Motion-weighted target volume and dose-volume histogram: A practical approximation of four-dimensional planning and evaluation

Background and purpose

In ITV-based 3D-planning, the information of volume occupancy versus respiratory phase is not utilized. We propose a motion-weighted CTV (mwCTV) delineation method, which carries some 4D-information into planning. This method allows plan optimization based on occupancy-weighting and generation of motion-weighted DVH (mwDVH) that approximate the DVHs of full 4D-dose accumulation.

Material and methods

Occupancy information from contours in 4D-CT is incorporated in the mwCTV generation. Higher-occupancy volumes receive higher dosimetric priority in planning. The temporally-weighted mwCTV is converted to a spatially-weighted mwCTV incorporating the temporal-weighting in mwDVH generation using the 3D-dose distribution. The mwDVHs were compared with DVHs of deformable-image-registration (DIR)-based 4D-dose accumulation and 3D-method for 10 cases.

Results

For all the cases, the mwDVH curves are closer to the 4D-calculated DVH than the 3D-DVHs are, indicating a better approximation of the 4D-DVH. The 70 Gy-covered percentage-CTV volume differed by −2.8% ± 0.8% between 3D and 4D, and 0.3% ± 0.7% between mwDVH and 4D-methods. The mean RMS values of the percentage-volume differences for the 4D-3D is 1.7 ± 1.1, while for the 4D-mwDVH is 0.4 ± 0.3.

Conclusion

The mwCTV and mwDVH method, which is simple in implementation and does not require DIR, is a practical approximation of DIR-based 4D-planning and evaluation.     

Bowel exposure in rectal cancer IMRT using prone, supine, or a belly board

Purpose

To investigate bowel exposure using prone, supine, or two different belly boards for rectal cancer intensity modulated RT plans using a full bladder protocol.

Methods and materials

For 11 volunteers four MR scans were acquired, on a flat table in prone, supine, and on two different belly boards (IT-V Medizintechnik GmbH® (BB1) and CIVCO® (BB2)), using a full bladder protocol. On each scan a 25 × 2 Gy IMRT plan was calculated.

Results

BB2 led to an average bowel area volume reduction of 20-30% at any dose level compared to prone. BB1 showed a smaller dose reduction effect, while no differences between prone and supine were found. Differences between BB2 and prone, supine or BB1 were significant up to a level of respectively, 45, 35, and 30 Gy. The reducing effect varied among individuals, except for the 50 Gy region, where no effect was found. An increase in bladder volume of 100 cc led to a significant bowel area V15 reduction of 16% independent of scan type.

Conclusions

In the low and intermediate dose region a belly board still attributes to a significant bowel dose reduction when using IMRT and a full bladder protocol. A larger bladder volume resulted in a significant decreased bowel area dose.     

Determining DVH parameters for combined external beam and brachytherapy treatment: 3D biological dose adding for patients with cervical cancer

Purpose

To compare two methods of DVH parameter determination for combined external beam and brachytherapy treatment of cervical cancer.

Materials and methods

Clinical treatment plans from five patients were used in this study. We simulated two applications given with PDR (32 × 60 cGy per application, given hourly) or HDR (4 × 7 Gy in two applications; each application of two fractions of 7 Gy, given within 17 h) standard and optimised treatment plans, all combined with IMRT (25 × 1.8 Gy). Additionally, we simulated an external beam (EBRT) boost to pathological lymph nodes or the parametrium (7 × 2 Gy).We determined D90 of the high-risk CTV (HR-CTV) and D_2cc of bladder and rectum in EQD2 in two ways. (1) ‘Parameter adding’: assuming a uniform contribution of the EBRT dose distribution and adding the values of DVH parameters for the two brachytherapy insertions, and (2) ‘distributions adding’: summing 3D biological dose distributions of IMRT and brachytherapy plans and subsequently determining the values of the DVH parameters. We took α/β = 10 Gy for HR-CTV, α/β = 3 Gy otherwise and half-time of repair 1.5 h.

Results

Without EBRT boost, ‘parameter adding’ yielded a good approximation. With an EBRT boost to lymph nodes, the total D90 HR-CTV was underestimated by 2.6 (SD 1.3)% for PDR and 2.8 (SD 1.4)% for HDR. This was even worse with a parametrium boost: 9.1 (SD 6.2)% for PDR and 9.9 (SD 6.2)% for HDR.

Conclusion

Without an EBRT boost ‘parameter adding’, as proposed by the GEC-ESTRO, yielded accurate results for the values for DVH parameters. If an EBRT boost is given ‘distributions adding’ should be considered.     

Unilateral radiotherapy for tonsil cancer: Potential dose distribution optimization with a simple two-field intensity-modulated radiation therapy beam arrangement

Background and purpose

To evaluate the feasibility and dosimetric optimization potential of a unilateral two-field intensity-modulated radiotherapy (IMRT) technique in the curative treatment of lateralized tonsil cancer.

Materials and methods

Six patients with lateralized tonsillar carcinoma were treated unilaterally with a two-field IMRT technique (oblique-anterior and oblique-posterior fields, with or without collimator and couch rotation). Alternative IMRT plans using seven non-opposed coplanar fields were compared with the two-field plans for each patient.

Results

Planning target volume (PTV) coverage was excellent with the two-field technique, using a relatively low number of monitor units (MU) (median, 441; range, 309-550). Dose constraints were respected for all organs at risk (OAR). Mean doses to contralateral parotid and submandibular glands were 3.9 and 17.7 Gy, respectively. Seven-field IMRT provided similar PTV coverage, with statistically significant better dose homogeneity and conformality. However, the mean delivered dose to the contralateral parotid (3.9 vs. 9.0 Gy, p = 0.001) as well as the mean number of MU (437 vs. 814, p = 0.002) and consequently machine time were lower with two-field IMRT.

Conclusions

Unilateral two-field IMRT is a simple and feasible technique providing excellent tumor coverage and optimal OAR sparing while reducing the number of MU and treatment time.     

Real-time dynamic MLC tracking for inversely optimized arc radiotherapy

Background and purpose

Motion compensation with MLC tracking was tested for inversely optimized arc radiotherapy with special attention to the impact of the size of the target displacements and the angle of the leaf trajectory.

Materials and methods

An MLC-tracking algorithm was used to adjust the MLC positions according to the target movements using information from an optical real-time positioning management system. Two plans with collimator angles of 45° and 90°, respectively, were delivered and measured using the Delta⁴® dosimetric device moving in the superior-inferior direction with peak-to-peak displacements of 5, 10, 15, 20 and 25 mm and a cycle time of 6 s.

Results

Gamma index evaluation for plan delivery with MLC tracking gave a pass rate higher than 98% for criteria 3% and 3 mm for both plans and for all sizes of the target displacement. With no motion compensation, the average pass rate was 75% for plan 1 and 70% for plan 2 for 25 mm peak-to-peak displacement.

Conclusion

MLC tracking improves the accuracy of inversely optimized arc delivery for the cases studied. With MLC tracking, the dosimetric accuracy was independent of the magnitude of the peak-to-peak displacement of the target and not significantly affected by the angle between the leaf trajectory and the target movements.     

Concomitant intensity modulated boost during whole breast hypofractionated radiotherapy - A feasibility and toxicity study

Background

Breast cancer sensitivity to large fraction size may be enhanced using hypofractionated concomitant boost radiotherapy (CBRT), thereby shortening overall treatment time. This ethics approved, prospective single cohort feasibility study was designed to evaluate the dosimetry and toxicity of CBRT using an intensity-modulated radiotherapy (IMRT) technique, compared with a standard sequential boost technique (SBT).

Methods

Fifteen women (11 right-sided; 4 left-sided) received 42.4 Gy to the whole breast and an additional 10.08 Gy to the tumor bed in 16 daily fractions, using IMRT and standard dose constraints. Each patient was replanned with the SBT, using mixed photon-electrons. Clinical target volume (CTV), dose evaluation volume (DEV), and organs at risk (OAR) dose distributions were compared with the SBT. Toxicity and treatment times were prospectively recorded.

Results

All 15 CBRT plans achieved the desired CTV (V_49.9Gy ? 99%) and DEV (V_49.9Gy ? 95%), coverage of the boost, compared with only 10 (66.7%, p = 0.03), and 12 (80%, p = 0.125) SBT plans, respectively. Ipsilateral lung (p < 0.0001), and heart (right-sided, p = 0.001; left-sided, p = 0.13) doses were lower. Grade 3 acute toxicity occurred in 1 (6.7%) patient. At 1 year, two (13.3%) additional patients had overall grade 2 late toxicity, compared with baseline. No grade 3-4 late toxicity was observed.

Conclusions

CBRT using IMRT improved boost coverage and lowered OAR doses, compared with SBT. Toxicities were acceptable using a daily boost of 3.28 Gy. While resource utilization was greater, overall treatment time was reduced.     

Association of urethral toxicity with dose exposure in combined high-dose-rate brachytherapy and intensity-modulated radiation therapy in intermediate- and high-risk prostate cancer

Introduction

To report acute and late toxicities in patients with intermediate- and high-risk prostate cancer treated with combined high-dose-rate brachytherapy (HDR-B) and intensity-modulated radiation therapy (IMRT).

Materials and methods

From March 2003 to September 2005, 64 men were treated with a single implant HDR-B with 21 Gy given in three fractions, followed by 50 Gy IMRT along with organ tracking. Median age was 66.1 years, and risk of recurrence was intermediate in 47% of the patients or high in 53% of the patients. Androgen deprivation therapy was received by 69% of the patients. Toxicity was scored according to the CTCAE version 3.0. Median follow-up was 3.1 years.

Results

Acute grade 3 genitourinary (GU) toxicity was observed in 7.8% of the patients, and late grades 3 and 4 GU toxicity was observed in 10.9% and 1.6% of the patients. Acute grade 3 gastrointestinal (GI) toxicity was experienced by 1.6% of the patients, and late grade 3 GI toxicity was absent. The urethral V₁₂₀ (urethral volume receiving ?120% of the prescribed HDR-B dose) was associated with acute (P = .047) and late ? grade 2 GU toxicities (P = .049).

Conclusions

Late grades 3 and 4 GU toxicity occurred in 10.9% and 1.6% of the patients after HDR-B followed by IMRT in association with the irradiated urethral volume. The impact of V₁₂₀ on GU toxicity should be validated in further studies.     

Inter-clinician variability in making dosimetric decisions in pediatric treatment: A balance between efficacy and late effects

Purpose

To investigate variability of clinical target volume (CTV) delineation and deviations according to doses delivered in normal tissue for abdominal tumor irradiation in children.

Material and methods

For a case of nephroblastoma six French pediatric radiation oncologists outlined post-operative CTV, on the same dosimetric CT scan according to the International Society for Pediatric Oncology 2001 protocol. On a reference CTV and organs at risk (OAR), we performed dosimetric planning with the constraints as 25.2 Gy for CTV, V_{20 max} to 50% for liver, V₁₂ <15% for kidney. Data were analyzed with Aquilab^© software.

Results

Final CTVs showed inter-clinician variability: 44.85-120.78 cm³. The recommended liver doses were not respected in four cases: V₂₀ from 74% to 88% of the volume; for kidney, in two cases: V₁₂ of 17.6% and 25%, respectively. For vertebral bodies, no deviations were noted.

Conclusion

Variability not only affected CTV delineation but also dose distribution to OAR with different compromises. This practice training demonstrates the hudge lack of data about correlation between dose, volume and risk of late effects in pediatric radiotherapy. We intend to record prospectively the dose/volume histogram of each OAR in a national database in order to characterize late effects occurring in relation to treatment modalities.     

The role of replanning in fractionated intensity modulated radiotherapy for nasopharyngeal carcinoma

Background and purpose

Anatomic changing frequently occurred during fractionated radiotherapy. The aims of this study were to model the potential benefit of adaptive IMRT replanning during fractionated radiotherapy and its potential advantage over clinical outcome in patients with nasopharyngeal carcinoma.

Materials and methods

Thirty-three patients with repeat CT imaging and replanning were retrospectively analyzed. 66 case-matched control patients without replanning were identified by matching for AJCC stage, gender, and age. Hybrid IMRT plans were generated to evaluate the dosimetric changing. Mann-Whitney-Wilcoxon tests were used to evaluate the effect of replanning on volumetric and dosimetric outcomes within individuals. Kaplan-Meier estimators were used to estimate the survival function of patients with or without replanning.

Results

The mean volume of the ipsilateral and contralateral parotid glands decreased during the treatment. The hybrid IMRT plans showed decreased doses to target volumes and increased doses to normal structures in replanning. The clinical outcome comparison indicated that the IMRT replanning improved the 3 years local progression-free survival for patients who had AJCC staged more than T₃ (T_3,4N_x) and ease the late effects for patients who had large lymph nodes (AJCC stage T_xN_2,3).

Conclusion

Repeat CT imaging and IMRT replanning were recommendatory for specific nasopharyngeal carcinoma patients.     

Current technological clinical practice in breast radiotherapy; results of a survey in EORTC-Radiation Oncology Group affiliated institutions

Purpose

To evaluate the current technological clinical practice of radiation therapy of the breast in institutions participating in the EORTC-Radiation Oncology Group (EORTC-ROG).

Materials and methods

A survey was conducted between August 2008 and January 2009 on behalf of the Breast Working Party within the EORTC-ROG. The questionnaire comprised 32 questions on 4 main topics: fractionation schedules, treatment planning methods, volume definitions and position verification procedures.

Results

Sixty-eight institutions out of 16 countries responded (a response rate of 47%). The standard fraction dose was generally 2 Gy for both breast and boost treatment, although a 2.67 Gy boost fraction dose is routinely given in British institutions. The main boost modality was electrons in 55%, photons in 47% and brachytherapy in 3% of the institutions (equal use of photon and electron irradiation in 5% of the institutions). All institutions used CT-based treatment planning. Wide variations are seen in the definition of the breast and boost target volumes, with margins around the resection cavity, ranging from 0 to 30 mm. Inverse planned IMRT is available in 27% and breath-hold techniques in 19% of the institutions. The number of patients treated with IMRT and breath-hold varied per institution. Electronic portal imaging for patient set-up is used by 92% of the institutions.

Conclusions

This survey provides insight in the current practice of radiation technology used in the treatment of breast cancer among institutions participating in EORTC-ROG clinical trials.     

‘Plan of the day’ adaptive radiotherapy for bladder cancer using helical tomotherapy

Background and purpose

This study assessed the potential of tomotherapy based Image Guided Radiotherapy (IGRT) to increase the accuracy of bladder irradiation using a ‘plan of the day’ adaptive radiotherapy (ART) technique.

Materials and methods

Ten patients with muscle invasive bladder cancer underwent bladder preservation with trimodality therapy in an ongoing trial. All patients received 64 Gy/32# to the whole bladder and seven of them received a boost of 68 Gy/32# to the tumour bed. The ART technique entailed the generation of six IMRT plans for each patient, using six isotropic PTVs of 5-30 mm applied to the bladder volume (CTV) to generate the PTVs. Megavoltage CT (MVCT) imaging was done to correct positioning errors and choose the ‘plan of the day’.

Results

Post treatment MVCT scans (315 scans) were used to generate multiple anisotropic PTVs for three hypothetical scenarios. Overall, coverage of anterior and superior walls required larger margins than other walls. Maximum geographical miss, in spite of IGRT, was noted for the superior (13.8%) and anterior walls (10.3%).

Conclusions

Plan of the day ART is a feasible and promising technique for optimal treatment and dose escalation in bladder cancer.     

Internal motion of the vagina after hysterectomy for gynaecological cancer

Background and purpose

The purpose of this study was to investigate position changes of the vagina after hysterectomy for early stage cervical or endometrial cancer and their impact on CTV-PTV margins. We also studied their correlation with surrounding organ filling.

Materials and methods

Fifteen patients underwent T2-weighted MR scans before and weekly during the course of their EBRT. The vaginal CTVs and the surrounding organs were delineated. PTV margins were derived from the boundaries of the CTVs in the main directions and correlated with changes in the volumes of organs at risk. Additionally we investigated the impact of margin sizes on CTV coverage.

Results

The vaginal CTVs change their position in the pelvis during time with a maximum in anterior-posterior direction. The 95% confidence level was 2.3 cm into the anterior or posterior direction, 1.8 cm to left or right and 1.5 cm towards the cranial. With a homogenous 1.5 cm CTV-PTV margin ?5% inadequately covered vaginal CTV was seen in only 3.3% of the measurements. This increased to 20.6% with a margin of 1.0 cm. Concerning the impact of organ filling on vaginal position changes we found the only significant correlation with rectal volume and shift of the vagina towards anterior-posterior.

Conclusion

To accommodate the changes in the position of the vaginal CTV inhomogeneous PTV margins should be generated with the largest size in the anterior-posterior direction. The position shifts were only weakly related to the volume of the rectum and not at all to the volumes of other parts of the bowel and the bladder.     

Clinical performance of a transmission detector array for the permanent supervision of IMRT deliveries

Background and purpose

Clinical evaluation of a novel dosimetric accessory serving the permanent supervision of MLC function.

Materials and methods

The DAVID system (PTW-Freiburg, Germany) is a transparent, multi-wire transmission ionization chamber, placed in the accessory holder of the treatment head. Since each of the 37 individual wires is positioned exactly below the associated leaf pair of the MLC, its signal records the opening of this leaf pair during patient treatment.

Results

The DAVID system closes a gap in the quality assurance program, permitting the permanent in-vivo verification of IMRT plans. During dosimetric plan verification with the 2D-ARRAY (PTW-Freiburg, Germany), reference values of the 37 DAVID signals are collected, with which the DAVID readings recorded during daily patient treatment are compared. This comparison is visually displayed in the control room, and warning and alarm levels of any discrepancies can be defined. The properties of the DAVID system as a transmission device, its sensitivity to beam delivery and leaflet errors as well as its stability have been analyzed for clinically relevant examples. In a recent version, the DAVID system has been equipped with 80 wires.

Conclusions

The DAVID system permits the on-line detection of clinically relevant MLC discrepancies in IMRT deliveries.     

Rectal dose variation during the course of image-guided radiation therapy of prostate cancer

Background and purpose

To investigate the change in rectal dose during the treatment course for intensity-modulated radiotherapy (IMRT) of prostate cancer with image-guidance.

Materials and methods

Twenty prostate cancer patients were recruited for this retrospective study. All patients have been treated with IMRT. For each patient, MR and CT images were fused for target and critical structure delineation. IMRT treatment planning was performed on the simulation CT images. Inter-fractional motion during the course of treatment was corrected using a CT-on-rails system. The rectum was outlined on both the original treatment plan and the subsequent daily CT images from the CT-on-rails by the same investigator. Dose distributions on these daily CT images were recalculated with the isocenter shifts relative to the simulation CT images using the leaf sequences/MUs based on the original treatment plan. The rectal doses from the subsequent daily CTs were compared with the original doses planned on the simulation CT using our clinical acceptance criteria.

Results

Based on 20 patients with 139 daily CT sets, 28% of the subsequent treatment dose distributions did not meet our criterion of V₄₀ < 35%, and 27% did not meet our criterion of V₆₅ < 17%. The inter-fractional rectal volume variation is significant for some patients.

Conclusions

Due to the large inter-fractional variation of the rectal volume, it is more favorable to plan prostate IMRT based on an empty rectum and deliver treatment to patients with an empty rectum. Over 70% of actual treatments showed better rectal doses than our clinical acceptance criteria. A significant fraction (27%) of the actual treatments would benefit from adaptive image-guided radiotherapy based on daily CT images.     

Comparison of second cancer risk due to out-of-field doses from 6-MV IMRT and proton therapy based on 6 pediatric patient treatment plans

Background and purpose

This study compared 6-MV IMRT and proton therapy in terms of organ specific second cancer lifetime attributable risks (LARs) caused by scattered and secondary out-of-field radiation.

Materials and methods

Based on simulated organ doses, excess relative and excess absolute risk models were applied to assess organ-specific LARs. Two treatment sites (cranium and central spine) were considered involving six treatment volumes and six patient ages (9-month, 4-year, 8-year, 11-year, 14-year, and adult).

Results

The LARs for thyroid cancer from a 6 cm diameter field treating a brain lesion in a 4-year old patient were estimated to be 1.1% and 0.3% in passive proton therapy and IMRT, respectively. However, estimated LARs for bladder cancer, more than 25 cm from the field edge for the same patient and treatment field, were estimated to be 0.2% and 0.02% from IMRT and proton therapy, respectively. Risks for proton beam scanning was found to be an order of magnitude smaller compared to passive proton therapy.

Conclusion

In terms of out-of-field risks, IMRT offers advantage close to the primary field and an increasing advantage for passive proton therapy is noticed with increasing distance to the field. Scanning proton beam therapy shows the lowest risks.     

Feasibility of using intravenous contrast-enhanced computed tomography (CT) scans in lung cancer treatment planning

Background and purpose

To investigate the feasibility of using intravenous contrast-enhanced computed tomography (CT) scans in 3-dimensional conformal radiotherapy (3D-CRT), stereotactic body radiation therapy (SBRT) and intensity-modulated radiotherapy (IMRT) treatment planning for lung cancers, respectively.

Materials and methods

Twelve patients with bulky lung tumors and 14 patients with small lung tumors were retrospectively analyzed. Each patient took two sets of CT in the same position with active breathing control (ABC) technique before and after intravenous contrast agent (CA) injections. Bulky tumors were planned with 3D-CRT, while SBRT plans were generated for patients with small tumors based on CT scans with intravenous CA. In addition, IMRT plans were generated for patients with bulky tumors to continue on a planning study. All plans were copied and replaced on the scans without intravenous CA. The radiation doses calculated from the two sets of CTs were compared with regard to planning volumes (PTV), the organ at-risk (OAR) and the lungs using Wilcoxon’s signed rank test.

Results

In comparisons for 3D-CRT plans, CT scans with intravenous CA reduced the mean dose and the maximum dose of PTV with significant differences (p < 0.05) that were within 1.0%. Comparing IMRT and SBRT plans, CT scans with intravenous CA obviously increased the minimum irradiation dose and dose of 95% volume of target received (D₉₅) for targets, respectively (p < 0.05). There was no statistical significance for lung parameters between two sets of scans in SBRT plans and IMRT plans.

Conclusions

The enhanced CT scans can be used for both target delineation and treatment planning in 3D-CRT. The dose difference caused by intravenous CA is small. But for SBRT and IMRT, the minimum irradiation dose in targets may be estimated to be increased up to 2.71% while the maximum dose may be estimated to be decreased up to 1.36%. However, the difference in dose distribution in most cases were found to be clinical tolerable.     

Toward an individualized target motion management for IMRT of cervical cancer based on model-predicted cervix-uterus shape and position

Background and Purpose

To design and evaluate a 3D patient-specific model to predict the cervix-uterus shape and position.

Methods and Materials

For 13 patients lying in prone position, 10 variable bladder filling CT-scans were acquired, 5 at planning and 5 after 40 Gy. The delineated cervix-uterus volumes in 2-5 pre-treatment CT-scans were used to generate patient-specific models that predict the cervix-uterus geometry by bladder volume. Model predictions were compared to delineations, excluding those used for model construction. The prediction error was quantified by the margin required around the predicted volumes to accommodate 95% of the delineated volume and by the predicted-to-delineated surface distance.

Results

The prediction margin was significantly smaller (average 50%) than the margin encompassing the cervix-uterus motion. The prediction margin could be decreased (from 7 to 5 mm at planning and from 10 to 8 mm after 40 Gy) by increasing (from 2 to 5) the number of CT-scans used for the model construction.

Conclusion

For most patients, even with a model based on only two CT-scans, the prediction error was well below the margin encompassing the cervix-uterus motion. The described approach could be used to create prior to treatment, an individualized treatment strategy.