Alan Kepka

Advances in the radiosurgical treatment of large inoperable arteriovenous malformations.

Radiosurgery has proven useful in the treatment of small arteriovenous malformations (AVMs) of the brain. However, the volume of healthy tissue irradiated around large lesions is rather significant, necessitating reduced radiation doses to avoid complications. As a consequence, this can produce poorer obliteration rates. Several strategies have been developed in the past decade to circumvent dose-volume problems with large AVMs, including repeated treatments as well as dose, and volume fractionation schemes. Although success on par with that achieved in lesions smaller than 3 ml remains elusive, improvements over the obliteration rate, the complication rate or both have been reported after conventional single-dose stereotactic radiosurgery (SRS). Radiosurgery with a marginal dose or peripheral dose < 15 Gy rarely obliterates AVMs, yet most lesions diminish in size posttreatment. Higher doses may then be reapplied to any residual nidi after an appropriate follow-up period. Volume fractionation divides AVMs into smaller segments to be treated on separate occasions. Doses > 15 Gy irradiate target volumes of only 5-15 ml, thereby minimizing the radiation delivered to the surrounding brain tissue. Fewer adverse radiological effects with the use of fractionated radiosurgery over standard radiosurgery have been reported. Advances in AVM localization, dose delivery, and dosimetry have revived interest in hypofractionated SRS. Investigators dispensing >or= 7 Gy per fraction minimum doses have achieved occlusion with an acceptable number of complications in 53-70% of patients. The extended latency period between treatment and occlusion, about 5 years for emerging techniques (such as salvage, staged volume, and hypofractionated radiotherapy), exposes the patient to the risk of hemorrhage during that period. Nevertheless, improvements in dose planning and target delineation will continue to improve the prognosis in patients harboring inoperable AVMs.

Tissue/dose compensation to reduce toxicity from combined radiation and chemotherapy for advanced head and neck cancers

SUMMARY This study was undertaken to quantify the reduction in normal tissue complications resulting from the aggressive management of advanced head and neck cancers (AHNCs) utilizing tissue/dose compensation (TDC). Thirty‐nine patients with AHNC were treated on an intensive chemotherapy + radiation regimen. Eighteen of 39 patients were treated using TDC; the remaining 21 patients were radiated without TDC (NTDC). Acute and chronic toxicities, swallowing, speech function, and quality of life were assessed. The TDC group had a smaller radiation dose gradient across the entire treatment volume. Unscheduled treatment breaks were required in 11% of TDC patients as compared with 43% of the NTDC group (P = 0.04). The TDC group had fewer Grade 3 or 4 acute and chronic toxicities and lower SOMA scores. At 3 months posttreatment, patients in the TDC group had better oral intake, lower pharyngeal residue, and better oropharyngeal swallowing efficiency and were able to swallow more bolus types. Patients in the TDC group also had better articulation. Use of TDC resulted in reduced treatment‐related interruptions, decreased acute and chronic toxicities, and better speech and swallowing functions. Techniques to improve radiation dose conformality around the target tissues while decreasing the radiation dose to the normal tissues should be an integral part of aggressive combined modality therapy.

The generalized geometry of eye plaque therapy.

A calculation is described that enables the rapid assessment of dose rate at various points of interest within the eye (lens, optic nerve, etc.) for the treatment of choroidal melanoma by plaque therapy. 125I seeds are used as the radiation source. The location of the plaque and its associated seeds relative to the eye (in a Cartesian coordinate system) is determined from the description of the tumor, as drawn and dimensioned on a fundus-view diagram by the ophthalmologist. This requires a computer to numerically solve an equation, which is derived in the framework of spherical geometry. Further results of this calculation yield data files that serve as the input to a conventional brachytherapy treatment planning program. This enables the visualization of the dose distribution within a plane that contains the major axis of the tumor in order to assess the adequacy of the treated volume.

Cardiac-Sparing Whole Lung IMRT in Children With Lung Metastasis

PURPOSE To demonstrate the dosimetric advantages of cardiac-sparing (CS) intensity modulated radiation therapy (IMRT) in children undergoing whole lung irradiation (WLI). METHODS AND MATERIALS Chest CT scans of 22 children who underwent simulation with 3-dimensional (n=10) or 4-dimensional (n=12) techniques were used for this study. Treatment planning was performed using standard anteroposterior-posteroanterior (S-RT) technique and CS-IMRT. Left and right flank fields were added to WLI fields to determine whether CS-IMRT offered any added protection to normal tissues at the junction between these fields. The radiation dose to the lung PTV, cardiac structures, liver, and thyroid were analyzed and compared. RESULTS CS-IMRT had 4 significant advantages over S-RT: (1) superior cardiac protection (2) superior 4-dimensional lung planning target volume coverage, (3) superior dose uniformity in the lungs with fewer hot spots, and (4) significantly lower dose to the heart when flank RT is administered after WLI. CONCLUSIONS The use of CS-IMRT and 4-dimensional treatment planning has the potential to improve tumor control rates and reduce cardiac toxicity in children receiving WLI.

SU‐GG‐T‐141: Current Status of the Histogram Analysis in Radiation Therapy (HART): An Open‐Source Software System

Purpose: HART is a useful tool in radiation therapy research utilizing 3D conformai radiation therapy (3DCRT) and intensity modulated radiation therapy(IMRT) techniques in the treatment of cancer. Various applications of the software were also presented and published earlier in different journals (Med Phys 36(6), p.2547 (2009); J Appl Clin Med Phys 11 (1), 2010). The main objective of this work was to review the applications of the program, and to present its current status. Method and Materials: Matlab based codes were primarily designed to read RTOG data formats exported from the Pinnacle3treatment planning system (TPS; Philips Healthcare, Best, Netherlands), and to write into a simpler HART format. This format is the basis to execute various applications in the software, such as the conventional and spatialdose‐volume (or surface) histogram (CSDH) analyses, universal plan indices (UPI) evaluation, biological modeling based outcome analyses (BMOA), radiobiological dose response modeling (DRM), and physical parameterization (PP) modules to estimate the differential attenuation coefficients and center of mass of a region of interest. The program executes efficiently due to the simple computational mechanism, graphical simulations, and flexible interactive modes. The CSDH computational module was the most applicable feature for the global users of HART in the past three years. The fundamental results in various applications were validated with the Pinnacle3 data. Results: Currently, HART offers CSDH computational modules, UPI evaluations, BMOA features, DRM simulations, and PP modules respectively for the IMRT and 3DCRT plans. The program is also available online. Conclusion: Several applications have been upgraded into a simpler, user‐friendly, and automated software package (HART). The open‐source mechanism would be useful to the radiation oncology community. We expect to develop HART for various applications in radiotherapy research, and its expansion to other TPSs in the future. This work was partially supported by NIH/NIDCD grant.