Search

Background Exploiting biologic imaging, studies have been performed to boost dose to gross intraprostatic tumor volumes (GTV) while reducing dose elsewhere in the prostate. Interest in proton beams has increased due to superior normal-tissue sparing they afford. Our goal was to dosimetrically compare 3D conformal proton boost plans with intensity-modulated radiation therapy (IMRT) plans with respect to target coverage and avoiding organs at risk. Methods Treatment planning computer tomography scans of ten patients were selected. For each patient, two hypothetical but realistic GTVs each with a fixed volume were contoured in different anatomical locations of the prostate. IMRT and proton beam plans were created with a prescribed dose of 50.4 Gy to the initial planning target volume (PTV) including the PTV of the seminal vesicles (PSV), 70.2 Gy to the PTV of the prostate (PPS), and 90 Gy to the PTV of the gross tumor volumes (PGTVs). For proton plans, uncertainties of range and patient setup were accounted for; apertures were adjusted until the dose-volume coverage of PTVs matched that of the IMRT plan. For both plans, prescribed PTV doses were made identical to allow for comparing normal-tissue doses. Results Protons delivered more homogeneous but less conformal doses to PGTVs than IMRT did and comparable doses to PSV and PPS. Volumes of bladder and rectum receiving doses higher than 65 Gy were similar for both plans. However, volumes receiving less than 65 Gy were significantly reduced, i.e., protons reduced integral dose by 45.6 % and 26.5 % for rectum and bladder, respectively. This volume-sparing was also seen in femoral heads and penile bulb. Conclusions Protons delivered comparable doses to targets in dose homogeneity and conformity and spared normal tissues from intermediate-to-low doses better than IMRT did. Further improvement of dose sparing and changes in homogeneity and conformity may be achieved by reducing proton range uncertainties and from implementing intensity modulation.

Purpose: Evaluation of KODAK RT2000 CR System for its practical use in replacing portal localization films. Methods: Patient setup verification is critical to accurately deliver a prescribed dose to a patient. We use portal film imaging on some of our old machines. KODAK RT2000 CR System was recently evaluated to replace the conventional portal films with digital imaging. Rando phantom was used to test the functionality and accuracy of the Kodak CR system. A treatment plan was generated using the CTimages of the Rando phantom; the plan was then exported to Siemens PRIMUS via ARIA. Portalimages were taken using KODAK photostimulable phosphor (PSP) system. The PSP system was read by scanning the phosphor using KODAK CR System. These digitized images were exported to Varian ARIA RT Chart and evaluated in Offline Review for registration of DRRs with the digital portalimage. DRRs from the treatment planning system and digital portalimages from KODAK CR System were matched and differences between the planned set‐up and the in‐room set‐up of phantom were measured with tools in Offline Review. Shifts in lateral, longitudinal and vertical directions along with tilt angle were obtained to finally register the DRRs with the digital portalimages. Results: We converted our old film‐based portalimaging system into a digital portalimaging system. These digital images can be shared across a network. A digital imaging system provides easy access through ARIA network for physician's approval of portalimages. Conclusions: We successfully integrated four different multi‐vendor modalities (Odyssey TPS from Optivus, Siemen's Primus, Varian ARIA and KODAK CR System) to develop a portal digital imaging system. The system increases accuracy of treatment, offers flexibility of offline review by a physician, and thus makes the whole process more efficient.

369 Background: The purpose of this study is to investigate dose distributions of proton and intensity-modulated radiation therapy (IMRT) photon treatment plans in patients with resected pancreatic adenocarcinoma, focusing specifically on dose reduction to the kidney, liver, and small bowel as organs at risk. Methods: Ten patients with pancreatic head adenocarcinoma underwent Whipple procedure between 2010 and 2013 were included in this study. Most of the patients had locally advanced disease (T3-4N1). All patients were simulated with contrast-enhanced CT imaging. The clinical target volume (CTV) consisted of the pre-operative extent of tumor plus a 10 mm manual expansion in all directions. The planning target volume (PTV) was generated by a further expansion on the CTV ranging from 10-15 mm. A dose of 50.4 Gy given in 28 fractions was delivered to the PTV. All plans were optimized to allow 95% isodose coverage of at least 95% of the PTV. Dose-volume histograms, conformity index (CI), uniformity index (UI), homogeneity index (HI), were calculated and analyzed in order to compare plans between the two modalities. The OAR being evaluated in this study are the kidneys, liver, small bowel, and spinal cord. To determine statistical significance, ANOVA and two-tailed paired t-tests were performed for all data parameters. Results: The proton plans resulted in a lower mean kidney dose (3.17 Gy vs. 9.59 Gy, p=0.039), a lower dose delivered to 1/3 of the liver, D1/3, (0.25 Gy vs. 4.56 Gy, p=0.003), and a lower mean liver dose (1.83 Gy vs. 5.24 Gy, p=0.021). See table for a summary of the results. Conclusions: For patients receiving postoperative radiotherapy for pancreatic cancer, the proton plans are technically feasible and dosimetrically appealing with superior organ at risk sparing compared to IMRT photon treatment plans.[Table: see text]

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.

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.

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.

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.