Tumor movements detected by multi-slice CT-based image fusion in the radiotherapy of lung cancer patients

The aim of our study was to detect the possible uncertainties arising from tumor movements in the daily routine treatment planning, in extreme breathing conditions. Ten patients with lung cancer were enrolled into the study. According to tumor location, five patients had peripheral and five had central tumor. After the normal planning CT scan, two more scans were made with the same CT parameters in maximal exhalation and in maximal inhalation. For planning, the normal breathing scans were used with the fusion of the maximal inhalation and maximal exhalation scans. After the fusion in all breathing phases the gross tumor volumes were contoured (GTV1, GTV2, GTV3). Around the GTV1 (normal breathing phase GTV) 3 planning target volumes (PTV) were generated with the margin of 0.5 cm, 1.5 cm and 2.5 cm (PTV1, PTV2, PTV3). Individual plans were generated to all PTVs. All GTV volumes were registered. In all cases volume deviations were registered in different breathing phases (min: 1.5%, max: 35.6%). For GTV coverage comparison the coverage index (CI) was used. In case of extreme breathing conditions, using 0.5 cm margin was sufficient to reach good coverage for central tumors. For peripheral tumors 1.5 cm margin had to be used for the acceptable coverage (CI: 0.85-1.00). In our study, extreme breathing conditions were analyzed. According to our results, CT scans used in the daily routine do not exactly represent the tumor midposition and the true tumor volume. Due to breathing synchronous tumor movements, 0.5 cm margin must be used for planning in central location. In peripheral tumors wider margin should be used.     

Dosimetric impact on changes in target volumes during intensity-modulated radiotherapy for nasopharyngeal carcinoma

Background and purposeTo assess anatomic changes during intensity modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) and to determine its dosimetric impact.Patients and methodsTwenty patients treated with IMRT for NPC were enrolled in this study. A second CT was performed at 38 Gy. Manual contouring of the macroscopic tumor volumes (GTV) and the planning target volumes (PTV) were done on the second CT. We recorded the volumes of the different structures, D98 %, the conformity, and the homogeneity indexes for each PTV. Volume percent changes were calculated.ResultsWe observed a significant reduction in tumor volumes (58.56 % for the GTV N and 29.52 % for the GTV T). It was accompanied by a significant decrease in the D98 % for the 3 PTV (1.4 Gy for PTV H, p = 0.007; 0.3 Gy for PTV I, p = 0.03 and 1.15 Gy for PTV L, p = 0 0.0066). In addition, we observed a significant reduction in the conformity index in the order of 0.02 (p = 0.001) and 0.01 (p = 0.007) for PTV H and PTV I, respectively. The conformity variation was not significant for PTV L. Moreover, results showed a significant increase of the homogeneity index for PTV H (+ 0.03, p = 0.04) and PTV L (+ 0.04, p = 0.01).ConclusionTumor volume reduction during the IMRT of NPC was accompanied by deterioration of the dosimetric coverage for the different target volumes. It is essential that a careful adaptation of the treatment plan be considered during therapy for selected patients.     

Dosimetric selection for helical tomotherapy based stereotactic ablative radiotherapy for early-stage non-small cell lung cancer or lung metastases

Background

No selection criteria for helical tomotherapy (HT) based stereotactic ablative radiotherapy (SABR) to treat early stage non-small cell lung cancer (NSCLC) or solitary lung metastases has been established. In this study, we investigate the dosimetric selection criteria for HT based SABR delivering 70 Gy in 10 fractions to avoid severe toxicity in the treatment of centrally located lesions when adequate target dose coverage is desired.

Materials and Methods

78 HT-SABR plans for solitary lung lesions were created to prescribe 70 Gy in 10 fractions to the planning target volume (PTV). The PTV was set to have ≥95% PTV receiving 70 Gy in each case. The cases for which dose constraints for ≥1 OAR could not be met without compromising the target dose coverage were compared with cases for which all target and OAR dose constraints were met.

Results

There were 23 central lesions for which OAR dose constraints could not be met without compromising PTV dose coverage. Comparing to cases for which optimal HT-based SABR plans were generated, they were associated with larger tumor size (5.72±1.96 cm vs. 3.74±1.49 cm, p<0.0001), higher lung dose, increased number of immediately adjacent OARs ( 3.45±1.34 vs. 1.66±0.81, p<0.0001), and shorter distance to the closest OARs (GTV: 0.26±0.22 cm vs. 0.88±0.54 cm, p<0.0001; PTV 0.19±0.18 cm vs. 0.48±0.36 cm, p = 0.0001).

Conclusion

Delivery of 70 Gy in 10 fractions with HT to meet all the given OAR and PTV dose constraints are most likely when the following parameters are met: lung lesions ≤3.78 cm (11.98 cc), ≤2 immediately adjacent OARs which are ≥0.45 cm from the gross lesion and ≥0.21 cm from the PTV.     

Inter-Fraction Tumor Volume Response during Lung Stereotactic Body Radiation Therapy Correlated to Patient Variables

PurposeAnalyze inter-fraction volumetric changes of lung tumors treated with stereotactic body radiation therapy (SBRT) and determine if the volume changes during treatment can be predicted and thus considered in treatment planning.ResultsAll tumors studied experienced volume change during treatment. Tumor increased in volume by an average of 15% and regressed by an average of 11%. The overall volume increase during treatment is contained within the planning target volume (PTV) for all tumors. Larger tumors increased in volume more than smaller tumors during treatment (q = 0.0029). The volume increase on CBCT was correlated to the treatment planning gross target volume (GTV) as well as internal target volumes (ITV) (q = 0.0085 and q = 0.0039 respectively) and could be predicted for tumors with a GTV less than 22 mL. The volume increase was correlated to the integral dose (ID) in the ITV at every fraction (q = 0.0049). The peak inter-fraction volume occurred at an earlier fraction in younger patients (q = 0.0122).ConclusionsWe introduced a new analysis method to follow inter-fraction tumor volume changes and determined that the observed changes during lung SBRT treatment are correlated to the initial tumor volume, integral dose (ID), and patient age. Furthermore, the volume increase during treatment of tumors less than 22mL can be predicted during treatment planning. The volume increase remained significantly less than the overall PTV expansion, and radiation re-planning was therefore not required for the purpose of tumor control. The presence of the studied correlations suggests that the observed volumetric changes may reflect some underlying biologic process rather than random fluctuations.     

Effect of patient positioning on carbon-ion therapy planned dose distribution to pancreatic tumors and organs at risk

PurposePancreatic tumor treatment dose distribution variations associated with supine and prone patient positioning were evaluated.MethodsA total of 33 patients with pancreatic tumors who underwent CT in the supine and prone positions were analyzed retrospectively. Gross tumor volume (GTV), planning target volume (PTV), and organs at risk (OARs) (duodenum and stomach) were contoured. The prescribed dose of 55.2 Gy (RBE) was planned from four beam angles (0°, 90°, 180°, and 270°). Patient collimator and compensating boli were designed for each field. Dose distributions were calculated for each field in the supine and prone positions. To improve dose distribution, patient positioning was selected from supine or prone for each beam field.ResultsCompared with conventional beam angle and patient positioning, D2cc of 1st-2nd portion of duodenum (D1-D2), 3rd-4th portion of duodenum (D3-D4), and stomach could be reduced to a maximum of 6.4 Gy (RBE), 3.5 Gy (RBE), and 4.5 Gy (RBE) by selection of patient positioning. V10 of D1-D2, D3-D4, and stomach could be reduced to a maximum of 7.2 cc, 11.3 cc, and 11.5 cc, respectively. D95 of GTV and PTV were improved to a maximum of 6.9% and 3.7% of the prescribed dose, respectively.ConclusionsOptimization of patient positioning for each beam angle in treatment planning has the potential to reduce OARs dose maintaining tumor dose in pancreatic treatment.     

Is abdominal compression useful in lung stereotactic body radiation therapy? A 4DCT and dosimetric lobe-dependent study

PurposeTo determine the usefulness of abdominal compression in lung stereotactic body radiation therapy (SBRT) depending on lobe tumor location.Materials and methodsTwenty-seven non-small cell lung cancer patients were immobilized in the Stereotactic Body Frame? (Elekta). Eighteen tumors were located in an upper lobe, one in the middle lobe and nine in a lower lobe (one patient had two lesions). All patients underwent two four-dimensional computed tomography (4DCT) scans, with and without abdominal compression. Three-dimensional tumor motion amplitude was determined using manual landmark annotation. We also determined the internal target volume (ITV) and the influence of abdominal compression on lung dose-volume histograms.ResultsThe mean reduction of tumor motion amplitude was 3.5 mm (p = 0.009) for lower lobe tumors and 0.8 mm (p = 0.026) for upper/middle lobe locations. Compression increased tumor motion in 5 cases. Mean ITV reduction was 3.6 cm³ (p = 0.039) for lower lobe and 0.2 cm³ (p = 0.048) for upper/middle lobe lesions. Dosimetric gain of the compression for lung sparing was not clinically relevant.ConclusionsThe most significant impact of abdominal compression was obtained in patients with lower lobe tumors. However, minor or negative effects of compression were reported for other patients and lung sparing was not substantially improved. At our institute, patients with upper or middle lobe lesions are now systematically treated without compression and the usefulness of compression for lower lobe tumors is evaluated on an individual basis.     

Impact of lung density on isolated lung tumor dose in VMAT using inline MR-Linac

PurposeThis study investigated the impact of lung density on the isolated lung tumor dose for volumetric modulated arc therapy (VMAT) in an inline magnetic resonance linear accelerator (MR-Linac) using the Monte Carlo (MC) simulation.MethodsCT images of the thorax phantoms with lung tumors of 1, 2, and 3 cm diameters were converted into voxel-base phantoms with lung densities of 0.1, 0.2, and 0.3 g/cm³, respectively. The dose distributions were calculated for partial-arc VMAT. The dose distributions were compared using dose differences, dose volume histograms, and dose volume indices.ResultsIn all cases, the inline magnetic field significantly enhanced the lung tumor dose compared to that at 0 T. For the 1 cm lung tumor, the inline magnetic field of 1 T increased the minimum dose of 95% of the Planning target volume (PTV D₉₅) by 14.0% in 0.1 g/cm³ lung density as compared to that in 0.3 g/cm³ at 0 T. In contrast, at 0 and 0.5 T, the PTV D₉₅ in 0.3 g/cm³ lung density was larger than that in lung density of 0.1 g/cm³. For the 2 cm lung tumor, a similar tendency to 1 cm was observed, whereas the dose impact of lung density was smaller than that for 1 cm. For the 3 cm lung tumor, the lung tumor dose was independent of lung density at 0.5 T and 1.0 T.ConclusionThe inline MR-Linac with the magnetic field over 1 T can enhance the PTV D₉₅ for VMAT regardless of the lung density.     

Dosimetric effect of uncorrected rotations in lung SBRT with stereotactic imaging guidance

PurposeTo evaluate the dosimetric impact of uncorrected rotations on the planning target volume (PTV) coverage for early stage non-small cell lung cancer patients treated with stereotactic body radiotherapy using Brainlab ExacTrac image guidance.MethodsTwenty-two patients were retrospectively selected. Two scenarios of uncorrected rotations were simulated with magnitude of 1°, 2°, 3° and 5°: (1) rotation around the treatment isocenter; and (2) roll and yaw rotations around a setup isocenter. The D₉₅ of PTV from recalculated dose on the rotated CT was compared to that from the clinical plan. A logistic regression model was used to predict the probability of dose differences between recalculated and original plans that are less than 2% based on the rotation angle, PTV volume, and distance between the treatment and setup isocenter.ResultsLogistic regression model showed the uncorrected isocentric rotations of up to 2.5° in all directions have negligible dosimetric impact. For non-isocentric rotations, a rotational error of 2° may cause significant under-dose of the PTV. Statistically significant (p < 0.05) parameters in the logistic regression model were angle for isocentric rotations, angle and distance for non-isocentric roll rotations, and angle, distance and the PTV volume for non-isocentric yaw rotations.ConclusionsThe severity of the dose deviations due to uncorrected rotations depends on the type and magnitude of the rotation, the volume of the PTV, and the distance between the treatment and setup isocenter, which should be taken into consideration when making clinical judgment of whether the rotational error could be ignored.     

Advanced dose calculation algorithms in lung cancer radiotherapy: Implications for SBRT and locally advanced disease in deep inspiration breath hold

PurposeEvaluating performance of modern dose calculation algorithms in SBRT and locally advanced lung cancer radiotherapy in free breathing (FB) and deep inspiration breath hold (DIBH).MethodsFor 17 patients with early stage and 17 with locally advanced lung cancer, a plan in FB and in DIBH were generated with Anisotropic Analytical Algorithm (AAA). Plans for early stage were 3D-conformal SBRT, 45 Gy in 3 fractions, prescribed to 95% isodose covering 95% of PTV and aiming for 140% dose centrally in the tumour. Locally advanced plans were volumetric modulated arc therapy, 66 Gy in 33 fractions, prescribed to mean PTV dose. Calculation grid size was 1 mm for SBRT and 2.5 mm for locally advanced plans. All plans were recalculated with AcurosXB with same MU as in AAA, for comparison on target coverage and dose to risk organs.ResultsLung volume increased in DIBH, resulting in decreased lung density (6% for early and 13% for locally-advanced group).In SBRT, AAA overestimated mean and near-minimum PTV dose (p-values < 0.01) compared to AcurosXB, with largest impact in DIBH (differences of up to 11 Gy). These clinically relevant differences may be a combination of small targets and large dose gradients within the PTV.In locally advanced group, AAA overestimated mean GTV, CTV and PTV doses by median less than 0.8 Gy and near-minimum doses by median 0.4–2.7 Gy.No clinically meaningful difference was observed for lung and heart dose metrics between the algorithms, for both FB and DIBH.ConclusionsAAA overestimated target coverage compared to AcurosXB, especially in DIBH for SBRT.     

Effect of the normal liver mean dose on intrahepatic recurrence in patients with hepatocellular carcinoma after receiving liver stereotactic body radiation therapy

Background and purposeThis study aims to evaluate whether dosimetric parameters affect the intrahepatic out-field recurrence or distant metastasis-free survival following the stereotactic body radiation therapy (SBRT) in patients with hepatocellular carcinoma (HCC).Materials and methodsA total of 76 patients with HCC who were treated with SBRT from January 2015 to May 2020 were included in this retrospective study. The main clinical endpoints considered were intrahepatic out-field free survival (OutFFS) and distant metastasis-free survival (DMFS). The target parameters and the liver were documented including tumor diameters, gross tumor volume (GTV), Liver minus GTV volume (LGV), and Liver minus GTV mean dose (LGD). Multivariable Cox regression with forward stepwise selection was performed to identify independent risk factors for OutFFS and DMFS. Maximally selected rank statistics were used to determine the most informative cut-off value for age and LGD.ResultsThe median follow-up was 28.2 months (range, 7.7–74.5 months). LGD higher than 12.54 Gy [HR, 0.861(0.747–0.993); p = 0.040] and age greater than 67-year-old [HR, 0.966(0.937–0.997); p = 0.030] are two independent predictors of OutFFS, previous TACE treatment [HR, 0.117(0.015–0.891); p = 0.038] was an independent predictor of DMFS.ConclusionsThe results of this study suggested that the higher the dose received by the normal liver (greater than 12.54 Gy) the better the intrahepatic out-field recurrence-free survival (RFS) rate. Further study is warranted to confirm and to better understand this phenomenon.     

Dosimetric study of Hounsfield number correction effect in areas influenced by contrast product in lungs case

BackgroundThe aim of the study was dosimetric effect quantification of exclusive computed tomography (CT) use with an intravenous (IV) contrast agent (CA ), on dose distribution of 3D-CRT treatment plans for lung cancer. Furthermore, dosimetric advantage investigation of manually contrast-enhanced region overriding, especially the heart.Materials and methodsTen patients with lung cancer were considered. For each patient two planning CT sets were initially taken with and without CA. Treatment planning were optimized based on CT scans without CA. All plans were copied and recomputed on scans with CA. In addition, scans with IV contrast were copied and density correction was performed for heart contrast enhanced. Same plans were copied and replaced to undo dose calculation errors that may be caused by CA. Eventually, dosimetric evaluations based on dose volume histograms (DVHs) of planning target volumes (PTV) and organs at-risk were studied and analyzed using the Wilcoxon’s signed rank test.ResultsThere is no statistically significant difference in dose calculation for the PTV maximum, mean, minimum doses, spinal cord maximum doses and lung volumes that received 20 and 30 Gy, between planes calculated with and without contrast scans (p > 0.05) and also for contrast scan, with manual regions overriding.ConclusionsDose difference caused by the contrast agent is negligible and not significant. Therefore, there is no justification to perform two scans, and using an IV contrast enhanced scan for dose calculation is sufficient.     

Adaptive volumetric modulated arc treatment planning for esophageal cancers using cone beam computed tomography

PurposeTo assess the potential of cone beam CT (CBCT) derived adaptive RapidArc treatment for esophageal cancers in reducing the dose to organs at risk (OAR).Methods and materialsTen patients with esophageal cancer were CT scanned in free breathing pattern. The PTV is generated by adding a 3D margin of 1 cm to the CTV as per ICRU 62 recommendations. The double arc RapidArc plan (Clin_RA) was generated for the PTV. Patients were setup using kV orthogonal images and kV-CBCT scan was acquired daily during first week of therapy, then weekly. These images were exported to the Eclipse TPS. The adaptive CTV which includes tumor and involved nodes was delineated in each CBCT image set for the length of the PTV. The composite CTV from first week CBCT was generated using Boolean union operator and 5 mm margin was added circumferentially to generate adaptive PTV (PTV1). Adaptive RapidArc plan (Adap_RA) was generated. NTCP and DVH of the OARs of the two plans were compared. Similarly, PTV2 was generated from weekly CBCT. PTV2 was evaluated for the coverage of 95% isodose of Adap_RA plan.ResultsThe PTV1 and PTV2 volumes covered by 95% isodose in adaptive plans were 93.51 ± 1.17% and 94.59 ± 1.43% respectively. The lung V_10Gy, V_20Gy and mean dose in Adap_RA plan was reduced by 17.43% (p = 0.0012), 34.64% (p = 0.0019) and 16.50% (p = 0.0002) respectively compared to Clin_RA. The Adap_RA plan reduces the heart D_35% and mean dose by 17.35% (p = 0.0011) and 17.16% (p = 0.0012). No significant reduction in spinal cord and liver doses were observed. NTCP for the lung (0.42% vs. 0.08%) and heart (1.39% vs. 0.090%) was reduced significantly in adaptive plans.ConclusionThe adaptive re-planning strategy based on the first week CBCT dataset significantly reduces the doses and NTCP to OARs.     

Is the lack of respiratory gating prejudicial for left breast TomoDirect treatments?

Background and purposeTomoDirect (TD) can only operate in free-breathing. The purpose of this study is to compare TD with breath-hold 3D conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT) techniques for left breast treatments, and to determine if the lack of respiratory gating is a handicap for cardiac sparing.Materials and methods15 patients treated for left breast had two computed tomography simulation, in free breathing (FB) and in deep-inspiration breath-hold (DIBH). Four treatments were planned: TD-FB, 3DCRT-FB, 3DCRT-DIBH and IMRT-DIBH. Dose to PTV, heart, lungs, right breast and patient were compared.ResultsA slightly lower cardiac mean dose is found for 3DCRT-DIBH than for TD-FB group (1.99 Gy Vs 2.89 Gy, p = 0.0462), while no statistical difference is found for heart V₂₀. TD-FB plans show the best PTV dose homogeneity (0.053, p < 0.001) and the lowest left lung mean dose (5.16 Gy, p < 0.001). No major differences are found for the other organs.ConclusionsTomoDirect and breath-hold 3DCRT are complementary techniques for left breast treatments: for a minority of patients, respiratory gating is mandatory to lower cardiac dose; for the remaining majority of patients, TomoDirect achieves better PTV homogeneity and reduced left lung dose, with cardiac dose equivalent to 3DCRT-DIBH.     

Gated carbon-ion scanning treatment for pancreatic tumour with field specific target volume and organs at risk

ObjectiveTo assess the feasibility of treatment planning for pancreatic tumours subject to respiratory motion using field-specific target volumes (FTV) and field-specific organs at risk (FOAR) using four-dimensional computed tomography (4DCT).MethodsFourteen pancreatic cancer patients underwent 4DCT. Radiation oncologists contoured the gross tumour volume (GTV), clinical target volume (CTV), spinal cord, duodenum, kidneys, and stomach. The gating duty cycle was set to 30 % around exhalation. FTV and FOAR were calculated using the 4DCT dataset. Planning target volumes (PTV) and planning organs at risk volumes (PRV) were defined as equal to FTV and FOAR, respectively. A dose of 55.2 Gy relative biological effectiveness (RBE) was planned to target the PTV from four beam angles. A single field uniform dose (SFUD) plan was selected. The dose distribution, including intrafractional motion changes, was generated.ResultsThe mean volume of target receiving 95 % of the planned doses was 96.4 ± 4.1 % to the GTV and 94.7 ± 0.9 % to the CTV. The highest dose to 2 cc of duodenal volume was 27.5 Gy (RBE). The volume of the stomach receiving ⩾30 Gy (RBE) was <7.0 cc in all patients. All metrics for OARs satisfied dose constraints.ConclusionDose to the CTV was covered sufficiently by the 4DCT-generated FTV, and dose to OARs was reduced by 4DCT-generated FOAR. This methodology may prevent adverse reactions while preserving local tumour control.     

A dosimetric analysis comparing electron beam with the MammoSite brachytherapy applicator for intact breast boost

IntroductionElectron beam radiation is the modality most often used to deliver an operative bed boost to breast cancer patients after completing whole breast radiation. However, electrons can potentially provide inadequate coverage. The MammoSite breast brachytherapy applicator may provide dosimetric advantages in the delivery of an operative bed boost and its role in this setting is not yet defined.Materials and methodsThe study population consisted of 15 patients with early stage breast cancer treated with partial breast irradiation (PBI) using the MammoSite device. For each patient, a theoretical boost plan using electrons and a second theoretical boost plan using the MammoSite applicator were created. To assess the adequacy of each boost plan, the PTV V90, PTV V95, and PTV V100 were calculated. To assess dose to normal tissues, the ipsilateral breast V50, ipsilateral lung V30, and heart V20 were calculated.ResultsThe mean PTV V100 for the MammoSite boost was 95.5%, compared to 77.4% for the electron boost (p < 0.001). The mean PTV V95 was 97.8%, compared to 93.3% for the electron boost (p = 0.02). The mean PTV V90, mean breast V50, mean lung V30, and mean heart V20 were not statistically different for MammoSite compared to electrons.ConclusionsA tumor bed boost using the MammoSite breast brachytherapy applicator provides superior target coverage and delivers similar doses to the ipsilateral breast and lung compared to a boost delivered with electrons. More investigation into the role of balloon brachytherapy in the delivery of a breast boost is warranted.     

Incorporation of tumor motion directionality in margin recipe: The directional MidP strategy

PurposePlanning target volume (PTV) definition based on Mid-Position (Mid-P) strategy typically integrates breathing motion from tumor positions variances along the conventional axes of the DICOM coordinate system. Tumor motion directionality is thus neglected even though it is one of its stable characteristics in time. We therefore propose the directional MidP approach (MidP dir), which allows motion directionality to be incorporated into PTV margins. A second objective consists in assessing the ability of the proposed method to better take care of respiratory motion uncertainty.Methods11 lung tumors from 10 patients with supra-centimetric motion were included. PTV were generated according to the MidP and MidP dir strategies starting from planning 4D CT.ResultsPTV_{MidP dir} volume didn’t differ from the PTV_MidP volume: 31351 mm³ IC95% [17242–45459] vs. 31003 mm³ IC95% [ 17347–44659], p = 0.477 respectively. PTV_{MidP dir} morphology was different and appeared more oblong along the main motion axis. The relative difference between 3D and 4D doses was on average 1.09%, p = 0.011 and 0.74%, p = 0.032 improved with directional MidP for D_99% and D_95%. D_2% was not significantly different between both approaches. The improvement in dosimetric coverage fluctuated substantially from one lesion to another and was all the more important as motion showed a large amplitude, some obliquity with respect to conventional axes and small hysteresis.ConclusionsDirectional MidP method allows tumor motion to be taken into account more tightly as a geometrical uncertainty without increasing the irradiation volume.     

Faisabilité et intérêt d’un nouvel algorithme de reconstruction des images TEP-18FDG (AW OSEM DR) pour la délimitation des volumes cibles en radiothérapie. À propos d’un cas de néoplasie ORL

ObjectiveWe compared two reconstruction methods for 18fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) images with “attenuation weighted ordered subset expectation maximization” using either the manufacturer-provided (AW-OSEM) or a “Detector response” (AW-OSEM DR) tomographic operator. We looked at the feasibility of using the latter reconstruction for radiotherapy target volumes definition in cancers of the superior aero-digestive tract (VADS). In this preliminary study, we first assessed the spatial resolution of images obtained with AW-OSEM and AW-OSEM DR on a Biograph™ 6, and secondly target volumes of radiotherapy “Gross Tumor Volume” (GTV), “Clinical Target Volume” (CTV) and “Planning Target Volume” (PTV) obtained with each of these reconstruction methods.Material and methodsThe spatial resolution was measured on a test object containing 4 radioactive point sources. Furthermore, radiotherapy target volumes have been defined with the software Eclipse™ on injected scanner (CT IV) and PET/CT (PET AW-OSEM and PET AW-OSEM DR) images.ResultsSpatial resolution was improved with AW-OSEM DR algorithm reconstruction compared to images obtained with AW-OSEM reconstruction (from 7.5 mm down to 5.4 mm for the highest reduction). GTV from AW-OSEM DR reconstruction with 42 and 50% of the “Standard uptake value maximum” (SUVmax) semi-automatic threshold (1.2 and 0.7 cm³ respectively) were lower than those obtained with AW-OSEM (3.6 and 2.2 cm³ respectively). They were also lower than GTV defined with CT IV (5.5 cm³). It was the same for CTV and PTV.ConclusionThis study showed that AW-OSEM DR reconstruction method allows less impaired spatial resolution than AW-OSEM. In the case of radiotherapy target volumes delineation, AW-OSEM DR may decrease the GTV, CTV and PTV and therefore the risk of side effects associated with organs at risk.