Ultrasound Evaluation of Carotid Atherosclerosis in Post-Radiotherapy Nasopharyngeal Carcinoma Patients, Type 2 Diabetics, and Healthy Controls.

Purpose To comprehensively evaluate and compare the degree of carotid atherosclerosis in patients treated with radiotherapy (RT) for nasopharyngeal carcinoma (NPC) and in patients with type 2 diabetes mellitus (DM), and using healthy subjects as controls. Materials and Methods The present study recruited 69 post-RT NPC patients without conventional cardiovascular risk factors, 70 type 2 diabetic patients without previous RT, and 76 healthy controls without conventional cardiovascular risk factors and previous RT. For each participant, 5 carotid atherosclerotic parameters, namely carotid intima-media thickness (CIMT), carotid arterial stiffness (CAS), presence of carotid plaque, carotid plaque score, and presence of ≥ 50 % carotid stenosis, were assessed using ultrasonography. The differences in these carotid atherosclerotic parameters between study groups were compared using ANCOVA or logistic regression after the adjustment for age and gender. Multiple comparisons were corrected using the Benjamini-Hochberg false discovery rate. Results Post-RT NPC patients and type 2 diabetics had a significantly higher CIMT, CAS and carotid plaque burden compared to the healthy subjects (corrected P-value, Pcor < 0.05). In addition, carotid atherosclerosis in post-RT NPC patients tended to be more severe with significantly higher CAS and carotid plaque burden than that in type 2 diabetics (Pcor < 0.05). Conclusion Neck RT for NPC is an independent risk factor of carotid atherosclerosis, and radiation induces more severe carotid atherosclerosis in post-RT NPC patients. Thus, assessment of carotid atherosclerosis using ultrasonography may be necessary for these patients and should be indicated in the routine follow-up of NPC.

Factors affecting target motion in stereotactic body radiotherapy of liver cancer using CyberKnife.

INTRODUCTION: In stereotactic body radiation therapy (SBRT) of solitary liver cancer, organ motion due to respiration is an important factor in the definition of planning target volume (PTV). This study evaluated the potential associations of target motion with gross tumour volume (GTV) size, tumour location, Child-Pugh score and intra-fraction treatment time in SBRT of liver cancer treated by CyberKnife. METHODS: Translational motion data of 145 liver cancer patients, who were previously treated by CyberKnife with free breathing under tumour tracking, were recorded in the log files of the motion tracking system and analysed. The factors including target location based on liver segments, Child-Pugh score which was an indication of liver cirrhosis, GTV size and intra-fraction treatment time were recorded and their associations with the magnitude of target movement were evaluated. RESULTS: Target location demonstrated significant association with the translational target motion in the supero-inferior (SI) and left-right (LR) directions but less in antero-posterior (AP) direction. Tumours located at the peripheral segments were more affected than the central segments. Child-Pugh score and GTV size were not significantly associated with target motion in any direction. Longer intra-fraction treatment time generally increased target motion in the SI and LR directions. CONCLUSION: In SBRT of liver cancer, the target motions in SI and LR directions were correlated with the location of target and treatment time, but not with Child-Pugh score and GTV size. These results should assist in deciding the GTV-PTV margin in SBRT treatment planning for solitary liver cancer.

A comparison of dose and set-up accuracy between flexed and extended neck positions in Helical Tomotherapy of nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC) patients treated with Helical Tomotherapy (HT) are commonly set up in an extended neck (EN) or a flexed neck (FN) position. This study investigated the dosimetric and set-up accuracy differences between these 2 set-up positions. Twenty NPC patients treated with HT from each set-up position were retrospectively recruited. HT plans were computed using the same target prescription and organs at risks (OARs) constraints for both set-up positions. The doses parameters of the target volumes and OARs were assessed. Daily megavoltage CT images were retrieved to obtain the set-up errors at 4th (C4) and 7th (C7) cervical levels. The mean values of these parameters were compared between the 2 set-up positions. The dose to NP target in FN group was more conformal than EN group, while the conformity of the neck targets in FN group were significantly lower. For the OARs, the temporal lobe, cerebellum, and hippocampus in FN group received significantly lower doses than the EN. However, the optic structures, brain stem, spinal cord, and parotid glands received higher doses in FN group. The systematic errors at C4 and C7 levels in FN group were larger in all translational directions except the ML direction at C7 level. With regard to radiotherapy of NPC patient using helical tomotherapy, FN position reduced doses to intracranial structures but increased doses to optic structures and other structures when compared with the EN position. In terms of set-up accuracy at the neck region, EN position was relatively better.

A dosimetric evaluation on applying RTOG-based and CT/MRI-based delineation methods to brachial plexus in radiotherapy of nasopharyngeal carcinoma treated with helical tomotherapy.

OBJECTIVE: In radiotherapy of nasopharyngeal carcinoma (NPC) patients, the brachial plexus (BP) situated at both sides of the neck is often irradiated to high dose. This study was to evaluate different BP delineation methods and analyse the dosimetric consequences when applying BP dose constraints in radiotherapy planning of NPC. METHODS: 15 NPC cases radically treated with helical tomotherapy were recruited. Apart from the original treatment plan (Plan A), two new plans (Plans B and C) with additional BP dose constraints were computed using the same planning CT images, structures and planning parameters. Plan B consisted of BP contours based on Radiation Therapy Oncology Group (RTOG)-endorsed atlas; while those in Plan C were based on MR images registered with the planning CT images. RESULTS: The mean BP volume by RTOG method was 19.04 ± 3.50 cm3 vs 10.44 ± 2.00 cm3 by CT/MRI method. The mean BP overlapping volume between the two contouring methods was 1.9 cm3 (0.38-4.03 cm3). There was significant difference between two methods (p < 0.001). The average Dmax, Dmean, D5%, D10% and D15% of both sides of BP in Plan A were significantly higher than those in both Plan B and Plan C. There were no significant dose differences in the targets and organs at risk (OARs) after applying dose constraints in Plan B and Plan C. CONCLUSION: RTOG method was recommended since larger BP volume provided better protection. Applying BP dose constraints during tomotherapy plan optimisation for NPC patients could significantly reduce the BP dose (p < 0.05) without compromising the doses to the targets and other OARs. ADVANCES IN KNOWLEDGE: This is the first study comparing the delineation method based on RTOG-endorsed atlas with the conventional CT/MRI delineation method for BP in tomotherapy of NPC patients. Our results showed that BP dose could be significantly reduced after applying the dose constraints without compromising the doses to the target volumes and other OARs. The RTOG method was more favoured as it gave a relatively larger BP volume and therefore offered better organ sparing.

A study on the post-radiotherapy changes of temporomandibular joint in nasopharyngeal carcinoma patients.

OBJECTIVE: Radiation-induced trismus, which is resulted from damage of the temporomandibular joint (TMJ), is one of the common late complications in nasopharyngeal carcinoma (NPC) patients after radical radiotherapy. This study investigated the radiation induced TMJ changes using ultrasonography in post-radiotherapy (post-RT) NPC patients. METHODS: 114 NPC patients, who had completed radiotherapy for more than 4 years, were assessed with the maximum incisal distance (MID) and ultrasonography examination of TMJ from which the maximum disc thickness of the joint disc, the condyle irregularity (CI), joint vascularity (JV) and relative muscle echogenicity were assessed. The same assessments were conducted on 100 age-matched normal subjects. The results were compared among the patients with and without trismus, and the control group. The mean doses to the TMJ were estimated using the treatment planning system and their correlation with the magnitude of MID was also investigated by the Pearson correlation test. RESULTS: 39 out of the 114 patients (34.2%) presented with trismus. The average mean TMJ for all patients was 41.4 Gy, in which patients with trismus was significantly higher than patients without trismus (p = 0.017). The mean MID of patient group was significantly lower than control group (p < 0.001). The mean maximum disc thickness of the patient group was significantly smaller than the control group, whereas the mean CI and JV were significantly higher in patient group. For relative muscle echogenicity, a higher percentage of the control group showed hyperechoic pterygoid muscle than the patient group. The mean total dose to the TMJs for the patient group was 41.4 Gy and there was a mild negative correlation between the mean TMJ dose and the MID (r = -350). CONCLUSION: The TMJ in post-RT NPC patients showed reduction of disc thickness, increase of CI and JV. Patients with trismus demonstrated thinner disc thickness and higher JV than those without trismus. Advances in knowledge: Our study was the first cross-sectional comparative study involving over 100 patients and normal subjects that used ultrasound to assess the radiation-induced morphological changes of TMJ. Post-RT TMJ changes characterized by the reduction of disc thickness, increase of CI and JV were detected in the NPC patients. The parameters used in this study were able to detect the morphological differences between the patient group and control group, and therefore can be effectively used to monitor the TMJ condition of post-RT NPC patients.

Evaluation of the dosimetric impact of applying flattening filter-free beams in intensity-modulated radiotherapy for early-stage upper thoracic carcinoma of oesophagus.

INTRODUCTION: Flattening filter-free (FFF) radiation beams have recently become clinically available on modern linear accelerators in radiation therapy. This study aimed to evaluate the dosimetric impact of using FFF beams in intensity-modulated radiotherapy (IMRT) for early-stage upper thoracic oesophageal cancer. METHODS: Eleven patients with primary stage upper thoracic oesophageal cancer were recruited. For each patient, two IMRT plans were computed using conventional beams (Con-P) and FFF beams (FFF-P), respectively. Both plans employed a five-beam arrangement and were prescribed with 64 Gy to (planning target volume) PTV1 and 54 Gy to PTV2 in 32 fractions using 6 MV photons. The dose parameters of the target volumes and organs at risks (OARs), and treatment parameters including the monitor units (MU) and treatment time (TT) for Con-P and FFF-P were recorded and compared. RESULTS: The mean D 5 of PTV1 and PTV2 were higher in FFF-P than Con-P by 0.4 Gy and 0.3 Gy, respectively. For the OARs, all the dose parameters did not show significant difference between the two plans except the mean V 5 and V 10 of the lung in which the FFF-P was lower (46.7% vs. 47.3% and 39.1% vs. 39.6%, respectively). FFF-P required 54% more MU but 18.4% less irradiation time when compared to Con-P. CONCLUSION: The target volume and OARs dose distributions between the two plans were comparable. However, FFF-P was more effective in sparing the lung from low dose and reduced the mean TT compared with Con-P. Long-term clinical studies are suggested to evaluate the radiobiological effects of FFF beams.