Some Considerations in Optimizing the Medical Physics Match

The Medical Physics Match has proven its usefulness to the AAPM community, but it is not universally utilized for a variety of reasons. This invited guest editorial explores the scholarly history of the match algorithm and suggests some avenues to optimize its future use

Breathing adapted radiotherapy: a 4D gating software for lung cancer

<p>Abstract</p> <p>Purpose</p> <p>Physiological respiratory motion of tumors growing in the lung can be corrected with respiratory gating when treated with radiotherapy (RT). The optimal respiratory phase for beam-on may be assessed with a respiratory phase optimizer (RPO), a 4D image processing software developed with this purpose.</p> <p>Methods and Materials</p> <p>Fourteen patients with lung cancer were included in the study. Every patient underwent a 4D-CT providing ten datasets of ten phases of the respiratory cycle (0-100% of the cycle). We defined two morphological parameters for comparison of 4D-CT images in different respiratory phases: tumor-volume to lung-volume ratio and tumor-to-spinal cord distance. The RPO automatized the calculations (200 per patient) of these parameters for each phase of the respiratory cycle allowing to determine the optimal interval for RT.</p> <p>Results</p> <p>Lower lobe lung tumors not attached to the diaphragm presented with the largest motion with breathing. Maximum inspiration was considered the optimal phase for treatment in 4 patients (28.6%). In 7 patients (50%), however, the RPO showed a most favorable volumetric and spatial configuration in phases other than maximum inspiration. In 2 cases (14.4%) the RPO showed no benefit from gating. This tool was not conclusive in only one case.</p> <p>Conclusions</p> <p>The RPO software presented in this study can help to determine the optimal respiratory phase for gated RT based on a few simple morphological parameters. Easy to apply in daily routine, it may be a useful tool for selecting patients who might benefit from breathing adapted RT.</p

Verifying 4D gated radiotherapy using time-integrated electronic portal imaging: a phantom and clinical study

<p>Abstract</p> <p>Background</p> <p>Respiration-gated radiotherapy (RGRT) can decrease treatment toxicity by allowing for smaller treatment volumes for mobile tumors. RGRT is commonly performed using external surrogates of tumor motion. We describe the use of time-integrated electronic portal imaging (TI-EPI) to verify the position of internal structures during RGRT delivery</p> <p>Methods</p> <p>TI-EPI portals were generated by continuously collecting exit dose data (aSi500 EPID, Portal vision, Varian Medical Systems) when a respiratory motion phantom was irradiated during expiration, inspiration and free breathing phases. RGRT was delivered using the Varian RPM system, and grey value profile plots over a fixed trajectory were used to study object positions. Time-related positional information was derived by subtracting grey values from TI-EPI portals sharing the pixel matrix. TI-EPI portals were also collected in 2 patients undergoing RPM-triggered RGRT for a lung and hepatic tumor (with fiducial markers), and corresponding planning 4-dimensional CT (4DCT) scans were analyzed for motion amplitude.</p> <p>Results</p> <p>Integral grey values of phantom TI-EPI portals correlated well with mean object position in all respiratory phases. Cranio-caudal motion of internal structures ranged from 17.5–20.0 mm on planning 4DCT scans. TI-EPI of bronchial images reproduced with a mean value of 5.3 mm (1 SD 3.0 mm) located cranial to planned position. Mean hepatic fiducial markers reproduced with 3.2 mm (SD 2.2 mm) caudal to planned position. After bony alignment to exclude set-up errors, mean displacement in the two structures was 2.8 mm and 1.4 mm, respectively, and corresponding reproducibility in anatomy improved to 1.6 mm (1 SD).</p> <p>Conclusion</p> <p>TI-EPI appears to be a promising method for verifying delivery of RGRT. The RPM system was a good indirect surrogate of internal anatomy, but use of TI-EPI allowed for a direct link between anatomy and breathing patterns.</p

SU‐FF‐T‐625: Estimation of Uncertainty for the Patient and Compensator Scatter Correction Factor in Proton Therapy D/MU Calculations

Purpose: Interest in the tissue sparing benefit of proton therapy is growing. For lung and prostate cancer patients specifically, studies have shown that radiation pneumonitis and rectal bleeding may be reduced by using proton therapy. To verify these benefits on a large scale, multi‐institutional studies are needed; however, a universal method of absolute dosimetry does not yet exist in proton therapy. Moreover, little is known about the conversion of absorbed dose values from phantom measurements to those inside a patient, the uncertainties related to this conversion or the effect of either on dose per monitor unit (D/MU) calculations. Thus, this study focuses on determining the uncertainty for one conversion factor (Fcsps), which accounts for scatter from the range compensator and internal patient scatter. Method and Materials: A sample of 16 prostate and 32 lung treatment fields was collected. Fcsps data was calculated by comparing pencil beam algorithm (PBA) and verification plan results. Then dose profiles were calculated parallel to the field axis and through the calibration point using Monte Carlo calculations (MCC) and PBA. The profiles were normalized to remove stopping power differences and compared. Differences in dose at the calibration point were taken as the uncertainty in Fcsps. Results: There was notable spread in the range of Fcsps data between prostate and thoracic regions which suggests dependence on patient anatomy. A maximum Fcsps value differed from unity by 7.4% indicating Fcsps as a significant factor in D/MU calculations. Differences between MCC and PBA calculated dose revealed as much as 6.9% uncertainty in dose calculations due largely to Fcsps. Additionally, positional errors of approximately 2 mm have potential to affect a 1.3% change in dose to the patient. Conclusion: In some cases, failing to account for Fcsps may substantially impact the dose delivered to the patient beyond acceptable uncertainties. © 2009, American Association of Physicists in Medicine. All rights reserved

MO‐C‐BRA‐03: The Future of Medical Physics: Challenges and Opportunities

Medical physics is experiencing profound changes, including some with an unpredictable impact on the professional, educational, and scientific aspects of the profession. Impending requirements for professional certification, increased sub‐specialization, and greater emphasis on the monetary benefits of a clinical career are among the changes that place future medical physics research in jeopardy, with a potential diminution in the innovation and creativity that have been the hallmark of progress leading to improvements in patient care over the past 50 years. The President's Symposium focuses on the research challenges and opportunities confronting the medical physics profession. A historical review shows how research has been a key factor in the evolution, expansion, and enhanced stature of medical physics in health care delivery. For young investigators contemplating a research career, challenges include the increasingly competitive environment for research funding, difficulties in balancing research versus clinical training in order to be eligible for professional certification, the lure of more stable employment with higher remuneration in the clinical setting, and an uncertain market for medical physicists desiring research careers. Research opportunities in medical physics are presented as a desirable component of medical physics educational programs. The balance of research, didactic education and clinical training in a medical physicist's education needs careful delineation. The assimilation of Ph.D. graduate and post‐doctoral students into educational programs and the practice of medical physics are explored in terms of possible pathways

A comparison of medical physics training and education programs: Canada and Australia

An overview and comparison of medical physics clinical training, academic education, and national certification/accreditation of individual professionals in Canada and Australia is presented. Topics discussed include program organization, funding, fees, administration, time requirements, content, program accreditation, and levels of certification/accreditation of individual Medical Physicists. Differences in the training, education, and certification/accreditation approaches between the two countries are highlighted. The possibility of mutual recognition of certified/accredited Medical Physicists is examined