Determining optimal clinical target volume margins on the basis of microscopic extracapsular extension of metastatic nodes in patients with non-small-cell lung cancer

Dosimetric comparison of free-breathing versus respiratory motion-managed radiotherapy via four-dimensional computed tomography-based volumetric-modulated arctherapy for lung cancer

PURPOSE

The aim of this study is to use respiratory motion-managed radiotherapy (RT) to reduce side effects and to compare dosimetric factors with free-breathing planning in patients with lung cancer.

MATERIALS AND METHODS

Simulation images were obtained in 10 respiratory phases with free breathing using four-dimensional computed tomography (4D-CT) scanner. Planning target volume (PTV) was created with 5mm margins in each direction of the internal target volume delineated using the maximum intensity projection. A volumetric arc treatment (VMAT) plan was created so that the prescribed dose would cover 98% of the PTV. Target volumes for the free-breathing VMAT plan were created according to ICRU Reports 62 and the same prescribed dose was used.

RESULTS

Patients were evaluated during January 2020. Median 63Gy (59.4-64) RT was administered. Median PTV volumes were 173.53 and 494.50cm3 (P=0.008) and dose covering 95% of PTV volume was 62.97 and 60.51Gy (P=0.13) in 4D-CT based and free-breathing VMAT plans, respectively. The mean and V50 heart dose was 6.03Gy (vs. 10.36Gy, P=0.043) and 8.2% (vs. 33.9%, P=0.007), and significantly lower in 4D-CT based VMAT plans and there was also found a non-significant reduction for other risky organ doses.

CONCLUSION

Ten patients treated with respiratory motion-managed RT with 4D-CT based VMAT technique. It was observed that PTV did not increase, the target was covered with 95% accuracy, and with statistical significance in heart doses, all risky organ doses were found to be less.

Evaluation of Microscopic Tumour Extension in Localized Stage Non-Small-Cell Lung Cancer for Stereotactic Radiotherapy Planning

Background: Stereotactic radiotherapy for localised stage non-small-cell lung carcinoma (NSCLC) is an alternative indication for patients who are inoperable or refuse surgery. A study showed that the microscopic tumour extension (ME) of NSCLC varied according to the histological type, which allowed us to deduce adapted margins for the clinical target volume (CTV). However, to date, no study has been able to define the most relevant margins for patients with stage 1 tumours. Methods: We performed a retrospective analysis including patients with adenocarcinoma (ADC) or squamous cell carcinoma (SCC) of localised stage T1N0 or T2aN0 who underwent surgery. The ME was measured from this boundary. The profile of the type of tumour spread was also evaluated. Results: The margin required to cover the ME of a localised NSCLC with a 95% probability is 4.4 mm and 2.9 mm for SCC and ADC, respectively. A significant difference in the maximum distance of the ME between the tumour-infiltrating lymphocytes (TILs), 0−10% and 50−90% (p < 0.05), was noted for SCC. There was a significant difference in the maximum ME distance based on whether the patient had chronic obstructive pulmonary disease (COPD) (p = 0.011) for ADC. Multivariate analysis showed a statistically significant relationship between the maximum microextension distance and size with the shrinkage coefficient. Conclusion: This study definitively demonstrated that the ME depends on the pathology subtype of NSCLC. According to International Commission on Radiation Units and Measurements (ICRU) reports, 50, 62 and 83 CTV margins, proposed by these results, should be added to the GTV (Gross tumour volume). When stereotactic body radiation therapy is used, this approach should be considered in conjunction with the dataset and other margins to be applied.

Radiotherapy for primary lung cancer

Herein are presented the recommendations from the Société française de radiothérapie oncologique regarding indications and modalities of lung cancer radiotherapy. The recommendations for delineation of the target volumes and organs at risk are detailed.

Evolving target volume concepts in locally advanced non-small cell lung cancer

Radiotherapy (RT) target volume concepts for locally advanced lung cancer have been under discussion for years. Although they may be as important as treatment doses, many aspects of them are still based on conventions, which, due to the paucity of prospective data, rely on long-term practice or on clinical knowledge and experience (e.g., on patterns of spread or recurrence). However, in recent years, large improvements have been made in medical imaging and molecular imaging methods have been implemented, which are of great interest in RT. For lung cancer, in recent years, 18F-fluoro-desoxy-glucose (FDG)-positron-emission tomography (PET)/computed tomography (CT) has shown a superior diagnostic accuracy as compare to conventional imaging and has become an indispensable standard tool for diagnostic workup, staging and response assessment. This offers the chance to optimize target volume concepts in relation to modern imaging. While actual recommendations as the EORTC or ESTRO-ACROP guidelines already include imaging standards, the recently published PET-Plan trial prospectively investigated conventional versus imaging guided target volumes in relation to patient outcome. The results of this trial may help to further refine standards. The current review gives a practical overview on procedures for pre-treatment imaging and target volume delineation in locally advanced non-small cell lung cancer (NSCLC) in synopsis of the procedures established by the PET-Plan trial with the actual EORTC and ACROP guidelines.

GOECP/SEOR radiotherapy guidelines for small-cell lung cancer

Small cell lung cancer (SCLC) accounts for approximately 20% of all lung cancers. The main treatment is chemotherapy (Ch). However, the addition of radiotherapy significantly improves overall survival (OS) in patients with non-metastatic SCLC and in those with metastatic SCLC who respond to Ch. Prophylactic cranial irradiation reduces the risk of brain metastases and improves OS in both metastatic and non-metastatic patients. The 5-year OS rate in patients with limited-stage disease (non-metastatic) is slightly higher than 30%, but less than 5% in patients with extensive-stage disease (metastatic). The present clinical guidelines were developed by Spanish radiation oncologists on behalf of the Oncologic Group for the Study of Lung Cancer/Spanish Society of Radiation Oncology to provide a current review of the diagnosis, planning, and treatment of SCLC. These guidelines emphasise treatment fields, radiation techniques, fractionation, concomitant treatment, and the optimal timing of Ch and radiotherapy. Finally, we discuss the main indications for reirradiation in local recurrence.

Phase II Study: The Outcome of Hypofractionated Involved-Field Radiation Therapy With Concurrent Chemotherapy for the Treatment of Locally Advanced Non-small Cell Lung Cancer

PURPOSE

This phase II study aimed to evaluate the efficacy and safety of hypofractionated involved-field radiation therapy (HypoFx-IFRT) in 2.5 Gy fractions and concurrent chemotherapy for locally advanced stage IIIA and B nonsmall cell lung cancer (LA-NSCLC) without prolonging treatment delivery time beyond 6 weeks. We analyzed the overall survival (OS), progression-free survival, and safety of the treatment.

METHODS AND MATERIALS

This prospective, single center, single-arm trial was initiated in 2010. All LA-NSCLC patients were treated with HypoFx-IFRT using 3-dimensional conformal radiation therapy. The median total dose of HypoFx-IFRT was 67.5 Gy (range, 60-70).

RESULTS

From December 2010 to October 2016, 36 patients were ultimately enrolled and evaluated. The trial closed early owing to slow accrual. The median follow-up duration was 50 months in all patients and 65 months in surviving patients. The 1-, 3-, and 5-year OS rates were 88.9% (95% confidence interval [CI], 78.6%-99.2%), 61.1% (95% CI, 45.2%-77.0%), and 54.1% (95% CI, 37.3%-70.9%), respectively. The median time for OS was not reached. The median time for progression-free survival was 10.7 months. The incidence rates of grade 3 radiation pneumonitis, esophagitis and esophageal stenosis were 8.3%, 2.8%, and 2.8%, respectively, and no acute or late toxicities of grade 4 or 5 were observed.

CONCLUSIONS

This study indicated that HypoFx-IFRT with concurrent chemotherapy yielded an acceptable safety profile and might be beneficial in the survival outcomes of patients with LA-NSCLC.

ESTRO ACROP guidelines for target volume definition in the treatment of locally advanced non-small cell lung cancer

Radiotherapy (RT) plays a major role in the curative treatment of locally advanced non-small cell lung cancer (NSCLC). Therefore, the ACROP committee was asked by the ESTRO to provide recommendations on target volume delineation for standard clinical scenarios in definitive (chemo)radiotherapy (RT) and adjuvant RT for locally advanced NSCLC. The guidelines given here are a result of the evaluation of a structured questionnaire followed by a consensus discussion, voting and writing procedure within the committee. Hence, we provide advice for methods and time-points of diagnostics and imaging before the start of treatment planning and for the mandatory and optional imaging to be used for planning itself. Concerning target volumes, recommendations are given for GTV delineation of primary tumour and lymph nodes followed by issues related to the delineation of CTVs for definitive and adjuvant radiotherapy. In the context of PTV delineation, recommendations about the management of geometric uncertainties and target motion are given. We further provide our opinions on normal tissue delineation and organisational and responsibility questions in the process of target volume delineation. This guideline intends to contribute to the standardisation and optimisation of the process of RT treatment planning for clinical practice and prospective studies.

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.

Stereotactic Radiotherapy for Oligometastases in Lymph Nodes-A Review

In recent years, the concept of oligometastases has become accepted and reports on stereotactic body radiotherapy as a treatment method have been published. Lesions in the brain, lung, and liver have been reported as target lesions. However, lymph node oligometastases could be a good candidate for stereotactic body radiotherapy as well. In this study, the usability of stereotactic body radiotherapy for oligometastases to lymph nodes is assessed by researching for each primary site. As a result, we could consider that stereotactic body radiotherapy could be almost well applied for lymph node oligometastases from the breast, gynecological organs, and prostate. However, doubts remain concerning the usefulness of stereotactic body radiotherapy for cervical node metastases from head and neck cancer or for mediastinal node metastases from lung or esophageal cancer since late toxicities have occurred with a large radiation dose at hypofractionation to major vessels or the central respiratory tract, especially in patients with irradiation histories. In addition, high-dose irradiation is required to control lymph node metastases from colorectal cancer due to its radioresistance, and severe late adverse events would therefore occur in adjacent organs such as the gastrointestinal tract. In cases of lymph node oligometastases with a primary tumor in the stomach or esophagus, stereotactic body radiotherapy should be used limitedly at present because this patient population is not so large and these metastases are often located close to organs at risk. Because of the varied status of recurrence and varied conditions of patients, it is difficult to determine the optimal dose for tumor control. It might be reasonable to determine the treatment dose individually based on dose constraints of adjacent organs. The oligometastatic state is becoming more frequently identified with more sensitive methods of detecting such oligometastases. In addition, there seems to be another type of oligometastases, so-called induced oligometastases, following successful systemic treatment. To determine the optimal indication of stereotactic body radiotherapy for lymph node oligometastases, further investigation about the mechanisms of oligometastases and further clinical studies including a phase III study are needed.

Is a clinical target volume (CTV) necessary for locally advanced non-small cell lung cancer treated with intensity-modulated radiotherapy? -a dosimetric evaluation of three different treatment plans

Background

The aim of this study was to determine the feasibility of omitting the clinical target volume (CTV) in patients with locally advanced non-small cell lung cancer (NSCLC) treated with intensity-modulated radiotherapy (IMRT) by comparing dosimetric characteristics of three different IMRT plans with or without CTV implementation.

Methods

Thirteen patients with stage III NSCLC were reviewed. Target volumes were contoured such that the planning target volume (PTV) derived from the gross tumor volume (GTV) directly was named PTV_g and that from GTV plus CTV margin was named PTV_c. The PTV margin to generate PTV_g or PTV_c was the same within each case. Three IMRT plans were retrospectively generated to deliver: (I) 60 Gy to PTV_g in plan_routine; (II) 60 Gy to PTV_c in plan_CTV, and (III) 50 Gy to PTV_c while the dose was simultaneously escalated to 60 Gy to PTV_g in plan_SIB, achieved using the simultaneous integrated boost (SIB) technique. Optimization was performed to minimize the dose volumes of the irradiated normal lung, heart, esophagus, and spinal cord. Dose distributions and dosimetric indexes for the target volumes and critical structures in the three plans were computed and compared.

Results

In plan_routine, the 50-Gy isodose line covered at least 95% of the GTV plus CTV margins in all 13 patients. The statistics showed better sparing of the organs at risk (OAR) in plan_routine than in plan_CTV, and the best OAR sparing in plan_SIB.

Conclusions

In patients with locally advanced lung cancer, IMRT planning without CTV implementation provides sufficient dose coverage of subclinical disease while reducing the dose to normal tissues. The omission of CTV was feasible in our cohort of patients. However, when CTV was implemented, IMRT planning that included the SIB technique had further dosimetric benefits to the patients. This strategy thus merits further evaluation in clinical trials.

European Organization for Research and Treatment of Cancer (EORTC) recommendations for planning and delivery of high-dose, high precision radiotherapy for lung cancer

PURPOSE

To update literature-based recommendations for techniques used in high-precision thoracic radiotherapy for lung cancer, in both routine practice and clinical trials.

METHODS

A literature search was performed to identify published articles that were considered clinically relevant and practical to use. Recommendations were categorised under the following headings: patient positioning and immobilisation, Tumour and nodal changes, CT and FDG-PET imaging, target volumes definition, radiotherapy treatment planning and treatment delivery. An adapted grading of evidence from the Infectious Disease Society of America, and for models the TRIPOD criteria, were used.

RESULTS

Recommendations were identified for each of the above categories.

CONCLUSION

Recommendations for the clinical implementation of high-precision conformal radiotherapy and stereotactic body radiotherapy for lung tumours were identified from the literature. Techniques that were considered investigational at present are highlighted.

Delineation of clinical target volume for postoperative radiotherapy in stage IIIA-pN2 non-small-cell lung cancer

With the high locoregional relapse rate and the improvement of radiation technology, postoperative radiotherapy (PORT) has been widely used in the treatment of completely resected stage IIIA-pN2 non-small-cell lung cancer (NSCLC). However, there is still no definitive consensus on clinical target volume for the pN2 subgroup. This review will discuss how to delineate the clinical target volume (CTV) for pN2 subgroups of IIIA-N2 NSCLC based on the published literature and to investigate the optimal PORT CTV in this cohort of patients. Besides overall survival (OS), locoregional recurrence (LR), and radiotherapy-related toxicity of this subset of the population in the modern PORT era, selection of proper patients will also be considered in this review. In summary, it is appropriate to include involved lymph node stations and uninvolved stations at high risk in PORT CTV for patients with pN2 disease when PORT is administered. PORT can reduce LR and has the potential to improve OS. In the current era of modern radiation technology, PORT can be administered safely with well-tolerated toxicity. Clinicopathological characteristics may be helpful in selecting proper candidates for PORT.

Intensity-modulated proton therapy for elective nodal irradiation and involved-field radiation in the definitive treatment of locally advanced non-small-cell lung cancer: a dosimetric study

BACKGROUND

Photon involved-field (IF) radiation therapy (IFRT), the standard for locally advanced (LA) non-small cell lung cancer (NSCLC), results in favorable outcomes without increased isolated nodal failures, perhaps from scattered dose to elective nodal stations. Because of the high conformality of intensity-modulated proton therapy (IMPT), proton IFRT could increase nodal failures. We investigated the feasibility of IMPT for elective nodal irradiation (ENI) in LA-NSCLC.

PATIENTS AND METHODS

IMPT IFRT plans were generated to the same total dose of 66.6-72 Gy received by 20 LA-NSCLC patients treated with photon IFRT. IMPT ENI plans were generated to 46 cobalt Gray equivalent (CGE) to elective nodal planning treatment volumes (PTV) plus 24 CGE to IF-PTVs.

RESULTS

Proton IFRT and ENI improved the IF-PTV percentage of volume receiving 95% of the prescribed dose (D95) by 4% (P < .01) compared with photon IFRT. All evaluated dosimetric parameters improved significantly with both proton plans. The lung percentage of volume receiving 20 Gy/CGE (V20) and mean lung dose decreased 18% (P < .01) and 36% (P < .01), respectively, with proton IFRT, and 11% (P = .03) and 26% (P < .01) with ENI. The mean esophagus dose decreased 16% with IFRT and 12% with ENI; heart V25 decreased 63% with both (all P < .01).

CONCLUSION

This study demonstrates the feasibility of IMPT for LA-NSCLC ENI. Potential decreased toxicity indicates that IMPT could allow ENI while maintaining a favorable therapeutic ratio compared with photon IFRT.

Moderately Escalated Hypofractionated (Chemo) Radiotherapy Delivered with Helical Intensity-Modulated Technique in Stage III Unresectable Non-Small Cell Lung Cancer

Purpose: To assess clinical outcomes and toxicities in patients with stage III unresectable non-small cell lung cancer (NSCLC) treated with a moderately escalated hypofractionated radiotherapy delivered with Helical Intensity-Modulated Technique in combination with sequential or concurrent chemotherapy.

Materials and Methods: Sixty-one consecutive patients considered non-progressive after two cycles of induction chemotherapy were treated with a moderately escalated hypofractionated radiation course of 30 daily fractions of 2.25–2.28 Gy each administered in 6 weeks up to a total dose of 67.5–68.4 Gy (range, 64.5–71.3 Gy). Thirty-two received sequential RT after two more cycles (total = 4 cycles) of chemotherapy, while 29 were treated with concurrent chemo-radiation. The target was considered the gross tumor volume and the clinically proven nodal regions, without elective nodal irradiation.

Results: With a median follow up of 27 months (range 6–40), 1-year and 2-year OS rate for all patients was 77 and 53%, respectively, with a median survival duration of 18.6 months in the sequential group and 24.1 months in the concomitant group. No Grade ≥4 acute and late toxicity was reported. Acute Grade 3 treatment-related pneumonitis was detected in 10% of patients. Two patients, both receiving the concurrent schedule, developed a Grade 3 acute esophagitis. The overall incidence of late Grade 3 lung toxicity was 5%. No patients experienced a Grade 3 late esophageal toxicity.

Conclusion: A moderately hypofractionated radiation course delivered with a Helical Intensity-Modulated Technique is a feasible treatment option for patients with unresectable locally advanced NSCLC receiving chemotherapy (sequentially or concurrently). Hypofractionated radiotherapy with a dedicated technique allows safely dose escalation, minimizing the effect of tumor repopulation that may occur with prolonged treatment time.

Place of proton radiotherapy in future radiotherapy practice

Proton beam therapy offers potential dosimetric advantages coupled with complexities not currently encompassed in the photon radiotherapy experience. The practice is evolving alongside other developments in oncology, which include higher precision of photon radiotherapy, greater understanding of the biological effect of radiation and its potential modification, and the recognition of new molecular targets with a plethora of agents aimed at affecting biological function. For proton therapy to have an impact on clinical practice requires full examination in rigorous clinical trials comparing proton with best photon therapy. Only the results of present and future studies, showing equivalent, superior, or even potentially worse clinical results will shape their application. The desired goal is to develop personalized treatment strategies of fractionation appropriate for protons potentially combined with targeted agents. We describe the steps in health technology assessment and the potential design of preclinical and clinical trials to define the role of proton therapy in the future.

Current challenges in clinical target volume definition: tumour margins and microscopic extensions

Determination of optimal clinical target volume (CTV) margins around gross tumour volume (GTV) for modern radiotherapy techniques, requiring more precise target definitions, is controversial and complex. Tumour localisation has been greatly improved using molecular imaging integrated with conventional imaging techniques. However, the exact incidence and extent of microscopic disease, to be encompassed by CTV, cannot be visualised by any techniques developed to date and remain uncertain. As a result, the CTV is generally determined by clinicians based on their experience and patients' histopathological data. In this article we review histopathological studies addressing the extent of subclinical disease and its possible correlation with tumour characteristics in various tumour sites. The data have been tabulated to facilitate a comparison between proposed margins by different investigations and with current margins generally accepted for each tumour site. It is concluded that there is a need for further studies to reach a consensus on the optimal CTV pertaining to each tumour site.

European Organisation for Research and Treatment of Cancer Recommendations for Planning and Delivery of High-Dose, High-Precision Radiotherapy for Lung Cancer

Purpose

To derive recommendations for routine practice and clinical trials for techniques used in high-dose, high-precision thoracic radiotherapy for lung cancer.

Methods

A literature search was performed to identify published articles considered both clinically relevant and practical to use. Recommendations were categorized under the following headings: patient selection, patient positioning and immobilization, tumor motion, computed tomography and [18F]fluorodeoxyglucose–positron emission technology scanning, generating target volumes, radiotherapy treatment planning, treatment delivery, and scoring of response and toxicity. The American College of Chest Physicians grading of recommendations was used.

Results

Recommendations were identified for each of the recommendation categories. Although most of the recommended techniques have not been evaluated in multicenter clinical trials, their use in high-precision thoracic radiotherapy and stereotactic body radiotherapy (SBRT) appears to be justified on the basis of available evidence.

Conclusion

Recommendations to facilitate the clinical implementation of high-precision conformal radiotherapy and SBRT for lung tumors were identified from the literature. Some techniques that are considered investigational at present were also highlighted.

Prospective evaluation of microscopic extension using whole-mount preparation in patients with hepatocellular carcinoma: Definition of clinical target volume for radiotherapy

BACKGROUND

To define the clinical target volume (CTV) for radiotherapy in patients with hepatocellular carcinoma (HCC).

METHODS

A prospective study was conducted to histologically evaluate the presence and the distance of microscopic extension (ME) for resected HCC on the basis of examination of whole-mount preparations of carcinoma tissue sections.

RESULTS

A total of 380 whole-mount slides prepared from tumor samples of 76 patients with HCC were examined. Patients with elevated pretreatment AFP levels exhibited higher risk of ME as compared to those with normal pretreatment AFP levels (93.9% vs. 69.8%, P < 0.01). ME positivity was 16.7% for Grade 1, 79.1% for Grade 2, and 96.3% for Grade 3 tumors (P < 0.01). The mean distance of ME was 0.0 ± 0.1 mm (range 0-0.2 mm) for Grade 1, 0.9 ± 0.9 mm (range 0-4.5 mm) for Grade 2, and 1.9 ± 1.9 mm (range 0-8.0 mm) for Grade 3 tumors (P < 0.01).

CONCLUSIONS

The CTV margins for tumor Grades 1, 2, and 3 HCC, are recommended to be 0.2 mm, 4.5 mm, and 8.0 mm beyond the gross tumor margin, respectively, to account for possible ME of the tumors in all patients.

Comparison of tumor volumes as determined by pathologic examination and FDG-PET/CT images of non-small-cell lung cancer: a pilot study

PURPOSE

To determine the cut-off standardized uptake value (SUV) on (18)F fluoro-2-deoxy-glucose (FDG) positron emission tomography/computed tomography (FDG-PET/CT) images that generates the best volumetric match to pathologic gross tumor volume (GTV(path)) for non-small-cell lung cancer (NSCLC).

METHODS AND MATERIALS

Fifteen patients with NSCLC who underwent FDG-PET/CT scans followed by lobectomy were enrolled. The surgical specimen was dissected into 5-7-mum sections at approximately 4-mm intervals and stained with hematoxylin and eosin. The tumor-containing area was outlined slice by slice and the GTV(path) determined by summing over all the slices, taking into account the interslice thickness and fixation-induced volume reduction. The gross tumor volume from the PET images, GTV(PET), was determined as a function of cut-off SUV. The optimal threshold or optimal absolute SUV was defined as the value at which the GTV(PET) was the same as the GTV(path).

RESULTS

The fixation process induced a volumetric reduction to 82% +/- 10% (range, 62-100%) of the original. The maximal SUV was 10.1 +/- 3.6 (range, 4.2-18.7). The optimal threshold and absolute SUV were 31% +/- 11% and 3.0 +/- 1.6, respectively. The optimal threshold was inversely correlated with GTV(path) and tumor diameter (p < 0.05), but the optimal absolute SUV had no significant correlation with GTV(path) or tumor diameter (p > 0.05).

CONCLUSION

This study evaluated the use of GTV(path) as a criterion for determining the optimal cut-off SUV for NSCLC target volume delineation. Confirmatory studies including more cases are being performed.