Antoine Delor

Helical tomotherapy for SIB and hypo-fractionated treatments in lung carcinomas: a 4D Monte Carlo treatment planning study.

PURPOSEnTo evaluate the impact of intra-fraction motion induced by regular breathing on treatment quality for helical tomotherapy treatments.nnnMATERIAL AND METHODSnFour patients treated by simultaneous-integrated boost (SIB) and three by hypo-fractionated stereotactic treatments (hypo-fractionated, 18 Gy/fraction) were included. All patients were coached to ensure regular breathing. For the SIB group, the tumor volume was delineated using CT information only (CTV(CT)) and the boost region was based on PET information (GTV(PET), no CTV extension). In the hypo-fractionated group, a GTV based on CT information was contoured. In both groups, ITVs were defined according to 4D data. The PTV included the ITV plus a setup error margin. The treatment was planned using the tomotherapy TPS on 3D CT images. In order to verify the impact of intra-fraction motion and interplay effects, dose calculations were performed using a previously validated Monte Carlo model of tomotherapy (TomoPen): first on the planning 3D CT (planned dose) and second, on the 10 phases of the 4D scan. For the latter, two dose distributions, termed interplay simulated or no interplay were computed with and without beamlet-phase correlation over the 10 phases and combined using deformable dose registration.nnnRESULTSnIn all cases, DVHs of interplay simulated dose distributions complied within 1% of the original clinical objectives used for planning, defined according to ICRU (report 83) and RTOG (trials 0236 and 0618) recommendations, for SIB and hypo-fractionated groups, respectively. For one patient in the hypo-fractionated group, D(mean) to the CTV(CT) was 2.6% and 2.5% higher than planned for interplay simulated and no interplay, respectively.nnnCONCLUSIONnFor the patients included in this study, assuming regular breathing, the results showed that interplay of breathing and tomotherapy delivery motions did not affect significantly plan delivery accuracy. Hence, accounting for intra-fraction motion through the definition of an ITV volume was sufficient to ensure tumor coverage.

Validation of the mid-position strategy for lung tumors in helical TomoTherapy

PURPOSEnTo compare the mid-position (MidP) strategy to the conventional internal target volume (ITV) for lung tumor management in helical TomoTherapy, using 4D Monte Carlo (MC) plan simulations.nnnMATERIALS AND METHODSnFor NSCLC patients treated by SBRT (n = 8) or SIB-IMRT (n = 7), target volumes and OARs were delineated on a contrast-enhanced CT, while 4D-CT was used to generate either ITV or MidP volumes with deformable registrations. PTV margins were added. Conformity indexes, volumetric and dosimetric parameters were compared for both strategies. Dose distributions were also computed using a 4D MC model (TomoPen) to assess how intra-fraction tumor motion affects tumor coverage, with and without interplay effect.nnnRESULTSnPTVs derived from MidP were on average 1.2 times smaller than those from ITV, leading to lower doses to OARs. Planned dose conformity to TVs was similar for both strategies. 4D MC computation showed that ITV ensured adequate TV coverage (D95 within 1% of clinical requirements), while MidP failed in 3 patients of the SBRT group (D95 to the TV lowered by 4.35%, 2.16% and 2.61%) due to interplay effect in one case and to breathing motion alone in the others.nnnCONCLUSIONSnCompared to the ITV, the MidP significantly reduced PTV and doses to OARs. MidP is safe for helical delivery except for very small tumors (<5 cc) with large-amplitude motion (>10mm) where the ITV might remain the most adequate approach.

An individualized radiation dose escalation trial in non-small cell lung cancer based on FDG-PET imaging.

AimThe aim of the study was to assess the feasibility of an individualized 18Fxa0fluorodeoxyglucose positron emission tomography (FDG-PET)-guided dose escalation boost in non-small cell lung cancer (NSCLC) patients and to assess its impact on local tumor control and toxicity.Patients and methodsA total of 13 patients with stagexa0II–III NSCLC were enrolled to receive a dose of 62.5u2009Gy in 25xa0fractions to the CT-based planning target volume (PTV; primary turmor and affected lymph nodes). The fraction dose was increased within the individual PET-based PTV (PTVPET) using intensity modulated radiotherapy (IMRT) with a simultaneous integrated boost (SIB) until the predefined organ-at-risk (OAR) threshold was reached. Tumor response was assessed during follow-up by means of repeat FDG-PET/computed tomography. Acute and late toxicity were recorded and classified according to the CTCAE criteria (Versionxa04.0). Local progression-free survival was determined using the Kaplan-Meier method.ResultsThe average dose to PTVPET reached 89.17u2009Gy for peripheral and 75u2009Gy for central tumors. After a median follow-up period of 29xa0months, seven patients were still alive, while six had died (four due to distant progression, two due to gradexa05 toxicity). Local progression was seen in two patients in association with further recurrences. One and 2-year local progression free survival rates were 76.9% and 52.8%, respectively. Three cases of acute gradexa03 esophagitis were seen. Two patients with central tumors developed late toxicity and died due to severe hemoptysis.ConclusionThese results suggest that axa0non-uniform and individualized dose escalation based on FDG-PET in IMRT delivery is feasible. The doses reached were higher in patients with peripheral compared to central tumors. This strategy enables good local control to be achieved at acceptable toxicity rates. However, dose escalation in centrally located tumors with direct invasion of mediastinal organs must be performed with great caution in order to avoid severe late toxicity.ZusammenfassungZielsetzungZiel der Studie war es, die Anwendbarkeit einer individualisierten Fluordesoxyglukose-Positronenemissionstomographie(FDG-PET)-geführten partiellen Dosissteigerung beim nichtkleinzelligen Lungenkarzinom (NSCLC) zu prüfen und deren Einfluss auf die lokale Tumorkontrolle und Toxizität zu beurteilen.Patienten und MethodenDreizehn Patienten mit NSCLC in Stadiumxa0II–III wurden in die Studie einbezogen und erhielten im Rahmen einer Radiochemotherapie eine Dosis von 62,5u2009Gy in 25xa0Fraktionen auf das CT-basierte Planungszielvolumen (PTV; primärer Tumor und betroffene Lymphknoten). Dabei wurde die Fraktionsdosis innerhalb des individuellen PET-basierten PTV (PTVPET) unter Anwendung einer intensitätsmodulierten Radiotherapie (IMRT) mit simultan-integriertem Boost (SIB) bis zum Erreichen der vordefinierten Organ-at-risk(OAR)-Grenze erhöht. In der Nachbeobachtungszeit wurde die Tumorantwort mit wiederholter FDG-PET/Computertomographie überprüft. Die frühe und späte Toxizität wurden erfasst und anhand der Common-Terminology-Criteria-for-Adverse-Events(CTCAE)-Kriterien (Versionxa04.0) klassifiziert. Das lokale progressionsfreie Überleben wurde anhand der Kaplan-Meier-Methode bestimmt.ErgebnisseDie Durchschnittsdosis auf das PTVPET erreichte 89,17u2009Gy für periphere und 75u2009Gy für zentrale Tumoren. Nach einer medianen Nachbeobachtungszeit von 29xa0Monaten waren 7xa0Patienten weiterhin am Leben, 6 waren verstorben (4 davon an Fernrezidiven, 2 an einer Toxizität fünften Grades). Bei 2xa0Patienten trat eine lokale Progression in Verbindung mit weiteren Rezidiven auf. Die lokalen progressionsfreien 1‑ und 2‑Jahres-Überlebensraten lagen bei 76,9u2009% bzw. 52,8u2009%. Es wurden 3xa0Fälle akuter Ösophagitiden dritten Grades beobachtet. Zwei Patienten mit zentralen Tumoren entwickelten eine späte Toxizität und verstarben infolge einer schwerwiegenden Hämoptyse.SchlussfolgerungGemäß diesen Ergebnissen ist für Patienten mit NSCLC eine im Rahmen der IMRT angewendete, auf der FDG-PET basierende individualisierte Dosiseskalation möglich. Die erreichte Strahlendosis ist bei peripheren Tumoren höher als bei zentralen. Mit dieser Strategie wird eine hohe lokale Kontrolle bei akzeptabler Toxizitätsrate erreicht. Dennoch sollte die Dosissteigerung für zentrale Tumoren mit direktem Eindringen in Mediastinalorgane mit äußerster Vorsicht erfolgen, um eine schwere späte Toxizität zu vermeiden.

LET dependence of the response of a PTW-60019 microDiamond detector in a 62 MeV proton beam

This study was initiated following conclusions from earlier experimental work, performed in a low-energy carbon ion beam, indicating a significant LET dependence of the response of a PTW-60019 microDiamond detector. The purpose of this paper is to present a comparison between the response of the same PTW-60019 microDiamond detector and an IBA Roos-type ionization chamber as a function of depth in a 62MeV proton beam. Even though proton beams are considered as low linear energy transfer (LET) beams, the LET value increases slightly in the Bragg peak region. Contrary to the observations made in the carbon ion beam, in the 62MeV proton beam good agreement is found between both detectors in both the plateau and the distal edge region. No significant LET dependent response of the PTW-60019 microDiamond detector is observed consistent with other findings for proton beams in the literature, despite this particular detector exhibiting a substantial LET dependence in a carbon ion beam.

Impact of motion induced artifacts on automatic registration of lung tumors in Tomotherapy

PURPOSEnTomotherapy MV-CT acquisitions of lung tumors lead to artifacts due to breathing-related motion. This could preclude the reliability of tumor based positioning. We investigate the effect of these artifacts on automatic registration and determine conditions under which correct positioning can be achieved.nnnMATERIALS AND METHODSnMV-CT and 4D-CT scans of a dynamic thorax phantom were acquired with various motion amplitudes, directions, and periods. For each acquisition, the average kV-CT image was reconstructed from the 4D-CT data and rigidly registered with the corresponding MV-CT scan in a region of interest. Different kV-MV registration strategies have been assessed.nnnRESULTSnAll tested registration methods led to acceptable registration errors (within 1.3u2009±u20091.2u2009mm) for motion periods of 3 and 6u2009s, regardless of the motion amplitude, direction, and phase difference. However, a motion period of 5u2009s, equal to half the Tomotherapy gantry period, induced asymmetric artifacts within MV-CT and significantly degraded the registration accuracy.nnnCONCLUSIONSnAs long as the breathing period differs from 5u2009s, positioning based on averaged images of the tumor provides information about its daily baseline shift, and might therefore contribute to reducing margins, regardless of the registration method.

Effect of continuous positive airway pressure administration during lung stereotactic ablative radiotherapy: a comparative planning study

PurposeBy increasing lung volume and decreasing respiration-induced tumour motion amplitude, administration of continuous positive airway pressure (CPAP) during stereotactic ablative radiotherapy (SABR) could allow for better sparing of the lungs and heart. In this study, we evaluated the effect of CPAP on lung volume, tumour motion amplitude and baseline shift, as well as the dosimetric impact of the strategy.MethodsTwenty patients with lung tumours referred for SABR underwent 4D-computed tomography (CT) scans with and without CPAP (CPAP/noCPAP) at two timepoints (T0/T1). First, CPAP and noCPAP scans were compared for lung volume, tumour motion amplitude, and baseline shift. Next, CPAP and noCPAP treatment plans were computed and compared for lung dose parameters (mean lung dose (MLD), lung volume receiving 20 Gy (V20Gy), 13 Gy (V13Gy), and 5 Gy (V5Gy)) and mean heart dose (MHD).ResultsOn average, CPAP increased lung volume by 8.0% (pu202f<u20090.001) and 6.3% (pu202f<u20090.001) at T0 and T1, respectively, but did not change tumour motion amplitude or baseline shift. As a result, CPAP administration led to an absolute decrease in MLD, lung V20Gy, V13Gy and V5Gy of 0.1u202fGy (pu202f=u20090.1), 0.4% (pu202f=u20090.03), 0.5% (pu202f=u20090.04) and 0.5% (pu202f=u20090.2), respectively, while having no significant influence on MHD.ConclusionsIn patients referred for SABR for lung tumours, CPAP increased lung volume without modifying tumour motion or baseline shift. As axa0result, CPAP allowed for axa0slight decrease in radiation dose to the lungs, which is unlikely to be clinically significant.ZusammenfassungZielsetzungAus der Erhöhung des Lungenvolumens und der Verringerung der atembedingten Tumorbewegungsamplitude beim Einsatz des kontinuierlichen positiven Atemwegsdrucks (CPAP „continuous positive airway pressure“) während der stereotaktischen ablativen Strahlentherapie (SABR „stereotactic ablative radiotherapy“) könnte ein erhöhter Schutz von Lunge und Herz resultieren. Diese Studie untersucht die Auswirkung der CPAP auf Lungenvolumen, Tumorbewegungsamplitude und „baseline shift“ sowie deren Einfluss auf die Dosisverteilung.MethodenVon 20xa0Patienten mit Lungentumoren, für die eine SABR indiziert ist, wurden zu zwei verschiedenen Zeitpunkten (T0/T1) 4‑D-Computertomographie-(CT-)Aufnahmen mit und ohne CPAP (CPAP/noCPAP) angefertigt. Zuerst wurden die CPAP- und noCPAP-Aufnahmen hinsichtlich Lungenvolumen, Tumorbewegungsamplitude und „baseline shift“ verglichen. Anschließend wurden CPAP- und noCPAP-Bestrahlungspläne erstellt und bezüglich der Dosisverteilung auf Herz und Lunge gegenübergestellt.ErgebnisseIm Durchschnitt vergrößerte CPAP das Lungenvolumen zu T0 und T1 um 8% (pu202f<u20090,001) bzw. 6,3% (pu202f<u20090,001), ohne Tumorbewegungsamplitude und „baseline shift“ zu verändern. Im Ergebnis verringerte die CPAP die mittlere Strahlendosis auf die Lunge um 0,1u202fGy (pu202f=u20090,1) und die Volumenparameter V20Gy, V13Gy und V5Gy jeweils um 0,4% (pu202f=u20090,03), 0,5% (pu202f=u20090,04) und 0,5% (pu202f=u20090,2), ohne die Strahlendosis auf das Herz zu beeinflussen.SchlussfolgerungBei Patienten, deren Lungentumor einer SABR unterzogen wurde, vergrößerte die CPAP das Lungenvolumen, ohne die Tumorbewegungsamplitude oder den „baseline shift“ zu beeinflussen. Infolgedessen wurde die Strahlendosis auf die Lunge leicht verringert, deren klinische Relevanz ist jedoch unwahrscheinlich.

SU-E-T-198: Comparison Between a PTW MicroDiamond Dosimeter and a Markus Chamber in a 62 MeV/n Carbon Ion Beam

Purpose: To investigate the linear energy transfer (LET) dependence of a PTW Freiburg microDiamond dosimeter, we compared its response to the response of a plane-parallel Markus chamber in a 62 MeV/n mono-energetic carbon ion beam. Methods: The response of both detectors has been studied as a function of depth in graphite by adding or removing graphite plates in front of the detectors. To account for fluctuations of the beam, we used two setups with different monitor chambers. The depth of the effective point of measurement of both detectors has been converted into a graphite equivalent depth using ICRU Report 73 data. As recommended by IAEA TRS-398, the response of the Markus chamber has been corrected for temperature, pressure, polarity effects and ion recombination. The latter required an additional experiment; to quantify the effect of volume recombination and initial recombination, measurements have been performed at different voltages and different dose rates. Results: As expected, the dominant process leading to ion recombination for carbon ion beam is the initial recombination. At the entrance, the ion recombination correction equals 1.1% and the value is approximately constant in the plateau region. Due to the increase of the LET in the Bragg peak region, we observe a strong increase of the ion recombination correction, up to 6.1% at the distal edge. Comparison between the microDiamond response and the Markus chamber response shows good agreement in the plateau region. However, we observe a 13.6% under response of the microDiamond in the Bragg peak. Conclusion: Increasing between 1% and 6%, the depth dependent ion recombination correction has to be applied to the Markus response. The comparison between the microDiamond and the Markus chamber indicates that there is an under-response of the microDiamond in the vicinity of the Bragg peak due to the increased LET.

OC-0378 helical tomotherapy dynamics are not an issue to treat lung tumors for patients coached to ensure regular breathing

Purpose/objective: To evaluate helical tomotherapy (HT) treatment delivery and breathing motion interplay effect on dose distributions using a comprehensive 4D Monte Carlo (MC) dose engine including non-rigid deformation of dose maps computed on a 4D CT scan. Material/methods: Treatment planning is usually performed on a 3DCT image, even though lung tumors may move during delivery. To mitigate this issue, 4DCT-based delineation and appropriate margin definition are used to ensure good tumor coverage. However, treatment beam and breathing-induced motions interplay may lead to clinically unacceptable delivered doses, irrespective of the margin definition technique used. The particular delivery scheme of HT, with synchronous motion of both the gantry and the treatment couch, raise concerns specific to this modality for treating lung tumors. To evaluate the effect of motion interplay on dose distributions, a 4D MC dose computation engine was devised: 1) the MC core was TomoPen, a previously validated MC model of tomotherapy; 2) dose maps were computed on a 4D CT scan (10 phases); 3) resulting dose maps were accumulated through non-rigid deformation. Regular breathing was ensured with patient audio coaching. The treatment sinogram was correlated to the measured breathing period. 4D dose distributions (“interplay simulated”) were computed for 7 patients with a large range of motion amplitudes (up to 11.4 mm in the superior-inferior direction). Those were compared to MC dose distributions calculated on the 3DCT (“planned” dose distributions) and also on the 4DCT with the entire sinogram computed on every single phase, thus accounting only for breathing motion assuming an infinitely slow treatment (“no interplay”). Generalized equivalent uniform doses (gEUDs) and typical DVHs metrics (D95, D2, V95, Dmean, …) were computed for the tumor volumes (CTV and GTV) and compared for all simulation modalities. Results: For all modalities and all 7 patients, dose distributions complied with local clinical requirements (reported as in ICRU 83, RTOG 0618 and 0236 depending on the cases studied). Between “interplay simulated” and “no interplay”, D95 and D2 for tumor volumes were within 2.2% whereas Dmean and gEUDs were within 1% . The maximum difference between planned dose and “interplay simulated” was a 3% increase in Dmean and gEUD (see figure (b)). Since the “no interplay” effect was in agreement within 0.1 % with “interplay simulated”, the difference was attributed to the different quality of images of the 3D and 4D CT data sets. Conclusions: For the patients included in this study, coached to ensure regular breathing, HT delivery and breathing motion interplay was found clinically negligible, confirming in practical clinical routine previous theoretical analysis. Thus, as with 3D conformal static delivery, the problem of covering moving lung tumors may be restricted to the sole definition of margins if gating or tracking technologies are not available.