Radiation Therapy Patients Research Articles

On the use of biomathematical models in patient‐specific IMRT dose QA

To investigate the use of biomathematical models such as tumor control probability (TCP) and normal tissue complication probability (NTCP) as new quality assurance (QA) metrics. Five different types of error (MLC transmission, MLC penumbra, MLC tongue and groove, machine output, and MLC position) were intentionally induced to 40 clinical intensity modulated radiation therapy (IMRT) patient plans (20 H&N cases and 20 prostate cases) to simulate both treatment planning system errors and machine delivery errors in the IMRT QA process. The changes in TCP and NTCP for eight different anatomic structures (H&N: CTV, GTV, both parotids, spinal cord, larynx; prostate: CTV, rectal wall) were calculated as the new QA metrics to quantify the clinical impact on patients. The correlation between the change in TCP∕NTCP and the change in selected DVH values was also evaluated. The relation between TCP∕NTCP change and the characteristics of the TCP∕NTCP curves is discussed. ΔTCP and ΔNTCP were summarized for each type of induced error and each structure. The changes/degradations in TCP and NTCP caused by the errors vary widely depending on dose patterns unique to each plan, and are good indicators of each plan's "robustness" to that type of error. In this in silico QA study the authors have demonstrated the possibility of using biomathematical models not only as patient-specific QA metrics but also as objective indicators that quantify, pretreatment, a plan's robustness with respect to possible error types.

PP135: Hypofractionated radiotherapy for locally advanced cancer of the base of the tongue for patients unfit for long-course radiotherapy. Report of two cases and review of the literature

Purpose Long-course concomitant radiochemotherapy is considered the standard therapy for locally advanced head and neck cancer. However, for unfit patients short-course hypofractionated radiotherapy is an appealing choice. Material We present the case of two patients presenting with progressive difficulties in swallowing and articulation that were referred to our department for radiochemotherapy for locally advanced squamous cell carcinoma of the base of the tongue. Method and material We decided to offer both patients a short-course of hypofractionated radiotherapy because of the denial of the one to have a long treatment course and the bad performance status of the other. Literature references support the use of different radiation therapy schedules for palliation of patients that are not candidates for the standard long-course radiotherapy. Sixteen fractions of 3.125 Gy give a total response rate of 73% and local control of 62% and 32% at one and three years, respectively. The HyPo trial (30 Gy/5fr/2 weeks and 6 Gy boost) reported an improvement in quality of life in 62% of patients. Both patients were referred for dental assessment and percutaneous gastric tube placement and had a planning CT scan of the head and neck. They were treated with 3D conformal radiotherapy receiving 30 Gy in 10 fractions in the primary tumor, neck and supraclavicular fossa and 15 Gy as a boost in the gross tumor volume in combination with weekly cisplatin. Reported toxicity was grade II mucositis. Results At the end of radiation therapy both patients had significant clinical improvement with substantial decrease of gross tumor volume and pain, increase of tongue mobility and improvement of articulation. Conclusion Although there are references in the literature of encouraging results by offering short course radiotherapy to patients with locally advanced head and neck cancer the optimum radiation therapy schedule has not been defined yet.

The Evaluation of a New Supportive Care Screening Tool for Radiation Therapy Patients

ObjectivesIndividuals undergoing radiation therapy for cancer may experience a wide range of supportive care needs that are frequently not addressed. A screening tool was designed and tested for psychometric properties (technical characteristics) to assist radiation therapists to quickly identify those patients who require additional intervention during the course of their radiation treatment, allowing early and timely referral and facilitating the provision of quality, in-depth, and patient-centred supportive care. MethodologyA comprehensive and itemized screening tool was designed to identify the patient concerns and distress level, capture the patient desire to be helped with specific concerns, and inform the centre of alternative help provided. The tool was administered simultaneously with the standardized instrument quality-of-life questionnaire. One hundred and fifteen radiation therapy patients completed both instruments on three occasions; the first two were 2 days apart, and the third, 2 weeks later. To test the new tool for reliability and sensitivity, the agreement between the responses on the first two occasions and those between the first and third occasions were analysed for both instruments. Correlations between the responses on the two instruments were also examined for concurrent validity. ResultsMcNemar's test and the simple kappa coefficient both showed high agreement between item scores on the new screening tool when the first and the second occasions were compared. When the first and the third occasions were compared, the former test showed a shift from high agreement to lesser agreement across the item scores. The latter showed a shift in more than 97.7% of the items from a higher agreement to a lesser agreement. The new tool's sensitivity to change was further reinforced by the data from the validated quality-of-life questionnaire, which showed a similar change over time; the Pearson product moment correlation coefficient fell on average from 0.75 to 0.58 for the first and the second comparisons respectively, with all P values less than .0001. Concurrent validity was found to be acceptable. ConclusionsThe new screening tool was found to be reliable and sensitive, with acceptable validity. It is anticipated that the screening intervention will allow radiation therapists to standardize and formalize their approach to supportive care in radiation therapy outpatient clinics and enhance their capacity to identify and address patient concerns in a timely manner.

Commissioning and implementation of an implantable dosimeter for radiation therapy

In this article we describe commissioning and implementation procedures for the Dose Verification System (DVS) with permanently implanted in vivo wireless, telemetric radiation dosimeters for absolute dose measurements. The dosimeter uses a semiconductor device called a metal–oxide semiconductor field‐effect transistor (MOSFET) to measure radiation dose. A MOSFET is a transistor that is generally used for amplifying or switching electronic signals. The implantable dosimeter was implemented with the goal of verifying the dose delivered to radiation therapy patients. For the purpose of acceptance testing, commissioning, and clinical implementation and to evaluate characteristics of the dosimeter, the following tests were performed: 1) temperature dependence, 2) reproducibility, 3) field size dependence, 4) postirradiation signal drift, 5) dependence on average dose rate, 6) linearity test, 7) angular dependence (different gantry angle position), 8) angular dependence (different DVS angle position), 9) dose rate dependence, 10) irradiation depth dependence, 11) effect of cone‐beam exposure to the dosimeter, and 12) multiple reading effect. The dosimeter is not currently calibrated for use in the kV range; nonetheless, the effect of the cone‐beam procedure on the MOSFET dosimeter was investigated. Phantom studies were performed in both air and water using an Elekta Synergy S Beam‐Modulator linear accelerator. Commissioning and clinical implementation for prostate cancer patients receiving external‐beam radiation therapy were performed in compliance with the general recommendations given for in vivo dosimetry devices. The reproducibility test in water at human body temperature (37°C) showed a 1.4% absolute difference, with a standard deviation of 5.72 cGy (i.e., SD=2.9%). The constancy test shows that the average readings at room temperature were 3% lower compared to the readings at human body temperature, with a SD=2%. Measurements were not dependent upon field size. Due to postirradiation signal drift, the following corrections are suggested: −2.8%, −2%, 0.5%, and 2.5% for the readings taken after 0.5, 1, 5, or 10 min, respectively. Different gantry angles did not influence the readings. The maximum error was less than 1% with a maximum SD=3.61cGy (1.8%) for the gantry angle of 45°. However, readings are dependent on the dosimeter orientation. The average dose reading was 7.89 cGy (SD=1.46cGy) when CBCT imaging was used for the pelvis protocol, and when postirradiation measurement was taken at 2.5 min (expected 2–3 cGy). The clinical implementation of the implantable MOSFET dosimeters for prostate cancer radiation therapy is described. Measurements performed for commissioning show that the dosimeter, if used within specifications, provides sufficient accuracy for its intended use in clinical procedures. The postradiation signal drift, temperature dependence, variation of reproducibility, and rotational isotropy could be encountered if the dosimeter is used outside the manufacturer's specifications. The dosimeter can be used as a tool for quantifying dose at depth, as well as to evaluate adherence between planned doses and the delivered doses. Currently, the system is clinically implemented with ±7% tolerance.PACS numbers: 87.53.‐j; 87.55.‐x

The impact of 99mTc-DTPA orbital SPECT in patient selection for external radiation therapy in Graves’ ophthalmopathy

In Graves' ophthalmopathy (GO), there is a demand to differentiate the immunologically active disease state, when immunosuppressive therapy is necessary, from the inactive state, when the patient would not benefit from it. We measured the inflammatory activity in the retrobulbar region using Tc-diethylene triamine pentaacetic acid (DTPA) SPECT before and after external radiation to determine whether this method is suitable for predicting the effectiveness of this therapy. Thirty-two patients with suspected active GO were involved in this retrospective study. The initial image, DTPA uptake value (UV) and its change after therapy were assessed to monitor the effect of the therapy and investigate whether a pretreatment scan is capable of predicting the outcome. Depending on the change in DTPA UV after radiotherapy, three patient groups were formed: decreased, increased or minimally changed (less than 1×10 injected dose (ID)/ml). The initial DTPA UVs of these groups were significantly different (P<0.001). Improvement was observed mainly in patients with higher initial values. When comparing the groups with low (<12×10 ID/ml) versus high (≥12×10 ID/ml) initial uptake, an unexpected increase was observed in the first group after therapy (mean: +2.89±2.66×10 ID/ml), whereas the average change in the DTPA UV was negative in the latter group as anticipated (-2.24±4.47×10 ID/ml, P<0.00001). We found that in GO patients a high DTPA UV may predict the response to orbital radiation therapy. DTPA orbital SPECT may be a suitable technique for the selection of GO patients for radiation therapy.

Efficacy and feasibility of chemotherapy and radiation therapy for borderline resectable pancreatic cancer in elderly patients.

320 Background: To date there have been few studies evaluating the efficacy and tolerability of aggressive neoadjuvant chemotherapy and radiation therapy (RT) for patients ≥70 years of age with borderline resectable pancreatic cancer (BRPC). Methods: We performed a retrospective review of our institutional experience treating BRPC from 2006 to June 2012. All patients were staged with a pancreas protocol CT scan, endoscopic ultrasound, and PET/CT scan. The diagnosis of BRPC was confirmed by our GI Tumor Board prior to treatment. Our institutional preference for preoperative chemotherapy included gemcitabine, paclitaxel and capecitabine (GTX). RT techniques included intensity modulated radiation therapy (IMRT) or stereotactic body radiation therapy (SBRT). Restaging scans were performed after RT completion and patients were then considered for surgical resection. The data was analyzed using Kaplan-Meier and Cox regression analysis. Results: This study included 72 BRPC patients with a median age of 65 years (range 36-87). 24 patients (33%) were ≥70 years old. Median follow up for all patients was 12.7 months. 56 patients (77%) received preoperative GTX. Of the patients ≥70 years, 7 were treated with IMRT and 17 with SBRT, compared to 8 who were treated with IMRT and 40 with SBRT in the younger cohort. In the older group, 11 patients (46%) underwent surgery with all attaining microscopically negative margins (R0), compared with 32 patients that underwent surgery in the younger cohort (61.7%), 29 of which received R0 margins (90.6%). Median survival for patients ≥70 years old was 12.6 months compared to 12.8 months for the younger patients. There was no difference in overall survival (p =.606) or progression free survival (p = .312) between the two groups. Multivariate analysis showed that surgery in the entire group was significantly associated with an improvement in overall survival (p = .011). Conclusions: Our data indicates that aggressive neoadjuvant chemotherapy and RT is equally effective for older patients. Neoadjuvant therapy for BRPC should not be withheld basely solely on patient age.

Thymoma: A Population-Based Study of the Management and Outcomes for the Province of British Columbia

Thymomas are rare neoplasms with variable clinical behavior. Our primary study aim was to analyze treatment practices and outcomes in a population-based cohort of thymoma patients. We hypothesized that stage I and II thymomas would have high cure rates with resection and adjuvant radiation, whereas locally advanced cases would benefit from multimodality therapy. All patients, diagnosed with thymoma or thymic carcinoma in British Columbia between 1994 and 2009, were identified using the British Columbia Cancer Agency Registry. Chart review was used to collect demographic and treatment data. Detailed pathology review was performed using the World Health Organization classification. One hundred and seventy-one patients were identified for analysis. The 5-year overall survival was 93.3%, 88.7%, 74.6%, 43.4% for stages I, II, III, and IV, respectively. Survival varied significantly among patients with thymoma compared with thymic carcinoma. In patients with stage II disease, adjuvant radiation did not confer an overall survival or recurrence-free survival benefit. Seventy-five patients had locally advanced disease. There was practice variation in treatment of these patients. Patients with thymoma undergoing trimodality treatment had a 5-year median overall survival of 80%, whereas patients with thymic carcinoma had poor outcomes despite aggressive treatment. Survival rates in this population-based series were comparable to those in previously published reports. The ideal management of thymic tumors involves a multidisciplinary approach, particularly in locally advanced disease and selection of patients for adjuvant radiation therapy.

Radiation oncology outpatient perceptions of patient-centred care: a cross-sectional survey

ObjectivesWe aimed to describe the proportion and characteristics of cancer patients who perceived that better care would have greatly improved their well-being in (1) specific and (2) multiple domains of...

High-quality four-dimensional cone-beam CT by deforming prior images

Due to a limited number of projections at each phase, severe view aliasing artifacts are present in four-dimensional cone beam computed tomography (4D-CBCT) when reconstruction is performed using conventional algorithms. In this work, we aim to obtain high-quality 4D-CBCT of lung cancer patients in radiation therapy by deforming the planning CT. The deformation vector fields (DVF) to deform the planning CT are estimated through matching the forward projection of the deformed prior image and measured on-treatment CBCT projection. The estimation of the DVF is formulated as an unconstrained optimization problem, where the objective function to be minimized is the sum of the squared difference between the forward projection of the deformed planning CT and the measured 4D-CBCT projection. A nonlinear conjugate gradient method is used to solve the DVF. As the number of the variables in the DVF is much greater than the number of measurements, the solution to such a highly ill-posed problem is very sensitive to the initials during the optimization process. To improve the estimation accuracy of DVF, we proposed a new strategy to obtain better initials for the optimization. In this strategy, 4D-CBCT is first reconstructed by total variation minimization. Demons deformable registration is performed to register the planning CT and the 4D-CBCT reconstructed by total variation minimization. The resulted DVF from demons registration is then used as the initial parameters in the optimization process. A 4D nonuniform rotational B-spline-based cardiac-torso (NCAT) phantom and a patient 4D-CBCT are used to evaluate the algorithm. Image quality of 4D-CBCT is substantially improved by using the proposed strategy in both NCAT phantom and patient studies. The proposed method has the potential to improve the temporal resolution of 4D-CBCT. Improved 4D-CBCT can better characterize the motion of lung tumors and will be a valuable tool for image-guided adaptive radiation therapy.

Abstract P5-11-02: Breast Cancer Radiation Therapy and the Risk of Developing Bronchiolitis Obliterans Organizing Pneumonia (BOOP): Communication of BOOP Risk by Breast Cancer Information Websites and General Medical Information Websites

Abstract Background: BOOP is an inflammatory pulmonary disorder consisting of organized polypoid granulation tissue in the distal airways extending into the alveolar ducts and alveoli. Clinical manifestations of BOOP include fever, cough, dyspnea on exertion, and fatigue. Patients with severe BOOP require hospitalization. The mainstay of BOOP treatment is high dose corticosteroids. Many patients relapse and require long term corticosteroids, often in combination with another immunosuppressant. Significant morbidity and disability may be associated with both the diagnosis of BOOP and the toxicities of treatment. The mortality rate of BOOP has been estimated to be about 5%. Radiation Therapy (RT) is an important component in the treatment of breast cancer (Breast Ca). Beginning in 1995, reports of BOOP occurring in Breast Ca RT patients began to appear in the medical literature. From 1995 to the present, 43 case study reports described 121 Breast Ca RT patients who developed BOOP within one year of their RT. From 1999 to 2011, seven epidemiological studies were published that suggested that the incidence of BOOP in Breast Ca RT patients was in the range of 2% to 3%. Objectives: The primary objective of this study was to determine if internet sources of Breast Ca information targeted to Breast Ca patients include BOOP information in their description of RT risks. The secondary objective was to determine if general medical websites conveyed BOOP/Breast Ca RT risk information. Methods: Eight websites specifically targeted to Breast Ca patients were reviewed. Sponsors of these websites included the US government, Breast Ca advocacy groups, and medical organizations. Seven general medical websites that contained BOOP/Breast Ca RT information were also reviewed. Results: There was no mention of BOOP in any of the websites targeted to Breast Ca patients. The websites included those from the National Cancer Institute, American Cancer Society, American Society of Therapeutic Radiology and Oncology, Susan G. Komen, and BreastCancer.org. The internet search identified seven general medical websites that did include information about the risk of BOOP from Breast Ca RT. Discussion: It is perplexing that none of the eight website sources for Breast Ca patients included any mention of the risk of BOOP associated with Breast Ca RT, whereas seven general medical internet sources did disclose this information. This disparity raises important issues and questions. The majority of BOOP/Breast Ca RT reports were published in pulmonology journals. Is this information being disseminated to providers of Breast Ca treatment? Many of the Breast Ca information websites stated that their information was up to date and was reviewed by leading Breast Ca physicians, so it remains an enigma that the BOOP/RT association was not disclosed. The lack of any information about BOOP and Breast Ca RT may indicate Breast Ca physician unawareness. An alternative explanation for this finding may be that these physicans are aware of the BOOP/RT association, but they believe that the rarity of BOOP diagnoses justifies omitting this information in internet-based information sources. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-11-02.

ICRP perspective on criteria of acceptability for medical radiological equipment

The International Commission on Radiological Protection (ICRP) does not have a specific publication or recent detailed advice on acceptability criteria and suspension levels for medical radiological equipment. However, a number of the Commission's publications clearly stress the need to carry out acceptance testing of radiological equipment. Such general recommendations are frequent in earlier and recent reports related to external radiation therapy. Over 30 y ago, the ICRP even included some examples of parameter accuracies concerning acceptance levels in connection with radiotherapy units. Later more general advices related to acceptability tests as important parts of various quality assurance programs were formulated for radiation therapy as well as for radiodiagnostics without going into details to give values for specific parameters. In the radiodiagnostic field, there are such general recommendations in reports related to equipment for X-ray interventional procedures, digital radiology and computed tomography. The ICRP highly supports the elaboration of detailed and clear acceptability and suspension criteria for equipment used in medical radiology carried out by organisations like International Atomic Energy Agency, International Electrotechnical Commission, European Commission, National Electrical Manufacturers Association (NEMA, USA) and others and consider such criteria as important parts of the quality programmes to guarantee good radiation safety conditions for patients in radiation therapy as well as in radiodiagnostics.

Physical Interactions of Charged Particles for Radiotherapy and Space Applications

In this paper, the basic physics by which energetic charged particles deposit energy in matter is reviewed. Energetic charged particles are used for radiotherapy and are encountered in spaceflight, where they pose a health risk to astronauts. They interact with matter through nuclear and electromagnetic forces. Deposition of energy occurs mostly along the trajectory of the incoming particle, but depending on the type of incident particle and its energy, there is some nonzero probability for energy deposition relatively far from the nominal trajectory, either due to long-ranged knock-on electrons (sometimes called delta rays) or from the products of nuclear fragmentation, including neutrons. In the therapy setting, dose localization is of paramount importance, and the deposition of energy outside nominal treatment volumes complicates planning and increases the risk of secondary cancers as well as noncancer effects in normal tissue. Statistical effects are also important and will be discussed. In contrast to radiation therapy patients, astronauts in space receive comparatively small whole-body radiation doses from energetic charged particles and associated secondary radiation. A unique aspect of space radiation exposures is the high-energy heavy-ion component of the dose. This is not present in terrestrial exposures except in carbon-ion radiotherapy. Designers of space missions must limit exposures to keep risk within acceptable limits. These limits are, at present, defined for low-Earth orbit, but not for deep-space missions outside the geomagnetosphere. Most of the uncertainty in risk assessment for such missions comes from the lack of understanding of the biological effectiveness of the heavy-ion component, with a smaller component due to uncertainties in transport physics and dosimetry. These same uncertainties are also critical in the therapy setting.

Assessment of the risk for developing a second malignancy from scattered and secondary radiation in radiation therapy.

With the average age of radiation therapy patients decreasing and the advent of more complex treatment options comes the concern that the incidences of radiation-induced cancer might increase in the future. The carcinogenic effects of radiation are not well understood for the entire dose range experienced in radiation therapy. Longer epidemiologic studies are needed to improve current risk models and reduce uncertainties of current risk model parameters. On the other hand, risk estimations are needed today to judge the risks versus benefits of modern radiation therapy techniques. This paper describes the current state-of-the-art in risk modeling for radiation-induced malignancies in radiation therapy, distinguishing between two volumes: first, the organs within the main radiation field receiving low or intermediate doses (typically between 0.1 and 50 Gy); and second, the organs far away from the treatment volume receiving low doses mainly due to scattered and secondary radiation (typically below 0.1 Gy). The dosimetry as well as the risk model formalisms are outlined. Furthermore, example calculations and results are presented for intensity-modulated photon therapy versus proton therapy.

Increasing Use of Technology With Palliative Radiation Therapy

Purpose/Objective(s): This study included 165,226 individuals diagnosed with colorectal cancer between 1988 and 2001. Colorectal cancer cases were identified from 16 population-based registries of the National Cancer Institute’s Surveillance, Epidemiology, and End Results program. Materials/Methods: Survival probabilities were compared among white and black patients. Kaplan-Meier curves and proportional hazard ratios from Cox regression analysis were calculated accounting for marital status, age, gender, stage at diagnosis and year of diagnosis. Patients lacking complete information were excluded from analysis. Results: Multivariate analysis demonstrated that older age, male gender, non-recent year of diagnosis, and advanced stage at diagnosis were associated with worse survival. Black race independently predicted for a worse survival compared with whites. Marital status was a greater predictor of survival when analyzed in conjunction with race: compared to married white patients, black single/separated/divorced (unmarried) and black married patients were found to have hazard ratios (HR) of 1.63 (1.56-1.71) and 1.21 (1.17-1.25), respectively. While stage I patients experienced better survival, when compared to white married patients, the HR for black unmarried and black married patients was 2.11 (1.84-2.41) and 1.35 (1.241.47), respectively. Conclusions: Marital status and race are independent predictors of colorectal cancer survival. Additional strategies must be defined that address the social factors that account for disparities in cancer outcome. Author Disclosure: A. Blackstock: E. Research Grant; NIH/NCI P30 CA012197-36. B. Lally: None. S. Isom: None. E. Paskett: None.

Significant Variation in Provider Discussion of Sexual Side Effects With Radiation Therapy Patients

Significant Variation in Provider Discussion of Sexual Side Effects With Radiation Therapy Patients

Magnetic Resonance-guided Focused Ultrasound Surgery for Painful Bone Metastases is a Safe and Effective Treatment in Patients for Whom Radiation Therapy Is Contraindicated: Results of a Multicenter Phase III Trial

Osseous metastases are a daunting problem in oncology. Radiation therapy (RT) is the primary treatment for most patients with painful bone metastases; however, about one-third do not get pain relief and others may have pain recurrence or not be candidates for RT. Magnetic resonance guided focused ultrasound surgery (MRgFUS) combines non-invasive focused ultrasound with MR guidance. Phase I-II studies demonstrated that MRgFUS resulted in high rates of pain relief with an excellent safety profile.

Patterns of Recurrence and the Role of Radiation Therapy in Ovarian Clear Cell Adenocarcinoma

Patterns of Recurrence and the Role of Radiation Therapy in Ovarian Clear Cell Adenocarcinoma

Using Respiratory Invariant Points Obtained From 4D Simulation Study to Provide Accurate Body Setup Correction for Gated Radiation Therapy Patients

Using Respiratory Invariant Points Obtained From 4D Simulation Study to Provide Accurate Body Setup Correction for Gated Radiation Therapy Patients

Online Optimization of Radiation Therapy Patient Scheduling

Purpose/Objective(s): An efficient radiation therapy patient scheduling on the linear accelerators (linacs) is crucial. First, it should ensure the delivery of the treatment with respect to all deadlines. Second, it should efficiently use the material resources to increase the number of patients seen in the center on a period of time. Different objectives and constraints have to be taken into account. The number of delayed patients and the waiting time are minimized while the rate of utilization of the linacs is maximized. As those goals are contradictory, generating a high quality solution is complex. For example, a palliative patient should receive a treatment within three days. Considering that the arrival of these patients to the center is unknown the rate of utilization cannot be optimized without exceeding the three days deadline. Furthermore, resource constraints are very tight: the number of patients treated reaches nearly the full capacity. Materials/Methods: We propose a hybrid algorithm using online and stochastic optimization. Online methods allow scheduling a patient whenever according to the preference of the user and stochastic tools authorize to infer the future in order to take into account prospective patients especially palliative patients whom have very tight deadlines to receive their treatment. Results: We have tested those techniques on randomly generated patients to get a planning for all of them. Comparing to the current strategy of the center, our algorithm have 75% less patients who exceed their deadline. Secondly, the rate of utilization of linacs is around the same: just a difference of 1%. Moreover, the average waiting time is more proportional to the deadline of each kind of patients. That is why, there are less patients exceeding their delays. Finally, we have compared those two strategies to the optimal solution. This last schedule outperforms all others strategies, however our method is the closest to the optimal. The gap is enough to hope making good improvements for the future. Conclusions: We are confident about the efficiency of this algorithm since the radio-oncology treatment center can obtain a good inference of future patients. This method will improve the access to the delivery system for the patients and for the center. Author Disclosure: M. Fortin: None. A. Legrain: None. N. Lahrichi: None. L. Rousseau: None.

Quantitative Assessment of Lung Function in Stage I and Stage III Lung Radiation Therapy Patients Using 4DCT-based Ventilation Imaging

To calculate ventilation: the lungs were segmented on the inhale and exhale phase of the 4DCT dataset. Once the lungs were appropriately segmented, a deformable image registration algorithm was used to link the lung voxel elements in the inhale phase to the exhale phase. Following spatial registration, corresponding Hounsfield Units were input into a density-change-based model for quantifying the local ventilation (Equation 1).