bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐62: Anatomy‐Based MLC Field Optimization for the Treatment of Gynecologic Malignancies
Authors: Nadeau S , Bouchard M , Germain I , Raymond P‐E , Beaulieu F , Beaulieu L , Roy R , Harel F , Gingras L
Published: June 2005

Purpose: To evaluate the use of a new inverse planning system with anatomy‐based field segmentation, as an alternative between “4‐field box” and beamlet‐based IMRT, to treat whole pelvis of women with resected gynecologic malignancies. Method and Materials: A solution has been elaborated with the assistance of an in‐house optimization tool named Ballista. This inverse planning system can generate anatomy‐based MLC fields and simultaneously optimize their orientation and weight. The selected geometry consists of 7 coplanar and 2 noncoplanar incidences. For 10 patients planned to receive 45 Gy for resected endometrial or cervix neoplasia, target volume and organ at risk (bowel, region “at risk to find bowel” (B RAR), bladder, rectum, bone marrow) were delineated. Using the Pinnacle3 planning system, four plans were generated for each patient: conventional 4‐field, enlarged 4‐field (aperture shaped to PTV), “step‐and‐shoot” IMRT and Ballista plans. Dose‐volume histograms, number of segments and monitor units (MU) were analyzed. Results: Planning target volume (PTV) coverage was similar for enlarged 4‐field, IMRT and Ballista plans, and follows the ICRU standard recommendations. Only 77.5 ± 1.9% (mean ± SEM) of PTV received the prescription dose if conventional plans were applied (p<0.001). The mean volume of B RAR receiving 45 Gy was: 4‐field, 49.7 ± 7.1%; enlarged 4‐field, 63.4 ± 5.8%; IMRT, 26.4 ± 3.1%; Ballista, 29.0 ± 3.0%. No statistical difference was noted between the ability of IMRT and Ballista to spare bowel (p=0.14), while Ballista plans were better than 4‐field (p<0.001). The mean number of segments for Ballista was 33.3 ± 2.3 vs 128.6 ± 2.6 for IMRT and the mean number of MU was 325.0 ± 11.8 vs 731.5 ± 25.0. Conclusion: Weight optimization, with anatomy‐based MLC fields, is a good alternative between manual planning and IMRT for the treatment of gynecologic malignancies. Clinical results of treatment tolerance will follow.
SU‐FF‐T‐65: Comparison of Dose to Rectum and Bladder with 3DCRT and IMRT Plans for the Treatment of Prostate
Authors: Reddy N , Sood B , Mazur A , Osian A , Sampath S , Ravi A , Poli J , Nori D
Published: June 2005

Purpose: Major goal of IMRT is to escalate dose to prostate while keeping doses to bladder and rectum equal to or less than that with 3DCRT. This study is to compare 3DCRT and IMRT to evaluate how far this goal has been achieved. Method and Materials: Dosimetry of 6‐field 3DCRT and 5‐field IMRT plans, generated for the same 32 patients, has been compared. With 3DCRT, prescription to SV and prostate was 45 and 75.6 Gy, respectively. With IMRT, prescription to SV and prostate was 45 and 81 Gy, respectively. IMRT required to keep doses to 30%, 50% and 70% of bladder and rectum less than 70%, 60% and 40% of 81 Gy and to cover 95% PTV with 95% isodose. Dose to rectum and bladder were estimated from DVH. Less than 5% difference in rectal and bladder doses between 3DCRT and IMRT was considered insignificant. Results: Higher the dose to rectum and bladder with 3DCRT, higher also was the dose with IMRT (P<0.001). Dose to 50% rectum with IMRT was equal to that with 3DCRT in 15 cases (47%) and more in 17 cases (53%). Dose to 10% of rectum with IMRT was equal to that with 3DCRT in 9 cases (28%) and more in 23 cases (72%). Dose to 50% and 10% bladder with IMRT were equal to that with 3DCRT in 7 cases (22%) and more in 25 cases (78%). Conclusion: Preliminary analysis suggested that the space between rectum and prostate+SV, and the volume of rectum and bladder in beams path are related to doses to these structures. Higher doses to rectum and bladder with IMRT are a result of trade‐off between doses to PTV, rectum and bladder. This may be acceptable because percent dose coverage to 95% PTV is better with IMRT (93–98%) than with 3DCRT (86–93%).
SU‐FF‐T‐67: Comparison of Linac Based Fractionated Stereotactic Radiotherapy and Tomotherapy for Treatment of Skull‐Base Tumors
Authors: Soisson E , Richards G , Mehta M , Tome W
Published: June 2005

Purpose: To compare and evaluate Tomotherapy and linac based fractionated stereotactic radiotherapy (FSRT) techniques in the treatment of lesions located in the base of skull. Method and Materials: Five patients with skull‐base tumors, originally planned for optical guided FSRT to prescribed doses of 50.4 to 54Gy were replanned using TomoTherapy treatment planning software. All original CT scans, MR‐CT fusion defined contours for target and normal structures, and PTV margins were used for Tomotherapy planning. Linac based plans utilized one of the following FSRT planning techniques: non‐coplanar or coplanar intensity modulated radiation therapy (IMRT), multiple non‐coplanar conformal arcs, and non‐coplanar conformal radiation therapy (CRT). These plans were used as the gold standard to which the Tomotherapy plans were compared. Results: Use of both linac based FSRT and helical tomotherapy generated highly conformal treatment plans. Criteria used for comparison included prescription isodose to target volume (PITV) ratios, inhomogeneity index (II), equivalent uniform dose (EUD) for PTV's, mean normalized total doses (NTDmean) for critical structures, and size of 10, 20, and 30Gy isodose volumes. Non‐coplanar linac based plans exhibited a 23% to 50% decrease in PITV ratios, increased II, similar EUD, and generally comparable to improved NTDmean for critical structures when compared to helical tomotherapy, which are coplanar by nature. Use of non‐coplanar field arrangements also resulted in a 14% to 72% reduction of these low dose isodose volumes when compared Tomotherapy. All criteria except for the II, which was much improved with Tomotherapy, were found to be similar when coplanar linac based plans were compared to helical tomotherapy plans. Conclusion: Results show a distinct advantage in using non‐coplanar beam arrangements for treatment of skull‐base tumors. In the case where disease spreads far inferiorly, limiting the ability to use non‐coplanar arrangements, Tomotherapy can be used to generate a comparable treatment plan.
SU‐FF‐T‐73: Effects of Beam Energies On IMRT Treatments of Large‐Sized Prostate Patients
Authors: Sun M , Ma L
Published: June 2005

Purpose: The energy dependence of intensity modulated beams for prostate cancer treatments has been extensively reported for regular sized patients. In this study, we evaluate whether 6‐MV intensity modulated beams can be used for treating large sized patients (⩾ 25 cm in anterior‐posterior separation and ⩾ 35 cm in lateral separation). Method and Materials: Five prostate patients with AP separations of 25 to 34 cm and lateral separations of 35 to 47 cm were planned for IMRT treatments. Each patient was planned with 6‐MV and 18‐MV beams for comparison. The plans were optimized using identical dose volume constraints on a commercial treatment planning system (Pinnacle, Phillips Medicals). To limit dose streaking effects outside of the PTV, we imposed the optimization constraints to the surrounding normal tissue extending from PTV with ∼1 cm margin to the skin surface. Dose volume histograms (DVH) of 6‐MV and 18‐MV plans were analyzed. Results: The DVH curves for PTV, GTV, rectum and bladder were found to be nearly indistinguishable between 6‐MV and 18‐MV treatment plans. The dose hot spots were marginally lower (0–2%) for the 6‐MV plans. The integral dose to the surrounding normal tissue was slightly (< 1% – 10%) higher for the 6‐MV plans. Considering the large volume of the surrounding normal tissue, such small difference suggested that the low entrance dose from the 18‐MV beam is mostly balanced out by the higher exit dose of the beam. Conclusion: Intensity modulated beams of 6 MV are equivalent to 18 MV for large prostate patient treatments.
SU‐FF‐T‐81: Mixed Beam Energy for IMRT Treatment of Prostate Carcinoma
Authors: Malhotra H , Avadhani J , de Boer S , Podgorsak M
Published: June 2005

Purpose: To investigate the technical and dosimetric properties of IMRT plans for prostate carcinoma using standard beam orientations with mixed beam energies. Method and Materials: A cohort of 10 patients previously treated with IMRT for prostate carcinoma was selected. For each patient, three additional IMRT plans were calculated using a standard coplanar 5‐beam arrangement and compared to the delivered treatment plan. All plans used 6 MV for the anterior oblique fields and the posterior field, while the two posterior oblique fields were either 10, 15, or 18 MV. An identical set of constraints was used for the PTV and organs at risk (rectum and bladder) and all plans were normalized to give 95% PTV coverage at 100% of the prescription dose. Competing plans were analyzed based on DVH, conformity index, total body integral dose (photon and neutron), and the total and compartmentalized number of MU. Results: Equivalent conformity of dose to the PTV was achieved in all plans. The photon integral dose and number of MU, however, were significantly higher for plans with only 6 MV beams, while the 6/18 MV combination resulted in the lowest value for each of these parameters. For the 6/15 and 6/18 MV plans, the number of MU to be delivered with the pair of higher energy beams was found to be comparable to the number of MU delivered in a standard 4‐ or 6‐field 3DCRT beam arrangement. Conclusion: While the neutron integral dose rapidly increases beyond 10 MV, its magnitude in a mixed beam energy plan has been shown to be comparable to the neutron dose encountered in 3DCRT for prostate carcinoma. The resulting decrease in photon integral dose achieved in IMRT plans with mixed beam energies may thus suggest the selection of higher energy for those beams requiring the greatest tissue penetration.
SU‐FF‐T‐93: A Clinical Comparison of Two IMRT Planning Systems for Small Field Conformal Therapy of Intracranial Lesions
Authors: Kmety‐Stevenson C , Brinkmann D , Kisrow K , Herman M , Stafford S , Brown P , McCollough K
Published: June 2005

Purpose: To evaluate BrainLab (BL) IMRT dose distributions for small intracranial lesions by comparing target dose coverage, homogeneity and conformity, and critical structures sparing, as well as agreement with measurements to a clinical Eclipse IMRT system. Method and Materials: Three clinical cases with varying volume lesions enclosing portions of organs at risk (OAR) were planned with BL and Eclipse IMRT modules for dynamic 120‐leaf MLC delivery on a Varian 21EX. Anatomical structures were contoured, and transferred to both systems to ensure a common starting point. Optimization was carried out using identical non‐coplanar beam orientations in combination with similarly specified dose goals and constraints. For two of the cases, highest priority was placed on PTV coverage, while the third required OAR sparing at the expense of PTV coverage. Plans were evaluated by dose‐volume histograms (maximum dose, conformity indices), and isodose lines (hot spots, 50% isodose volume irregularity). BL dose distributions were validated with chamber (absolute dose) and film (fluence) measurements, and Eclipse dose calculations for imported BL dynamic MLC files. Results: Ignoring the superior immobilization of the BL system for patient set‐up, BL and Eclipse IMRT modules provided clinically comparable target coverage and dose homogeneity, with differences in target dose conformity, critical structures sparing, and agreement with measurements. BL plans showed better dose homogeneity up to 5% for the smaller tumors, conformity up to 25% for the larger tumors, and consistently better critical structures sparing up to 11%. Absolute dose measurements were in closer agreement for the BL plans, while selected line profiles through the fluences revealed departures from experiment in the low dose penumbra region for BL plans and high dose/high gradient regions for Eclipse plans. Conclusion: BL and Eclipse IMRT modules generate effective treatment plans with differences requiring further investigation, including determination of their clinical significance.
SU‐FF‐T‐95: Dosimetric Comparison of Helical TomoTherapy Treatment and Step‐And‐Shoot Intensity‐Modulated Radiotherapy Treatment On Stereotactic Radiosurgery
Authors: Han C , Liu A , Schultheiss T , Pezner R , Chen Y , Wong J
Published: June 2005

Purpose: To evaluate the feasibility of Helical TomoTherapy for stereotactic radiosurgery, and to compare the dose conformity, dose uniformity, and dose gradient between plans of Helical TomoTherapy and step‐and‐shoot intensity‐modulated radiotherapy (IMRT) generated by the NOMOS CORVUS system. Method and Materials: Thirteen patients with intracranial tumors treated with stereotactic radiosurgery by step‐and‐shoot IMRT were analyzed. Tumor sizes varied from 1.45 cc to 40.78 cc. Two step‐and‐shoot IMRT treatment plans, one (IMRT I) with gantry angle restriction due to the existence of beam stopper at our institute and the other (IMRT II) with those constraints removed, were generated using the CORVUS system. Helical TomoTherapy treatment plans were generated for each case with identical anatomic contouring and prescription. The three plans were compared using dose conformity index, homogeneity index and dose gradient score index. Results: IMRT II plans without field angle constraints resulted in better dose conformity and steeper dose drop‐off outside the targets compared to IMRT I with beam stopper restriction. Statistical analysis showed that TomoTherapy plans were better compared to the two step‐and‐shoot IMRT plans by dosimetric study. The average dose conformity index for TomoTherapy is 1.33 (range: 1.14 – 1.60). For IMRT II plans, it is 1.39 (range: 1.17 – 1.89). The dose gradient score index, with 100 being optimal, is 37.3 (range: 16.5 – 52.7) for TomoTherapy plans, and 18.9 (range: −31.1 – 36.2) for IMRT II. Dose homogeneity index does not show statistical difference for the three treatment plans. The average treatment time for TomoTherapy plans is 47 minutes. Conclusion: TomoTherapy treatment planning showed significantly better results compared to the step‐and‐shoot IMRT treatment planning in dose conformity and dose gradient for intracranial stereotactic radiosurgery. The treatment time using TomoTherapy was comparable to that using step‐and‐shoot IMRT. Conflict of Interest: Research partially supported by TomoTherapy Incorporated.
SU‐FF‐T‐96: Improvement in IMRT Delivery for Head and Neck Patients Using Simplified IMRT Plans and Enhanced IMRT Delivery System
Authors: Xia P , Ludlum E , Bucci KM , Gliessmann S , Verhey LJ
Published: June 2005

Purpose: To demonstrate the feasibility of simplified IMRT plans and improved delivery times without significantly degraded plan quality. Method and Materials: Five patients with nasopharynx tumors were selected for evaluation. The plan quality was assessed based on tumor coverage, multiple defined endpoints for sensitive structures, plan dose conformality and homogeneity index. The treatment plans were generated using direct machine parameter based optimization in a commercial treatment planning system. The numbers of beam angles varied from 7‐9. For each plan, the average total numbers of segments were gradually reduced from 98, 63, 48, to 24, while maintaining the planning dose constraints and number of beam angles. Treatment times are based on the latest IMRT delivery option (console 9) installed on a Siemens LINAC. Results: Improvements are two‐fold: (1) reduction of segments and (2) technical changes within the delivery system. All plans achieved the same tumor coverage, delivering >95% of tumor volumes to 70Gy (GTV), 59.4Gy (CTV), and 54Gy (elective CTV) simultaneously. As the number of segments decreased from 98 to 24, the average maximum doses to the brainstem changed from 50,8, 50.4, 51.3, to 55.1 Gy and from 41.9, 42.2, 41.5 to 42.3 Gy to the spinal cord while the average mean parotid doses were 27.0, 26.7, 26.7, and 28.5Gy. As the total number of segments decreased, the average plan conformal indices were 0.63, 0.61, 0.65, and 0.46, and the average dose homogeneity indices were 89%, 87%, 88%, and 84%. Optimized communication within the LINAC control system reduced the inter‐segment delay from six to two seconds. Conclusion: For patients with nasopharyngeal tumors treated with IMRT, 50 segments might be sufficient to achieve clinical requirements. With the latest IMRT delivery system, the treatment time excluding patient setup can be reduced to 6‐8 minutes. Conflict of Interest: Research supported by Siemens.
SU‐FF‐T‐103: Implementation of the Tungsten‐Compensator Based Intensity‐Modulated Radiotherapy (IMRT)
Authors: Lian J , Chang S , Cullip T , Deschesne K , Schreiber E , Gardner W , Potter L , Euliss W
Published: June 2005

Purpose: One of the methods to deliver the intensity‐modulated radiotherapy (IMRT) beams is by using physical compensators. The static nature of the compensator intensity modulation shortens the treatment time, simplify the dose optimization and reduces the leakage effect from MLC‐IMRT. The purpose of this project is to study the feasibility of intensity modulation by a high density material, tungsten. The commissioning process, including the packing issue and dose modeling method, are described in details, which will be helpful for other institutions to implement this technique. Method and Materials: The consistency of filling tungsten and durability of the compensator were tested by the repetitive filling/handling. One symmetrical and one asymmetrical step function‐type compensators were manufactured for dose modeling purpose. Mapcheck device and ion chamber were used to measure the dose attenuation at different field size, depth and off‐axis distance. In‐house make treatment planning system (TPS) was modified to incorporate the attenuation, scattering and beam hardening effects from the tungsten material. IMRT plans were made for 15 prostate, H&N and breast cancer patients. Intensity map and dose were acquired by the Mapcheck and compared to the TPS predictions. Results: The filling of the material is consistent with the maximum discrepancy 2.9% and 1.5%, respectively, for the intraoperator and interoperator filling tests. No compensator quality degeneration was found for two compensators after 30 fractions under normal and strenuous handling. Three dose calculation related parameters were fit using the data acquired on symmetrical and asymmetrical compensators. For 15 patients' plans, the measured intensity maps show that 97%±2% of points in the field have dose difference less than 5% from the TPS calculated. Conclusion: The tungsten compensator based IMRT was implemented by our group. The dose distribution discrepancy between the measured data and TPS calculation is small and meets the requirement of clinical needs.
SU‐FF‐T‐118: On the Relationship Between Risk Management and IMRT Treatment Plan Optimization
Authors: Romeijn H , Dempsey J
Published: June 2005

Purpose: We assess the suitability of using biological and voxel‐based penalty criteria vs. different types of dose‐volume histogram (DVH) constraints that have been proposed for fluence map optimization (FMO) in IMRT by developing a rigorous relationship between treatment plan evaluation criteria based on the DVH and voxel‐based penalty criteria. Method and Materials: Viewing the IMRT FMO problem as the problem of shaping the dose distributions in structures, an analogy was established with risk management problems from the area of financial engineering. Results: On the one hand, traditional DVH constraints (bounding the dose received by a pre‐specified proportion of a structure) and CVaR constraints (bounding the tail mean dose received by a pre‐specified proportion of the structure) can be viewed as dominance constraints of the dose distribution in a structure with respect to some reference dose distribution. On the other hand, most commonly used biological criteria (tumor control probability (TCP), generalized equivalent uniform dose (gEUD), normal tissue complication probability (NTCP)) are equivalent to voxel‐based penalty functions, which can be viewed as utility functions that measure the desirability of dose received by voxels. We demonstrated that dominance based on traditional DVH constraints is equivalent to dominance with respect to all non‐decreasing voxel‐based penalty functions, while dominance based on CVaR constraints is equivalent to dominance with respect to all non‐decreasing convex voxel‐based penalty functions. Conclusion: If measures based on and including TCP, NTCP, and gEUD (with a∉(0,1)) are deemed sufficient to describe the effect of a dose distribution on a structure, traditional DVH constraints should not be imposed on these dose distributions. However, if traditional DVH constraints are deemed necessary to describe the effect of a dose distribution on a structure, particularly in the case of parallel structures, e.g., the liver, the abovementioned biological criteria cannot be used as alternatives to DVH constraints.
SU‐FF‐T‐141: Effects of Lung Inhomogeneity for An Intensity Modulated Field
Authors: Watanabe Y , Bull S
Published: June 2005

Purpose: To study the effects of inhomogeneity for intensity modulated fields using slab phantoms. Method and Materials: Tissue equivalent solid slab phantoms (20×20 cm2 and varying thickness) were used to create inhomogeneous medium. A 4‐cm thick lung equivalent material was used to simulate lung inhomogeneity. Radiographic films were placed at 1‐cm upstream and at 2‐cm downstream positions relative to the lung material along the beam axis. Note that the electronic equilibrium in the beam direction was achieved at these locations. Ten 5‐mm wide bar patterns placed at every 1‐cm were generated using the sliding window technique for intensity modulated fields. We used a 6MV photon beam of a Varian 2100CD with 52‐leaf MLC. A concept of modulation transfer function (MTF) was applied for the analyses. Results: The bar pattern of the beam intensity was smoothed at the depth of 5‐cm in the phantom, becoming a dose profile similar to sine waves on the plane transverse to the beam axis. There was a clear difference of dose profiles between the homogeneous case and the 4‐cm lung case. The latter exhibits a smaller attenuation of the amplitude of the sinusoidal waves. MTF measurements showed that there were five peaks between 0 and 0.2 mm−1 for the homogeneous case; but, there were only three for the lung case. The MTF values of the sine waves were 0.783 and 0.914 for the homogeneous and the lung cases, respectively. Conclusion: Using a sinusoidally modulated field, we have found that the effects of 4‐cm thick lung are to increase the amplitude of the sine waves and to smooth the narrow fields. The application of MTF concept helps us with deeper understanding of the heterogeneity effects for intensity modulated fields.
SU‐FF‐T‐142: Error Analysis of An Independent MU Calculation Program for IMRT Fields
Authors: Zhu T , Finlay J , Dimofte A
Published: June 2005

Purpose: To evaluate the accuracy of an independent monitor unit calculation program for dose‐per‐MU verification of IMRT fields. The MU calculation program runs on a PC and is based on a scatter‐factor‐based empirical model to determine D/MU. This algorithm provides a head‐scatter model for IMRT fields. Method and Materials: The D/MU of IMRT fields at the same point (mostly the isocenter) was compared between treatment planning system and the independent MU calculation program. Here MU for an IMRT field refers to the total MU. The fractional MU of each segment of an IMRT field, defined as the MU for the segment per total MU, was assumed to be the same. The commercial treatment planning system is based on a pencil‐beam convolution algorithm with headscatter modeling. D/MU of a subset of IMRT fields, which is delivered to an IMRT phantom, was compared among the treatment planning system calculations, the independent MU calculations, and measurements. Results: Among 24 patients examined, the difference of D/MU for all IMRT fields delivered to a point agreed to within 7% for 91% (22/24) of patients, the same acceptance criteria using measurement, with the maximum error of 8.4%. This error is slightly worse then the measurement, where 100% of patients are within 7% limit. When each individual IMRT field is examined, 21% (33/160) of the fields have a discrepancy larger than 7%. Most of those fields (78.8%) lie in the valley region of an IMRT field. Conclusion: The independent MU calculation program can effectively verify the dose calculation accuracy for most IMRT fields. Only in few instances (9%), which invariably involves the calculation point to be in very low dose region, actual measurements are needed to further verify the accuracy of dose calculation for IMRT field.
SU‐FF‐T‐153: Influence of Ionization Chamber Size for Intensity Modulation Treatment Planning Modeling
Authors: Venencia C , Besa P , Somarriba F
Published: June 2005

Purpose: Intensity modulation treatment planning systems (TPS) modeling requiere beam data collection of depth dose curves and dose profiles for open fields. The internal ionization chamber diameter is related with the width of the penumbra. The purpose of this work is to model a photon beam for Intensity Modulation Radiotherapy (IMRT) using two chambers with different sizes and compare the modeling results with film measurements using standard dynamic IMRT patterns. Method and Materials: The TPS used was CadPlan/Helios. The treatment energy used was 6 MeV generated by a linear accelerator Clinac 21EX equipped with a 120‐leaf multileaf (MLC). The ionization chambers used were Wellhofer IC‐10 (0.14cc) with internal diameter of 6 mm and a PTW Pint Point 31014 (0.015cc) with an internal diameter of 2 mm. Five standards IMRT patterns were used for comparisson. Grid calculation size was 2.5×2.5 mm2 and 1.25×1.25 mm2. To match calculated to film‐measured isodoses, external MLC generated registration points were used. Measured isodoses were done using Kodak EDR2 film. Comparisson between calculated and measured isodoses were done by gamma evaluation (3mm/3% and 2mm/2%) using RIT113 software. Results: Measurements of dose profiles with Pint Point detector showed narrower penumbra (20%–80% penumbra width at 5 cm depth in water were 4.0 mm for the Pint Point chamber and 6.0 mm with the IC‐10). Detector noise and measuring time increased with Pint Point chamber. Single pencil beam kernels generated from profiles measurements at 5 depths were sharper with the Pint Point detector. Agreement between calculated and measured isodoses was better with the smaller detector in all the standard IMRT patterns, especially at the high dose gradient regions. Conclusions: For CadPlan/Helios TPS, beam modeling for IMRT improves using an ionization chamber with smaller internal diameter.
SU‐FF‐T‐165: Replacement of Film and Ion Chamber Measurements by Electronic Portal Dosimetry for IMRT QA
Authors: Beltran C , Herman M
Published: June 2005

Purpose: To evaluate replacing film and ion chamber measurements with EPID portal dosimetry for IMRT QA. Method and Materials: IMRT plans are generated in commercially available planning software and a prediction for each field is generated for a square solid water phantom (with the gantry set to 0 deg), a bullet phantom and an aSi EPID. Each IMRT field is delivered to the solid water phantom exposing individual radiographic films. A high dose region and critical structure region is identified in the bullet phantom predicted dose distribution. The IMRT fields are delivered to the bullet phantom with an ion chamber at the high dose region, and repeated with the ion chamber at the critical structure region. The IMRT fields are then delivered to the EPID and a dosimetric image is obtained using commercially available software. The dose delivered to the film is analyzed and compared with the prediction. The ion chamber measurements are compared to the prediction in the bullet phantom. The EPID prediction vs. acquired portal dose is analyzed. EPID results are compared to film and ion chamber results to determine if the EPID can be used as a replacement for film and/or the ion chamber measurements. Results: Preliminary results indicate that the EPID with commercially available portal dosimetry software has a high dosimetric sensitivity, in the range of 1 to 2 cGy, and sub millimeter special resolution. This is suitable for film replacement. Conclusion: The EPID with commercially available portal dosimetry software can be used as a replacement for film given proper calibration of both the imager and software model. Further research is being done in order to determine if the ion chamber measurement can be similarly replaced. Conflict of Interest: Varian Medical Systems partially funded this research.
SU‐FF‐T‐177: A Study On Output Factors for Gamma Knife Model B2 Unit with Various Dosimeters
Authors: Yeh K , Hsieh H , Chen C , Huang K , Chiou J , Hsu Y , Tu H , Huang C , Su C , Huang Y
Published: June 2005

Purposes: To verify the output factors (OFs) of Gamma Knife Model B2 by various conventional dosimeters and to determine an effective correction factor for compensating the dosimeter sizes. Method and Materials: The TLDs, radiochromic films, PTW 31002 ion chamber and the diamond detector were used to obtain the OFs, normalized to the 18 mm helmet, for four helmets. The factors were measured in the centre of an 80 mm polystyrene spherical phantom that was positioned at the mechanical center of the machine. The dosimeters were placed in the center of the sphere using different cassettes and oriented their effective center in the center of helmet coordinate system. Based on the volumetric averaging theory we used the specificity of dose profile of the 4 mm helmet to correct the measurement by the integrated Gaussian curve method. Results: The relative OFs measured with TLDs/ion chamber, before applying correction factors, were 0.977/0.967, 0.905/0.845 and 0.755/0.313 for the 14, 8 and 4 mm helmets, respectively. After applying correction factors, the results show a reasonable agreement with the data used in the current RTP system for Gamma Knife procedure. The results also showed great spatial accuracy. The symmetry of spatial distribution was 1.84%, 0.59%, 1.25%, and 1.16% for the 4, 8, 14 and 18 mm helmets, respectively. And the distance between mechanical center and dosimetric center was less than 0.25mm for all four helmets. Conclusion: The accuracy of the measurements was affected by a number of factors, especially the dosimeter size. This work provides the potential for using conventional dosimeters, with appropriate correction factor, to determine and to evaluate the clinical dosimetric parameters for Gamma Knife Unit for routine QA procedure. With the verification of spatial accuracy, Gamma Knife unit could be used to treat functional disorder case accurately.
SU‐FF‐T‐178: A Study On the Reproducibility of Tangential Breast Fields Using Online Electronic Portal Images
Authors: Prabhakar R , Ganesh T , Joshi R , Julka P , Rath G , Pant G
Published: June 2005

Purpose: To study the reproducibility of tangential breast treatment technique using online portal imaging system.Introduction: Treatment verification and reproducibility is an important step in radiotherapy to achieve a better tumor control. Care should be taken to ensure the same dose to be delivered in the same volume of irradiation. Electronic portal imaging technique plays a vital role in accomplishing the above task by studying the setup error and correct the same before the treatment delivery. Method and Materials: Twelve patients of carcinoma of breast were selected for this study and CT based planning was performed with simple tangential fields. The patients were then treated on a 6MV linear accelerator equipped with an electronic portal imaging device. Portal images were acquired for both medial and lateral tangential fields for 10 fractions and intra and the inter‐fraction studies were performed for all the patients. The parameters such as central lung distance (CLD), Central beam edge to skin distance, central irradiated width and cranio‐caudal distances were measured on the acquired portal image. In the intra‐fraction study lead markers were placed on the patient skin to study the breast movement during treatment. Results: The maximum variation of the marker during the treatment was 1.8 mm with a standard deviation of 0.575 mm. Similarly the CLD, CBESD, CIW and CCD were analyzed for the intra and inter‐fraction variation. Conclusion: Online portal imaging device is an important tool for ensuring the proper delivery of planned dose. Our result suggests that intra‐fraction motion of the breast has less impact on the treatment volume.
SU‐FF‐T‐183: Application of a Gantry‐Mounted Diode Array System for QA Dosimetry of High‐Energy Photon Beams
Authors: Ahmad M , Chen Z , Song H , Lund M , Deng J , Nath R
Published: June 2005

Purpose: To investigate the utility of a commercial diode‐array system mounted on the gantry of linear accelerators to perform relative QA dosimetry of photon beams at different gantry angles. Method and Materials: The diode‐array Profiler (Sun Nuclear Corp.) was mounted on the head of the linac. Beam profiles were measured at multiple gantry angles for 6 and 10 MV photon beams. Flatness, asymmetry, and central‐axis relative output were determined. Dynamically‐wedged (EDW) profiles were measured at various gantry positions for different wedge angles. For a given EDW field, the speed of the Y‐jaw motion was varied by changing the number of MUs for studying the effect of jaw speed on the EDW profile. The potential effects of gravity and leaf speed on the dynamic delivery of MLC‐based IMRT beams were also investigated. The IMRT fields were designed such that the MLC leaves move against or along gravity when the linac gantry is at horizontal position. The MLC leaf speed was varied by changing the total MU. Results: (1) The gantry angle has no influence on the flatness, asymmetry, and the central‐axis output of the clinical beams. (2) Our data validated the delivery of EDW treatments at any gantry position. (3) For IMRT fields, the beam profiles are accurately reproduced at any gantry angle for all leaf speeds. No gravity effect on dMLC delivery was observed. However, the diode‐array system was able to detect a difference of about 3% in beam profiles produced by leafs traveling in opposite directions at a high leaf speed of 2.5 cm/sec, attributable to the communication time lag between MLC controller and the Linac beam control but not to gravity. Conclusion: The gantry‐mounted linear diode array Profiler is an efficient tool for performing QA of basic beam characteristics, EDWs, and dMLC, especially at different gantry angles.
SU‐FF‐T‐188: Correlation Between in Vivo Electron Diodes Response and Nominal Surface Dose for Broad Electron Beams
Authors: Li T , Tong S , Su M , Grant D , Torres C , Kim T , Chu K
Published: June 2005

Purpose: To establish correlation between in vivo diodes response and nominal surface dose Ds for broad electron beams, thus simplifying the calibration process for electron diodes. Method and Materials: The nominal surface dose Ds defined by TG25 was extracted from electron PDD data that were measured by cylindrical ion chamber (RK chamber, Scanditronix‐Wellhofer) on a Varian 2100C Linac at 100 cm SSD. Cone factors were measured using ion chamber (Capintec PR‐06) at dmax. A QED p‐type electron diode with Model 1131 dosimeter (Sun Nuclear Corp.) was calibrated to the dose at dmax for 9 MeV electron beam at 100 cm SSD using 10×10 cone. Diode readings using this calibration factor were then obtained with 10×10 cone and 15×15 cone for 6, 9, 12, 16 and 20 MeV electron beams delivering 200 MUs. The same diode was then re‐calibrated to the dose at dmax for 12 MeV electron beam. The above measurements were repeated with 10×10 cone and 25×25 cone to reconfirm our hypothesis. Results: The diode readings were first divided by cone factors, and then the corrected readings were plotted against nominal skin dose. For diodes calibrated by 9 MeV electrons, the correlation coefficient R‐squared value were 0.9954 and 0.9796 for 10×10 cone and 15×15 cone respectively. For diodes calibrated by 12 MeV electrons, the R‐squared value were 0.9967 and 0.9980 for 10×10 cone and 25×25 cone respectively. Conclusion: The correlation between in vivo p‐type diode response and nominal surface dose Ds for broad electron beams has been empirically established and confirmed. The diode response corrected by cone factor demonstrated a clear correlation with nominal surface dose Ds. This correlation can significantly simplify the electron diode calibration process. It can also be potentially used to monitor relative skin dose along with dmax dose at the same time.
SU‐FF‐T‐194: Evaluation of a Commercial Diode Array (Tomodose) for Tomotherapy Beam Profile Measurements
Authors: Wagner T , Langen K , Poole D , Meeks S , Willoughby T , Ruchala K , Olivera G
Published: June 2005

Purpose: TomoDose, a commercial diode array (Sun Nuclear Corporation, Melbourne, FL) is used to measure the radiation field in a TomoTherapy Hi* Art linear accelerator. The performance of TomoDose is evaluated by comparing the diode measurements with (i) ion chamber based water tank measurements and (ii) data from an on‐board ion chamber array mounted opposite the linac. Method and Materials: TomoDose has an active area that is rectangular (530 mm by 96 mm) to cover to the maximum field size (50 mm by 400 mm) of the tomotherapy beam. A total of 223 diodes allow a measure of the lateral and longitudinal beam profiles on the central axis and longitudinal profiles 50, 100, and 150 mm off‐axis. Both central axis profiles were compared with ion chamber data obtained in a water tank during an annual quality assurance test. Over a period of about seven weeks, the central axis lateral profile was monitored and compared with profile measurements obtained using the treatment machine's on‐board detector system. Results: TomoDose measurements agreed well with the ion chamber data. A repeated measurement of the lateral profile revealed subtle changes in this profile. Identical trends in profile change were independently measured using an on‐board detector array system. These changes were used for diagnosis of the system's components and can be used to provide early signs of component wear and tear. Conclusion: TomoDose is accurate and can be used for regular, e.g. monthly, monitoring of the beam profiles. It is sensitive to subtle changes in the profile that may be used to provide early warning signs of developing problems. Conflict of Interest: Two of the co‐authors are employees of TomoTherapy, Inc.
SU‐FF‐T‐203: In Vivo Dosimetry Using Disposable MOSFET Dosimeters for Total Body Irradiation
Authors: Briere TM , Tailor RC , Tolani NB , Prado KL , Lane RG , Woo SY , Ha CS , Gillin MT , Beddar AS
Published: June 2005

Purpose: The “OneDose” MOSFET dosimeter, manufactured by Sicel Technologies, is used for individualized patient dosimetry measurements for radiation therapy. These dosimeters, which are pre‐calibrated by the manufacturer, are designed for single use for conventional radiation therapy treatments. We tested the usefulness, reliability and applicability of these dosimeters for use in total body irradiation procedures, where the field sizes, distances, and irradiation conditions differ substantially from the standard conditions used for factory calibration Method and Materials: We have compared the response of OneDose dosimeters with that of Thermoluminescent Dosimeters (TLDs) calibrated “in‐house”. OneDose dosimeters were paired with two TLDs and were placed beneath bolus to provide adequate build‐up. The detectors with build‐up were then taped to the skin of the patient at various sites of interest, including the head, neck, umbilicus and lungs. In most cases, cerrobend lung blocks were used. Readings of the OneDose were taken immediately following irradiation. The TLDs were read 2 – 4 days later. Results: Of the four patients studied thus far, the doses measured at the head, neck, and umbilicus fell between 105 and 210 cGy. For these sites agreement with the TLDs was generally within ±5%. Measured doses for the regions of the lung showed greater variability. This may be due to placement errors or the lower doses (< 20 cGy) and steeper dose gradients that occurred when the lungs were shielded with cerrobend blocks. Conclusion: The dose measured by the OneDose detector shows relatively good agreement with that measured by TLDs in total body irradiation. Our research plan includes study of another six patients, with the intent of being more precise in the placement of the dosimeters in the region of the lung. Conflict of Interest Information: ASB has a sponsored research agreement with Sicel Technologies, Inc. for the study of implantable sensors.
SU‐FF‐T‐391: A New Look at Helmet Output Factor Utility in Gamma Knife Treatments
Authors: Griffin S , DeWerd L , Kunugi K
Published: June 2005

Purpose: To characterize the volume dose distribution of Gamma Knife (GK) stereotactic radiosurgery units to compare point‐measurement based helmet factors and volume‐based measurements of dose. Method and Materials: Helmet factors were determined using radiochromic film and ionization chamber measurements as well as TLD arrays. Novel methods have been used to determine and characterize the volume of dose delivered by the GK unit. These methods include using large volume ionization chambers and deconvolving the measurement to remove volume averaging effects and creating a film phantom that allows us to map the entire dose volume in 3 dimensions by using cubes of radiochromic film. Results: The preliminary work done using traditional methods to determine helmet factors has shown that a single point measurement may be insufficient when delivering doses of the magnitude seen in GK treatments. Analysis using TLDs and radiochromic film indicate that non‐uniform dose distributions exist. It has also been shown that the isocenter of the GK does not always correspond with the point of maximum dose. Additionally, helmet factor determination is dependent on the size of the dosimeter being used, thus larger dosimeters demonstrate volume averaging effects preventing the proper determination of helmet factors. Conclusion: GK treatment is the preferred modality for a number of cranial treatments, and physicians are continually prescribing smaller margins. For this reason, it is vital that the dosimetry of the GK be representative of what the patient receives. While point and plane dosimetry techniques may be adequate when delivering radiation from one direction, 3‐D techniques must be developed for modalities like the GK, in which dose is delivered with multiple sources simultaneously and almost isotropically.
SU‐FF‐T‐397: Characteristics of a Double‐Focused μMLC
Authors: Fischer M , Todorovic M , Cremers F , Schmidt R
Published: June 2005

Purpose: Micro multi‐leaf collimators (μMLC) are widely used as add‐on to linear accelerators for the generation of small irregular shaped beams. The purpose of this paper is to measure the dosimetric characteristics of a double‐focused μMLC. The dose field generated by a double‐focused μMLC has a steep dose gradient at all field edges and is therefore able to spare the healthy tissue better than a single‐focused μMLC Method and Materials: At our department we have mounted a double‐focused μMLC on a Siemens Primus linear accelerator. Base on the separate gantry sensor, this μMLC is independent from the type or manufacturer of the linac. The basic dosimetric properties, such as transmission or leakage, depth‐dose curves and penumbra, have been measured by use of radiographic and radiochromic films, pinpoint ionization chambers and our multi‐purpose QA‐Phantom (Easy Cube). Results: Transmission and leakage between the leaves are due to their special focusing design very low. The depth doses distributions for different field sizes generated by the μMLC are identical to the depth doses for the same field sizes generated by the MLC integrated in the linac. Therefore the μMLC affects only the off‐axis ratio. Due to the double‐focusing characteristics the penumbra is small and identical for the field length and width. The penumbra gradient does not differ significantly with different field sizes. Conclusion: The mechanical investigations show that the μMLC can securely be used with a Siemens Primus linear accelerator. The measured dosimetric properties show a small penumbra that is identical in both directions (inplane and crossplane). This is important if the μMLC is applied for stereotactic and intensity modulated radiotherapy.
SU‐FF‐T‐402: Dosimetric Comparison of Different MLC Systems for IMSRT
Authors: Heydarian M , Fung B , Laperriere N
Published: June 2005

Purpose: To compare different MLC systems for intensity modulated stereotactic radiotherapy (IMSRT) of intracranial tumours with different sizes and complexities. Method and Materials: Radionics treatment planning and delivery systems, including a Mini Multileaf Collimator (MMLC) are routinely used at our institution for stereotactic radiotherapy of intracranial lesions. A Varian Millennium MLC has also been commissioned to eliminate the maximum field size limitation (10×12 cm) of MMLC. The two MLC systems have different dosimetric parameters, mainly due to different leaf thicknesses and isocentric distances. In this work we explore the effects of these differences on IMSRT of intracranial tumours. Radionics treatment planning system (XK‐RT3) is used for planning 3 clinical cases in this study. Identical beam arrangement and optimisation parameters were chosen for the two systems. Comparison parameters include: 2D and 3D dose distributions, dose heterogeneity (DH), maximum, minimum and median doses as well as dose volume histograms (DVH) for the target volume; and maximum dose, median dose, dose of 10%, 20% and 50% volumes (D10, D20 and D50) and DVHs for the OAR. The OAR dose volume data are presented for a normalised dose, when 95% of the tumour received at least 95% of the prescribed dose. Results: DVH data have shown that the two systems are overall comparable in terms of tumour dose coverage. However, Radionics MMLC had the advantage of delivering the prescribed doses using fewer segments and less number of monitor units by up to 35% and 48%, respectively and therefore less dose to the surrounding normal structures and better sparing of OARs by up to 7%. Conclusion: In this work we have shown that the two MLC systems are overall clinically comparable, with Radionics MMLC marginally better sparing normal tissues. The Varian MLC however has the advantage of larger field size and better isocentric clearance.