Investigations of peripheral dose for helical tomotherapy.

PURPOSE: Whenever treating a patient with percutaneous radiotherapy, a certain amount of dose is inevitably delivered to healthy tissue. This is mainly due to beam's entry and exit in the region of the target volume. In regions distant from the target volume, dose is delivered by leakage from the MLC and head scatter from the accelerator head and phantom scatter from the target volume (peripheral dose). Helical tomotherapy is a form of radiation therapy with a uniquely designed machine and delivery pattern which influence the peripheral dose. The goal of this work was to investigate peripheral dose in helical tomotherapy. The experiments were used to establish a complex characterization of the peripheral dose. MATERIALS AND METHODS: A 30*30*60cm(3) slab phantom and TLD-100 (Lithium fluoride) were used for the experiments. Treatment procedures were generated with the tomotherapy planning system (TPS). Additionally, procedures were created on the Operator Station of the tomotherapy system without a calculation of the dose distribution. The peripheral dose which was produced by a typical tomotherapy treatment plan was measured. Furthermore, these procedures were used to differentiate the parts of the peripheral dose in phantom scatter dose and head scatter and leakage dose. Additionally, the relation between peripheral dose and treatment time and between peripheral dose and delivered dose was investigated. Additionally, the peripheral dose was measured in an Alderson phantom. RESULTS: Distances of 30cm or more resulted in a decrease of the peripheral dose to less than 0.1% of the target dose. The measured doses have an offset of approximately 1cGy in comparison to the calculated doses from the TPS. The separated head scatter and leakage dose was measured in the range of 1cGy for typical treatments. Furthermore, the investigations show a linear correlation between head scatter leakage dose and treatment time and between scatter dose parts and delivered dose. A peripheral dose of 0.28% of the target dose was measured in the Alderson phantom at a distance of 17.5cm from the edge of the target volume. CONCLUSIONS: The peripheral dose delivered by a tomotherapy treatment is clinically unobjectionable. The measurements confirmed a linear correlation between head scatter and leakage and treatment time and between scatter dose and delivered dose.

Clinical evaluation of a laser surface scanning system in 120 patients for improving daily setup accuracy in fractionated radiation therapy.

PURPOSE: To evaluate the clinical suitability of a specific optical surface imaging system to detect setup errors in fractionated radiation therapy. METHODS AND MATERIALS: The setup correction accuracy of a 3-dimensional laser imaging system was analyzed for 6 different tumor locations with 20 patients each. For each patient, the setup corrections of the megavoltage computed tomography (MVCT) images of a TomoTherapy unit (TomoTherapy, Madison, WI) were compared with those of the laser system for the first 10 fractions. For the laser system, the reference surface either was obtained from the DICOM (Digital Imaging and Communications in Medicine) surface structure delineated on the planning computed tomography images or was acquired with the system itself at the first fraction after the MVCT-based setup correction. Data analysis was performed for both reference types. RESULTS: By use of the DICOM reference image, systematic shifts between 3 and 9 mm were found, depending on the tumor location. For the optical reference, no clinically relevant systematic shifts were found. MVCT-based setup corrections were detected with high accuracy, and only small movements were observed during treatment. CONCLUSIONS: Using a reference image acquired with the laser system itself after MVCT-based setup correction appears more reliable than importing the DICOM reference surface. After generation of the optical reference, the laser system may be used to derive setup corrections over a certain number of fractions, but additional radiologic imaging may still be necessary on a regular basis (eg, weekly) or if the corrections of the optical system appear implausibly large. Nevertheless, such a combined application may help to reduce the imaging dose for the patient.

CT-myelography for high-dose irradiation of spinal and paraspinal tumors with helical tomotherapy: revival of an old tool.

BACKGROUND AND PURPOSE: High-dose irradiation or reirradiation of spinal and paraspinal tumors is a challenge particularly in the presence of metal artifacts after surgery. Image-guided advanced intensity-modulated radiotherapy delivers high-dose radiation to the tumor sparing the spinal cord. Precise delineation of the spinal cord is necessary treating para- and intraspinal tumors with a sufficient dose. PATIENTS AND METHODS: The use of myelo-CT was evaluated in 23 patients with spinal and paraspinal tumors. All patients had had previous surgery with metal implants in the radiation area. All patients had an indication for high-dose irradiation. Treatment planning was performed using nonenhanced and contrast-enhanced myelo-CT in the same position and immobilization and both CT scans were matched. Treatment was performed by using a tomotherapy treatment unit. RESULTS: Contouring of the myelon in all slices of the myelo-CT was possible in 20 of 23 patients. All these patients were treated with doses of median 69.4 Gy in 2 Gy/1.8 Gy single doses using daily image guidance. One patient received an integrated boost with a TD/SD of 70/2.3 Gy. No side effects have been observed so far during a median follow-up of 15.5 months. No separation between tumor and myelon could be observed in 3 patients. CONCLUSION: Myelo-CT offers a distinct delineation of the myelon and the paraspinal tumor in case of artifacts due to metal implants after surgery. Using this tool in combination with advanced image guidance and IMRT techniques, patients with relatively radioresistent paraspinal tumors might have the chance of improved local control using higher target doses.

Leakage of the Siemens 160 MLC multileaf collimator on a dual energy linear accelerator.

Multileaf collimators (MLCs) have been in clinical use for many years and meanwhile are commonly used to deliver intensity-modulated radiotherapy (IMRT) beams. For this purpose it is important to know their dosimetric properties precisely, one of them being inter- and intraleaf leakage. The Siemens 160 MLC features a single focus design with flat-sided and tilted leaves instead of tongue-and-groove. The leakage performance of the 160 MLC was investigated on a dual energy linear accelerator Siemens ARTISTE with 6 MV and 18 MV photon energies. While the intraleaf leakage amounted to nearly the same dose for 6 and for 18 MV, a much higher interleaf leakage for 6 MV was measured. It could be reduced by simply rotating the collimator, and also by changing the voltage applied to the beam steering coils. The leakage of the 160 MLC is shown to be sensitive to beam alignment. This is of special interest for dual energy accelerators, as the two focal spots of both energies, neither in position nor in shape, do not necessarily always coincide. As a consequence of that, a higher leakage can be expected for one out of two energies for the 160 MLC.

Technical performance of a commercial laser surface scanning system for patient setup correction in radiotherapy.

In conformal radiotherapy, careful setup of the patient and setup verification prior to irradiation is essential. The technical performance of a commercial 3D-surface imaging system (Galaxy, LAP Laser, Lüneburg, Germany) for patient setup correction was evaluated. The system reconstructs a 3D-surface model by scanning the patient with a laser line while a camera records its reflections. This surface model is then compared with a reference model and a setup correction with 6 degrees of freedom is derived. The calibration stability of the system was investigated using the daily check phantom of the manufacturer. The accuracy and reproducibility of the system were investigated with an anthropomorphic phantom by performing 1D- and 3D-shifts with and without breathing of the phantom, respectively. In addition, measurements in a healthy volunteer were performed. With a few exceptions, the day-by-day variations of the calibration were <0.5mm in LAT and LNG direction and <1.5mm in VRT direction, respectively. Besides day-by-day variations, also baseline-shifts of up to 3mm were observed. The lowest observed accuracy of the system in detecting pre-defined shifts of the rigid phantom was found in lateral direction. Here, mean deviations of -0.15 ± 0.46 mm for 1D-shifts and -0.12 ± 0.26 mm for 3D-shifts were found. For the ventilated phantom, the lowest observed accuracy was found in vertical direction with mean deviations of 1.16 ± 0.6mm for 1D-shifts and -0.45 ± 0.57 mm for 3D-shifts. In a healthy volunteer, the accuracy was lowest in longitudinal direction with 1.7 ± 1.5mm. The overall technical accuracy of the surface imaging system can be considered to be acceptable for application in fractionated radiotherapy. For special radiotherapy techniques such as SBRT, an increased accuracy might be necessary. To define the clinical role of the system, patient studies for different target locations are required.

Dynamic jaws and dynamic couch in helical tomotherapy.

PURPOSE: To investigate the next generation of helical tomotherapy delivery with dynamic jaw and dynamic couch movements. METHODS AND MATERIALS: The new technique of dynamic jaw and dynamic couch movements is described, and a comparative planning study is performed. Ten nasopharyngeal cancer patients with skull base infiltration were chosen for this comparison of longitudinal dose profiles using regular tomotherapy delivery, running-start-stop treatment, and dynamic jaw and dynamic couch delivery. A multifocal simultaneous integrated boost concept was used (70.4Gy to the primary tumor and involved lymph nodes; 57.4Gy to the bilateral cervical lymphatic drainage pathways, 32 fractions). Target coverage, conformity, homogeneity, sparing of organs at risk, integral dose, and radiation delivery time were evaluated. RESULTS: Mean parotid dose for all different deliveries was between 24.8 and 26.1Gy, without significant differences. The mean integral dose was lowered by 6.3% by using the dynamic technique, in comparison with a 2.5-cm-field width for regular delivery and 16.7% with 5-cm-field width for regular delivery. Dynamic jaw and couch movements reduced the calculated radiation time by 66% of the time required with regular 2.5-cm-field width delivery (199 sec vs. 595 sec, p < 0.001). CONCLUSIONS: The current delivery mode of helical tomotherapy produces dose distributions with conformal avoidance of parotid glands, brain stem, and spinal cord. The new technology with dynamic jaw and couch movements improves the plan quality by reducing the dose penumbra and thereby reducing the integral dose. In addition, radiation time is reduced by 66% of the regular delivery time.

Surface dose in the treatment of breast cancer with helical tomotherapy.

PURPOSE: Investigation of the effects of breathing motion- and misregistration-induced errors on the superficial dose in the treatment of breast cancer using helical tomotherapy (HT). MATERIAL AND METHODS: Surface dose measurements were performed with thermoluminescence dosimetry (TLD). Two treatment plans with different planning target volume (PTV) definitions of the left breast were used: PTVskin had its ventral border exactly on skin level, while PTVair included also a 10-mm extension ventral to the PTVskin. With a thoracic static phantom, misregistration errors in an HT were simulated. A dynamic phantom was used to simulate a breathing patient during HT. Surface doses of breast cancer patients were measured both for an HT (179 points) and a conventional three-dimensional conformal treatment (70 points). RESULTS: In the static phantom misregistration setup, dose deviations of -31.9% for PTVskin to +35.4% for PTVair could be observed. The dynamic phantom measurements resulted in surface dose deviations from those in a static position between 0.8% and 3.8% without a significant difference for the PTV definitions. The measured surface doses on patients averaged (mean +/- standard deviation) 1.65 +/- 0.13 Gy for the HT and 1.42 +/- 0.11 Gy for the three-dimensional conformal treatment. CONCLUSION: HT enables a homogeneous and reproducible surface dose with small dose deviations in the treatment of breast cancer. HT is a feasible method to treat breast cancer under free shallow breathing of the patient using a treatment plan with a ventral PTV border on the skin level.

Megavoltage CT in helical tomotherapy - clinical advantages and limitations of special physical characteristics.

Helical tomotherapy is a form of image-guided intensity-modulated radiotherapy that introduces the ring gantry concept into radiation oncology. The system is a combination of a therapeutic linear accelerator and a megavoltage CT-scanner. This work describes the clinical experience with megavoltage CT with 456 patients in more than 11000 fractions. It also provides a review of the current literature of the possibilities and limitations of megavoltage CT. Between July 2006 and October 2008 456 patients were treated with helical tomotherapy and a pretreatment megavoltage CT was performed in 98.1% of the 11821 fractions to perform position control and correction. CT image acquisition was done with 3.5 MV x-rays in the helical tomotherapy machine. MVCT was used for dose recalculations to quantify doses distributions in cases of changing geometry, tumor shrinkage or presence of metal implants. Inverse treatment planning for prostate cancer patients with bilateral hip replacements was performed based upon an MVCT. A mean 3D-correction vector of 7.1mm with a considerable variation was detected and immediately corrected. Mean shifts were lateral 0.9mm (sd 5.0mm), mean longitudinal shift 1.0mm (sd 5.1mm) and mean vertical shift 3.2mm (sd 5.2mm). The MVCT enables imaging of anatomical structures in the presence of dental metal or orthopedic implants. Especially in these cases, dose recomputations can increase the precision of dose calculations. Due to a mean 3d correction vector of more than 7mm and a variation of corrections of more than 5mm daily image-guidance is recommended to achieve a precise dose application. The MVCT shows evident advantages in cases with metal implants but has limitations due to a reduced soft tissue contrast. Compared with megavoltage cone-beam-CT the tomotherapy fan beam CT adds less extra dose fore the patient and has a better soft tissue contrast.

Influence of intravenous contrast agent on dose calculation in 3-D treatment planning for radiosurgery of cerebral arteriovenous malformations.

PURPOSE: To investigate the influence of local density increase by i.v. contrast agent on dose calculation in linac-based radiosurgery (RS) of cerebral arteriovenous malformations (AVMs). MATERIAL AND METHODS: RS was performed after three-dimensional (3-D) treatment planning using a total number of nine to 14 beams. Mean target volume was 5.3 cm(3) (range, 0.1-41.2 cm(3)). Mean maximum diameter was 23.2 mm (range, 8-51 mm). Dose deviation was estimated and calculated from the enhanced and unenhanced datasets of 30 patients. Dose calculation was performed using the same RS treatment plan on both datasets. Both plans were standardized to 1 Gy at isocenter with the same dose weight for all beams. RESULTS: Mean difference of Hounsfield units (DeltaHU) between enhanced and unenhanced CT was 152 HU (range, 50-350 HU). The estimated dose deviation was

Dosimetric comparison of image guidance by megavoltage computed tomography versus bone alignment for prostate cancer radiotherapy.

BACKGROUND AND PURPOSE: Daily image guidance in irradiation of prostate cancer can be based on simple portal images or on soft-tissue imaging. This study compares daily bone alignment with daily pretreatment megavoltage computed tomography (MVCT). PATIENTS AND METHODS: Ten patients with a total of 356 fractions were analyzed. Before each fraction, the patient was positioned to match the prostate on pretreatment MVCT and planning CT. In seven fractions, rectum distension prevented a satisfactory match and the fraction was restarted after the patient went to the restroom. After treatment, organs were manually contoured on each daily MVCT and doses recalculated. Bone alignment was simulated by a software that matches the bones on MVCT and planning CT. RESULTS: In the seven interrupted fractions, median improvement of rectum volume receiving full fraction dose was 14 cm(3) between simulated treatment before and actual treatment after the patient went to the restroom. In the 349 noninterrupted fractions, the average difference of the isodose that covers 95% of the prostate between actual treatment position and simulated bone match position was < 1% and there was no significant change in the rectum volume with a fraction dose > or = 2 Gy. CONCLUSION: Full fraction dose rectum irradiation can be avoided with daily MVCT by interruption of single fractions. There was no relevant benefit of daily MVCT in the noninterrupted fractions with the margins used in this study.

Reirradiation of multiple brain metastases with helical tomotherapy. A multifocal simultaneous integrated boost for eight or more lesions.

BACKGROUND AND PURPOSE: : Recurrent brain metastases or new brain lesions after whole-brain radiotherapy represent a therapeutic challenge. While several treatment methods for single or few lesions have been described, options for multiple lesions are limited. This case report is intended to show an approach of whole-brain reirradiation with a simultaneous multifocal integrated boost using helical tomotherapy. Technique, feasibility, and acute side effects are presented. PATIENTS AND METHODS: : Two patients with multiple relapsed brain metastases (eight and eleven lesions) were reirradiated after previous whole-brain radiotherapy (total dose of 40 Gy 18 months before). Whole-brain reirradiation was performed using helical tomotherapy with a total dose of 15 Gy (single dose 1.5 Gy) and a multifocal simultaneous integrated boost with a total dose of 30 Gy (single dose 3 Gy) to the brain lesions. The boost planning target volume was delineated around the lesions visible on MRI plus a 2-mm margin. Follow-up of these patients was 6 and 12 months. RESULTS: : Radiation plans with excellent conformity and homogeneity were obtained. High dose exposure to normal brain tissue was kept minimal. Mean radiation time was 13 min. The only acute side effect observed was a mild headache over 2 days at the end of treatment. So far, no further side effects and no signs of recurrence have been observed. CONCLUSION: : Helical tomotherapy offers new treatment options for the reirradiation of multiple brain metastases. The number of cases treated with the described protocol is very limited but it is considered a promising option for patients that have responded well to the initial radiotherapy and are in a good performance status.

Helical tomotherapy. Experiences of the first 150 patients in Heidelberg.

BACKGROUND AND PURPOSE: Helical tomotherapy was introduced into clinical routine at the Department of Radiation Oncology, University Hospital of Heidelberg, Germany, in July 2006. This report is intended to describe the experience with the first 150 patients treated with helical tomotherapy. Patient selection, time effort, handling of daily image guidance with megavoltage (MV) CT, and quality of radiation plans shall be assessed. PATIENTS AND METHODS: Between July 2006 and May 2007, 150 patients were treated with helical tomotherapy in the University Hospital of Heidelberg. Mean age was 60 years with a minimum of 30 years and a maximum of 85 years. 79 of these patients received radiotherapy as a part of multimodal treatment pre- or postoperatively, 17 patients received treatment as a combined radiochemotherapy. 76% were treated with curative intent. Radiotherapy sites were central nervous system (n = 7), head and neck (n = 28), thoracic (n = 37), abdominal (n = 58) and skeletal system (n = 20). Most common tumor entities were prostate cancer (n = 28), breast cancer (n = 17), gastrointestinal tumors (n = 19), pharyngeal carcinoma (n = 14), lymphoma (n = 13), metastatic disease (bone n = 14, liver n = 6, lung n = 4, lymph node n = 2), sarcoma (n = 8), malignant pleural mesothelioma (n = 5), ovarian cancer treated with whole abdominal irradiation (n = 4), lung cancer (n = 3), skin malignancies (n = 3), chordoma (n = 2), meningioma (n = 2), one ependymoma and one medulloblastoma treated with craniospinal axis irradiation (n = 2), and others (n = 4). Nine patients were treated with single-fraction radiosurgery, nine with image-guided spinal reirradiation, and twelve patients were treated at multiple targets simultaneously. A pretreatment MV-CT scan was performed in 98.2% of the 3,026 fractions applied. After matching with the kilovoltage planning CT, corrections for translations and rotation around longitudinal axis (roll) were done. RESULTS: Mean time on table was 24.8 min for the mentioned tumor entities with fractionated radiation, mean treatment time 10.7 min. Mean correction vector after MV-CT registration was 6.9 mm. With helical tomotherapy it was possible to achieve highly conformal dose distributions for targets of all sizes and multiple targets within one procedure. Image guidance with MV-CT allowed daily position correction and safe and precise treatment application. This was feasible even if the desired immobilization was not possible due to obesity, claustrophobia, pain, or neurologic or orthopedic impairment. CONCLUSION: Helical tomotherapy and daily image guidance with MV-CT could fast be introduced into daily clinical routine. This technique allows precise intensity-modulated radiotherapy (IMRT) in standard cases and offers new treatment options in a huge variety of difficult cases.

Evaluating target coverage and normal tissue sparing in the adjuvant radiotherapy of malignant pleural mesothelioma: helical tomotherapy compared with step-and-shoot IMRT.

PURPOSE: To evaluate the potential of helical tomotherapy in the adjuvant treatment of malignant pleural mesothelioma and compare target homogeneity, conformity and normal tissue dose with step-and-shoot intensity-modulated radiotherapy. METHODS AND MATERIALS: Ten patients with malignant pleural mesothelioma who had undergone neoadjuvant chemotherapy with cisplatin and permetrexed followed by extrapleural pneumonectomy (EPP) were treated in our department with 54 Gy to the hemithorax delivered by step-and-shoot IMRT. A planning comparison was performed by creating radiation plans for helical tomotherapy. The different plans were compared by analysing target homogeneity using the homogeneity indices HI(max) and HI(min) and target conformity by using the conformity index CI(95). To assess target coverage and normal tissue sparing TV(90), TV(95) and mean and maximum doses were compared. RESULTS: Both modalities achieved excellent dose distributions while sparing organs at risk. Target coverage and homogeneity could be increased significantly with helical tomotherapy compared with step-and-shoot IMRT. Mean dose to the contralateral lung could be lowered beyond 5 Gy. CONCLUSIONS: Our planning study showed that helical tomotherapy is an excellent option for the adjuvant intensity-modulated radiotherapy of MPM. It is capable of improving target coverage and homogeneity.

Accuracy of a commercial optical 3D surface imaging system for realignment of patients for radiotherapy of the thorax.

Accurate and reproducible patient setup is a prerequisite to fractionated radiotherapy. To evaluate the applicability and technical performance of a commercial 3D surface imaging system for repositioning of breast cancer patients, measurements were performed in a rigid anthropomorphic phantom as well as in healthy volunteers. The camera system records a respiration-gated surface model of the imaged object, which may be registered to a previously recorded reference model. A transformation is provided, which may be applied to the treatment couch to correct the setup of the patient. The system showed a high stability and detected pre-defined shifts of phantoms and healthy volunteers with an accuracy of 0.40 +/- 0.26 mm and 1.02 +/- 0.51 mm, respectively (spatial deviation between pre-defined shift and suggested correction). The accuracy of the suggested rotational correction around the vertical axis was always better than 0.3 degrees in phantom measurements and 0.8 degrees in volunteers, respectively. Comparison of the suggested setup correction with that detected by a second and independently operated marker-based optical system provided consistent results. The results demonstrate that the camera system provides highly accurate setup corrections in a phantom and healthy volunteers. The most efficient use of the system for improving the setup accuracy in breast cancer patients has to be investigated in routine patient treatments.

Long-term results and predictive factors of three-dimensional conformal salvage radiotherapy for biochemical relapse after prostatectomy.

PURPOSE: Salvage radiotherapy (RT) is used to treat patients with biochemical failure after radical prostatectomy (RP). Although retrospective series have demonstrated that salvage RT will result in biochemical response in approximately 75% of patients, long-term response is much lower (20-40%). The purpose of this study was to determine prognostic factors related to the prostate-specific antigen (PSA) outcome after salvage RT. METHODS AND MATERIALS: Between 1991 and 2004, 171 patients received salvage RT at the University of Heidelberg. Patient age, margin status, Gleason score, tumor grading, pathologic tumor stage, pre-RP and pre-RT PSA levels, and time from RP to rise of PSA were analyzed. RESULTS: Median follow-up time was 39 months. The 5-year overall and clinical relapse-free survival were 93.8% and 80.8%, respectively. After RT serum PSA decreased in 141 patients (82.5%). The 5-year biochemical relapse-free survival was 35.1%. Univariate analysis showed following statistically significant predictors of PSA recurrence after RT: preoperative PSA level (p = 0.035), pathologic tumor classification (p = 0.001), Gleason score (p < 0.001), tumor grading (p = 0.004), and pre-RT PSA level (p = 0.031). On multivariate analysis, only Gleason score (p = 0.047) and pre-RT PSA level (p = 0.049) were found to be independently predictive of PSA recurrence. CONCLUSIONS: This study represents one of the largest retrospective studies analyzing the outcome of patients treated with salvage RT at a single institution. Our findings suggest that patients with Gleason score <7 and low pre-RT PSA levels are the best candidates for salvage RT, whereas patients with high-grade lesions should be considered for additional treatment (e.g., hormonal therapy).

Inversely planned intensity modulated radiotherapy of the breast including the internal mammary chain: a plan comparison study.

The aim of this paper is to evaluate the benefit of inversely planned intensity modulated radiotherapy (IMRT) in the adjuvant irradiation of breast cancer when internal mammary lymph nodes are included in the treatment volume. 20 patients treated with 3D-planned conventional radiotherapy (CRT) following breast conserving surgery were included in the study. We chose 10 patients with left-sided and 10 patients with right-sided tumors. All treatment volumes included the internal mammary chain. For plan comparison to the applied CRT plan an inverse IMRT-plan in, step-and-shoot'-technique was calculated. For all patients IMRT resulted in an improved conformity of dose distribution to the target volume compared to CRT (mean COIN95: 0.798 vs. 0.514 with COIN95 = C1 * C2 (C1= fraction of CTV that is covered by > 95% of the prescribed dose and C2 = volume of CTV that is covered by > 95% of the prescribed dose/total volume that is covered by > 95% of the prescribed dose). In all cases with matching adjacent beams, the homogeneity in the target volume was improved. The volume of the ipsilateral lung irradiated with a dose higher than 20 Gy was reduced with IMRT from 24.6% to 13.1% compared to CRT. For left-sided target volume the heart volume with a dose higher than 30 Gy was reduced from 6.2% to 0.2%. The presented plan comparison study for irradiation of the breast and the parasternal lymph nodes showed a substantial improvement of the dose distribution by inversely planned IMRT compared to CRT. This is visible for the target volume, the ipsilateral lung and, in case of left-sided target volume, the heart. Despite an increase in integral dose to the entire normal tissue, the application of IMRT might be clinically advantageous in cases where no satisfying dose distribution can be obtained by CRT.

[Lung dose depending on exact patient positioning during total body irradiation (TBI). Isoeffectiveness considerations to assess the risk of interstitial pneumonia after TBI]. / Lungendosis in Abhängigkeit von der Lagerungsgenauigkeit bei Ganzkörperbestrahlungen (TBI). Isoeffektivitätsüberlegungen zur Einschätzung des Risikos einer interstitiellen Pneumonitis nach Ganzkörperbestrahlung.

PURPOSE: In this case report, we studied the effect of patient's movements on total lung dose during total body irradiation (TBI). The dose-effect relationship regarding the development of interstitial pneumonitis and the problem of defining a threshold value are discussed. Based on considerations about the isoeffects we calculated the pneumonitis risk in dependence of increasing lung dose. PATIENTS AND METHOD: We calculated dose-volume histograms of the lung for defined lateral deviations (0-3 cm) from the isocenter. Total dose was 12 Gy, given in six fractions over 3 days. Lung shields were used after a total dose of 9 Gy. Lung shields were transferred into the Helax-TMS planning system to quantify the influence of lateral deviation to lung dose. RESULTS: The child's lateral deviation amounted up to 3 cm. Median dose of the whole lung amounted up to 11.64 Gy depending on lateral deviation. DISCUSSION: In TBI, the lung limits the total dose. To estimate the risk of radiation pneumonitis, we calculated the isoeffective lung dose of our TBI regime for a fractionation scheme of 2 Gy daily using a formalism of van Dyk. The increase of median lung dose from 9.76 to 11.64 Gy would isoeffectively correspond to the increase from 19 Gy (no deviation) to 20.9 Gy (3 cm lateral deviation) with conventional fractionation. According to Burman, a pneumonitis risk of approximately 20% could be expected. CONCLUSION: With an estimated pneumonitis risk of approximately 20%, in indication for irradiation in general anesthesia seems to be reasonable. This is practicable in cooperation with radiation oncologists, anesthesists and pediatricians and should be included into therapeutic concepts.