Stereotactic high dose fraction radiation therapy of extracranial tumors using an accelerator. Clinical experience of the first thirty-one patients

The implementation of ablative hypofractionated radiotherapy for stereotactic treatments in the brain and body: observations on efficacy and toxicity in clinical practice

Radiosurgery has a long history dating back to the 1950s. Only in the last decade or so have advances in radiation delivery and visualization allowed export of this paradigm to extracranial sites. This review evaluates the efficacy and safety of such ablative radiation courses using dose per fraction schedules of 10 Gy or above. Retrospective published experience in functional and benign tumor radiosurgery is reviewed. Prospective controlled clinical trials in ablative cancer therapy of early-stage lung cancer and metastatic disease in the brain, liver, and spine are reviewed.

Exploring the possibility of unique molecular, biological, and tissue effects with hypofractionated radiotherapy

High-dose hypofractionated radiotherapy is feasible because of technological advances that allow for the precise delivery of radiation to a target volume that contains a limited amount of normal tissue. No longer constrained by the normal tissue response of large fields, very large doses of radiation can be delivered. However, with the application of high doses of radiation to very precise treatment volumes, we find ourselves wondering if the fundamental principles that govern conventional radiotherapy apply. The conventions of tumor hypoxia, reoxygenation, tumor repopulation, and intrinsic radiosensitivity are all likely to be unique or play new roles in tumor or normal tissue response. With that in mind, we highlight several facets of tumor or normal tissue response in which a better understanding of tumor biology and radiation biology could be beneficial to the application of high dose per fraction treatment modalities or in which caution should be exercised.

A rationale for the targeted treatment of oligometastases with radiotherapy

An oligometastatic state has been proposed wherein patients with metastases limited in number and location may benefit from local therapy directed at all known sites of metastases. We describe here the clinical and biological basis for the oligometastatic state. We present evidence for a potentially curative approach to patients with oligometastases using stereotactic body radiotherapy (SBRT) and we review the literature for SBRT directed at specific metastatic sites in the lungs, liver and multiple organs.

Hepatocellular carcinoma: radiation therapy

Although whole liver tolerance to radiation therapy (RT) is low, hepatocellular carcinoma (HCC) can be treated with focal high-dose RT, using a variety of advanced and specialized treatment strategies. Technical advancements in external beam RT that facilitate the safe delivery of RT to a wide spectrum of patients include conformal RT planning, breathing motion management, and image-guided RT. A variety of doses and RT fractionation schemes have been used safely alone or in combination with other therapies such as transarterial chemoembolization. Charged particles, produced from very specialized treatment units, are associated with particularly desirable dose distributions allowing tumoricidal doses to be delivered with sustained tumor control and little toxicity, even in the presence of Child-Pugh class B or C cirrhosis. Another strategy to deliver RT to HCC is hepatic arterial delivery of radioisotopes, such as microspheres tagged with yttrium-90. Liver toxicity is more likely in patients with reduced liver reserve and/or tumors infiltrating the majority of the liver. Phase II studies and a small phase III trial have demonstrated activity of hepatic arterial radioisotopes in HCC, providing rationale for large confirmatory randomized trials. Recurrences after RT occur most often within the liver, outside the high-dose irradiated volume, and outcomes after RT to very large and/or diffuse HCC are poor, providing rationale for combining RT with other therapies or novel radiation sensitizers. Given the vascular properties of HCC, there is rationale for investigating RT with anti-vascular endothelial growth factor-targeted agents.

Stereotactic body radiation therapy: transcending the conventional to improve outcomes

BACKGROUND

Intracranial delivery of high-dose radiation treatment with stereotactic techniques has paved the way for treatment of extracranial sites.

METHODS

The authors review the evolution of stereotactic body radiation therapy (SBRT) and its application to tumors in the lung and abdomen, addressing both the technical concerns associated with treatment delivery and the emerging clinical data.

RESULTS

Radiation delivery systems have overcome the obstacles with immobilization, respiration, visualization, and daily reproducible imaging. Lung SBRT has been associated with local control rates of over 90%, and liver SBRT has ranged from 55% to 93%. SBRT is being explored in other sites such as the pancreas and kidney. Mature data from ongoing trials will be available in the next 5 years.

CONCLUSIONS

Modern stereotactic radiation treatment techniques allow the safe delivery of high doses to extracranial sites with minimal toxicity, which results in improved outcomes.

[Feasibility and efficacy of cyberknife radiotherapy for lung cancer: early results]

PURPOSE

High-dose robotic stereotactic irradiation can be achieved with high precision using the CyberknifeM system equipped with the Synchrony respiratory tracking device. Cyberknife irradiation can overcome some limitations of conventional radiotherapy including errors due to breathing motion and patient setup. High dose levels are of interest for tumours that have shown a dose-response relationship including lung tumours. We reviewed the treatments and outcomes for the first French patients with lung tumours treated at the Cyberknife centre of Nice.

PATIENTS AND METHODS

Thirty four patients were treated between November 2006 and November 2007 at the Cyberknife centre of Nice, Centre Lacassagne, France. Thirty had untreated primary lung cancer, 4 had colorectal metastasis to the lung. We evaluated the feasibility and reliability of fiducial placement, toxicity and early outcomes. Objective tumour response was assessed on thoracic CT scan every three months.

RESULTS

There was no grade 3-4 toxicity. Toxicity (11%) mainly consisted of grade 1-2 asthenia. Crude overall tumour response rate was 96% for all assessable patients and 91% at 3 and 6 months, respectively. The use of one fiducial ensured minimal toxicity (no grade III pneumothorax) while allowing reliable tumour tracking as shown by the low infield failure rate (no geographic miss). Diagnostic procedure was performed during fiducial placement when required.

CONCLUSION

Early toxicity and tumour control rates from this population suggest that the use of a unique fiducial for a Cyberknife treatment was safe and effective for the treatment of selected primary and secondary lung tumours. This strategy is corroborated by similar control rates in the literature. Longer follow-up are awaited.

Automated non-coplanar beam direction optimization improves IMRT in SBRT of liver metastasis

PURPOSE

To investigate whether automatically optimized coplanar, or non-coplanar beam setups improve intensity modulated radiotherapy (IMRT) treatment plans for stereotactic body radiotherapy (SBRT) of liver tumors, compared to a reference equi-angular IMRT plan.

METHODS

For a group of 13 liver patients, an in-house developed beam selection algorithm (Cycle) was used for generation of 3D-CRT plans with either optimized coplanar-, or non-coplanar beam setups. These 10 field, coplanar and non-coplanar setups, and an 11 field, equi-angular coplanar reference setup were then used as input for generation of IMRT plans. For all plans, the PTV dose was maximized in an iterative procedure by increasing the prescribed PTV dose in small steps until further increase was prevented by constraint violation(s).

RESULTS

For optimized non-coplanar setups, D(PTV, max) increased by on average 30% (range 8-64%) compared to the corresponding reference IMRT plan. Similar increases were observed for D(PTV, 99%) and gEUD(a). For optimized coplanar setups, mean PTV dose increases were only approximately 4%. After re-scaling all plans to the clinically applied dose, optimized non-coplanar configurations resulted in the best sparing of organs at risk (healthy liver, spinal cord, bowel).

CONCLUSION

Compared to an equi-angular beam setup, computer optimized non-coplanar setups do result in substantial improvements in IMRT plans for SBRT of liver tumors.

Radiation safety issues with positron-emission/computed tomography simulation for stereotactic body radiation therapy

Stereotactic body radiation therapy (SBRT) simulations using a Stereotactic Body Frame (SBF: Elekta, Stockholm, Sweden) were expanded to include 18F-deoxyglucosone positron-emission tomography (FDG PET) for treatment planning. Because of the length of time that staff members are in close proximity to the patient, concerns arose over the radiation safety issues associated with these simulations. The present study examines the radiation exposures of the staff performing SBRT simulations, and provides some guidance on limiting staff exposure during these simulations. Fifteen patients were simulated with PET/CT using the SBF. Patients were immobilized in the SBF before the FDG was administered. The patients were removed from the frame, injected with FDG, and allowed to uptake for approximately 45 minutes. After uptake, the patients were repositioned in the SBF. During the repositioning, exposure rates were recorded at the patient's surface, at the SBF surface, and at 15 cm, 30 cm, and 1 m from the SBF. Administered dose and the approximate time spent on patient repositioning were also recorded. The estimated dose to staff was compared with the dose to staff performing conventional diagnostic PET studies. The average length of time spent in close proximity (<50 cm) to the patient after injection was 11.7 minutes, or more than twice the length of time reported for diagnostic PET staff. That time yielded an estimated average dose to the staff of 26.5 microSv per simulation. The annual occupational exposure limit is 50 mSv. Based on dose per simulation, staff would have to perform nearly 1900 SBRT simulations annually to exceed the occupational limit. Therefore, at the current rate of 50-100 simulations annually, the addition of PET studies to SBRT simulations is safe for our staff. However, ALARA ("as low as reasonably achievable") principles still require some radiation safety considerations during SBRT simulations. The PET/CT-based SBRT simulations are safe and important for treatment planning that optimizes biologic dose distribution with highly accurate and reproducible target definition.

Image-guided radiotherapy for liver cancer using respiratory-correlated computed tomography and cone-beam computed tomography

PURPOSE

To evaluate a novel four-dimensional (4D) image-guided radiotherapy (IGRT) technique in stereotactic body RT for liver tumors.

METHODS AND MATERIALS

For 11 patients with 13 intrahepatic tumors, a respiratory-correlated 4D computed tomography (CT) scan was acquired at treatment planning. The target was defined using CT series reconstructed at end-inhalation and end-exhalation. The liver was delineated on these two CT series and served as a reference for image guidance. A cone-beam CT scan was acquired after patient positioning; the blurred diaphragm dome was interpreted as a probability density function showing the motion range of the liver. Manual contour matching of the liver structures from the planning 4D CT scan with the cone-beam CT scan was performed. Inter- and intrafractional uncertainties of target position and motion range were evaluated, and interobserver variability of the 4D-IGRT technique was tested.

RESULTS

The workflow of 4D-IGRT was successfully practiced in all patients. The absolute error in the liver position and error in relation to the bony anatomy was 8 +/- 4 mm and 5 +/- 2 mm (three-dimensional vector), respectively. Margins of 4-6 mm were calculated for compensation of the intrafractional drifts of the liver. The motion range of the diaphragm dome was reproducible within 5 mm for 11 of 13 lesions, and the interobserver variability of the 4D-IGRT technique was small (standard deviation, 1.5 mm). In 4 patients, the position of the intrahepatic lesion was directly verified using a mobile in-room CT scanner after application of intravenous contrast.

CONCLUSION

The results of our study have shown that 4D image guidance using liver contour matching between respiratory-correlated CT and cone-beam CT scans increased the accuracy compared with stereotactic positioning and compared with IGRT without consideration of breathing motion.

Four-dimensional computed tomography scan analysis of tumor and organ motion at varying levels of abdominal compression during stereotactic treatment of lung and liver

PURPOSE

To investigate the effectiveness of different abdominal compression levels on tumor and organ motion during stereotactic body radiotherapy of lower lobe lung and liver tumors using four-dimensional (4D)-CT scan analysis.

METHODS AND MATERIALS

Three 4D-CT scans were acquired for 10 patients first using with no compression and then compared with two different levels of abdominal compression. The position of the tumor and various organs were defined at the peak inspiratory and expiratory phases and compared to determine the maximum motion.

RESULTS

Mean (+/-SD) medium compression force (MC) and high compression force (HC) were 47.6 +/- 16.0 N and 90.7 +/- 27.1 N, respectively. Mean overall tumor motion was 13.6 mm (2sigma [2 sigma] 11.5-15.6), 8.3 mm (2sigma 6.0-10.5), and 7.2 mm (2sigma 5.4-9.0) for no compression, MC, and HC, respectively. A significant difference in the control of both superior-inferior (SI) and overall motion of tumors was seen with the application of MC and HC when compared with no compression (p < 0.0001 for both). High compression force improved SI and overall tumor motion compared with MC, but this was only significant for SI motion (p = 0.04 and p = 0.06). Significant control of organ motion was only seen in the pancreas (p = 0.01).

CONCLUSIONS

Four-dimensional CT shows significant control of both lower lobe lung and liver tumors using abdominal compression. High levels of compression improve SI tumor motion when compared with MC.

Stereotactic Body Radiation Therapy: Evaluation of Setup Accuracy and Targeting Methods for a New Couch Integrated Immobilization System

A new stereotactic frame system was designed at Indiana University to utilize the precision motion control of newer accelerator couches and treat obese patients previously untreatable in other frame systems during stereotactic body radiation therapy (SBRT). The repositioning accuracy and target reproducibility of this frame was evaluated in the treatment of both lung and liver tumors. The external coordinate system on the new frame was validated using a phantom system. Translational motions were carried out using couch motors. Five patients were treated with SBRT and twenty-three verification CT scans were acquired. The displacement of the gross tumor volume (GTV) and adjacent vertebral body between the original CT scan and the verification CT scans was determined. The mean setup accuracy for the patient study was less than 5 mm. Mean displacement of the GTV was 3.0 mm (0.0–6.0 mm) in the lateral (x) direction, 4.1 mm (0.0–8.9 mm) in the superior-inferior (y) direction, and 2.6 mm (0.0–10.0 mm) in the cranio-caudal (z) direction. Comparison of vertebral body position showed mean displacement of 2.4 mm (0.0 to 8.0 mm), 1.9 mm (0.0 mm to 2.0 mm), and 0.9 mm (0.0 to 5.0 mm) for the same shift directions. Repositioning could be accurately carried out from an initial reference position using the treatment couch controllers. Adequate set-up accuracy using a frame system capable of accommodating wide girth patients was achieved and was comparable to other published studies for narrower frames. With these results, a 5 mm expansion for PTV margins remains the standard for our institution.

Can protons improve SBRT for lung lesions? Dosimetric considerations

BACKGROUND AND PURPOSE

The aim of the present study was to investigate potential dosimetric benefits of proton therapy for hypofractionated stereotactic body radiotherapy (SBRT).

MATERIALS AND METHOD

Twelve patients undergoing hypofractionated SBRT at the Medical University Vienna were selected. Passively scattered protons (PT) and intensity modulated proton therapy (IMPT) were evaluated against a conformal photon technique (3D-CRT), assuming a fractionation of 3x15Gy, prescribed to the 65% isodose. For all treatment techniques shallow breathing with abdominal compression (SB+AC) was compared with a deep inspiration breath hold technique (DIBH). Treatment planning was done with XiO (CMS, USA). Target conformity, dose-volume histograms (DVH) and various associated dosimetric parameters were considered for the planning target volume (PTV), lung, heart and esophagus.

RESULTS

For both breathing conditions conformity indices were very similar. They were between 0.75 and 0.78 for IMPT and 3D-CRT and around 0.55 for PT using 2-3 beams. Irrespective of treatment modality, DVHs for the ipsilateral lung were improved with the DIBH technique. For the PT technique, the 2Gy isodose (V2Gy) covered on average 7-9% less lung volume compared to 3D-CRT, for IMPT this reduction was more than 10%. Volumes covered the 4 and 6Gy isodoses were 2-4% smaller for IMPT, but very similar for PT and 3D-CRT. Both proton techniques achieved full sparing of the contralateral lung and superior sparing of the heart. Maximum doses to the heart and esophagus were on average around 3Gy for 3D-CRT and almost 0Gy for both proton techniques. For 3D-CRT average V2Gy values for the heart could be reduced from 64% in shallow breathing to 34% in DIBH. V2Gy for protons was negligible.

CONCLUSIONS

Only small dosimetric differences were found between photons and protons for SBRT of lung lesions. Whether these small dosimetric benefits translate in reduced side effects or have the potential to improve local control rates remains to be demonstrated in clinical studies.

Is there a role for advanced radiation therapy technologies in the treatment of pancreatic adenocarcinoma?

Pancreatic cancer remains a highly challenging problem in oncology. Oncologists continue to search for therapies that are more effective than those currently available to improve on the existing poor treatment results. Persistence of both systemic and local disease causes high rates of morbidity and mortality for patients. Radiation continues to play a role in the treatment of pancreatic cancer, in both the adjuvant and locally advanced settings. Efforts to improve on the results of radiotherapy have led to the use of new and improved technologies. This review discusses a variety of these technological improvements and their current and potential future roles in the clinic.

Hypofractionation in radiation therapy and its impact

A brief history of the underlying principles of the conventional fractionation in radiation therapy is discussed, followed by the formulation of the hypothesis for hypofractionated stereotactic body radiation therapy (SBRT). Subsequently, consequences of the hypothesis for SBRT dose shaping and dose delivery techniques are sketched. A brief review of the advantages of SBRT therapy in light of the existing experience is then provided. Finally, the need for new technological developments is advocated to make SBRT therapies more practical, safer, and clinically more effective. It is finally concluded that hypofractionated SBRT treatment will develop into a new paradigm that will shape the future of radiation therapy by providing the means to suppress the growth of most carcinogen-induced carcinomas and by supporting the cure of the disease.

Conformal radiotherapy for hepatocellular carcinoma

Technical advancements in radiation therapy (RT) have facilitated the safe delivery of conformal, dose-escalated radiation to a wide spectrum of hepatocellular carcinoma (HCC) patients. A variety of doses and RT fractionation schemes have been used, and RT has been used in combination with transarterial chemoembolization (TACE). Compared to untreated historical controls or those treated with TACE alone, outcomes following RT alone or TACE and RT are better. Despite advances in RT delivery, liver toxicity following RT remains a dose-limiting factor, and investigations to better understand the pathophysiology of RT-induced liver toxicity are warranted. For most tumors, RT can provide sustained local control. However, HCC tends to recur within the liver away from the irradiated volume, providing rationale for combining RT with systemic or regional therapies. There is a particular interest in combining RT with anti-VEGF-targeted agents for their independent activity in HCC as well as their radiation sensitization properties. Randomized trials of RT are warranted.

The evolving role of radiation therapy in hepatocellular carcinoma

Technical advancements in imaging, in radiation therapy (RT) planning and RT delivery, have facilitated the safe delivery of conformal radiation therapy to patients with unresectable hepatocellular carcinoma (HCC). Although experience in liver cancer RT is limited, the RT technologies and tools to deliver RT safely are being disseminated rapidly. A variety of doses and RT fractionations have been used to treat HCC, and RT has been used in combination with other therapies including transarterial hepatic chemoembolization (TACE). Outcomes following RT alone or RT and TACE appear better than outcomes following similar historical controls of TACE alone, however, randomized trials of RT are needed. The first site of recurrence following RT is most often within the liver, away from the high dose volume, providing rationale for combining RT with regional or systemic therapies. Given the vascular properties of HCC, the combination of RT with anti-VEGF targeted agents may improve outcomes further.

CyberKnife robotic radiosurgery system for tumor treatment

Defined by its high level of accuracy and rapid radiation dose fall-off, radiosurgery has emerged as an effective radiation technique over the past few decades. Although it was once limited to conditions of the brain, head and neck regions, technological advances in computing and imaging have allowed the application of radiosurgery to conditions throughout the entire body. Using advanced imaging and robotics, the CyberKnife (Accuray, Inc., Sunnyvale, CA, USA) is one of few systems capable of delivering radiosurgery with exquisite accuracy to tumors, cancers and other conditions throughout the body. This review focuses on the development, technology, clinical efficacy and future directions of the CyberKnife.

Stereotactic body radiation therapy: a comprehensive review

Stereotactic body radiation therapy (SBRT) is a novel technique that takes advantage of the technologic advancements in image guidance and radiation dose delivery to direct ablative doses to tumors with acceptable toxicity that was not previously achievable with conventional techniques. SBRT requires a high degree of confidence in tumor location provided by high quality diagnostic and near real-time imaging studies for accurate treatment delivery and precise assessment of physiologic tumor motion. In addition, stringent dosimetric parameters must be applied, paying close attention to the spatial arrangement of functional subunits in the adjacent normal tissues, to optimize clinical outcomes. Phase I/II trials for tumors of the lung, liver, spine, pancreas, kidney, and prostate provide evidence that the potent doses delivered with SBRT may provide results that rival surgery while avoiding the typical morbidities associated with that invasive approach. Further clinical study in the form of multi-institutional Phase II trials is currently underway, and ultimately collaborative efforts on a national level to support Phase III trials will be necessary, to firmly establish SBRT as a comparable noninvasive alternative to surgery.

Hypofractionated stereotactic radiotherapy with and without transarterial chemoembolization for small hepatocellular carcinoma not eligible for other ablation therapies: Preliminary results for efficacy and toxicity

AIM

To investigate the efficacy and toxicity of hypofractionated stereotactic radiotherapy for the treatment of patients presenting with hepatocellular carcinoma (HCC) in a single institutional setting.

METHODS

Sixteen patients who presented with solitary HCC, including two patients with a tumor thrombus of the portal veins, were treated with stereotactic radiotherapy with or without transarterial chemoembolization. The criteria for stereotactic radiotherapy were existence of technical difficulties for other ablation therapies, inoperable disease or refusal to undergo surgery, tumor staged as Grade A or B according to the Child-Pugh classification, and solitary tumor distant from the gastrointestinal tract and kidney with a tumor volume <100 cm(3). In 14 of 16 patients, a total dose of 35- 50 Gy was delivered in 5-7 fractions over 5-9 days.

RESULTS

At the end of a mean follow-up of 612 days (median 611 days; range 244-994 days), all patients were alive. Eight of 16 patients had complete responses and seven others were judged as stable with lipiodol accumulation. In one patient, local recurrence developed after 489 days. Intrahepatic recurrences developed outside the treated volume in six patients and no extrahepatic metastases developed during follow-up. No serious treatment-related toxic manifestations developed.

CONCLUSIONS

Stereotactic radiotherapy for HCC with or without transarterial chemoembolization is feasible therapy and provides good local control with a short treatment period. Stereotactic radiotherapy may be of clinical benefit in patients who are inoperable or for whom there are difficulties in other ablation therapies.

PTV dose prescription strategies for SBRT of metastatic liver tumours

PURPOSE

Recently we have demonstrated that our in-house developed algorithm for automated plan generation for fully non-coplanar SBRT of liver patients (designated Cycle) yields plans that are superior to conventionally generated plans of experienced dosimetrists. Here we use Cycle in the comparison of plans with prescription isodoses of 65% or 80% of the isocentre dose.

METHODS

Plans were generated using CT-data of 15 previously treated patients. For each patient, both for the 65%- and the 80% strategy, Cycle was used to generate a plan with the maximum isocentre dose, D(isoc), while strictly obeying a set of hard constraints for the organs at risk (OAR). Plans for the two strategies were compared using D(isoc), D(PTV,99%) (the minimum dose delivered to 99% of the PTV), and the generalised equivalent uniform dose, gEUD(PTV)(a), for several values of the parameter a. Moreover, for the OARs, the distance to the constraint values was analysed.

RESULTS

The 65% strategy resulted in treatment plans with a higher D(isoc) (average 17.6%, range 7.6-31.1%) than the 80% strategy, at the cost of a somewhat lower D(PTV,99%) (average -2.0%, range -9.6% to 9.3%). On average, voxels with a dose in the 65% strategy, lower than the minimum PTV dose in the 80% strategy, were within 0.2cm from the PTV surface. For a-10, the 65% strategy yielded on average a significantly (P<0.01) higher gEUD(PTV)(a) than the 80% strategy, whereas for highly negative a-values the 80% approach was slightly better, although not significantly. Large variations between patients were observed. Generally, for the OAR the approach to the constraint levels was similar for the two strategies.

CONCLUSION

On average, PTV dose delivery is superior with the 65% strategy. However, apart from the isocentre dose, for each applied PTV dose parameter at least one patient would have been better off with the 80% dose prescription strategy.

[Advances in radio-oncology. From precision radiotherapy with photons to ion therapy with protons and carbon ions]

Modern techniques in radiation oncology, such as fractionated stereotactic radiotherapy (FSRT), stereotactic radiosurgery (SRS) or intensity modulated radiotherapy (IMRT) allow the application of high local doses to defined treatment volumes, while normal structures in close vicinity can be spared; high local control rates can be achieved, while treatment-related toxicity can be minimized. Innovative Hi-Art tomotherapy systems offer an alternative, combining a 6 MV photon accelerator with a CT scanner. Ion beams, such as protons and carbon ions, have been shown to be beneficial for distinct tumor entities. Both offer a characteristic physical dose distribution with an inverse dose profile contributing to beneficial dose conformality. Carbon ions also offer the advantage of increased relative biological effectiveness. For certain tumor types, a significant increase in local control and survival rates could be obtained with carbon ions.

Hypofractionated stereotactic radiotherapy for primary and secondary intrapulmonary tumors: first results of a phase I/II study

PURPOSE

To evaluate the feasibility, efficacy, and side effects of dose escalation in hypofractionated stereotactic radiotherapy (hfSRT) for intrapulmonary tumors with the Novalis system (BrainLAB AG, Heimstetten, Germany).

PATIENTS AND METHODS

From 07/2003 to 01/2005, 21 patients/39 tumors were treated with 5 x 7 Gy (n = 21; total dose 35 Gy) or 5 x 8 Gy (n = 18; total dose 40 Gy). There were three cases of primary lung cancer, the remainder were metastases. Median gross tumor volume (GTV) and planning target volume (PTV) were 2.89 cm(3) (range, 0.15-67.94 cm(3)) and 25.75 cm(3) (range, 7.18-124.04 cm(3)), respectively.

RESULTS

Rates of complete remission, partial remission, no change, and progressive disease were 51%, 33%, 3%, and 13%, respectively. No grade 4 toxicity occurred, nearly all patients had grade 1 initially. One grade 3 toxicity, i.e., dyspnea, was documented for a period of 6 months after therapy. Radiosurgery quality assurance guidelines could be met.

CONCLUSION

hfSRT of primary and secondary lung tumors using a schedule of five fractions at 7-8 Gy each was well tolerated. Further dose escalation is planned.

Four-Dimensional Treatment Planning for Stereotactic Body Radiotherapy

PURPOSE

To investigate the influence of tumor motion on the calculation of four-dimensional (4D) dose distributions of the gross tumor volume (GTV) in pulmonary stereotactic body radiotherapy.

METHODS AND MATERIALS

For 7 patients with eight pulmonary tumors, a respiratory-correlated 4D-computed tomography study was acquired. The internal target volume was the sum of all tumor positions in the planning 4D-computed tomography study, and a 5-mm margin was used for generation of the planning target volume. Three-dimensional (3D) treatment plans were generated with a dose prescription of 3 x 12.5 Gy to the planning target volume enclosing the 65% and 80% isodose. After model-based nonrigid image registration, the 4D dose distributions were calculated.

RESULTS

No significant difference was found in the dose to the GTV with the tumor in the end-exhalation, end-inhalation, or mid-ventilation phase of the breathing cycle. The high-dose region was confined to the solid tumor, and lower doses were delivered to the surrounding pulmonary tissue of lower density. This nonstatic, variant dose distribution increased the 4D dose to the GTV by 6.2%, on average, compared with calculations using on a static dose distribution during the breathing cycle. The 4D accumulation resulted in a biologic effective dose (BED) of 143 +/- 8 Gy and 106 +/- 4 Gy to the GTV in the plan-65% and plan-80%, respectively. The dose to the ipsilateral lung was not different between the 3D and 4D dose calculations or between plan-65% and plan-80%.

CONCLUSIONS

In this study, the dose to the GTV was not decreased or blurred in the 4D plan compared with the 3D plan. The 3D doses to the GTV, internal target volume, and dose at the isocenter were good approximations of the 4D dose calculations. The 3D dose at the planning target volume margin underestimated the 4D dose significantly.

Clinical outcome of stereotactic body radiotherapy of 54 Gy in nine fractions for patients with localized lung tumor using a custom-made immobilization system

PURPOSE

The aim of this study was to investigate the clinical outcome of stereotactic body radiotherapy (SBRT) of 54 Gy in nine fractions for patients with localized lung tumor using a custom-made immobilization system.

METHODS AND MATERIALS

The subjects were 19 patients who had localized lung tumor (11 primaries, 8 metastases) between May 2003 and October 2005. Treatment was conducted on 19 lung tumors by fixed multiple noncoplanar conformal beams with a standard linear accelerator. The isocentric dose was 54 Gy in nine fractions. The median overall treatment time was 15 days (range 11-22 days). All patients were immobilized by a thermo-shell and a custom-made headrest during the treatment.

RESULTS

The crude local tumor control rate was 95% during the follow-up of 9.4-39.5 (median 17.7) months. In-field recurrence was noted in only one patient at the last follow-up. The Kaplan-Meier overall survival rate at 2 years was 89.5%. Grade 1 radiation pneumonia and grade 1 radiation fibrosis were observed in 12 of the 19 patients. Treatment-related severe early and late complications were not observed in this series.

CONCLUSION

The stereotactic body radiotherapy of 54 Gy in nine fractions achieved acceptable tumor control without any severe complications. The results suggest that SBRT can be one of the alternatives for patients with localized lung tumors.

Investigation of the dosimetric effect of respiratory motion using four-dimensional weighted radiotherapy

We have developed a four-dimensional weighted radiotherapy (4DW-RT) technique. This method involves designing the motion of the linear accelerator beam to coincide with the tumour motion determined from 4D-CT imaging while including a weighting factor to account for irregular motion and limitations of the delivery system. Experiments were conducted with a moving phantom to assess limitations of the delivery system when applying this method. Although the multi-leaf collimator motion remains within the tolerance of the linear accelerator, the extent of motion was less than 1 mm larger than the designed one, and there was a net system latency of approximately 0.2 s. The dose distributions were measured and simulated using different weighting factors and motion scenarios. The breathing characteristics (period, extent of motion, drift and standard deviations) of 32 patients were evaluated using the Varian RPM system. Breathing variability was assessed by plotting the average breathing motion as a function of the breathing phase. Simulations were carried out to determine the optimal weighting factor based on typical patient breathing characteristics. These results establish that the 4DW-RT method demonstrates potential for dose escalation without increasing exposure to healthy tissue.

Target coverage in image-guided stereotactic body radiotherapy of liver tumors

PURPOSE

To determine the effect of image-guided procedures (with computed tomography [CT] and electronic portal images before each treatment fraction) on target coverage in stereotactic body radiotherapy for liver patients using a stereotactic body frame (SBF) and abdominal compression. CT guidance was used to correct for day-to-day variations in the tumor's mean position in the SBF.

METHODS AND MATERIALS

By retrospectively evaluating 57 treatment sessions, tumor coverage, as obtained with the clinically applied CT-guided protocol, was compared with that of alternative procedures. The internal target volume-plus (ITV(+)) was introduced to explicitly include uncertainties in tumor delineations resulting from CT-imaging artifacts caused by residual respiratory motion. Tumor coverage was defined as the volume overlap of the ITV(+), derived from a tumor delineated in a treatment CT scan, and the planning target volume. Patient stability in the SBF, after acquisition of the treatment CT scan, was evaluated by measuring the displacement of the bony anatomy in the electronic portal images relative to CT.

RESULTS

Application of our clinical protocol (with setup corrections following from manual measurements of the distances between the contours of the planning target volume and the daily clinical target volume in three orthogonal planes, multiple two-dimensional) increased the frequency of nearly full (> or = 99%) ITV(+) coverage to 77% compared with 63% without setup correction. An automated three-dimensional method further improved the frequency to 96%. Patient displacements in the SBF were generally small (< or = 2 mm, 1 standard deviation), but large craniocaudal displacements (maximal 7.2 mm) were occasionally observed.

CONCLUSION

Daily, CT-assisted patient setup may substantially improve tumor coverage, especially with the automated three-dimensional procedure. In the present treatment design, patient stability in the SBF should be verified with portal imaging.

The Use of Gated and 4D CT Imaging in Planning for Stereotactic Body Radiation Therapy

The localization of treatment targets is of utmost importance for patients receiving stereotactic body radiation therapy (SBRT), where the dose per fraction is large. While both setup or respiration-induced motion components affect the localization of the treatment volume, the purpose of this work is to describe our management of the intrafraction localization uncertainty induced by normal respiration. At our institution, we have implemented gated computed tomography (CT) acquisition with an active breathing control system (ABC), and 4-dimensional (4D) CT using a skin-based marker and retrospective respiration phase-based image sorting. During gated simulation, 3D CT images were acquired corresponding to end-inhalation and end-exhalation. For 4D CT imaging, 3D CT images were acquired corresponding to 8 phases of the respiratory cycle. In addition to gated or 4D CT images, we acquired a conventional free-breathing CT (FB). For both gated and 4D CT images, the target contours were registered to the FB scan in the planning system. These contours were then combined in the FB image set to form the internal target volume (ITV). Dynamic conformal arc treatment plans were generated for the ITV using the FB scan and the gated or 4D scans with an additional 7-mm margin for patient setup uncertainty. We have described our results for a pancreas and a lung tumor case. Plans were normalized so that the PTV received 95% of the prescription dose. The dose distribution for all the critical structures in the pancreas and lung tumor cases resulted in increased sparing when the ITV was defined using gated or 4D CT images than when the FB scan was used. Our results show that patient-specific target definition using gated or 4D CT scans lead to improved normal tissue sparing.

Image-Guidance for Stereotactic Body Radiation Therapy

The term stereotactic body radiation therapy (SBRT) describes a recently introduced external beam radiation paradigm by which small lesions outside the brain are treated under stereotactic conditions, in a single or few fractions of high-dose radiation delivery. Similar to the treatment planning and delivery process for cranial radiosurgery, the emphasis is on sparing of adjacent normal tissues through the creation of steep dose gradients. Thus, advanced methods for assuring an accurate relationship between the target volume position and radiation beam geometry, immediately prior to radiation delivery, must be implemented. Such methods can employ imaging techniques such as planar (e.g., x-ray) or volumetric (e.g., computed tomography [CT]) approaches and are commonly summarized under the general term image-guided radiation therapy (IGRT). This review summarizes clinical experience with volumetric and ultrasound based image-guidance for SBRT. Additionally, challenges and potential limitations of pre-treatment image-guidance are presented and discussed.

Investigation of optimal beam margins for stereotactic radiotherapy of lung-cancer using Monte Carlo dose calculations

This work investigated the selection of beam margins in lung-cancer stereotactic body radiotherapy (SBRT) with 6 MV photon beams. Monte Carlo dose calculations were used to systematically and quantitatively study the dosimetric effects of beam margins for different lung densities (0.1, 0.15, 0.25, 0.35 and 0.5 g cm(-3)), planning target volumes (PTVs) (14.4, 22.1 and 55.3 cm3) and numbers of beam angles (three, six and seven) in lung-cancer SBRT in order to search for optimal beam margins for various clinical situations. First, a large number of treatment plans were generated in a commercial treatment planning system, and then recalculated using Monte Carlo simulations. All the plans were normalized to ensure that 95% of the PTV at least receives the prescription dose and compared quantitatively. Based on these plans, the relationships between the beam margin and quantities such as the lung toxicity (quantified by V20, the percentage volume of the two lungs receiving at least 20 Gy) and the maximum target (PTV) dose were established for different PTVs and lung densities. The impact of the number of beam angles on the relationship between V20 and the beam margin was assessed. Quantitative information about optimal beam margins for lung-cancer SBRT was obtained for clinical applications.

Dose as a function of lung volume and planned treatment volume in helical tomotherapy intensity-modulated radiation therapy-based stereotactic body radiation therapy for small lung tumors

PURPOSE

To evaluate the limitations of Hi-Art Helical Tomotherapy (Middleton, WI) stereotactic body radiotherapy (SBRT) for lung lesions, and to provide an initial report on patients treated with this method. Stereotactic body radiotherapy was shown to be an effective, well-tolerated treatment for early-stage, non-small-cell lung carcinoma (NSCLC). The Radiation Therapy Oncology Group (RTOG) 0236 protocol is currently evaluating three-dimensional conformal SBRT that delivers 60 Gy in three fractions.

METHODS AND MATERIALS

Inverse treatment planning for hypothetical lung gross tumor volumes (GTV) and planned treatment volume (PTV) expansions were performed. We tested the hypothesis that the maximum acceptable dose (MAD) to be delivered to the lesion by SBRT could be predicted by PTV and lung volume. Dose constraints on normal tissue were as designated by the RTOG protocol. Inverse planning was performed to find the maximum tolerated SBRT dose up to 60 Gy.

RESULTS

Regression analysis of the data obtained indicated a linear relationship between MAD, PTV, and lung volume. This generated two equations which may be useful predictive tools. Seven patients with Stage I and II NSCLC treated at the University of Virginia with this method tolerated the treatment extremely well, and suffered no greater than grade I toxicity, with no evidence of disease recurrence in follow-up from 2-20 months.

CONCLUSIONS

Helical tomotherapy SBRT for lung lesions is well-tolerated. In addition, the likely MAD for patients considered for this type of treatment can be predicted by PTV and lung volume.