Joann I. Prisciandaro

TECHNICAL ASPECTS OF DAILY ONLINE POSITIONING OF THE PROSTATE FOR THREE-DIMENSIONAL CONFORMAL RADIOTHERAPY USING AN ELECTRONIC PORTAL IMAGING DEVICE

PURPOSE To develop a real-time electronic portal imaging device (EPID) procedure to identify intraprostatic gold markers and correct daily variations in target position during external beam radiotherapy for prostate cancer. METHODS AND MATERIALS Pretherapy electronic portal images (EPIs) were acquired with a small portion of the therapeutic 18-MV dose from an orthogonal pair of treatment fields. The position of the intraprostatic gold markers on the EPIs was aligned with that on the simulation digitally reconstructed radiographs. If the initial three-dimensional target displacement (3DI) exceeded 5 mm or rotations exceeded 3 degrees, the beam was realigned before the remainder of the dose was delivered. Field-only EPIs were then acquired for all fields and offline analysis was performed to determine the final 3D target placement (3DF). RESULTS Twenty patients completed protocol-specified treatment, and all markers were identified on 99.6% of the pretherapy EPIs. Overall, 53% of treatment fractions were realigned. The mean 3DI was 5.6 mm in all patients (range 3.7-9.3), and the mean 3DF was 2.8 mm (range 1.6-4.0), which was statistically significant (p < 0.001). Rotational corrections were made on 15% of treatments. Mean treatment duration was 1.4 min greater for protocol patients than for similar patients in whom localization was not performed. CONCLUSIONS Frequent field misalignment occurs when external fiducial marks are used for patient alignment. Misalignments can be readily and rapidly identified and corrected with an EPID-based online correction procedure that integrates commercially available equipment and software.

Effect of radiation therapy on permanent pacemaker and implantable cardioverter-defibrillator function

BACKGROUND Radiation therapys (RTs) effects on cardiac implantable electronic devices (CIEDs) such as implantable cardioverter-defibrillators (ICDs) and pacemakers (PMs) are not well established, leading to device removal or relocation in preparation for RT. OBJECTIVE To determine the effect of scattered RT on CIED performance. METHODS We analyzed 69 patients--50 (72%) with PMs and 19 (28%) with ICDs--receiving RT at the University of Michigan. Collected data included device model, anatomic location, and treatment beam energies, treatment type, and estimated dose to the device. Patients were treated with either high-energy (16-MV) and/or low-energy (6 MV) photon beams with or without electron beams (6-16 MeV). The devices were interrogated with pre- and post-RT and/or weekly with either in-treatment or home interrogation, depending on the patients dependence on the device and the estimated or measured delivered dose. Outcomes analyzed were inappropriate ICD therapies, device malfunctions, or device-related clinical events. RESULTS The PMs were exposed to 84.4 ± 99.7 cGy of radiation, and the ICDs were exposed to 92.1 ± 72.6 cGy of radiation. Two patients with ICDs experienced a partial reset of the ICD with the loss of historic diagnostic data after receiving 123 and 4 cGy, respectively. No device malfunction or premature battery depletion was observed at 6-month follow-up from RT completion. CONCLUSIONS CIED malfunction due to indirect RT exposure is uncommon. Regular in-treatment or home interrogation should be done to detect and treat these events and to ensure that diagnostic data are preserved.

Beta counting system for fast fragmentation beams

A new beta counting system has been developed at the National Superconducting Cyclotron Laboratory to study the beta decay of exotic nuclei produced by fast fragmentation. This system uses a double-sided silicon strip detector to detect both fragment implants and their subsequent beta decays; these events are correlated on a pixel-by-pixel basis, providing a direct measurement of the decay time with specific particle identification information regarding the parent nucleus. The experimental capabilities of this system are described, and future plans discussed.

A methodology to determine margins by EPID measurements of patient setup variation and motion as applied to immobilization devices.

Assessment of clinic and site specific margins are essential for the effective use of three-dimensional and intensity modulated radiation therapy. An electronic portal imaging device (EPID) based methodology is introduced which allows individual and population based CTV-to-PTV margins to be determined and compared with traditional margins prescribed during treatment. This method was applied to a patient cohort receiving external beam head and neck radiotherapy under an IRB approved protocol. Although the full study involved the use of an EPID-based method to assess the impact of (1) simulation technique, (2) immobilization, and (3) surgical intervention on inter- and intrafraction variations of individual and population-based CTV-to-PTV margins, the focus of the paper is on the technique. As an illustration, the methodology is utilized to examine the influence of two immobilization devices, the UON thermoplastic mask and the Type-S head/ neck shoulder immobilization system on margins. Daily through port images were acquired for selected fields for each patient with an EPID. To analyze these images, simulation films or digitally reconstructed radiographs (DRRs) were imported into the EPID software. Up to five anatomical landmarks were identified and outlined by the clinician and up to three of these structures were matched for each reference image. Once the individual based errors were quantified, the patient results were grouped into populations by matched anatomical structures and immobilization device. The variation within the subgroup was quantified by calculating the systematic and random errors (sigma(sub) and sigma(sub)). Individual patient margins were approximated as 1.65 times the individual-based random error and ranged from 1.1 to 6.3 mm (A-P) and 1.1 to 12.3 mm (S-I) for fields matched on skull and cervical structures, and 1.7 to 10.2 mm (L-R) and 2.0 to 13.8 mm (S-I) for supraclavicular fields. Population-based margins ranging from 5.1 to 6.6 mm (A-P) and 3.7 to 5.7 mm (S-I) were calculated for the corresponding skull/cervical field and 9.3 to 10.0 mm (L-R) and 6.3 to 6.6 mm (S-I) for the supraclavicular fields, respectively. The reported CTV-to-PTV margins are comparable to a value 7-15 mm based on traditional Mayo margins, but in some cases exceed the default values established in RTOG Head and Neck studies. The data suggests that the population-based margins provide sufficient coverage for the majority of the patients. However, the population-derived margins are excessive for some patients and insufficient for others, suggesting that a re-evaluation of current treatment margins for individual patients is warranted. Finally, this methodology provides direct evidence of treatment variation and thus can demonstrate with confidence, the superiority of one technique over another.

Utilizing an electronic portal imaging device to monitor light and radiation field congruence

A method to investigate light and radiation field congruence utilizing a commercially available amorphous silicon electronic portal imaging device (EPID) was developed. This method employed an EPID, the associated EPI software, and a diamond‐shaped template. The template was constructed from a block tray in which Sn/Pb wires, 1 mm in diameter, were embedded into a diamond shaped groove milled into the tray. The collimator jaws of the linac were aligned such that the light field fell directly on the corners of the diamond. A radiation detection algorithm within the EPI software determined the extent of the radiation field. The light and radiation field congruence was evaluated by comparing the vertexes of the diamond reference structure to the detected radiation field. In addition, the digital jaw settings were recorded and later compared to the light field detected on the films and EPIs. Three linear accelerators were tracked for a period ranging from 2–8 months. Light radiation field congruence tests with films and EPIs were comparable, yielding a difference of less than 0.6 mm, well within the allowed 2‐mm tolerance. A disparity was observed in the magnitude of the detected light field. The X and Y dimensions of the light field measured with film differed by less than or equal to 1.4 mm from the digital collimator settings, whereas the values extracted from the EPIs differed by up to 2.5 mm. Based on these findings, EPIs were found to be a quick and reliable alternative to film for qualitative and relative analyses. PACS number(s): 87.53.Xd, 87.56.Fc, 87.53.Oq, 87.52.–g, 87.53.–j

Single or multi-channel vaginal cuff high-dose-rate brachytherapy: Is replanning necessary prior to each fraction?

PURPOSE Adjuvant high-dose-rate vaginal brachytherapy (VB) is commonly used in endometrial cancer. We evaluated the dosimetric and cost differences of using either a single plan or replan prior to each fraction for single- and multi-channel VB. METHODS AND MATERIALS We evaluated 84 fractions from 25 patients at our institution (16 single-channel patients each 3 fractions; 9 multi-channel patients each 4 fractions). All fractions were preceded by a computed tomographic (CT) simulation scan, after which a unique treatment plan was generated, dose points per International Commission on Radiation Units and Measurements (ICRU) 38. We calculated the dose to critical organs based on a decay-and-treat method utilizing the original catheter dwell-times for the initial fraction, and also the interfractional motion of the critical organ points between the initial and the subsequent CT scans. RESULTS The absolute mean dose difference was 14 cGy for bladder and 15 cGy for rectum between the replan and decay methods for single-channel, and 14 cGy for both organ points for the multi-channel cylinder. The bladder and rectum doses were not found to be significantly different between the replan and decay methods for either single-channel (bladder, P = .08; rectum, P = .19) or multi-channel cylinders (bladder, P = .85; rectum, P = .10). The mean interfractional displacement of the organ points between the initial and subsequent CT scans was 1.10 cm for the bladder and 0.67 cm for the rectum for single-channel, and 0.87 cm and 0.51 cm for multi-channel cylinders. The maximum interfractional motion was seen in the transverse plane for both organ points for both types of cylinders. At our institution, the decay method was 19% and 22% more cost-effective for single-channel and multi-channel cylinders, respectively. CONCLUSIONS Our data show no dosimetric advantage, but higher costs, associated with replanning prior to each fraction for both single- and multi-channel VB. Fractional replanning should not be utilized on a routine basis.

Dosimetric review of cardiac implantable electronic device patients receiving radiotherapy

A formal communication process was established and evaluated for the management of patients with cardiac implantable electronic devices (CIEDs) receiving radiation therapy (RT). Methods to estimate dose to the CIED were evaluated for their appropriateness in the management of these patients. A retrospective, institutional review board (IRB) approved study of 69 patients with CIEDs treated with RT between 2005 and 2011 was performed. The treatment sites, techniques, and the estimated doses to the CIEDs were analyzed and compared to estimates from published peripheral dose (PD) data and three treatment planning systems (TPSs) — UMPlan, Eclipses AAA and Acuros algorithms. When measurements were indicated, radiation doses to the CIEDs ranged from 0.01–5.06 Gy. Total peripheral dose estimates based on publications differed from TLD measurements by an average of 0.94 Gy (0.05–4.49 Gy) and 0.51 Gy (0–2.74 Gy) for CIEDs within 2.5 cm and between 2.5 and 10 cm of the treatment field edge, respectively. Total peripheral dose estimates based on three TPSs differed from measurements by an average of 0.69 Gy (0.02–3.72 Gy) for CIEDs within 2.5 cm of the field edge. Of the 69 patients evaluated in this study, only two with defibrillators experienced a partial reset of their device during treatment. Based on this study, few CIED‐related events were observed during RT. The only noted correlation with treatment parameters for these two events was beam energy, as both patients were treated with high‐energy photon beams (16 MV). Differences in estimated and measured CIED doses were observed when using published PD data and TPS calculations. As such, we continue to follow conservative guidelines and measure CIED doses when the device is within 10 cm of the field or the estimated dose is greater than 2 Gy for pacemakers or 1 Gy for defibrillators. PACS number: 87.55.N‐

Essentials and guidelines for clinical medical physics residency training programs: executive summary of AAPM Report Number 249

There is a clear need for established standards for medical physics residency training. The complexity of techniques in imaging, nuclear medicine, and radiation oncology continues to increase with each passing year. It is therefore imperative that training requirements and competencies are routinely reviewed and updated to reflect the changing environment in hospitals and clinics across the country. In 2010, the AAPM Work Group on Periodic Review of Medical Physics Residency Training was formed and charged with updating AAPM Report Number 90. This work group includes AAPM members with extensive experience in clinical, professional, and educational aspects of medical physics. The resulting report, AAPM Report Number 249, concentrates on the clinical and professional knowledge needed to function independently as a practicing medical physicist in the areas of radiation oncology, imaging, and nuclear medicine, and constitutes a revision to AAPM Report Number 90. This manuscript presents an executive summary of AAPM Report Number 249. PACS number: 87.10.‐e

Revisiting fetal dose during radiation therapy: evaluating treatment techniques and a custom shield

To create a comprehensive dataset of peripheral dose (PD) measurements from a new generation of linear accelerators with and without the presence of a newly designed fetal shield, PD measurements were performed to evaluate the effects of depth, field size, distance from the field edge, collimator angle, and beam modifiers for common treatment protocols and modalities. A custom fetal lead shield was designed and made for our department that allows external beam treatments from multiple angles while minimizing the need to adjust the shield during patient treatments. PD measurements were acquired for a comprehensive series of static fields on stack of Solid Water. Additionally, PDs from various clinically relevant treatment scenarios for pregnant patients were measured using an anthropomorphic phantom that was abutted to a stack of Solid Water. As expected, the PD decreased as the distance from the field edge increased and the field size decreased. On average, a PD reduction was observed when a 90° collimator rotation was applied and/or when the tertiary MLCs and jaws defined the field aperture. However, the effect of the collimator rotation (90° versus 0°) in PD reduction was not found to be clinically significant when the tertiary MLCs were used to define the field aperture. In the presence of both the MLCs and the fetal shield, the PD was reduced by 58% at a distance of 10 cm from the field edge. The newly designed fetal shield may effectively reduce fetal dose and is relatively easy to setup. Due to its design, we are able to use a broad range of treatment techniques and beam angles. We believe the acquired comprehensive PD dataset collected with and without the fetal shield will be useful for treatment teams to estimate fetal dose and help guide decisions on treatment techniques without the need to perform pretreatment phantom measurements. PACS numbers: 87.53.Bn, 87.55.D-, 87.55.N.To create a comprehensive dataset of peripheral dose (PD) measurements from a new generation of linear accelerators with and without the presence of a newly designed fetal shield, PD measurements were performed to evaluate the effects of depth, field size, distance from the field edge, collimator angle, and beam modifiers for common treatment protocols and modalities. A custom fetal lead shield was designed and made for our department that allows external beam treatments from multiple angles while minimizing the need to adjust the shield during patient treatments. PD measurements were acquired for a comprehensive series of static fields on a stack of Solid Water. Additionally, PDs from various clinically relevant treatment scenarios for pregnant patients were measured using an anthropomorphic phantom that was abutted to a stack of Solid Water. As expected, the PD decreased as the distance from the field edge increased and the field size decreased. On average, a PD reduction was observed when a 90° collimator rotation was applied and/or when the tertiary MLCs and jaws defined the field aperture. However, the effect of the collimator rotation (90° versus 0°) in PD reduction was not found to be clinically significant when the tertiary MLCs were used to define the field aperture. In the presence of both the MLCs and the fetal shield, the PD was reduced by 58% at a distance of 10 cm from the field edge. The newly designed fetal shield may effectively reduce fetal dose and is relatively easy to setup. Due to its design, we are able to use a broad range of treatment techniques and beam angles. We believe the acquired comprehensive PD dataset collected with and without the fetal shield will be useful for treatment teams to estimate fetal dose and help guide decisions on treatment techniques without the need to perform pretreatment phantom measurements. PACS number(s): 87.53.Bn, 87.55.D‐, 87.55.N

Technical Report: Evaluation of peripheral dose for flattening filter free photon beams

PURPOSE To develop a comprehensive peripheral dose (PD) dataset for the two unflattened beams of nominal energy 6 and 10 MV for use in clinical care. METHODS Measurements were made in a 40 × 120 × 20 cm(3) (width × length × depth) stack of solid water using an ionization chamber at varying depths (dmax, 5, and 10 cm), field sizes (3 × 3 to 30 × 30 cm(2)), and distances from the field edge (5-40 cm). The effects of the multileaf collimator (MLC) and collimator rotation were also evaluated for a 10 × 10 cm(2) field. Using the same phantom geometry, the accuracy of the analytic anisotropic algorithm (AAA) and Acuros dose calculation algorithm was assessed and compared to the measured values. RESULTS The PDs for both the 6 flattening filter free (FFF) and 10 FFF photon beams were found to decrease with increasing distance from the radiation field edge and the decreasing field size. The measured PD was observed to be higher for the 6 FFF than for the 10 FFF for all field sizes and depths. The impact of collimator rotation was not found to be clinically significant when used in conjunction with MLCs. AAA and Acuros algorithms both underestimated the PD with average errors of -13.6% and -7.8%, respectively, for all field sizes and depths at distances of 5 and 10 cm from the field edge, but the average error was found to increase to nearly -69% at greater distances. CONCLUSIONS Given the known inaccuracies of peripheral dose calculations, this comprehensive dataset can be used to estimate the out-of-field dose to regions of interest such as organs at risk, electronic implantable devices, and a fetus. While the impact of collimator rotation was not found to significantly decrease PD when used in conjunction with MLCs, results are expected to be machine model and beam energy dependent. It is not recommended to use a treatment planning system to estimate PD due to the underestimation of the out-of-field dose and the inability to calculate dose at extended distances due to the limits of the dose calculation matrix.