Reduction of rectal doses by removal of gas in the rectum during vaginal cuff brachytherapy

Objective

The goal of this work was to evaluate whether the volume reduction related to removal of gas in the rectum could be translated in lower doses to organs at risk (OAR) during vaginal cuff brachytherapy (VBT).

Material and methods

Fourteen pairs of brachytherapy planning CT scans derived from 11 patients were re-segmented and re-planned using the same parameters. The only difference between pairs of CTs was the presence or lack of gas in the rectum. The first CT showed the basal status and the second was carried out after gas removal with a tube. A set of values derived from bladder and rectum dose–volume histograms (DVH) and dose–surface histograms (DSH) were extracted. Moreover the cylinder position related to the patient craniocaudal axis was recorded.

Results

Rectum volume decreased significantly from 77.8?±?45 to 55.43?±?17.6 ml (p?=?0.0052) after gas removal. Such volume diminution represented a significant reduction on all rectal DVH parameters analyzed except D_25?% and D_50?%. DSH parameter results were similar to previous ones. A nonsignificant increase of the bladder volume was observed and was associated with an increase of the DVH metrics analyzed.

Conclusion

Removal of gas pockets is a simple and inexpensive maneuver that decreases rectal dose parameters on VBT, which can be translated as a better therapeutic ratio. It also suggests that other actions directed to empty the rectum could have a similar effect.     

In vivo diode dosimetry vs. computerized tomography and digitally reconstructed radiographs for critical organ dose calculation in high-dose-rate brachytherapy of cervical cancer

Purpose

To investigate the correlation between the dose predicted by the treatment planning system using digitally reconstructed radiographs or three-dimensional (3D)-reconstructed CT images and the dose measured by semiconductor detectors, under clinical conditions of high-dose-rate brachytherapy of the cervix uteri.

Patients and methods

Thirty-two intracavitary brachytherapy applications were performed for 12 patients with cancer of the cervix uteri. The prescribed dose to Point A was 7 Gy. Dose was calculated for both International Commissioning on Radiation Units and Measurements (ICRU) bladder and rectal points based on digitally reconstructed radiographs and for 3D CT images-based volumetric calculation of the bladder and rectum. In vivo diode dosimetry was performed for the bladder and rectum.

Results

The ICRU reference point and the volumes of 1, 2, and 5 cm³ received 3.6 ± 0.9, 5.6 ± 2.0, 5.1 ± 1.7, 4.3 ± 1.4 and 5.0 ± 1.2, 5.3 ± 1.3, 4.9 ± 1.1, and 4.2 ± 0.9 Gy for the bladder and rectum, respectively. The ratio of the 1 cm³ and the ICRU reference point dose to the diode dose was 1.8 ± 0.7 and 1.2 ± 0.5 for the bladder and 1.9 ± 0.6 and 1.7 ± 0.5 for the rectum, respectively.

Conclusions

3D image-based dose calculation is the most accurate and reliable method to evaluate the dose given to critical organs. In vivo diode dosimetry is an important method of quality assurance, but clinical decisions should be made based on 3D-reconstructed CT image calculations.     

Influence of brachytherapy applicators geometry on dose distribution in cervical cancer

Aim

Although the relationship between the dose delivered to adjacent organs (urinary bladder and rectum) and the frequency and severity of treatment complications has been reported in many series, the factors influencing pelvic dose distribution are not well defined. The aim of the study was to assess retrospectively the influence of the size of cervical cancer brachytherapy applicators (ovoids and uterine tandems) on pelvic dose distribution and the impact of various therapy-dependent factors on patient anatomy and on dose distribution in particular applications.

Patients and Method

The subject of this study were 356 cervical cancer patients treated with Selectron LDR as a part of their radical radiotherapy. Analysed factors included preceding external beam radiotherapy (EBRT) or brachytherapy applications, use of general anaesthesia for application and the system of pellet loading.

Results

Significant correlation was found between the size of applicators and doses to bladder, rectum and points B: larger vaginal applicators produced lower dose in bladder and rectum and higher dose in point B (all p<0.0001), longer uterine tandems produced lower dose in rectum and higher dose in point B (both p<0.0001). Significant decrease in the frequency of use of large applicators (ovoids: p<0.0001, tandems: p=0.055) and worsening of dose distribution, i.e. higher doses to critical organs (respectively: bladder p=0.0012, rectum p=0.02) and lower point B dose (p=0.0001) were observed at consecutive brachytherapy applications. Similar situation occurred in patients, who received EBRT prior to brachytherapy (ovoids: p<0.001, tandem: p=0.04, bladder dose: p=0.009, rectal dose: p=0.073, point B dose: p=0.059). Vaginal applicators were larger (p=0.026) and the dose distribution was better (bladder: p=0.023, rectum: p=0.002, point B: p=0.0001) in patients who had their insertions performed under general anaesthesia. The comparison of 2 consecutively used systems of pellet loading revealed more favourable dose distribution: lower dose for bladder (p=0.014) and higher dose for point B (p<0.0001) for the system, which utilised more sources in ovoids and in the distal part of the uterine tandem, in spite of more frequent use of smaller applicators in this group of patients. In multivariate analysis ovoid size was related to preceding external beam radiotherapy (p=0.025). Uterine tandem length was dependent on the number of preceding intracavitary applications (p<0.001) and preceding external beam radiotherapy (p=0.007). Bladder dose was related to preceding brachytherapy (p=0.011) and the pattern of pellet loading (p=0.031). Rectal dose was dependent only on the use of general anaesthesia during application (p=0.001) and point B dose was dependent on the pattern of pellet loading (p<0.001) and marginally — on the use of preceding external beam radiotherapy (p=0.06).

Conclusions

The results of this study allow for identification of treatment-related factors determining pelvic dose distribution in cervical cancer brachytherapy and may potentially enable optimisation of this distribution in particular clinical situation.     

Patient-specific dosimetry for intracavitary 32P-chromic phosphate colloid therapy of cystic brain tumours

Purpose

³²P-chromic phosphate colloid treatments of astrocytoma and craniopharyngioma cystic brain tumours in paediatric patients are conventionally based on a sphere model under the assumption of uniform uptake. The aims of this study were to determine the distribution of the absorbed dose delivered by ³²P on a patient-specific basis and to evaluate the accuracy with which this can be predicted from a pretherapy administration of ^99mTc-Sn colloid.

Methods

Three patients were treated with ³²P-chromic phosphate colloid following ^99mTc-Sn colloid administrations. Convolution dosimetry was performed using pretherapy and posttherapy sequential SPECT imaging, and verified with EGSnrc Monte Carlo radiation transport simulations. Mean absorbed doses to the cyst wall and dose–volume histograms were also calculated and compared with those obtained by the sphere model approach.

Results

Highly nonuniform uptake distributions of both the ^99mTc and ³²P colloids were observed and characterized by dose–volume histograms to the cyst wall. Mean absorbed doses delivered to the cyst wall, obtained with the convolution method, were on average 21 % (SD 18 %) and 50 % (SD 30 %) lower than those predicted by the ^99mTc distribution and the uniform assumption of the sphere model, respectively.

Conclusion

Absorbed doses delivered to the cyst wall by ³²P are more accurately predicted from image-based patient-specific convolution dosimetry than from simple sphere models. These results indicate the necessity to perform personalized treatment planning and verification for intracavitary irradiation of cystic brain tumours treated with radiocolloids. Patient-specific dosimetry can be used to guide the frequency and levels of repeated administrations and would facilitate data collection and comparison to support the multicentre trials necessary to progress this therapy.     

Comparison of IMRT and VMAT plans with different energy levels using Monte-Carlo algorithm for prostate cancer

Purpose

To make dosimetric comparisons of volumetric-modulated arc therapy (VMAT) and 7-field intensity-modulated radiotherapy (IMRT) with dynamic MLCs using the Monaco treatment planning system with Monte Carlo algorithm.

Materials and methods

Single-arc VMAT and 7-field IMRT treatment plans were compared for 12 intermediate risk prostate cancer patients treated with prostate and seminal vesicle radiotherapy. For all patients, the prescribed dose was 78 Gy delivered in 39 fractions. The dosimetric data of IMRT and VMAT plans with 6, 10 and 15 MV energies were compared. The comparison was made for target volume, organs at risk (OAR) doses, and for monitor units (MU).

Results

The normal tissue surrounding the target were lower in VMAT plans compared to IMRT plans. VMAT plans achieved lower doses to all OARs for nearly all dosimetric endpoints. VMAT plans achieved 9.4, 9.0 and 7.0 % relative decrease in MUs required for RT delivery, for 6, 10 and 15 MV energy levels, respectively. The target volume and OAR dosimetric values did not differ significantly between 6, 10 and 15 MV photon energies.

Conclusion

VMAT plans were found to be dosimetrically equivalent to IMRT plans for prostate cancer patients, with better rectum and bladder sparing and fewer MUs required.     

Comparison of different adjuvant radiotherapy approaches in childhood bladder/prostate rhabdomyosarcoma treated with conservative surgery

Background and Purpose

Multimodality treatment approaches provide high local control and satisfying overall survival (OS) for children with localized bladder and/or prostate rhabdomyosarcoma (BP-RMS). However, current strategies including surgery and conventional radiotherapy are compromised by high rates of long-term genitourinary adverse effects. Therefore, a planning study combining organ preserving surgery with three different innovative adjuvant radiotherapy approaches was performed.

Patients and Methods

A case of a 21-month-old boy with BP-RMS treated with polychemotherapy according to the CWS 2002-P protocol, prostatectomy, partial cystectomy, and adjuvant high dose rate brachytherapy (HDR-BT) was used to perform a planning study comparing HDR-BT with intensity-modulated radiotherapy (IMRT) and intensity-modulated proton therapy (IMPT) planning.

Results

All modalities provide good coverage of the target volume and spare critical normal tissues. Rectum doses could be reduced by 2/3 using IMPT and by 1/3 using BT compared to IMRT. In terms of sparing the pelvis growth plates, BT and IMPT are also superior to IMRT.

Conclusion

All modalities provide good sparing of normal tissue. BT and IMPT are superior to IMRT with regard to doses on rectum and growth plates. BT is equivalent to IMPT in adequately selected tumors.     

Zur Problematik dosimetrischer Verfahren bei der Bestimmung der Strahlendosis am Rektum in der HDR-Brachytherapie des Zervixkarzinoms

Background

Dosage measurements in brachytherapy of cervix carcinoma are usually obtained with semiconductor dosimeters intrarectally and calculated using approximation methods for additional points, e. g. chosen according to ICRU Report 38. This procedure allows minimizing organ risk dosages and avoiding side effects. This study compares actual dosage measurements with computed approximations.

Method s

In 75 applications the measured actual rectum dosage was analyzed retrospectively. Using graphic approximation methods in conjunction with the localization radiographs the expected dose values at 5 detector points of the intrarectal semiconductor dosimeter and at the ICRU rectal reference point were determined. Prospectively for 11 additional applications the expected dosage for various points within the rectum were computed during therapy planning and additionally for specific reference points corresponding to Fletcher’s lymphatic trapezoid and Chassagne’s pelvic wall points.

Results

The retrospective evaluation showed that 95% of values determined by graphic approximation methods varied by as much as ±30% from measured values. Factors causing errors were incorrect assessment of the applicator’s spatial positioning, non-orthogonal radiographs, incorrect calibration of the semiconductor probe, movement of applicator and/or probe in the time between radiograph and application. In the prospective group 95% of deviations between measured and calculated values lay within an interval of ±40% (Figure 1). Possible sources of error could be similar to those in using the graphic approximation, although the reconstruction of spatial positioning of the applicator is possibly more exact. Doses determined at the ICRU rectal reference point were 5.6±2.5 Gy in the retrospective analysis and 6.1±1.6 Gy in the prospective study (Figure 2). The standard deviation of measured values at the specific reference points was ±30%. The mean dosage distribution was nearly symmetrical with regard to the body axis, i. e. to the applicator position. Reasons for the relatively large standard deviation are e. g. difficulties in defining the reference points as well as in identifying them on the radiographs, also differences in applicator positioning.

Conclusions

The retrospective analysis led to a larger error than the prospective one. The graphic approximation method should only be utilized when computer-assisted treatment planning is not possible. Conspicuous are the differences between values obtained in computer planning and actual measured values. As these deviations cannot always be explained unequivocally, both computation and measurement should always be conducted in order to obtain an adequate survey of dosage distribution within the rectum. Computer planning offers the additional advantage of determining the dose at various other reference points.     

Target volume coverage and dose to organs at risk in prostate cancer patients

Purpose

On the basis of correct Hounsfield unit to electron density calibration, cone-beam computed tomography (CBCT) data provide the opportunity for retrospective dose recalculation in the patient. Therefore, the consequences of translational positioning corrections and of morphological changes in the patient anatomy can be quantified for prostate cancer patients.

Materials and methods

The organs at risk were newly contoured on the CBCT data sets of 7 patients so as to evaluate the actual applied dose. The daily dose to the planning target volume (PTV) was recalculated with and without the translation data, which result from the real patient repositioning.

Results

A CBCT-based dose recalculation with uncertainties less than 3?% is possible. The deviations between the planning CT and the CBCT without the translational positioning correction vector show an average dose difference of ??8?% inside the PTV. An inverse proportional relation between the mean bladder dose and the actual volume of the bladder could be established. The daily applied dose to the rectum is about 1–54?% higher than predicted by the planning CT.

Conclusion

A dose calculation based on CBCT data is possible. The daily positioning correction of the patient is necessary to avoid an underdosage in the PTV. The new contouring of the organs at risk— the bladder and rectum—allows a better appraisal to be made of the total applied dose to these organs.     

Time course of late rectal- and urinary bladder side effects after MRI-guided adaptive brachytherapy for cervical cancer

Background and purpose

To analyze the time course of late rectal- and urinary bladder complications after brachytherapy for cervical cancer and to compare the incidence- and prevalence rates thereof.

Patients and methods

A total of 225 patients were treated with external-beam radiotherapy (EBRT) and magnetic resonance imaging (MRI)-guided brachytherapy with or without chemotherapy. Late side effects were assessed prospectively using the Late Effects in Normal Tissue—Subjective, Objective, Management and Analytic (LENT/SOMA) scale. The parameters analyzed were time to onset, duration, actuarial incidence- (occurrence of new side effects during a defined time period) and prevalence rates (side effects existing at a defined time point).

Results

Median follow-up was 44 months. Side effects (grade 1–4) in rectum and bladder were present in 31 and 49 patients, 14 and 27 months (mean time to onset) after treatment, respectively. All rectal and 76?% of bladder side effects occurred within 3 years after radiotherapy. Mean duration of rectal events was 19 months; 81?% resolved within 3 years of their initial diagnosis. Mean duration of bladder side effects was 20 months; 61?% resolved within 3 years. The 3- and 5-year actuarial complication rates were 16 and 19?% in rectum and 18 and 28?% in bladder, respectively. The corresponding prevalence rates were 9 and 2?% (rectum) and 18 and 21?% (bladder), respectively.

Conclusion

Late side effects after cervical cancer radiotherapy are partially reversible, but their time course is organ-dependent. The combined presentation of incidence- and prevalence rates provides the most comprehensive information.     

The effect of bladder contrast on dose calculation in volumetric modulated arc therapy planning in patients treated for postoperative prostate cancer

Purpose

The aim of this study was to evaluate the effect of contrast agent on dose calculation in volumetric modulated arc therapy (VMAT) in the post-prostatectomy setting.

Methods and material

Ten patients were studied. Each patient received planning computed tomography (CT) images with contrast agent. All of the plans were done on virtually simulated contrast-free CT scans. The plan approved by the radiation oncologist was replicated to the contrast CT series. In both of the plans the same monitor unit was used. The doses calculated from the two plans were compared in regard to target volumes and organs at risk. A paired sample t-test was used to evaluate the differences in cumulative dose volume histogram between the two plans.

Results

We showed that the use of contrast agent may cause significant differences in dose distribution. There was a significant decrease in doses received by planning target volume (PTV70), rectum V65 Gy, rectum V40 Gy, bladder V65 Gy, penile bulb V40 Gy in plans with contrast-enhanced CT sets. The decrease in mean, maximum and minimum doses received by PTV70 also contributed to the significant decrease in conformity index.

Conclusions

Using a contrast agent at the time of CT simulation may cause significant differences in dose distribution. For this reason, the plan should always be carried out on non-contrast CT data sets to avoid additional errors in the treatment planning process.

     

Dosimetric investigation of LDR brachytherapy 192Ir wires by Monte Carlo and TPS calculations

Purpose

The aim of this study was to investigate the dose rate distribution around ¹⁹²Ir wires used as radioactive sources in low-dose-rate brachytherapy applications.

Materials and methods

Monte Carlo modeling of a 0.3-mm diameter source and its surrounding water medium was performed for five different wire lengths (1–5 cm) using the MCNP software package.

Results

The computed dose rates per unit of air kerma at distances from 0.1 up to 10 cm away from the source were first verified with literature data sets. Then, the simulation results were compared with the calculations from the XiO CMS commercial treatment planning system.

Conclusion

The study results were found to be in concordance with the treatment planning system calculations except for the shorter wires at close distances.     

Localization and quantification of the delivered dose to the spinal cord

Purpose

The goal of the present work was to localize and quantify the actual delivered dose to the cervical spinal cord (SC) during head and neck cancer (H&N) treatment.

Materials and methods

A total of 20 H&N patients treated with bilateral nodal irradiation with helical tomotherapy (HT) were analyzed. Daily MVCTs were performed for image guidance. On every second MVCT, the SC was recontoured and the delivered dose for the given treatment fraction (12 fractions per patient) was recalculated. The magnitude and localization (CT slice, spinal cord quadrant) of the Dmax to the SC on the planning CT (PLAN-Dmax) and of the actual delivered Dmax (a-Dmax) were analyzed.

Results

A systematic deviation from the PLAN-Dmax was observed in 15 out of 20 patients. Large interpatient variability of the a-Dmax in the spinal cord was noted (4.5?±?4?%). Intrapatient variability in a-Dmax was, generally, minimal (1.8?±?2.7?%). Throughout the treatment course, the higher dose was located in the same CT slices and in the same quadrants (anterior right and anterior left) for the same patient.

Conclusion

Exact localization and quantification of the change of the a-Dmax can be made for most patients by recalculating the dose on the daily IGRT-MVCTs. This could be helpful in assessing whether replanning is necessary in patients with doses close to the known tolerance doses of the spinal cord.     

Radiation dose from multidetector row CT imaging for acute stroke

Introduction

The objective of this study was to determine the radiation dose delivered during comprehensive computed tomography (CT) imaging for acute stroke.

Methods

All CT examinations performed over 18 months using our acute stroke protocol were included. Protocol includes an unenhanced CT head, CT angiography from the arch to vertex, CT perfusion/permeability, and an enhanced CT head. All imaging was acquired with a 64-MDCT. Examinations where any element of the protocol was repeated or omitted due to mistimed injection or patient motion were excluded. Dose-length products (DLP) for all components of each examination were obtained from dose reports generated at the time of acquisition, separating neck, and head calculations. Effective doses for each examination were calculated using the DLP and normalized values of effective dose per DLP appropriate for the body regions imaged.

Results

Ninety-five examinations were included. Mean DLP was 6,790.0 mGy·cm. Effective doses ranged from 11.8 to 27.3 mSv, mean effective dose of 16.4 mSv. Mean effective dose for acquisition of the unenhanced head was 2.7 mSv. Largest contribution to effective dose was the CTA with a mean effective dose of 5.4 mSv. Mean effective dose for the CT perfusion was 4.9 mSv.

Conclusion

A comprehensive CT acute stroke protocol delivered a mean effective dose of 16.4 mSv, which is approximately six times the dose of an unenhanced CT head. These high-dose results must be balanced with the benefits of the detailed anatomic and physiologic data obtained. Centers should implement aggressive dose reduction strategies and freely use MR as a substitute.     

Individualized dosimetry in patients undergoing therapy with 177Lu-DOTA-D-Phe1-Tyr3-octreotate

Purpose

In recent years, targeted radionuclide therapy with [¹⁷⁷Lu-DOTA⁰, Tyr³]octreotate for neuroendocrine tumours has yielded promising results. This therapy may be further improved by using individualized dosimetry allowing optimization of the absorbed dose to the tumours and the normal organs. The aim of this study was to investigate the feasibility and reliability of individualized dosimetry based on SPECT in comparison to conventional planar imaging.

Methods

Attenuation-corrected SPECT data were analysed both by using organ-based volumes of interest (VOIs) to obtain the total radioactivity in the organ, and by using small VOIs to measure the tissue radioactivity concentration. During the first treatment session in 24 patients, imaging was performed 1, 24, 96 and 168 h after [¹⁷⁷Lu-DOTA⁰, Tyr³]octreotate infusion. Absorbed doses in non tumour-affected kidney, liver and spleen were calculated and compared for all three methods (planar imaging, SPECT organ VOIs, SPECT small VOIs).

Results

Planar and SPECT dosimetry were comparable in areas free of tumours, but due to overlap the planar dosimetry highly overestimated the absorbed dose in organs with tumours. Furthermore, SPECT dosimetry based on small VOIs proved to be more reliable than whole-organ dosimetry.

Conclusion

We conclude that SPECT dosimetry based on small VOIs is feasible and more accurate than conventional planar dosimetry, and thus may contribute towards optimising targeted radionuclide therapy.     

Dreidimensional geplante kleinvolumige Konformationsbestrahlung des lokalen Prostatakarzinoms

Aim

Recent data have shown a significant reduction of acute side effects by means of a threedimensional planned conformal radiotherapy of carcinoma of the prostate compared to treatment techniques used before. Theoretically, an optimized field coverage of the planning target volume should result in a reduction of treated bladder and rectum volumes. We studied the effects of individualized blocks on treatment volumes, planning target volumes, irradiated bladder and rectum volumes on basis of threedimensional treatment planning by means of beam’s-eye-view technique.

Patients and Method

We compared dose-volume-histograms of 2 different planning models, a (fictitious) open 4-field-box-technique and a technique with conformal blocked fields designed from the beam’s-eye view display (prescribed dose 66 Gy, daily single fraction 2 Gy). Plans of 115 patients with localized prostate cancer treated from January 1994 to February 1996 were analyzed.

Results

Using individualized fields treatment volume (covered by the 90%-isodose) was reduced by 23% on the average in comparison to the planning model without blocks. The averaged difference of treated volume and planning target volume, as a grade of efficiency of conformation, was reduced by 38% (496 cm³ vs. 303 cm³) using individualized blocks. 23% of the treated bladder volume and 13% of the treated rectum volume had been saved on the average. Nevertheless at least 11.5% of the bladder volume and 27.6% of the contoured rectum volume were treated with the prescribed dose (66 Gy=100%).

Conclusions

The comparison of dose-volume-histogram-data showed that especially high dose volumes of organs at risk had been saved by means of individualized blocks created from the beam’s-eye-view. The blocks did not affect the dose distribution of the planning target volume adversely. Consequently the impact of these data on the extent of side effects and local tumor control has to be proven.     

Radiation-induced bilateral optic neuropathy in cancer of the nasopharynx

Case Report

A case history of unanticipated radiation-induced bilateral optic neuropathy, 18 months after induction chemotherapy and radiation therapy for a locally advanced nasopharyngeal carcinoma, is presented. Retrospective reanalysis of the radiation therapy technique, with emphasis on the doses received by the optic pathway structures, was performed. These re-calculations revealed unexpectedly high doses in the range 79 to 82 Gy (cumulative external and brachytherapy dose) at the level of the optic nerves, which explained the observed radiation injury.

Conclusion

Routine implementation of computed tomography for 3D dose planning purposes is therefore advocated. Review of the current literature confirms the importance of 3D dose planning in avoiding this complication and highlights the role of MRI in establishing the diagnosis of radiation-induced optic neuropathy.     

Pelvic Ewing sarcomas

Purpose

The goal of the present work was to assess the potential advantage of intensity-modulated radiotherapy (IMRT) over three-dimensional conformal radiotherapy (3D-CRT) planning in pelvic Ewing’s sarcoma.

Patients and methods

A total of 8 patients with Ewing sarcoma of the pelvis undergoing radiotherapy were analyzed. Plans for 3D-CRT and IMRT were calculated for each patient. Dose coverage of the planning target volume (PTV), conformity and homogeneity indices, as well as further parameters were evaluated.

Results

The average dose coverage values for PTV were comparable in 3D-CRT and IMRT plans. Both techniques had a PTV coverage of V₉₅ >?98?% in all patients. Whereas the IMRT plans achieved a higher conformity index compared to the 3D-CRT plans (conformity index 0.79?±?0.12 vs. 0.54?±?0.19, p?=?0.012), the dose distribution across the target volumes was less homogeneous with IMRT planning than with 3D-CRT planning. This difference was statistically significant (homogeneity index 0.11?±?0.03 vs. 0.07?±?0.0, p?=?0.035). For the bowel, D_mean and D_1%, as well as V₂ to V₆₀ were reduced in IMRT plans. For the bladder and the rectum, there was no significant difference in D_mean. However, the percentages of volumes receiving at least doses of 30, 40, 45, and 50 Gy (V₃₀ to V₅₀) were lower for the rectum in IMRT plans. The volume of normal tissue receiving at least 2 Gy (V₂) was significantly higher in IMRT plans compared with 3D-CRT, whereas at high dose levels (V₃₀) it was significantly lower.

Conclusion

Compared to 3D-CRT, IMRT showed significantly better results regarding dose conformity (p?=?0.012) and bowel sparing at dose levels above 30 Gy (p?=?0.012). Thus, dose escalation in the radiotherapy of pelvic Ewing’s sarcoma can be more easily achieved using IMRT.     

The incidence of radioepidermitis and the dose-response relationship in parotid gland cancer patients treated with 125I seed brachytherapy

Background

We studied the incidence and dose–response relationship of radioepidermitis in parotid gland carcinoma patients treated with [¹²⁵I] seed brachytherapy in the hopes of designing an optimized pre-implant treatment plan that would reduce the incidence and severity of radioepidermitis in patients receiving this therapy.

Patients and methods

Between January 2007 and May 2010, 100 parotid gland cancer patients were treated postoperatively with [¹²⁵I] seed brachytherapy. The matched peripheral dose (MPD) was 80–140 Gy, and [¹²⁵I] seed activity was 0.7–0.8 mCi. The mean dose delivered to the skin was calculated in the post-implant CT on day 0 following implantation. Grades of acute and late dermatitis were evaluated at 2, 6, 12, and 18 months post-implantation.

Results

Most patients experienced grade 0–2 acute and late skin side effects (86 and 97?%, respectively), though a small subset developed severe complications. Most grade 1–3 effects resolved within 6 months of implantation, though some grade 1–3 effects and all grade 4 effects remained unchanged throughout the 18-month follow-up period. Grade 3 and 4 effects were most prominent (75 and 25?%, respectively) with doses of 110–140 Gy; doses higher than 140 Gy produced only grade 4 effects.

Conclusion

[¹²⁵I] seed brachytherapy produced acceptable levels of acute and late radioepidermitis with a good clinical outcome. A mean dose under 100 Gy delivered to the skin was safe, though doses of 110–140 Gy should be given with caution and extra monitoring; doses greater than 140 Gy are dangerous and likely to produce grade 4–5 effects.

     

A dose-effect correlation for radioiodine ablation in differentiated thyroid cancer

Purpose

The aim of this study was to determine the range of absorbed doses delivered to thyroid remnants, blood, and red marrow from fixed administrations of radioiodine and to ascertain whether the success of ablation is more dependent on these absorbed doses than on the administered activity.

Methods

Twenty-three patients received 3,000 MBq radioiodine following near-total thyroidectomy. The maximum absorbed dose to remnants was calculated from subsequent single photon emission tomography scans. Absorbed doses delivered to blood and red marrow were calculated from blood samples and from whole-body retention measurements. The protein bound iodine (PBI) was also calculated.

Results

Maximum absorbed doses to thyroid remnants ranged from 7 to 570 Gy. Eighteen of the 23 patients had a successful ablation. A significant difference was seen between the absorbed doses delivered to thyroid remnants, blood, and red marrow for those patients that had a successful ablation compared to those with a failed ablation (p?=?0.030, p?=?0.043 and p?=?0.048, respectively). The difference between the PBI values acquired at day 1 and day 6 were also indicative of response (p?=?0.074).

Conclusions

A successful ablation is strongly dependent on the absorbed dose to the thyroid remnant. Dosimetry-based personalized treatment can prevent both sub-optimal administrations, which entails further radioiodine therapy, and excessive administration of radioactivity, which increases the potential for radiation toxicity.