Comparison between Acuros XB and Brainlab Monte Carlo algorithms for photon dose calculation.

PURPOSE: The Acuros® XB dose calculation algorithm by Varian and the Monte Carlo algorithm XVMC by Brainlab were compared with each other and with the well-established AAA algorithm, which is also from Varian. METHODS: First, square fields to two different artificial phantoms were applied: (1) a "slab phantom" with a 3 cm water layer, followed by a 2 cm bone layer, a 7 cm lung layer, and another 18 cm water layer and (2) a "lung phantom" with water surrounding an eccentric lung block. For the slab phantom, depth-dose curves along central beam axis were compared. The lung phantom was used to compare profiles at depths of 6 and 14 cm. As clinical cases, the CTs of three different patients were used. The original AAA plans with all three algorithms using open fields were recalculated. RESULTS: There were only minor differences between Acuros and XVMC in all artificial phantom depth doses and profiles; however, this was different for AAA, which had deviations of up to 13% in depth dose and a few percent for profiles in the lung phantom. These deviations did not translate into the clinical cases, where the dose-volume histograms of all algorithms were close to each other for open fields. CONCLUSION: Only within artificial phantoms with clearly separated layers of simulated tissue does AAA show differences at layer boundaries compared to XVMC or Acuros. In real patient CTs, these differences in the dose-volume histogram of the planning target volume were not observed.

Reduction of dosimetric impact of intrafractional prostate motion during helical tomotherapy.

BACKGROUND: In this study, the interplay between intrafractional prostate motion and helical tomotherapy (HT) radiation delivery with respect to treatment planning parameters, such as jaw size and pitch factor, was investigated. METHODS: Four treatment plans were created using two jaw widths (i.e., 1.05 and 2.5 cm) and two pitch factors (i.e., 0.287 and 0.574). A phantom with a slit for a film, attached to the motion platform, was used to simulate two-dimensional prostate motion in the superior-inferior and anterior-posterior directions. Doses were measured using gafchromic EBT films in the sagittal position. Each treatment plan was delivered to the static and dynamic phantom. Dose measurements performed with the dynamic phantom were quantitatively compared to static phantom doses in terms of dose-area histograms (DAH) for the planning target volume (PTV) and prostate, percentage of prostate and PTV receiving the prescription dose, and the minimum dose received by 95% of the prostate. RESULTS: Larger jaw width (2.5 cm) provided more adequate coverage of the PTV and prostate: D(95) of the moving prostate was 1.9 Gy for both plans with the jaw size 2.5 cm. When the jaw size was 1.05 cm, D(95) of the prostate and the PTV dropped to 1.5 Gy and 1.4 Gy, respectively. For a given jaw size, prostate and PTV dose coverage do not appear to be significantly dependent on the pitch factor. CONCLUSION: In the absence of an optimal motion management technique, the correct choice of the planning parameters is important to overcome larger under- and overdosage caused by intrafractional prostate motion during HT.

[Stereotactic radiation therapy with a modified linear accelerator in patients with brain metastases]. / Stereotaktische Strahlentherapie am adaptierten Linearbeschleuniger bei Patienten mit Hirnmetastasen.

UNLABELLED: The aim of the study was to analyze the results of stereotactic radiotherapy using a linear accelerator in patients with brain metastases. We quantified the following clinical parameters: tumor response and tumor control after therapy, survival, and side effects. Results of the treatment were compared with those from traditional treatment strategies such as surgery and whole brain irradiation. Sixty patients with brain metastases (80 lesions, 36 men and 24 women, mean age 57 years) were treated with stereotactic radiotherapy. The mean follow-up time was 13 months. CONCLUSION: Stereotactic radiotherapy is an important option in the treatment strategy for patients with brain metastases. In comparison to whole brain irradiation, stereotactic radiotherapy achieved a higher local tumor control with a lower rate of side effects. In comparison to surgery, stereotactic radiotherapy has the advantages of shorter treatment time and lower treatment-related morbidity and mortality.

Daily CT planning during boost irradiation of prostate cancer. Feasibility and time requirements.

BACKGROUND: In the irradiation of prostate cancer internal organ movement leads to uncertainties in the daily localization of the clinical target volume. Therefore more or less large safety margins are added when designing the treatment portals. With daily CT planning internal organ movement can be compensated to some extent, safety margins can be reduced and irradiated normal tissue can be spared. The feasibility of daily CT-based 3D treatment planning is studied in a patient with localized prostate carcinoma using a new patient positioning system. METHODS: Daily CT planning was applied during boost irradiation of a patient with prostate cancer: After patient immobilization the pelvis was scanned in 3 mm CT slices. Planning was done with the BrainSCAN planning system for stereotactic body irradiation. The prostate was contoured in all slices and the safety margins of the micromultileafs were automatically set to the distance chosen by the physician (0.8 cm). Patient positioning was done with the BrainLAB ExacTrac positioning system on the basis of skin attached stereotactic body markers. Before each treatment verification images of the isocenter were taken. RESULTS: The total time requirement for planning and irradiation was about 1 hour 15 minutes. Patient positioning on the treatment couch took about 10 minutes. The accuracy of the positioning system was good (75% of the deviations were smaller than 3 mm). The shift of the single markers from CT scan to CT scan was more extensive than those of the center of all 7 markers combined (47% of the deviations were smaller than 3 mm). The location of the markers seems to influence the magnitude of their dislocation. CONCLUSION: Daily CT planning is feasible but time consuming. The new patient positioning system ExacTrac is an interesting tool especially for daily CT planning since conventional simulation can be omitted.

[Prostatic carcinoma: problems in the interpretation of rectal dose-volume histograms]. / Prostatakarzinom: Zur Problematik bei der Interpretation rektaler Dosis-Volumen-Histogramme.

BACKGROUND: Dose-volume histograms (DVHs) are used for the prediction and calculation of late radiation side effects. In literature the predictive value of rectal DVHs is controversially discussed. Differences in contouring might contribute to the contradicting results. In particular the cranial and caudal border of the contoured organ are not uniformly defined. PATIENTS AND METHODS: The DVHs of 12 patients who were treated with conformal radiotherapy for prostate cancer were investigated. Six of the patients suffered from mild rectal bleeding as a late side effect of radiotherapy. Six patients without rectal bleeding (minimal follow-up 30 months) matched for age, concomitant disease and treatment concept served as controls. Four different DVHs with 4 different definitions of the cranial and caudal rectal border were generated for each patient. For each of the 48 DVHs the percent volume fractions (V50, V80, V95) and absolute volume fractions (aV50, aV80, aV95) were calculated that received more than 50%, 80% and 95% of the reference dose. RESULTS: For every patient there were considerable variations in the volume fractions depending on the definition of the rectum borders (Table 1). The mean and median values of the percent and absolute volume fractions of the bleeding patients were higher than those of the non-bleeders no matter how the rectum borders were defined. None of the volume fractions could totally separate bleeding from non-bleeding patients. CONCLUSION: There is a high variability of absolute and percent volume fractions of rectal DVHs depending on how the rectal borders were defined. For the comparison and for the interpretation of rectal DVHs a uniform definition would be helpful.

Volume-based dose optimization in brachytherapy.

PURPOSE: We address the question of how to optimize the dwell time distribution in brachytherapy with a stepping source if a minimal tumor dose is prescribed within the planning target volume (PTV). METHODS AND MATERIALS: For a given PTV, reference points inside and at the surface of the PTV are generated and dose constraints are prescribed. The dose at these reference points can be calculated if the positions of the sources are known. We determine a set of dwell times such that the dose constraints are fulfilled, and at the same time, the total irradiation time is minimized. The simplex algorithm allows us to find a solution (if any exists) for this problem. RESULTS: The performance of this method has been tested for a geometrically simple PTV. This method gives better results than conventionally used algorithms for dwell time optimization. CONCLUSION: The method described in this paper allows a volume-oriented optimization for brachytherapy dose distribution. The algorithm guarantees finding a dwell time distribution which fulfills the prescribed dose constraints, if any solution exists.

Treatment planning for conformal stereotactic radiotherapy.

Due to three dimensional planning techniques it is possible to conform the high dose region precisely to a target volume inside the brain. Special patient fixation and positioning systems allow a high precision in repositioning of the patient thus allowing fractionated stereotactic radiotherapy. Conformation can be achieved with many different irradiation techniques for example with a linear accelerator using noncoplanar arcs or conformal static beams. Noncoplanar arc therapy with multiple isocenters and conformal static beam therapy with one isocenter are compared. In both cases the DVHs of the planning target volume and normal tissue are calculated and discussed.

Oxygen tension in transplanted mouse osteosarcomas during fractionated high-LET- and low-LET radiotherapy--predictive aspects for choosing beam quality?

PURPOSE: The lower OER of high-LET radiations, compared to conventional (low-LET) radiations, has often been put forward as an argument for using high-LET radiotherapy in the management of hypoxic tumours. Among the different neutron beams used in therapy, the reactor fission neutrons have the lowest OER. The aim of the present study is to follow the variations of tumour oxygenation status during fractionated irradiation with different radiation qualities. Little information is available so far after fractionated high-LET irradiation. In addition, the RBE of reactor fission neutrons for effects on tumours and on normal tissues are compared. MATERIAL AND METHODS: Murine OTS 64-osteosarcomas were transplanted in 102 balb-C mice and irradiated by 36 Gy of photons in fractions of 3 Gy five times a week (group P-36/3) or by 12 Gy of reactor fission neutrons in fractions of 2 Gy two times a week (group N-12/2). Irradiations started at a tumor volume of 500 to 600 mm3. A third group received no radiotherapy, but all investigations (group CG). Tumor volume and tumor oxygenation were measured once a week under therapy and during three weeks after therapy. For in vivo-evaluation of oxygen status a computerized polarographic needle electrode system (KIMOC pO2 histograph, Eppendorf) was used. The median pO2 and the hypoxic fraction (pO2 values < 5 mm Hg) of single tumors and of total groups were calculated from pooled histograms and from row data as well. RESULTS: In correlation with the increase of tumor volume, from day 1 to day 42 of follow-up the median pO2 decreased from 20 mm to 8 mm Hg and the hypoxic fraction increased from 7% to 31%. After fractionated photon therapy a growth delay of three weeks was observed. Six weeks after beginning of the irradiation the median tumor volume had been doubled again. After fission neutron therapy growth delay continued until the end of the follow-up period. In both of the irradiated groups a significant decrease of median pO2 values and an increase of the hypoxic fraction were observed under radiotherapy. Hypoxia was more intensive after neutrons with a decrease of the median pO2 from 20 mm Hg to 1 mm Hg vs. 10 mm Hg after photon therapy and with an increase of the hypoxic fraction from 7% to 78% vs. 36% respectively. Two weeks after the end of therapy the median pO2 and the hypoxic fraction of both treated groups reached the levels prior to irradiation indicating a complete reoxygenation. CONCLUSION: During fractionated irradiation of murine osteosarcomas with photons and reactor fission neutrons, a marked hypoxia was observed for both radiation qualities, but hypoxia was more intense during fractionated neutron irradiation. After irradiation, a complete reoxygenation occurred in both groups independently of the degree of hypoxia observed during the treatment. The RBE of reactor fission neutrons, after fractionated irradiation, was much higher for effects on murine osteosarcomas compared to their RBE observed for normal tissues in previous experiments. Present data are in agreement with our clinical observations on more than 300 patients treated with reactor fission neutrons for advanced and hypoxic tumours with various histologies.

[Inverse radiotherapy planning]. / Inverse Bestrahlungsplanung.

BACKGROUND: In clinical practice it sometimes happens that with currently available conformal radiotherapy techniques no satisfactory dose distribution can be achieved. In these cases inverse radiotherapy planning and intensity modulated radiotherapy may give better solutions. METHOD: Inverse planning is a technique using a computer program to automatically achieve a treatment plan which has an optimal merit. This merit may either depend on dose or dose-volume constraints like minimum and maximum doses in the target region or critical organs, respectively, or biological indices like the complication free tumor control rate. As the result of inverse planning the inhomogeneous intensity fluence of the beams is calculated. These fluence distributions may be generated by beam compensators or multi-leaf collimation. RESULTS: Clinical studies to prove the advantage of inverse planning are already on the way. It has been shown that this technology is safe and that the dose distributions which can be achieved are superior to conventional methods. CONCLUSIONS: Inverse treatment planning and intensity modulated radiation therapy will almost certainly come to be the technique of choice for selected clinical cases.

Palliative radiotherapy of malignant melanoma with reactor fission neutron therapy (RENT): a prospective study.

To study the efficacy and safety of relatively low-dosed reactor fission neutron therapy (RENT) at the research reactor of the Technical University Munich, we treated 33 superficial lesions of 20 patients with advanced malignant melanoma by neutron beam alone (n = 22), mixed neutron/electron beam (n = 5), or by neutron beam after incomplete surgery (n = 6). Median tumor volume was 17.0 cm3. Median dose for neutron beam alone was 8.0 Gy and for mixed beam 3.0 Gy n + 45.3 Gy e-. Local tumor response, local control time, survival and treatment related toxicity were followed prospectively over a time period of 52 months. Overall response rate (CR;PR) after neutron beam alone and mixed beam therapy was 64% (CR: 36%) and 100% (CR: 60%), respectively. Observed differences between complete (CR) and incomplete (PR, NC) responding lesions were as follows: median tumor volume: 2.0 vs. 51.5 cm3, local control time: 13.3 vs. 3.7 months, median survival: 19.8 vs. 9.0 months. No severe acute or late sequelae could be observed. In conclusion, low-dosed RENT is an effective and well tolerated palliative treatment of superficial malignant melanoma utilizing the biologic advantage of diminished cellular repair capacity. Because melanoma lesions of small size (< or = 6 cm3) tend to respond completely, neutron beam should be performed at an early stage.

[Remarks on the dosage problem in HDR brachytherapy]. / Anmerkungen zum Problem der Doiserung in der HDR-Branchytherapie.

BACKGROUND: In HDR brachytherapy activity distributions can be achieved which were unknown in LDR brachytherapy. For this reason the classical dosage systems can only be used with caution in HDR brachytherapy. METHODS: Different simple applications are used to investigate the effect of various activity distributions on dose and integrated reference air kerma. RESULTS: Within the classical LDR dosage systems dose and integrated reference air kerma were equivalent. Due to the possibility to "optimize" the activity distribution in HDR brachytherapy this is not longer the case. Different optimization algorithms and different optimization goals may lead to quite different activity distributions and different integrated reference air kerma values even if the source positions are the same. For target volume oriented optimization schemes a dosage system is described which is based on dose-volume-histograms. CONCLUSIONS: A widely accepted dosage system in HDR brachytherapy is missing. The dosage system described in this paper may be useful in solving this problem.

[Dose-volume histograms and 3-D planning in breast-saving therapy of breast carcinoma]. / Dosis-Volumen-Histogramme und 3D-Planung bei der brusterhaltenden Therapie des Mammakarzinoms.

AIM: Improvement of the dose homogeneity in radiation treatment of the intact breast using 3D-planning and dose volume histograms. PATIENTS AND METHOD: 3D-planning, including the calculation of dose volume histograms of the planning target volume, was performed on 15 patients, who underwent radiation therapy with tangential photon beams. A standard plan and 2 modified or optimized plans were evaluated. Different dosimetric parameters like maximum dose, mean dose, standard deviation and the fractional volume which receives doses from 95 to 105% of the reference dose were compared and correlated with breast size. RESULTS: With increasing breast size standard planning leads to increased overdosage, both in magnitude and volume. Individual optimization by modifying weights and wedges gives no improvement in dose homogeneity, whereas a photon energy of 10 MV results in a more homogeneous dose distribution. The drawback of the higher energy is the increased underdosage of the skin. CONCLUSION: Using the standard geometry of tangential fields the dose homogeneity cannot be improved significantly by 3D-planning, compared to our standard technique.

[3-Dimensional irradiation planning in brain tumors. The advantages of the method and the clinical results]. / Dreidimensionale Bestrahlungsplanung bei Hirntumoren. Vorteile der Methode und klinische Ergebnisse.

PURPOSE: Radiotherapy became an important component in the treatment of brain gliomas. The aim of this study is to analyse several advantages of the three-dimensional conformal radiation therapy in comparison with a two-dimensional conventional technique and to present the clinical results of 43 patients with brain gliomas treated according to a three-dimensional planning. PATIENTS AND METHOD: Between January 1994 and December 1995, 43 patients with malignant brain gliomas (WHO III and IV) were treated in our department according to a three-dimensional treatment planning. The patients received a total irradiation dose of 60 Gy, 2 Gy/day, 5 days/week. The rate of survival was analysed in relation with the known prognostical factors: histology, Karnofsky index, age, resection status. In 10 patients a three-dimensional treatment planning was compared with a conventional two-dimensional planning: the volume of the normal brain tissue irradiated to high dose levels (95% isodose) and the normal tissue complication probability (NTCP) for the brain by Kutcher and Lyman were comparatively analysed. RESULTS: The survival rate for the whole group was 14 months. The histology of the tumor, age, Karnofsky index and resection status were important prognostical factors. The three-dimensional planning allows a 15 to 20% reduction in the volume of normal brain tissue irradiated to high dose levels (95% isodose). The NTCP is significantly lower using the three-dimensional technique (range 0.03% to 13%), in comparison with the two-dimensional conventional technique (range 0.1% to 26%). The value of NTCP increases with tumor volume. CONCLUSIONS: Concerning the tumor control and survival rate, the three-dimensional treatment planning shows no advantages compared to the standard conventional methods. The main advantage of the three-dimensional treatment planning is the possibility to spare normal brain tissue. The possibility to integrate mathematical models in the evaluation of the therapy could give this technique new dimensions.

Iridium 192 high-dose-rate brachytherapy--a useful alternative therapy for localized prostate cancer?

We report on a novel protocol involving iridium 192 high-dose-rate brachytherapy and follow-up of up to 130 months in patients with prostatic carcinoma. Using regional anesthesia, five to seven hollow needles are placed within the prostate by perineal puncture under ultrasound guidance. A 9-Gy prostate dose is applied followed by 30 min of hyperthermia (since 1991). This treatment is repeated once after 7 days; 2 weeks later, 18 x 2-Gy external beam radiation (small-field prostate) is added as percutaneous dose saturation. Since 1984 we have treated 40 patients with this protocol. Local tumor control was achieved by means of prostatic biopsy at 18 months after therapy and determination of prostate-specific antigen (PSA) values in about 70% of the patients; after a mean follow-up period of more than 6 years (16-130 months), 80% of the patients show either no evidence of disease or stable disease. We therefore conclude that iridium 192 high-dose-rate brachytherapy is a useful alternative in the treatment of localized prostate cancer in patients who are not eligible for radical prostatectomy.

[A proposal for dosage and volume specification and documentation in HDR brachytherapy]. / Vorschlag zur Dosis- und Volumenspezifikation und Dokumentation in der HDR-Brachytherapie.

BACKGROUND: Modern computer-aided brachytherapy techniques and the various clinical and radiobiological methods require a review and standardization of dose specification and documentation in brachytherapy. METHOD: The methods and the extent of the dose specification and documentation have been analysed on the base of known international and national procedure. A new modified report has been prepared for the standardized dose specification for HDR-brachytherapy techniques. RESULT: Brachytherapy treatments are supposed to be documented in 3 different levels (I to III), the extent of which depending on the treated volume, the therapeutic aim and the equipment available. CONCLUSION: The extent of documentation and dose specification proposed in this paper requires the close cooperation of radio-oncologists and medical physicists. It seems to be advantageous to use prepared sheets or computer prints in order to minimize the time and efforts for a sufficient documentation.