, 32 patients received radiochemotherapy. In 15 of these patients, dose escalation above 66.6 Gy was achieved. No Grade 4 toxicities occurred. After a median follow-up time of 27.2 months, the estimated median survival time was 19.3 months. During the observation period, one INR was observed in 23 evaluable patients.

CONCLUSIONS

FDG-PET-confined target volume definition in radiochemotherapy of NSCLC, based on a contrast-oriented source-to-background algorithm, was associated with a low risk of INR. It might provide improved tumor control because of dose escalation.

Conventional 3D staging PET/CT in CT simulation for lung cancer: impact of rigid and deformable target volume alignments for radiotherapy treatment planning

OBJECTIVE

Positron emission tomography (PET)/CT scans can improve target definition in radiotherapy for non-small cell lung cancer (NSCLC). As staging PET/CT scans are increasingly available, we evaluated different methods for co-registration of staging PET/CT data to radiotherapy simulation (RTP) scans.

METHODS

10 patients underwent staging PET/CT followed by RTP PET/CT. On both scans, gross tumour volumes (GTVs) were delineated using CT (GTV(CT)) and PET display settings. Four PET-based contours (manual delineation, two threshold methods and a source-to-background ratio method) were delineated. The CT component of the staging scan was co-registered using both rigid and deformable techniques to the CT component of RTP PET/CT. Subsequently rigid registration and deformation warps were used to transfer PET and CT contours from the staging scan to the RTP scan. Dice's similarity coefficient (DSC) was used to assess the registration accuracy of staging-based GTVs following both registration methods with the GTVs delineated on the RTP PET/CT scan.

RESULTS

When the GTV(CT) delineated on the staging scan after both rigid registration and deformation was compared with the GTV(CT)on the RTP scan, a significant improvement in overlap (registration) using deformation was observed (mean DSC 0.66 for rigid registration and 0.82 for deformable registration, p = 0.008). A similar comparison for PET contours revealed no significant improvement in overlap with the use of deformable registration.

CONCLUSIONS

No consistent improvements in similarity measures were observed when deformable registration was used for transferring PET-based contours from a staging PET/CT. This suggests that currently the use of rigid registration remains the most appropriate method for RTP in NSCLC.

Management of patients with head and neck tumours presenting at diagnosis with a synchronous second cancer at another anatomic site

AIMS

To understand management strategies and outcomes of patients diagnosed with a head and neck tumour and a synchronous second cancer developed at another anatomic site.

MATERIALS AND METHODS

Retrospective analysis of all patients diagnosed with a head and neck carcinoma and a synchronous cancer and engaged in curative-intent treatments. To evaluate therapeutic strategies, each patient's treatment process was divided into sequential therapeutic modalities and corresponding targets (head and neck and/or synchronous tumour) were identified. Patient outcome was analysed with an intent-to-treat approach.

RESULTS

Forty-three patients were entered into the study (mean age=57.4 years). Synchronous tumours concerned the lung (57.8%), oesophagus (31.1%) or other sites (11.1%). Treatments were complex, including one to four consecutive modalities, with a mean duration of 4.6 months. When both tumours were advanced, treatments were frequently initiated with dual-spectrum chemotherapy (66.7%). In other situations, a locoregional treatment was often (81.1%) proposed immediately. When both tumours were in early stages, this initial locoregional treatment could be extended to target both tumours together (30.0%). For patients whose tumours differed in severity, this locoregional treatment targeted only one tumour (85%); priority was given to the most advanced one (76.5%). Nine patients had definitive treatment interruption. Associated risk factors were a low body mass index (P=0.03) and advanced-stage tumours (P=0.01). Thirty-one patients died (72.1%) with a median time to death of 7.7 months. The median follow-up for survivors was 46.2 months. Three-year overall survival was 33.9%. Low body mass index (P=0.001), advanced-stage synchronous tumours (P=0.03) and oesophageal primaries (P=0.03) altered the overall survival. Three-year locoregional and metastatic progression-free survival was 40.8 and 62.5%, respectively. Low body mass index (P=0.01) and advanced-stage synchronous tumours (P=0.01) increased the risk of disease failure.

CONCLUSIONS

Head and neck tumours diagnosed with a synchronous cancer are a complex challenge. Despite a severe prognosis, patients who are not underweight, presenting with lower-stage tumours (especially the synchronous tumour) and without oesophageal involvement could most benefit from aggressive treatments.

Geometrical analysis of radiotherapy target volume delineation: a systematic review of reported comparison methods

Radiotherapy target volume definition is a critical step in the radiotherapy treatment planning process for all tumour sites. New technology may improve the identification of tumour from normal tissue for the purposes of target volume definition. In assessing the proffered benefits of new technologies, rigorous methods of comparison are necessary. A review of published studies was conducted using PubMed (National Library of Medicine) between 1 January 1995 and 1 January 2009 using predefined search terms. The frequency of usage of the various methods of geometrical comparison (simple volume assessment, centre of mass analysis, concordance index and volume edge analysis) was recorded. Sixty-three studies were identified, across a range of primary tumour sites. The most common method of target volume analysis was simple volume measurement; this was described in 84% of the papers analysed. The concordance index type analysis was described in 30%, the centre of mass analysis in 9.5% and the volume edge analysis in 4.8%. In reporting geometrical differences between target volumes no standard exists. However, to optimally describe geometrical changes in target volumes, simple volume change and a measure of positional change should be assessed.

Gradient-based delineation of the primary GTV on FDG-PET in non-small cell lung cancer: a comparison with threshold-based approaches, CT and surgical specimens

PURPOSE

The aim of this study was to validate a gradient-based segmentation method for GTV delineation on FDG-PET in NSCLC through surgical specimen, in comparison with threshold-based approaches and CT.

MATERIALS AND METHODS

Ten patients with stage I-II NSCLC were prospectively enrolled. Before lobectomy, all patients underwent contrast enhanced CT and gated FDG-PET. Next, the surgical specimen was removed, inflated with gelatin, frozen and sliced. The digitized slices were used to reconstruct the 3D macroscopic specimen. GTVs were manually delineated on the macroscopic specimen and on CT images. GTVs were automatically segmented on PET images using a gradient-based method, a source to background ratio method and fixed threshold values at 40% and 50% of SUV(max). All images were finally registered. Analyses of raw volumes and logarithmic differences between GTVs and GTV(macro) were performed on all patients and on a subgroup excluding the poorly defined tumors. A matching analysis between the different GTVs was also conducted using Dice's similarity index.

RESULTS

Considering all patients, both lung and mediastinal windowed CT overestimated the macroscopy, while FDG-PET provided closer values. Among various PET segmentation methods, the gradient-based technique best estimated the true tumor volume. When analysis was restricted to well defined tumors without lung fibrosis or atelectasis, the mediastinal windowed CT accurately assessed the macroscopic specimen. Finally, the matching analysis did not reveal significant difference between the different imaging modalities.

CONCLUSIONS

FDG-PET improved the GTV definition in NSCLC including when the primary tumor was surrounded by modifications of the lung parenchyma. In this context, the gradient-based method outperformed the threshold-based ones in terms of accuracy and robustness. In other cases, the conventional mediastinal windowed CT remained appropriate.

Dosimetric implications of the addition of 18 fluorodeoxyglucose-positron emission tomography in CT-based radiotherapy planning for non-small-cell lung cancer

Summary The aim of this study was to assess the impact of F-18 fluorodeoxyglucose-positron emission tomography (FDG-PET) CT on radiotherapy planning parameters for patients treated curatively with radiotherapy for non-small-cell lung cancer (NSCLC). Five patients with stages I-III NSCLC underwent a diagnostic FDG-PET CT (dPET CT), planning FDG-PET CT (pPET CT) and a simulation CT (RTP CT). For each patient, three radiation oncologists delineated a gross tumour volume based on RTP CT alone, and fused with dPET CT and pPET CT. Standard expansions were used to generate PTVs, and a 3D conformal plan was created. Normal tissue doses were compared between plans. Coverage of pPET CT PTV by the plans based on RTP CT and dPET CT was assessed, and tumour control probabilities were calculated. Mean PTV was similar between RTP CT, dPET CT and pPET CT, although there were significant inter-observer differences in four patients. The plans, however, showed no significant differences in doses to lung, oesophagus, heart or spinal cord. The RTP CT plan and dPET CT plan significantly underdosed the pPET PTV in two patients with minimum doses ranging from 12 to 63% of prescribed dose. Coverage by the 95% isodose was suboptimal in these patients, but this did not translate into poorer tumour control probability. The effect of fused FDG-PET varied between observers. The addition of dPET and pPET did not significantly change the radiotherapy planning parameters. Although FDG-PET is of benefit in tumour delineation, its effect on normal tissue complication probability and tumour control probability cannot be predicted.

Autocontouring and manual contouring: which is the better method for target delineation using 18F-FDG PET/CT in non-small cell lung cancer?

Previously, we showed that a CT window and level setting of 1,600 and -300 Hounsfield units, respectively, and autocontouring using an (18)F-FDG PET 50% intensity level correlated best with pathologic results. The aim of this study was to compare this autocontouring with manual contouring, to determine which method is better.

METHODS

Seventeen patients with non-small cell lung cancer underwent (18)F-FDG PET/CT before surgery. The maximum diameter on pathologic examination was determined. Seven sets of gross tumor volumes (GTVs) were defined. The first set (GTV(CT)) was contoured manually using only CT information. The second set (GTV(Auto)) was autocontoured using a 50% intensity level for (18)F-FDG PET images. The third set (GTV(Manual)) was manually contoured using a visual method on PET images. The other 4 sets combined CT and (18)F-FDG PET images fused to one another to become composite volumes: GTV(CT+Auto), GTV(CT+Manual), GTV(CT-Auto), and GTV(CT-Manual). To quantitate the degree to which CT and (18)F-FDG PET defined the same region of interest, a matching index was calculated for each case. The maximum diameter of GTV was compared with the maximum diameter on pathologic examination.

RESULTS

The median GTV(CT), GTV(Auto), GTV(Manual), GTV(CT+Auto), GTV(CT+Manual), GTV(CT-Auto), and GTV(CT-Manual) were 6.96, 2.42, 4.37, 7.46, 10.17, 2.21, and 3.38 cm(3), respectively. The median matching indexes of GTV(CT) versus GTV(CT+Auto), GTV(Auto) versus GTV(CT+Auto), GTV(CT) versus GTV(CT+Manual), and GTV(Manual) versus GTV(CT+Manual) were 0.86, 0.65, 0.88, and 0.81, respectively. Compared with the maximum diameter on pathologic examination, the correlations of GTV(CT), GTV(Auto), GTV(Manual), GTV(CT+Auto), and GTV(CT+Manual) were 0.87, 0.83, 0.93, 0.86, and 0.94, respectively.

CONCLUSION

The matching index was higher for manual contouring than for autocontouring using a 50% intensity level on (18)F-FDG PET images. When using a 50% intensity level to contour the target of non-small cell lung cancer, one should also consider using manual contouring of (18)F-FDG PET to check for any missed disease.

PET and PET-CT in radiation treatment planning for lung cancer

This review analyzes PET images in radiotherapy treatment planning for lung cancer patients and discusses the most controversial current issues. Computed tomography images are commonly used to assess location and extension of target volumes and organs at risk in radiotherapy treatment planning. Although PET is more sensitive and specific, contouring on PET images is difficult because tumor margins are indistinct, due to heterogeneous (18)fluorodeoxyglucose uptake distribution and limited spatial resolution. The best target delineation criteria have not yet been established. In non-small-cell lung cancer, PET appears to improve sparing of organs at risk and reduce the risk of toxicity; prescribed doses can be increased. Data are scarce on small-cell lung cancer.

18F-fluorodeoxyglucose-positron emission tomography and pathologic tumor size in early-stage invasive cervical cancer

PURPOSE

Cervical cancer tumor size determined by 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) thresholding of the maximum standardized uptake value (SUVMax) has been correlated with the determined tumor size by computed tomography and magnetic resonance imaging. The purpose of this study was to evaluate the relationship between preoperative FDG-PET tumor size and pathologic tumor diameter in patients with early-stage cervical cancer who were undergoing radical hysterectomy.

PATIENTS AND METHODS

Forty patients with early-stage cervical cancer underwent pretreatment FDG-PET/computed tomography before radical hysterectomy and lymph node dissection. Primary tumor diameter was defined on FDG-PET as the largest diameter of the 3-dimensional volumetric isocontour of the 40% threshold of the SUVMax. The FDG-PET measurements were compared with the tumor diameter and the histological diameter of the pathologic specimen using regression analysis, paired t test, and unpaired t test.

RESULTS

The FDG-PET tumor diameter measurements were correlated to the pathologic tumor diameter in the surgical specimen with a coefficient of determination (R2) of 0.951 and a correlation coefficient of 0.757 (P < 0.0001).

CONCLUSION

There is a high level of correlation in the FDG-PET and the pathologic tumor measurements in the early-stage cervical cancer.

Comparison of standardized uptake value-based positron emission tomography and computed tomography target volumes in esophageal cancer patients undergoing radiotherapy

PURPOSE

To study various standardized uptake value (SUV)-based approaches to ascertain the best strategy for delineating metabolic tumor volumes (MTV).

METHODS AND MATERIALS

Twenty-two consecutive previously treated esophageal cancer patients with positron emission tomography (PET) imaging and computed tomography (CT)-based radiotherapy plans were studied. At the level of the tumor epicenter, MTVs were delineated at 11 different thresholds: SUV ≥2, ≥2.5, ≥3, ≥3.5 (SUV(n)); ≥40%, ≥45%, and ≥50% of the maximum (SUV(n%)); and mean liver SUV + 1, 2, 3, and 4 standard deviations (SUV(Lnσ)). The volume ratio and conformality index were determined between MTVs, and the corresponding CT/endoscopic ultrasound-based gross tumor volume (GTV) at the epicenter. Means were analyzed by one-way analysis of variance for repeated measures and further compared using a paired t test for repeated measures.

RESULTS

The mean conformality indices ranged from 0.33 to 0.48, being significantly (p < 0.05) closest to 1 at SUV(2.5) (0.47 ± 0.03) and SUV(L4σ) (0.48 ± 0.03). The mean volume ratios ranged from 0.39 to 2.82, being significantly closest to 1 at SUV(2.5) (1.18 ± 0.36) and SUV(L4σ) (1.09 ± 0.15). The mean value of the SUVs calculated using the SUV(L4σ) approach was 2.4.

CONCLUSIONS

Regardless of the SUV thresholding method used (i.e., absolute or relative to liver mean), a threshold of approximately 2.5 yields the highest conformality index and best approximates the CT-based GTV at the epicenter. These findings may ultimately aid radiation oncologists in the delineation of the entire GTV in esophageal cancer patients.

PET/CT imaging to guide cervical cancer therapy

Fluorodeoxyglucose positron emission tomography (FDG-PET)/computed tomography has been utilized for many oncologic indications. It has been found to be especially useful in the management of patients with carcinoma of the uterine cervix. PET imaging defines the extent of the disease at diagnosis. It aids in selecting therapy, such as surgery, radiation therapy, chemotherapy or combinations thereof. For radiotherapy, the metabolically active disease can be specifically targeted with radiotherapy planning. Once therapy is complete, FDG-PET is utilized to evaluate the metabolic response to therapy. The 3-month post-therapy PET scan has been demonstrated to be highly predictive of long-term survival outcome. Surveillance after completion of therapy and evaluation of clinically suspected recurrent disease are also uses of FDG-PET in patients with cervical cancer.

Phantom study on radiotherapy planning using PET/CT--delineation of GTV by evaluating SUV

We assessed the usefulness of PET/CT images to determine the target volume in radiotherapy planning by evaluating the standardized uptake value (SUV). We evaluated the imaging conditions and image-reconstruction conditions of PET/CT useful for treatment planning by collecting (18)F-FDG images of acrylic spheres (10-48 mm in diameter) in a phantom. The (18)F-FDG concentration in the spheres was 10-fold higher than that of the phantom. The contours were delineated according to the SUV by the threshold and regions of interest (ROI) methods. Comparisons of two- and three-dimensional (2D and 3D) acquisition images indicated that the sharpness and quantitative qualities of the sphere boundaries were better in the former than in the latter. In the extraction of outlines using the SUV, outlines obtained at an SUV of 40-50% of the maximum agreed well with the actual acrylic sphere size. 2D acquisition images are more suitable for delineating target volume contours, although 3D acquisition images are more popular in diagnostic imaging. An SUV of 40-50% of the maximum is suggested to be appropriate for GTV contouring of sphere tumors with homogenously distributed (18)F-FDG.

Utilization of advanced imaging technologies for target delineation in radiation oncology

PURPOSE

The aim of this study was to evaluate the utilization of advanced imaging technologies for target delineation among radiation oncologists in the United States.

METHODS

A random sample of 1,600 radiation oncologists was contacted by Internet, e-mail, and fax and questioned regarding the use of advanced imaging technologies, clinical applications, and future plans for use. Advanced imaging technologies were defined as any of the following that were directly incorporated into radiation therapy planning: MRI, PET, single-photon emission CT, 4-D CT, functional MRI, and MR spectroscopy.

RESULTS

Of 1,089 contactable physicians, 394 (36%) responded. Of respondents, 65% were in private practice and 35% were in academic practice. The proportion using any advanced imaging technology for target delineation was 95%. However, the majority reported only rare (in <25% of their patients; 46.6%) or infrequent (in 25%-50% of their patients; 26.0%) utilization. The most commonly used technologies were 2-[(18)F]fluoro-2-deoxyglucose PET (76%), MRI (72%), and 4-D CT (44%). The most common cancers treated using image-guided target delineation were those of the lung (83%), central nervous system (79%), and head and neck (79%). Among users of advanced imaging technologies, 66% planned to increase use; 30% of nonusers planned to adopt these technologies in the future.

CONCLUSIONS

Advanced imaging technologies are widely used by US radiation oncologists for target delineation. Although the majority of respondents used them in <50% of their patients, the frequency of utilization is expected to increase. Studies determining the optimal application of these technologies in radiation therapy planning are needed.

On the use of hyperpolarized helium MRI for conformal avoidance lung radiotherapy

We wanted to illustrate the feasibility of using hyperpolarized helium magnetic resonance imaging (HPH-MRI) to obtain functional information that may assist in improving conformal avoidance of ventilating lung tissue during thoracic radiotherapy. HPH-MRI images were obtained from a volunteer patient and were first fused with a proton density-weighted (PD(w)) MRI to provide corresponding anatomic detail; they were then fused with the treatment planning computed tomography scan of a patient from our treatment planning database who possessed equivalent thoracic dimensions. An optimized treatment plan was then generated using the TomoTherapy treatment planning system, designating the HPH-enhancing regions as ventilation volume (VV). A dose-volume histogram compares the dosimetry of the lungs as a paired organ, the VV, and the lungs minus the VV. The clinical consequences of these changes was estimated using a bio-effect model, the parallel architecture model, or the local damage (f(dam)) model. Model parameters were chosen from published studies linking the incidence of grade 3+ pneumonitis, with the dose and volume irradiated. For two hypothetical treatment plans of 60 Gy in 30 fractions delivered to a right upper-lobe lung mass, one using and one ignoring the VV as an avoidance structure, the mean normalized total dose (NTD(mean)) values for the lung subvolumes were: lungs = 12.5 Gy₃ vs. 13.52 Gy₃, VV = 9.94 Gy₃ vs. 13.95 Gy₃, and lungs minus VV = 16.69 Gy₃ vs. 19.16 Gy₃. Using the f(dam) values generated from these plans, one would predict a reduction of the incidence of grade 3+ radiation pneumonitis from 12%-4% when compared with a conventionally optimized plan. The use of HPH-MRI to identify ventilated lung subvolumes is feasible and has the potential to be incorporated into conformal avoidance treatment planning paradigms. A prospective clinical study evaluating this imaging technique is being developed.

Functional imaging of colorectal cancer: positron emission tomography, magnetic resonance imaging, and computed tomography

In the past 10 years, overall survival and disease-free survival of patients with colorectal cancer (CRC) has improved substantially because of a combination of factors: (1) more accurate staging as a result of advances in imaging technology; (2) refinements in surgical technique; (3) 'curative' metastasectomy for patients with limited metastatic disease; (4) improvements in radiation therapy planning and greater precision of radiation therapy delivery; and (5) increasing chemotherapeutic options, including antiangiogenic and vascular targeting drugs. In this era of 'personalized medicine,' the increasingly individualized treatment of patients with CRC has highlighted the need for functional imaging techniques in addition to conventional anatomic-based imaging. This review discusses the contribution of positron emission tomography to the clinical management of CRC. In addition, evolving techniques such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), DCE computed tomography (perfusion CT), diffusion-weighted MRI, and blood oxygenation level-dependent MRI that might have a future role will be covered.

Personnel radiation dose considerations in the use of an integrated PET-CT scanner for radiotherapy treatment planning

The acquisition of radiotherapy planning scans on positron emission tomography (PET)-CT scanners requires the involvement of radiotherapy radiographers. This study assessed the radiation dose received by these radiographers during this process. Radiotherapy planning (18)F-fluorodeoxyglucose ((18)F-FDG) PET-CT scans were acquired for 28 non-small cell lung cancer patients. In order to minimise the radiation dose received, a two-stage process was used in which the most time-consuming part of the set-up was performed before the patient received their (18)F-FDG injection. Throughout this process, the radiographers wore electronic personal dosemeters and recorded the doses received at different stages of the process. The mean total radiation dose received by a radiotherapy radiographer was 5.1+/-2.6 microSv per patient. The use of the two-stage process reduced the time spent in close proximity to the patient by approximately a factor of four. The two-stage process was effective in keeping radiation dose to a minimum. The use of a pre-injection set-up session reduces the radiation dose to the radiotherapy radiographers because of their involvement in PET-CT radiotherapy treatment planning scans by approximately a factor of three.