Hansjoerg Wertz

Potential Effect of Robust and Simple IMRT Approach for Left-Sided Breast Cancer on Cardiac Mortality

PURPOSE Three-dimensional (3D) treatment planning has reduced the cardiac dose in postoperative radiotherapy for breast cancer; however, the overall cardiac toxicity is still an issue because of more aggressive adjuvant treatment. Toxicity models have suggested that a reduction of the heart volume treated to high doses might be particularly advantageous. We compared aperture-based multifield intensity-modulated radiotherapy (IMRT) plans to 3D-planned tangent fields using dose-volume histograms, cardiac toxicity risk, and the robustness to positioning errors. METHODS AND MATERIALS For 14 computed tomography data sets of patients with left-sided breast cancer (unfavorable thoracic geometry), a 3D treatment plan and an IMRT plan were created. The dose-volume histograms were evaluated for the target and risk organs. Excess risk of cardiac mortality was calculated for both approaches using a relative seriality model. Positioning errors were simulated by moving the isocenter. RESULTS IMRT reduced the maximal dose to the left ventricle by a mean of 30.9% (49.14 vs. 33.97 Gy). The average heart volume exposed to >30 Gy was reduced from 45 cm(3) to 5.84 cm(3). The mean dose to the left ventricle was reduced by an average of 10.7% (10.86 vs. 9.7 Gy), and the mean heart dose increased by an average of 24% (from 6.85 to 8.52 Gy). The model-based reduction of the probability for excess therapy-associated cardiac death risk was from 6.03% for the 3D plans to 0.25% for the IMRT plans. CONCLUSION Aperture-based IMRT for left-sided breast cancer significantly reduces the maximal dose to the left ventricle, which might translate into reduced cardiac mortality. Biological modeling might aid in deciding to treat with IMRT but has to be validated prospectively.

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.

Patient-specific 3D pretreatment and potential 3D online dose verification of Monte Carlo-calculated IMRT prostate treatment plans.

PURPOSE Fast and reliable comprehensive quality assurance tools are required to validate the safety and accuracy of complex intensity-modulated radiotherapy (IMRT) plans for prostate treatment. In this study, we evaluated the performance of the COMPASS system for both off-line and potential online procedures for the verification of IMRT treatment plans. METHODS AND MATERIALS COMPASS has a dedicated beam model and dose engine, it can reconstruct three-dimensional dose distributions on the patient anatomy based on measured fluences using either the MatriXX two-dimensional (2D) array (offline) or a 2D transmission detector (T2D) (online). For benchmarking the COMPASS dose calculation, various dose-volume indices were compared against Monte Carlo-calculated dose distributions for five prostate patient treatment plans. Gamma index evaluation and absolute point dose measurements were also performed in an inhomogeneous pelvis phantom using extended dose range films and ion chamber for five additional treatment plans. RESULTS MatriXX-based dose reconstruction showed excellent agreement with the ion chamber (<0.5%, except for one treatment plan, which showed 1.5%), film (∼100% pixels passing gamma criteria 3%/3 mm) and mean dose-volume indices (<2%). The T2D based dose reconstruction showed good agreement as well with ion chamber (<2%), film (∼99% pixels passing gamma criteria 3%/3 mm), and mean dose-volume indices (<5.5%). CONCLUSION The COMPASS system qualifies for routine prostate IMRT pretreatment verification with the MatriXX detector and has the potential for on-line verification of treatment delivery using T2D.

Evaluation of a 2D detector array for patient-specific VMAT QA with different setups.

For pre-treatment plan verification of advanced treatment techniques such as intensity-modulated arc therapy, a fast and reliable dosimetric device is required. In this study, we investigated the suitability of MatriXX in different setups for verification of volumetric modulated arc therapy (VMAT) plans. If MatriXX is used in a stationary phantom (MULTICube), the measured dose is dependent on the beam angle. For the first setup (MatriXX/MULTICube), we developed correction factors (CFs) for each detector element (1020 CFs). We investigated the accuracy of these CFs by verifying 12 VMAT plans. In the second setup, we also assessed the suitability of MatriXX in a dedicated holder. Using this setup (MatriXX/Holder), 30 additional VMAT plans were verified. Deviations of up to ∼17% and ∼11% were noted for one of the ion chambers at 90° and 180° gantry positions. The influence of the beam angle dependence (MULTICube) can explicitly be seen when a gamma criterion of 2%/2 mm was chosen. An overall improvement of 4.3% of passing pixels (pp) was noted after applying beam angular-dependent CFs. When the gamma criterion was 3%/3 mm, the %pp was ≥ 95% without and ∼100% with correction. With the second setup, MatriXX/holder, we showed excellent agreement between measurements and calculations. The %pp averaged over all plans (30 VMAT treatment plans) was nearly ∼100%. The combination of MatriXX with MULTICube or with holder proved to be a fast and reliable method for pretreatment verification of arc therapy with sufficient accuracy.

Einfluss von bildgestützter translatorischer Isozentrumskorrektur auf die Dosisverteilung bei 3-D-Konformationsbestrahlung der Prostata

Hintergrund und Ziel:Interfraktionäre Prostatabewegungen während der Strahlentherapie durch unterschiedliche Ausdehnungen des Rektums können sich negativ auf die Behandlungsqualität auswirken. Die Autoren untersuchten den Einfluss einer bildgestützten linearen Translationskorrektur des Isozentrums auf die Dosisverteilung bei einer dreidimensionalen konformen Bestrahlungstechnik.Material und Methodik:Die Planungs-CTs von sieben Patienten mit leerem und erweitertem Rektum wurden analysiert. Es wurde je ein Referenzplan für Planungszielvolumen (PTV) und Boost (Prostata) auf dem CT-Datensatz mit leerem Rektum mit einer Vier-Felder-Technik berechnet. Der Bestrahlungsplan wurde auf das CT mit erweitertem Rektum übertragen. Dabei wurde zunächst keine Lagekorrektur des Isozentrums durchgeführt, und der Patient wurde relativ zu knöchernen Strukturen ausgerichtet. Danach wurde die Lage des Isozentrums durch eine lineare Translation korrigiert. Die dosimetrischen Konsequenzen und klinischen Auswirkungen wurden analysiert bzw. abgeschätzt.Ergebnisse:Organbewegungen verminderten die Dosisabdeckung der Prostata (95%-Isodose) während einzelner simulierter Behandlungsfraktionen um bis zu –21,0 Prozentpunkte (%-P; Boostplan) und bis zu –14,9%-P in den Samenblasen (PTV-Plan). Die mittlere Dosis im Rektum stieg um bis zu 18,3%-P (PTV-Plan) an. Eine bildgestützte lineare Translationskorrektur (Mittel 6,4 ± 3,4 mm; Maximum 10,8 mm) verbesserte die Dosisabdeckung der Prostata (95%-Isodose) um bis zu 12,7%-P (Boostplan), während die mittlere Dosis im Rektum um bis zu –8,9%-P (PTV-Plan) im Vergleich zum unkorrigierten Plan reduziert werden konnte. Für die Gesamtbehandlung wurde näherungsweise eine Reduktion der Nebenwirkungswahrscheinlichkeit beim Rektum durch die Lagekorrektur um ca. 5%-P errechnet.Schlussfolgerung:Bildgestützte Isozentrumskorrektur durch lineare Translation kann die Behandlungsqualität beim Prostatakarzinom verbessern, wenn geometrische Diskrepanzen innerhalb gewisser Grenzen bleiben.Background and Purpose:Interfractional prostate motion during radiotherapy due to variation in rectal distension can have negative consequences. The authors investigated the dosimetric consequences of a linear translational position correction based on image guidance when a three-dimensional conformal treatment technique was used.Material and Methods:Planning CTs of seven patients with empty and distended rectum were analyzed. A reference plan for the planning target volume (PTV) and the boost were calculated on the CT dataset with the empty rectum with a standard four-field technique. The treatment plan was transferred to the CT with the distended rectum for an uncorrected setup (referenced to bony anatomy) and a corrected setup after position correction of the isocenter. The dosimetric consequences were analyzed.Results:Organ motion decreased the coverage of the prostate by the 95% isodose during simulated single treatment fractions by up to –21.0 percentage points (%-p; boost plan) and by up to –14.9%-p for the seminal vesicles (PTV plan). The mean rectum dose increased by up to 18.3%-p (PTV plan). Linear translational correction (mean 6.4 ± 3.4 mm, maximum 10.8 mm) increased the coverage of the prostate by the 95% isodose by up to 12.7%-p (boost plan), while the mean rectum dose was reduced by up to –8.9%-p (PTV plan). For the complete treatment a reduction of complication probability of the rectum of approximately 5%-p was calculated.Conclusion:The use of an image guidance system with linear translational correction can improve radiation treatment accuracy for prostate cancer, if geometric changes are within certain limits.

Dosimetric consequences of a translational isocenter correction based on image guidance for intensity modulated radiotherapy (IMRT) of the prostate.

Interfractional prostate motion during radiotherapy can have deleterious clinical consequences. It has become clinical practice to re-position the patient according to ultrasound or other imaging techniques. We investigated the dosimetric consequences of the linear translational position correction (isocenter correction) when a conformal IMRT technique with nine fields was used. Treatment plans of seven patients with empty and distended rectums were analyzed. The reference plans were calculated on the CT with an empty rectum. The treatment plans were transferred to a second CT with a distended rectum for an uncorrected setup of the patient referenced to bony anatomy and a corrected setup after translational position correction of the isocenter. The dosimetric consequences (with and without correction) were analyzed. For single treatment fractions, organ motion decreased the volume of the prostate encompassed by the 95% isodose (V95%) by up to -24%-p (percentage points). The mean rectum dose increased by up to 41%-p. Linear translational correction increased V95% of the prostate by up to 17%-p while the mean rectum dose was reduced by up to -23%-p compared to the uncorrected setup. Linear translational correction can improve radiation treatment accuracy for prostate cancer if geometrical changes are within certain limits.

[Dosimetric impact of image-guided translational isocenter correction for 3-D conformal radiotherapy of the prostate].

Hintergrund und Ziel:Interfraktionäre Prostatabewegungen während der Strahlentherapie durch unterschiedliche Ausdehnungen des Rektums können sich negativ auf die Behandlungsqualität auswirken. Die Autoren untersuchten den Einfluss einer bildgestützten linearen Translationskorrektur des Isozentrums auf die Dosisverteilung bei einer dreidimensionalen konformen Bestrahlungstechnik.Material und Methodik:Die Planungs-CTs von sieben Patienten mit leerem und erweitertem Rektum wurden analysiert. Es wurde je ein Referenzplan für Planungszielvolumen (PTV) und Boost (Prostata) auf dem CT-Datensatz mit leerem Rektum mit einer Vier-Felder-Technik berechnet. Der Bestrahlungsplan wurde auf das CT mit erweitertem Rektum übertragen. Dabei wurde zunächst keine Lagekorrektur des Isozentrums durchgeführt, und der Patient wurde relativ zu knöchernen Strukturen ausgerichtet. Danach wurde die Lage des Isozentrums durch eine lineare Translation korrigiert. Die dosimetrischen Konsequenzen und klinischen Auswirkungen wurden analysiert bzw. abgeschätzt.Ergebnisse:Organbewegungen verminderten die Dosisabdeckung der Prostata (95%-Isodose) während einzelner simulierter Behandlungsfraktionen um bis zu –21,0 Prozentpunkte (%-P; Boostplan) und bis zu –14,9%-P in den Samenblasen (PTV-Plan). Die mittlere Dosis im Rektum stieg um bis zu 18,3%-P (PTV-Plan) an. Eine bildgestützte lineare Translationskorrektur (Mittel 6,4 ± 3,4 mm; Maximum 10,8 mm) verbesserte die Dosisabdeckung der Prostata (95%-Isodose) um bis zu 12,7%-P (Boostplan), während die mittlere Dosis im Rektum um bis zu –8,9%-P (PTV-Plan) im Vergleich zum unkorrigierten Plan reduziert werden konnte. Für die Gesamtbehandlung wurde näherungsweise eine Reduktion der Nebenwirkungswahrscheinlichkeit beim Rektum durch die Lagekorrektur um ca. 5%-P errechnet.Schlussfolgerung:Bildgestützte Isozentrumskorrektur durch lineare Translation kann die Behandlungsqualität beim Prostatakarzinom verbessern, wenn geometrische Diskrepanzen innerhalb gewisser Grenzen bleiben.Background and Purpose:Interfractional prostate motion during radiotherapy due to variation in rectal distension can have negative consequences. The authors investigated the dosimetric consequences of a linear translational position correction based on image guidance when a three-dimensional conformal treatment technique was used.Material and Methods:Planning CTs of seven patients with empty and distended rectum were analyzed. A reference plan for the planning target volume (PTV) and the boost were calculated on the CT dataset with the empty rectum with a standard four-field technique. The treatment plan was transferred to the CT with the distended rectum for an uncorrected setup (referenced to bony anatomy) and a corrected setup after position correction of the isocenter. The dosimetric consequences were analyzed.Results:Organ motion decreased the coverage of the prostate by the 95% isodose during simulated single treatment fractions by up to –21.0 percentage points (%-p; boost plan) and by up to –14.9%-p for the seminal vesicles (PTV plan). The mean rectum dose increased by up to 18.3%-p (PTV plan). Linear translational correction (mean 6.4 ± 3.4 mm, maximum 10.8 mm) increased the coverage of the prostate by the 95% isodose by up to 12.7%-p (boost plan), while the mean rectum dose was reduced by up to –8.9%-p (PTV plan). For the complete treatment a reduction of complication probability of the rectum of approximately 5%-p was calculated.Conclusion:The use of an image guidance system with linear translational correction can improve radiation treatment accuracy for prostate cancer, if geometric changes are within certain limits.

Fast kilovoltage/megavoltage (kVMV) breathhold cone-beam CT for image-guided radiotherapy of lung cancer

Long image acquisition times of 60-120 s for cone-beam CT (CBCT) limit the number of patients with lung cancer who can undergo volume image guidance under breathhold. We developed a low-dose dual-energy kilovoltage-megavoltage-cone-beam CT (kVMV-CBCT) based on a clinical treatment unit reducing imaging time to < or =15 s. Simultaneous kVMV-imaging was achieved by dedicated synchronization hardware controlling the output of the linear accelerator (linac) based on detector panel readout signals, preventing imaging artifacts from interference of the linacs MV-irradiation and panel readouts. Optimization was performed to minimize the imaging dose. Single MV-projections, reconstructed MV-CBCT images and images of simultaneous 90 degrees kV- and 90 degrees MV-CBCT (180 degrees kVMV-CBCT) were acquired with different parameters. Image quality and imaging dose were evaluated and compared to kV-imaging. Hardware-based kVMV synchronization resulted in artifact-free projections. A combined 180 degrees kVMV-CBCT scan with a total MV-dose of 5 monitor units was acquired in 15 s and with sufficient image quality. The resolution was 5-6 line pairs cm(-1) (Catphan phantom). The combined kVMV-scan dose was equivalent to a kV-radiation scan dose of approximately 33 mGy. kVMV-CBCT based on a standard linac is promising and can provide ultra-fast online volume image guidance with low imaging dose and sufficient image quality for fast and accurate patient positioning for patients with lung cancer under breathhold.

Breath-Hold Target Localization With Simultaneous Kilovoltage/Megavoltage Cone-Beam Computed Tomography and Fast Reconstruction

PURPOSE Hypofractionated high-dose radiotherapy for small lung tumors has typically been based on stereotaxy. Cone-beam computed tomography and breath-hold techniques have provided a noninvasive basis for precise cranial and extracranial patient positioning. The cone-beam computed tomography acquisition time of 60 s, however, is beyond the breath-hold capacity of patients, resulting in respiratory motion artifacts. By combining megavoltage (MV) and kilovoltage (kV) photon sources (mounted perpendicularly on the linear accelerator) and accelerating the gantry rotation to the allowed limit, the data acquisition time could be reduced to 15 s. METHODS AND MATERIALS An Elekta Synergy 6-MV linear accelerator, with iViewGT as the MV- and XVI as the kV-imaging device, was used with a Catphan phantom and an anthropomorphic thorax phantom. Both image sources performed continuous image acquisition, passing an angle interval of 90° within 15 s. For reconstruction, filtered back projection on a graphics processor unit was used. It reconstructed 100 projections acquired to a 512 × 512 × 512 volume within 6 s. RESULTS The resolution in the Catphan phantom (CTP528 high-resolution module) was 3 lines/cm. The spatial accuracy was within 2-3 mm. The diameters of different tumor shapes in the thorax phantom were determined within an accuracy of 1.6 mm. The signal-to-noise ratio was 68% less than that with a 180°-kV scan. The dose generated to acquire the MV frames accumulated to 82.5 mGy, and the kV contribution was <6 mGy. CONCLUSION The present results have shown that fast breath-hold, on-line volume imaging with a linear accelerator using simultaneous kV-MV cone-beam computed tomography is promising and can potentially be used for image-guided radiotherapy for lung cancer patients in the near future.

Patient-specific online dose verification based on transmission detector measurements

BACKGROUND AND PURPOSE Since IMRT-techniques lead to an increasingly complicated environment, a patient specific IMRT-plan verification is recommended. Furthermore, verifications during patient irradiation and 3D dose reconstruction have the potential to improve treatment delivery, accuracy and safety. This study provides a detailed investigation of the new transmission detector (DTD) Dolphin (IBA Dosimetry, Germany) for online dosimetry. MATERIALS AND METHODS The clinical performance of the DTD was tested by dosimetric plan verification in 2D and 3D for 18 IMRT-sequences. In 2D, DTD measurements were compared to a pre-treatment verification method and a treatment planning system by gamma index and dose difference evaluations. In 3D, dose-volume-histogram (DVH) indices and gamma analysis were evaluated. Furthermore, the error detection ability was tested with leaf position uncertainties and deviations in the linear accelerator (LINAC) output. RESULTS The DTD measurements were in excellent agreement to reference measurements in both 2D (γ3%,3mm=(99.7±0.6)% <1, ΔD±5%=(99.5±0.5)%) and 3D. Only a small dose underestimation (<2%) within the target volume was observed when analyzing DVH-indices. Positional errors of the leaf banks larger than 1mm and errors in LINAC output larger than 2% were identified with the DTD. CONCLUSIONS The DTD measures the delivered dose with sufficient accuracy and is therefore suitable for clinical routine.