AAPM medical physics practice guideline 10.a.: Scope of practice for clinical medical physics.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline (MPPG) represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiation requires specific training, skills, and techniques as described in each document. As the review of the previous version of AAPM Professional Policy (PP)-17 (Scope of Practice) progressed, the writing group focused on one of the main goals: to have this document accepted by regulatory and accrediting bodies. After much discussion, it was decided that this goal would be better served through a MPPG. To further advance this goal, the text was updated to reflect the rationale and processes by which the activities in the scope of practice were identified and categorized. Lastly, the AAPM Professional Council believes that this document has benefitted from public comment which is part of the MPPG process but not the AAPM Professional Policy approval process. The following terms are used in the AAPM's MPPGs: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Assessing the Effects of Participant Preference and Demographics in the Usage of Web-based Survey Questionnaires by Women Attending Screening Mammography in British Columbia.

BACKGROUND: Increased usage of Internet applications has allowed for the collection of patient reported outcomes (PROs) and other health data through Web-based communication and questionnaires. While these Web platforms allow for increased speed and scope of communication delivery, there are certain limitations associated with this technology, as survey mode preferences vary across demographic groups. OBJECTIVE: To investigate the impact of demographic factors and participant preferences on the use of a Web-based questionnaire in comparison with more traditional methods (mail and phone) for women participating in screening mammography in British Columbia, Canada. METHODS: A sample of women attending the Screening Mammography Program of British Columbia (SMPBC) participated in a breast cancer risk assessment project. The study questionnaire was administered through one of three modes (ie, telephone, mail, or website platform). Survey mode preferences and actual methods of response were analyzed for participants recruited from Victoria General Hospital. Both univariate and multivariate analyses were used to investigate the association of demographic factors (ie, age, education level, and ethnicity) with certain survey response types. RESULTS: A total of 1192 women successfully completed the study questionnaire at Victoria General Hospital. Mail was stated as the most preferred survey mode (509/1192, 42.70%), followed by website platform (422/1192, 35.40%), and telephone (147/1192, 12.33%). Over 80% (955/1192) of participants completed the questionnaire in the mode previously specified as their most preferred; mail was the most common method of response (688/1192, 57.72%). Mail was also the most preferred type of questionnaire response method when participants responded in a mode other than their original preference. The average age of participants who responded via the Web-based platform (age 52.9, 95% confidence interval [CI] 52.1-53.7) was significantly lower than those who used mail and telephone methods (age 55.9, 95% CI 55.2-56.5; P<.001); each decade of increased age was associated with a 0.97-fold decrease in the odds of using the website platform (P<.001). Web-based participation was more likely for those who completed higher levels of education; each interval increase leading to a 1.83 increase in the odds of website platform usage (P<.001). Ethnicity was not shown to play a role in participant preference for the website platform (P=.96). CONCLUSIONS: It is beneficial to consider participant survey mode preference when planning to collect PROs and other patient health data. Younger participants and those of higher education level were more likely to use the website platform questionnaire; Web-based participation failed to vary across ethnic group. Because mail questionnaires were still the most preferred survey mode, it will be important to employ strategies, such as user-friendly design and Web-based support, to ensure that the patient feedback being collected is representative of the population being served.

Medical Physics Residency Consortium: collaborative endeavors to meet the ABR 2014 certification requirements.

In 2009, Mary Bird Perkins Cancer Center (MBPCC) established a Radiation Oncology Physics Residency Program to provide opportunities for medical physics residency training to MS and PhD graduates of the CAMPEP-accredited Louisiana State University (LSU)-MBPCC Medical Physics Graduate Program. The LSU-MBPCC Program graduates approximately six students yearly, which equates to a need for up to twelve residency positions in a two-year program. To address this need for residency positions, MBPCC has expanded its Program by developing a Consortium consisting of partnerships with medical physics groups located at other nearby clinical institutions. The consortium model offers the residents exposure to a broader range of procedures, technology, and faculty than available at the individual institutions. The Consortium institutions have shown a great deal of support from their medical physics groups and administrations in developing these partnerships. Details of these partnerships are specified within affiliation agreements between MBPCC and each participating institution. All partner sites began resident training in 2011. The Consortium is a network of for-profit, nonprofit, academic, community, and private entities. We feel that these types of collaborative endeavors will be required nationally to reach the number of residency positions needed to meet the 2014 ABR certification requirements and to maintain graduate medical physics training programs.

Endoscopic Retrograde Cholangiopancreatography Under General Anesthesia Compared to Conscious Sedation Study.

Background: Endoscopic retrograde cholangiopancreatography (ERCP) is used to diagnose and treat pancreatic and biliary disease. The current standard is to conduct ERCP under conscious sedation (CS). Patient movement and agitation during ERCP under CS can result in procedure failure and complications. Aiming to reduce procedure failure rates and complications, Kelowna General Hospital (KGH) in British Columbia, Canada transitioned to performing ERCP under general anesthesia (GA) as the practice standard. Objective: To determine if conducting ERCP under GA compared to CS decreases procedure complications, particularly post-ERCP pancreatitis (PEP). Methods: The charts of 2,198 patients who underwent ERCP at KGH between 2015 and 2020 were reviewed. Before September 17, 2017, ERCP was performed under CS (n = 1,316). Afterwards, ERCP was conducted under GA (n = 882). Demographic, clinical, and procedural data were extracted. The data were analyzed using univariate and multivariate statistical analysis. Results: Procedure failure rates (CS = 9 percent, GA = 3 percent, P < 0.001) decreased in the GA cohort after adjusting for age, sex, and co-morbidities. Thirty-day mortality, intensive care unit (ICU) transfer, returns post-discharge, PEP, and cholangitis rates were similar between cohorts. Conclusion: Performing ERCP under GA compared to CS resulted in an increase in procedural success rates. Other complication rates were similar between groups.

Comparison of action levels for patient-specific quality assurance of intensity modulated radiation therapy and volumetric modulated arc therapy treatments.

PURPOSE: To perform a comprehensive and systematic comparison of fixed-beam IMRT and volumetric modulated arc therapy (VMAT) patient-specific QA measurements for a common set of geometries using typical measurement methods. METHODS: Fixed-beam IMRT and VMAT plans were constructed for structure set geometries provided by AAPM Task Group 119. The plans were repeatedly delivered across multiple measurement sessions, and the resulting dose distributions were measured with (1) radiochromic film and ionization chamber and (2) a commercial two-dimensional diode array. The resulting QA measurements from each delivery technique were then analyzed, compared, and tested for statistically significant differences. RESULTS: Although differences were noted between QA results for some plans, neither modality showed consistently better agreement of measured and planned doses: of the 22 comparisons, IMRT showed better QA results in 11 cases, and VMAT showed better QA results in 11 cases. No statistically significant differences (p < 0.05) between IMRT and VMAT QA results were found for point doses measured with an ionization chamber, planar doses measured with radiochromic film, or planar doses measured with a two-dimensional diode array. CONCLUSIONS: These results suggest that it is appropriate to apply patient-specific QA action levels derived from fixed-beam IMRT to VMAT.

Evaluation of Clinical and Pathological Factors to Predict High Risk of Recurrence in Patients With Stage II Colon Cancer.

BACKGROUND: The ability to predict patients with stage II colon cancer at high risk of recurrence is currently limited to certain clinicopathologic factors. PATIENTS AND METHODS: This population-based study reviewed various prognostic factors to identify those associated with worse time to recurrence (TTR) and improved disease-specific survival (DSS), and to subsequently develop a prognostic index (PI) to identify high risk cancers. RESULTS: Multivariate analyses revealed factors significant for TTR and DSS. A PI derived from the TTR risk factors identified 3 risk groups using 5-year rate without relapse: 88% for low-risk, 81% for intermediate-risk, and 59% for high risk. CONCLUSION: This model was better at identifying high risk patients than using equally weighted standard risk factors.

Potential of discrete Gaussian edge feathering method for improving abutment dosimetry in eMLC-delivered segmented-field electron conformal therapy.

PURPOSE: The purpose of this work was to investigate the potential of discrete Gaussian edge feathering of the higher energy electron fields for improving abutment dosimetry in the planning volume when using an electron multileaf collimator (eMLC) to deliver segmented-field electron conformal therapy (ECT). METHODS: A discrete (five-step) Gaussian edge spread function was used to match dose penumbras of differing beam energies (6-20 MeV) at a specified depth in a water phantom. Software was developed to define the leaf eMLC positions of an eMLC that most closely fit each electron field shape. The effect of 1D edge feathering of the higher energy field on dose homogeneity was computed and measured for segmented-field ECT treatment plans for three 2D PTVs in a water phantom, i.e., depth from the water surface to the distal PTV surface varied as a function of the x-axis (parallel to leaf motion) and remained constant along the y-axis (perpendicular to leaf motion). Additionally, the effect of 2D edge feathering was computed and measured for one radially symmetric, 3D PTV in a water phantom, i.e., depth from the water surface to the distal PTV surface varied as a function of both axes. For the 3D PTV, the feathering scheme was evaluated for 0.1-1.0-cm leaf widths. Dose calculations were performed using the pencil beam dose algorithm in the Pinnacle(3) treatment planning system. Dose verification measurements were made using a prototype eMLC (1-cm leaf width). RESULTS: 1D discrete Gaussian edge feathering reduced the standard deviation of dose in the 2D PTVs by 34, 34, and 39%. In the 3D PTV, the broad leaf width (1 cm) of the eMLC hindered the 2D application of the feathering solution to the 3D PTV, and the standard deviation of dose increased by 10%. However, 2D discrete Gaussian edge feathering with simulated eMLC leaf widths of 0.1-0.5 cm reduced the standard deviation of dose in the 3D PTV by 33-28%, respectively. CONCLUSIONS: A five-step discrete Gaussian edge spread function applied in 2D improves the abutment dosimetry but requires an eMLC leaf resolution better than 1 cm.

Target localization accuracy in a respiratory phantom using BrainLAB ExacTrac and 4DCT imaging.

This study evaluated the accuracy of measuring the motion of an internal target using four-dimensional computed tomography (4DCT) scanning and the BrainLAB ExacTrac X-ray imaging system. Displacements of a metal coil implanted in a commercial respiratory phantom were measured in each system and compared to the known motion. A commercial respiratory motion phantom containing a metal coil as a surrogate target was used. Phantom longitudinal motions were sinusoidal with a 4.0 second period and amplitudes ranging from 5-25 mm. We acquired 4DCT and ExacTrac images of the coil at specified respiratory phases and recorded the coordinates of the coil ends. Coil displacement relative to the 0% phase (full-inhale) position were computed for the ExacTrac and 4DCT imaging systems. Coil displacements were compared to known displacements based on the phantom's sinusoidal motion. Coil length distortion due to 4DCT phase binning was compared to the known physical length of the coil (31 mm). The maximum localization error for both coil endpoints for all motion settings was 3.5 mm for the 4DCT and 0.8 mm for the ExacTrac gating system. Coil length errors measured on the 4DCT were less than 0.8 mm at end inhale/exhale phases, but up to 8.3 mm at mid-inhalation phases at the largest motion amplitude (25 mm). Due to the fast image acquisition time (100 ms), no coil distortion was observable in the ExacTrac system. 4DCT showed problems imaging the coil during mid-respiratory phases of higher velocity (phases 20%-30% and 70%-80%) due to distortion caused by residual motion within the 4DCT phase bin. The ExacTrac imaging system was able to accurately localize the coil in the respiratory phantom over all phases of respiration. For our clinic, where end-respiration phases from 4DCT may be used for treatment planning calculations, the ExacTrac system is used to measure internal target motion. With the ExacTrac system, planning target size and motion uncertainties are minimized, potentially reducing internal target volume margins in gated radiotherapy.

A phase I/II study of altered fractionated IMRT alone for intermediate T-stage oropharyngeal carcinoma.

BACKGROUND AND PURPOSE: To prospectively assess the feasibility and efficacy of an accelerated and hyperfractionated intensity- modulated radiation therapy (IMRT) schedule for intermediate T-stage oropharyngeal cancer. PATIENTS AND METHODS: Patients with T3 or unfavorable T2 oropharyngeal squamous cell carcinoma were eligible; a three-dose level simultaneous integrated boost IMRT strategy was used, delivering 78, 69, and 60 Gy to gross disease, high-risk and low-risk target areas, respectively, in 60 twice daily fractions over 6 weeks. No sequential/concomitant systemic treatment or up-front radical surgery was allowed. Median follow-up is 41.7 months (range: 3.5-80.8 months). RESULTS: 25 patients were treated from 11/2002 to 11/2005. 92% of the individual fractions were delivered as scheduled. Grade 3 mucosal and skin toxicity was 100% and 72%, respectively, none of which persisted beyond 12 weeks; a percutaneous endoscopic gastrostomy tube was temporarily placed in 60% of patients. The estimated locoregional progression-free, distant metastases-free, and overall survival rates at 3 years were 86.3% ± 7.4%, 76.4% ± 9.6%, and 70.0% ± 9.6%, respectively. At the same time interval, the actuarial prevalence of grade 3+ CTCAE v3.0 toxicity was 26.1%. CONCLUSION: While the routine clinical use of this exploratory schedule is discouraged, it may represent the basis for future developments.

Evaluation of a commercial flatbed document scanner and radiographic film scanner for radiochromic EBT film dosimetry.

The purpose of this study was to quantify the performance and assess the utility of two different types of scanners for radiochromic EBT film dosimetry: a commercial flatbed document scanner and a widely used radiographic film scanner. We evaluated the Epson Perfection V700 Photo flatbed scanner and the Vidar VXR Dosimetry Pro Advantage scanner as measurement devices for radiochromic EBT film. Measurements were made of scan orientation effects, response uniformity, and scanner noise. Scanners were tested using films irradiated with eight separate 3x3cm2 fields to doses ranging from 0.115-5.119 Gy. ImageJ and RIT software was used for analyzing the Epson and Vidar scans, respectively. For repeated scans of a single film, the measurements in each dose region were reproducible to within +/- 0.3% standard deviation (SD) with both scanners. Film-to-film variations for corresponding doses were measured to be within +/- 0.4% SD for both Epson scanner and Vidar scanners. Overall, the Epson scanner showed a 10% smaller range of pixel value compared to the Vidar scanner. Scanner noise was small: +/- 0.3% SD for the Epson and +/- 0.2% for the Vidar. Overall measurement uniformity for blank film in both systems was better than +/- 2%, provided that the leading and trailing 2 cm film edges were neglected in the Vidar system. In this region artifacts are attributed to the film rollers. Neither system demonstrated a clear measurement advantage. The Epson scanner is a relatively inexpensive method for analyzing radiochromic film, but there is a lack of commercially available software. For a clinic already using a Vidar scanner, applying it to radiochromic film is attractive because commercial software is available. However, care must be taken to avoid using the leading and trailing film edges.

Dosimetric predictors of diarrhea during radiotherapy for prostate cancer.

PURPOSE: To investigate dosimetric predictors of diarrhea during radiotherapy (RT) for prostate cancer. PATIENTS AND METHODS: All patients who underwent external-beam radiotherapy as part of treatment for localized prostate cancer at the University of Texas Medical Branch, Galveston, TX, USA, from May 2002 to November 2006 were extracted from the own database. From the cumulative dose-volume histogram (DVH), the absolute volumes (V-value) of intestinal cavity (IC) receiving 15, 30, and 45 Gy were extracted for each patient. Acute gastrointestinal toxicity was prospectively scored at each weekly treatment visit according to CTC (Common Toxicity Criteria) v2.0. The endpoint was the development of peak grade >or= 2 diarrhea during RT. Various patient, tumor, and treatment characteristics were evaluated using logistic regression. RESULTS: 149 patients were included in the analysis, 112 (75.2%) treated with whole-pelvis intensity-modulated radiotherapy (WP-IMRT) and 37 (24.8%) with prostate-only RT, including or not including, the seminal vesicles (PORT +/- SV). 45 patients (30.2%) developed peak grade >or= 2 diarrhea during treatment. At univariate analysis, IC-V(15) and IC-V(30), but not IC-V(45), were correlated to the endpoint; at multivariate analysis, only IC-V(15) (p = 0.047) along with peak acute proctitis (p = 0.041) was independently correlated with the endpoint. CONCLUSION: These data provide a novel and prostate treatment-specific "upper limit" DVH for IC.

Comparison of three strategies to delineate the bowel for whole pelvis IMRT of prostate cancer.

PURPOSE: To compare three different contouring approaches of the bowel before and during whole pelvis IMRT of localized prostate cancer. MATERIALS: Nine patients were randomly selected among those treated for localized prostate cancer at UTMB from March 2004 to August 2006. On the planning CT, besides the usual organs at risk (OAR), for each patient we contoured the bowel according to three different definitions: each bowel segment ('BS'); 'BS+1', BS uniformly expanded by 1cm; intestinal cavity ('IC') or the 'container' of the bowel loops up to the pelvic/abdominal walls. For each patient we generated three rival plans each considering a different bowel definition, otherwise identical. Provided that the same target coverage and other OAR spare had been achieved, plans were compared for their ability to minimize bowel dose at planning. Furthermore, after co-registering 6 weekly CT to the initial planning CT for each patient, we investigated which of the three definitions would allow the best bowel protection also during treatment. RESULTS: All definitions provided a very similar average bowel DVH at planning. During treatment BS allowed an average approximately 20 cc more of bowel to receive at least 45 Gy over BS+1 and IC (p=0.008 and 0.029, respectively); on the contrary bowel V45 between IC and BS+1 were not significantly different (p=0.65). CONCLUSION: A definition that takes into account internal organ motion is warranted to maximize bowel protection during treatment.

Dosimetric predictors of laryngeal edema.

PURPOSE: To investigate dosimetric predictors of laryngeal edema after radiotherapy (RT). METHODS AND MATERIALS: A total of 66 patients were selected who had squamous cell carcinoma of the head and neck with grossly uninvolved larynx at the time of RT, no prior major surgical operation except for neck dissection and tonsillectomy, treatment planning data available for analysis, and at least one fiberoptic examination of the larynx within 2 years from RT performed by a single observer. Both the biologically equivalent mean dose at 2 Gy per fraction and the cumulative biologic dose-volume histogram of the larynx were extracted for each patient. Laryngeal edema was prospectively scored after treatment. Time to endpoint, moderate or worse laryngeal edema (Radiation Therapy Oncology Group Grade 2+), was calculated with log rank test from the date of treatment end. RESULTS: At a median follow-up of 17.1 months (range, 0.4- 50.0 months), the risk of Grade 2+ edema was 58.9% +/- 7%. Mean dose to the larynx, V30, V40, V50, V60, and V70 were significantly correlated with Grade 2+ edema at univariate analysis. At multivariate analysis, mean laryngeal dose (continuum, hazard ratio, 1.11; 95% confidence interval, 1.06-1.15; p < 0.001), and positive neck stage at RT (N0-x vs. N +, hazard ratio, 3.66; 95% confidence interval, 1.40-9.58; p = 0.008) were the only independent predictors. Further stratification showed that, to minimize the risk of Grade 2+ edema, the mean dose to the larynx has to be kept < or =43.5 Gy at 2 Gy per fraction. CONCLUSION: Laryngeal edema is strictly correlated with various dosimetric parameters; mean dose to the larynx should be kept < or =43.5 Gy.

Is there a "mucosa-sparing" benefit of IMRT for head-and-neck cancer?

PURPOSE: To investigate whether intensity-modulated radiation therapy (IMRT) allows more mucosal sparing than standard three-field technique (3FT) radiotherapy for early oropharyngeal cancer. METHODS AND MATERIALS: Whole-field IMRT plans were generated for 5 patients with early-stage oropharyngeal cancer according to Radiation Therapy Oncology Group 0022 (66 Gy/30 fractions/6 weeks) guidelines with and without a dose objective on the portion of mucosa not overlapping any PTV. 3FT plans were also generated for the same 5 patients with two fractionation schedules: conventional fractionation (CF) to 70 Gy/35 fractions/7 weeks and concomitant boost (CB) to 72 Gy/40 fractions/6 weeks. Cumulative dose volume histograms (DVHs) of the overall mucosal volume (as per in-house definition) from all trials were compared after transformation into the linear quadratic equivalent dose at 2 Gy per fraction with a time factor correction. RESULTS: Compared with IMRT without dose objective on the mucosa, a 30-Gy maximum dose objective on the mucosa allows approximately 20% and approximately 12% mean absolute reduction in the percentage of mucosa volume exposed to a dose equivalent to 30 Gy (p < 0.01) and 70 Gy (p < 0.01) at 2 Gy in 3 and 7 weeks, respectively, without detrimental effect on the coverage of other regions of interest. Without mucosal dose objective, IMRT is associated with a larger amount of mucosa exposed to clinically relevant doses compared with both concomitant boost and conventional fractionation; however, if a dose objective is placed, the reverse is true, with up to approximately 30% reduction in the volume of the mucosa in the high-dose region compared with both concomitant boost and conventional fractionation (p < 0.01). CONCLUSIONS: Intensity-modulated radiation therapy can be potentially provide more mucosal sparing than traditional approaches.

An Internet-Based Means of Monitoring Quality of Life in Post-Prostate Radiation Treatment: A Prospective Cohort Study.

BACKGROUND: Widespread integration of the Internet has resulted in an increase in the feasibility of using Web-based technologies as a means of communicating with patients. It may be possible to develop secure and standardized systems that facilitate Internet-based patient-reported outcomes which could be used to improve patient care. OBJECTIVE: This study investigates patient interest in participating in an online post-treatment disease outcomes and quality of life monitoring program developed specifically for patients who have received radiation treatment for prostate cancer at a regional oncology center. METHODS: Patients treated for prostate cancer between 2007 and 2011 (N=1113) at the British Columbia Cancer Agency, Centre for the Southern Interior were invited by mail to participate in a standardized questionnaire related to their post-treatment health. Overall participation rates were calculated. In addition, demographics, access to broadband Internet services, and treatment modalities were compared between participants and nonparticipants. RESULTS: Of the 1030 eligible invitees, 358 (358/1030, 34.7%) completed the online questionnaire. Participation rates were higher in individuals younger than age 60 when compared to those age 60 or older (42% vs 31%) and also for those living in urban areas compared with rural (37% vs 29%) and in those who received brachytherapy versus external beam radiotherapy (EBRT) (41% vs 31%). Better participation rates were seen in individuals who had access to Internet connectivity based on the different types of broadband services (DSL 35% for those with DSL connectivity vs 29% for those without DSL connectivity; cable 35% vs 32%; wireless 38% vs 26%). After adjusting for age, the model indicates that lack of access to wireless broadband connectivity, living in a rural area, and receiving EBRT were significant predictors of lower participation. CONCLUSIONS: This study demonstrates that participation rates vary in patient populations within the interior region of British Columbia, especially with older patients, those in rural areas, and those with limited access to quality Internet services.

PTV margin determination in conformal SRT of intracranial lesions.

The planning target volume (PTV) includes the clinical target volume (CTV) to be irradiated and a margin to account for uncertainties in the treatment process. Uncertainties in miniature multileaf collimator (mMLC) leaf positioning, CT scanner spatial localization, CT-MRI image fusion spatial localization, and Gill-Thomas-Cosman (GTC) relocatable head frame repositioning were quantified for the purpose of determining a minimum PTV margin that still delivers a satisfactory CTV dose. The measured uncertainties were then incorporated into a simple Monte Carlo calculation for evaluation of various margin and fraction combinations. Satisfactory CTV dosimetric criteria were selected to be a minimum CTV dose of 95% of the PTV dose and at least 95% of the CTV receiving 100% of the PTV dose. The measured uncertainties were assumed to be Gaussian distributions. Systematic errors were added linearly and random errors were added in quadrature assuming no correlation to arrive at the total combined error. The Monte Carlo simulation written for this work examined the distribution of cumulative dose volume histograms for a large patient population using various margin and fraction combinations to determine the smallest margin required to meet the established criteria. The program examined 5 and 30 fraction treatments, since those are the only fractionation schemes currently used at our institution. The fractionation schemes were evaluated using no margin, a margin of just the systematic component of the total uncertainty, and a margin of the systematic component plus one standard deviation of the total uncertainty. It was concluded that (i) a margin of the systematic error plus one standard deviation of the total uncertainty is the smallest PTV margin necessary to achieve the established CTV dose criteria, and (ii) it is necessary to determine the uncertainties introduced by the specific equipment and procedures used at each institution since the uncertainties may vary among locations.

Accuracy and precision of cone-beam computed tomography guided intensity modulated radiation therapy.

PURPOSE: To assess the accuracy and precision of cone-beam computed tomography (CBCT)-guided intensity modulated radiation therapy (IMRT). METHODS AND MATERIALS: A 7-field intensity modulated radiation therapy plan was constructed for an anthropomorphic head phantom loaded with a custom cassette containing radiochromic film. The phantom was positioned on the treatment table at 9 locations: 1 "correct" position and 8 "misaligned" positions along 3 orthogonal axes. A commercial kilovoltage cone-beam computed tomography (kV-CBCT) system (VolumeView, Elekta AB, Stockholm, Sweden) was then used to align the phantom prior to plan delivery. The treatment plan was delivered using the radiation therapy delivery system (Infinity; Elekta AB) 3 times for each of the 9 positions, allowing film measurement of the delivered dose distribution in 3 orthogonal planes. Comparison of the planned and delivered dose profiles along the major axes provided an estimate of the accuracy and precision of CBCT-guided IMRT. RESULTS: On average, targeting accuracy was found to be within 1 mm in all 3 major anatomic planes. Over all 54 measured dose profiles, the means and standard errors of the displacement of the center of the field between the measured and calculated profiles for each of the right-left, anterior-posterior, and superior-inferior axes were +0.08 ± 0.07 mm, +0.60 ± 0.08 mm, and +0.78 ± 0.16 mm, respectively. Agreement between planned and measured 80% profiles was less than 0.4 mm on either side along the right-left axis. A systematic shift of the measured profile of slightly less than 1 mm in anterior and superior directions was noted along the anterior-posterior and superior-inferior axes, respectively. CONCLUSIONS: Submillimeter targeting accuracy can be achieved using a commercial kV-CBCT IGRT system.

Ultrasound-planned high-dose-rate prostate brachytherapy: dose painting to the dominant intraprostatic lesion.

PURPOSE: To demonstrate the feasibility of using high-dose-rate (HDR) brachytherapy to deliver 125% of the prescription dose to the dominant intraprostatic lesion (DIL) as defined on multiparametric MRI while respecting critical organ dose constraints. METHODS AND MATERIALS: Twenty-six patients with biopsy-proven predominantly unilateral prostate cancer consented to a university ethics-approved Phase 2 study of selective dose escalation. Combined information from endorectal T2 MRI sequences, dynamic contrast enhancement, and apparent diffusion coefficient maps was used to contour the DIL and prostate. Images were fused to intraoperative transrectal ultrasound for transposition of the DIL. Treatment consisted of two fractions of 10 Gy HDR brachytherapy to the entire prostate with 12.5 Gy to the DIL, combined with 46 Gy in 23 fractions of external beam radiotherapy. RESULTS: All patients had intermediate- or high-risk disease; 25 of 26 had a visible DIL (mean volume, 2.9 cm(3); SD, 1.8). Mean percentage of prostate receiving prescription dose (V100) was 98.1% (SD, 1.2). Mean dose to 90% of the DIL was 13.4 Gy (SD, 1.0). The coverage of the DIL was excellent with a mean of 95.7% (SD, 5.0) receiving the planned escalation of 25%. Established dose constraints to rectum and urethra were respected in all cases; where DIL coverage was limited by proximity to urethra or rectum, a mean dose to 90% of the DIL of 12.3 Gy was achieved. CONCLUSIONS: Modest dose escalation to the DIL (25-30%) using ultrasound-planned HDR brachytherapy is feasible for selected intermediate- and high-risk patients while respecting critical organ constraints and is achievable within the practice setting of a community cancer center.