Physics and imaging for targeting of oligometastases

Surgical management and minimally invasive approaches for the treatment of metastatic sarcoma

Soft tissue sarcomas describe a very heterogeneous group of soft tissue tumors mainly arising in the lower extremities. If diagnosed at an early stage and a complete resection of the primary tumor is achieved, the patients' prognosis is excellent. However, metastatic tumor spread is common with only limited treatment possibilities. Despite an improved insight into tumor biology of sarcomas, no notable improvement has been gained in the last 20 years regarding prognosis of patients. Metastatic lung disease has long been the preserve of systemic treatments, local treatments being considered in a purely palliative intention. Several studies have objectified benefit to the local treatment of metastases, especially in an oligometastatic state. The development of techniques for stereotactic radiotherapy on the one hand and the refusal or contraindication for surgery on the other hand inaugurated studies in this direction. Besides surgery and radiotherapy, other local modalities have been investigated in the last few years such as thermal therapy (radiofrequency and laser ablation) or combined modalities (isolated limb perfusion and deep-wave hyperthermia plus chemotherapy) to help patients with metastatic soft tissue sarcoma. Minimally invasive, image-guided therapies such as thermal ablation should be considered particularly in patients who are not suitable surgical candidates or may have exhausted all other viable surgical options. Some of these techniques will be reviewed in this article, and their value for the patients will be evaluated in the light of indication from tumor biology and technical feasibility. These highly selected and specific procedures should only be performed after decision making in an interdisciplinary sarcoma-board.

Extending the Frontiers Beyond Thermal Ablation by Radiofrequency Ablation: SBRT, Brachytherapy, SIRT (Radioembolization)

Metastatic spread of the primary is still defined as the systemic stage of disease in treatment guidelines for various solid tumors. This definition is the rationale for systemic therapy. Interestingly and despite the concept of systemic involvement, surgical resection as a local treatment has proven to yield long-term outcomes in a subset of patients with limited metastatic disease, supporting the concept of oligometastatic disease. Radiofrequency ablation has yielded favorable outcomes in patients with hepatocellular carcinoma and colorectal metastases, and some studies indicate its prognostic potential in combined treatments with systemic therapies. However, some significant technical limitations apply, such as size limitation, heat sink effects, and unpredictable heat distribution to adjacent risk structures. Interventional and non-invasive radiotherapeutic techniques may overcome these limitations, expanding the options for oligometastatic patients and cytoreductive concepts. Current data suggest very high local control rates even in large tumors at any given location in the human body. The article focusses on the characteristics and possibilities of stereotactic body radiation therapy, interstitial high-dose-rate brachytherapy, and Yttrium-90 radioembolization. In this article, we discuss the differences of the technical preferences as well as their impact on indications. Current data is presented and discussed with a focus on application in oligometastatic or cytoreductive concepts in different tumor biologies.

Local ablative treatments of oligometastases from head and neck carcinomas

BACKGROUND

Median survival for recurrent/metastatic (unknown poly/oligometastatic status) head and neck cancer patients (HNSCC) is ten months with best systemic treatment. Metastatic ablation shows promising results in selected patients with several tumor types. We aimed to assess the role of surgery and stereotactic ablative body radiotherapy (SABR) with respect to survival in HNSCC.

MATERIALS AND METHODS

Published data on metastatic HNSCC treated ablatively were analyzed.

RESULTS

Five-year survival rates after pulmonary/liver metastasectomy exceed 20% in selected patients. Two-year survival after lung SABRT of metastasectomy yields 35%. Interesting data on survival and tolerance are reported in other metastatic sites.

CONCLUSION

Surgery yields the best level of evidence. However, non-invasive SABR is efficient and well-tolerated in lung/liver, bone and other metastatic locations. Systemic treatment may be given sequentially with ablative treatments, or omitted in well-identified situations. Proper patient selection for local ablative treatment and optimal therapeutic sequence should be assessed in randomized trials.

Oligometastasis as a predictor for occult disease

Oligometastasis can be defined as a state of limited metastases that is potentially amenable to ablative local therapy; the success of such therapy depends on whether or not additional occult metastases exist. A model is presented here to predict occult metastases given detectable oligometastases. Predictions were based on Bayes' theorem, in conjunction with descriptions of the statistical distributions for the sizes and numbers of hematogenous metastases. The background probability for occult metastases in individuals with oligometastases increased markedly with relatively minor increases in metastatic potential. With each additional metastasis detected the chance of further occult metastases increased. These latter increases were incremental and proportionately smaller with the more metastatic tumors. Long disease free intervals had a major effect to decrease in the probability of further occult disease. Demonstration of oligometastases depends heavily upon the sensitivity of radiological imaging techniques, where the proportion of detectable metastases relates to the position of the distribution of metastasis growth times with respect to the detection threshold. Given the limitations of radiological methods, and the possibility that the oligometastases detected may be the only disease, an aggressive approach appears indicated.

Spinal cord compression in childhood pediatric malignancies: multicenter egyptian study

OBJECTIVES

To assess the magnitude of management delay of pediatric malignant spinal cord compression (MSCC).

METHODS

Twenty-four patients with MSCC were recruited from 3 Egyptian pediatric oncology centers and assessed for MSCC clinical presentations, evaluation, and treatment response.

RESULTS

There was a median delay of 42 days from the onset of symptom until confirmed diagnosis. All studied patients presented inability to walk; 79% had pain (more in older patients) and 17% had sphincteric dysfunction. A total of 58.3% had a single level of cord compression, 41.7% had multiple levels. Thoracic spine was commonly involved (41%). Final diagnosis was: neuroblastoma (29.2%), soft-tissue sarcomas (20.8%), neuroectodermal tumor (16.6%), non-Hodgkin lymphoma (12.5%), astrocytoma (4.2%), malignant teratoma (8.4%), Wilms tumor (4.2%), and leukemia (4.2%). Magnetic resonance imaging of the spine was diagnostic in all cases. A total of 83.3% of patients received emergency steroid therapy and 75% showed improvement. Disease-specific therapy was multimodality therapy in 88.5% with 71.42% showing improvement. Lymphomas had the best neurological outcome (100%) followed by soft-tissue sarcomas (80%) and neural tumors (72.7%). The 3-year overall survival was 79.2%.

CONCLUSIONS

Spinal cord compression is a serious complication and unacceptable management delay can result in preventable loss of function. Emergency magnetic resonance imaging evaluation is the most sensitive diagnostic imaging. Majority of patients improve after definitive therapy.

[Oligometastatic disease, a new concept: stereotactic irradiation for lung metastases. Literature review]

Metastatic lung disease has long been the preserve of systemic treatments, local treatments being considered in a purely palliative intention. Several studies have objectified benefit to the local treatment of metastases, especially oligometastases. Surgery then took an important place in this setting, but the development of techniques for stereotactic radiotherapy on the one hand and the refusal or contraindication for surgery on the other hand led authors to conduct studies in this direction. This literature review describes the realization of stereotactic radiotherapy in treating pulmonary oligometastases and evaluates criteria for the selection of patients who would benefit. A comparison between the results of different studies on this technique allowed to show its effectiveness for local control, overall survival and tolerance. Stereotactic radiotherapy has emerged as a viable alternative, effective and well tolerated with local control rates comparable to that obtained by surgery (74 to 100%). Quality of life after stereotactic radiotherapy should be in a near future an important parameter to support this therapeutic choice, and needs to be precisely assessed.

Stereotactic body radiation therapy for abdominal oligometastases: a biological and clinical review

Advances in imaging and biological targeting have led to the development of stereotactic body radiation therapy (SBRT) as an alternative treatment of extracranial oligometastases. New radiobiological concepts, such as ceramide-induced endothelial apoptosis after hypofractionated high-dose SBRT, and the identification of patients with oligometastatic disease by microRNA expression may yet lead to further developments. Key factors in SBRT are delivery of a high dose per fraction, proper patient positioning, target localisation, and management of breathing-related motion. Our review addresses the radiation doses and schedules used to treat liver, abdominal lymph node (LN) and adrenal gland oligometastases and treatment outcomes. Reported local control (LC) rates for liver and abdominal LN oligometastases are high (median 2-year actuarial LC: 61 -100% for liver oligometastases; 4-year actuarial LC: 68% in a study of abdominal LN oligometastases). Early toxicity is low-to-moderate; late adverse effects are rare. SBRT of adrenal gland oligometastases shows promising results in the case of isolated lesions. In conclusion, properly conducted SBRT procedures are a safe and effective treatment option for abdominal oligometastases.

Potential underestimation of the internal target volume (ITV) from free-breathing CBCT

PURPOSE

Localization prior to delivery of SBRT to free-breathing patients is performed by aligning the planning internal target volume (ITV) from 4DCT with an on-board free-breathing cone-beam CT (FB-CBCT) image. The FB-CBCT image is assumed to also generate an ITV that captures the full range of motion, due to the acquisition spanning multiple respiratory cycles. However, the ITV could potentially be underestimated when the ratio of time spent in inspiration versus time spent in expiration (I/E ratio) deviates from unity. Therefore, the aim of this study was to investigate the effect of variable I/E ratios on the FB ITV generated from a FB-CBCT scan.

METHODS

This study employed both phantom and patient imaging data. For the phantom study, five periodic respiratory cycles were simulated with different I/E ratios. Six patient respiratory cycles with variable I/E ratios were also selected. All profiles were then programmed into a motion phantom for imaging and modified to exhibit three peak-to-peak motion amplitudes (0.5, 1.0, and 2.0 cm). Each profile was imaged using two spherical targets with 1.0 and 3.0 cm diameters. 2D projections were acquired with full gantry rotation of a kiloVoltage (kV) imager mounted onto the gantry of a modem linear accelerator. CBCT images were reconstructed from 2D projections using a standard filtered back-projection reconstruction algorithm. Quantitative analyses for the phantom study included computing the change in contrast along the direction of target motion as well as determining the area (which is proportional to the target volume) inside of the contour extracted using a Canny edge detector. For the patient study, projection data that were previously acquired under an investigational 4D CBCT slow-gantry imaging protocol were used to generate both FB-CBCT and 4D CBCT images. Volumes were then manually contoured from both datasets (using the same window and level) for quantitative comparison.

RESULTS

The phantom study indicated a reduction in contrast at the inferior edge of the ITV (corresponding to inspiration) as the ratio decreased, for both simulated and patient respiratory cycles. For the simulated phantom respiratory cycles, the contrast reduction of the smallest I/E ratio was 27.6% for the largest target with the smallest amplitude and 89.7% for the smallest target with the largest amplitude. For patient respiratory cycles, these numbers were 22.3% and 94.0%, respectively. The extracted area from inside of the target contours showed a decreasing trend as the I/E ratio decreased. In the patient study, the FB-CBCT ITVs of both lung tumors studied were underestimated when compared with their corresponding 4D CBCT ITV. The underestimations found were 40.1% for the smaller tumor and 24.2% for the larger tumor.

CONCLUSIONS

The ITV may be underestimated in a FB-CBCT image when a patient's respiratory pattern is characterized by a disparate length of time spent in inspiration versus expiration. Missing the full target motion information during on-board verification imaging may result in localization errors.

Biodegradable PLGA based nanoparticles for sustained regional lymphatic drug delivery

The purpose of this work is to evaluate biodegradable drug carriers with defined size, hydrophobicity, and surface charge density for preferential lymphatic uptake and retention for sustained regional drug delivery. PLGA-PMA:PLA-PEG (PP) nanoparticles of defined size and relative hydrophobicity were prepared by nanoprecipitation method. These were compared with PS particles of similar sizes and higher hydrophobicity. PLGA-PMA:PLGA-COOH (PC) particles at 80:20, 50:50, and 20:80 ratios were prepared by nanoprecipitation for the charge study. Particle size and zeta potential were characterized by dynamic light scattering and laser doppler anemometry, respectively. Particles were administered in vivo to rats subcutaneously. Systemic and lymph node uptake was evaluated by marker recovery. Lymphatic uptake and node retention of PP nanoparticles was shown to be inversely related to size. Lymphatic uptake and node retention of PP particles, as compared to PS particles, was shown to be inversely related to hydrophobicity. Lastly, lymphatic uptake and node retention of PC nanoparticles were directly related to the anionic charge on the particles. In vivo lymphatic uptake and retention in a rat model indicates that the 50 nm PP particles are ideal for sustained regional delivery into the lymphatics for prevention/treatment of oligometastases.

Biodegradable PLGA based nanoparticles for sustained regional lymphatic drug delivery

The purpose of this work is to evaluate biodegradable drug carriers with defined size, hydrophobicity, and surface charge density for preferential lymphatic uptake and retention for sustained regional drug delivery. PLGA-PMA:PLA-PEG (PP) nanoparticles of defined size and relative hydrophobicity were prepared by nanoprecipitation method. These were compared with PS particles of similar sizes and higher hydrophobicity. PLGA-PMA:PLGA-COOH (PC) particles at 80:20, 50:50, and 20:80 ratios were prepared by nanoprecipitation for the charge study. Particle size and zeta potential were characterized by dynamic light scattering and laser doppler anemometry, respectively. Particles were administered in vivo to rats subcutaneously. Systemic and lymph node uptake was evaluated by marker recovery. Lymphatic uptake and node retention of PP nanoparticles was shown to be inversely related to size. Lymphatic uptake and node retention of PP particles, as compared to PS particles, was shown to be inversely related to hydrophobicity. Lastly, lymphatic uptake and node retention of PC nanoparticles were directly related to the anionic charge on the particles. In vivo lymphatic uptake and retention in a rat model indicates that the 50 nm PP particles are ideal for sustained regional delivery into the lymphatics for prevention/treatment of oligometastases.

Refinement of treatment setup and target localization accuracy using three-dimensional cone-beam computed tomography for stereotactic body radiotherapy

PURPOSES

To quantitatively compare two-dimensional (2D) orthogonal kV with three-dimensional (3D) cone-beam CT (CBCT) for target localization; and to assess intrafraction motion with kV images in patients undergoing stereotactic body radiotherapy (SBRT).

METHODS AND MATERIALS

A total of 50 patients with 58 lesions received 178 fractions of SBRT. After clinical setup using in-room lasers and skin/cradle marks placed at simulation, patients were imaged and repositioned according to orthogonal kV/MV registration of bony landmarks to digitally reconstructed radiographs from the planning CT. A subsequent CBCT was registered to the planning CT using soft tissue information, and the resultant "residual error" was measured and corrected before treatment. Posttreatment 2D kV and/or 3D CBCT images were compared with pretreatment images to determine any intrafractional position changes. Absolute averages, statistical means, standard deviations, and root mean square (RMS) values of observed setup error were calculated.

RESULTS

After initial setup to external marks with laser guidance, 2D kV images revealed vector mean setup deviations of 0.67 cm (RMS). Cone-beam CT detected residual setup deviations of 0.41 cm (RMS). Posttreatment imaging demonstrated intrafractional variations of 0.15 cm (RMS). The individual shifts in three standard orthogonal planes showed no obvious directional biases.

CONCLUSIONS

After localization based on superficial markings in patients undergoing SBRT, orthogonal kV imaging detects setup variations of approximately 3 to 4 mm in each direction. Cone-beam CT detects residual setup variations of approximately 2 to 3 mm.

Emerging role of intensity-modulated radiation therapy in anorectal cancer

Although radiation therapy has an established role to play in the management of rectal and anal tumors, there are often treatment-related morbidities that negatively impact on patients. There is a long-standing interest in radiation oncology on maximizing treatment efficacy while minimizing treatment-related toxicities, which can be pronounced in the treatment of pelvic malignancies. Intensity-modulated radiation therapy is a recently introduced technology that has the potential to increase the efficacy:toxicity ratio. It has been implemented in the treatment of prostate and head and neck tumors with success. This article reviews the rationale for its use in treating anorectal tumors and discusses early clinical data supporting its continued investigation.

Integration of Cone-Beam CT in Stereotactic Body Radiation Therapy

This report describes the technique and initial experience using cone beam CT (CBCT) for localization of treatment targets in patients undergoing stereotactic body radiation therapy (SBRT). Patients selected for SBRT underwent 3-D or 4-D CT scans in a customized immobilization cradle. GTV, CTV, ITV, and PTV were defined. Intensity-modulated radiation beams, multiple 3-D conformal beams, or dynamic conformal arcs were delivered using a Varian 21EX with 120-leaf MLC. CBCT images were obtained prior to each fraction, and registered to the planning CT by using soft tissue and bony structures to assure accurate isocenter localization. Patients were repositioned for treatment based on the CBCT images. Radiographic images (kV, MV, or CBCT) were taken before and after beam delivery to further assess set-up accuracy. Ten patients with lung, liver, and spine lesions received 29 fractions of treatment using this technique. The prescription doses ranged 1250 ~ 6000 cGy in 1 ~ 5 fractions. Compared to traditional 2-D matching using bony structures, CBCT corrects target deviation from 1 mm to 15 mm, with an average of 5 mm. Comparison of pre-treatment to post-treatment radiographic images demonstrated an average 2 mm deviation (ranging from 0–4 mm). Improved immobilization may enhance positioning accuracy. Typical total “in-room” times for the patients are approximately 1 hour. CBCT-guided SBRT is feasible and enhances setup accuracy using 3-D anatomical information.

Advanced radiation therapy technologies in the treatment of rectal and anal cancer: intensity-modulated photon therapy and proton therapy

Intensity-modulated photon radiation therapy (RT; IMRT) and proton therapy are advanced radiation technologies that permit improved conformation of radiation dose to target structures while limiting irradiation of surrounding normal tissues. Application of these technologies in the treatment of rectal and anal cancer is attractive, based on the potential reduction in radiation treatment toxicities that are frequently incurred in the pelvis and perineum. Furthermore, conformal RT might also allow for dose escalation to target areas, leading to improved tumor control. This review discusses the underlying principles of IMRT. In addition, the rationale and clinical data regarding the efficacy of radiation dose escalation for rectal and anal cancer will be highlighted, as well as tolerance of pelvic organs to RT and chemotherapy. Finally, preliminary results of IMRT in the treatment of lower gastrointestinal tract cancers will be reviewed. The potential and rationale for proton therapy in treatment of these malignancies are also discussed.

Deep-inspiration breath-hold kilovoltage cone-beam CT for setup of stereotactic body radiation therapy for lung tumors: Initial experience

We report our initial experience with deep-inspiration breath-hold (DIBH) cone-beam CT (CBCT) on the treatment table, using the kilovoltage imager integrated into our linear accelerator, for setting up patients for DIBH stereotactic body radiation therapy (SBRT) for lung tumors. Nine patients with non-small cell lung cancer (seven stage I), were given 60Gy in three fractions. All nine patients could perform a DIBH for 35s. For each patient we used a diagnostic reference CT volume image acquired during a DIBH to design an SBRT plan consisting of 7-10 noncoplanar conformal beams. Four patients were setup by registering DIBH kilovoltage projection radiographs or megavoltage portal images on the treatment table to digitally reconstructed radiographs from the reference CT. Each of the last 14 fractions out of a total of 27 was setup by acquiring a CBCT volume image on the treatment table in three breath-holds. The CBCT and reference CT volume images were directly registered and the shift was calculated from the registration. The CBCT volume images contained excellent detail on soft tissue and bony anatomy for matching to the reference CT. Most importantly, the tumor was always clearly visible in the CBCT images, even when it was difficult or impossible to see in the radiographs or portal images. The accuracy of the CBCT method was confirmed by DIBH megavoltage portal imaging and each treatment beam was delivered during a DIBH. CBCT acquisition typically required five more minutes than radiograph acquisition but the overall setup time was often shorter using CBCT because repeat imaging was minimized. We conclude that for setting up SBRT treatments of lung tumors, DIBH CBCT is feasible, fast and may result in less variation among observers than using bony anatomy in orthogonal radiographs.

Image guided respiratory gated hypofractionated Stereotactic Body Radiation Therapy (H-SBRT) for liver and lung tumors: Initial experience

To evaluate our initial experience with image guided respiratory gated H-SBRT for liver and lung tumors. The system combines a stereoscopic x-ray imaging system (ExacTrac X-Ray 6D) with a dedicated conformal stereotactic radiosurgery and radiotherapy linear accelerator (Novalis) and ExacTrac Adaptive Gating for dynamic adaptive treatment. Moving targets are located and tracked by x-ray imaging of implanted fiducial markers defined in the treatment planning computed tomography (CT). The marker position is compared with the position in verification stereoscopic x-ray images, using fully automated marker detection software. The required shift for a correct, gated set-up is calculated and automatically applied. We present our acceptance testing and initial experience in patients with liver and lung tumors. For treatment planning CT and Fluorodeoxyglucose-Positron Emission Tomography (FDG-PET) as well as magnetic resonance imaging (MRI) taken at free breathing and expiration breath hold with internal and external fiducials present were used. Patients were treated with 8-11 consecutive fractions to a dose of 74.8-79.2 Gy. Phantom tests demonstrated targeting accuracy with a moving target to within +/-1 mm. Inter- and intrafractional patient set-up displacements, as corrected by the gated set-up and not detectable by a conventional set-up, were up to 30 mm. Verification imaging to determine target location during treatment showed an average marker position deviation from the expected position of up to 4 mm on real patients. This initial evaluation shows the accuracy of the system and feasibility of image guided real-time respiratory gated H-SBRT for liver and lung tumors.

Stereotactic Body Radiation Therapy (SBRT) for lung metastases

The curative treatment of oligometastases with radiotherapy remains an area of active investigation. We hypothesise that treating oligometastases with SBRT can prolong life and potentially cure patients, while in patients with multiple lung metastases SBRT can improve quality of life. Fifty patients with lung metastases were treated on this study. Individuals with five or fewer total lesions were treated with curative intent. Individuals with > five metastases were treated palliatively. Most patients (62%) received 5 Gy/fraction for a total of 50 Gy. The number of targets treated per patient ranged from one to five (mean 2.6). Tumor sizes ranged from 0.3-7.7 cm in maximal diameter (median 2.1 cm). Mean follow-up was 18.7 months. Local control of treated lesions was obtained in 42 of 49 evaluable patients (83%). Of the 125 total lesions treated, eight progressed after treatment (94% crude local control). The median overall survival time from time of treatment completion of the curatively treated patients was 23.4 months. The progression-free survival of the same group of patients was 25% and 16% at 12 and 24 months, respectively. Grade 1 toxicity occurred in 35% of all the patients, 6.1% had grade 2 toxicity, and 2% had grade 3 toxicity. Excellent local tumor control rates with low toxicity are seen with SBRT. Median survival time and progression-free survival both appear better than that achieved with standard care alone. Long-term progression-free survival can be seen in a subset of patients when all tumors are targeted.

Outcome After Radiotherapy Alone for Metastatic Spinal Cord Compression in Patients With Oligometastases

Purpose

To investigate outcome and prognosis of metastatic spinal cord compression (MSCC) patients with oligometastatic disease treated with radiotherapy alone.

Patients and Methods

Oligometastatic disease was defined as involvement of three or fewer vertebrae and lack of other bone or visceral metastases. Five hundred twenty-one patients with oligometastatic disease and MSCC were evaluated for functional outcome, ambulatory status, local control of MSCC, and survival. Furthermore, seven potential prognostic factors were investigated.

Results

Motor function improved in 40% (n = 207), remained stable in 54% (n = 279), and deteriorated in 7% (n = 35) of patients. Fifty-eight (54%) of 107 nonambulatory patients became ambulatory, and 388 (94%) of 414 ambulatory patients remained ambulatory. Improved functional outcome was significantly associated with tumor type and slower development of motor deficits (> 14 days). Local control at 1, 2, and 3 years was 92%, 88%, and 78%, respectively. Improved local control was significantly associated with long-course radiotherapy. Survival at 1, 2, and 3 years was 71%, 58%, and 50%, respectively. Better survival was significantly associated with tumor type, ambulatory status, slower development of motor deficits, and long-course radiotherapy. Patients who developed motor deficits slowly (onset > 14 days before initiating treatment) were further analyzed. In this subgroup, the best results were observed for myeloma/lymphoma and breast cancer patients. No patient had progression of motor deficits. One hundred percent (myeloma/lymphoma) and 99% (breast cancer) of patients were ambulatory after radiotherapy. One-year local control was 100% and 98%, 1-year survival was 94% and 89%.

Conclusion

Given the limitations of a retrospective review, improved outcome of patients with oligometastatic MSCC was associated with myeloma/lymphoma and breast cancer, slower development of motor deficits, and a more prolonged course of radiation.

Hypofractionated stereotactic body radiation therapy (SBRT) for limited hepatic metastases

PURPOSE

To evaluate the feasibility and efficacy of hypofractionated stereotactic body radiation therapy (SBRT) for the treatment of liver metastases.

METHODS AND MATERIALS

The records of 69 patients with 174 metastatic liver lesions treated with SBRT between April 2001 and October 2004 were reviewed. The most common primary tumors were colorectal (n = 20), breast (n = 16), pancreas (n = 9), and lung (n = 5). The mean number of lesions treated per patient was 2.5 (range, 1-6). The longest diameter of the lesions ranged in size from 0.6 to 12.2 cm (median, 2.7 cm). Dose per fraction ranged from 2 Gy to 6 Gy, with a median total dose of 48 Gy (range, 30-55 Gy). Dose was prescribed to the 100% isodose line (IDL), with the 80% IDL covering the gross tumor volume with a minimum margin of 7 mm.

RESULTS

The median follow up was 14.5 months. Sixty patients were evaluable for response based on an abdominal computed tomography scan obtained at a minimum of 3 months after completion of SBRT. The actuarial overall infield local control rate of the irradiated lesions was 76% and 57% at 10 and 20 months, respectively. The median overall survival time was 14.5 months. The progression-free survival rate was 46% and 24% at 6 and 12 months, respectively. None of the patients developed Grade 3 or higher toxicity.

CONCLUSION

Hypofractionated SBRT provides excellent local control with minimal side effects in selected patients with limited hepatic metastases.