Patient teaching in radiation therapy may include restrictions on applying skin products owing to concerns that the presence of such materials may increase skin dose. These restrictions may create unnecessarily complicated and conflicting self-care instructions.

To determine what thickness of skin product is necessary to produce a clinically meaningful dose increase to the skin, and provide recommendations for evidence-based patient instructions.

Dosimetric measurements and Monte Carlo simulations were used to calculate skin dose under 0–1·5 mm thicknesses of two common classes of skin product for a variety of treatment geometries. The thickness of product required to produce a clinically significant dose increase to the skin was determined.

The thickness of product required to create a clinically meaningful dose increase was >0·7 mm for 10 × 10 cm2 fields and >1·5 mm for 1 × 1 cm2 fields. A typical application of product would be only 0·3 mm.

It seems unrealistic to anticipate patients using sufficiently large quantities of skin product to be of clinical concern. We therefore recommend that there are no dosimetric reasons to restrict the use of these types of skin products during radiation therapy for common treatment scenarios.

The objective was to determine diode characteristics before actual dose verification on human phantom and patients.

The reliability and stability of equipment, signal stability, precision, dose response linearity, field flatness, perturbation of radiation dose, plastic to water conversion factor (Kpl), ionisation chambers (ICs) and diode calibration were determined. Correction factors for tray (CFtray), wedge (CFwedge), field size (CFFS), SSD (CFSSD), angle (CFangle) and block (CFblock) were found. Patient dose monitor, Isorad diode (n-type) and IC (PTW Frieburg), Co-60 unit (Theratron), ATOM Adult male human phantom (Model 701-D, CIRS) were used.

Good signal stability, precise data, and linear dose response, variation of 0·500% and 5·000% in field flatness and perturbation tests, respectively, were noted. Kpl was 1·006 for IC PTW Frieburg TW30013, 0114. The diode calibration factor was 0·989. CFtray, CFFS, CFSSD, CFangle, CFblock were 1·001, 1·001, 0·997, 1·006 and 0·990, respectively. CFwedge were 1·024, 1·030 and 1·038 for 30°, 45° and 60° wedges, respectively. The verification of above correction factors (CFs) on Nasopharynx and lung of human phantom was also done.

The aim of this study was to assess the efficacy of IMRT with concomitant boost simultaneous integrated boost-intensity modulated radiotherapy (SIB-IMRT) compared with conventional radiation in the setting of sequential chemoradiotherapy (induction chemoradiotherapy(ICRT)) for patients with advanced oropharynx cancer (OPC).

A single-institutional retrospective review was conducted on 84 patients (conventional radiation, n = 36; SIB-IMRT, n = 48) with stage III and IV OPC, who underwent definitive ICRT from 2002 to 2012. The study endpoints included overall survival (OS) and locoregional control (LRC).

The median follow-up of the matched cohorts resulted similar (30 months for 3D-radiation technique versus 37 months for IMRT), and baseline characteristics were generally balanced between the two groups. However, patients managed with conventional radiation were less likely to have positron emission tomography-computed tomography (PET-CT) for staging and to receive induction chemotherapy with TPF. A multivariate Cox proportional hazard model showed that OS and LRC were associated with several known prognostic factors, along with radiation modality (SIB-IMRT versus conventional radiation, hazard ratio 0·27, p = 0·004; hazard ratio 0·31, p = 0·006; for OS and LRC, respectively).

The adoption of SIB-IMRT versus conventional radiation may produce a clinical benefit in OS and LRC among patients receiving ICRT for advanced OPC.

Current guidelines for image-guided cervical cancer brachytherapy planning recommend both computed tomography (CT) and magnetic resonance imaging (MRI) for adequate visualisation of the applicator and soft tissues, respectively. MRI-only planning would be ideal as it would save time within the patient pathway and avoid the concomitant CT exposures. However, applicator visualisation on MRI is usually achieved using fluid-filled fiducial marker tubes, which can be awkward to use and suffer from unwanted air bubble artefacts. Therefore, a new fiducial-free imaging technique was developed.

A dual echo time (TE) turbo spin echo sequence was used, at 1·5 T, to provide both T2-weighted images (100 ms TE) for tissue visualisation and strongly proton density-weighted images (17 ms TE) for improved applicator visualisation. In-house software was used to automatically segment the applicator in the short TE images (using Otsu's method) and transfer the information to the long TE images to provide a single fused dataset.

The method was evaluated successfully using titanium applicators in three patient cases and using a plastic applicator in a tissue-equivalent gel phantom.

The dual-echo technique provides a simple and efficient method for improving the visualisation of brachytherapy applicators in cervical cancer MRI images without the need for marker tubes.

Patients having a course of radiotherapy (RT) must be appropriately immobilised for stability and accuracy. Having opened a new cancer service in June 2009 and commenced treating lower gastrointestinal cancers in 2010, a prone belly board device (BBD) was introduced as the standard radiotherapy immobilisation. A training package was created to aid clinical skills retention of therapeutic radiographers and manage setup quality. Setup reproducibility using the BBD was retrospectively assessed with electronic portal image (EPI) verified geometric displacements as the main outcome measure both before and after the introduction of training.

Twenty retrospective Pinnacle computed tomography-planned patients and their geometric displacements on treatment were evaluated between 2010 and 2011—ten prior to (Patient Group A) and ten following training (Patient Group B). The only inclusion criterion was that patients were immobilised for RT on the Medtec ContouraTM carbon fibre BBD. Patients were prone and were treated to 45–50·4 Gy in 25–28 fractions on a 6–10 MV LinAc equipped with EPI. Reproducibility was assessed by comparing geometric measurement of the bony pelvis on the Pinnacle digitally reconstructed radiograph (DRR) with an EPI captured at day 0, 1, 2 and weekly during treatment for each patient. Systematic and random errors were analysed with respect to the average geometric displacement with standard deviation per patient between the Pinnacle DRR and the EPI.

The age range was 41–77 years and there were 15 male and five female patients with diagnosed rectal cancers (T3–T4, N0–N2, M0). Three hundred and seventy one images were analysed. An improvement in population systematic and random error was most notable in the superior–inferior direction (Patient Group A Σpop = 3·1 mm, σpop = 3·6 mm to Patient Group B Σpop = 2·0 mm, σpop = 2·3 mm, respectively).

There is evidence that the use of the BBD is more reproducible when accompanied by a task-specific training package. Based on the results of this study, further work will be carried out on training standardisation for patient positioning with a BBD for reducing systematic and random geometric displacements.

To compare the outcome among patients with invasive bladder cancer treated with cystectomy alone with outcome among those treated with combined-modality treatment in a randomised phase III trial.

Patients with histologically confirmed invasive non-metastatic bladder cancer T2-3, N0 and M0 were randomly assigned to two arms: Arm 1: of which all patients underwent radical cystectomy (RC) alone; and Arm 2, of which all patients were subjected to maximal transurethral resection of bladder tumour, followed 2 weeks later by combined chemoradiotherapy. The whole pelvis received 46 Gy in 23 fractions over 4·5 weeks. Chemotherapy was administered concomitantly with radiotherapy with: cisplatin 70 mg/m2 q. 3 weeks and Gemcitabine 300 mg/m2 D 1, 8 and 15 q. 3 weeks for two cycles. Patients who had complete response were shifted to phase II treatment: 20 Gy/10 fractions/2 weeks to the bladder. Patients with residual tumour underwent RC.

Of the 80 patients assigned Arm 2, a visibly completed transurethral resection of the bladder tumour was possible in 48 patients (60%). Phase I of combined chemoradiotherapy (CCRT) was accomplished in 74 patients. Post-induction urologic evaluation revealed no evidence of disease in 62 patients (83·8%) and residual disease in 12 patients (16·2%). Phase II of CCRT was completed in 58 of the 62 patients. The median follow-up for all patients is 27 months (range: 4–49). The 3-year overall survival (OS) for the combined-modality group and for the surgery group were 61 and 63%, respectively (p = 0·425), whereas the disease-specific survival (DSS) for each group was 69 and 73%, respectively (p = 0·714). The 3-year OS with bladder preservation for Arm 2 patients was 50%.

Multivariate analysis for the whole series showed that tumour stage and performance status (PS) were the only factors independently associated with DSS, although PS was the only factor independently associated with OS. In addition, residual disease after transurethral resection of the bladder tumour in Arm 2 patients was independently associated with both DSS and OS.

Acute toxicity was moderate and most of the late toxicities were grade 2 with no grade 4 toxicity and no treatment-related deaths, none required cystectomy for bladder contraction.

This study demonstrates that trimodality bladder-preserving approach represents a valid alternative for suitable patients. The OS and DSS rates of patients treated with trimodality bladder-preserving protocol are comparable to the results reported on patients treated with immediate radical cystectomy.

A pilot study was undertaken to find significance of vascular endothelial growth factor (VEGF) and cancer antigen (CA 15.3) in breast cancer patients.

Total 70 patients with breast cancer were divided into triple negative breast cancer (TNBC) and non-TNBC depending on oestrogen receptors, progesterone receptors or HER-2/neu receptors status. Serum CA 15.3 and VEGF levels were evaluated with enzyme-linked immunosorbent assay at the time of diagnosis and were correlated with age, tumour size and stage of the disease in both the groups. Spearman's test was used to find the correlation.

VEGF levels were found to be >400 pg/ml in 27 patients, 19 (54·33%) of them were TNBC and only 8 (22·87%) non-TNBC. Mean values of the VEGF were, 784·34 pg/ml in TNBC and 334·60 pg/ml non-TNBC patients, respectively. CA 15.3 level was found to be higher in non-TNBC group (60·72 U/ml) than in TNBC group (45·24 U/ml). In all patients significant correlation was found between serum CA 15.3 level and tumour size and stage of the disease. In non-TNBC patients significant correlation was seen between CA 15.3 values and stage of the disease, but VEGF had no correlation with any of the disease parameters. In TNBC patients, there was no correlation between CA 15.3 level and any of the disease parameters but VEGF showed a significant correlation with both tumour size and stage of the disease.

Expression profile of VEGF was high in TNBC than non-TNBC patients. VEGF serves to be a better biomarker as compared with CA 15.3 in TNBC patients.

Geometric uncertainties limit the accuracy of three-dimensional conformal radiotherapy treatments. This study aims to evaluate typical random and systematic set-up errors and analyse the impact of no action level (NAL) correction protocol on systematic set-up errors and clinical target volume (CTV)–planning target volume (PTV) margins.

A total 668 pairs of orthogonal electronic portal images were compared with digitally reconstructed radiographs from computed tomography planning scans for 100 patients consecutively treated during 2011. Patients were divided into groups depending on the treated anatomical region. Patient-specific and population random and systematic set-up errors were calculated. Impact of application of NAL correction protocol on systematic set-up errors and CTV–PTV expansions were evaluated.

Population set-up errors resulted from about 1 mm in head and neck to 2–3 mm in prostate, rectum, lung, breast and gynaecological districts. Patient-specific systematic set-up errors were higher for breast and gynaecological districts and application of NAL correction protocol gave significant reductions, even higher than 30%. Calculated CTV–PTV margins ranged from 10 mm on left–right direction for prostate to 20 mm on superior–inferior direction for lung.

Set-up errors resulted reasonably controlled and application of NAL correction protocol could further improve the level of accuracy. However, the NAL application alone did not seem to add any substantial benefit on CTV–PTV total margins without the adoption of corrective strategies to reduce other important uncertainties limiting accuracy of three-dimensional conformal radiotherapy.

The main aim was to use pre-calculated correction factors and calibration factors for measurement of accuracy of dose delivery before implementation of such in vivo dosimetry on real patients visiting for first radiation treatment. These factors were verified by generating the most common treatment plans on human phantom except for breast and colon using cobalt-60 unit.

Six treatment plans were generated, i.e. nasopharynx, bladder, prostate, brain, larynx and lung of human phantom, total 18 fields were planned keeping in view the correction factors which are to be verified. MULTIDATA Decision Support System 2.5, Shimadzu simulator, Isorad diode-n type, electrometer patient dose monitor and ATOM Adult male human phantom were used.

For 18 fields, the dose delivery was accurate in the range 0·29–6·74%. The deviation between measured and expected doses to nasopharynx, lung, bladder, prostate, brain and larynx cases of human phantom ranged from 1·44–3·89%, 0·29–0·54%, 0·44–6·18%, 0·54–5·16%, 0·33–4·90%, 5·58–6·74%, respectively. In 30 palliative patient cases, the first radiation treatment was also monitored. The accuracy of dosimety ranged from 1·05% to 5·35%. This study is helpful to identify areas of improvement in treatment of patients like quality control/quality assurance (QA) of treatment planning system, beam data modifications, machine repair maintenance, QA audit in radiotherapy.

To compare the contours and dose volume histograms (DVH) parameters of the high-risk clinical target volume (HRCTV) contoured on computed tomography (CT) using clinical findings at brachytherapy, clinical findings at brachytherapy with magnetic resonance imaging (MRI) at diagnosis and HRCTV defined on MRI at brachytherapy in cervical cancer patients.

Fifteen patients undergoing MRI-guided image-based brachytherapy underwent both CT and MRI after applicator insertion. Two sets of contours were defined on CT. In the first set, the HRCTV was defined with the help of clinical findings at brachytherapy (CT-HRCTV). In the second set, HRCTV was defined with MRI at diagnosis and clinical findings at brachytherapy (CT-HRCTVdmri). This was compared with the HRCTV defined on MRI at brachytherapy (MR-HRCTV). The doses to the organs at risk (OARs) were compared for CT and MRI.

A significant overestimation of the maximum width and width at point A was observed for CT-HRCTV (p −0·00; 0·00) and CT-HRCTVdmri (p −0·03; 0·01), respectively. The height was underestimated with CT-HRCTV in patients with intrauterine disease extension. For a single fraction, the mean difference in the D90 for the CT contours was <1 Gy. The doses to the OARs were comparable.

CT may be an alternative when facilities for MRI image-based brachytherapy are lacking, provided at least one MRI is available before brachytherapy.

The aim of this work was to determine if volumetric modulated arc therapy (VMAT) plans, created for constant dose-rate (cdrVMAT) delivery are a viable alternative to step and shoot five-field intensity modulated radiation therapy (IMRT).

The cdrVMAT plans, inverse planned on a treatment planning system with no solution to account for couch top or rails, were created for delivery on a linear accelerator with no variable dose rate control system. A series of five-field IMRT and cdrVMAT plans were created using dual partial arcs (gantry rotating between 260° and 100°) with 4° control points for ten prostate patients with the average rectal constraint incrementally increased. Pareto fronts were compared for the planning target volume homogeneity and average rectal dose between the two techniques for each patient. Also investigated were tumour control probability and normal tissue complication probability values for each technique. The delivery parameters [monitor units (MU) and time] and delivery accuracy of the IMRT and VMAT plans were also compared.

Pareto fronts showed that the dual partial arc plans were superior to the five-field IMRT plans, particularly for the clinically acceptable plans where average rectal doses were less for rotational plans (p = 0·009) with no statistical difference in target homogeneity. The cdrVMAT plans had significantly more MU (p = 0·005) but the average delivery time was significantly less than the IMRT plans by 42%. All clinically acceptable cdrVMAT plans were accurate in their delivery (gamma 99·2 ± 1·1%, 3%3 mm criteria).

Accurate delivery of dual partial arc cdrVMAT avoiding the couch top and rails has been demonstrated.

During radiation therapy, unwanted scatter to healthy tissues outside the target field may occur. Children and adolescents are more sensitive to radiation injury, and the thyroid gland is particularly susceptible to these effects.

To assess acute changes in thyroid function and volume in children and adolescents undergoing radiotherapy for a variety of non-thyroid cancers.

Thirty-one children and adolescents underwent radiation therapy of various body areas in which the thyroid was not included. Thyroid-stimulating hormone (TSH), thyroxine (T4), free thyroxine (fT4), triiodothyronine (T3), anti-thyroperoxidase antibodies and thyroglobulin were measured before, on the last day and at 1 and 3 months after the end of radiotherapy. Ultrasound scans were taken and 6- and 24-hour 131I uptake was measured before and after treatment. The scattered dose to the thyroid region was estimated with a treatment planning system or measured with thermoluminescent dosimeters.

The median radiation dose scattered to the thyroid was 296·6 cGy (IQR 16·7–1,709·0). Levels of TSH (p = 0·575), T4 (p = 0·950), fT4 (p = 0·510), T3 (p = 0·842), thyroglobulin (p = 0·620) and anti-thyroid peroxidase antibodies (p = 0·546) were statistically similar at all four time points. There were no differences between pre- and post-radiotherapy thyroid volume and 131I uptake (p = 0·692 and 0·92, respectively).

More sensitive methods may be required to ascertain whether acute injury to the follicular epithelium occurs with lower radiation doses scattered to the thyroid.

We propose to use the PTV dose–volume factor (PDVF) to evaluate treatment plans of prostate volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT).

PDVF was used to compare the variation of planning target volume (PTV) coverage between VMAT and IMRT because of weight loss of patient.

VMAT and IMRT plans of five patients (prostate volume = 32–86·5 cm3) using the 6 MV photon beams were created with the external contour reduced by depths of 0·5–2 cm to reflect the weight loss. Moreover, integral doses (volume integral of the patient dose) and prostate tumour control probability (TCP) were calculated.

We found that reduced depth resulted in PDVF decreasing 0·03 ± 4·7 × 10−4 (VMAT) and 0·04 ± 9·7 × 10−3 (IMRT) per cm for patients. The decrease of PDVF or degradation of PTV coverage was found more significant in IMRT plans than VMAT with patient size reduction. The integral dose did not change significantly between VMAT and IMRT, while the prostate TCP increased with an increase of reduced depth.

We concluded that PDVF can be successfully used to evaluate the variation of PTV coverage because of weight loss of patient in prostate VMAT and IMRT. Degradation of PTV coverage in prostate VMAT is less significant than IMRT regarding patient size reduction.

In the era of dose escalation for localised prostate cancer, the dose–volume histogram (DVH) is integral to the assessment of rectum and bladder dose constraints. However, reliance on a single planning computerised tomography-based (P-CT) dose distribution may not account for variations in delivered dose that results from deformation of the prostate, bladder and rectum. This study uses cone-beam CT (CBCT) datasets from five patients to investigate the concordance between the dose prediction from the initial treatment plan and the dose delivered during treatment.

The intensity-modulated radiation therapy distribution used for treatment was superimposed on alternate day CBCT images for each patient. Dose metrics and absolute volumes for the prostate, rectum and bladder were extracted from the CBCT-based DVH. Differences in dose and volumes were compared with the P-CT values, and significance was tested using the Wilcoxon signed-rank test.

For all five case studies, the prostate dose coverage on CBCT plans was lower than predicted with an average reduction of 3% in mean dose. Significant differences in rectal volumes and dose were observed in two out of five and four out of five patients, respectively. Reductions in bladder volume and subsequent increases in dose were observed for three out of five patients.

The DVH from P-CT was unable to consistently predict the dose delivered to the bladder and rectum. The current bowel and bladder preparation protocols used at our institution did not eliminate variation in bladder and rectum volumes for the five patients included in this study.

The optimal delivery of radiation therapy to achieve maximum tumour cell kill while limiting damage to normal tissues underlies any radiation therapy treatment protocol. The biological effectiveness of radiation therapy is closely related to cellular reproductive activity. The scheduling of dose fraction to a time where actively dividing cells are at their most radiosensitive stage (RS) has potential to enhance therapeutic efficacy.

A prime number is a natural number >1 whose only divisors are 1 and the number itself.

We propose that the use of prime numbers in the scheduling of radiotherapy treatments could maximise biological effectiveness by facilitating the irradiation of the greatest number of cells at their most RS stage, and ultimately improve the therapeutic ratio of radiation therapy.

The theoretical clinical implementation of this concept into the scheduling of radiation therapy is discussed.

To verify the accuracy of two common absorbed dose calculation algorithms in comparison to Monte Carlo (MC) simulation for the planning of the pituitary adenoma radiation treatment.

After validation of Linac's head modelling by MC in water phantom, it was verified in Rando phantom as a heterogeneous medium for pituitary gland irradiation. Then, equivalent tissue-air ratio (ETAR) and collapsed cone convolution (CCC) algorithms were compared for a conventional three small non-coplanar field technique. This technique uses 30 degree physical wedge and 18 MV photon beams.

Dose distribution findings showed significant difference between ETAR and CCC of delivered dose in pituitary irradiation. The differences between MC and dose calculation algorithms were 6.40 ± 3.44% for CCC and 10.36 ± 4.37% for ETAR. None of the algorithms could predict actual dose in air cavity areas in comparison to the MC method.

Difference between calculation and true dose value affects radiation treatment outcome and normal tissue complication probability. It is of prime concern to select appropriate treatment planning system according to our clinical situation. It is further emphasised that MC can be the method of choice for clinical dose calculation algorithms verification.

Recurrence is frequent in surgically treated non-functioning pituitary adenomas (NFPA). The use of radiation therapy (RT) to prevent recurrence has to be weighted against the potential side effects, particularly, hypopituitarism. Our objective was to evaluate the efficacy and safety of RT in postoperative patients with NFPA with adenoma remnant.

The 3- and 5-year outcome of 51 patients with NFPA with a remnant after surgery that received RT (cases) was compared with that of 61 subjects who did not receive RT (controls). Cases and controls were matched for postoperative remnant size, cavernous sinus invasion, age and gender.

Tumour volume decreased in the radiated group from a median of 1,601 mm3 to 816 mm3 after 5 years of follow-up (p = 0·01, 50% tumour volume reduction). In the non-radiated controls median tumour volume decreased at 3 years but increased again after 5 years (baseline 1,415 mm3, 5 years 1,204 mm3, p = 0·93). Recurrence rate was 4% for the radiated group and 29% for the controls (OR 0·10, 95% CI 0·01–0·04, p = 0·02). Although pituitary hormone deficiencies at baseline were more prevalent in the radiated group, after 5 years, both groups showed a significant worsening of pituitary function. No RT-related side effects were recorded.

Postoperative RT is effective in preventing tumour regrowth in NFPA patients with postoperative remnants. The fact that hypopituitarism is highly prevalent even in non-radiated patients should allow a more generalised use of this treatment modality.

In radiation therapy, to spare normal surrounding tissues, either Multileaf Collimators or Cerrobend blocks are used.

The current study focuses on the relative dose distribution under the areas protected by Cerrobend blocks.

A dual-energy linear accelerator and a Cobalt-60 machine were utilised as radiation sources. Several blocks were designed using commercially available materials to shield radiation fields. The relative dose distribution was then evaluated using extended dose range 2 films.

Results showed that the dose distribution under protected areas depends on several parameters including the width and height of protecting blocks, incident photon beam energy, radiation field size and source to surface distance. An increase in Cerrobend block height from 80 to 95 mm significantly decreases the dose at the protected areas.

An increase in the block width and photon energy decreases the relative dose deposition at the protected area. However, electron and neutron contaminations should also be taken into consideration.

Due to the discontinuation of the widely used low-dose rate (LDR) Caesium afterloader units, many centres in the past 10 years have moved from LDR Selectron treatments to Iridium 192 afterloaders. While the majority of UK centres have opted for high-dose rate (HDR) units, the Christie have invested in two pulsed dose rate (PDR) afterloaders alongside a move to full 3D-planned gynaecological brachytherapy.

To share the experience and learning curve involved in the implementation of a 3D-guided PDR brachytherapy service.

The specific logistical and practical challenges of implementing a PDR service are discussed alongside the more general challenges of implementing 3D-guided magnetic resonance (MR) based brachytherapy. A multidisciplinary approach was undertaken to streamline the patient pathway and give all disciplines a forum to discuss service improvements and resolve problems.

The lessons learned throughout this experience can inform the decisions of departments that may wish to implement a PDR service or indeed a 3D image-guided HDR brachytherapy service in the future. The focus on the utilisation of lean principles to the patient pathway, improved multidisciplinary working and enhancing service efficiency is of interest to all centres.

To quantify the amount of inter-fractional pitch for rectal carcinoma patients, to investigate the dosimetric impact of pitch on the target volume and critical structures and to determine a tolerance where no pitch correction is required.

Daily pre-treatment images of rectal carcinoma patients were analysed to determine the residual pitch compared with the computed tomography (CT) planning scan. The dosimetric impact of pelvic rotation was modelled. The dose coverage of the clinical target volume (CTV) and small bowel were evaluated using dose–volume histograms.

Pre-treatment images had a mean of 0·27° and standard deviation was 2·23°. The volume of CTV receiving 95% of the prescription dose altered by 0·1% when up to ±10° of pitch was simulated.

No clinically significant change in CTV coverage was found (when ±10° of pitch was simulated). A tolerance of ±10° of pitch has been implemented for rectal carcinoma patients treated with three-dimensional conformal radiotherapy in our institution, when daily pre-treatment imaging with a zero action threshold for translational shifts is used.