No abstract

Almost one third of HGG patients can undergo only a biopsy and not debulking surgery. Although radiotherapy improves survival, only 50% of them complete the treatment. An individualised approach to these patients is needed to facilitate a correct analysis of therapy results. New therapies must be investigated in these patients.

The Monte Carlo code MCNP (Monte Carlo N-Particle) has a significant history dating to the early years of the Manhattan Project. More recently, MCNP has been used successfully to solve many problems in the field of medical physics. In radiotherapy applications MCNP has been used successfully to calculate the bremsstrahlung spectra from medical linear accelerators, for modeling the dose distributions around high dose rate brachytherapy sources, and for evaluating the dosimetric properties of new radioactive sources used in intravascular irradiation for prevention of restenosis following angioplasty. MCNP has also been used for radioimmunotherapy and boron neutron capture therapy applications. It has been used to predict fast neutron activation of shielding and biological materials. One area that holds tremendous clinical promise is that of radiotherapy treatment planning. In diagnostic applications, MCNP has been used to model X-ray computed tomography and positron emission tomography scanners, to compute the dose delivered from CT procedures, and to determine detector characteristics of nuclear medicine devices. MCNP has been used to determine particle fluxes around radiotherapy treatment devices and to perform shielding calculations in radiotherapy treatment rooms. This manuscript is intended to provide to the reader a comprehensive summary of medical physics applications of the MCNP code.

Object Radiosurgery is an important and well-accepted method in the management of brain metastases. Using conventional frame-based techniques, high lesional control rates are expected. The introduction of image-guided techniques allows for improved patient comfort and workflow. Some controversy exists as to the accuracy of imageguided techniques and consequently the impact they might have on control of brain metastases (as opposed to the level of control achieved with frame-based methods). The authors describe their initial 15-month experience with image-guided radiosurgery (IGRS) using Novalis with ExacTrac for management of brain metastases. Methods The authors reviewed the cases of brain metastasis treated by means of IGRS in their tertiary regional radiation oncology service over a 15-month period. During the study period 54 patients (median age 57.9 years) harboring 108 metastases were treated with IGRS. The median time from cancer diagnosis to development of brain metastasis was 12 months (range 0–144 months). The median tumor volume was 0.98 cm3 (range 0.03–19.07 cm3). The median prescribed dose was 18 Gy to the 80% isodose line (range 14–20 Gy). Lesions were followed with postradiosurgery MR imaging every 2–3 months following treatment. Results The median follow-up period was 9 months (range 0–20 months). Median actuarial survival was 8.6 months following IGRS. Eight patients with 18 lesions died within the first 2 months after the procedure, before scheduled follow-up imaging. Thus 90 lesions (in 46 patients) were followed up with imaging studies. Lesions that were unchanged or reduced in size were considered to be under control. The 6-month actuarial lesion control rate was 88%. Smaller lesions (< 1 cm3) had a statistically improved likelihood of complete imaging response (loss of all contrast-enhancement p = 0.01). Conclusions Image-guided radiosurgical treatment of brain metastases resulted in high rates of tumor control comparable to control rates reported for frame-based methods. High control rates were seen for small lesions in which spatial precision in dose delivery is critical. These data suggests that in regard to lesion control, IGRS using Novalis with ExacTrac is equivalent to frame-based radiosurgery methods.

No abstract