Calibrating TrueBeam jaws by considering collimator walkout to improve the dose uniformity at abutting field junctions.

Jaw positions on a linear accelerator are calibrated to have accurate field size values over the range of jaw positions and to have excellent junctions when matching fields. It is sufficient to have field size accuracy on the order of a millimeter for most clinical applications but good junctions require submillimeter precision and accuracy in the jaw positioning. Presented is a method to measure collimator walkout with the MV imager and a mathematical model to determine an optimal origin for calibrating jaws on the TrueBeam accelerator. The calibration procedure uses the jaw position encoders which are sufficiently accurate and precise enough to achieve a homogeneous junction dose for abutting fields.

Fixed-jaw technique to improve IMRT plan quality for the treatment of cervical and upper thoracic esophageal cancer.

The purpose of this study was to investigate the potential advantages of the fixed-jaw technique (FJT) over the conventional split-field technique (SFT) for cervical and upper thoracic esophageal cancer (EC) patients treated with intensity-modulated radiotherapy. The SFT and FJT plans were generated for 15 patients with cervical and upper thoracic EC. Dosimetric parameters and delivery efficiency were compared. An area ratio (AR) of the jaw opening to multileaf collimator (MLC) aperture weighted by the number of monitor units (MUs) was defined to evaluate the impact of the transmission through the MLC on the dose gradient outside the PTV50.4, and the correlation between the gradient index (GI) and AR was analyzed. The FJT plans achieved a better GI and AR (P < 0.001). There was a positive correlation between the GI and AR in the FJT (r = 0.883, P < 0.001) and SFT plans (r = 0.836, P < 0.001), respectively. Moreover, the mean dose (Dmean ), V5Gy -V40Gy for the lungs and the Dmean , V5Gy -V50Gy for the body-PTV50.4 in the FJT plans were lower than those in the SFT plans (P < 0.05). The FJT plans demonstrated a reduction trend in the doses to the spinal cord PRV and heart, but only the difference in the heart Dmean reached statistical significance (P < 0.05). The FJT plans reduced the number of MUs and subfields by 5.5% and 17.9% and slightly shortened the delivery time by 0.23 min (P < 0.05). The gamma-index passing rates were above 95% for both plans. The FJT combined with target splitting can provide superior organs at risk sparing and similar target coverage without compromising delivery efficiency and should be a preferred intensity-modulated radiotherapy planning method for cervical and upper thoracic EC patients.

Potential reduction of lung dose via VMAT with jaw tracking in the treatment of single-isocenter/two-lesion lung SBRT.

PURPOSE/OBJECTIVES: Due to higher radiosensitivity, non-target normal tissue dose is a major concern in stereotactic body radiation therapy (SBRT) treatment. The aim of this report was to estimate the dosimetric impact, specifically the reduction of normal lung dose in the treatment of single-isocenter/two-lesion lung SBRT via volumetric modulated arc therapy with jaw tracking (JT-VMAT). MATERIALS/METHODS: Twelve patients with two peripherally located early-stage non-small-cell-lung cancer (NSCLC) lung lesions underwent single-isocenter highly conformal non-coplanar JT-VMAT SBRT treatment in our institution. The mean isocenter to tumors distance was 5.6 ± 1.9 (range 4.3-9.5) cm. The mean combined planning target volume (PTV) was 38.7 ± 22.7 (range 5.0-80.9) cc. A single isocenter was placed between the two lesions. Doses were 54 and 50 Gy in three and five fractions, respectively. Plans were optimized in Eclipse with AcurosXB algorithm utilizing jaw tracking options for the Truebeam with a 6 MV-FFF beam and standard 120 leaf millennium multi-leaf collimators. For comparison, the JT-VMAT plans were retrospectively re-computed utilizing identical beam geometry, objectives, and planning parameters, but without jaw tracking (no JT-VMAT). Both plans were normalized to receive the same target coverage. The conformity and heterogeneity indices, intermediate-dose spillage [D2cm , R50, Gradient Index (GI), Gradient Distance (GD)], organs at risks (OAR) doses including normal lung as well as modulation factor (MF) were compared for both plans. RESULTS: For similar target coverage, GI, R50, GD, as well as the normal lung V5, V10, V20, mean lung dose (MLD), and maximum dose received by 1000 cc of lungs were statistically significant. Normal lung doses were reduced by 8%-11% with JT-VMAT. Normal lung dose increased as a function of tumor distance from isocenter. For the other OAR, up to 1%-16% reduction of non-target doses were observed with JT-VMAT. The MF and beam-on time were similar for both plans, however, MF increased as a function of tumors distance, consequently, delivering higher dose to normal lungs. CONCLUSION: Utilizing jaw tracking options during optimization for single-isocenter/two-lesion lung SBRT VMAT plans reduced doses to the normal lung and other OAR, reduced intermediate-dose spillage and provided superior/similar target coverage. Application of jaw tracking did not affect delivery efficiency and provided excellent plan quality with similar MF and beam-on time. Jaw tracking is recommended for future clinical SBRT plan optimization.

Fully automated searching for the optimal VMAT jaw settings based on Eclipse Scripting Application Programming Interface (ESAPI) and RapidPlan knowledge-based planning.

PURPOSE: Eclipse treatment planning system has not been able to optimize the jaw positions for Volumetric Modulated Arc Therapy (VMAT). The arbitrary and planner-dependent jaw placements define the maximum field size within which multi-leaf-collimator (MLC) sequences can be optimized to modulate the beam. Considering the mechanical constraints of MLC transitional speed and range, suboptimal X jaw settings may impede the optimization or undermine the deliverability. This work searches optimal VMAT jaw settings automatically based on Eclipse Scripting Application Programming Interface (ESAPI) and RapidPlan knowledge-based planning. METHODS AND MATERIALS: Using an ESAPI script, the X jaws of rectal VMAT plans were initially set to conform the planning-target-volume (PTV), and were gradually extended toward the isocenter (PTV center) in 5-7 mm increments. Using these jaw pairs, 592 plans were automatically created for 10 patients and quantitatively evaluated using a comprehensive scoring function. A published RapidPlan model was evoked by ESAPI to generate patient-specific optimization objectives without manual intervention. All candidate plans were first stored as text files to save storage space, and only the best, worst, and conformal plans were consequently recreated for comparison. RESULTS: Although RapidPlan estimates dose-volume histogram (DVH) based on individual anatomy, the geometry-based expected dose (GED) algorithm does not recognize different jaw settings but uses PTV-conformal jaws as default; hence, identical DVHs were observed regardless of planner-defined jaws. Therefore, ESAPI finalized dose-volume calculation and eliminated the plans with unacceptable hotspots before comparison. The plan quality varied dramatically with different jaw settings. Trade-offs among different organs-at-risk (OARs) were collectively considered by the proposed scoring method, which identified the best and worst plans correctly. The plans using conformal jaws were neither the best nor the worst of all candidates. CONCLUSIONS: VMAT plans using optimal jaw locations can be created automatically using ESAPI and RapidPlan. Conformal jaws are not the optimal choice.

The Use of Hyperbaric Oxygen for the Prevention and Management of Osteoradionecrosis of the Jaw: A Dana-Farber/Brigham and Women's Cancer Center Multidisciplinary Guideline.

BACKGROUND: Osteoradionecrosis of the jaw (ORN) is an infrequent yet potentially devastating complication of radiation therapy to the head and neck region. Treatment options include antimicrobial therapy, local sequestrectomy, resection, and the use of hyperbaric oxygen (HBO). Published data on ORN are difficult to compare because of the lack of a universally accepted classification and staging system, and the literature on the use of HBO to either prevent or successfully manage ORN is controversial and inconclusive. Therefore, we aimed to establish a standard approach for using HBO at our institution. MATERIALS AND METHODS: A literature search was conducted of articles published in the English language between January 1980 and January 2016. Retrieved articles were evaluated by two independent reviewers. Isolated case reports, abstracts, case series, review articles, and cohort studies without a control group were excluded; summary data were extracted from the remaining studies. A panel of experts from Head and Neck Oncology and Oral Medicine from the Dana-Farber Cancer Institute and Brigham and Women's Hospital reviewed the summary data and established multidisciplinary guidelines on the use of HBO for the prevention and management of ORN. RESULTS: Seven studies were evaluated and reviewed by the multidisciplinary panel. There was no consistent evidence in support of HBO for either the prevention or management of ORN. CONCLUSION: Based on the available evidence and expert opinion, routine use of HBO for the prevention or management of ORN is not recommended and is rarely used at our institution. The Oncologist 2017;22:343-350 IMPLICATIONS FOR PRACTICE: The Division of Head and Neck Oncology of Dana-Farber/Brigham and Women's Cancer Center does not recommend the routine use of HBO for the prevention or management of ORN. Adjunctive HBO may be considered for use on a case-by-case basis in patients considered to be at exceptionally high risk who have failed conservative therapy and subsequent surgical resection.

Two-stage implant placement technique for the management of irradiated jaws: An animal study.

STATEMENT OF PROBLEM: Radiotherapy results in diminished bone remodeling capacity and an elevated risk of osteoradionecrosis, which can negatively influence the survival rate of dental implants. Patients receiving radiotherapy are advised not to receive dental implants during or soon after completing their radiotherapy. PURPOSE: The purpose of this animal study was to investigate a 2-stage implant placement technique designed to diminish applied trauma on irradiated bone. MATERIAL AND METHODS: Two groups of white New Zealand rabbits received radiotherapy in ascending doses (2, 4, 8 Gy), while a nonirradiated group served as control. Three weeks after completion of the last radiotherapy session, one of the irradiated groups and the control group received titanium dental implants bilaterally in the femur head. For the second irradiated group, an osteotomy was performed, and the surgical wound was left to heal for 2 weeks before implant placement. All animals were sacrificed 4 weeks after implant placement, and histomorphometric analysis was used to study bone-implant contact (n=14, α=.05). RESULTS: Statistical analysis revealed significantly higher (F=159, P<.001) bone-implant contact in the 2-stage (40.2 ±1.9) implant placement technique than in the immediately placed implants (21.2 ±2.3) in irradiated bone. Both of the groups had a significantly lower bone-to-implant contact ratio than the non-irradiated control (64.2 ±3.8). CONCLUSIONS: Within the limitations of this animal study, the 2-stage implant placement technique could be used to reduce trauma in irradiated bone and to improve wound healing around dental implants.

A comparative study of identical VMAT plans with and without jaw tracking technique.

The unwanted radiation transmission through the multileaf collimators could be reduced by the jaw tracking technique which is commercially available on Varian TrueBeam accelerators. On the basis of identical plans, this study aims to investigate the dosimetric impact of jaw tracking on the volumetric-modulated arc therapy (VMAT) plans. Using Eclipse treatment planning system (TPS), 40 jaw-tracking VMAT plans with various tumor volumes and shapes were optimized. Fixed jaw plans were created by editing the jaw coordinates of the jaw-tracking plans while other parameters were identical. The deliverability of this artificial modification was verified using COMPASS system via three-dimentional gamma analysis between the measurement-based reconstruction and the TPS-calculated dose distribution. Dosimetric parameters of dose-volume histogram (DVH) were compared to assess the improvement of dose sparing for organs at risk (OARs) in jaw-tracking plans. COMPASS measurements demonstrated that over 96.9% of structure volumes achieved gamma values less than 1.00 at criteria of 3 mm/3%. The reduction magnitudes of maximum and mean dose to various OARs ranged between 0.06% ~ 6.76% (0.04 ~ 7.29 Gy) and 0.09% ~ 7.81% (0.02 ~ 2.78 Gy), respectively, using jaw tracking, agreeing with the disparities of radiological characteristics between MLC and jaws. Jaw tracking does not change the delivery efficiency and total monitor units. The dosimetric comparison of VMAT plans with and without jaw tracking confirms the physics hypotheses that reduced transmission through tracking jaws will reduce doses to OARs without sacrificing the target dose coverage because it is meant to be covered by radiation beams going through the opening.

The Comparison of the Efficacy of Blue Light-Emitting Diode Light and 980-nm Low-Level Laser Light on Bone Regeneration.

The aim of this study is to histologically compare effects of blue light-emitting diode (LED) light (400-490 nm) and Ga-Al-As low-level diode laser light (980 nm) on bone regeneration of calvarial critical-sized defects in rats. Thirty Wistar Albino rats were included in the study. The experimental groups were as follows: blue LED light (400-490 nm) group (LED); 980-nm low-level laser light group (LL); and no-treatment, control group (CL). A critical-sized defect of 8 mm was formed on calvaria of rats. Each animal was sacrificed 21 days after defect formation. Calvarias of all rats were dissected and fixated for histological examination. Histomorphometric measurements of total horizontal length of the newly produced bone tissue, total vertical length of the newly produced bone tissue, and diameter of the newly produced longest bone trabecula were performed with a computer program in micrometers. There was a statistically significant increase in the total horizontal length and total vertical length in LL and LED groups compared to that in the CL group (P < 0.05), while there was no statistical difference between LED and LL groups (P > 0.05). A statistically significant difference was observed in the longest bone trabecula and LL groups compared to that in CL (P < 0.05), but not between LED-CL and LED-LL groups (P > 0.05). In conclusion, blue LED light significantly enhances bone regeneration in critical-sized defects when compared with CL group, but does not have a statistically significant effect on bone regeneration when compared with 980-nm low-level laser light.

Irradiated patients and survival rate of dental implants: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Radiotherapy has been considered a contraindication for rehabilitation with dental implants because it can change the survival rate of implants. Nevertheless, the installation of implants in irradiated patients has been used with varying success. PURPOSE: The purpose of this systematic review was to compare the success rate of implants placed in irradiated human bone tissue with that of implants placed in nonirradiated areas. MATERIAL AND METHODS: Searches were performed in the EMBASE, Cochrane, and PubMed/Medline databases up to December 2013 to identify clinical trials addressing the subject. This systematic review was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The relative risks of implant failure and survival curves were calculated considering a confidence interval of 95%. Heterogeneity was analyzed by using a funnel chart. RESULTS: A total of 40 studies involving 2220 participants and 9231 dental implants were selected. The survival curve of the studies indicated a survival rate of 84.3% for implants installed in irradiated bone tissue. The meta-analysis indicated statistically significant differences (P<.001) between item success rates of implants placed in irradiated areas and those of implants placed in nonirradiated areas. CONCLUSIONS: Dental implants installed in the irradiated area of an oral cavity have a high survival rate, but strict monitoring is needed to prevent complications, thereby reducing possible failures.

Radiotherapy associated with higher rates of dental implant loss.

DATA SOURCES: Cochrane Oral Health Group's Trials Register, CENTRAL, Medline via PubMed and EMBASE; no restrictions on language, published before February 1st 2013. STUDY SELECTION: Observational studies reporting outcomes from irradiated and non-irradiated patients were eligible for inclusion as were randomised controlled trials (RCTs) and controlled clinical trials (CCTs) assessing irradiated patients submitted to different implant-based treatment protocols. DATA EXTRACTION AND SYNTHESIS: Screening of titles, abstracts and full texts was by two reviewers, with disagreements resolved through discussion, consensus, or failing this by consultation with a third reviewer. Data extraction was in duplicate and attempts were made to contact authors for missing data. Risk of bias was assessed using adapted versions of the Cochrane Collaboration's tool (for RCTs and CCTs) and the Newcastle-Ottawa scale for observational studies. RESULTS: Fifteen trials with 10,150 implants were included with 1,689 (14.3%) placed in irradiated mouths. There were 13 case series and two RCTs. three of the studies were on hyperbaric oxygen (HBO) therapy. Neither of the RCTs was rated as low risk of bias. Mean survival rates ranged from 46.3% to 98% with pooled estimates showing that implant failure was statistically significantly higher in irradiated patients compared to patients who had not undergone radiotherapy (an increase of 174%) with a risk ratio of 2.74 (95% confidence interval {CI}: 1.86, 4.05; p<0.00001). In maxillary sites, the risk ratio was 5.96 (95% CI:2.71, 13.12;p<0.00001) with the risk of loss increasing to 496%. Hyperbaric oxygen therapy did not reduce the risk of implant failure showing a risk ratio of 1.28 (95% CI:0.19, 8.82). CONCLUSIONS: Irradiation of the head was linked to increased failure rate of implants compared to failure rates in patients who had not undergone radiotherapy. The failure rate was higher in the maxilla and HBO therapy did not improve implant survival.

No trials on extraction/ non-extraction of teeth prior to radiotherapy.

DATA SOURCES: The Cochrane Oral Health Group's Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Medline, Embase, Cancerlit and CINAHL databases were searched. STUDY SELECTION: Randomised controlled trials comparing extraction of teeth prior to radiotherapy with leaving teeth in situ during radiotherapy to the jaws were to be selected. DATA EXTRACTION AND SYNTHESIS: Three review authors independently assessed the results of the searches for inclusion in the review. RESULTS: No randomised controlled trials were found. CONCLUSIONS: There are no randomised controlled trials to assess the effect of extracting teeth prior to radiotherapy compared to leaving teeth in the mouth during radiotherapy to the jaws.

Dental extractions prior to radiotherapy to the jaws for reducing post-radiotherapy dental complications.

BACKGROUND: Radiotherapy as part of head and neck cancer treatment leaves patients requiring much dental rehabilitation in a compromised environment that is difficult for the patient and the dental team to manage. OBJECTIVES: To assess the effects of maintaining the patient's natural dentition during radiotherapy in comparison to extracting teeth before radiotherapy in areas that are difficult to access by the patient and the dentist, should reduction in mouth opening occur after radiotherapy to the jaws. SEARCH METHODS: We searched the Cochrane Oral Health Group's Trials Register (to 22 November 2012), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2012, Issue 11), MEDLINE via OVID (1946 to 22 November 2012), EMBASE via OVID (1980 to 22 November 2012), CANCERLIT via PubMed (1950 to 22 November 2012), CINAHL via EBSCO (1980 to 22 November 2012) and reference lists of articles. We advertised for currently ongoing studies via the Cochrane Oral Health Group website and the Cochrane Oral Health Group Twitter feed.  SELECTION CRITERIA: Randomised controlled trials comparing extraction of teeth prior to radiotherapy with leaving teeth in situ during radiotherapy to the jaws. DATA COLLECTION AND ANALYSIS: Three review authors independently assessed the results of the searches for inclusion in the review.  MAIN RESULTS: No randomised controlled trials were found. AUTHORS' CONCLUSIONS: There are no randomised controlled trials to assess the effect of extracting teeth prior to radiotherapy compared to leaving teeth in the mouth during radiotherapy to the jaws.

Histological findings on jaw osteonecrosis associated with bisphosphonates (BONJ) or with radiotherapy (ORN) in humans.

OBJECTIVE: To describe the histological features of bone tissue harvested from patients affected by jaw osteonecrosis associated with bisphoshponates (BONJ) or with radiotherapy (ORN), in undecalcified ground sections. MATERIALS AND METHODS: Sixteen bone tissue samples from 14 patients with BONJ and two patients with ORN were processed in order to obtain both ground, undecalcified sections and decalcified sections. The sections underwent histometric and morphometric analysis. RESULTS: Bone tissue samples obtained from patients with BONJ or ORN of the jaws shared some histological characteristics. Common histological features included the loss of bone architecture, the absence of a proper Haversian system and proper marrow spaces, the presence of necrotic spots of non-mineralized tissue, areas of empty osteocytic lacunae next to areas of hypercellularity, the presence of resorption pits with rare osteoclast-like cells and the presence of bacteria and of an inflammatory infiltrate. A violet rib of tissue characterized by large resorption pits facing was frequently observed between the mineralized bone and the inflammatory infiltrate. CONCLUSIONS: The histological features of BONJ and ORN are similar and resemble those of osteomyelitis. Even though it is not clear whether infection is the cause or consequence of bone exposure, inflammatory cells, bacteria or their products may have a massive, direct lytic effect on bone tissue challenged by bisphosphonates.

Osteoradionecrosis of the jaws: a review of conservative and surgical treatment options.

Although surgery still is the most important treatment modality in the management of head and neck cancer, radiotherapy is increasingly being used. Consequently, the majority of head and neck cancer patients are at risk of developing osteoradionecrosis of the jaws, which is the most serious and important complication of radiotherapy. This review presents the etiology, pathophysiology, diagnosis, classification, and prevention of osteoradionecrosis. In addition, the body of evidence regarding conservative as well as surgical treatment of osteoradionecrosis is reviewed, and studies on complications, tumor recurrence and patient survival, dental rehabilitation, and functional and aesthetic outcome after surgical treatment for osteoradionecrosis are discussed.

Radiotherapy and the oral environment the effects of radiotherapy on the hard and soft tissues of the mouth and its management.

Radiation therapy plays an important role in the care of patients with head and neck cancer. When the oral cavity and the salivary glands are exposed to high doses of radiation, there can be dramatic effects on the patient's oral health. The clinical consequences of radiation can include mucositis, hyposalivation, taste loss, osteoradionecrosis, radiation caries and trismus. This paper looks at the available literature regarding the effects of radiotherapy on the oral environment and outlines practical clinical approaches to prevent or reduce the adverse side effects of treatment.

Effects of radiotherapy to the jaws. I: The scale of the problem.

Cancer care has become one of the main targets of the National Health Service in England and with cancer patients surviving longer, it is likely that head and neck cancer patients will make up a large proportion of patients seen within secondary care settings in the future. The management of these patients can be very difficult for a number of reasons. Part one of this paper attempts to highlight the major oral health problems encountered by these patients during and after their cancer treatment and supported by the current literature. Part two of this series will address the dental management of head and neck oncology patients undergoing radiotherapy with particular attention of possible improvement to current management strategies for these patients.

Computerized tomography, stereolithography and dental implants in the rehabilitation of oral cancer patients.

UNLABELLED: As survival rates improve it is important to consider the quality of life for oral cancer patients post-treatment. The primary goal is removal of the tumour, however, with a gradual increase in survival rates, post-operative rehabilitation is now becoming increasingly important. Specialists in restorative dentistry, along with oral and maxillofacial surgeons, general dental practitioners and other members of the multidisciplinary team play a vital role in planning treatment for, and rehabilitating, these patients. This paper presents a case series to show how recent advances in computerized tomography (CT) and the use of stereolithographic models can help in the rehabilitation of oral cancer patients. CLINICAL RELEVANCE: The principles discussed can also be applied to other patients undergoing dental implant treatment to help plan and carry out treatment and improve the quality of peri-implant tissues.

Effect of jaw size in megavoltage CT on image quality and dose.

PURPOSE: Recently, the jaw size for the TomoTherapy Hi-Art II(®) (TomoTherapy Inc., Madison, WI) was reduced from 4 mm (J4) to 1 mm (J1) to improve the longitudinal (IEC-Y) resolution in megavoltage computed tomography (MVCT) images. This study evaluated the effect of jaw size on the image quality and dose, as well as the dose delivered to the lens of the eye, which is a highly radiosensitive tissue. METHODS: MVCT image quality (image noise, uniformity, contrast linearity, high-contrast resolution, and full width at half-maximum) and multiple scan average dose (MSAD) were measured at different jaw sizes. A head phantom and photoluminescence glass dosimeters (PLDs) were used to measure the exposed lens dose (cGy). Different MVCT scan modes (pitch = 1, 2, and 3) and scan lengths (108 mm, 156 mm, and 204 mm) were applied in the MSAD and PLDs measurements. RESULTS: The change in jaw size from J4 to J1 produced no change or only a slight improvement in image noise, uniformity, contrast linearity, and high-contrast resolution. However, the full-width at half-maximum reduced from approximately 7.2 at J4 to 4.5 mm at J1, which represents an enhancement in the longitudinal resolution. The MSAD at the center point changed from approximately 0.69-2.32 cGy (peripheral: 0.83-2.49 cGy) at J4 to 0.85-2.81 cGy (peripheral: 1.05-2.86 cGy) at J1. The measured lens dose increased from 0.92-3.36 cGy at J4 to 1.06-3.91 cGy at J1. CONCLUSIONS: The change in jaw size improved longitudinal resolution. The MVCT imaging dose of approximately 3.86 cGy, 1.92 cGy, and 1.22 cGy was delivered at a pitch of 1, 2, and 3, respectively, per fraction in the head and neck treatment plans. Therefore, allowance for an approximately 15% increase in lens dose over that with J4 should be provided with J1.

Dosimetric effects of jaw tracking in step-and-shoot intensity-modulated radiation therapy.

The purpose of this work was to determine the dosimetric benefit to normal tissues by tracking the multi-leaf collimator (MLC) apertures with the photon jaws in step-and-shoot intensity-modulated radiation therapy (IMRT) on the Varian 2100 platform. Radiation treatment plans for ten thoracic, three pediatric, and three head and neck cancer patients were converted to plans with the jaws tracking each segment's MLC apertures, and compared to the original plans in a commercial radiation treatment planning system (TPS). The change in normal tissue dose was evaluated in the new plan by using the parameters V5, V10, and V20 (volumes receiving 5, 10 and 20 Gy, respectively) in the cumulative dose-volume histogram for the following structures: total lung minus gross target volume, heart, esophagus, spinal cord, liver, parotids, and brainstem. To validate the accuracy of our beam model, MLC transmission was measured and compared to that predicted by the TPS. The greatest changes between the original and new plans occurred at lower dose levels. In all patients, the reduction in V20 was never more than 6.3% and was typically less than 1%; the maximum reduction in V5 was 16.7% and was typically less than 3%. The variation in normal tissue dose reduction was not predictable, and we found no clear parameters that indicated which patients would benefit most from jaw tracking. Our TPS model of MLC transmission agreed with measurements with absolute transmission differences of less than 0.1% and, thus, uncertainties in the model did not contribute significantly to the uncertainty in the dose determination. We conclude that the amount of dose reduction achieved by collimating the jaws around each MLC aperture in step-and-shoot IMRT is probably not clinically significant.

Thermal increase in the oral mucosa and in the jawbone during Nd:YAG laser applications. Ex vivo study.

OBJECTIVE: Literature reports bactericidal and biostimulant effects for Nd:YAG laser procedures on bone and oral mucosa but the possible overheating can cause damage to anatomical structures. The aim of the study was to evaluate the is the evaluation of thermal increase in different levels of oral tissues: mucosa, periosteum and bone during defocused application of Nd:YAG laser at different parameters. STUDY DESIGN: Superficial thermal evaluation was performed in pig jaws with a thermal camera device; deep thermal evaluation was realized by 4 thermocouples placed at a subperiosteal level and at 1,2 and 4 mm depth in the jaw bone. Laser applications of 1 minute were performed 5 times (with a pause of 1 minute) on a surface of 4 cm² with a Nd:YAG laser (MSP mode, 320 micrometer fiber, defocused mode) with different parameters. Temperatures were recorded before and after laser applications and after each pause in order to evaluate also the thermal relaxation of tissues. RESULTS: At submucosal level, mean thermal increase was between 1.1°C and 13.2°C, at 1 mm depth between 1.1°C and 8.5°C, at 2 mm depth between 1.1°C and 6.8°C, at 4 mm depth between 1.0°C and 5.3°C. Temperature decrease during the rest time period was variable between 0°C and 2.5°C. CONCLUSIONS: Temperatures reached during clinical procedures with parameters reported in the literature in biostimulation protocols (1.25-2 Watts) for the five minutes of application are not dangerous for biological structures. The decrease in temperature during the rest time period is less considerable in the bone in comparison to oral mucosa.