Prashanth Nookala

Analysis of Intensity-Modulated Radiation Therapy (IMRT), Proton and 3D Conformal Radiotherapy (3D-CRT) for Reducing Perioperative Cardiopulmonary Complications in Esophageal Cancer Patients

Background. While neoadjuvant concurrent chemoradiotherapy has improved outcomes for esophageal cancer patients, surgical complication rates remain high. The most frequent perioperative complications after trimodality therapy were cardiopulmonary in nature. The radiation modality utilized can be a strong mitigating factor of perioperative complications given the location of the esophagus and its proximity to the heart and lungs. The purpose of this study is to make a dosimetric comparison of Intensity-Modulated Radiation Therapy (IMRT), proton and 3D conformal radiotherapy (3D-CRT) with regard to reducing perioperative cardiopulmonary complications in esophageal cancer patients. Materials. Ten patients with esophageal cancer treated between 2010 and 2013 were evaluated in this study. All patients were simulated with contrast-enhanced CT imaging. Separate treatment plans using proton radiotherapy, IMRT, and 3D-CRT modalities were created for each patient. Dose-volume histograms were calculated and analyzed to compare plans between the three modalities. The organs at risk (OAR) being evaluated in this study are the heart, lungs, and spinal cord. To determine statistical significance, ANOVA and two-tailed paired t-tests were performed for all data parameters. Results. The proton plans showed decreased dose to various volumes of the heart and lungs in comparison to both the IMRT and 3D-CRT plans. There was no difference between the IMRT and 3D-CRT plans in dose delivered to the lung or heart. This finding was seen consistently across the parameters analyzed in this study. Conclusions. In patients receiving radiation therapy for esophageal cancer, proton plans are technically feasible while achieving adequate coverage with lower doses delivered to the lungs and cardiac structures. This may result in decreased cardiopulmonary toxicity and less morbidity to esophageal cancer patients.

Evaluation of normal tissue exposure in patients receiving radiotherapy for pancreatic cancer based on RTOG 0848

BACKGROUND Pancreatic cancer is a highly aggressive malignancy. Chemoradiotherapy (CRT) is utilized in many cases to improve locoregional control; however, toxicities associated with radiation can be significant given the location of the pancreas. RTOG 0848 seeks to evaluate chemoradiation using either intensity-modulated radiation therapy (IMRT) or 3D conformal photon radiotherapy (3DCRT) modalities as an adjuvant treatment. The purpose of this study is to quantify the dosimetric changes seen when using IMRT or 3D CRT photon modalities, as well as proton radiotherapy, in patients receiving CRT for cancer of the pancreas treated per RTOG 0848 guidelines. MATERIALS Ten patients with pancreatic head adenocarcinoma treated between 2010 and 2013 were evaluated in this study. All patients were simulated with contrast-enhanced CT imaging. Separate treatment plans using IMRT and 3DCRT as well as proton radiotherapy were created for each patient. All planning volumes were created per RTOG 0848 protocol. Dose-volume histograms (DVH) were calculated and analyzed in order to compare plans between the three modalities. The organs at risk (OAR) evaluated in this study are the kidneys, liver, small bowel, and spinal cord. RESULTS There was no difference between the IMRT and 3DCRT plans in dose delivered to the kidneys, liver, or bowel. The proton radiotherapy plans were found to deliver lower mean total kidney doses, mean liver doses, and liver D1/3 compared to the IMRT plans. The proton plans also gave less mean liver dose, liver D1/3, bowel V15, and bowel V50 in comparison to the 3DCRT. CONCLUSIONS For patients receiving radiotherapy per ongoing RTOG 0848 for pancreatic cancer, there was no significant difference in normal tissue sparing between IMRT and 3DCRT treatment planning. Therefore, the choice between the two modalities should not be a confounding factor in this study. The proton plans also demonstrated improved OAR sparing compared to both IMRT and 3DCRT treatment plans.

SU‐E‐T‐100: How to Improve the Dose Accuracy for Gantry Angle Dependent Patient Specific IMRT QA Using 2D Ion Chamber Array with Octavius Phantom

PURPOSE To determine the cross calibration factors which can predict more accurate dose distribution for fixed beam IMRT QA using Octavius phantom. METHODS The ion chamber based Octavius 2D-array detector (PTW, Freiburg, Germany) is a step in the right direction to measure the absolute dose and dose distribution for patient specific IMRT QA. However, the directional dependency of this detector made it less than desirable for angle dependent IMRT QA. We evaluated the new Octavius system (PTW, Freiburg, Germany) for angle dependent IMRT QA which compensates the response due to directional dependency. The system is designed for full arc VMAT QA, but does not always work for the discrete angle IMRT QA due to non-averaging of errors caused by directional dependence of detectors. The proposed method uses correction factors for each gantry angle. The dose for a 10cm × 10cm open field for each gantry angle was calculated by treatment planning system and measured using the Octavius phantom. The correction factors were determined at each gantry angle and the dose distribution was renormalized at each angle using correction factors. RESULTS The discrepancy between measured and planned dose per monitor unit depended on the gantry angle and were in the range of +-4% using the PTW method. Using our method, uncertainty due to the detector angle dependency was eliminated. CONCLUSIONS The new method removes the angle dependency of ion chamber based 2D array detector for the fixed beam IMRT QA. It provides fast, accurate and more realistic results for angle dependent IMRT QA.

Protons Offer Reduced Tissue Exposure for Patients Receiving Radiation Therapy for Pancreatic Cancer

Abstract Purpose: Pancreatic cancer is a highly aggressive malignancy. Chemoradiation therapy (CRT) is used in many cases to improve local-regional control; however, toxicities associated with radiation can be significant given the location of the pancreas. The purpose of this study is to quantify the dosimetric changes seen when using photons or protons in patients receiving CRT for cancer of the pancreas. Patients and Methods: Ten patients with pancreatic head adenocarcinoma treated between 2010 and 2013 were evaluated in this study. All patients underwent simulation with contrast-enhanced computed tomography imaging. Separate treatment plans using proton radiation therapy, intensity-modulated radiation therapy, and 3-dimensional photon radiation therapy modalities were created for each patient. Dose-volume histograms were calculated and analyzed to compare plans between the 3 modalities. The organs at risk evaluated in this study are the kidneys, liver, small bowel, and spinal cord. To determine statis...

A comparison of proton and photon radiotherapy in reducing cardiac exposure for patients receiving radiation therapy for distal and esophagogastric junction cancer.

167 Background: Recent studies indicate that radiation exposure to heart may have a greater impact on perioperative cardiac morbidities than do other clinical factors. The purpose of this study is to investigate dose distributions of proton and photon treatment plans in patients (pts) with distal and esophagogastric junction (GEJ) carcinoma, focusing specifically on dose reduction to cardiac structures. Methods: Ten pts between 2010 and 2013 were included in this study. Three separate plans were generated for each patient: 3D proton plan, 3D photon plan, and Intensity modulated radiotherapy (IMRT) photon plan. The clinical target volume (CTV) consisted of the pre-operative extent of tumor plus a 10mm manual expansion in all directions. The planning target volume (PTV) was generated by a further expansion on the CTV ranging from 10-15mm. A dose of 50.4Gy given in 28 fractions was delivered to the PTV. All plans were optimized to allow 90% isodose coverage of at least 95% of the PTV. Dose-volume histograms ...

SU‐E‐T‐186: Treatment Planning Dose Accuracy of Whole Breast Irradiation Using Field‐In‐Field Technique

PURPOSE To evaluate the planned dose accuracy of whole breast irradiation using field-in-field technique by comparing with 2D array detector measurements and Monte Carlo simulations. METHODS The ion chamber based Octavius 2D-array detector (PTW, Freiburg, Germany) was used to measure the absolute dose and dose distributions of tangential field-in-field breast irradiation. A commercially available treatment planning system (Eclipse V10.0, Varian, Palo Alto CA USA) was used to calculate the absolute dose and dose distributions. Phantom geometry was simplified for the measurements and for Monte Carlo simulations, but its size and shape were similar to typical breast. The dose accuracy of the treatment planning system was evaluated and the desirable points for monitor unit calculation were recommended based on the results of the study. RESULTS The discrepancy between measured and planned dose distribution depended on the location of the monitor unit calculation point. The differences were larger when monitor unit calculation point was closer to the irradiated edges of phantom. The doses calculated by the treatment planning system near the center of the irradiated field were about 2% higher than measured doses. There was good agreement between the measured doses and those predicted by Monte Carlo methods. CONCLUSION Because of inadequate treatment of scatter in the irradiation of breast with tangential ports, the dose predictions by a treatment planning system do not always agree with the actual measurements. The treatment planning algorithm evaluated in this study over-compensates for the loss of scatter in tangential ports glancing the sloping surface of a typical breast. The choice of the prescription point can have significant effect on the dose prediction and the actual dose delivered. Keeping the prescription point away from the field edges will help improve the agreement between the calculated and measured dose.

SU‐E‐T‐839: Treatment Planning Comparison Between IMRT and Protons Involving Patch Fields

Purpose: To compare treatment plans on select complex cases using IMRT and protons involving patch‐field technique Methods: IMRT is used to treat tumors adjacent to critical structures. This is achieved by a dose optimizing algorithm that creates field segments using MLC and modulating the photon fluence to treat different parts of the tumor and conformally avoiding nearby critical structures. Proton beams offer an alternate way to treat such tumors and avoid critical structures. Properties of proton beams important to treatment planning are the ease with which a proton beam can be stopped at the desired depth in a medium as well as its sharp distal dose fall off near the end of the range. In a patch‐field proton beam arrangement a shoot through beam is used to treat majority of the tumor and a patching beam treats remaining tumor near the critical structures. The patching beam stops distally on the lateral edge of the shoot through beam. The weighting and the distal overlap between the shoot‐through and the patching beams are optimized to conformally cover the entire tumor. Here we are comparing treatment plans for different tumor sites using IMRT and proton beams involving patch‐field arrangements. Results: The isodose distributions and dose volume histograms (DVH) were compared between the two treatment modalities. Both IMRT and proton plans do a good job of conformally irradiating the tumor. But overall, proton plans do a better job of sparing the critical structures. One clear advantage of proton beams is the avoidance of low dose to normal tissues surrounding the tumor leading to a lower integral dose Conclusions: Complex tumors surrounding critical structures can be treated effectively with IMRT or proton beams. But protons are more effective in sparing critical structures and they give lower dose to normal tissues than IMRT.

A practical approach for electron monitor unit calculation

Electron monitor unit (MU) calculation requires measured beam data such as the relative output factor (ROF) of a cone, insert correction factor (ICF) and effective source-to-surface distance (ESD). Measuring the beam data to cover all possible clinical cases is not practical for a busy clinic because it takes tremendous time and labor. In this study, we propose a practical approach to reduce the number of data measurements without affecting accuracy. It is based on two findings of dosimetric properties of electron beams. One is that the output ratio of two inserts is independent of the cone used, and the other is that ESD is a function of field size but independent of cone and jaw opening. For the measurements to prove the findings, a parallel plate ion chamber (Markus, PTW 23343) with an electrometer (Cardinal Health 35040) was used. We measured the outputs to determine ROF, ICF and ESD of different energies (5-21 MeV). Measurements were made in a Plastic Water phantom or in water. Three linear accelerators were used: Siemens MD2 (S/N 2689), Siemens Primus (S/N 3305) and Varian Clinic 21-EX (S/N 1495). With these findings, the number of data set to be measured can be reduced to less than 20% of the data points.

SU-FF-T-607: Immobilization, Treatment Planning and Treatment Delivery for Breast Irradiation with Protons

Purpose: To describe a technique for partial breast irradiation with proton beam radiotherapy.Method and Materials: A breast patient post lumpectomy is fitted with a special brassiere to reproducibly support the ipsilateral breast while compressing the contralateral breast. The patient then lies prone in a PVC half cylindrical pipe, supported from shoulder up and below the abdomen by foam bead cushions. The air from the cushions is evacuated resulting in rigid immobilization. The breast area is then immobilized with a urethane based foaming agent producing custom immobilization of the ipsilateral breast. Next, the patient undergoes a treatment planningCT scan of the thorax. The physician contours the tumor bed to include surgical clips and then contours organs at risk. A 3D conformal treatment plan is then developed. For every treatment, the patient is fitted with the treatment brassiere, and positioned prone in the custom immobilization device. Orthogonal and treatment angle diagnostic x‐ray images are taken prior to treatment and are compared with the treatment planning DRRs to reproduce the treatment position according to the plan. The titanium clips are used in the alignment process. At least two fields are treated each day delivering a daily dose of 4.0 cobalt Gray equivalent, and a total dose of 40 cobalt Gray equivalent in 10 fractions. Results: 60 patients have been treated so far. Immobilization procedure is highly reproducible. A comparison with a photon plan demonstrates the clear advantage of a protontreatment to spare the organs at risk, including a significant decrease in skindose.Conclusion: The immobilization procedure provides an accurate and reproducible breast positioning, and minimizes respiratory motion. The procedure has been well tolerated by most patients treated so far. Protons provide significant normal tissue sparing as compared to photontreatments and the clinical results look encouraging.

SU‐GG‐T‐495: Proton Treatment Planning of Complex Cases with Patch‐Fields

Purpose: To illustrate the use of patch field arrangements to treat geometrically complex tumors with proton beams. Method and Materials: One very important property of a high‐energy proton beam is the ease with which it can be stopped at a desired depth in a medium and the sharp distal dose fall‐off near the end of range. This leads to the creation of straightforward beam arrangements to treat very complex tumor shapes. One variation of these beam arrangements is the patch field arrangement. These patch field arrangements are a powerful tool in proton therapy planning. A geometrically complex tumor, e.g., one wrapped around a critical structure, can be treated by a patch field arrangement in which one beam, called a shoot‐through beam, irradiates a part of the tumor. Patching another beam from a different direction and distally stopping this beam on the lateral edge of the shoot‐through beam irradiates the tumor not treated by the shoot‐through beam. We will show how proton patch fields can be used to treat complex clinical cases. Results: We present two plans showing the use of proton patch fields to treat two clinical cases. These cases demonstrate the simplicity of the patch field beam arrangements and the ease with which critical structures can be conformally spared and tumors can be fully irradiated. In addition, these beam arrangements are quite simple to set up clinically. Conclusion: In any clinical practice, one is frequently faced with difficult cases in which tumors, because of their proximity to critical structures, can neither be fully resected nor can they be safely treated with conventional radiation.Proton irradiation, because of its superior dosimetric characteristics, offers treatment options for such cases.