ABSTRACT
Proton therapy dose is affected by relative biological effectiveness differently than X-ray therapies. The current clinically accepted weighting factor is 1.1 at all positions along the depth-dose profile. However, the relative biological effectiveness correlates with the linear energy transfer, cell or tissue type, and the dose per fraction causing variation of relative biological effectiveness along the depth-dose profile. In this article, we present a simple relative biological effectiveness-weighted treatment planning risk assessment algorithm in 2-dimensions and compare the results with those derived using the standard relative biological effectiveness of 1.1. The isodose distribution profiles for beams were accomplished using matrices that represent coplanar intersecting beams. These matrices were combined and contoured using MATLAB to achieve the distribution of dose. There are some important differences in dose distribution between the dose profiles resulting from the use of relative biological effectiveness = 1.1 and the empirically derived depth-dependent values of relative biological effectiveness. Significant hot spots of up to twice the intended dose are indicated in some beam configurations. This simple and rapid risk analysis could quickly evaluate the safety of various dose delivery schema.
Subject(s)
Proton Therapy , Protons , Radiometry , Relative Biological Effectiveness , Dose-Response Relationship, Radiation , Humans , Linear Energy Transfer , Proton Therapy/adverse effects , Proton Therapy/methods , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted , Risk AssessmentABSTRACT
Considerable evidence now exists to show that that the relative biological effectiveness (RBE) changes considerably along the proton depth-dose distribution, with progressively higher RBE values at the distal part of the modulated, or spread out Bragg peak (SOBP) and in the distal dose fall-off (DDF). However, the highly variable nature of the existing studies (with regards to cell lines, and to the physical properties and dosimetry of the various proton beams) precludes any consensus regarding the RBE weighting factor at any position in the depth-dose profile. We have thus conducted a systematic study on the variation in RBE for cell killing for two clinical modulated proton beams at Indiana University and have determined the relationship between the RBE and the dose-averaged linear energy transfer (LETd) of the protons at various positions along the depth-dose profiles. Clonogenic assays were performed on human Hep2 laryngeal cancer cells and V79 cells at various positions along the SOBPs of beams with incident energies of 87 and 200 MeV. There was a marked variation in the radiosensitivity of both cell lines along the SOBP depth-dose profile of the 87 MeV proton beam. Using Hep2 cells, the D(0.1) isoeffect dose RBE values (normalized against (60)Co) were 1.46 at the middle of SOBP, 2.1 at the distal end of the SOBP and 2.3 in the DDF. For V79 cells, the D(0.1) isoeffect RBE for the 87 MEV beam were 1.23 for the proximal end of the SOBP: 1.46 for the distal SOBP and 1.78 for the DDF. Similar D(0.1) isoeffect RBE values were found for Hep2 cells irradiated at various positions along the depth-dose profile of the 200 MeV beam. Our experimentally derived RBE values were significantly correlated (P = 0.001) with the mean LETd of the protons at the various depths, which confirmed that proton RBE is highly dependent on LETd. These in vitro data suggest that the RBE of the proton beam at certain depths is greater than 1.1, a value currently used in most treatment planning algorithms. Thus, the potential for increased cell killing and normal tissue damage in the distal regions of the proton SOBP may be greater than originally thought.
Subject(s)
Proton Therapy , Animals , Cell Death/radiation effects , Cell Line, Tumor , Cricetinae , Dose-Response Relationship, Radiation , Humans , Linear Energy Transfer , Radiation Tolerance , Radiometry , Relative Biological Effectiveness , X-RaysABSTRACT
PURPOSE: To determine nurse practitioners' (NPs') knowledge and reported practices regarding breast cancer screening in a climate of conflicting guidelines. DATA SOURCE: A descriptive, cross-sectional survey design was used to examine approaches to cancer screening among NPs in western New York. CONCLUSIONS: Among the 175 NP respondents, agreement with the accepted answers for the individual breast cancer-screening items ranged from 51% to 80%; responses did not vary by age group or gender. Overall, 54% demonstrated agreement with three or more of four breast cancer-screening items. IMPLICATIONS FOR PRACTICE: These findings suggest the need to implement educational interventions as one means of decreasing variation in breast cancer screening among NPs. Also, the development and endorsement of a single set of evidence-based breast cancer-screening guidelines would promote adoption of a single screening recommendation.
Subject(s)
Breast Neoplasms/prevention & control , Health Knowledge, Attitudes, Practice , Mass Screening/psychology , Nurse Practitioners/psychology , Adult , Aged , Breast Neoplasms/psychology , Cross-Sectional Studies , Female , Humans , Male , Mass Screening/methods , Middle Aged , Practice Guidelines as TopicABSTRACT
PURPOSE: To determine nurse practitioners' (NPs') knowledge, practice, and attitudes about tobacco cessation counseling and lung cancer early detection. DATA SOURCE: A descriptive, cross-sectional survey design was used to examine NPs' approaches to primary and secondary prevention of tobacco use among patients in western New York. CONCLUSIONS: Among the 175 respondents, NPs appropriately counseled tobacco users on tobacco cessation. However, there was limited understanding of first-line pharmacological agents used for tobacco cessation and of how to manage treatment for a patient at high risk for lung cancer. IMPLICATIONS FOR PRACTICE: These findings suggest the need to implement professional educational programs aimed at conveying not only the importance of tobacco cessation counseling but also information on the most effective first-line pharmacological agents and appropriate management options for patients at increased risk of developing lung cancer.
Subject(s)
Health Knowledge, Attitudes, Practice , Nurse Practitioners/education , Nurse Practitioners/standards , Smoking Cessation/methods , Smoking Prevention , Adult , Clinical Competence , Counseling , Cross-Sectional Studies , Female , Humans , Lung Neoplasms/prevention & control , Male , Middle Aged , New York , Nurse's Role , Nurse-Patient Relations , Risk Factors , Surveys and QuestionnairesABSTRACT
PURPOSE: To examine the effect of proton beam irradiation on subfoveal choroidal neovascular membranes (CNVM) associated with age-related macular degeneration (AMD).Randomized, prospective, sham-controlled, double-masked treatment trial. METHODS: Thirty-seven subjects with subfoveal CNVM due to AMD were randomly assigned to 16-Gy proton irradiation delivered in two fractions 24 hours apart or to sham control treatment. Recruitment was halted at 37 subjects for ethical reasons regarding randomization to sham treatment when Food and Drug Administration approval of Visudyne was anticipated. RESULTS: Proton irradiation was associated with a trend toward stabilization of visual acuity, but this association did not reach statistical significance. No correlations were found within the fluorescein angiography data, including greatest linear dimension of CNVM total size, area of active leakage, area of associated subretinal hemorrhage, and intensity. CONCLUSIONS: With the acceptance of photodynamic therapy, future studies will require more complex design and larger sample size to determine whether radiation can play either a primary or adjunctive role in treating these lesions.
