Simultaneous integrated boost intensity-modulated radiotherapy for treatment of locally advanced non-small-cell lung cancer: a retrospective clinical study

Objective:

To evaluate the clinical efficacy and safety of simultaneous integrated boost intensity-modulated radiotherapy (SIB-IMRT) for patients with locally advanced non-small-cell lung cancer (LANSCLC).

Methods:

48 patients with LANSCLC treated with SIB-IMRT from January 2010 to April 2012 were retrospectively analysed. A radiation dose of 45–63 Gy (median dose, 51.58 Gy) was delivered to the planning target volume (1.8–2.0 Gy daily fractions) simultaneously with 55.0–74.2 Gy (median dose, 63 Gy) to the planning gross tumour volume (2.00–2.25 Gy daily fractions). 45 patients received concurrent/sequential chemotherapy. The overall survival (OS), locoregional recurrence-free survival (LRFS) and progression-free survival (PFS) were estimated using the Kaplan–Meier method. Treatment-related pneumonitis and oesophagitis were graded according to the Common Terminology Criteria for Adverse Events v. 4.0.

Results:

By 1 July 2013, 29 of the 48 patients were dead. The median follow-up time for the survivors was 28 months (19–44 months). The median OS and PFS were 21 and 14 months, respectively. The median LRFS time was not reached. The 2-year LRFS, OS and PFS were 62.5%, 45.1% and 28.0%, respectively. Two patients experienced Grade 3 treatment-related pneumonitis, two patients experienced Grade 5 treatment-related pneumonitis and two patients had ≥Grade 3 oesophagitis.

Conclusion:

SIB-IMRT appears to be an effective therapeutic option in patients with LANSCLC and warrants further evaluation with increased number of patients in prospective clinical trials.

Advances in knowledge:

This study explores the feasibility of delivering tumoricidal doses of radiation to primary lesions in non-small-cell lung cancer.The true value of radiotherapy confined to the thorax is indisputable in the treatment of locally advanced non-small-cell lung cancer (LANSCLC). However, even with standard chemoradiation, it is difficult to achieve durable local control, and this contributes to the high morbidity and mortality of patients with non-small-cell lung cancer (NSCLC).¹ Despite a demonstrated positive association between the radiation dose and tumour control,² results of the Radiation Therapy Oncology Group (RTOG) 0617 clinical (Phase III) trial showed that the overall survival (OS) of Stage III NSCLC patients given high-dose (74 Gy) conformal radiation therapy with concurrent chemotherapy was no better than that of patients given the standard dose (60 Gy).³The unpublished data showed that the higher dose had no further effects on improving the OS during the RTOG 0617 trial, and the reason still remained unclear, the radiation-induced decline in quality of life may be responsible for this.⁴ Thus, researchers turned their attention to focus on better ways of delivering radiation to tumours, while sparing surrounding normal structures. Initially, the radiation dose applied to the gross tumour was identical to that directed at targeted nodal areas, but logic suggests that the dose required to control subclinical lesions should be lower than that of the primary disease.Simultaneous integrated boost (SIB) is a recent modality applied in conjunction with intensity-modulated radiotherapy (IMRT) in the treatment of malignancies.^5,6 Simultaneous integrated boost–intensity-modulated radiotherapy (SIB-IMRT) simultaneously delivers a higher dose to the primary disease and a relatively lower dose to the subclinical disease or selected other regions. However, outcomes for SIB-IMRT in LANSCLC remain to be determined.Herein, we retrospectively analysed clinical outcomes of patients with LANSCLC treated with SIB-IMRT to evaluate the feasibility of this technology and to provide evidence in support of future clinical study.     

Submandibular gland sparing in intensity-modulated radiotherapy for N0-stage nasopharyngeal carcinoma

Objective:

This study evaluated and quantified the feasibility of submandibular gland (SMG) sparing in intensity-modulated radiotherapy (IMRT) for N0-stage nasopharyngeal carcinoma (NPC).

Methods:

Ten patients with N0-stage NPC were enrolled in the study. Four IMRT plans were produced for each, with different limiting conditions. In plan A, SMG sparing was ignored; in plans B, C and D, the mean dose to SMGs was restricted to 39 Gy. In addition, at least 95% of planning target volume (PTV)-IIa (PTV of clinical target volume involving level IIa lymph node) in plan C and 90% of PTV-IIa in plan D were required to have a 60 Gy covering.

Results:

The average mean dose to SMGs was 54.6 ± 3.6 Gy in plan A and was lower 39.3 ± 0.3, 49.3 ± 1.9 and 46.7 ± 2.8 Gy in plans B, C and D, respectively. The volume of PTV-IIa covered by 60 Gy was 98.9%, 81.6%, 95.2% and 90.8% in plans A, B, C and D, respectively, and showed a parallel association between dose reduction to SMGs and the covering deficit of PTV-IIa.

Conclusion:

Reducing the mean dose received by SMG to 39 Gy or less in IMRT for N0-stage NPC is feasible.Xerostomia is the most prevalent sequela following radiotherapy of nasopharyngeal carcinoma (NPC),¹ but can be reduced by parotid gland sparing using intensity-modulated radiotherapy (IMRT) techniques. In recent years, the submandibular gland (SMG) was found to play an important role in the secretion of saliva,^2,3 contributing up to 90% of unstimulated salivary output as well as contributing to a patient''s subjective sense of moisture. Therefore, sparing the SMGs from high-dose irradiation would be useful in reducing the symptoms of xerostomia.SMGs are located inside the area of neck node level Ib and anterior to the level II region. Level II neck nodes are generally elected to receive prophylactic irradiation. It has been reported that with three-dimensional conformal radiotherapy for head and neck cancers,⁴ the SMGs would receive an unplanned dose of 62 Gy on average. Preservation of SMG function was reported for head and neck cancer treated with IMRT.^5–7 However, data from our institution showed that the average unplanned dose received by SMGs was 58 Gy in IMRT of N0-stage NPC, although level I neck nodes were omitted for selected irradiations.To our knowledge, the abovementioned studies focused only on the contralateral SMG (cSMG).^5–7 However, is it possible to spare the bilateral SMGs in N0-stage NPC patients but what will be the subsequent trade-off of dose distribution to planning target volume 1 (PTV1) around the SMG area? This study was designed to address this question, and the results will be a valuable reference in planning the IMRT of NPC.     

Variation in patient position and impact on carbon-ion scanning beam distribution during prostate treatment

Objective:

We assessed the impact of changes in patient position on carbon-ion scanning beam distribution during treatment for prostate cancer.

Methods:

68 patients were selected. Carbon-ion scanning dose was calculated. Two different planning target volumes (PTVs) were defined: PTV1 was the clinical target volume plus a set-up margin for the anterior/lateral sides and posterior side, while PTV2 was the same as PTV1 minus the posterior side. Total prescribed doses of 34.4 Gy [relative biological effectiveness (RBE)] and 17.2 Gy (RBE) were given to PTV1 and PTV2, respectively. To estimate the influence of geometric variations on dose distribution, the dose was recalculated on the rigidly shifted single planning CT based on two dimensional–three dimensional rigid registration of the orthogonal radiographs before and after treatment for the fraction of maximum positional changes.

Results:

Intrafractional patient positional change values averaged over all patients throughout the treatment course were less than the target registration error = 2.00 mm and angular error = 1.27°. However, these maximum positional errors did not occur in all 12 treatment fractions. Even though large positional changes occurred during irradiation in all treatment fractions, lowest dose encompassing 95% of the target (D₉₅)-PTV1 was >98% of the prescribed dose.

Conclusion:

Intrafractional patient positional changes occurred during treatment beam irradiation and degraded carbon-ion beam dose distribution. Our evaluation did not consider non-rigid deformations, however, dose distribution was still within clinically acceptable levels.

Advances in knowledge:

Inter- and intrafractional changes did not affect carbon-ion beam prostate treatment accuracy.The depth dose distribution for a charged particle beam exhibits a Bragg peak at the end of range, which is particularly sensitive to variation in tissue density along its path length. For this reason, changes in patient position perturb charged particle beams more strongly than photon beams.¹ Of the two major treatment uncertainties, intrafractional motion and interfractional changes, treatment accuracy for the prostate appears more strongly affected by interfractional changes.^2–7 Clinical protocols now incorporate several approaches to overcoming these uncertainties, including acquisition of radiographs or cone beam CT images.However, despite these technical solutions to intra- and interfractional changes and improvements in patient positional accuracy during the patient set-up procedure, treatment accuracy may also be affected by positional changes during treatment. Most treatment centres do not check patient positional accuracy after treatment beam irradiation, because approaches to adjusting distribution in the next fraction to compensate for under-/overdosage in the preceding have not been developed and because patient position is assumed not to change during treatment. Our hospital has been providing carbon-ion scanning beam treatment since 2011.⁸ The average time from complete patient set-up to complete beam irradiation was 2.6 min. Although this is relatively short, we have no quantitative data on the effect of patient positional change on carbon-ion scanning dose distribution.In this study, we evaluated patient positional change during treatment and its impact on carbon-ion scanning dose distribution in treatment of the prostate.     

Vaginal displacement during course of adjuvant radiation for cervical cancer: results from a prospective IG-IMRT study

Objective:

To compare internal target volume (ITV) generated using population-based displacements (ITV_study) with empty and full bladder scan fusion (ITV_EBFB) for organ-at-risk (OAR) doses during adjuvant intensity-modulated radiation therapy (IMRT) for cervical cancer.

Methods:

From January 2011 to October 2012, patients undergoing IMRT were included. CT simulation was carried out after inserting vault markers. Planning target volume (PTV)_EBFB received 50 Gy per 25 fractions. Pre-treatment megavoltage CT (MVCT) was performed. MVCTs were registered using bony landmarks with Day 1 MVCT. Displacement of the centre of mass of markers was measured along each axis. Directional ITV was calculated using mean ± 2 standard deviations (SDs) (ITV_study). Replanning was performed using PTV study, and OAR doses were compared with PTV_EBFB using Wilcoxon test.

Results:

A total of 348/386 data sets were evaluable for 16 patients. The median vaginal displacement was 1.2 mm (SD, 1.3 mm), 4.0 mm (SD, 3.5 mm) and 2.8 mm (SD, 3.3 mm) in the mediolateral, superoinferior and anteroposterior directions, respectively. The ITV margins were 4.1, 10.3 and 10.6 mm. ITV_study and ITV_EBFB were 115.2 cm³ (87.7–152.2 cm³) and 151 cm³ (95.7–277.1 cm³) (p < 0.0001), respectively. PTV_study and PTV_EBFB were 814 and 881 cm³ (p < 0.0001), respectively. Median doses to the bladder were lower with the PTV_study (46.2 Gy vs 43.2 Gy; p = 0.0001), and a similar trend was observed in the volume of the small bowel receiving 40 Gy (68.2 vs 60.1 cm³; p = 0.09).

Conclusion:

Population-based PTV margins can lead to reduction in OAR doses.

Advances in knowledge:

Population-based ITV may reduce OAR doses while executing adjuvant IMRT for cervical cancer.Adjuvant pelvic radiation for cervical and endometrial cancers is recommended in patients with adverse histopathological features following surgery.^1,2 Although it improves outcomes, it is associated with increased acute and late bowel morbidity.^1,2 Recently published results of the Radiation Therapy Oncology Group (RTOG) Phase II study demonstrate that the use of pelvic intensity-modulated radiation therapy (IMRT) is associated with reduced treatment-related acute and short-term gastrointestinal (GI) toxicity, and this can be achieved without worsening disease control.³ However, implementing IMRT may be challenging owing to the unpredictable nature of vaginal displacements during the course of external radiation. Therefore, the RTOG recommends that for planning IMRT, both empty and full bladder (EBFB) scans should be obtained for localizing residual vagina and for generating the internal target volume (ITV).⁴ These recommendations are being followed by two ongoing Phase III randomized controlled trials that aim at reducing acute and late bowel toxicity of adjuvant pelvic radiation.^5,6 Although this strategy may ensure that all extreme displacements arising out of variations in bladder filling are accounted for, this may result in increased planning target volume (PTV) and thereby increased dose to adjacent organs at risk (OAR). Strong correlation has been reported between the dose received by the bowel and late bowel morbidity after adjuvant pelvic radiation for cervical cancer.⁷ The present study was initiated with an aim of evaluating vaginal displacement for the post-hysterectomy cohort and to investigate if population-based ITV could reduce dose to OARs.     

Dosimetric planning study for the prevention of anal complications after post-operative whole pelvic radiotherapy in cervical cancer patients with hemorrhoids

Objective:

Radiation-induced anal toxicity can be induced by low radiation doses in patients with haemorrhoids. The object of this study was to determine the dosimetric benefits of different whole pelvic radiotherapy (WPRT) techniques in terms of dose delivered to the anal canal in post-operative patients with cervical cancer.

Methods:

The planning CT images of 10 patients with cervical cancer undergoing postoperative radiotherapy were used for comparison of three different plans. All patients had been treated using the conventional box technique WPRT (CV-WPRT), and we tried low-margin-modified WPRT (LM-WPRT), three-dimensional conformal techniques WPRT (CF-WPRT) and intensity-modulated WPRT (IM-WPRT) planning for dosimetric comparison of the anal canal, retrospectively.

Results:

Mean anal canal doses of the IM-WPRT were significantly lower (p < 0.05) than those of CV-WPRT, LM-WPRT and CF-WPRT, and V₁₀, V₂₀, V₃₀ and V₄₀ to the anal canal were also significantly lower for IM-WPRT (p < 0.05). The proportion of planning target volumes (PTVs) that received ≥98% of the prescribed dose for all plans was >99%, and the proportion that received ≥108% of the prescribed dose for IM-WPRT was <2%. Volumes of bladders and rectums that received ≥30 or ≥40 Gy were significantly lower for IM-WPRT than for three of the four-field WPRT plans (p = 0.000).

Conclusion:

IM-WPRT can significantly reduce radiation dose delivered to the anal canal and does not compromise PTV coverage. In patients with haemorrhoids, IM-WPRT may be of value for the prevention of anal complications.

Advances in knowledge:

Although tolerance of the anal canal tends to be ignored in patients undergoing post-operative WPRT, patients with haemorrhoids may suffer complications at low radiation doses. The present study shows IM-WPRT can be meaningful in these patients.     

Simultaneously modulated accelerated radiation therapy reduces severe oesophageal toxicity in concomitant chemoradiotherapy of locally advanced non-small-cell lung cancer

Objective:

The aim of this study was to evaluate the potential of simultaneously modulated accelerated radiation therapy (SMART) to reduce the incidence of severe acute oesophagitis in the treatment of unresectable locally advanced non-small-cell lung cancer (LANSCLC).

Methods:

21 patients were treated with SMART and concomitant platinum-based chemotherapy. The prescribed doses were limited to 54 Gy at 1.8 Gy per day to the zones of presumed microscopic extent while simultaneously maintaining doses of 66 Gy at 2.2 Gy per day to the macroscopic disease. The whole treatment was delivered over 30 fractions and 6 weeks. Dosimetric parameters of SMART and the standard technique of irradiation [intensity-modulated radiation therapy (IMRT)] were compared. Acute toxicity was prospectively recorded.

Results:

The highest grade of oesophagitis was 62% (13 patients) grade 1, 33% (7 patients) grade 2 and 5% (1 patient) grade 3. Three (14%) patients experienced acute grade 2 pneumonitis. There was no grade 4 oesophageal or pulmonary toxicity. Doses to the organs at risk were significantly reduced in SMART compared with IMRT [oesophagus: V_50Gy, 28.5 Gy vs 39.9 Gy (p = 0.003); V_60Gy, 7.1 Gy vs 30.7 Gy (p = 0.003); lung: V_20Gy, 27.4 Gy vs 30.1 Gy (p = 0,002); heart: V_40Gy, 7.3 Gy vs 10.7 Gy (p = 0.006); spine: D_max, 42.4 Gy vs 46.4 Gy (p = 0.003)]. With a median follow-up of 18 months (6–33 months), the 1-year local control rate was 70% and the disease-free survival rate was 47%.

Conclusion:

SMART reduces the incidence of severe oesophagitis and improves the whole dosimetric predictors of toxicity for the lung, heart and spine.

Advances in knowledge:

Our study shows that SMART optimizes the therapeutic ratio in the treatment of LANSCLC, opening a window for dose intensification.     

Parametrized rectal dose and associations with late toxicity in prostate cancer radiotherapy

Objective:

We investigated possible associations between planned dose–volume parameters and rectal late toxicity in 170 patients having radical prostate cancer radiotherapy.

Methods:

For each patient, the rectum was outlined from anorectal junction to sigmoid colon, and rectal dose was parametrized using dose–volume (DVH), dose–surface (DSH) and dose–line (DLH) histograms. Generation of DLHs differed from previous studies in that the rectal dose was parametrized without first unwrapping onto 2-dimensional dose–surface maps. Patient-reported outcomes were collected using a validated Later Effects in Normal Tissues Subjective, Objective, Management and Analytic questionnaire. Associations between dose and toxicity were assessed using a one-sided Mann–Whitney U test.

Results:

Associations (p < 0.05) were found between equieffective dose (EQD2₃) and late toxicity as follows: overall toxicity with DVH and DSH at 13–24 Gy; proctitis with DVH and DSH at 25–36 Gy and with DVH, DSH and DLH at 61–67 Gy; bowel urgency with DVH and DSH at 10–20 Gy. None of these associations met statistical significance following the application of a Bonferroni correction.

Conclusion:

Independently confirmed associations between rectal dose and late toxicity remain elusive. Future work to increase the accuracy of the knowledge of the rectal dose, either by accounting for interfraction and intrafraction rectal motion or via stabilization of the rectum during treatment, may be necessary to allow for improved dose–toxicity comparisons.

Advances in knowledge:

This study is the first to use parametrized DLHs to study associations with patient-reported toxicity for prostate radiotherapy showing that it is feasible to model rectal dose mapping in three dimensions.     

Evaluation of hippocampus dose for patients undergoing intensity-modulated radiotherapy for nasopharyngeal carcinoma

Objective:

To evaluate the dose received by the hippocampus among patients undergoing intensity-modulated radiotherapy (IMRT) for nasopharyngeal cancer.

Methods:

10 patients with biopsy-proven, locally advanced nasopharyngeal cancer constituted the study population. The total prescribed dose to the planning target volume (PTV) was 70 Gy (D95%) delivered in 2.12-Gy daily fractions using IMRT. Using established anatomical guidelines, MRI co-registration and the assistance of a board-certified neuroradiologist, the right and left hippocampi were delineated on axial imaging from the CT scan obtained at simulation for each patient beginning at the most anterior portion of the lateral ventricle. IMRT treatment plans were generated without dose–volume constraints to the hippocampus. A range of dose–volume statistics was calculated.

Results:

The mean hippocampus volume was 6.01 ± 2.61 cm³. The mean V20 was 72.2%; V40 was 22.0%; V50 was 10.2%; and V60 was 5.5%. The average mean, minimum and maximum hippocampus doses were 30.27 Gy (range, 19.08–47.99 Gy); 17.54 Gy (range, 11.66–33.17 Gy); and 54.95 Gy (range, 35.59–75.57 Gy), respectively. The hippocampus received a maximum dose exceeding 70 Gy in 30% of cases.

Conclusion:

Our dosimetric analysis suggests that, for patients undergoing IMRT for nasopharyngeal cancer, the hippocampus routinely receives significantly high doses.

Advances in knowledge:

The hippocampus receives a fair amount of incidental radiation during treatment for nasopharyngeal cancer. Given the importance of this structure with respect to memory and neurocognitive function, consideration should be given to identifying the hippocampus as a critical organ at risk in the IMRT optimization process.Although intensity-modulated radiotherapy (IMRT) has supplanted two-dimensional and three-dimensional radiotherapies as the standard treatment for patients with head and neck cancer, it has become increasingly clear that the generation of highly conformal plans with steep fall-off gradients may come at the expense of significant doses to non-delineated extra-target organs.¹ Owing to the anatomical proximity of many head and neck cancers to the central nervous system, studies investigating the effects of radiation exposure on specific structures in the brain responsible for neurocognitive functioning may be warranted.Located within the temporal lobes, the hippocampus is a horseshoe-shaped paired structure that is a critical component of the limbic system. Its functions relate to the formation of new memories, spatial navigation and the connection of emotions and senses, such as smell and sound, to memories. Although the tolerance of this structure to radiation has yet to be fully established, it has been hypothesized that incidental exposure to this structure may contribute to both short-term toxicity, such as lack of inhibition and disequilibrium, as well as long-term memory loss.² Thus, the purpose of this study was to conduct a dosimetric analysis in patients with nasopharyngeal cancer treated by IMRT to assess incidental exposure to the hippocampus.     

Ischaemic heart disease incidence and mortality in an extended cohort of Mayak workers first employed in 1948–1982

Objective:

Incidence and mortality from ischaemic heart disease (IHD) was studied in an extended cohort of 22,377 workers first employed at the Mayak Production Association during 1948–82 and followed up to the end of 2008.

Methods:

Relative risks and excess relative risks per unit dose (ERR/Gy) were calculated based on the maximum likelihood using Epicure software (Hirosoft International Corporation, Seattle, WA). Dose estimates used in analyses were provided by an updated “Mayak Worker Dosimetry System—2008”.

Results:

A significant increasing linear trend in IHD incidence with total dose from external γ-rays was observed after having adjusted for non-radiation factors and dose from internal radiation {ERR/Gy = 0.10 [95% confidence interval (CI): 0.04 to 0.17]}. The pure quadratic model provided a better fit of the data than did the linear one. No significant association of IHD mortality with total dose from external γ-rays after having adjusted for non-radiation factors and dose from internal alpha radiation was observed in the study cohort [ERR/Gy = 0.06 (95% CI: <0 to 0.15)]. A significant increasing linear trend was observed in IHD mortality with total absorbed dose from internal alpha radiation to the liver after having adjusted for non-radiation factors and dose from external γ-rays in both the whole cohort [ERR/Gy = 0.21 (95% CI: 0.01 to 0.58)] and the subcohort of workers exposed at alpha dose <1.00 Gy [ERR/Gy = 1.08 (95% CI: 0.34 to 2.15)]. No association of IHD incidence with total dose from internal alpha radiation to the liver was found in the whole cohort after having adjusted for non-radiation factors and external gamma dose [ERR/Gy = 0.02 (95% CI: not available to 0.10)]. Statistically significant dose effect was revealed in the subcohort of workers exposed to internal alpha radiation at dose to the liver <1.00 Gy [ERR/Gy = 0.44 (95% CI: 0.09 to 0.85)].

Conclusion:

This study provides strong evidence of IHD incidence and mortality association with external γ-ray exposure and some evidence of IHD incidence and mortality association with internal alpha-radiation exposure.

Advances in knowledge:

It is the first time the validity of internal radiation dose estimates has been shown to affect the risk of IHD incidence.     

Stereotactic body radiation therapy for a new lung cancer arising after pneumonectomy: dosimetric evaluation and pulmonary toxicity

Objective:

To evaluate the tolerance of stereotactic body radiation therapy (SBRT) for the treatment of secondary lung tumours in patients who underwent previous pneumonectomy.

Methods:

12 patients were retrospectively analysed. The median maximum tumour diameter was 2.1 cm (1–4.5 cm). The median planning target volume was 20.7 cm³ (2.4–101.2 cm³). Five patients were treated with a single fraction of 26 Gy and seven patients with fractionated schemes (3 × 10 Gy, 4 × 10 Gy, 4 × 12 Gy). Lung toxicity, correlated with volume (V) of lung receiving >5, >10 and >20 Gy, local control and survival rate were assessed. Median follow-up was 28 months.

Results:

None of the patients experienced pulmonary toxicity > grade 2 at the median dosimetric lung parameters of V₅, V₁₀ and V₂₀ of 23.1% (range 10.7–56.7%), 7.3% (2.2–27.2%) and 2.7% (0.7–10.9%), respectively. No patients required oxygen or had deterioration of the performance status during follow-up if not as a result of clinical progression of disease. The local control probability at 2 years was 64.5%, and the overall survival at 2 years was 80%.

Conclusion:

SBRT appears to be a safe and effective modality for treating patients with a second lung tumour after pneumonectomy.

Advances in knowledge:

Our results and similar literature results show that when keeping V₅, V₁₀ V₂₀ <50%, <20% and <7%, respectively, the risk of significant lung toxicity is acceptable. Our experience also shows that biologically effective dose 10 >100 Gy, necessary for high local control rate, can be reached while complying with the dose constraints for most patients.     

Ultralow-dose CT with tin filtration for detection of solid and sub solid pulmonary nodules: a phantom study

Objectives:

To investigate the diagnostic performance of advanced modelled iterative reconstruction (ADMIRE) to filtered back projection (FBP) when using an ultralow-dose protocol for the detection of solid and subsolid pulmonary nodules.

Methods:

Single-energy CT was performed at 100 kVp with tin filtration in an anthropomorphic chest phantom with solid and subsolid pulmonary nodules (2–10 mm, attenuation, 20 to −800 HU at 120 kVp). The mean volume CT dose index (CTDI_vol) of the standard chest protocol was 2.2 mGy. Subsequent scans were obtained at 1/8 (0.28 mGy), 1/20 (0.10 mGy) and 1/70 (0.03 mGy) dose levels by lowering tube voltage and tube current. Images were reconstructed with FBP and ADMIRE. One reader measured image noise; two readers determined image quality and assessed nodule localization.

Results:

Image noise was significantly reduced using ADMIRE compared with FBP (ADMIRE at a strength level of 5 : 70.4% for 1/20; 71.6% for 1/8; p < 0.001). Interobserver agreement for image quality was excellent (k = 0.88). Image quality was considered diagnostic for all images at 1/20 dose using ADMIRE. Sensitivity of nodule detection was 97.1% (100% for solid, 93.8% for subsolid nodules) at 1/20 dose and 100% for both nodule entities at 1/8 dose using ADMIRE 5. Images obtained with 1/70 dose had moderate sensitivity (overall 85.7%; solid 95%; subsolid 73.3%).

Conclusion:

Our study suggests that with a combination of tin filtration and ADMIRE, the CTDI_vol of chest CT can be lowered considerably, while sensitivity for nodule detection remains high. For solid nodules, CTDI_vol was 0.10 mGy, while subsolid nodules required a slightly higher CTDI_vol of 0.28 mGy.

Advances in knowledge:

Detection of subsolid nodules is feasible with ultralow-dose protocols.     

Evidence of dose saving in routine CT practice using iterative reconstruction derived from a national diagnostic reference level survey

Objective:

To assess the influence and significance of the use of iterative reconstruction (IR) algorithms on patient dose in CT in Australia.

Methods:

We examined survey data submitted to the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) National Diagnostic Reference Level Service (NDRLS) during 2013 and 2014. We compared median survey dose metrics with categorization by scan region and use of IR.

Results:

The use of IR results in a reduction in volume CT dose index of between 17% and 44% and a reduction in dose–length product of between 14% and 34% depending on the specific scan region. The reduction was highly significant (p < 0.001, Wilcoxon rank-sum test) for all six scan regions included in the NDRLS. Overall, 69% (806/1167) of surveys included in the analysis used IR.

Conclusion:

The use of IR in CT is achieving dose savings of 20–30% in routine practice in Australia. IR appears to be widely used by participants in the ARPANSA NDRLS with approximately 70% of surveys submitted employing this technique.

Advances in knowledge:

This study examines the impact of the use of IR on patient dose in CT on a national scale.     

Volumetric-modulated arc stereotactic body radiotherapy for prostate cancer: dosimetric impact of an increased near-maximum target dose and of a rectal spacer

Objective:

In volumetric-modulated arc therapy (VMAT) prostate stereotactic body radiotherapy (SBRT), dose coverage of the planning target volume (PTV) becomes challenging when the sparing of rectum, bladder and urethra is strictly pursued. Our current 35-Gy-in-five-fraction plans only assure 33.2 Gy to ≥95% PTV (V33.2PTV ≥ 95%). Looking for an improved V33.2PTV, increased near-maximum target dose (D_2%) and prostate–rectum spacer insertion were tested.

Methods:

For 11 patients, two VMAT plans, with D_2% ≤ 37.5 Gy (Hom) or D_2% ≤ 40.2 Gy (Het), on each of two CT studies, before or after spacer insertion, were computed. All plans assured V33.2PTV ≥95%, and <1 cm³ of rectum, bladder and urethra receiving ≥35 Gy. By hypothesis testing, several dose–volume metrics for target coverage and rectal sparing were compared across the four groups of plans. The impact of spacer insertion on the fractions of rectum receiving more than 18, 28 and 32 Gy (VXr) was further tested by linear correlation analysis.

Results:

By hypothesis testing, the increased D_2% was associated with improvements in target coverage, whereas spacer insertion was associated with improvements in both target coverage and rectal VXr. By linear correlation analysis, spacer insertion was related to the reductions in rectal VXr for X ≥ 28 Gy.

Conclusion:

A slightly increased D_2% or the use of spacer insertion was each able to improve V33.2PTV. Their combined use assured V33.2PTV ≥ 98% to all our patients. Spacer insertion was further causative for improvements in rectal sparing.

Advances in knowledge:

For VMAT plans in prostate SBRT, the distinct dosimetric usefulness of increased D_2% and of the use of spacer insertion were validated in terms of target coverage and rectal sparing.     

Optimizing the flattening filter free beam selection in RapidArc?-based stereotactic body radiotherapy for Stage I lung cancer

Objective:

To optimize the flattening filter-free (FFF) beam selection in stereotactic body radiotherapy (SBRT) treatment for Stage I lung cancer in different fraction schemes.

Methods:

Treatment plans from 12 patients suffering from Stage I lung cancer were designed using the 6XFFF and 10XFFF beams in different fraction schemes of 4 × 12, 3 × 18 and 1 × 34 Gy. Plans were evaluated mainly in terms of organs at risk (OARs) sparing, normal tissue complication probability (NTCP) estimation and treatment efficiency.

Results:

Compared with the 10XFFF beam, 6XFFF beam showed statistically significant lower dose to all the OARs investigated. The percentage of NTCP reduction for both lung and chest wall was about 10% in the fraction schemes of 4 × 12 and 3 × 18 Gy, whereas only 7.4% and 2.6% was obtained in the 1 × 34 Gy scheme. For oesophagus, heart and spinal cord, the reduction was greater with the 6XFFF beam, but their absolute estimates were <10⁻⁶%. The mean beam-on time for 6XFFF and 10XFFF beams at 4 × 12, 3 × 18 and 1 × 34 Gy schemes were 2.2 ± 0.2 vs 1.5 ± 0.1, 3.3 ± 0.9 vs 2.0 ± 0.5 and 6.3 ± 0.9 vs 3.5 ± 0.4 min, respectively.

Conclusion:

The 6XFFF beam obtains better OARs sparing and lower incidence of NTCP in SBRT treatment of Stage I lung cancer, whereas the 10XFFF beam improves the treatment efficiency. To balance the OARs sparing and intrafractional variation owing to the prolonged treatment time, the authors recommend using the 6XFFF beam in the 4 × 12 and 3 × 18 Gy schemes but the 10XFFF beam in the 1 × 34 Gy scheme.

Advances in knowledge:

This study optimizes the FFF beam selection in different fraction schemes in SBRT treatment of Stage I lung cancer.     

A pragmatic approach to determine the optimal kVp in cone beam CT: balancing contrast-to-noise ratio and radiation dose

Objectives:

To determine the optimal kVp setting for a particular cone beam CT (CBCT) device by maximizing technical image quality at a fixed radiation dose.

Methods:

The 3D Accuitomo 170 (J. Morita Mfg. Corp., Kyoto, Japan) CBCT was used. The radiation dose as a function of kVp was measured in a cylindrical polymethyl methacrylate (PMMA) phantom using a small-volume ion chamber. Contrast-to-noise ratio (CNR) was measured using a PMMA phantom containing four materials (air, aluminium, polytetrafluoroethylene and low-density polyethylene), which was scanned using 180 combinations of kVp/mA, ranging from 60/1 to 90/8. The CNR was measured for each material using PMMA as background material. The pure effect of kVp and mAs on the CNR values was analysed. Using a polynomial fit for CNR as a function of mA for each kVp value, the optimal kVp was determined at five dose levels.

Results:

Absorbed doses ranged between 0.034 mGy mAs⁻¹ (14 × 10 cm, 60 kVp) and 0.108 mGy mAs⁻¹ (14 × 10 cm, 90 kVp). The relation between kVp and dose was quasilinear (R² > 0.99). The effect of mA and kVp on CNR could be modelled using a second-degree polynomial. At a fixed dose, there was a tendency for higher CNR values at increasing kVp values, especially at low dose levels. A dose reduction through mA was more efficient than an equivalent reduction through kVp in terms of image quality deterioration.

Conclusions:

For the investigated CBCT model, the most optimal contrast at a fixed dose was found at the highest available kVp setting. There is great potential for dose reduction through mA with a minimal loss in image quality.     

Dosimetric benefits of hemigland stereotactic body radiotherapy for prostate cancer: implications for focal therapy

Objective:

Compared with standard, whole-gland (WG) therapies for prostate cancer, focal approaches may provide equivalent oncologic outcomes with fewer adverse effects. The purpose of this study was to compare organ-at-risk (OAR) dosimetry between hemigland (HG) and WG stereotactic body radiotherapy (SBRT) plans.

Methods:

Volumetric-modulated arc radiotherapy-based SBRT plans were designed to treat the left HG, right HG and WG in eight patients, using five fractions of 8 Gy. OARs of interest included the contralateral HG, rectum, urinary bladder, urethra, penile bulb and contralateral neurovascular bundle.

Results:

Rectal V_80% (the percentage of a normal structure receiving a dose of 80%) and V_90% were significantly lower with HG plans than with WG plans (median values of 4.4 vs 2.5 cm³ and 2.1 vs 1.1 cm³, respectively, p < 0.05 by Student''s t-test). Bladder V_50% was also reduced significantly in HG plans (32.3 vs 17.4 cm³, p < 0.05), with a trend towards reduction of V_100% (3.4 vs 1.3 cm³, p = 0.09). Urethral maximum dose and mean doses to the penile bulb and contralateral neurovascular bundle were also reduced significantly (42.0 vs 39.7 Gy, p < 0.00001; 13.3 vs 9.2 Gy, p < 0.05; and 40.2 vs 19.3 Gy, p < 0.00001, respectively).

Conclusion:

Targeting an HG volume rather than a WG volume when delivering SBRT can offer statistically significant reductions for all OARs. Given the large magnitude of the reduction in dose to these OARs, it is anticipated that HG SBRT could offer a superior toxicity profile when compared with WG SBRT. This is likely to be most relevant in the context of salvaging a local failure after radiation therapy.

Advances in knowledge:

The dosimetric feasibility of HG SBRT is demonstrated. When compared with WG SBRT plans, the HG plans demonstrate statistically significant and large magnitude reduction in doses to the rectum, bladder, urethra, penile bulb and contralateral neurovascular bundle, suggesting the possibility of improved toxicity outcomes with HG SBRT. This is likely to be most relevant in the context of salvaging a local failure after radiation therapy.     

Creation of a dental X-ray unit with a contactless exposure control switch

Objective:

A new dental radiographic unit (DXRU) with a contactless switch for adjusting exposure conditions and a foot-pedal exposure switch was developed to prevent bacterial or viral contamination from patients and was compared with a conventional DXRU with a panel push-button switch with respect to user friendliness.

Methods:

45 fourth-year dental school students carried out intraoral radiography using both types of DXRU. Errors regarding dose shortages of X-rays were compared and a questionnaire completed.

Results:

22 (49%) of the 45 students failed to provide the correct radiographic exposure and the number of errors was 32 for the conventional DXRU, and 4 (9%) students failed to provide the correct radiographic exposure and the number of errors was 4 for our new DXRU, at the first stage (p < 0.001). At the second stage, the number of students who failed to provide the correct radiographic exposure and the number of errors decreased to 12 and 16, respectively, for the conventional DXRU (p < 0.05). 37 (82%) of the 45 students preferred our DXRU because of its contactless switch and the push-pedal exposure switch.

Conclusions:

These data suggested that our new contactless mechanism should be used for other DXRUs for contamination control.     

The effective dose of different scanning protocols using the Sirona GALILEOS? comfort CBCT scanner

Objectives:

To determine the effective dose and CT dose index (CTDI) for a range of imaging protocols using the Sirona GALILEOS^® Comfort CBCT scanner (Sirona Dental Systems GmbH, Bensheim, Germany).

Methods:

Calibrated optically stimulated luminescence dosemeters were placed at 26 sites in the head and neck of a modified RANDO^® phantom (The Phantom Laboratory, Greenwich, NY). Effective dose was calculated for 12 different scanning protocols. CTDI measurements were also performed to determine the dose–length product (DLP) and the ratio of effective dose to DLP for each scanning protocol.

Results:

The effective dose for a full maxillomandibular scan at 42 mAs was 102 ± 1 μSv and remained unchanged with varying contrast and resolution settings. This compares with 71 μSv for a maxillary scan and 76 μSv for a mandibular scan with identical milliampere-seconds (mAs) at high contrast and resolution settings.

Conclusions:

Changes to mAs and beam collimation have a significant influence on effective dose. Effective dose and DLP vary linearly with mAs. A collimated maxillary or mandibular scan decreases effective dose by approximately 29% and 24%, respectively, as compared with a full maxillomandibular scan. Changes to contrast and resolution settings have little influence on effective dose. This study provides data for setting individualized patient exposure protocols to minimize patient dose from ionizing radiation used for diagnostic or treatment planning tasks in dentistry.