Treating recurrent metastatic breast cancer to the skin with proton therapy.

Proton therapy offers unique physical properties that make it an excellent choice for treating metastatic breast cancer, particularly when recurrent disease occurs near previously irradiated tissues. This case study demonstrates the dosimetric benefits of proton therapy in patients with metastatic breast cancer to the skin. The case consists of one patient with 5 separate areas treated with Pencil Beam Scanning (PBS) proton therapy over a period of 2 years using Monte Carlo calculation and robust optimization. The results demonstrate that proton therapy effectively spared healthy tissues while delivering the prescribed dose to the tumor. This case demonstrates the feasibility of developing effective radiation plans for skin metastases using proton therapy, highlighting its dosimetric advantages and minimal impact on nearby organs.

X-ray microbeam irradiation of the contusion-injured rat spinal cord temporarily improves hind-limb function.

Spinal cord injury is a devastating condition with no effective treatment. The physiological processes that impede recovery include potentially detrimental immune responses and the production of reactive astrocytes. Previous work suggested that radiation treatment might be beneficial in spinal cord injury, although the method carries risk of radiation-induced damage. To overcome this obstacle we used arrays of parallel, synchrotron-generated X-ray microbeams (230 µm with 150 µm gaps between them) to irradiate an established model of rat spinal cord contusion injury. This technique is known to have a remarkable sparing effect in tissue, including the central nervous system. Injury was induced in adult female Long-Evans rats at the level of the thoracic vertebrae T9-T10 using 25 mm rod drop on an NYU Impactor. Microbeam irradiation was given to groups of 6-8 rats each, at either Day 10 (50 or 60 Gy in-beam entrance doses) or Day 14 (50, 60 or 70 Gy). The control group was comprised of two subgroups: one studied three months before the irradiation experiment (n = 9) and one at the time of the irradiations (n = 7). Hind-limb function was blindly scored with the Basso, Beattie and Bresnahan (BBB) rating scale on a nearly weekly basis. The scores for the rats irradiated at Day 14 post-injury, when using t test with 7-day data-averaging time bins, showed statistically significant improvement at 28-42 days post-injury (P < 0.038). H&E staining, tissue volume measurements and immunohistochemistry at day ≈ 110 post-injury did not reveal obvious differences between the irradiated and nonirradiated injured rats. The same microbeam irradiation of normal rats at 70 Gy in-beam entrance dose caused no behavioral deficits and no histological effects other than minor microglia activation at 110 days. Functional improvement in the 14-day irradiated group might be due to a reduction in populations of immune cells and/or reactive astrocytes, while the Day 10/Day 14 differences may indicate time-sensitive changes in these cells and their populations. With optimizations, including those of the irradiation time(s), microbeam pattern, dose, and perhaps concomitant treatments such as immunological intervention this method may ultimately reach clinical use.

Interleaved carbon minibeams: an experimental radiosurgery method with clinical potential.

PURPOSE: To evaluate the efficacy of "interleaved carbon minibeams" for ablating a 6.5-mm target in a rabbit brain with little damage to the surrounding brain. The method is based on the well-established tissue-sparing effect of arrays of thin planes of radiation. METHODS AND MATERIALS: Broad carbon beams from the National Aeronautics and Space Agency Space Radiation Facility at Brookhaven National Laboratory were segmented into arrays of parallel, horizontal, 0.3-mm-thick planar beams (minibeams). The minibeams' gradual broadening in tissues resulted in 0.525-mm beam thickness at the target's proximal side in the spread-out Bragg peak. Interleaving was therefore implemented by choosing a 1.05 mm beam spacing on-center. The anesthetized rabbit, positioned vertically on a stage capable of rotating about a vertical axis, was exposed to arrays from four 90° angles, with the stage moving up by 0.525 mm in between. This produced a solid radiation field at the target while exposing the nontargeted tissues to single minibeam arrays. The target "physical" absorbed dose was 40.2 Gy. RESULTS: The rabbit behaved normally during the 6-month observation period. Contrast magnetic resonance imaging and hematoxylin and eosin histology at 6 months showed substantial focal target damage with little damage to the surrounding brain. CONCLUSION: We plan to evaluate the method's therapeutic efficacy by comparing it with broad-beam carbon therapy in animal models. The method's merits would combine those of carbon therapy (i.e., tight target dose because of the carbon's Bragg-peak, sharp dose falloff, and high relative biological effectiveness at the target), together with the method's low impact on the nontargeted tissues. The method's smaller impact on the nontargeted brain might allow carbon therapy at higher target doses and/or lower normal tissue impact, thus leading to a more effective treatment of radioresistant tumors. It should also make the method more amenable to administration in either a single dose fraction or in a small number of fractions.

Evaluation of the eclipse electron Monte Carlo dose calculation for small fields.

Varian Medical Systems (Palo Alto, CA) has implemented the Monte Carlo electron dose calculation algorithm (eMC) in the Eclipse treatment planning system. Previous algorithms for electron treatment planning were limited in their calculation ability for small field depth doses and monitor units. An old rule of thumb to approximate the limiting cutout size for an electron field was determined by the lateral scatter equilibrium and approximated by E (MeV)/2.5 in centimeters of water. In this study we compared eMC calculations and measurements of depth doses, isodose distributions and monitor units for several different energy and small field cutout size combinations at different SSDs. Measurements were made using EBT film (International Specialty Products, Wayne, NJ) and a PinPoint Ion Chamber (PTW, Hicksville, NY). Our results indicate that the eMC algorithm can accurately predict depth doses, isodose distributions and monitor units (within 2.5%) for field sizes as small as 3.0 cm diameter for energies in the 6 to 20 MeV range at 100 cm SSD. Therefore, the previous energy dependent rule of thumb does not apply to the Eclipse electron Monte Carlo code. However, at extended SSDs (105-110 cm), the results show good agreement (within 4 %) only for higher energies (12, 16, and 20 MeV) for a field size of 3 cm.

Increased plasma levels of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 in lung and breast cancer are altered during chest radiotherapy.

PURPOSE: Does the release of plasma matrix metalloproteinase-9 (MMP-9) by radiation-activated airway epithelial cells and infiltrating inflammatory cells play a role in the radiation damage or repair process in the lungs? We evaluated lung damage by ionizing radiation using plasma levels of MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), and MMP-3 as biologic markers of tissue damage, and also their relationship to changes in pulmonary epithelial permeability, clinical signs and symptoms, and lung structural changes. METHODS AND MATERIALS: Seven serial studies were conducted in each of 8 patients undergoing chest radiotherapy (RT) for lung or breast cancer, beginning before the first treatment (baseline) and then biweekly to approximately 100 days during and after RT. Chest radiographs were monitored for each patient. Sandwich enzyme-linked immunoassays (ELISA) were used to measure plasma MMP-3, MMP-9, and TIMP-1 levels. Lung permeability was evaluated by measuring the rate of epithelial clearance of approximately 150 microCi ( approximately 5.6 MBq) inhaled (99m)Tc diethylenetriamine pentaacetate aerosol (DTPA). RESULTS: Lung and breast cancer resulted in very high plasma levels of MMP-9 (126-893 ng/mL) and TIMP-1 (496-8985 ng/mL) in all subjects studied before initiation of RT. This compares with plasma MMP-9 and TIMP-1 values in healthy volunteers of 29 +/- 11 ng/mL and 436 +/- 86 ng/mL, respectively. RT was followed by a sharp decrease in plasma MMP-9 within the first 2 weeks, but without a corresponding change in TIMP-1. In contrast, plasma MMP-3 levels, which are generally increased with inflammation, were elevated in only 1 of 5 subjects. CONCLUSION: Lung and breast cancer are associated with high plasma levels of MMP-9 and TIMP-1. These high baseline plasma levels of MMP-9 were reduced in the first 2 weeks of RT in 7 of 8 subjects, and TIMP-1 plasma levels remained high in all subjects. The decrease in plasma MMP-9 after initiation of chest RT appears to reflect a suppressive effect on cancer-induced cellular responses rather than a primary role for MMP-9 in radiation-induced lung damage. Likewise, the lack of a rise in plasma MMP-3 levels does not support a role for MMP-3 in tissue injury or repair in the lung. It remains to be determined whether plasma MMP-9 measurements will serve as a useful parameter in predicting cancer relapse.