Feasibility of Optical Surface-Guidance for Position Verification and Monitoring of Stereotactic Body Radiotherapy in Deep-Inspiration Breath-Hold.

BACKGROUND: Reductions in tumor movement allow for more precise and accurate radiotherapy with decreased dose delivery to adjacent normal tissue that is crucial in stereotactic body radiotherapy (SBRT). Deep inspiration breath-hold (DIBH) is an established approach to mitigate respiratory motion during radiotherapy. We assessed the feasibility of combining modern optical surface-guided radiotherapy (SGRT) and image-guided radiotherapy (IGRT) to ensure and monitor reproducibility of DIBH and to ensure accurate tumor localization for SBRT as an imaging-guided precision medicine. METHODS: We defined a new workflow for delivering SBRT in DIBH for lung and liver tumors incorporating SGRT and IGRT with cone beam computed tomography (CBCT) twice per treatment fraction. Daily position corrections were analyzed and for every patient two points retrospectively characterized: an anatomically stable landmark (predominately Schmorl's nodes or spinal enostosis) and a respiratory-dependent landmark (predominately surgical clips or branching vessel). The spatial distance of these points was compared for each CBCT and used as surrogate for intra- and interfractional variability. Differences between the lung and liver targets were assessed using the Welch t-test. Finally, the planning target volumes were compared to those of free-breathing plans, prepared as a precautionary measure in case of technical or patient-related problems with DIBH. RESULTS: Ten patients were treated with SBRT according this workflow (7 liver, 3 lung). Planning target volumes could be reduced significantly from an average of 148 ml in free breathing to 110 ml utilizing DIBH (p < 0.001, paired t-test). After SGRT-based patient set-up, subsequent IGRT in DIBH yielded significantly higher mean corrections for liver targets compared to lung targets (9 mm vs. 5 mm, p = 0.017). Analysis of spatial distance between the fixed and moveable landmarks confirmed higher interfractional variability (interquartile range (IQR) 6.8 mm) than intrafractional variability (IQR 2.8 mm). In contrast, lung target variability was low, indicating a better correlation of patients' surface to lung targets (intrafractional IQR 2.5 mm and interfractional IQR 1.7 mm). CONCLUSION: SBRT in DIBH utilizing SGRT and IGRT is feasible and results in significantly lower irradiated volumes. Nevertheless, IGRT is of paramount importance given that interfractional variability was high, particularly for liver tumors.

Establishing stereotactic body radiotherapy with flattening filter free techniques in the treatment of pulmonary lesions - initial experiences from a single institution.

BACKGROUND: Stereotactic body radiotherapy (SBRT) using flattening filter free (FFF)-techniques has been increasingly applied during the last years. However, clinical studies investigating this emerging technique are still rare. Hence, we analyzed toxicity and clinical outcome of pulmonary SBRT with FFF-techniques and performed dosimetric comparison to conventional techniques using flattening filters (FF). MATERIALS AND METHODS: Between 05/2014 and 06/2015, 56 consecutive patients with 61 pulmonary lesions were treated with SBRT in FFF-mode. Central lesions received 8 × 7.5 Gy delivered to the conformally enclosing 80 %-isodose, while peripheral lesions were treated with 3 × 15 Gy, prescribed to the 65 %-isodose. Early and late toxicity (after 6 months) as well as initial clinical outcomes were evaluated. Furthermore, [deleted] plan quality and efficiency were evaluated by analyzing conformity, beam- on and total treatment delivery times in comparison to plans with FF-dose application. RESULTS: Median follow-up time was 9.3 months (range 1.5-18.0 months). Early toxicity was low with only 5 patients (8.9 %) reporting CTCAE 2° or higher side-effects. Only one patient (1.8 %) was diagnosed with radiation-induced pneumonitis CTCAE 3°, while 2 (3.6 %) patients suffered from pneumonitis CTCAE 2°. After 6 months, no toxicity greater than CTCAE 2° was reported. 1-year local progression-free survival, distant progression-free survival and overall survival were 92.8 %, 78.0 %, and 94.4 %, respectively. While plan quality was similar for FFF- and FF-plans in respect to conformity (p = 0.275), median beam-on time as well as total treatment time were significantly reduced for SBRT in FFF-mode compared to FF-mode (p ≤ 0.001, p ≤ 0.001). CONCLUSIONS: Patient treatment with SBRT using FFF-techniques is safe and provides promising clinical results with only modest toxicity at significantly increased dose delivery speed.

New multileaf collimator with a leaf width of 5 mm improves plan quality compared to 10 mm in step-and-shoot IMRT of HNC using integrated boost procedure.

PURPOSE: To investigate whether a new multileaf collimator with a leaf width of 5 mm (MLC-5) over the entire field size of 40 x 40 cm(2) improves plan quality compared to a leaf width of 10 mm (MLC-10) in intensity-modulated radiotherapy (IMRT) with integrated boost for head and neck cancer. PATIENTS AND METHODS: A plan comparison was performed for ten patients with head and neck cancer. For each patient, seven plans were calculated: one plan with MLC-10 and nine beams, four plans with MLC-5 and nine beams (with different intensity levels and two-dimensional median filter sizes [2D-MFS]), and one seven-beam plan with MLC-5 and MLC-10, respectively. Isocenter, beam angles and planning constraints were not changed. Mean values of common plan parameters over all ten patients were estimated, and plan groups of MLC-5 and MLC-10 with nine and seven beams were compared. RESULTS: The use of MLC-5 led to a significantly higher conformity index and an improvement of the 90% coverage of PTV1 (planning target volume) and PTV2 compared with MLC-10. This was noted in the nine- and seven-beam plans. Within the nine-beam group with MLC-5, a reduction of the segment number by up to 25% at reduced intensity levels and for increased 2D-MFS did not markedly worsen plan quality. Interestingly, a seven-beam IMRT with MLC-5 was inferior to a nine-beam IMRT with MLC-5, but superior to a nine-beam IMRT with MLC-10. CONCLUSION: The use of an MLC-5 has significant advantages over an MLC-10 with respect to target coverage and protection of normal tissues in step-and-shoot IMRT of head and neck cancer.

4D-CT-based target volume definition in stereotactic radiotherapy of lung tumours: comparison with a conventional technique using individual margins.

PURPOSE: To investigate the dosimetric benefit of integration of 4D-CT in the planning target volume (PTV) definition process compared to conventional PTV definition using individual margins in stereotactic body radiotherapy (SBRT) of lung tumours. MATERIAL AND METHODS: Two different PTVs were defined: PTV(conv) consisting of the helical-CT-based clinical target volume (CTV) enlarged isotropically for each spatial direction by the individually measured amount of motion in the 4D-CT, and PTV(4D) encompassing the CTVs defined in the 4D-CT phases displaying the extremes of the tumour position. Tumour motion as well as volumetric and dosimetric differences and relations of both PTVs were evaluated. RESULTS: Volumetric examinations revealed a significant reduction of the mean PTV by 4D-CT from 57.7 to 40.7 cm(3) (31%) (p<0.001). A significant inverse correlation was found for the motion vector and the amount of inclusion of PTV(4D) in PTV(conv) (r=-0.69, 90% confidence limits: -0.87 and -0.34, p=0.007). Mean lung dose (MLD) was decreased significantly by 17% (p<0.001). CONCLUSIONS: In SBRT of lung tumours the mere use of individual margins for target volume definition cannot compensate for the additional effects that the implementation of 4D-CT phases can offer.

Uncertainty estimation in intensity-modulated radiotherapy absolute dosimetry verification.

PURPOSE: Intensity-modulated radiotherapy (IMRT) represents an important method for improving RT. The IMRT relative dosimetry checks are well established; however, open questions remain in reference dosimetry with ionization chambers (ICs). The main problem is the departure of the measurement conditions from the reference ones; thus, additional uncertainty is introduced into the dose determination. The goal of this study was to assess this effect systematically. METHODS AND MATERIALS: Monte Carlo calculations and dosimetric measurements with five different detectors were performed for a number of representative IMRT cases, covering both step-and-shoot and dynamic delivery. RESULTS: Using ICs with volumes of about 0.125 cm(3) or less, good agreement was observed among the detectors in most of the situations studied. These results also agreed well with the Monte Carlo-calculated nonreference correction factors (c factors). Additionally, we found a general correlation between the IC position relative to a segment and the derived correction factor c, which can be used to estimate the expected overall uncertainty of the treatment. CONCLUSION: The increase of the reference dose relative standard uncertainty measured with ICs introduced by nonreference conditions when verifying an entire IMRT plan is about 1-1.5%, provided that appropriate small-volume chambers are used. The overall standard uncertainty of the measured IMRT dose amounts to about 2.3%, including the 0.5% of reproducibility and 1.5% of uncertainty associated with the beam calibration factor. Solid state detectors and large-volume chambers are not well suited to IMRT verification dosimetry because of the greater uncertainties. An action level of 5% is appropriate for IMRT verification. Greater discrepancies should lead to a review of the dosimetric procedure, including visual inspection of treatment segments and energy fluence.

Correction of patient positioning errors based on in-line cone beam CTs: clinical implementation and first experiences.

BACKGROUND: The purpose of the study was the clinical implementation of a kV cone beam CT (CBCT) for setup correction in radiotherapy. PATIENTS AND METHODS: For evaluation of the setup correction workflow, six tumor patients (lung cancer, sacral chordoma, head-and-neck and paraspinal tumor, and two prostate cancer patients) were selected. All patients were treated with fractionated stereotactic radiotherapy, five of them with intensity modulated radiotherapy (IMRT). For patient fixation, a scotch cast body frame or a vacuum pillow, each in combination with a scotch cast head mask, were used. The imaging equipment, consisting of an x-ray tube and a flat panel imager (FPI), was attached to a Siemens linear accelerator according to the in-line approach, i.e. with the imaging beam mounted opposite to the treatment beam sharing the same isocenter. For dose delivery, the treatment beam has to traverse the FPI which is mounted in the accessory tray below the multi-leaf collimator. For each patient, a predefined number of imaging projections over a range of at least 200 degrees were acquired. The fast reconstruction of the 3D-CBCT dataset was done with an implementation of the Feldkamp-David-Kress (FDK) algorithm. For the registration of the treatment planning CT with the acquired CBCT, an automatic mutual information matcher and manual matching was used. RESULTS AND DISCUSSION: Bony landmarks were easily detected and the table shifts for correction of setup deviations could be automatically calculated in all cases. The image quality was sufficient for a visual comparison of the desired target point with the isocenter visible on the CBCT. Soft tissue contrast was problematic for the prostate of an obese patient, but good in the lung tumor case. The detected maximum setup deviation was 3 mm for patients fixated with the body frame, and 6 mm for patients positioned in the vacuum pillow. Using an action level of 2 mm translational error, a target point correction was carried out in 4 cases. The additional workload of the described workflow compared to a normal treatment fraction led to an extra time of about 10-12 minutes, which can be further reduced by streamlining the different steps. CONCLUSION: The cone beam CT attached to a LINAC allows the acquisition of a CT scan of the patient in treatment position directly before treatment. Its image quality is sufficient for determining target point correction vectors. With the presented workflow, a target point correction within a clinically reasonable time frame is possible. This increases the treatment precision, and potentially the complex patient fixation techniques will become dispensable.

The influence of breathing motion on intensity modulated radiotherapy in the step-and-shoot technique: phantom measurements for irradiation of superficial target volumes.

For intensity modulated radiotherapy (IMRT) of deep-seated tumours, dosimetric variations of the original static dose profiles due to breathing motion can be primarily considered as blurring effects known from conventional radiotherapy. The purpose of this dosimetric study was to clarify whether these results are transferable to superficial targets and to quantify the additional effect of fractionation. A solid polystyrene phantom and an anthropomorphic phantom were used for film and ion chamber dose measurements. The phantoms were installed on an electric driven device and moved with a frequency of 6 or 12 cycles per minute and an amplitude of 4 mm or 10 mm. A split beam geometry of two adjacent asymmetric fields and an IMRT treatment plan with 12 fields for irradiation of the breast were investigated. For the split beam geometry the dose modifications due to unintended superposition of partial fields were reduced by fractionation and completely smoothed out after 20 fractions. IMRT applied to the moving phantom led to a more homogeneous dose distribution compared to the static phantom. The standard deviation of the target dose which is a measure of the dose homogeneity was 10.3 cGy for the static phantom and 7.7 cGy for a 10 mm amplitude. The absolute dose values, measured with ionization chambers, remained unaffected. Irradiation of superficial targets by IMRT in the step-and-shoot technique did not result in unexpected dose perturbations due to breathing motion. We conclude that regular breathing motion does not jeopardize IMRT of superficial target volumes.

Measurements of characteristics of time pattern in dose delivery in step-and-shoot IMRT.

BACKGROUND AND PURPOSE: Although intensity-modulated radiotherapy (IMRT) has already shown its clinical benefit, there are some issues which are not yet fully understood. Among these is the question whether the protracted dose delivery due to the lowered dose rate has any radiobiological consequences. To investigate this question, an exact characterization of dose rate profiles in typical clinical plans is needed. Furthermore, such a characterization may lead to an increased knowledge how to improve IMRT technically. MATERIAL AND METHODS: A new IMRT phantom which allows precise measurement of up to nine points of interest simultaneously with pin-point ionization chambers was developed. To examine dose rates, a new software tool (GRAYHOUND) was developed which can measure doses in short time intervals of up to 0.5 s. 250 points in four clinical IMRT plans were examined. A set of parameters was defined to describe the dose rate profiles including the effective fraction time (eft, which is the percentage of the fraction time in which any dose is delivered to a specific point), and a quotient of the percentage of dose delivered in high dose pulses (> 0.01 Gy/s) divided by the percentage of fraction time needed to deliver this dose (d(HD)/t(HD)). RESULTS: These quotients are excellent markers for the inhomogeneity of dose rate delivery in IMRT. In both parameters a wide variance in points of the same plan and between different plans was found. For example, eft ranged between 11.6% and 37.3% in high dose points and the time in which high dose rates are delivered to a single high dose point ranged between 3.6% and 10.1% of total fraction time. CONCLUSIONS: These data show a great inhomogeneity of dose rates not only between different plans but also between different points in the same plan. Biological investigations are needed to quantify the relevance of these inhomogeneities. The parameters which are introduced in this work may be suitable to compare different optimization algorithms in IMRT.

Radiobiological investigation of dose-rate effects in intensity-modulated radiation therapy.

BACKGROUND AND PURPOSE: Intensity-modulated radiation therapy (IMRT) has proven extraordinary capability in physical terms such as target conformity, dose escalation in the target volume, and sparing of neighboring organs at risk. The radiobiological consequences of the protracted dose delivery for cell survival and cell cycle progression are still unclear and shall be examined in this study. MATERIAL AND METHODS: Human lymphoblasts (TK6) and human melanoma cells (MeWo) were irradiated with protocols of increasing dose protraction. In addition, a new biophysical phantom was developed and used to transfer clinical IMRT plans to experimental cell irradiation. Clonogenic cell survival and cell cycle analysis were performed after various irradiation experiments. RESULTS: In a first series of experiments, melanoma cells showed a highly significant increase of survival of 6.0% after protracted dose delivery of 2 Gy compared to conventional fast application with the same dose. Lymphoblastoid cells also showed a significant increase of survival of 2.2%. Experiments with patient plans in the phantom confirmed the trend of increased cell survival after protracted dose delivery. Cells were irradiated at 13 points in four different IMRT plans. In comparison to irradiation with application of the same dose in a classic four-field box, a significantly increased survival of 5.1% (mean value) was determined. CONCLUSION: Even at fraction times of 15-30 min the protracted dose delivery increases the survival rates in cell culture. The altered survival rates indicate the importance of the dose rate in the effectivity of IMRT. Besides physical parameters the consideration of biological factors might contribute to the optimization of IMRT in the future.

Stereotactic intensity modulated radiation therapy and inverse treatment planning for tumors of the head and neck region: clinical implementation of the step and shoot approach and first clinical results.

PURPOSE/OBJECTIVE: The aim of this analysis is to evaluate the feasibility of inverse treatment planning and intensity modulated radiation therapy (IMRT) for head and neck cancer in daily clinical routine. A step and shoot IMRT approach was developed which allows the treatment of large target volumes without the need to use a split beam technique. By using the IMRT approach better protection of different organs at risk in the head and neck region may be achieved and an escalation of the dose in the tumor should be possible. We evaluated the feasibility of the treatment technique and the patient tolerance to the treatment. First clinical results are reported. MATERIALS AND METHODS: Between 1999 and 2002, 48 patients with a carcinoma of the head and neck region were treated with curative intention. All patients were treated in a patient-specific Scotch-Cast mask. Patients who required treatment of the lymph node levels I-VI, were additionally positioned by a vacuum pillow in order to immobilize the upper part of the thorax. For inverse treatment planning, the software module KonRad was used which was integrated into the VIRTUOS planning system. Each treatment plan was verified using quantitative film dosimetry in a head and neck phantom. The step and shoot IMRT technique with a multileaf collimator integrated in a Primus (Siemens) accelerator was used for treatment. For all target volumes the whole target including the lymph nodes were covered completely by the IMRT treatment. RESULTS: The mean total dose for the target volumes of macroscopic disease ranged between 63.0 and 64.1 Gy. The mean total dose of microscopic disease ranged between 55.2 and 60.1 Gy. The mean percentage of planning target volume receiving <90% of the prescribed dose ranged between 3.0 and 11.5%. For the treatment, the median number of beams was seven (range: five to nine). The time to deliver the treatment ranged between 9 and 18 min. The results of the verification revealed a mean deviation between measured and calculated absolute doses for the 48 patients of 0.1+/-1.4%. Including the phantom verification the IMRT treatment of the patients could be started approximately after five working days. The treatment was well tolerated by all patients. The 2-year actuarial overall survival was 92% and the 2-year actuarial local control rate was 93%. According to the Radiation Therapy Oncology Group (RTOG), no higher acute toxicity than Grade 3 was seen. Observation of the late effects revealed only one transient Grade 4 toxicity of the bone and only four patients had a xerostomia higher than Grade 1. CONCLUSION: The use of an inversely-planned and intensity-modulated step and shoot approach is feasible in clinical routine for head and neck tumors. Treatment could be applied as planned and no increased toxicity was found. Compared to other IMRT approaches for the head and neck region the used technique allows the treatment of the primary tumor and the lymph nodes level I-VI with only one intensity modulated treatment volume. The presented technique avoids to match conventional radiotherapy fields and IMRT fields, and therefore, reduce the risk of overdosage or underdosage at the matching line. Compared to conventional treatment techniques IMRT shows advantages in tumor dose and dose at the organs at risk.

Intensity modulated radiotherapy (IMRT) for recurrent, residual, or untreated skull-base meningiomas: preliminary clinical experience.

OBJECTIVE: To investigate the feasibility of using intensity modulated radiotherapy (IMRT) for complex-shaped benign meningiomas of the skull base and report clinical experience. METHODS: Twenty patients with benign skull-base meningiomas WHO degrees I (histopathologically proven in 16/20) were treated with IMRT between June 1998 and August 1999. Each tumor was complex in shape and adherent to, or encompassed, organs at risk (cranial nerves, optic apparatus, and brainstem). All patients, immobilized in a customized head mask integrated into a stereotactic system, were planned on an inverse treatment planning system using 5 or 7 coplanar, equidistant beams and 5 intensity steps. Each treatment plan was verified extensively before treatment. Follow-up with MRI and clinical examination was performed at 6 and 18 weeks and every 6 months thereafter. RESULTS: Target volumes ranged from 27 to 278 cc (median: 108 cc). Mean dose in 32 fractions ranged between 55.8 and 58.2 Gy. At median follow-up of 36 months (range: 31-43 months), pre-existing neurologic symptoms improved in 12/20 (60%), remained stable in 7/20 (35%), and worsened in 1 (5%) patient. Radiographic follow-up revealed significant tumor shrinkage 6 weeks post-IMRT in 2 patients and partial remission in 3 more patients at 9-17 months; other tumor volumes remained stable. There was no radiation-induced peritumoral edema, increase in tumor size, or new onset of neurologic deficits. Transient acute treatment side effects included nausea and vomiting and single occurrences of conjunctivitis/increased tearing and serous tympanitis. CONCLUSION: IMRT in the treatment of central nervous system meningiomas is feasible and safe, offering highly conformal irradiation for complex-shaped skull-base tumors while sparing adjacent critical structures. If the tumor remissions seen here are found in the ongoing treatments, IMRT may be considered the treatment of choice for inoperable or subtotally resected meningiomas and for otherwise difficult-to-treat, complex-shaped tumors of the central nervous system adjacent to critical structures, with the potential of dose escalation for malignant tumors.

Fractionated stereotactic radiotherapy for craniopharyngiomas.

PURPOSE: To investigate outcome and toxicity after fractionated stereotactic radiation therapy (FSRT) in patients with craniopharyngiomas. METHODS AND MATERIALS: Twenty-six patients with craniopharyngiomas were treated with FSRT between May 1989 and February 2001. Median age was 33.5 years (range: 5-57 years). Nine patients received FSRT after surgery as primary treatment, and 17 patients were irradiated for recurrent tumor or progressive growth after initial surgery. Median target dose was 52.2 Gy (range: 50.0-57.6 Gy) with conventional fractionation. Follow-up included MRI and neurologic, ophthalmologic, and endocrinologic examinations. RESULTS: The median follow-up was 43 months (range: 7-143 months). The actuarial local control rate and actuarial overall survival rates were 100% and 100%, respectively, at 5 years and 100% and 83%, respectively, at 10 years. Four patients showed complete response, 14 patients showed partial response, and 8 patients remained stable. In 5 patients, vision improved after radiation therapy. Acute toxicity was mild. One patient required cyst drainage 3 months after radiotherapy. Late toxicity after radiotherapy included impairment of hormone function in 3 out of 18 patients at risk. We did not observe any vision impairment, radionecrosis, or secondary malignancies. CONCLUSIONS: FSRT is effective and safe in the treatment of cystic craniopharyngiomas. Toxicity is extremely low using this conformal technique.

[Inversely planned intensity modulated radiotherapy for irradiation of a woman with breast cancer and funnel chest]. / Invers geplante intensitätsmodulierte Strahlenbehandlung bei einer Patientin mit rechtsseitigem Mammakarzinom und Trichterbrust.

BACKGROUND: A 44-year old woman with breast cancer was transferred to our institution for irradiation. Due to a pronounced funnel chest no satisfying dose distribution was obtained by conventional techniques. Thus an intensity-modulated radiotherapy (IMRT) based on inverse optimisation was carried out. IMRT was compared to conventional techniques regarding dose distribution and feasibility. PATIENT AND METHODS: Tumor site was in the right middle lower quadrant. Target volume included the right breast and the parasternal lymph nodes. Target dose was 50.4 Gy. Based on inverse optimisation irradiation was carried out in "step-and-shoot"-technique with twelve intensity modulated beams with six intensity steps. Additionally, treatment plans were calculated using conventional techniques (technique A with two tangential wedged 6-MV photon beams, technique B with additional oblique 15-MeV electron portal). We analysed conformality and homogeneity of target volume and dose distribution within normal tissue. RESULTS: Dose conformality was substantially improved by IMRT. Dose homogeneity was slightly decreased compared to technique A. Lung volume irradiated with a dose higher than 20 Gy was reduced from 56.8% with technique A and 40.1% with technique B, respectively to 22.1% with IMRT. Treatment was tolerated well by the patient without relevant side effects. Mean treatment time was 19.5 min. CONCLUSION: The inversely planned IMRT using multiple beam directions is suitable for breast irradiation following breast conserving surgery. In the present case of a woman with funnel chest lung dose was substantially reduced without reduction of target dose. In which was the complex treatment technique leads to a clinically detectable advantage is examined at present, in the context of a study.

[Dosimetric verification of IMRT treatment plans at the German Cancer Research Center (DKFZ)]. / Dosimetrische Verifikation von IMRT-Gesamtplänen am Deutschen Krebsforschungszentrum Heidelberg.

The present paper describes a method for the individual dosimetric verification of IMRT treatment plans. The German Cancer Research Center (Deutsches Krebsforschungszentrum; DKFZ) has implemented the intensity modulated radiotherapy (IMRT) since 1997. So far, 246 patients with head and neck cancer, cancer of the prostate, breast, and vertebral column, as well as mesothelioma of the pleura have been treated. Every IMRT plan is transferred into a special IMRT verification phantom, recalculated, and dosimetrically verified. Absolute dose distributions are measured with Kodak EDR films and compared with the results of the dose calculation. After correction of the optical density in relationship to the dose, EDR films are able to measure the absolute dose with an accuracy of +/- 2% compared to an ionization chamber. A visual C++ software tool has been developed to correlate and evaluate the film dose distributions with the corresponding slices of the 3D dose cube. Beside the overlay of absolute or relative isodoses and dose profiles, the median dose within correlated regions of interest (ROIs) is also included in the quantitative dose evaluation. The deviation between EDR film dosimetry and dose calculation is delta D = -0.3% +/- 2.3%. After introduction of the verification software, the total verification time (including handling, correlation, evaluation, and documentation of the data), could be reduced to less than 2 hours.

Treatment of brain metastases in patients with non-small cell lung cancer (NSCLC) by stereotactic linac-based radiosurgery: prognostic factors.

A restrospective study of patients with brain metastases from non-small cell lung cancer (NSCLC) is performed to identify patients who benefit from radiosurgery and to determine prognostic factors for survival. Eighty-six consecutive patients with a total of 110 brain metastases from NSCLC were treated with linac-based radiosurgery. Six patients with eight brain metastases who received radiosurgery as a focal boost to whole brain radiotherapy where excluded. Median age at treatment was 60 years. Median dose was 20 Gy/80%-isodose. A chi(2)-test was used to identify potential prognostic factors for local control of brain metastases and survival of the patients. Median follow-up was 6 months (range 1 1/2-77 months) with 17/80 patients still alive. Median actuarial survival was significantly longer (P<0.004) in patients with metachronous onset of brain metastases in comparison to synchronous onset (8.3 vs. 3.3 months). Survival was significantly increased after radiosurgery in the absence of extracranial tumor progression (P<0.03). Eleven patients (14%) developed new brain metastases after radiosurgery after a latency of median 5 months. Actuarial local control rate was 96% after 3 months. Local control was significantly increased with a prescribed dose > or=18 Gy/80%-isodose (P<0.01). We conclude that especially patients with poor prognostic factors and a limited number of brain metastases may be palliatively treated with radiosurgery alone. This approach allows to effectively control CNS manifestation of the disease and can be integrated into chemotherapeutic protocols.

Intensity-modulated radiotherapy of the female breast.

Current methods for intensity-modulated radiotherapy (IMRT) in breast cancer use forward planning based on equivalent radiological path length to design intensity modulated tangential beams. Compared to conventional tangential techniques, dose reduction of organs at risk is limited using these techniques. We developed a method for intensity modulation of multiple beams for adjuvant radiotherapy of breast cancer by application of a virtual bolus defined on CT for inverse optimization. This method enables multibeam IMRT, which provides improved sparing of lung and heart tissue. In this paper, we present the general aspects of this approach and an evaluation of the optimum beam configuration for IMRT based on inverse treatment planning. We compared this method to conventional techniques. Different clinical examples illustrate the possible indications and feasibility of this new approach. This method is superior to conventional techniques because of the reduction of high-dose area of a substantial cardiac volume in those cases where the parasternal lymph nodes are part of the target volume.

[Virtual bolus for inversion radiotherapy planning in intensity-modulated radiotherapy of breast carcinoma within the scope of adjuvant therapy]. / Virtueller Bolus zur inversen Bestrahlungsplanung bei intensitätsmodulierter Radiotherapie des Mammakarzinoms im Rahmen der adjuvanten Therapie.

BACKGROUND: Intensity modulated radiotherapy (IMRT) provides better sparing of normal tissue. We investigated the feasibility of inverse treatment planning for IMRT in adjuvant radiotherapy for breast cancer. MATERIAL AND METHODS: In addition to radiotherapy planning in conventional technique with tangential wedged 6-MV-photon beams we performed inversely planned IMRT (KonRad). In the CT scans for treatment planning we defined a 10-mm bolus of -60 HE density. The influence of this bolus on planning optimization was determined by optimization without and dose calculation with and without bolus. Dose calculation after dose optimization with bolus was performed using different bolus thickness to determine the influence of the bolus on dose calculation. The results were compared with dose distribution in conventional technique. RESULTS: Inverse optimization with a dose algorithm which considers tissue inhomogeneity results in unintended dose increase at the patient surface. With a virtual 10-mm bolus used for inverse optimization the dose increase was reduced. Thus, skin sparing was identical to conventional planning. The relative dose distribution was negligibly affected by the use of a 10-mm bolus. Difference in absolute dose was 3.4% compared to calculation without bolus. Therefore, the bolus must be removed before final dose calculation. CONCLUSION: The realization of inverse optimization for IMRT of the breast requires the use of a virtual bolus. Thereby, IMRT in accordance to the consensus recommendations of the EORTC, BCCG and EUSOMA is possible. Especially, the same target definition as in conventional technique may be used. IMRT techniques with a conventional beam arrangement of two tangential fields or multiple beam techniques can be realized.