Evaluation and analysis of risk factors of hearing impairment for nasopharyngeal carcinoma treated using intensity-modulated radiotherapy

BACKGROUND

Treating nasopharyngeal carcinoma (NPC) with radiotherapy frequently causes hearing impairment (HI). HI risk data haven't been evaluated quantitatively. This study aimed to analyze the probability of HI and sever HI (SHI), develop a nomogram to quantify individual prediction, and provide dose limitation suggestions.

METHODS AND MATERIALS

This single-center, retrospective study was conducted based on 588 adolescents and young adults with non-metastatic NPC treated using intensity modulated radiation therapy (IMRT) at Sun Yat-sen University Cancer Center between 2010 and 2016. A least absolute shrinkage and selection operator (LASSO) logistic regression model and univariate analysis were used to screen potential risk factors. The concordance index and a calibration curve evaluated the nomogram models' predictive ability, with bootstrap resampling validation.

RESULTS

We analyzed 588 patients with NPC, with a median follow-up of 103.4 months. HI occurred in 39.5 % of patients, with 29.7 % experiencing SHI. Two factors were classified as precursors for HI (volume 45 Gy of the inner ear (IEV45) and volume 50 Gy of the internal auditory canal (IACV50)), and IACmin and IACV60 for SHI, respectively. Prognostic nomograms were developed to predict HI and SHI probabilities, showing excellent discriminative abilities (c-index values = 0.806 and 0.793, respectively). We also suggested IEV45 < 50 % and/or IACV50 < 40 % as rational dose limitations for HI, and IACmin < 44 Gy and/or the IACV60 < 40 % for SHI.

CONCLUSION

Comprehensive analysis could predict the risk of HI and SHI in NPC after IMRT, proposing rational dose limitations and improving long-term quality of life.

Clinical guided computer tomography decisions are advocated in potentially severely injured trauma patients: a one-year audit in a level 1 trauma Centre with long pre-hospital times

BACKGROUND

The International Commission on Radiological Protection's (ICRP) justification principles state that an examination is justified if the potential benefit outweighs the risk for radiation harm. Computer tomography (CT) contributes 50% of the radiation dose from medical imaging, and in trauma patients, the use of standardized whole body CT (SWBCT) increases. Guidelines are lacking, and reviews conclude conflictingly regarding the benefit. We aimed to study the degree of adherence to ICRP's level three justification, the individual dose limitation principle, in our institution.

METHODS

This is a retrospective clinical audit. We included all 144 patients admitted with trauma team activation to our regional Level 1 trauma centre in 2015. Injuries were categorized according to the Abbreviated Injury Scale (AIS) codes. Time variables, vital parameters and interventions were registered. We categorized patients into trauma admission SWBCT, selective CT or no CT examination strategy groups. We used descriptive statistics and regression analysis of predictors for CT examination strategy.

RESULTS

The 144 patients (114 (79.2%) males) had a median age of 31 (range 0-91) years. 105 (72.9%) had at least one AIS ≥ 2 injury, 26 (18.1%) in more than two body regions. During trauma admission, at least one vital parameter was abnormal in 46 (32.4%) patients, and 73 (50.7%) underwent SWBCT, 43 (29.9%) selective CT and 28 (19.4%) no CT examination. No or only minor injuries were identified in 17 (23.3%) in the SWBCT group. Two (4.6%) in the selective group were examined with a complement CT, with no new injuries identified. A significantly (p < 0.001) lower proportion of children (61.5%) than adults (89.8%) underwent CT examination despite similar injury grades and use of interventions. In adjusted regression analysis, patients with a high-energy trauma mechanism had significantly (p = 0.028) increased odds (odds ratio = 4.390, 95% confidence interval 1.174-16.413) for undergoing a SWBCT.

CONCLUSION

The high proportion of patients with no or only minor injuries detected in the SWBCT group and the significantly lower use of CT among children, indicate that use of a selective CT examination strategy in a higher proportion of our patients would have approximated the ICRP's justification level three, the individual dose limitation principle, better.

Optimal dose limitation strategy for bone marrow sparing in intensity-modulated radiotherapy of cervical cancer

BACKGROUND

To quantify the dosimetric parameters of different bone marrow sparing strategies and to determine the optimal strategy for cervical cancer patients undergoing postoperative intensity-modulated radiotherapy (IMRT).

METHODS

Fifteen patients with cervical cancer were selected for analysis. The planning target volume (PTV) and the organs at risks (OAR) including small bowel, bladder, rectum, femoral heads, os coxae (OC), lumbosacral spine (LS) and bone marrow (BM) were contoured. For each patient, four IMRT plans with different strategies were generated, including one plan without BM as the dose-volume constraint, namely IMRT (N) plan, and three bone marrow sparing (BMS-IMRT) plans. The three BMS-IMRT plans used the BM, OC, OC and LS respectively, as the BM OAR, namely as IMRT (BM), IMRT (OC) and IMRT (OC + LS) plans. Dose volumes for the target and the OARs were compared using analysis of variance (ANOVA).

RESULTS

Compared with IMRT (N) plans, the dose to the small bowel, bladder, rectum and femoral heads showed no increase in the three BMS-IMRT plans. However, the irradiated dose to BM, OC and LS significantly decreased. In particular, the mean dose of BM, OC and LS decreased by about 5Gy (p < 0.05) in IMRT (BM) plans while the average volume receiving ≥20, ≥30, ≥40Gy decreased by 7.1-24.2%. The LS volume receiving 40Gy showed the highest decrease (about 31.2%, p < 0.05) in IMRT (OC + LS) plans. On the other hand, in comparison with IMRT (BM), IMRT (OC) reduced the dose volume of to the OC, but increased the dose to LS while IMRT (OC + LS) plans reduced both the OC and the LS volume at all dose levels. Specifically, the V20 of OC and LS in the IMRT (OC + LS) plan decreased by 11.5 and 11.2%, respectively.

CONCLUSION

By introducing the os coxae and lumbosacral spine as the dose-volume constraints, the IMRT plans exhibited the best sparing of the bone marrow without compromising the dose to surrounding normal structures. Therefore, we recommend adding the os coxae and lumbosacral spine as the BM OAR in such plans.

Cochlea sparing with a stratified scheme of dose limitation employed in intensity-modulated radiotherapy for nasopharyngeal carcinoma: A dosimetry study

Hearing loss is 1 of the major complications after radiotherapy in nasopharyngeal carcinoma (NPC) patients, how to minimize dose to cochlea in order to reduce the incidence of sensorineural hearing loss is a critical task. This study is to investigate a stratified scheme of cochlea sparing based on T stage in intensity-modulated radiotherapy. We designed a comparison between 2 plans of cochlea sparing plan (C-Plan) and regular noncochlea sparing plan (R-Plan) from 19 NPC patients with 2, 3, 8, and 6 cases of T1, T2, T3, and T4 stage, respectively. The outcomes showed that target coverage parameters and dose-volume histogram features were of no significant difference, with a significant difference in dose distribution between C-Plan and R-Plan in cochlea and eustachian, e.g., ipsilateral cochlea D_mean 4619.75 ± 1134.09 cGy in C-Plan and 5061.03 ± 1121.09 cGy in R-Plan (p = 0.000), contralateral cochlea D_mean 4386.73 ± 945.14 cGy in C-Plan and 4991.38 ± 961.21 cGy in R-Plan (p = 0.000). Meanwhile, there was no significant difference in dose distribution in spinal cord, brainstem, and other OARs. Our dosimetry study showed cochlea sparing in intensity-modulated radiotherapy for NPC reduced cochlea dose to different extent, so we suggested a stratified scheme of cochlea sparing based on T stage could be a useful and practical tool for both physicists and radiation doctors.

Can placing lead-rubber inferolateral to the light beam diaphragm limit ionising radiation to multiple radiosensitive organs?

INTRODUCTION

This article investigates a practical method of reducing the impact of scattered radiation during a lateral radiographic projection of the elbow. The light beam diaphragm (LBD) is generally accepted to limit ionising radiation using horizontal and longitudinal lead shutters, yet this article evidences further dose limitation by placing lead-rubber inferolateral to the LBD device.

METHODS

Using an anthropomorphic phantom and arm construction scattered radiation was recorded at multiple radiosensitive organs. A 15 cc ionisation chamber (model 10100 AT TRIAD) was placed on each radiosensitive organ (eye, thyroid, breast, testes, spleen and ovaries) measuring exposure rate (μGy/s). Dose readings were recorded before and after the placement of lead-rubber inferolateral to the LBD. A paired two sample t-test was undertaken affirming how likely dose limitation was attributable to chance (p < 0.05).

RESULTS

Descriptive and inferential statistics demonstrate dose reduction to radiosensitive organs (right eye 53%, right breast 53%, left eye 39%, thyroid 13%, left ovary 9%, testes 6%, left breast 3% and spleen 2%) upon placement of the lead-rubber inferolateral to the LBD. The paired two sample t-test demonstrated statistically significant dose limitation (t = 2.04, df = 7, p = 0.04) thus significant for radiographic practice.

CONCLUSION

Placement of lead-rubber inferolateral to the LBD limits dose to multiple radiosensitive organs. Right (53%) and left (39%) eye lens, right breast (53%), thyroid (13%), left ovary (9%), testes (6%), left breast (3%) and spleen (2%) statistically demonstrate dose limiting opportunities to patients.