Comparison of dosimetric impact of intra-fractional setup discrepancy between multiple- and single-isocenter approaches in linac-based stereotactic radiotherapy of multiple brain metastases.

INTRODUCTION: Treatment of multiple brain metastases by linac-based stereotactic radiotherapy (SRT) can employ either a multiple-isocenter (MI) or single-isocenter (SI) approach. The purposes of this study were to evaluate the dosimetric results of MI and SI approaches and compare the impacts of intra-fractional setup discrepancies on the robustness of respective approaches using isocenter shifts, whether the same magnitude of translational and rotational effects could lead to a significant difference between the two approaches. METHODS: Twenty-two patients with multiple brain metastases treated by linac-based SRT were recruited. Treatment plans were computed with both the MI and SI approaches. For the MI approach, the isocenter was located at the geometric center of each planning target volumes (PTVs), whereas the isocenter of the SI approach was located midway between the PTV centroids. To simulate the intra-fractional errors, isocenter displacements including translational and rotational shifts were hypothetically applied. Apart from the dosimetric outcomes of the two approaches, the impact of the isocenter shifts on PTVs and organs at risk (OARs) were recorded in terms of the differences (δ) in dose parameters relative to the reference plan and was then compared between the MI and SI approaches. RESULTS: Both MI and SI plans met the plan acceptance criteria. The mean Paddick conformity index (Paddick CI) and Dmax of most OARs between MI and SI plans did not show a significant difference, except that higher doses to the left optic nerve and optic chiasm were found in SI plans (p = 0.03). After the application of the isocenter shifts, δCI increased with an increase in the magnitude of the isocenter shift. When comparing between MI and SI plans, the δCIs were similar (p > 0.05) for all extents of translational shifts, but δCIs were significantly higher in SI plans after application of all rotations particularly ±1.5° and ±2.0° shifts. Despite the result that the majority of δDMax of OARs were higher in the SI plans, only the differences in the left optic nerve and chiasm showed generally consistent significance after both translational ≥±1 mm and rotational shifts of ≥±1 ∘ $^\circ $ . CONCLUSION: Both MI and SI approaches could produce clinically acceptable plans. However, isocenter shifts brought dosimetric impacts to both MI and SI approaches and the effects increased with the increase of the shift magnitude. Although similar impacts were shown in plans of both approaches after translational isocenter shift, SI plans were relatively more vulnerable than MI plans to rotational shifts.

Dynamics of oxygen level-driven regulators in modulating autophagy in colorectal cancer cells.

Colorectal cancer is a common cancer with metachronous distant metastases still threatening overall survival. Tumor oxygen level influences tumor radiosensitivity in relation to autophagy and apoptosis. The objective of this study is to evaluate the expression and interaction between multiple key regulators in different oxygen levels. Human colorectal adenocarcinoma HT-29 cells were cultured in 1% or 10% oxygen level and irradiated by 2 Gy with different incubation time. Autophagy key regulators, AMPK, HIFs and JNK were evaluated by Western blot. Sequential autophagy key regulator activation was observed in the order of AMPK, HIF-1α, HIF-2α and JNK. 10% oxygen level could promote autophagy with similar degree of autophagy activation as 1% oxygen level in 48-h while irradiation could slightly inhibit autophagy. The results of this study supported prior evaluation of oxygen level and autophagy regulators for improving treatment efficacy and indicated the possible directions in developing individualized radiotherapy by selective targeting of hypoxic regions.

A dosimetric comparison of the use of equally spaced beam (ESB), beam angle optimization (BAO), and volumetric modulated arc therapy (VMAT) in head and neck cancers treated by intensity modulated radiotherapy.

INTRODUCTION: Previous studies have shown that the beam arrangement had significant influence on plan quality in intensity modulated radiotherapy (IMRT). This study aimed to evaluate the dosimetric performance of beam arrangement methods by employing equally spaced beams (ESB), beam angle optimization (BAO), and volumetric modulated arc therapy (VMAT) in the planning of five types of head and neck (H&N) cancers treated by IMRT. METHODS: Five plans of different beam arrangement methods were optimized for 119 H&N cancer patients with the prescription of 66-70 Gy for high-risk planning target volume (PTV), 60 Gy for intermediate risk PTV, 54 Gy for low-risk PTV using a simultaneously integrated boost method. The five-beam arrangement methods were: ESB, coplanar BAO (BAOc), noncoplanar BAO (BAOnc), two-arc VMAT (VMAT2), and three-arc VMAT (VMAT3). The H&N cancers included cancers of nasopharynx, oral cavity, larynx, maxillary sinus, and parotid. Although the partial arc VMAT could be used in cases where the PTVs were situated at one side of the head such as the parotid, this arrangement was not included because it was intended to include only the beam arrangements that were applicable to all the types of head and neck cancers in the study. The plans were evaluated using a "figure-of-merit" known as uncomplicated target conformity index (UTCI). In addition, PTV conformation number and homogeneity index, normal tissue integral dose, and organ at risk (OAR) doses were also used. The mean values of these parameters were compared among the five plans. RESULTS: All treatment plans met the preset dose requirements for the target volumes and OARs. For nasopharyngeal cancer, VMAT3 and BAOnc demonstrated significantly higher UTCI. For cancer of oral cavity, most beam arrangement showed similar UTCI except ESB, which was relatively lower. For cancer of larynx, there was no significant difference in UTCI among the five-beam arrangement methods. For cancers of maxillary sinus and parotid gland, the two BAO methods showed marginally higher UTCI among all the five methods. CONCLUSION: Individual methods showed dosimetric advantages on certain aspects, and the UTCI of the BAO treatment plans are marginally greater in the case of maxillary sinus and parotid gland. However, if treatment time was included into consideration, VMAT plans would be recommended for cancers of the nasopharynx, oral cavity, and larynx.

Intrafractional motion management in external beam radiotherapy.

The recent advancements in radiotherapy technologies have made delivery of the highly conformal dose to the target volume possible. With the increasing popularity of delivering high dose per fraction in modern radiotherapy schemes such as in stereotactic body radiotherapy and stereotactic body ablative therapy, high degree of treatment precision is essential. In order to achieve this, we have to overcome the potential difficulties caused by patient instability due to immobilization problems; patient anxiety and random motion due to prolonged treatment time; tumor deformation and baseline shift during a treatment course. This is even challenging for patients receiving radiotherapy in the chest and abdominal regions because it is affected by the patient's respiration which inevitably leads to tumor motion. Therefore, monitoring of intrafractional motion has become increasingly important in modern radiotherapy. Major intrafractional motion management strategies including integration of respiratory motion in treatment planning; breath-hold technique; forced shallow breathing with abdominal compression; respiratory gating and dynamic real-time tumor tracking have been developed. Successful intrafractional motion management is able to reduce the planning target margin and ensures planned dose delivery to the target and organs at risk. Meanwhile, the emergency of MRI-linear accelerator has facilitated radiation-free real-time monitoring of soft tissue during treatment and could be the future modality in motion management. This review article summarizes the various approaches that deal with intrafractional target, organs or patient motion with discussion of their advantages and limitations. In addition, the potential future advancements including MRI-based tumor tracking are also discussed.

Development of a normal tissue complication probability (NTCP) model for radiation-induced hypothyroidism in nasopharyngeal carcinoma patients.

BACKGROUND: The objectives of this study were to build a normal tissue complication probability (NTCP) model of radiation-induced hypothyroidism (RHT) for nasopharyngeal carcinoma (NPC) patients and to compare it with other four published NTCP models to evaluate its efficacy. METHODS: Medical notes of 174 NPC patients after radiotherapy were reviewed. Biochemical hypothyroidism was defined as an elevated level of serum thyroid-stimulating hormone (TSH) value with a normal or decreased level of serum free thyroxine (fT4) after radiotherapy. Logistic regression with leave-one-out cross-validation was performed to establish the NTCP model. Model performance was evaluated and compared by the area under the receiver operating characteristic curve (AUC) in our NPC cohort. RESULTS: With a median follow-up of 24 months, 39 (22.4%) patients developed biochemical hypothyroidism. Gender, chemotherapy, the percentage thyroid volume receiving more than 50 Gy (V50), and the maximum dose of the pituitary (Pmax) were identified as the most predictive factors for RHT. A NTCP model based on these four parameters were developed. The model comparison was made in our NPC cohort and our NTCP model performed better in RHT prediction than the other four models. CONCLUSIONS: This study developed a four-variable NTCP model for biochemical hypothyroidism in NPC patients post-radiotherapy. Our NTCP model for RHT presents a high prediction capability. TRIAL REGISTRATION: This is a retrospective study without registration.

Sonographic appearance of thyroid glands in patients treated with intensity-modulated radiotherapy or conventional radiotherapy for nasopharyngeal carcinoma.

BACKGROUND: This study aimed to investigate the sonographic appearances of the thyroid glands in nasopharyngeal carcinoma (NPC) patients whose cervical lymph nodes were treated with conventional radiotherapy (RT) or intensity-modulated radiotherapy (IMRT). The post-RT sonographic appearances of the thyroid glands in NPC patients were also correlated with the thyroid function. METHODS: One hundred and three NPC patients who had completed RT of cervical lymph nodes using the anterior cervical field, 30 NPC patients who had completed RT of cervical lymph nodes using IMRT, and 61 healthy subjects were included in the study. Thyroid glands were sonographically assessed for their size, echogenicity, vascularity, and internal architecture. Thyroid function tests were also performed on each subject. RESULTS: In comparison with the patients with abnormal thyroid function, the thyroid glands of the patients with normal thyroid function tended to be homogeneous and to have greater volume and echogenicity index (p < 0.05). Compared with those of the healthy subjects, the thyroid glands of patients previously treated with IMRT and those treated with the anterior cervical field showed significantly lower thyroid volume, lower incidence and number of nodules, and higher vascularity index (p < 0.05). CONCLUSIONS: The patient's history of previous RT should be taken into consideration in the sonographic examination of the thyroid gland post-RT. © 2014 Wiley Periodicals, Inc. J Clin Ultrasound 43:210-223, 2015.

Evaluation of the influence of tumor location and size on the difference of dose calculation between Ray Tracing algorithm and Fast Monte Carlo algorithm in stereotactic body radiotherapy of non-small cell lung cancer using CyberKnife.

This study evaluated the extent of improvement in dose predication accuracy achieved by the Fast Monte Carlo algorithm (MC) compared to the Ray Tracing algorithm (RAT) in stereotactic body radiotherapy (SBRT) of non-small cell lung cancer (NSCLC), and how their differences were influenced by the tumor site and size. Thirty-three NSCLC patients treated with SBRT by CyberKnife in 2011 were recruited. They were divided into the central target group (n = 17) and peripheral target group (n = 16) according to the RTOG 0236 guidelines. Each group was further divided into the large and small target subgroups. After the computation of treatment plans using RAT, a MC plan was generated using the same patient data and treatment parameters. Apart from the target reference point dose measurements, various dose parameters for the planning target volume (PTV) and organs at risk (OARs) were assessed. In addition, the "Fractional Deviation" (FDev) was also calculated for comparison, which was defined as the ratio of the RAT and MC values. For peripheral lung cases, RAT produced significantly higher dose values in all the reference points than MC. The FDev of all reference point doses and dose parameters was greater in the small target than the large target subgroup. For central lung cases, there was no significant reference point and OAR dose differences between RAT and MC. When comparing between the small target and large target subgroups, the FDev values of all the dose parameters and reference point doses did not show significant difference. Despite the shorter computation time, RAT was inferior to MC, in which the target dose was usually overestimated. RAT would not be recommended for SBRT of peripheral lung tumors regardless of the target size. However, it could be considered for large central lung tumors because its performance was comparable to MC.

Sonographic appearance of submandibular glands in patients treated with external beam radiotherapy for nasopharyngeal carcinoma.

PURPOSE: The purpose of this study was to investigate the sonographic (US) appearances of submandibular glands in patients with nasopharyngeal carcinoma after external beam radiotherapy (RT) and compare them with those of healthy subjects. METHODS: A total of 81 nasopharyngeal carcinoma patients treated with RT and 66 healthy subjects were recruited and underwent submandibular gland US. Bilateral submandibular glands were assessed for their size, echogenicity, echogenicity margin sharpness, and echotexture. RESULTS: The mean ± SD transverse dimension of submandibular glands in patients treated with RT (2.5 ± 0.4 cm) was significantly smaller than that of healthy subjects (3.3 ± 0.4 cm) (p < 0.05). Submandibular glands in patients treated with RT tended to be heterogeneous (72%) with hypoechoic areas (46%) and ill-defined margins (89%). However, there were no statistically significant differences in echogenicity and conspicuity of intraglandular ducts of submandibular glands between patients and healthy subjects. CONCLUSIONS: RT-induced changes of the submandibular glands were demonstrated on US.

Respiratory 4D-Gating F-18 FDG PET/CT Scan for Liver Malignancies: Feasibility in Liver Cancer Patient and Tumor Quantitative Analysis.

PURPOSE: To evaluate the potential clinical role and effectiveness of respiratory 4D-gating F-18 FDG PET/CT scan for liver malignancies, relative to routine (3D) F-18 FDG PET/CT scan. MATERIALS AND METHODS: This study presented a prospective clinical study of 16 patients who received F-18 FDG PET/CT scan for known or suspected malignant liver lesions. Ethics approvals were obtained from the ethics committees of the Hong Kong Baptist Hospital and The Hong Kong Polytechnic University. Liver lesions were compared between the gated and ungated image sets, in terms of 1) volume measurement of PET image, 2) accuracy of maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), and 3) accuracy of total lesion glycoses (TLG). Statistical analysis was performed by using a two-tailed paired Student t-test and Pearson correlation test. RESULTS: The study population consisted of 16 patients (9 males and 7 females; mean age of 65) with a total number of 89 lesions. The SUVmax and SUVmean measurement of the gated PET images was more accurate than that of the ungated PET images, compared to the static reference images. An average of 21.48% (p < 0.001) reduction of the tumor volume was also observed. The SUVmax and SUVmean of the gated PET images were improved by 19.81% (p < 0.001) and 25.53% (p < 0.001), compared to the ungated PET images. CONCLUSIONS: We have demonstrated the feasibility of implementing 4D PET/CT scan for liver malignancies in a prospective clinical study. The 4D PET/CT scan for liver malignancies could improve the quality of PET image by improving the SUV accuracy of the lesions and reducing image blurring. The improved accuracy in the classification and identification of liver tumors with 4D PET image would potentially lead to its increased utilization in target delineation of GTV, ITV, and PTV for liver radiotherapy treatment planning in the future.

Clinical Evaluation of Fiducial Marker Pre-Planning for Virtual Bronchoscopic Navigation Implantation in Lung Tumour Patients Treated With CyberKnife.

Purpose: For the treatment of invisible lung tumours with CyberKnife (CK), fiducial markers (FMs) were implanted as an internal surrogate under virtual bronchoscopic navigation (VBN). This research aims to study the benefits of introducing an additional procedure in assigning the optimal FM positions using a pre-procedure planning system and performing virtual simulation before implantation. The objectives were 1) to reduce the duration of the FM implantation procedure, 2) to reduce the radiation exposure in dose area product (DAP) (dGy*cm2) to patients, and 3) to increase the number of FMs implanted around the tumour. Methods and Materials: This study is retrospective, single-centre, and observational in nature. A total of 32 patients were divided into two groups. In Group 1, 18 patients underwent conventional VBN FM implantation. In Group 2, 14 patients underwent additional pre-procedure planning and simulation. The steps of pre-procedure planning include 1) importing CT images into the treatment planning system (Eclipse, Varian Medical Systems, Inc.) and delineating five to six FMs in their ideal virtual positions and 2) copying the FM configuration into VBN planning software (LungPoint Bronchus Medical, Inc.) for verification and simulation. Finally, the verified FMs were deployed through VBN with the guidance of the LungPoint planning software. Results: A total of 162 FMs were implanted among 35 lesions in 32 patients aged from 37 to 92 (median = 66; 16 men and 16 women). Results showed that 1) the average FM insertion time was shortened from 41 min (SD = 2.05) to 23 min (SD = 1.25), p = 0.00; 2) the average absorbed dose of patients in DAP was decreased from 67.4 cGy*cm2 (SD = 14.48) to 25.3 cGy*cm2 (SD = 3.82), p = 0.01 (1-tailed); and 3) the average number of FMs implanted around the tumour was increased from 4.7 (SD = 0.84) to 5.6 (SD = 0.76), p = 0.00 (1-tailed). Conclusion: Pre-procedure planning reduces the FM implantation duration from 41.1 to 22.9 min, reduces the radiation exposure in DAP from 67.4 to 25.3 dGy*cm2, and increases the number of FMs inserted around the tumour from 4.7 to 5.6.

Radiation-induced changes in peripheral nerve by stereotactic radiosurgery: a study on the sciatic nerve of rabbit.

A large fractional dose in radiotherapy produces better radiobiological results, but there is always a concern of radiation-induced damage to the normal tissues, especially peripheral nerves. This study was to evaluate the radiation-induced changes of sciatic nerve treated by stereotactic radiosurgery (SRS) in rabbit. A localization test was performed on 3 rabbits to determine the reference landmarks to the location of the sciatic nerve of rabbit in CT. Another 12 rabbits were irradiated by a dose of 25 Gy at the sciatic nerve using SRS with 5 non-coplanar arcs. The rabbits were randomized into 3 groups and euthanised at 3, 5, and 7 months after radiotherapy, respectively. Apart from the sensory and motor tests performed on the rabbits, segments of the sciatic nerve were prepared for hematoxylin and eosin staining. Histologic and ultra-structural examinations including morphometric analyses were conducted and compared with the control (non-irradiated side). Apart from the loosening of myelin layers at 5 months, no prominent changes were shown at 3 and 5 months after irradiation. At 7 months, despite the fact that the sensation and motor function tests remained intact, ultra-structural examination showed obvious vacuolation, degeneration and necrosis of the axons with myelin fragmentation. In addition, morphometric analysis indicated that, when compared with the control, there was significant reduction in fiber diameter, increase of myelin thickness and decrease of G ratio (P < 0.01). Although it remained functionally intact, a focal single dose of 25 Gy caused significant microscopic damage to the rabbit sciatic nerve at 7 months after irradiation. Escalating doses with large single fractional dose involving peripheral nerves should be carried out with caution.

Radiation induced temporal lobe necrosis in nasopharyngeal cancer patients after radical external beam radiotherapy.

Radiation-induced temporal lobe necrosis (TLN) is one of the late post-radiotherapy complications in nasopharyngeal cancer (NPC) patients. Since NPC is common to have skull base infiltration, irradiation of the temporal lobes is inevitable despite the use of the more advanced intensity-modulated radiotherapy (IMRT). Moreover, the diagnosis and treatment of TLN remain challenging. In this review, we discuss the diagnosis of TLN with conventional and advanced imaging modalities, onset and predictive parameters of TLN development, the impact of IMRT on TLN in terms of incidence and dosimetric analyzes, and the recent advancements in the treatment of TLN.

JNK Pathway Mediates Low Oxygen Level Induced Epithelial-Mesenchymal Transition and Stemness Maintenance in Colorectal Cancer Cells.

(1) Background: Epithelial-mesenchymal transition (EMT) and cancer cell stemness maintenance (SM) are important factors for cancer metastasis. Although hypoxia has been considered as a possible factor for EMT induction and promotion of SM, studies in this area, apart from hypoxia-inducible factor (HIF) pathways and severe hypoxia, are scant. This study aimed to evaluate the effects of different oxygen levels on EMT induction and SM and elucidate the signaling pathways involved in colorectal cancer cells. (2) Methods: Cell morphological analysis, migration assay, immunofluorescence staining of cytoskeleton and Western blotting were performed on human colorectal cancer cells HT-29, DLD-1, and SW-480 cultured at 1%, 10%, and normal (21%) O2 levels. The role played by c-Jun N-terminal kinase (JNK) was evaluated through the use of the specific JNK inhibitor SP600125. (3) Results: This study evaluated 1% and 10% O2 are possible conditions for EMT induction and SM. This study also demonstrated the partial relieve of EMT induction and SM by SP600125, showing the importance of the JNK pathway in these processes. Furthermore, this study proposed a novel pathway on the regulation of Akt by JNK-c-Jun. (4) Conclusions: This study suggests 10% O2 as another possible condition for EMT induction, and SM and JNK pathways play important roles in these processes through multiple factors. Inhibition of JNK could be explored as treatment for inhibiting metastasis in colorectal cancer cells.

Hypoxia-Induced Epithelial-Mesenchymal Transition in Cancers: HIF-1α and Beyond.

Metastasis is the main cause of cancer-related mortality. Although the actual process of metastasis remains largely elusive, epithelial-mesenchymal transition (EMT) has been considered as a major event in metastasis. Besides, hypoxia is common in solid cancers and has been considered as an important factor for adverse treatment outcomes including metastasis. Since EMT and hypoxia potentially share several signaling pathways, many recent studies focused on investigate the issue of hypoxia-induced EMT. Among all potential mediators of hypoxia-induced EMT, hypoxia-inducible factor-1α (HIF-1α) has been studied extensively. Moreover, there are other potential mediators that may also contribute to the process. This review aims to summarize the recent reports on hypoxia-induced EMT by HIF-1α or other potential mediators and provide insights for further investigations on this issue. Ultimately, better understanding of hypoxia-induced EMT may allow us to develop anti-metastatic strategies and improve treatment outcomes.

A longitudinal study on parotid and submandibular gland changes assessed by magnetic resonance imaging and ultrasonography in post-radiotherapy nasopharyngeal cancer patients.

OBJECTIVES: With regard to the intensity modulated radiotherapy (IMRT) of nasopharyngeal carcinoma (NPC) patients, this longitudinal study evaluated the radiation-induced changes in the parotid and submandibular glands in terms of gland size, echogenicity and haemodynamic parameters. METHODS: 21 NPC patients treated by IMRT underwent MRI and ultrasound scans before radiotherapy, and at 6, 12, 18 and 24 months after treatment. Parotid and submandibular gland volumes were measured from the MRI images, whereas the parotid echogenicity and haemodynamic parameters including the resistive index, pulsatility index, peak systolic velocity and end diastolic velocity were evaluated by ultrasonography. Trend lines were plotted to show the pattern of changes. The correlations of gland doses and the post-RT changes were also studied. RESULTS: The volume of the parotid and submandibular glands demonstrated a significant drop from pre-RT to 6 months post-RT. The parotid gland changed from hyperechoic before RT to either isoechoic or hypoechoic after treatment. The resistive index and pulsatility index decreased from pre-RT to 6 month post-RT, then started to increase at 12 month time interval. Both peak systolic velocity and end diastolic velocity increased after 6 months post-RT then followed a decreasing trend up to 24 months post-RT. There was mild correlation between post-RT gland dose and gland volume, but not with haemodynamic changes. CONCLUSIONS: Radiation from IMRT caused shrinkage of parotid and submandibular glands in NPC patients. It also changed the echogenicity and vascular condition of the parotid gland. The most significant changes were observed at 6 months after radiotherapy. ADVANCES IN KNOWLEDGE: It is the first paper that reports on the longitudinal changes of salivary gland volume, echogenicity and haemodynamic parameters altogether in NPC patients after radiotherapy. The results are useful for the prediction of glandular changes that is associated with xerostomia, which help to provide timely management of the complication when the patients attend follow-up visits.

A Review on the Special Radiotherapy Techniques of Colorectal Cancer.

Colorectal cancer is one of the commonest cancers worldwide. Radiotherapy has been established as an indispensable component of treatment. Although conventional radiotherapy provides good local control, radiotherapy treatment side-effects, local recurrence and distant metastasis remain to be the concerns. With the recent technological advancements, various special radiotherapy treatment options have been offered. This review article discusses the recently-developed special radiotherapy treatment modalities for various conditions of colorectal cancer ranging from early stage, locally advanced stage, recurrent, and metastatic diseases. The discussion focuses on the areas of feasibility, local control, and survival benefits of the treatment modalities. This review also provides accounts of the future direction in radiotherapy of colorectal cancer with emphasis on the coming era of personalized radiotherapy.

A Review on the Assessment of Radiation Induced Salivary Gland Damage After Radiotherapy.

Head and neck cancers are common in Southern China including Hong Kong. Intensity modulated radiotherapy has been the treatment of choice for these patients. Although radiotherapy provides good local control, radiotherapy treatment side-effects are still inevitable due to close proximity of the organs at risk from the target volume. Xerostomia, which is caused due to the damage of salivary glands, is one of the main radiation induced toxicities in post-radiotherapy head and neck patients. This review article discusses the methods for the assessing of radiation induced salivary gland changes including the gland morphology and saliva flow rate. The discussion also includes the recovery of the salivary gland after radiotherapy and how it is affected by the dose. It is expected that the future direction in monitoring the recovery of salivary glands will focus in cellular or molecular levels, and the development of imaging biomarker.

Comparison of sonographic appearance of normal and postradiotherapy parotid glands: a preliminary study.

This study was undertaken to evaluate and compare the grey-scale and Doppler sonographic features of postradiotherapy (RT) and normal parotid glands. A total of 10 patients with previous head and neck RT and with different degrees of xerostomia were included. Another 10 healthy subjects, who are age and gender-matched with the 10 patients, were also recruited. Grey-scale and Doppler ultrasound examinations of parotid glands were performed on both the patients and healthy subjects. The parotid glands were assessed for their size, echogenicity, echotexture, conspicuity of intraparotid ducts, blood flow velocity and vascular resistance. Results showed that post-RT parotid glands tended to be smaller than normal parotid glands with a significant difference in the transverse dimension (p < 0.05). Normal parotid glands appeared homogeneous, hyperechoic relative to the adjacent muscles and had marginally seen intraparotid ducts. Post-RT parotid glands were heterogeneous, isoechoic (50%) or hypoechoic (50%) relative to the adjacent muscles, and the intraparotid ducts were either marginally (50%) or obviously (50%) seen on ultrasound. The PSV, RI and PI of normal parotid glands were significantly higher than that of post-RT parotid glands (p < 0.05). However, the difference in EDV between normal and post-RT parotid glands was not significant (p > 0.05). In conclusion, ultrasound is useful in assessing parotid glands. To avoid image misinterpretation, post-RT changes in the sonographic appearance of parotid glands should be considered in examining patients with previous head and neck RT.

Effects of multileaf collimator parameters on treatment planning of intensity-modulated radiotherapy.

In inverse planning of intensity-modulated radiotherapy (IMRT), the setting of multileaf collimator (MLC) parameters affects the optimization algorithms and dose distribution. We investigated the effects of varying the MLC leaf width, leaf insertion percentage, and leaf increment in treatment planning of IMRT in 3 cancer cases: nasopharynx, esophagus, and prostate. Inverse planning of the 3 cancer cases was performed using the XiO treatment planning system. MLCs with 0.5 and 1.0 cm were used to evaluate the leaf width effect, whereas leaf insertions of 20%, 50%, and 80% were used to demonstrate the effect of leaf insertion percentage, and leaf increments of 0.5, 1.0, and 2.0 cm were used to study the leaf increment effect. The treatment plans were evaluated by dose profiles, tumor control probability (TCP), and normal tissue complication probability (NTCP). The 0.5-cm MLC leaves showed better TCPs and NTCPs than the 1.0-cm leaves in the 3 cancer cases, although the differences were less than 2.5%. For the leaf insertion percentage, the dose profile differences among the 3 levels of increments were minimal, and their differences in TCP and NTCP were extremely small (< 1.5%). The effect of leaf increment was more prominent, dose profile, TCPs, and NTCPs were best for the smallest leaf increment and they deteriorated as the leaf increment increased. Narrower leaves gave slightly better sparing of organs at risk (OAR)s; changing the leaf insertion percentage brought about negligible changes, whereas increasing the leaf increment significantly degraded the treatment plans.

Comparison of set up accuracy among three common immobilisation systems for intensity modulated radiotherapy of nasopharyngeal carcinoma patients.

INTRODUCTION: In intensity modulated radiotherapy (IMRT) of nasopharyngeal carcinoma (NPC) patients, an effective immobilisation system is important to minimise set up deviation. This study evaluated the effectiveness of three immobilisation systems by assessing their set up deviations. METHODS: Patients were randomly assigned to one of the three immobilisation systems: (1) supine on head rest and base plate (HB); (2) supine with alpha cradle supporting the head and shoulder (AC); (3) supine with vacuum bag supporting the head and shoulder (VB). CBCT was conducted weekly for each patient on the linear accelerator. Image registration was conducted at the nasopharynx (NP) and cervical regions. The translational displacements (latero-medial, antero-posterior and cranio-caudal), rotational displacements (pitch, yaw and roll) and 3D vectors obtained at the NP and cervical regions were recorded and compared among the three systems. RESULTS: The mean translational and rotational deviations were within 3 mm and 2°, respectively, and the range of 3D vector was 1.53-3.47 mm. At the NP region, the AC system demonstrated the smallest translational and rotational deviations and 3D vector. The differences were significant except for the latero-medial, yaw and roll directions. Similarly, at the cervical region, the AC system showed smaller translational and rotational deviations and 3D vector, with only the cranio-caudal and yaw deviations that did not reach statistical significance. CONCLUSIONS: Set up deviation was greater in the neck than the NP region. The set up accuracy of the AC system was better than the other two systems, and it is recommended for IMRT of NPC patients in our institution.