An overview of radiological manifestations of acquired dental developmental disturbances in paediatric head and neck cancer survivors.

OBJECTIVES: In paediatric cancer survivors treated with chemotherapy and radiotherapy therapy, late effects on dental development are quite common. Oral radiologists are not familiar with the radiographic images of these specific dental consequences of chemotherapy and radiotherapy. With the goal of educating colleagues, to raise awareness of the needs of survivors, and to identify directions for future research, we present dental radiographs of survivors treated for head and neck rhabdomyosarcoma with chemotherapy and radiotherapy. Also, based on the survivors reviewed, a radiographic inventory of commonly found late dental developmental effects seen in conjunction with treatment is presented. METHODS: Panoramic radiographic findings of five illustrative cases are presented, from a group of 42 survivors of head and neck rhabdomyosarcoma treated at the Academic Medical Center Amsterdam, The Netherlands over the past 25 years. RESULTS: Five cases showing dental developmental disorders are presented. These cases show an association of the location of the radiation field and the developmental stage of the teeth with the severity of the effect on dental development. We also report an inventory of severe and moderate effects of chemotherapy and radiotherapy on the development of molars and anterior teeth. CONCLUSIONS: This paper presents five cases and a radiographic inventory to illustrate disturbances of dental development associated with chemotherapy and radiotherapy in children. Medical and dental professionals involved in the treatment of cancer survivors are relatively unaware of the dental consequences of radiation therapy and the age dependency of specific regional effects. These effects can be severe, with great impact on quality of life. Further research in this area could help improve planning of radiation therapy for children, potentially preventing or limiting dental or maxillofacial sequelae.

Precision of aiming with a portable X-ray device (Nomad Pro 2) compared to a wall-mounted device in intraoral radiography.

METHODS AND MATERIALS: 20 operators obtained intraoral radiographs of four regions (bitewing, upper molar, lower molar and upper anterior) in five mannequins, using HH and WM devices. Beam-aiming devices were fitted with metal cross-wires to project on image sensors. Deviation from ideal perpendicular incidence of beam was calculated, based on positions of cross-wires relative to gold-standard positions (i.e. average of 10-fold precise aiming by authors via WM system). Analytic models relied on Wilcoxon signed-rank test and mixed model analyses. RESULTS: Mean deviations from perfect aim were 2.88˚ (± 1.80˚) for WM and 3.06˚ (± 1.90˚) for HH methods. The difference among all operators (HH vs WM) was 0.17˚ (± 2.48˚), which was not significant. Seven operators showed better aim by HH device (13 by WM system); and in one instance, this difference was significant. CONCLUSIONS: Aiming precision proved similar for HH and WM methods of intraoral radiography, although individual operators may perform better using one of these modalities. Aim is not an expected limiting factor for image quality in HH (vs WM) diagnostics.

Ambient dose during intra-oral radiography with current techniques: Part 2 quantifying the remnant beam - an in vivo study.

OBJECTIVES:: (1) To find a safe reference transmission factor for the remnant beam to be used when assessing the remnant beam during intra-oral radiography. (2) To identify factors such as exposure type, side (left or right), gender and age that might significantly affect transmission. METHODS:: Measurements were performed in the remnant beam during 323 intra-oral exposures of 43 patients. The exposure parameters were 60 kV and 7 mA. These measurements were compared with values in the same setting, but without a patient present to arrive at a transmission value. Differences between types of exposure [bitewing (BW), incisor and canine (IC) periapical, premolar and molar (PM) periapical], exposure side (left or right), gender and age were statistically analysed. The reference value was based on the exposure yielding the highest transmission value, to which a safety margin of two standard deviations (SDs) was added, and then rounding up. RESULTS:: The respective mean transmission values (SD) for BW, IC and PM exposures were as follows: 1.78% (1.15%), 0.639% (0.63%) and 2.60% (0.98%). The differences between PM and IC and between BW and IC were significant (p > 0.01). The differences between exposure side, gender and age were not significant. The reference transmission value, which was calculated from the highest mean transmission percentage for PM (2.60%) plus twice the SD (0.98%) and rounding up, was 5%. CONCLUSIONS:: A transmission factor of 5% could be used to assess the remnant beam during intra-oral radiography. Anterior exposures led to significantly lower transmission values than posterior exposures.

Ambient dose during intraoral radiography with current techniques: Part 1 conversion factor for scattered radiation using a rectangular collimator.

OBJECTIVES:: The aim of this study was to establish a conversion factor for assessing the scattered radiation produced during intraoral radiography with a rectangular collimator in areas where the remnant beam is not present. The dose level in the remnant beam will be addressed in another study. METHODS:: A radiological phantom (Rando) in the upright position was exposed to radiation delivered by a Planmeca Intra X-ray unit over 9 exposure geometries (right side of a full mouth series). For each geometry, the scattered radiation dose was measured at 5 locations in the horizontal plane and 4 locations in the vertical plane in front of the patient. The measurements were corrected for background and leakage radiation. An inventory of the distributions of the different geometries with respect to their share of the total workload was created in order to assign the correct weightings of the total ambient scattered radiation for the different geometries. The weightings were used to construct a scattered radiation pattern for a representative mix of exposures. The maximum value found in this pattern was used to arrive at a safe conversion factor. RESULTS:: The scattered ambient radiation dose was evenly distributed over the horizontal plane. The scattered ambient radiation dose ranged from 20 to 65% lower in the vertical plane. CONCLUSIONS:: The conversion factor established for scattered ambient radiation was 0.05 µSv per mAs at 1 meter. This factor is 3-fold lower than the conversion factors reported previously.

The value of thyroid shielding in intraoral radiography.

OBJECTIVES: To evaluate the utility of the application of a thyroid shield in intraoral radiography when using rectangular collimation. METHODS: Experimental data were obtained by measuring the absorbed dose at the position of the thyroid gland in a RANDO(®) (The Phantom Laboratory, Salem, NY) male phantom with a dosemeter. Four protocols were tested: round collimation and rectangular collimation, both with and without thyroid shield. Five exposure positions were deployed: upper incisor (Isup), upper canine (Csup), upper premolar (Psup), upper molar (Msup) and posterior bitewing (BW). Exposures were made with 70 kV and 7 mA and were repeated 10 times. The exposure times were as recommended for the exposure positions for the respective collimator type by the manufacturer for digital imaging. The data were statistically analyzed with a three-way ANOVA test. Significance was set at p < 0.01. RESULTS: The ANOVA test revealed that the differences between mean doses of all protocols and geometries were statistically significant, p < 0.001. For the Isup, thyroid dose levels were comparable with both collimators at a level indicating primary beam exposure. Thyroid shield reduced this dose with circa 75%. For the Csup position, round collimation also revealed primary beam exposure, and thyroid shield yield was 70%. In Csup with rectangular collimation, the thyroid dose was reduced with a factor 4 compared with round collimation and thyroid shield yielded an additional 42% dose reduction. The thyroid dose levels for the Csup, Psup, Msup and BW exposures were lower with rectangular collimation without thyroid shield than with round collimation with thyroid shield. With rectangular collimation, the thyroid shield in Psup, Msup and BW reduced the dose 10% or less, where dose levels were already low, implying no clinical significance. CONCLUSIONS: For the exposures in the upper anterior region, thyroid shield results in an important dose reduction for the thyroid. For the other exposures, thyroid shield augments little to the reduction achieved by rectangular collimation. The use of thyroid shield is to be advised, when performing upper anterior radiography.