Independent Jaws Research Articles

Should dentists perform independent jaw wiring for weight loss? A principlist analysis

This article presents an ethical analysis for the practice of jaw wiring as an independent weight loss intervention by dentists. The four foundational principles of autonomy, nonmaleficence, beneficence and justice serve as a framework for evaluating the ethical dimensions of the practice, and whether it can be justified. The ethical analysis of this weight loss procedure requires dentists to debate the potential benefits with possible harms, while respecting the autonomy and desires of the patient. While patients possess a fundamental right to autonomous decision-making, conceding to their autonomy is not absolute and dentists need to balance their decisions with considerations of beneficence and nonmaleficence. The ethical analysis concludes that dentists who refuse requests to independently perform jaw wiring for purely weight loss purposes are ethically justified within the principlist framework when the principles of nonmaleficence and beneficence are at stake. The wellbeing and health of the patient, as well as professional obligations, justify their refusal.

Awareness on resonance frequency analysis in dental implantology among dental practitioners and dental students.

In a partial or entirely independent jaw, oral implantology is a technique in dentistry used to enhance the function of mastication, esthetics, and phonation. An important diagnostic aspect for the effectiveness of implant therapy is the stability of the implants. This study aims to measure dental professionals' and dental students' knowledge of resonance frequency analysis (RFA) in dental implantology. This study aims to measure dental professionals' and dental students' knowledge of RFA in dental implantology. One hundred ninety-nine dentists and dental students participated in an online survey study that was delivered through Google Forms. For statistical analysis, tabulated data from the Excel sheets were transferred into the SPSS program. The Chi-square test is also used to examine clinical relevance. According to the study's findings, 60% of the respondents were male and 46% of those who responded were dental professionals. The respondents were primarily between the ages of 18 and 22 (36%). The majority of dental undergraduates and graduates were found to be knowledgeable about the various techniques used to gauge implant stability (P = 0.04 < 0.05). Within the limitations of this study, it was found that most of the dental students and dental practitioners participating in this study were aware of implant stability. The majority of the respondents were aware that RFA was used to measure primary and secondary stability and osseointegration.

Implementation and commissioning of an integrated micro-CT/RT system with computerized independent jaw collimation

To design, construct, and commission a set of computer-controlled motorized jaws for a micro-CT∕RT system to perform conformal image-guided small animal radiotherapy. The authors designed and evaluated a system of custom-built motorized orthogonal jaws, which allows the delivery of off-axis rectangular fields on a GE eXplore CT 120 preclinical imaging system. The jaws in the x direction are independently driven, while the y-direction jaws are symmetric. All motors have backup encoders, verifying jaw positions. Mechanical performance of the jaws was characterized. Square beam profiles ranging from 2×2 to 60×60 mm2 were measured using EBT2 film in the center of a 70×70×22 mm3 solid water block. Similarly, absolute depth dose was measured in a solid water and EBT2 film stack 50×50×50 mm3. A calibrated Farmer ion chamber in a 70×70×20 mm3 solid water block was used to measure the output of three field sizes: 50×50, 40×40, and 30×30 mm2. Elliptical target plans were delivered to films to assess overall system performance. Respiratory-gated treatment was implemented on the system and initially proved using a simple sinusoidal motion phantom. All films were scanned on a flatbed scanner (Epson 1000XL) and converted to dose using a fitted calibration curve. A Monte Carlo beam model of the micro-CT with the jaws has been created using BEAMnrc for comparison with the measurements. An example image-guided partial lung irradiation in a rat is demonstrated. The averaged random error of positioning each jaw is less than 0.1 mm. Relative output factors measured with the ion chamber agree with Monte Carlo simulations within 2%. Beam profiles and absolute depth dose curves measured from the films agree with simulations within measurement uncertainty. Respiratory-gated treatments applied to a phantom moving with a peak-to-peak amplitude of 5 mm showed improved beam penumbra (80%-20%) from 3.9 to 0.8 mm. A set of computer-controlled motorized jaws for a micro-CT∕RT system were constructed with position reliably better than a tenth of a millimeter. The hardware system is ready for image-guided conformal radiotherapy for small animals with capability of respiratory-gated delivery.

Dose distribution analysis of physical and dynamic wedges by using an intensity-modulated radiotherapy MatriXX

This study investigated differences between the physical wedge and the dynamic wedge distributions of radiation by using an intensity-modulated radiotherapy (ImRT) MatriXX. The linear accelerator used X-rays with energy levels of 6 MV and 10 MV to adjust the collimator by motoring the independent jaws (X1, X2, Y1, Y2) for setting wedge angles of 15, 30, 45, and 60 degrees. The collimator field size was set as 10 × 10 cm2 or 20 × 20 cm2 at the maximum dose point. The dose distribution for each wedge had ±5% and ±11% errors for field sizes of 10 × 10 cm2 and 20 × 20 cm2, respectively. The error was greatest at a wedge angle of 45 degrees and was pronounced at the end of the dynamic wedge where Y1 and Y2 met. Consequently, concluded that the dose distributions were similar for both wedges for the field size of a small beam profile. The beam dose was greatly increased at the end of the dynamic wedge. A more precise estimate of the therapeutic dose of radiation for a dynamic wedge that nearly matches that of the physical wedge can be achieved by correcting of the increasing part of the beam dose. The findings imply that a heavy wedge filter should not be used when calculating the isodose distribution and the therapeutic dose.

A new isocentric technique for exact geometric matching in the radiotherapy of the breast and ipsilateral supraclavicular fossa using dual asymmetric jaws

BackgroundIn some clinical situations breast or chest wall radiotherapy for cancer is given in association with supraclavicular fossa irradiation. Often the treatment is delivered by two tangential fields to the breast or chest wall and an anterior field that irradiates the supraclavicular region. The tissue between the breast or chest wall and the supraclavicular region may be under or overdosed, because of the junction between the two tangential fields and the anterior field. PurposeTo present a new isocentric technique for exact geometric matching between the two tangential fields and the anterior field. MethodsPatients are positioned with both arms raised. Using three-dimensional trigonometry, two half-fields, with isocenter between the breast and the supraclavicular region, are easily matched. The tangential fields have a collimator rotation to protect the lung without additional shielding. The correct gantry, collimator and couch positions are defined for the anterior field to match the tangential fields. ConclusionsA general formula for exact geometric matching in radiotherapy of the breast and supraclavicular fossa is presented. The method does not require additional shielding to eliminate divergence other than the four independent jaws. The result is simple to implement in modern delivery facilities.

A jaw calibration method to provide a homogeneous dose distribution in the matching region when using a monoisocentric beam split technique

Asymmetric collimators are currently available in most of linear accelerators. They involve a lot of clinical improvements, such as the monoisocentric beam split technique that is more and more used in many external radiotherapy treatments. The tolerance established for each independent jaw positioning is 1 mm. Within this tolerance, a gap or overlap of the collimators up to 2 mm can occur in the half beams matching region, causing dose heterogeneities up to 40%. In order to solve this dosimetric problem, we propose an accurate jaw calibration method based on the Monte Carlo modeling of linac photon beams. Simulating different jaw misalignments, the dose distribution occurring in the matching region for each particular configuration is precisely known, so we can relate the misalignment of the jaws with the maximum heterogeneity produced. From experimental measurements using film dosimetry, and taking into account Monte Carlo results, we obtain the actual misalignment of each jaw. By direct inspection of the readings of the potentiometers that control the position of the jaws, high precision correction can be performed, adjusting the obtained misalignments. In the linac studied, the dose heterogeneity in the junction performed with X jaws (those farther from the source), and 6 MV photon beam was initially over 12%, although each jaw was within the tolerance in position. After jaw calibration, the heterogeneity was reduced to below 3%. With this method, we are able to reduce the positioning accuracy to 0.2 mm. Consequently, the dose distribution in the junction of abutted fields is highly smoothed, achieving the maximum dose heterogeneity to be less than 3%.

SU‐GG‐T‐293: The Use of Field Centre Profiles in the Matching of Linear Accelerator Photon Beams

Purpose: As part of commissioning, parameters such as PDD, output and boundary profiles were used to match four Siemens accelerators, two Primus and two Oncor units. The respective parameters agreed generally to within 1%. However, subsequent dose measurements in dual asymmetric fields on the four units showed a maximum difference of 3–4% between a Primus and an Oncor unit. Further measurements were performed to investigate the potential use of “Field Centre Profiles” (FCPs) in “matching” linear accelerator photon beams. Method and Materials: The Field Centre Profile (FCP) is the ratio of the dose at an off axis point for a given field size to the dose at the axis of collimator rotation for the same field size and depth. FCPs were generated by measuring dose at the geometric centre of a symmetric 10×10 cm field on the central axis in a solid water phantom and on a number of off axis points along a diagonal axis — whilst maintaining the same field size using independent jaws. In addition, the off axis dose measurements were normalised to the central axis dose. FCPs were measured for a range of depths from dmax to 20 cm and to a maximum diagonal distance of 21.2 cm (X, Y=15cm) on all machines. Results: (a) FCP values were higher in magnitude (1–2%) compared to the corresponding points on the 40×40 cm diagonal boundary profiles. (b) FCPs from a Primus and an Oncor unit were significantly different, 3–4% maximum, compared to a maximum difference of 2% from a comparison of boundary profiles. Conclusion: It is postulated that Field Centre Profiles are more sensitive to flattening filter shape than 40×40 cm boundary profiles. Field Centre Profiles are a potentially useful parameter in matching linear accelerators.

SU-GG-T-99: Dynamic Delivery of IMRT Using Independent Jaws

Purpose: This study aims to evaluate a jaw-trajectory algorithm for delivering intensity-modulated beams using independent jaws in dynamic mode. Method and Materials: The algorithm builds up an optimization model for the problem of generating jaw trajectories for a desired beam intensity map and solves the problem with adaptive simulated annealing technique. Like leaf trajectory for MLC, a jaw trajectory is composed of a series of control points. When delivering a beam in dynamic mode, all four conventional jaws move continuously and independently. The performance of the proposed algorithm was evaluated through comparing the delivery time of dynamic jaws (DJaw) with that of dynamic MLC (DMLC) for 74 intensity maps of prostate cases and 45 maps of nasopharynx cases. The preconditions for the comparison were that MLC leaves had a width of 1 cm; MLC Leaf trajectories were generated with the algorithm proposed by Spirou et al (Med. Phys, 1994); DJaw delivered desired intensity maps as accurately as or even more accurately than DMLC. Results: DJaw delivery time was 1.8±0.76 and 2.6±1.6 times of DMLC's for 74 intensity maps of prostate cases and 45 large-size intensity maps of nasopharynx cases respectively. For 8 prostate maps, DJaw delivery time actually was shorter than DMLC's, because those maps were small and had minor intensity modulations. Conclusion: Although the delivery time of DJaw usually is longer than that of DMLC, and the difference increases with the size and the complexity of intensity map, the absolute delivery time of DJaw is expected to be 20mins or less. Plus its advantages (i.e., continuous spatial resolution, sharper penumbra, no interleaf leakage or tongue and groove effect, low cost and easy maintenance) over DMLC, DJaw has the potential to become the choice of some (small) institutes for their IMRT practice.

SU-GG-T-77: Application and Dosimetric Analysis of Multiple Static Tangential Intensity-Modulated Radiotherapy Beams in An Elliptic Paraboloid-Shaped Superficial Tumor

Purpose is to evaluate dosimetric efficacy for LINAC‐based IMRT for an elliptic paraboloid‐shaped shallow target. Method and Materials: This study includes a case with advanced facial multi‐focal basal cell carcinoma. The lesion variably extended entire face, up to 3.5 cm deep. A simulation target was created in a cylindrical water phantom for evaluating different plans. All IMRT plans comprised of eleven coplanar 6‐MV photon beams with 5mm sMLC. Only outer portion of each beam opens to the PTV. Identical beam constraints with 4mm MLC stepping were used. In group A, the MLC travels along the shorter dimension of PTV cross section, while in group B, MLC moves alone the longer dimension. 50.0 Gy is normalized to 95% of PTV in all plans. Results:Dose for the organ at risk (OAR) was shown reduction in both groups, when the independent jaw blocks more open field. The mean dose reduction was 15.9% and 18.9% respectively when the jaw moved from +2 cm to 0 cm (half beam blocked. More significant improvement (> 27%) in dose sparing was indicated with the jaw set further into the field. No consistent trend of changes in dose homogeneities was found, except when the jaw partially blocked the PTV. In the final clinic case, more than 90% of PTV received the prescribed 45Gy dose with about 19% meaningful dose heterogeneity (effective 50Gy for majority of treated areas), and satisfactory dose conformity. Treatments were comfortably fitted in 15‐minute daily schedule. The treatment resulted in an excellent clinical outcome without cosmetic complications seen during the first 12 month follow‐ups. Conclusion: This study demonstrates the feasibility of the application of LINAC based individualized IMRT for an elliptic paraboloid‐shaped superficial target. Further clinical trials will be designed for the treatment of chest malignancy.

SU‐GG‐T‐494: Dosimetric Uncertainties in Matched IMRT and Conventional Fields for Head and Neck Cancer Radiotherapy

Purpose: Two techniques using IMRT for treatment of head and neck tumors are commonly employed: (A) extended‐field IMRT (EF‐IMRT) with a single isocenter; (B) Beam‐split method with an AP field for the low neck/supraclavicular fossa. Beam‐split technique used in the latter approach introduced dosimetric uncertainties at the matchline due to imprecise calibration of the independent jaw or MLC positions. The objective of this study is to evaluate the potential matchline dose variation if such a systematic error occurs. Method and Materials: Five patients with nasopharyngeal cancer treated with EF‐IMRT technique were replanned with the beam‐split approach. A midline cord block was used in the AP fields. To simulate the effect of a systematic error in jaw/MLC positions, analyses were performed with the conventional field(s) matched exactly and shifted ± 1,2,&amp;3mm (superior‐inferior) relative to the IMRT fields. Dose covering 95% of the tumor volume (D95) was measured for a 1.2 cm thick volume of the CTV centered at the matchline (mCTV) to assess tumor volume dose coverage. Dose encompassing 1 cc (D1cc) of the spinal cord volume within the IMRT fields were analyzed. Results: For the beam‐pslit technique, overlap of the AP beam with the IMRT fields led to dose increases in D1cc of the spinal cord by 3.14Gy ±0.57Gy, 5.45Gy ± 1.97Gy, and 9.9Gy ± 5.33Gy for 1, 2, and 3 mm overlaps, respectively. A gap between the AP field and the IMRT fields led to dose reductions in D95 of the mCTV by 4.55 ±1.86Gy, 8.38 ± 2.52 Gy, 13.92 ± 0.36Gy for 1, 2 and 3 mm gaps, respectively. Conclusion: Systematic errors due to independent jaw/MLC imprecision can potentially lead to concerning dosimetric variations when matching conventional and IMRT fields in head and neck radiotherapy. Stringent quality assurance on MLC/jaw positions is required when the beam‐split method is applied.

Head and neck field matching verification using three dimensional PAGAT polymer gel dosimetry

Independent jaw collimation on modern linear accelerators allows matching of non-diverging field edges (laterals and anterior) when using head and neck treatment techniques. It is a common practice to split a head and neck cancer radiotherapy treatment volume into two separate abutting mono-isocenter fields because the treatment volume lies above and below the line of the shoulders. In a standard three field technique parallel-opposed lateral fields are used to treat the primary tumour site, upper and mid-cervical nodes and a single anterior field is used to treat the lower neck and superior mediastinal lymph nodes. If these fields are non-diverging fields, there is a possibility of creating an under dose or over dose region at the junction of the abutting fields. The purpose of this study was to evaluate the suitability of the PAGAT polymer gel dosimeter as a tool for verification of the dosimetric match of non-diverging field junctions of a mono-isocenter setup.

New anthropomorphic talking robot—investigation of the three-dimensional articulation mechanism and improvement of the pitch range

We developed a new three-dimensional talking robot WT-6 (Waseda Talker-No. 6), which generates speech sounds by mechanically simulating articulatory motions as well as aeroacoustic phenomenon in the vocal tract. WT-6 consists of a 17-DOF mechanism (1-DOF lungs, 5-DOF vocal cords, 1-DOF jaws, 5-DOF tongue, and 4-DOF lips). It has 3-D lips, tongue, jaw, and velum, which form the 3-D vocal tract structure. It also has an independent jaw opening/closing mechanism, which controls the relative tongue position in the vocal tract as well as the oral opening. The previous robot, which had a 2-D tongue [J. Acoust. Soc. Am. 117, 2541 (2005)], was not enough to realize precise closure to produce humanlike consonants such as /s/ or /r/. The new tongue, which could be controlled to form the 3-D shape, makes it possible to produce more realistic vocal tract shape. The vocal cord model was also improved by adding a new pitch control mechanism pushing from the side of the vocal cords. The pitch range becomes broader than the previous robot, which is enough to reproduce normal human speech. Preliminary experimental results showed that synthesized speech quality improves for vowels /a/, /u/ and /o/. Some experimental results and video demonstration of the talking robot will be presented.

IMRT dose escalation for positive para-aortic lymph nodes in patients with locally advanced cervical cancer while reducing dose to bone marrow and other organs at risk

Purpose To evaluate the feasibility of dose-escalated para-aortic lymph node (PALN) intensity modulated radiation therapy (IMRT) in reducing the dose to bone marrow, bowel, spinal cord, and kidneys, compared with conventional radiation techniques of PALNs in patients with locally advanced cervical cancer and PALN metastases. Methods and materials Computed tomography scans and MRI studies of 5 cervical cancer patients with PALN involvement were transferred to an IMRT treatment planning workstation (Eclipse/Helios) for image fusion and definition of target volumes and critical structures. The positive PALNs identified on fused computed tomography–magnetic resonance images were defined as the gross target volume (GTV), and the PALN region was defined as the planning target volume. There were 2 distinct treatment regions: the PALN region superior to the isocenter and the whole-pelvis region inferior to the isocenter. Three treatment planning techniques were compared: AP/PA (both regions), 4-field box (both regions), and PALN-IMRT with 4-field box to the whole-pelvis field. With IMRT, the radiation dose to the GTV was escalated from the conventional 45 Gy to 60 Gy (2.4 Gy/fraction), whereas the planning target volume and whole-pelvis region received 45 Gy. The treatment planning isocenter was placed at the L4–L5 vertebral body interspace, and this allowed the two treatment regions to be abutted using independent jaws. Results This study has demonstrated the feasibility of escalating the dose delivered to grossly positive PALNs to 60 Gy (2.4 Gy/fraction) with a 95.6% median GTV coverage, concomitantly with conventional treatment of the whole-pelvis region. PALN-IMRT significantly reduced V 40 bone marrow compared to the AP/PA and 4-field box techniques with a median of 21.3%, 98%, and 49.7%, respectively. The PALN-IMRT and 4-field box techniques showed a reduction in V 45 bowel over the AP/PA technique, but a level of statistical significance was not reached. The spinal cord received a significantly higher maximum dose when PALNs were treated with AP/PA fields. Alternatively, the use of the 4-field box technique yielded a significant increase in V 22 kidney on both sides. The placement of the treatment planning isocenter at the L4–L5 interspace allowed the PALN-IMRT and whole-pelvis regions to be treated with a relatively uniform dose at the abutment region. Conclusion In this dosimetric analysis, we demonstrated that dose-escalated PALN-IMRT with conventional whole-pelvis radiotherapy is feasible with significant sparing of critical normal structures compared to PALN conventional radiation techniques.

Suitability of using multileaf collimator (MLC) for photon field matching

This study evaluated and presented the results on the suitability of using a Siemens double-focused multileaf collimator (MLC) for photon field matching. The study was conducted using film-based dosimetry for measurements and a Theraplan Plus (version 3.8) treatment planning system (TPS) for planning comparisons and additional field matching investigations. In this study, it was found that the double-focused MLC field matching closely resembled that of the independent jaws, with the exception that the MLC had a nonuniform match line—a-match line formed by a different size leaf pair gap—overlap at a different join-up position. In addition, it was found that the dose change varied linearly with the MLC leaf pair gap-overlap (from 3-mm gap to 3-mm overlap) by 11 ± 1%/mm. Using intrafraction “feathering” of the junction, a reduction of the dose change from 11 ± 1%/mm to 6.5 ± 1%/mm occurred when the junction was moved once and from 11 ± 1%/mm to 4 ± 1%/mm when moved twice. Based on the results, the study suggested that MLC positioning error tolerances of ±2 mm might be too large for photon field matching. On the other hand, a combination of reducing the tolerance to ±1 mm and intrafraction junction moves (twice by ±1 cm off matching axis) could reduce the maximum peak height—trough low at the junction to within a required range of −5 to +7% in planning target volume (PTV) dose heterogeneity.

A three-field breast treatment technique with precise geometric matching using multileaf collimator–equipped linear accelerators

Purpose Many authors have studied the problems associated with the three-field breast treatment, yet the proposed solutions present their own difficulties. This study presents a technique that overcomes these difficulties, reduces scatter to the contralateral breast, and improves setup reproducibility. Methods and materials Patients are set up with both arms raised superiorly on a breast board. A precise field-match is achieved by rotating the couch and collimator of the tangents, while the supraclavicular field is half-beam blocked using an independent jaw. The posterior borders of the tangents are conformally defined by multileaf collimation. Measurements were performed to verify the field matching and evaluate scatter doses. Results A smooth dose transition was found at the match line at all depths. Corner blocks and lower wedges were not used, which reduced the scatter to the contralateral breast compared with our prior technique. Conclusion The technique achieves a precise match while removing constraints on the tangents’ length and decreasing scatter dose. Procedures for simulation, planning, and treatment have been devised, along with a new patient setup routine incorporating orthogonal setup films and tattoos. This technique has been successfully implemented in routine treatment since September 2001. A program calculating the setup parameters is available at our website.

PET-guided IMRT for cervical carcinoma with positive para-aortic lymph nodes—a dose-escalation treatment planning study

Purpose : To evaluate a treatment planning method for dose escalation to the para-aortic lymph nodes (PALNs) based on positron emission tomography (PET) with intensity-modulated radiotherapy (IMRT) for cervical cancer patients with PALN involvement. One goal of this process was not to modify the traditional treatment of the pelvic region. Methods and Materials : PET images for 4 cervical cancer patents with PALN involvement were registered with their corresponding CT scans. Positive PALNs were identified on PET images, and the surrounding critical structures were delineated on CT images. The treatment machine central axis (CAX) was placed at the level of the L4-L5 vertebral body interspace. There were two distinct treatment regions: the para-aortic bed superior to the CAX and the whole pelvis region inferior to the CAX. IMRT was used for treatment planning of PALN bed irradiation. The positive PALNs identified on PET images were defined as the gross target volume, and the para-aortic bed was defined as the clinical target volume. The radiation doses were escalated from the conventional 45 Gy to 59.4 Gy for the gross target volume and 50.4 Gy for the clinical target volume in 33 fractions. The pelvis area was treated with conventional treatment methods, AP-PA beams to 50.4 Gy in 28 fractions with a brachytherapy implant boost. The placement of the CAX allowed the two treatment regions to be abutted using the treatment machine’s independent jaws. Results : Dose escalation to positive PALNs, as identified on PET images, and the PALN bed is feasible with IMRT. Treatment plans for 4 patients revealed that escalated prescription doses could be delivered to target volumes while maintaining acceptable doses to the surrounding critical structures. Strategic placement of the treatment isocenter allows the IMRT region (PALN bed) and whole pelvis fields to be treated with a relatively uniform dose distribution in the abutment region. Conclusion : This study indicates that PET-guided IMRT could be used in a clinical trial in an attempt to escalate doses delivered to patients with cervical cancer who have positive PALNs.

63 The influence of join up change on dose uniformity across photon field junctions bymeans of matching half block fields using independent jaws

63 The influence of join up change on dose uniformity across photon field junctions bymeans of matching half block fields using independent jaws

822 Poster Radiotherapeutic management of patients with head and neck cancer, the influence of join up change on dose uniformity across photon field junctions by means of matching half block fields using independent jaws

822 Poster Radiotherapeutic management of patients with head and neck cancer, the influence of join up change on dose uniformity across photon field junctions by means of matching half block fields using independent jaws

Implementing multiple static field delivery for intensity modulated beams.

A clinically oriented two-dimensional intensity-modulated beam delivery method is implemented using multiple static segmented fields, i.e., the "step-and-shoot" approach. Starting with a desired al" intensity distribution, it creates a multiple-level intensity approximation, and then constructs a sequence of segmented fields to deliver the multiple-level intensities using multileaf collimator (MLC) and independent backup jaws. The approach starts with a simple grouping of all the nonzero intensity values into a minimum number of clusters for a user specified deviation tolerance for the ideal plan. The k-means clustering algorithm is then employed to find the optimal levels of intensity that minimize the discrepancies between the ideal and the approximated intensities, without violating the user specified deviation tolerance. The multiple-level intensities are then decomposed into a sequence of machine deliverable segments. Apart from the first segment for each gantry angle, all the other segments are arranged to minimize the total travel distance of the leaves. The first segment covers the entire irradiated area and is used for treatment verification by electronic portal imaging. The implementation issues due to the physical constraints of the MLCs are also addressed.

Use of segmental boost fields in the irradiation of inguinal lymphatic nodes

En face electron fields to boost inguinal lymphatics have been used by oncologists for many years. With the introduction of multileaf collimators (MLC) and independent jaws, the practice of creating segmental fields to boost areas of interest has expanded. Typical anterior-posterior opposing field treatment of the pelvis may now be enhanced to include additional anterior segments to boost lymphatic tissue at a predetermined depth. This report illustrates the clinical implementation of one such segmental boost technique. Computer generated isodose plans utilize manual contour and CT-generated data for analysis of inguinal lymphatic depths. Potential areas of field overlap are discussed as well as the use of combined 6 and 15 MV photon energies to reduce areas of inhomogeneous dose. Technical details associated with MLC field size limits and other clinical factors are also discussed in relationship to smooth treatment delivery.