Florian Stieler

Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer

INTRODUCTION Volumetric modulated arc therapy (VMAT), a complex treatment strategy for intensity-modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares VMAT against established IMRT and 3D-conformal radiation therapy (3D-CRT) delivery techniques. METHODS Based on CT datasets of 9 patients treated for prostate cancer step-and-shoot IMRT, serial tomotherapy (MIMiC), 3D-CRT and VMAT were compared with regard to plan quality and treatment efficiency. Two VMAT approaches (one rotation (VMAT1x) and one rotation plus a second 200 degrees rotation (VMAT2x)) were calculated for the plan comparison. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D(95%) (dose encompassing 95% of the target volume). For plan efficiency evaluation, treatment time and number of monitor units (MU) were considered. RESULTS For MIMiC/IMRT(MLC)/VMAT2x/VMAT1x/3D-CRT, mean CI was 1.5/1.23/1.45/1.51/1.46 and HI was 1.19/1.1/1.09/1.11/1.04. For a prescribed dose of 76 Gy, mean doses to organs-at-risk (OAR) were 50.69 Gy/53.99 Gy/60.29 Gy/61.59 Gy/66.33 Gy for the anterior half of the rectum and 31.85 Gy/34.89 Gy/38.75 Gy/38.57 Gy/55.43 Gy for the posterior rectum. Volumes of non-target normal tissue receiving > or =70% of prescribed dose (53 Gy) were 337 ml/284 ml/482 ml/505 ml/414 ml, for > or =50% (38 Gy) 869 ml/933 ml/1155 ml/1231 ml/1993 ml and for > or =30% (23 Gy) 2819 ml/3414 ml/3340 ml/3438 ml /3061 ml. D(95%) was 69.79 Gy/70.51 Gy/71,7 Gy/71.59 Gy/73.42 Gy. Mean treatment time was 12 min/6 min/3.7 min/1.8 min/2.5 min. CONCLUSION All approaches yield treatment plans of improved quality when compared to 3D-conformal treatments, with serial tomotherapy providing best OAR sparing and VMAT being the most efficient treatment option in our comparison. Plans which were calculated with 3D-CRT provided good target coverage but resulted in higher dose to the rectum.

Radiotherapy for Early Mediastinal Hodgkin Lymphoma According to the German Hodgkin Study Group (GHSG): The Roles of Intensity-Modulated Radiotherapy and Involved-Node Radiotherapy

PURPOSE Cure rates of early Hodgkin lymphoma (HL) are high, and avoidance of late complications and second malignancies have become increasingly important. This comparative treatment planning study analyzes to what extent target volume reduction to involved-node (IN) and intensity-modulated (IM) radiotherapy (RT), compared with involved-field (IF) and three-dimensional (3D) RT, can reduce doses to organs at risk (OAR). METHODS AND MATERIALS Based on 20 computed tomography (CT) datasets of patients with early unfavorable mediastinal HL, we created treatment plans for 3D-RT and IMRT for both the IF and IN according to the guidelines of the German Hodgkin Study Group (GHSG). As OAR, we defined heart, lung, breasts, and spinal cord. Dose-volume histograms (DVHs) were evaluated for planning target volumes (PTVs) and OAR. RESULTS Average IF-PTV and IN-PTV were 1705 cm(3) and 1015 cm(3), respectively. Mean doses to the PTVs were almost identical for all plans. For IF-PTV/IN-PTV, conformity was better with IMRT and homogeneity was better with 3D-RT. Mean doses to the heart (17.94/9.19 Gy for 3D-RT and 13.76/7.42 Gy for IMRT) and spinal cord (23.93/13.78 Gy for 3D-RT and 19.16/11.55 Gy for IMRT) were reduced by IMRT, whereas mean doses to lung (10.62/8.57 Gy for 3D-RT and 12.77/9.64 Gy for IMRT) and breasts (left 4.37/3.42 Gy for 3D-RT and 6.04/4.59 Gy for IMRT, and right 2.30/1.63 Gy for 3D-RT and 5.37/3.53 Gy for IMRT) were increased. Volume exposed to high doses was smaller for IMRT, whereas volume exposed to low doses was smaller for 3D-RT. Pronounced benefits of IMRT were observed for patients with lymph nodes anterior to the heart. IN-RT achieved substantially better values than IF-RT for almost all OAR parameters, i.e., dose reduction of 20% to 50%, regardless of radiation technique. CONCLUSIONS Reduction of target volume to IN most effectively improves OAR sparing, but is still considered investigational. For the time being, IMRT should be considered for large PTVs especially when the anterior mediastinum is involved.

Experimental validation of a commercial 3D dose verification system for intensity-modulated arc therapies

We validate the dosimetric performance of COMPASS®, a novel 3D quality assurance system for verification of volumetric-modulated arc therapy (VMAT) treatment plans that can correlate the delivered dose to the patients anatomy, taking into account the tissue inhomogeneity. The accuracy of treatment delivery was assessed by the COMPASS® for 12 VMAT plans, and the resulting assessments were evaluated using an ionization chamber and film measurements. Dose-volume relationships were evaluated by the COMPASS® for three additional treatment plans and these were used to verify the accuracy of treatment planning dose calculations. The results matched well between COMPASS® and measurements for the ionization chamber (≤3%) and film (73-99% for gamma((3%/3 mm)) < 1 and 98-100% for gamma((5%/5 mm)) < 1) for the phantom plans. Differences in dose-volume statistics for the average dose to the PTV were within 2.5% for three treatment plans. For the structures located in the low-dose region, a maximum difference of <9% was observed. In its current implementation, the system could measure the delivered dose with sufficient accuracy and could project the 3D dose distribution directly on the patients anatomy. Slight deviations were found for large open fields. These could be minimized by improving the COMPASS® in-built beam model.

Clinical Implementation of Volumetric Intensity-Modulated Arc Therapy (VMAT) with ERGO++

Background and Purpose:Volumetric modulated arc therapy (VMAT) has the potential to deliver dose distributions comparable to the established intensity-modulated radiotherapy techniques for a multitude of target paradigms. Prior to implementing VMAT into their clinical routine in December 2008, the authors evaluated the dose calculation/delivery accuracy of 24 sample VMAT plans (prostate and anal cancer target paradigms) with film and ionization dosimetry. After the start of the clinical program, in vivo measurements with a rectal probe were performed.Material and Methods:The VMAT plans were generated by the treatment-planning system (TPS) ERGO++ (Elekta, Crawley, UK) and transferred to a phantom. Film dosimetry was performed with Kodak EDR2 films, and evaluated with dose profiles and γ-index analysis. Appropriate ionization chambers were used for absolute dose measurements in the phantom and for in vivo measurements. The ionization chamber was used with localization of the measurement volume based on positioning cone-beam computed tomography.Results:Plans were transferred from ERGO++ to the record and verify (R&V) system/linear accelerator (linac). The absolute dose deviations recorded with the ionization chamber were 1.74% ± 1.62% across both indications. The γ-index analysis of the film dosimetry showed no deviation > 3%/3 mm in the high-dose region. On in vivo measurements, a deviation between calculation and measurement of 2.09% ± 2.4% was recorded, when the chamber was successfully positioned in the high-dose region.Conclusion:VMAT plans can be planned and treated reproducibly in high quality after the commissioning of the complete delivery chain consisting of TPS, R&V system and linac. The results of the individual plan verification meet the commonly accepted requirements. The first in vivo measurements confirm the reproducible precision of the delivered dose during clinical treatments.ZusammenfassungHintergrund und Ziel:Die volumetrisch modulierte Arc-Therapie (VMAT) bietet die Möglichkeit, für einige Planparadigmata zur bisher etablierten intensitätsmodulierten Strahlentherapie vergleichbare Dosisverteilungen zu generieren. Vor der im Dezember 2008 erfolgten Einführung von VMAT in die eigene klinische Routine überprüften die Autoren Dosisberechnung und Bestrahlungsgenauigkeit anhand von 24 VMAT-Plänen (Anal- und Prostatakarzinomplanungsparadigmata) mittels Film- und Ionisationsdosimetrie. Erste Patientenbestrahlungen wurden mittels rektaler In-vivo-Dosimetrie verifiziert.Material und Methodik:Die VMAT-Pläne wurden mit dem Planungssystem ERGO++ (Elekta, Crawley, UK) generiert und in einem Phantom verifiziert. Filmdosimetrie wurde mittels Kodak-EDR2-Film, Dosisprofilen und der γ-Analyse realisiert. Geeignete Ionisationskammern wurden für absolute Dosismessungen im Phantom und für die In-vivo-Dosimetrie verwendet. Ein Cone-Beam-Computertomogramm wurde für die Lokalisation des Messvolumens der Ionisationskammer im Rektum verwendet.Ergebnisse:Die Pläne wurden durchgängig fehlerfrei von ERGO++ an das „record and verify“-(R&V-)System und an den Beschleuniger übertragen. Die mittlere Abweichung der Absolutdosimetrie betrug 1,74% ± 1,62%. Die γ-Index-Analyse der Filmdosimetrie zeigte keine Abweichung > 3%/3 mm im Hochdosisbereich. Die In-vivo-Messungen ergaben nach erfolgreicher Positionierung im Hochdosisbereich eine mittlere Abweichung zwischen berechneter und applizierter Dosis von 2,09% ± 2,4%.Schlussfolgerung:VMAT-Pläne können auf Basis der klinisch zugelassenen Kette aus Planungs-, R&V- und Bestrahlungssystem nach adäquater Kommissionierung reproduzierbar erzeugt und zuverlässig bestrahlt werden. Die Ergebnisse der Individualplanverifikation erfüllen die allgemein akzeptierten Bedingungen. Erste in vivo ermittelte Dosen bestätigen die Präzision der Dosisapplikation im klinischen Einsatz.

Deep Inspiration Breath Hold-Based Radiation Therapy: A Clinical Review.

Several recent developments in linear accelerator-based radiation therapy (RT) such as fast multileaf collimators, accelerated intensity modulation paradigms like volumeric modulated arc therapy and flattening filter-free (FFF) high-dose-rate therapy have dramatically shortened the duration of treatment fractions. Deliverable photon dose distributions have approached physical complexity limits as a consequence of precise dose calculation algorithms and online 3-dimensional image guided patient positioning (image guided RT). Simultaneously, beam quality and treatment speed have continuously been improved in particle beam therapy, especially for scanned particle beams. Applying complex treatment plans with steep dose gradients requires strategies to mitigate and compensate for motion effects in general, particularly breathing motion. Intrafractional breathing-related motion results in uncertainties in dose delivery and thus in target coverage. As a consequence, generous margins have been used, which, in turn, increases exposure to organs at risk. Particle therapy, particularly with scanned beams, poses additional problems such as interplay effects and range uncertainties. Among advanced strategies to compensate breathing motion such as beam gating and tracking, deep inspiration breath hold (DIBH) gating is particularly advantageous in several respects, not only for hypofractionated, high single-dose stereotactic body RT of lung, liver, and upper abdominal lesions but also for normofractionated treatment of thoracic tumors such as lung cancer, mediastinal lymphomas, and breast cancer. This review provides an in-depth discussion of the rationale and technical implementation of DIBH gating for hypofractionated and normofractionated RT of intrathoracic and upper abdominal tumors in photon and proton RT.

A comparison of several modulated radiotherapy techniques for head and neck cancer and dosimetric validation of VMAT

PURPOSE Volumetric modulated arc therapy (VMAT) has the potential to shorten treatment times for fluence modulated radiotherapy. We compared dose distributions of VMAT, step-and-shoot IMRT and serial tomotherapy for typical head and neck (H&N) planning target volumes (PTV) with sparing of one parotid, a complex paradigm and a situation often encountered in H&N radiotherapy. Finally, we validated the dosimetric accuracy of VMAT delivery. MATERIAL AND METHODS Based on CT datasets of 10 patients treated for H&N cancer (PTV1:60 Gy/PTV2:56 Gy) with IMRT (7/9 fields), serial tomotherapy (MIMiC) and VMAT were compared with regard to plan quality and treatment efficiency. Plan quality was assessed by calculating homogeneity/conformity index (HI/CI), mean dose to parotid and brain stem and the maximum dose to the spinal cord. For plan efficiency evaluation, total treatment time (TTT) and number of monitor units (MU) were considered. A dosimetric evaluation of VMAT was performed using radiosensitive film, ion chamber and 2D-array. RESULTS For MIMiC/IMRT(7F)/IMRT(9F)/VMAT, mean CI was 1.98/2.23/2.23/1.82, HI(PTV1) was 1.12/1.20/1.20/1.11 and HI(PTV2) was 1.11/1.15/1.13/1.12. Mean doses to the shielded parotid were 19.5 Gy/14.1 Gy/13.9 Gy/14.9 Gy and the spinal cord received maximum doses of 43.6 Gy/40.8 Gy/41.6 Gy/42.6 Gy. The mean MUs were 2551/945/925/521 and the mean TTT was 12.8 min/7.6 min/8.5 min/4.32 min. The ion chamber measurements showed an absolute deviation of 0.08 ± 1.10% and 98.45 ± 3.25% pixels passed γ-analyses for 3%/3mm and 99.95 ± 0.09% for 5%/5mm for films. 2D-array measurements reported an agreement for 3%/3mm of 95.65 ± 2.47%-98.33 ± 0.65% and for 5%/5mm 99.79 ± 0.24%-99.92 ± 0.09% depending on the measurement protocol. CONCLUSION All treatment paradigms produced plans of excellent quality and dosimetric accuracy with IMRT providing best OAR sparing and VMAT being the most efficient treatment option in our comparison of treatment plans with high complexity.

Performance of an atlas-based autosegmentation software for delineation of target volumes for radiotherapy of breast and anorectal cancer

BACKGROUND AND PURPOSE To validate atlas-based autosegmentation for contouring breast/anorectal targets. METHODS AND MATERIALS ABAS uses atlases with defined CTVs as template cases to automatically delineate target volumes in other patient CT-datasets. Results are compared with manually contoured CTVs of breast/anorectal cancer according to RTOG-guidelines. The impact of using specific atlases matched to individual patient geometry was evaluated. Results were quantified by analyzing Dice Similarity Coefficient (DSC), logit(DSC) and Percent Overlap (PO). DSC >0.700 and logit(DSC) >0.847 are acceptable. In addition a new algorithm (STAPLE) was evaluated. RESULTS ABAS produced good results for the CTV of breast/anorectal cancer targets. Delineation of inguinal lymphatic drainage, however, was insufficient. Results for breast CTV were (DSC: 0.86-0.91 ([0,1]), logit(DSC): 1.82-2.36 ([-∞,∞]), PO: 75.5-82.89%) and for anorectal CTVA (DSC: 0.79-0.85, logit(DSC): 1.40-1.77, PO: 68-73.67%). CONCLUSIONS ABAS produced satisfactory results for these clinical target volumes that are defined by more complex tissue interface geometry, thus streamlining and facilitating the radiotherapy workflow which is essential to face increasing demand and limited resources. STAPLE improved contouring outcome. Small target volumes not clearly defined are still to be delineated manually. Based on these results, ABAS has been clinically introduced for precontouring of CTVs/OARs.

A fast radiotherapy paradigm for anal cancer with volumetric modulated arc therapy (VMAT)

Background/PurposeRadiotherapy (RT) volumes for anal cancer are large and of moderate complexity when organs at risk (OAR) such as testis, small bowel and bladder are at least partially to be shielded. Volumetric intensity modulated arc therapy (VMAT) might provide OAR-shielding comparable to step-and-shoot intensity modulated radiotherapy (IMRT) for this tumor entity with better treatment efficiency.Materials and methodsBased on treatment planning CTs of 8 patients, we compared dose distributions, comformality index (CI), homogeneity index (HI), number of monitor units (MU) and treatment time (TTT) for plans generated for VMAT, 3D-CRT and step-and-shoot-IMRT (optimized based on Pencil Beam (PB) or Monte Carlo (MC) dose calculation) for typical anal cancer planning target volumes (PTV) including inguinal lymph nodes as usually treated during the first phase (0-36 Gy) of a shrinking field regimen.ResultsWith values of 1.33 ± 0.21/1.26 ± 0.05/1.3 ± 0.02 and 1.39 ± 0.09, the CIs for IMRT (PB-Corvus/PB-Hyperion/MC-Hyperion) and VMAT are better than for 3D-CRT with 2.00 ± 0.16. The HIs for the prescribed dose (HI36) for 3D-CRT were 1.06 ± 0.01 and 1.11 ± 0.02 for VMAT, respectively and 1.15 ± 0.02/1.10 ± 0.02/1.11 ± 0.08 for IMRT (PB-Corvus/PB-Hyperion/MC-Hyperion). Mean TTT and MUs for 3D-CRT is 220s/225 ± 11MU and for IMRT (PB-Corvus/PB-Hyperion/MC-Hyperion) is 575s/1260 ± 172MU, 570s/477 ± 84MU and 610s748 ± 193MU while TTT and MU for two-arc-VMAT is 290s/268 ± 19MU.ConclusionVMAT provides treatment plans with high conformity and homogeneity equivalent to step-and-shoot-IMRT for this mono-concave treatment volume. Short treatment delivery time and low primary MU are the most important advantages.

Intensity modulated radiosurgery of brain metastases with flattening filter-free beams

PURPOSE Flattening filter free (FFF) irradiation potentially reduces treatment delivery time in radiosurgery thus eliminating intrafraction motion and increasing patient comfort. We compared plan quality and efficiency of VMAT and IMRT plans for FFF- and standard delivery for brain metastases with single fraction doses of 20 Gy and validated the dosimetric accuracy of the FFF delivery. MATERIAL AND METHODS CT data of 15 patients with brain metastases were included in this study. For every patient, 2 IMRT- and 2 VMAT-plans were created using a high-resolution MLC with two different delivery modes (6MV standard vs. 6MV FFF). Plan quality and efficiency was assessed by analysis of conformity, homogeneity, dose gradients, treatment delivery time and number of monitor units (MU). Dosimetric evaluation was performed for 10 FFF plans with radiochromic film and ion chamber. RESULTS Plan quality was similar for both approaches. FFF provided a mean treatment time reduction of 51.5% with similar MU for VMAT and IMRT for this low-modulation paradigm. The dosimetric validations showed an absolute dose deviation of +0.93 ± 0.99% and γ-index analysis (3%/3mm and 3%/1mm) resulted in agreement of 99.08 ± 1.58% respectively 93.46 ± 2.41%. CONCLUSION FFF radiosurgery is an efficient technique for intensity modulated hypofractionated or single fraction treatments with similar plan quality when compared to flattened beams at reduced treatment time.

Flattening-filter-free intensity modulated breath-hold image-guided SABR (Stereotactic ABlative Radiotherapy) can be applied in a 15-min treatment slot

Hypofractionated image-guided stereotactic ablative radiotherapy (igSABR) is effective in small lung/liver lesions. Computer-assisted breath-hold reduces intrafraction motion but, as every gating/triggering strategy, reduces the duty cycle, resulting in long fraction times if combined with intensity-modulated radiotherapy (IMRT). 10 MV flattening-filter-free IMRT reduces daily fraction duration to <10 min for single doses of 5-20 Gy.