Prospective Comparison of Hypofractionated Versus Normofractionated Intensity-Modulated Radiotherapy in Breast Cancer: Late Toxicity Results of the Non-Inferiority KOSIMA Trial (ARO2010-3).

Purpose: To compare the late toxicity profile of hypofractionation and normofractionation for whole-breast radiotherapy in breast cancer (BC) patients after conserving surgery. Methods: Sixty-year-old or older patients with pTis-pT3, pN0-pN1a, M0 BC were recruited and stratified to hypofractionated (arm R-HF) or normofractionated (arm L-NF) intensity-modulated radiotherapy (IMRT), for right- and left-sided BC, respectively, in this single-center, non-randomized, non-inferiority trial. A boost was allowed if indicated. The primary outcome was the cumulative percentage of patients developing grade III fibrosis, grade I telangiectasia, and/or grade II hyperpigmentation after 2 years, with a pre-specified non-inferiority margin of 15% increase from an expected 2-year toxicity rate of 20%. Results: The Median follow-up was 4.93 (0.57-8.65) years for R-HF and 5.02 (0.65-8.72) years for L-NF (p=0.236). The median age was 68 (60-83 and 60-80) years, respectively. In total, 226 patients were recruited (107 for R-HF and 119 for L-NF), with 100 and 117 patients suitable for assessment, respectively. A boost was delivered in 51% and 53% of each arm, respectively. Median PTV volumes were 1013.6 (273-2805) cm3 (R-HF) and 1058.28 (315-2709) cm3 (L-NF, p=0.591). The 2-year primary endpoint rate was 6.1% (95% CI 1.3-11.7, n=5 of 82) and 13.3% (95% CI 7-20.2, n=14 of 105), respectively (absolute difference -7.2%, one-sided 95% CI ∞ to -0.26, favoring R-HF). No local recurrence-free- or overall-survival differences were found. Conclusion: In this prospective non-randomized study, hypofractionation did not have higher toxicity than normofractionated whole-breast IMRT.

Local dose rate effects in implantable cardioverter-defibrillators with flattening filter free and flattened photon radiation.

PURPOSE: In the beam penumbra of stereotactic body radiotherapy volumes, dose rate effects in implantable cardioverter-defibrillators (ICDs) may be the predominant cause for failures in the absence of neutron-generating photon energies. We investigate such dose rate effects in ICDs and provide evidence for safe use of lung tumor stereotactic radioablation with flattening filter free (FFF) and flattened 6 Megavolt (MV) beams in ICD-bearing patients. METHODS: Sixty-two ICDs were subjected to scatter radiation in 1.0, 2.5, and 7.0 cm distance to 100 Gy within a 5â€¯× 5 cm2 radiation field. Radiation was applied with 6 MV FFF beams (constant dose rate of 1400 cGy/min) and flattened (FLAT) 6 MV beams (430 cGy/min). Local dose rates (LDR) at the position of all ICDs were measured. All ICDs were monitored continuously. RESULTS: With 6 MV FFF beams, ICD errors occurred at distances of 1.0 cm (LDR 46.8 cGy/min; maximum ICD dose 3.4 Gy) and 2.5 cm (LDR 15.6 cGy/min; 1.1 Gy). With 6 MV FLAT beams, ICD errors occurred only at 1 cm distance (LDR 16.8 cGy/min; 3.9 Gy). No errors occurred at an LDR below 7 cGy/min, translating to a safe distance of 2.5 cm (1.5 Gy) in flattened and 7 cm (0.4 Gy) in 6 MV FFF beams. CONCLUSION: A LDR in ICDs larger than 7 cGy/min may cause ICD malfunction. At identical LDR, differences between 6 MV FFF and 6 MV FLAT beams do not yield different rates of malfunction. The dominant reason for ICD failures could be the LDR and not the total dose to the ICD. For most stereotactic treatments, it is recommended to generate a planning risk volume around the ICD in which LDR larger than 7 cGy/min are avoided.

Multiple direction needle-path planning and inverse dose optimization for robotic low-dose rate brachytherapy.

PURPOSE: Robotic systems to assist needle placements for low-dose rate brachytherapy enable conformal dose planning only restricted to path planning around risk structures. We report a treatment planning system (TPS) combining multiple direction needle-path planning with inverse dose optimization algorithms. METHODS: We investigated in a path planning algorithm to efficiently locate needle injection points reaching the target volume without puncturing risk structures. A candidate needle domain with all combinations of trajectories is used for the optimization process. We report a modular algorithm for inverse radiation plan optimization. The initial plan with V100>99% is generated by the "greedy optimizer". The "remove-seed algorithm" reduces the number of seeds in the high dose regions. The "depth-optimizer" varies the insertion depth of the needles. The "coverage-optimizer" locates under-dosed areas in the target volume and supports them with an additional amount of seeds. The dose calculation algorithm is benchmarked on an image set of a phantom with a liver metastasis (prescription dose Dpr=100Gy) and is re-planned in a commercial CE-marked TPS to compare the calculated dose grids using a global gamma analysis. The inverse optimizer is benchmarked by calculating 10 plans on the same phantom to investigate the stability and statistical variability of the dose parameters. RESULTS: The path planning algorithm efficiently removes 72.5% of all considered injection points. The candidate needle domain consists of combinations of 1971 tip points and 827 injection points. The global gamma analysis with gamma 1%=2.9Gy, 1mm showed a pass rate of 98.5%. The dose parameters were V100=99.1±0.3%, V150=76.4±2.5%, V200=44.5±5.5% and D90=125.9±3.6Gy and 10.7±1.3 needles with 34.0±0.8 seeds were used. The median of the TPS total running time was 4.4minutes. CONCLUSIONS: The TPS generates treatment plans with acceptable dose coverage in a reasonable amount of time. The gamma analysis shows good accordance to the commercial TPS. The TPS allows taking full advantage of robotic navigation tools to enable a new precise and safe method of minimally invasive low-dose-rate brachytherapy.

Prospective assessment of mask versus frame fixation during Gamma Knife treatment for brain metastases.

PURPOSE: The newest generation of the Leksell Gamma Knife (GK) allows frame based as well as frameless treatment. We here report outcomes of a prospective non-randomized study on mask fixation (MF) versus frame fixation (FF) for GK treatment of brain metastases. METHODS: The decision for FF or MF was made on a case-by-case basis. Factors considered were patients' preference, proximity of critical structures, V12 and treatment time. Either stereotactic radiosurgery or fractionated stereotactic radiotherapy in up to 3 fractions was performed. For MF, a PTV margin of 1 mm was added. Follow-up included quarterly MRI scans. The primary outcome was local control. Secondary endpoints were progression-free survival (PFS), overall survival (OS) and the incidence of radionecrosis. RESULTS: A total of 197 lesions (169 FF and 28 MF) were treated in 76 patients (59 FF and 17 MF). 187 lesions were treated with SRS and 10 with FSRT. Median dose was 22 Gy in both groups and median follow-up was 9.3 months. There was a higher local failure rate (HR: 3.69; 95%CI: 1.13-12.0; p = 0.03) with 11 local failures in the FF and none in the MF cohort. No differences were observed between the groups for OS (median: n.r. vs. 16.9 months; HR:1.00; 95%CI: 0.41-2.46; p = 0.999) and PFS (median: 6.9 vs. 8.4 months; HR: 0.92; 95%CI: 0.47-1.79; p = 0.800). Three cases of radionecrosis occurred with FF but none with MF (p = 0.67). CONCLUSIONS: Gamma Knife treatment with MF does not result in worse outcome or increased rates of radionecrosis in this non-randomized study.

Validation of frame-based positioning accuracy with cone-beam computed tomography in Gamma Knife Icon radiosurgery.

BACKGROUND: Frame based positioning accuracy in Gamma Knife (GK) stereotactic radiosurgery (SRS) is extremely high but removal of a post may be necessary to enable the treatment in selected patients. OBJECTIVE: To verify the positioning accuracy in clinical scenarios with 4 and 3 posts in patients and phantoms using cone-beam CT (CBCT) of Gamma Knife Icon™. METHODS: We analyzed positioning accuracy for 12 patients with standard 4 post setup using pretreatment CBCT (pre-CBCT) on GK Icon™ and report 4 patients with different clinical scenarios (removal of a post). We performed phantom measurements to verify the frame accuracy via CBCT in different clinical scenarios without the influence of the human patient. RESULTS: Mean frame accuracy for 12 patients with 4 posts was 0.35 mm/0.34 degree. Mean motion during treatment was 0.11 mm/0.04 degree. For two of the clinical scenarios where a post was removed, we found acceptable deviations within 0.66 mm/0.61 degree. For 2 patients, a deviation of 2.94 mm/-3.47 degree and 1.85 mm/-0.74 degree was found and replanning was necessary. Phantom measurements showed good agreement when planning MR/CT was performed with 4 or 3 post. Larger deviations of 0.86 mm/0.88 degree were detected when a post was removed after planning MR/CT. CONCLUSION: The frame accuracy with 4 posts before and during GK treatments is as high as expected. For clinical situations, where a post is removed after planning-CT/MR, pre-treatment position verification is strongly suggested using stereotactic CBCT or the P-CT/MR should be repeated to avoid possible mistreatments.

Accelerating total body irradiation with large field modulated arc therapy in standard treatment rooms without additional equipment.

PURPOSE: The aim of this study was to develop a generic and ultra-efficient modulated arc technique for treatment with total body irradiation (TBI) without additional equipment in standard treatment rooms. METHODS: A continuous gantry arc between 300° and 70° composed of 26 subarcs (5° per subarc) using a field size of 40 × 40 cm(2) was used to perform the initial beam data measurements. The profile was measured parallel to the direction of gantry rotation at a constant depth of 9 cm (phantom thickness 18 cm). Beam data were measured for single 5° subarcs, dissecting the individual contribution of each subarc to a certain measurement point. The phantom was moved to 20 measurement positions along the profile. Then profile optimization was performed manually by varying the weighting factors of all segments until calculated doses at all points were within ± 1 %. Finally, the dose distribution of the modulated arc was verified in phantom thicknesses of 18 and 28 cm. RESULTS: The measured profile showed a relative mean dose of 99.7 % [standard deviation (SD) 0.7 %)] over the length of 200 cm at a depth of 9 cm. The measured mean effective surface dose (at a depth of 2 cm) was 102.7 % (SD 2.1 %). The measurements in the 28 cm slab phantom revealed a mean dose of 95.9 % (SD 2.9 %) at a depth of 14 cm. The mean dose at a depth of 2 cm was 111.9 % (SD 4.1 %). Net beam-on-time for a 2 Gy fraction is approximately 8 min. CONCLUSION: This highly efficient modulated arc technique for TBI can replace conventional treatment techniques, providing a homogeneous dose distribution, dosimetric robustness, extremely fast delivery, and applicability in small treatment rooms, with no need for additional equipment.

Arc therapy for total body irradiation--a robust novel treatment technique for standard treatment rooms.

BACKGROUND AND PURPOSE: We developed a simple and robust total body irradiation (TBI) method for standard treatment rooms that obviates the need for patient translation devices. METHODS AND MATERIALS: Two generic arcs with rectangular segments for a patient thickness of 16 and 20 cm (arc16/arc20) were generated. An analytical fit was performed to determine the weights of the arc segments depending on patient thickness and gantry angle. Stability and absolute dose for both arcs were measured using EBT3 films in a range of solid water slab phantom thicknesses. Additionally ionization chamber measurements were performed every 10 cm at a source surface distance (SSD) of ∼ 200 cm. RESULTS: The measured standard deviation for arc16 is ± 3% with a flatness ⩽ 9.0%. Arc20 had a standard deviation of ± 3% with a flatness ⩽ 7.3% for all measured thicknesses. The theoretical curves proved to be accurate for the prediction of the segment weightings for the two arcs. In vivo measurements for the first 22 clinical patients showed a dose deviation of less than 3%. CONCLUSIONS: Arc therapy is a convenient and stable method for TBI. This cost-effective approach has been introduced clinically, obviating the need for field patches and to physically move the patient.

Comparison of anisotropic aperture based intensity modulated radiotherapy with 3D-conformal radiotherapy for the treatment of large lung tumors.

PURPOSE/OBJECTIVE(S): IMRT allows dose escalation for large lung tumors, but respiratory motion may compromise delivery. A treatment plan that modulates fluence predominantly in the transversal direction and leaves the fluence identical in the direction of the breathing motion may reduce this problem. MATERIALS/METHODS: Planning-CT-datasets of 20 patients with Stage I-IV non small cell lung cancer (NSCLC) formed the basis of this study. A total of two IMRT plans and one 3D plan were created for each patient. Prescription dose was 60 Gy to the CTV and 70 Gy to the GTV. For the 3D plans an energy of 18 MV photons was used. IMRT plans were calculated for 6 MV photons with 13 coplanar and with 17 noncoplanar beams. Robustness of the used method of anisotropic modulation toward breathing motion was tested in a 13-field IMRT plan. RESULTS: As a consequence of identical prescription doses, mean target doses were similar for 3D and IMRT. Differences between 3D and 13- and 17-field IMRT were significant for CTV Dmin (43 Gy vs. 49.1 Gy vs. 48.6 Gy; p<0.001) and CTV D(95) (53.2 Gy vs. 55.0 Gy vs. 55.4 Gy; p=0.001). The D(mean) of the contralateral lung was significantly lower in the 17-field plans (17-field IMRT vs. 13- vs. 3D: 12.5 Gy vs. 14.8 Gy vs. 15.8 Gy: p<0.05). The spinal cord dose limit of 50 Gy was always respected in IMRT plans and only in 17 of 20 3D-plans. Heart D(max) was only marginally reduced with IMRT (3D vs. 13- vs. 17-field IMRT: 38.2 Gy vs. 36.8 Gy vs. 37.8 Gy). Simulated breathing motion caused only minor changes in the IMRT dose distribution (~0.5-1 Gy). CONCLUSIONS: Anisotropic modulation of IMRT improves dose delivery over 3D-RT and renders IMRT plans robust toward breathing induced organ motion, effectively preventing interplay effects.

A novel lateral disequilibrium inclusive (LDI) pencil-beam based dose calculation algorithm: evaluation in inhomogeneous phantoms and comparison with Monte Carlo calculations.

PURPOSE: Pencil-beam (PB) based dose calculation for treatment planning is limited by inaccuracies in regions of tissue inhomogeneities, particularly in situations with lateral electron disequilibrium as is present at tissue/lung interfaces. To overcome these limitations, a new "lateral disequilibrium inclusive" (LDI) PB based calculation algorithm was introduced. In this study, the authors evaluated the accuracy of the new model by film and ionization chamber measurements and Monte Carlo simulations. METHODS: To validate the performance of the new LDI algorithm implemented in Corvus 09, eight test plans were generated on inhomogeneous thorax and pelvis phantoms. In addition, three plans were calculated with a simple effective path length (EPL) algorithm on the inhomogeneous thorax phantom. To simulate homogeneous tissues, four test plans were evaluated in homogeneous phantoms (homogeneous dose calculation). RESULTS: The mean pixel pass rates and standard deviations of the gamma 4%/4 mm test for the film measurements were (96 +/- 3)% for the plans calculated with LDI, (70 +/- 5)% for the plans calculated with EPL, and (99 +/- 1)% for the homogeneous plans. Ionization chamber measurements and Monte Carlo simulations confirmed the high accuracy of the new algorithm (dose deviations < or = 4%; gamma 3%/3 mm > or = 96%). CONCLUSIONS: LDI represents an accurate and fast dose calculation algorithm for treatment planning.

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 gamma-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 gamma-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.

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.

Optimization of the gafchromic EBT protocol for IMRT QA.

Quality assurance of external beam (radio)therapy (EBT) requires tools with specific characteristics. A radiochromic film dubbed "Gafchromic EBT" (G-EBT) that is particularly suited for external beam therapy because of its features was introduced in 2004. Its characteristics, especially the high spatial resolution, make it suitable for measurement of dose distributions in radiotherapy, especially intensity-modulated radiation therapy (IMRT). While several aspects of the film characteristics have been previously reported separately, we present a comprehensive evaluation centered on practical IMRT verification, leading to an optimized protocol. Therefore the constancy within one batch, the relationship between optical density (OD) and dose (dose range between 1.4 Gy and 8.4 Gy) and the dose rate dependence for four dose rates (55, 108, 217, 441 MU/min) were investigated. In addition to these characteristics, energy dependence between two energies (50kV and 6 MV), tissue equivalency, post irradiation coloration over one month, pressure and temperature sensitivity were evaluated. We then optimized the protocol using the G-EBT films, in combination with an EPSON-Expression 1680 pro flatbed scanner, for IMRT QA, while either striving to keep the compound error as small as possible or trying to reduce evaluation time. As a basis for this protocol optimization, the characteristics of the scanner (such as inhomogeneity of the scanning field) and its software (such as consequences of extracting only the red color channel) had to be determined first. The interaction of film and scanner (variation of the OD depending on the scanning direction or the scanning resolution) was assessed as well. Using the optimized protocol for IMRT QA, the compound error could be reduced to approximately 2% for a quality-driven approach and maximum 5.5% for an approach attempting to reduce procedure time. While the quality-driven approach provides appropriate accuracy for individual patient QA, the procedure-time driven approach can only be used for preliminary measurements.

[Serial tomotherapy vs. MLC-IMRT (multileaf collimator intensity modulated radiotherapy) for simultaneous boost treatment large intracerebral lesions]. / Serielle Tomotherapie vs. MLC-IMRT (Multileaf Collimator Intensity Modulated Radiotherapy) für die simultane Boostbestrahlung mehrerer grösserer Hirnfiliae.

INTRODUCTION: Recent data suggest that a radiosurgery boost treatment for up to three brain metastases in addition to whole brain radiotherapy (WBRT) is beneficial. Sequential treatment of multiple metastatic lesions is time-consuming and optimal normal tissue sparing is not trivial for larger metastases when separate plans are created and are only superimposed afterwards. Sequential Tomotherapy (see image I) with noncoplanar arcs and Multi-field IMRT may streamline the process and enable easy simultaneous treatment. We compared plans for 2-3 intracerebral targets calculated with Intensity Modulated Radiotherapy (IMRT) based on treatment with MLC or sequential Tomotherapy using the Peacock-System (see image II). Treatment time was not to exceed 90 min on a linac with standard dose rate. MIMiC plans without treatment-time restrictions were created as a benchmark. MATERIALS AND METHODS: Calculations are based on a Siemens KD2 linac with a dose rate of 200 MU/min. Step-and-Shoot IMRT is performed with a standard MLC (2 x 29 leaves, 1 cm), serial Tomotherapy with the Multivane-Collimator MIMiC (NOMOS Inc. USA) (see image II). Treatment plans are created with Corvus 5.0. To create plans with good conformity we chose a noncoplanar beam- and arc geometry for each approach (IMRT 4-, MIMiC 5-couch angles). The benchmark MIMiC plans with maximally steep dose gradients had 9 couch angles. For plan comparison reasons, 10 Gy were prescribed to 90% of the PTV. Steepness of dose gradients, homogeneity and conformity were assessed by the following parameters: Volume encompassed by certain isodoses outside the target as well as homogeneity and conformity as indicated by Homogeneity- and Conformity-Index. RESULTS: Plans without treatment-time restrictions had slightest dose to organ at risk (OAR), normal tissue and least Conformity-index. MIMiC- and MLC-IMRT based plans can be treated within the intended period of 90 min, all plans met the required dose (see Table 2). MLC based plans resulted in higher dose to organs at risk (OAR) (see table 1) and dose to tissue outside the targets (see table 3), as indicated by a higher CI (see image III). The HI was similar for all calculated plans (see image IV). DISCUSSION: When treatment plans resulting in a similar treatment time were compared, serial Tomotherapy showed minor advantages over MLC based IMRT with regard to conformity, OAR sparing, and steepness of dose gradients. Both methods are inferior to serial Tomotherapy with ideal plan quality disregarding treatment efficiency. Treating multiple metastases in less than 1 h would therefore be possible on a LINAC with high dose rate and bidirectional rotation with minor compromises on gradient steepness.

Improving dose homogeneity in large breasts by IMRT: efficacy and dosimetric accuracy of different techniques.

PURPOSE: Evaluation of a simplified intensity-modulated irradiation (IMRT), a three-field (MFT), and a conventional two-tangential-field technique regarding dose homogeneity, target coverage, feasibility and, for the first time, dosimetric reliability in patients with large breasts treated postoperatively for breast cancer on a low-energy linac. MATERIAL AND METHODS: CT datasets of ten patients with relatively large breast volumes treated for breast cancer were selected. For each patient, four treatment plans were created: low-energy conventional (C-LE), high-energy conventional (C-HE), three-field (MFT), and a two-field aperture-based IMRT technique. Apertures for the IMRT and MFT were created with the aid of a three-dimensional dose display. Dosimetric accuracy of each technique was evaluated in an anthropomorphic thorax/breast phantom. RESULTS: The mean of planning target volumes receiving < 95% or > 105% of the prescribed total dose was reduced from 16.0% to 13.9% to 10.4% to 8.9% in the C-LE, C-HE, MFT, and IMRT plans, respectively. Phantom dose measurements agreed well with the calculated dose within the breast tissue. CONCLUSION: Aperture-based IMRT using two tangential incident beam directions, as well as a three-field technique with inverse optimization, provide a better alternative to the standard wedged tangential beams for patients with large breasts treated on low-energy linacs while maintaining the efficiency of the treatment-planning and delivery process.

Evaluation of calculation algorithms implemented in different commercial planning systems on an anthropomorphic breast phantom using film dosimetry.

PURPOSE: To evaluate the accuracy of dose calculation algorithms of different planning systems for postoperative tangential radiotherapy in breast cancer. MATERIAL AND METHODS: On a CT dataset of an anthropomorphic phantom, a structure set of the left lung, clinical target volume (CTV), planning target volume, heart, and external contour were delineated. The dataset was processed by six radiation oncology centers participating in this multicenter dosimetry project. Conventional plans with two tangential wedged fields were generated in MasterPlan, Pinnacle, Eclipse, TMS, and PrecisePLAN. Plan calculations were done using the beam data of local linacs. The dose distributions were verified under local conditions with Gafchromic-EBT films. RESULTS: In all planning systems, deviations between calculation and measurement were around +/-3% in the CTV in the measured plane. Only small areas with deviations of +/-5% were detected. Pencil-beam (PB) calculations overestimated the dose inside the lung by up to 23%. Collapsed cone (CC) underestimated the lung dose by up to 6%. CONCLUSION: CC calculates the dose distribution more accurately than PB. Inside regions with electron disequilibrium, however, the dose is slightly underestimated.

On the performances of different IMRT Treatment Planning Systems for selected paediatric cases.

BACKGROUND: To evaluate the performance of seven different TPS (Treatment Planning Systems: Corvus, Eclipse, Hyperion, KonRad, Oncentra Masterplan, Pinnacle and PrecisePLAN) when intensity modulated (IMRT) plans are designed for paediatric tumours. METHODS: Datasets (CT images and volumes of interest) of four patients were used to design IMRT plans. The tumour types were: one extraosseous, intrathoracic Ewing Sarcoma; one mediastinal Rhabdomyosarcoma; one metastatic Rhabdomyosarcoma of the anus; one Wilm's tumour of the left kidney with multiple liver metastases. Prescribed doses ranged from 18 to 54.4 Gy. To minimise variability, the same beam geometry and clinical goals were imposed on all systems for every patient. Results were analysed in terms of dose distributions and dose volume histograms. RESULTS: For all patients, IMRT plans lead to acceptable treatments in terms of conformal avoidance since most of the dose objectives for Organs At Risk (OARs) were met, and the Conformity Index (averaged over all TPS and patients) ranged from 1.14 to 1.58 on primary target volumes and from 1.07 to 1.37 on boost volumes. The healthy tissue involvement was measured in terms of several parameters, and the average mean dose ranged from 4.6 to 13.7 Gy. A global scoring method was developed to evaluate plans according to their degree of success in meeting dose objectives (lower scores are better than higher ones). For OARs the range of scores was between 0.75 +/- 0.15 (Eclipse) to 0.92 +/- 0.18 (Pinnacle(3) with physical optimisation). For target volumes, the score ranged from 0.05 +/- 0.05 (Pinnacle(3) with physical optimisation) to 0.16 +/- 0.07 (Corvus). CONCLUSION: A set of complex paediatric cases presented a variety of individual treatment planning challenges. Despite the large spread of results, inverse planning systems offer promising results for IMRT delivery, hence widening the treatment strategies for this very sensitive class of patients.

Optimization of extracranial stereotactic radiation therapy of small lung lesions using accurate dose calculation algorithms.

BACKGROUND: The aim of this study was to compare and to validate different dose calculation algorithms for the use in radiation therapy of small lung lesions and to optimize the treatment planning using accurate dose calculation algorithms. METHODS: A 9-field conformal treatment plan was generated on an inhomogeneous phantom with lung mimics and a soft tissue equivalent insert, mimicking a lung tumor. The dose distribution was calculated with the Pencil Beam and Collapsed Cone algorithms implemented in Masterplan (Nucletron) and the Monte Carlo system XVMC and validated using Gafchromic EBT films. Differences in dose distribution were evaluated. The plans were then optimized by adding segments to the outer shell of the target in order to increase the dose near the interface to the lung. RESULTS: The Pencil Beam algorithm overestimated the dose by up to 15% compared to the measurements. Collapsed Cone and Monte Carlo predicted the dose more accurately with a maximum difference of -8% and -3% respectively compared to the film. Plan optimization by adding small segments to the peripheral parts of the target, creating a 2-step fluence modulation, allowed to increase target coverage and homogeneity as compared to the uncorrected 9 field plan. CONCLUSION: The use of forward 2-step fluence modulation in radiotherapy of small lung lesions allows the improvement of tumor coverage and dose homogeneity as compared to non-modulated treatment plans and may thus help to increase the local tumor control probability. While the Collapsed Cone algorithm is closer to measurements than the Pencil Beam algorithm, both algorithms are limited at tissue/lung interfaces, leaving Monte-Carlo the most accurate algorithm for dose prediction.

Intensity-modulated radiation therapy (IMRT) with different combinations of treatment-planning systems and linacs: issues and how to detect them.

PURPOSE: To compare different combinations of intensity-modulated radiation therapy (IMRT) system components with regard to quality assurance (QA), especially robustness against malfunctions and dosimetry. MATERIAL AND METHODS: Three different treatment-planning systems (TPS), two types of linacs and three multileaf collimator (MLC) types were compared: commissioning procedures were performed for the combination of the TPS Corvus 5.0 (Nomos) and KonRad v2.1.3 (Siemens OCS) with the linacs KD2 (Siemens) and Synergy (Elekta). For PrecisePLAN 2.03 (Elekta) measurements were performed for Elekta Synergy only. As record and verify (R&V) system Multi-Access v7 (IMPAC) was used. The use of the serial tomotherapy system Peacock (Nomos) was investigated in combination with the Siemens KD2 linac. RESULTS: In the comparison of calculated to measured dose, problems were encountered for the combination of KonRad and Elekta MLC as well as for the Peacock system. Multi-Access failed to assign the collimator angle correctly for plans with multiple collimator angles per beam. Communication problems of Multi-Access with both linacs were observed, resulting in incorrect recording of the treatment. All reported issues were addressed by the manufacturers. CONCLUSION: For the commissioning of IMRT systems, the whole chain from the TPS to the linac has to be investigated. Components that passed the commissioning in another clinical environment can have severe malfunctions when used in a new environment. Therefore, not only single components but the whole chain from planning to delivery has to be evaluated in commissioning and checked regularly for QA.