Ryan Jones

3D DOSE VERIFICATION USING TOMOTHERAPY CT DETECTOR ARRAY

PURPOSE To evaluate a three-dimensional dose verification method based on the exit dose using the onboard detector of tomotherapy. METHODS AND MATERIALS The study included 347 treatment fractions from 24 patients, including 10 prostate, 5 head and neck (HN), and 9 spinal stereotactic body radiation therapy (SBRT) cases. Detector sonograms were retrieved and back-projected to calculate entrance fluence, which was then forward-projected on the CT images to calculate the verification dose, which was compared with ion chamber and film measurement in the QA plans and with the planning dose in patient plans. RESULTS Root mean square (RMS) errors of 2.0%, 2.2%, and 2.0% were observed comparing the dose verification (DV) and the ion chamber measured point dose in the phantom plans for HN, prostate, and spinal SBRT patients, respectively. When cumulative dose in the entire treatment is considered, for HN patients, the error of the mean dose to the planning target volume (PTV) varied from 1.47% to 5.62% with a RMS error of 3.55%. For prostate patients, the error of the mean dose to the prostate target volume varied from -5.11% to 3.29%, with a RMS error of 2.49%. The RMS error of maximum doses to the bladder and the rectum were 2.34% (-4.17% to 2.61%) and 2.64% (-4.54% to 3.94%), respectively. For the nine spinal SBRT patients, the RMS error of the minimum dose to the PTV was 2.43% (-5.39% to 2.48%). The RMS error of maximum dose to the spinal cord was 1.05% (-2.86% to 0.89%). CONCLUSIONS An excellent agreement was observed between the measurement and the verification dose. In the patient treatments, the agreement in doses to the majority of PTVs and organs at risk is within 5% for the cumulative treatment course doses. The dosimetric error strongly depends on the error in multileaf collimator leaf opening time with a sensitivity correlating to the gantry rotation period.

What Are Medical Students in the United States Learning About Radiation Oncology? Results of a Multi-Institutional Survey

PURPOSE The purposes of this study were to assess the exposure that medical students (MSs) have to radiation oncology (RO) during the course of their medical school career, as evidenced by 2 time points in current medical training (ie, first vs fourth year; MS1s and MS4s, respectively) and to assess the knowledge of MS1s, MS4s, and primary care physicians (PCPs) about the appropriateness of RT in cancer management in comparison with RO attendings. METHODS We developed and beta tested an electronic survey divided into 3 parts: RO job descriptions, appropriateness of RT, and toxicities of RT. The surveys were distributed to 7 medical schools in the United States. A concordance of >90% (either yes or no) among RO attendings in an answer was necessary to determine the correct answer and to compare with other subgroups using a χ(2) test (P<.05 was significant). RESULTS The overall response rate for ROs, MS1s, MS4s, and PCPs was 26%; n (22 + 315 + 404 + 43)/3004. RT misconceptions decreased with increasing level of training. More than 1 of 10 MSs did not believe that RT alone could cure cancer. Emergent oncologic conditions for RT (eg, spinal cord compression, superior vena cava syndrome) could not be identified by >1 of 5 respondents. Multiple nontoxicities of RT (eg, emitting low-level radiation from the treatment site) were incorrectly identified as toxicities by >1 of 5 respondents. MS4s/PCPs with an RO rotation in medical school had improved scores in all prompts. CONCLUSIONS Although MS knowledge of general RT principles improves from the first to the fourth year, a large knowledge gap still exists between MSs, current PCPs, and ROs. Some basic misconceptions of RT persist among a minority of MSs and PCPs. We recommend implementing formal education in RO fundamentals during the core curriculum of medical school.

Radiation therapy of post-mastectomy patients with positive nodes using fixed beam tomotherapy

PURPOSES To develop an optimized dosimetric class solution for post-mastectomy irradiation for fixed beam tomotherapy (FBT). METHODS AND MATERIALS CT simulation scans from 10 post-mastectomy patients were used to generate plans with planning target volumes (PTVs) that included the chest wall, axillary nodes and supraclavical nodes using FBT and helical tomotherapy (HT) with 3D and IMRT modes and the resultant dosimetry was compared to conventional IMRT. FBT IMRT plans were analyzed with both 4 (4FBT) and 11-field (11FBT) plans. Important organs at risk (OARs) included the heart, ipsilateral and contralateral lungs, esophagus and contralateral breast. In all plans, the spinal cord and contralateral lung were completely blocked while the heart and ipsilateral lung were directionally blocked. Doses to the contralateral breast were minimized. Each plan was evaluated for its delivery time, percentile volume of lung receiving x Gy (V(x)) and dose received by x percent volume (D(x)). D(1) and D(5) were used to measure the maximum dose to the OAR or PTV, D(95) and D(99) were used to measure the minimal dose to the PTV. RESULTS Compared to the conventional IMRT technique, HT IMRT, 11FBT IMRT and 11FBT 3D significantly reduced the D(1) of the heart in cases of left-sided tumors by 13%, 41% and 36%, and the V(10) of ipsilateral lung in all cases by 26%, 49% and 46%, respectively. A close to 90% reduction in the contralateral breast dose was also observed with the 11FBT plans. Target dose homogeneity of 11FBT 3D plans is inferior to that of the HT and conventional IMRT plans but the treatment delivery time, 7.59 min, was significantly shorter by 3 min. 4FBT IMRT resulted in clinically unacceptable heterogeneity with high dose regions in both the PTV and normal tissue. CONCLUSIONS A class solution based on an 11 beam configuration was established to optimize the dosimetry of fixed beam tomotherapy planning for post-mastectomy patients. The 11FBT plans were deliverable in clinically efficient treatment times.

Techniques for intraoperative radiation therapy for early-stage breast carcinoma

Intraoperative radiation therapy (IORT) is a method of accelerated partial breast irradiation developed to replace other longer courses of radiotherapy with a single radiation session administered at the time of breast-conserving surgery. The purpose of this review is to summarize the advantages and disadvantages of breast IORT techniques that are currently available, as well to consider potential alternative techniques for breast IORT or ultra-short course breast radiotherapy. Furthermore, we highlight the published outcomes for the IORT treatment approaches including: electron therapy, superficial photon therapy and other techniques. Potential future directions of IORT are explored including novel IORT techniques utilizing intraoperative brachytherapy with in-room imaging and rapid treatment planning.

Standardized evaluation of simultaneous integrated boost plans on volumetric modulated arc therapy

The purpose of this paper is to quantify the capability of the RapidArc (RA) planning system to deliver highly heterogeneous doses for simultaneous integrated boost (SIB) in both a phantom and patients. A cylindrical planning target volume (PTV) with a diameter of 6 cm was created in a cylindrical phantom. A smaller boost tumor volume (BTV) in the PTV with varying diameters (0.625-2.5 cm), positions and shapes was also created. Five previously treated patients with brain tumors were included in the study. Original gross tumor volumes (average 41.8 cm(3)) and PTVs (average 316 cm(3)) were adopted as the BTV and the PTV in the new plans. 30 Gy was prescribed to the PTV. Doses varying from 35 to 90 Gy were prescribed to the BTV. Both SIB and sequential boost (SEQ) plans were created on RA to meet the prescription. A set of reference plans was also created on the helical tomotherapy (HT) platform. Normalized dose contrast (NDC) and the integral dose were used to evaluate the quality of plans. NDC was defined as the dose contrast between BTV and PTV-BTV, normalizing to the ideal scenario where the contrast is the ratio between prescribed doses to the BTV and PTV. NDC above 90% was observed with BTV dose less than 60 Gy. NDC was minimally affected by the size of BTV but adversely affected by the complexity of the shape of the BTV. In the phantom plans, a peak of NDC was observed with 45 Gy (150% of PTV dose) to the BTV; for BTVs at the center of the PTV, the increase in the integral dose was less than 2% and remained constant for all dose levels in the phantom plans but a linear increase in the integral dose was observed with the HT plans. In the patient plans, an 11% average increase in the integral dose was observed with SIB plans and 60 Gy to the BTV, lower than the 30% average increase in the SEQ plans by RA and 25% by HT. The study showed not only that SIB by RA can achieve superior plans compared with SEQ plans on the same platform and SIB plans on HT, but also the feasibility to optimize prescription dose in a SIB plan. A maximal therapeutic ratio can be achieved with BTV dose 50-100% higher than the PTV dose, depending on the shape and position of the tumor.

Feasibility of non-coplanar tomotherapy for lung cancer stereotactic body radiation therapy

To quantify the dosimetric gains from non-coplanar helical tomotherapy (HT) arcs for stereotactic body radiation therapy (SBRT) of lung cancer, we created oblique helical arcs by rotating patients CT images. Ten, 20 and 30 degrees of yaws were introduced in the treatment planning for a patient with a hypothetical lung tumor at the upper, middle and lower portion of the right lung, and the upper and middle left lung. The planning target volume (PTV) was 43 cm3. 60 Gy was prescribed to the PTV. Dose to organs at risk (OARs), which included the lungs, heart, spinal cord and chest wall, was optimized using a 2.5 cm jaw, 0.287 pitch and modulation factor of 2.5. Composite plans were generated by dose summation of the resultant plans. These plans were evaluated for its conformity index (Rx) and percentile volume of lung receiving radiation dose of x Gy (Vx). Conformity index was defined by the ratio of x percent isodose volume and PTV. The results show that combination of non-coplanar arcs reduced R50 by 4.5%, R20 by 26% and R10 by 30% on average. Non-coplanar arcs did not affect V20 but reduced V10 and V5 by 10% and 24% respectively. Composite of the non-coplanar arcs also reduced maximum dose to the spinal cord by 20–39%. Volume of chest wall receiving higher than 30 Gy was reduced by 48% on average. Heart dose reduction was dependent on the location of the PTV and the choice of non-coplanar orientations. Therefore we conclude that non-coplanar HT arcs significantly improve critical organ sparing in lung SBRT without changing the PTV dose coverage.

STAT RAD: A Potential Real-Time Radiation Therapy Workflow

The American Cancer Society estimates that approximately 1.5 million people in the United States will be diagnosed with cancer, and 560,000 will die of cancer in 2010 (Jemal et al., 2010). These numbers are projected to increase rapidly in the near future due to national demographics with a large number of Americans reaching retirement age over the next 15-20 years, resulting in a doubling of projected new cancer diagnoses in 2050 to 3 million (Hayat et al., 2007). Most cancer deaths involve extensive locoregional tumors or metastatic disease to brain, lung, liver, or bone causing pain, disability, and decreased quality of life. As treatments for cancer improve, patients are living longer with advanced cancer than ever before, and the management of metastatic disease is becoming increasingly more multi-disciplinary and complex with patients treated simultaneously with systemic therapy, surgery, and radiation. It is well documented that cancer-related pain is often inadequately controlled in the palliative care setting, and both the pain and opioid medication interfere with patient function and quality of life (Bruera & Kim, 2003; Cleeland et al., 1994; McGuire, 2004). Radiotherapy is an important treatment for the alleviation of pain and suffering for cancer patients. It prevents pathologic bone fractures, and palliates tumor-induced obstruction, bleeding, and pain that is not well palliated with pharmacologic treatment (Halperin et al., 2008).

SU-E-T-332: TomoTherapy Patient Treatment Delivery QA Utilizing Phantom-Less Exit-Detector Patient Delivery Coupled with Monte Carlo Dose Calculations: Validation.

PURPOSE To describe and validate a pre-treatment end-to-end patient dose verification system for TomoTherapy capable of detecting plan transfer, dose calculation, and plan delivery errors and evaluating the dosimetric impact of those errors. METHODS The MCLogQA method for TomoTherapy utilizes a pre-treatment Monte Carlo (MC) dose calculation, post-delivery log file examination and exit-detector based MLC sinogram comparison to confirm intended machine performance. The delivered leaf sinogram is then used with MC for dose reconstruction to evaluate the dosimetric impact of any delivery discrepancies by examining target and OAR DVH metrics. A traditional phantom/ion chamber-based QA plan was created and delivered for ten randomly selected patients to evaluate the accuracy of the MCLogQA algorithms. The ion chamber dose measurements were compared with MC dose calculated using the log file and exit detector data collected during the delivery. Delivered linac output and MLC opening deviations found using the MCLogQA method are reported for 10 patients. RESULTS The MCLogQA reconstructed dose agreed with ion chamber measurements within 1%, while the planned dose deviated from measurement by 2-5%. Analysis of the 10 patients treatment delivery demonstrated that the output during TomoTherapy delivery can vary by approximately 2%. Although patient plans vary from -0.6% to 1.6%, the MLC leaf errors were consistent across fractions for the same patient (excluding one patient). The MCLogQA methods capability of evaluating the impact of deliver errors on patient geometry is demonstrated. CONCLUSION The agreement of MC dose calculations utilizing measured delivered sinograms with ion chamber measurements validates the delivered sinogram based QA method. Our system QAs the on-patient TPS dose computation via MC dose recalculation. Plan transfer and delivery errors are validated by using measured delivered sonograms. Patient dose affects are validated by dose volume metric comparison. Our procedure is an effective and efficient alternative to traditional phantom-based TomoTherapy plan specific QA. Research supported by Funding Opportunity Number CMS-1C1-12-0001 from Centers for Medicare and Medicaid Services, Center for Medicare and Medicaid Innovation. The contents are solely the responsibility of the authors and have not been approved by the Department of Health and Human Services, Centers for Medicare & Medicaid Services.

SU‐GG‐T‐126: Non‐Coplanar Helical Tomotherapy for Stereotactic Body Radiation Therapy of Lung Cancer

Purposes: To study the potential dosimetric gains from non‐coplanar helical tomotherapy (HT) in improving stereotactic body radiation therapy(SBRT) of lungcancer.Methods and materials: Non‐coplanar helical arcs were created by introducing a couch yaw in the CTimage and contours. Treatment plans were subsequently generated on a patient with a total lung volume of 3722 cc. PTVs (43 cc) were placed at upper, middle and lower lobes of the right lung, and the upper and middle lobes of the left lung, respectively. 60 Gy was prescribed to the 95% of PTV. Seven non‐coplanar arcs ranging from −30° to 30° were optimized at each location using HT software. Final plans were composites of these individual arcs. Conformality (Rx) and percentile volume of the lung receiving radiationdose of x Gy (Vx) and doses to heart and chest wall were evaluated. Results: Non‐coplanar arcs did not reduce R50 but significantly reduced R10 and R20 by 10–35% and 7–23%, depending on the number of noncoplanar arcs and location of the tumor. V20 of lung stays constant with the number of the non‐coplanar arcs. V10 is reduced by 17–35% for tumors located on the left lung. V5 is reduced for all tumor locations by 10–30%. Further optimization revealed that heartdose for the tumor located on the middle right lung can be reduced by 50–82% depending on the degree of couch yaw. The chest wall volume receiving 30Gy or higher is reduced for all tumor locations, most significantly for tumors on the left lung with a highest reduction of 77% comparing with coplanar plan. Conclusions: Non‐coplanar HT arcs reduce the volume of lung receiving low dose in a SBRTtreatment without compromising other dosimetric metrics. They also reduce doses to the heart and chest wall when tumor is in the proximity.

SU‐DD‐A1‐04: Dose Reconstruction Using Helical Tomotherapy Detector Data

Purpose: To reconstruct dose delivered to head‐and‐neck patients using detector signals from a helical tomotherapy machine. Methods: Data from five nasopharyngeal cancer patients treated on a Hi‐Art Helical TomoTherapy unit with daily MVCT scans were analyzed. Each patient received a total of 25 treatment fractions. Nine evenly distributed fractions were selected in this analysis. During treatment, X‐rays penetrated the patient and deposited energy on the same CT detectors used for imaging and the signal was back‐projected to entrance fluence by removing attenuation using a dose verification tool provided by TomoTherapy. The fluence was then projected on the patients CT to calculate delivered radiation dose. The method was first validated on quality assurance (QA) plans delivered on a cylindrical phantom and then applied on patient treatment plans. Results: Point check on the phantom for QA measurement resulted in an average error of 1.36% (range −0.22% to 3.73%). A 2.1% systematic error on patients was observed by comparing the average reconstructed dose and the planned dose. Random errors of PTV mean dose were between −1% and 2.1%. The variation of max doses to optical nerves, chiasm, brain stem, spinal cord, larynx, right eye and lens were within 5% of the planned dose but the reconstructed doses to the left eye and lens was more than 5% higher than the planned dose for 4 out of 5 the patients with a maximum percentile error of 16% and absolute error of 1.5 Gy in the entire treatment. Conclusions: Dose verification using detector data offers comparable accuracy to ion chamber measurement on the phantom plans. The error on patients is larger but still within 5% for most organs. Therefore, dose reconstruction based on MVCT images and detector data can be used to effectively detect any gross deviation from the treatment plan.