A methodology for incorporating functional bone marrow sparing in IMRT planning for pelvic radiation therapy

Background and purpose

The purpose of this study was to design a radiation therapy treatment planning approach that would spare hematopoietically active bone marrow using [¹⁸F]FLT PET imaging.

Materials and methods

We have developed an IMRT planning methodology to incorporate functional PET imaging using [¹⁸F]FLT scans. Plans were generated for two simulated cervical cancer patients, where pelvic active bone marrow regions were incorporated as avoidance regions based on the ranges: SUV4 ? 4; 4 > SUV3 ? 3; and 3 > SUV2 ? 2. Dose objectives were set to reduce bone marrow volume that received 10 (V₁₀) and 20 (V₂₀) Gy.

Results

Active bone marrow regions identified by [¹⁸F]FLT with an SUV ? 2, SUV ? 3, and SUV ? 4 represented an average of 43.0%, 15.3%, and 5.8%, respectively of the total osseous pelvis for the two cases studied. Improved dose-volume histograms for all identified bone marrow SUV volumes and decreases in V₁₀, and V₂₀ were achieved without clinically significant changes to PTV or OAR doses.

Conclusions

Incorporation of [¹⁸F]FLT PET in IMRT planning provides a methodology to reduce radiation dose to active bone marrow without compromising PTV or OAR dose objectives in pelvic malignancies.     

The value of magnetic resonance imaging in target volume delineation of base of tongue tumours - A study using flexible surface coils

Introduction

Magnetic resonance imaging (MRI) provides superior diagnostic accuracy over computed tomography (CT) in oropharyngeal tumours. Precise delineation of the gross tumour volume (GTV) is mandatory in radiotherapy planning when a GTV boost is required. CT volume definition in this regard is poor. We studied the feasibility of using flexible surface (flex-L) coils to obtain MR images for MR-CT fusion to assess the benefit of MRI over CT alone in planning base of tongue tumours.

Methods

Eight patients underwent CT and MRI radiotherapy planning scans with an immobilisation device. Distortion-corrected T1-weighted post-contrast MR scans were fused to contrast-enhanced planning CT scans. GTV, clinical target and planning target volumes (CTV, PTV) and organs at risk (OAR) were delineated on CT, then on MRI with blinding to the CT images. The volumetric and spatial differences between MRI and CT volumes for GTV, CTV, PTV and OAR were compared. MR image distortions due to field inhomogeneity and non-linear gradients were corrected and the need for such correction was evaluated.

Results

The mean primary GTV was larger on MRI (22.2 vs. 9.5 cm³, p = 0.05) than CT. The mean primary and nodal GTV (i.e. BOT and macroscopic nodes) was significantly larger on MRI (27.2 vs. 14.4 cm³, p = 0.05). The volume overlap index (VOI) between MRI and CT for the primary was 0.34 suggesting that MRI depicts parts of the primary tumour not detected by CT. There was no significant difference in volume delineation between MR and CT for CTV, PTV, nodal CTV and nodal PTV. MRI volumes for brainstem and spinal cord were significantly smaller due to improved organ definition (p = 0.002). Susceptibility and gradient-related distortions were not found to be clinically significant.

Conclusion

MRI improves the definition of tongue base tumours and neurological structures. The use of MRI is recommended for GTV dose-escalation techniques to provide precise depiction of GTV and improved sparing of spinal cord and brainstem.     

Quantitative evaluation of cone-beam computed tomography in target volume definition for offline image-guided radiation therapy of prostate cancer

Purpose

To quantitatively evaluate cone-beam CT (CBCT) in target volume definition in an offline image guidance environment.

Methods and materials

Fifteen patients each with five helical CTs (HCT) and eight CBCTs were included. A single physician manually delineated prostate and seminal vesicles (SVs) on each CT. The clinical target volume (CTV) was prostate for low risk group (G1), plus SVs for intermediate risk group (G2). The internal target volumes (ITVs) on CBCT (ITV_CBCT) were constructed and compared with ITV_HCT. The following comparisons were performed: CTV and ITV in HCT and CBCT; similarity of ITVs using overlap index (OI); surface differences between ITVs; quality assurance of ITV_CBCT using CTV from weekly CBCT; and dosimetric evaluations of ITV_HCT coverage on plans from ITV_CBCT.

Results

There was no statistical significant difference of CTV or ITV. The ITV OIs were 91%/88% for G1/G2 patients. They improved significantly with 1-2 mm margins. Therefore, the ITVs were mostly within 2 mm. The CTVs from weekly CBCT had >95% overlap with ITV_CBCT. The ITV dose differences (D₉₅, and D_mean) were <0.3%.

Conclusions

It is feasible to use CBCT for target definition in offline image guidance, thereby eliminating the separate helical CT scan process.     

The importance of patient characteristics for the prediction of radiation-induced lung toxicity

Purpose

Extensive research has led to the identification of numerous dosimetric parameters as well as patient characteristics, associated with lung toxicity, but their clinical usefulness remains largely unknown. We investigated the predictive value of patient characteristics in combination with established dosimetric parameters.

Patients and methods

Data from 438 lung cancer patients treated with (chemo)radiation were used. Lung toxicity was scored using the Common Toxicity Criteria version 3.0. A multivariate model as well as two single parameter models, including either V₂₀ or MLD, was built. Performance of the models was expressed as the AUC (Area Under the Curve).

Results

The mean MLD was 13.5 Gy (SD 4.5 Gy), while the mean V₂₀ was 21.0% (SD 7.3%). Univariate models with V₂₀ or MLD both yielded an AUC of 0.47. The final multivariate model, which included WHO-performance status, smoking status, forced expiratory volume (FEV₁), age and MLD, yielded an AUC of 0.62 (95% CI: 0.55-0.69).

Conclusions

Within the range of radiation doses used in our clinic, dosimetric parameters play a less important role than patient characteristics for the prediction of lung toxicity. Future research should focus more on patient-related factors, as opposed to dosimetric parameters, in order to identify patients at high risk for developing radiation-induced lung toxicity more accurately.     

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.     

Boosting the tumor bed from deep-seated tumors in early-stage breast cancer: A planning study between electron, photon, and proton beams

Purpose

To assess the potential dosimetric advantages and drawbacks of photon beams (modulated or not), electron beams (EB), and protons as a boost for the tumor bed in deep-seated early-stage breast cancer.

Material and methods

Planning CTs of 14 women with deep-seated tumors (i.e., ?4 cm depth) were selected. The clinical target volume (CTV) was defined as the area of architectural distortion surrounded by surgical clips. The planning treatment volume (PTV) was the CTV plus 1 cm margin. A dose of 16 Gy in 2 Gy fractions was prescribed. Organs at risk (OARs) were heart, lungs, breasts, and a 5-mm thick skin segment on the breast surface. Dose-volume metrics were defined to quantify the quality of concurrent treatment plans assessing target coverage and sparing of OAR. The following treatment techniques were assessed: photon beams with either static 3D-conformal, dynamic arc (DCA), static gantry intensity-modulated beams (IMRT), or RapidArc (RA); a single conformal EB; and intensity-modulated proton beams (IMPT). The goal for this planning effort was to cover 100% of the CTV with ?95% of the prescribed dose and to minimize the volume inside the CTV receiving >107% of the dose.

Results

All techniques but DCA and EB achieved the planning objective for the CTV with an inhomogeneity ranging from 2% to 11%. RA showed the best conformity, EB the worst. Contra-lateral breast and lung were spared by all techniques with mean doses <0.5 Gy (zero for protons). The ipsi-lateral lung received a mean dose <10% of that prescribed with photon beams and <2% with IMPT, increasing to 17% with EB. The heart, in left-sided breast tumors, received also the highest dose with EB. The skin was best protected with RA with a mean dose of 5.4 Gy and V_15Gy = 2.4%.

Conclusions

Boosting the tumor bed in early-stage breast cancer with optimized photon or proton beams may be preferred to EB especially for deep-seated targets. The marked OAR (i.e., ipsi-lateral breast, lung, heart, and skin surface) dose-sparing effect may allow for a potential long-term toxicity risk reduction and better cosmesis. DCA or RA may also be considered alternative treatment options for patients eligible for accelerated partial breast irradiation trials.     

Radiotherapy of malignant gliomas: Comparison of volumetric single arc technique (RapidArc), dynamic intensity-modulated technique and 3D conformal technique

Purpose

The analysis was designed to identify the optimal radiation technique for patients with malignant glioma.

Methods

A volumetric-modulated radiation treatment technique (RapidArc), an IMRT technique and a 3D conformal technique were calculated on computed tomograms of 14 consecutive patients with malignant glioma. The treatment plans were compared with each other using dose-volume histograms.

Results

The 3D conformal technique showed a good PTV coverage, if PTV was distant to organs at risk (OAR). If PTV was nearby OAR, the 3D technique revealed a poor PTV coverage in contrast to both intensity-modulated techniques. The conventional IMRT technique showed a slightly better PTV coverage than RapidArc. The advantages of RapidArc were a shorter treatment time, less monitor units and a small V_107%.

Conclusions

If PTV is distant to OAR, the use of 3D conformal technique is sufficient. Otherwise an intensity-modulated technique should be used. RapidArc was faster than conventional IMRT and should be preferred if PTV coverage is adequate.     

The effect of delineation method and observer variability on bladder dose-volume histograms for prostate intensity modulated radiotherapy

Purpose

To quantify the effect of delineation method on bladder DVH, observer variability (OV) and contouring time for prostate IMRT plans.

Materials and methods

Planning CT scans and IMRT plans of 30 prostate cancer patients were anonymized. For 20 patients, 1 observer delineated the bladder using 9 methods. The effect of delineation method on the DVH curve, discrete dose levels and delineation time was quantified. For the 10 remaining CTs, 6 observers delineated bladder wall using 4 methods. Observer-based volume variation and intraclass correlation coefficient (ICC) were used to describe the dosimetric effects of OV.

Results

Manual delineation of the bladder wall (BW_m) was significantly slower than any other method (mean: 20 min vs. ?13 min) and the dosimetric effect of OV was significantly larger (V70 Gy ICC: 0.78 vs. 0.98). Only volumes created using a 2.5 mm contraction from the outer surface, and a method providing a consistent wall volume, showed no notable dosimetric differences from BW_m in both absolute and relative volume.

Conclusions

Automatic contractions from the outer surface provide quicker, more reproducible and reasonably accurate substitutes for BW_m. The widespread use of automatic contractions to create a bladder wall volume would assist in the consistent application of IMRT dose constraints and the interpretation of reported dose.     

4D-CT-based target volume definition in stereotactic radiotherapy of lung tumours: Comparison with a conventional technique using individual margins

Purpose

To investigate the dosimetric benefit of integration of 4D-CT in the planning target volume (PTV) definition process compared to conventional PTV definition using individual margins in stereotactic body radiotherapy (SBRT) of lung tumours.

Material and methods

Two different PTVs were defined: PTV_conv consisting of the helical-CT-based clinical target volume (CTV) enlarged isotropically for each spatial direction by the individually measured amount of motion in the 4D-CT, and PTV_4D encompassing the CTVs defined in the 4D-CT phases displaying the extremes of the tumour position. Tumour motion as well as volumetric and dosimetric differences and relations of both PTVs were evaluated.

Results

Volumetric examinations revealed a significant reduction of the mean PTV by 4D-CT from 57.7 to 40.7 cm³ (31%) (p < 0.001). A significant inverse correlation was found for the motion vector and the amount of inclusion of PTV_4D in PTV_conv (r = −0.69, 90% confidence limits: −0.87 and −0.34, p = 0.007). Mean lung dose (MLD) was decreased significantly by 17% (p < 0.001).

Conclusions

In SBRT of lung tumours the mere use of individual margins for target volume definition cannot compensate for the additional effects that the implementation of 4D-CT phases can offer.     

Target volume delineation variation in radiotherapy for early stage rectal cancer in the Netherlands

Purpose

The aim of this study was to measure and improve the quality of target volume delineation by means of national consensus on target volume definition in early-stage rectal cancer.

Methods and materials

The CTV’s for eight patients were delineated by 11 radiation oncologists in 10 institutes according to local guidelines (phase 1). After observer variation analysis a workshop was organized to establish delineation guidelines and a digital atlas, with which the same observers re-delineated the dataset (phase 2). Variation in volume, most caudal and cranial slice and local surface distance variation were analyzed.

Results

The average delineated CTV volume decreased from 620 to 460 cc (p < 0.001) in phase 2. Variation in the caudal CTV border was reduced significantly from 1.8 to 1.2 cm SD (p = 0.01), while it remained 0.7 cm SD for the cranial border. The local surface distance variation (cm SD) reduced from 1.02 to 0.74 for anterior, 0.63 to 0.54 for lateral, 0.33 to 0.25 for posterior and 1.22 to 0.46 for the sphincter region, respectively.

Conclusions

The large variation in target volume delineation could significantly be reduced by use of consensus guidelines and a digital delineation atlas. Despite the significant reduction there is still a need for further improvement.     

Treatment of large stage I-II lung tumors using stereotactic body radiotherapy (SBRT): Planning considerations and early toxicity

Purpose

To study the dosimetric predictors of early clinical toxicity following SBRT in patients with lung tumors and planning target volumes (PTV) exceeding 80 cm³.

Methods

Eighteen consecutive patients who were treated using volumetric modulated arc therapy (RapidArc™) were assessed. All were either unfit or refused to undergo surgery or chemoradiotherapy. PTV planning objectives were as used in the ROSEL study protocol. Clinical toxicity was scored using Common Toxicity Criteria AE4.0. Lung volumes receiving 5, 10, 15, and 20 Gy (V₅, V₁₀, V₁₅ and V₂₀) and mean lung dose were assessed and correlated to symptomatic radiation pneumonitis (RP).

Results

Median age, age-adjusted Charlson-comorbidity score and PTV size were 74, 7.5 and 137 cm³, respectively. At a median follow-up of 12.8 months, 8 deaths were recorded: 5 arising from comorbidity, 2 were potentially treatment-related and 1 had local recurrence. RP was reported in 5 patients (grade 2 in 3 and grade 3 in 2). All RP occurred in plans without a high priority optimization objective on contralateral lung. Acute RP was best predicted by contralateral lung V₅ (p < 0.0001).

Conclusion

After SBRT using RapidArc in lung tumors >80 cm³, the contralateral lung V₅ best predicts RP. Limiting contralateral lung V₅ to <26% may reduce acute toxicity.     

Dose-volume thresholds and smoking status for the risk of treatment-related pneumonitis in inoperable non-small cell lung cancer treated with definitive radiotherapy

Purpose

To identify clinical risk factors and dose-volume thresholds for treatment-related pneumonitis (TRP) in patients with non-small cell lung cancer (NSCLC).

Methods and materials

Data were retrospectively collected from patients with inoperable NSCLC treated with radiotherapy with or without chemotherapy. TRP was graded according to Common Terminology Criteria for Adverse Events, version 3.0, with time to grade ?3 TRP calculated from start of radiotherapy. Clinical factors and dose-volume parameters were analyzed for their association with risk of TRP.

Results

Data from 576 patients (75% with stage III NSCLC) were included in this study. The Kaplan-Meier estimate of the incidence of grade ?3 TRP at 12 months was 22%. An analysis of dose-volume parameters identified a threshold dose-volume histogram (DVH) curve defined by V₂₀ ?25%, V₂₅ ?20%, V₃₅ ?15%, and V₅₀ ?10%. Patients with lung DVHs satisfying these constraints had only 2% incidence of grade ?3 TRP. Smoking status was the only clinical factor that affected the risk of TRP independent of dosimetric factors.

Conclusions

The risk of TRP varied significantly, depending on radiation dose-volume parameters and patient smoking status. Further studies are needed to identify biological basis of smoking effect and methods to reduce the incidence of TRP.     

Image and laparoscopic guided interstitial brachytherapy for locally advanced primary or recurrent gynaecological cancer using the adaptive GEC ESTRO target concept

Purpose

To retrospectively assess treatment outcome of image and laparoscopic guided interstitial pulsed dose rate brachytherapy (PDR-BT) for locally advanced gynaecological cancer using the adaptive GEC ESTRO target concept.

Materials and methods

Between June 2005 and December 2010, 28 consecutive patients were treated for locally advanced primary vaginal (nine), recurrent endometrial (12) or recurrent cervical cancer (seven) with combined external beam radiotherapy (EBRT) and interstitial PDR-BT. Treatment was initiated with whole pelvic EBRT to a median dose of 45 Gy followed by PDR-BT using the Martinez Universal Perineal Interstitial Template (MUPIT). All implants were virtually preplanned using MRI of the pelvis with a dummy MUPIT in situ. The GEC ESTRO high risk clinical target volume (HR CTV), intermediate risk clinical target volume (IR CTV) and the organs at risk (OAR) were contoured and a preplan for implantation was generated (BrachyVision, Varian). The subsequent implantation was performed under laparoscopic visualisation. Final contouring and treatment planning were done using a post-implant CT. Planning aim of PDR-BT was to deliver 30 Gy in 50 hourly pulses to HR CTV. Manual dose optimisation was performed with the aim of reaching a D90 > 80 Gy in the HR CTV calculated as the total biologically equivalent to 2 Gy fractions of EBRT and BT (EQD2). Dose to the OAR were evaluated using dose volume constraints for D_2cc of 90 Gy for bladder and 70 Gy for rectum and sigmoid.

Results

For HR CTV the median volume was 26 cm³ (7-91 cm³). Coverage of the HR CTV was 97% (90-100%) and D90 was 82 Gy (77-88 Gy). The D_2cc for bladder, rectum, and sigmoid were 65 Gy (47-81 Gy), 61 Gy (50-77 Gy), and 52 Gy (44-68 Gy), respectively. Median follow up was 18 months (6-61 months). The actuarial 2 years local control rate was 92% (SE 5), while disease-free survival and overall survival were 59% (SE 11) and 74%, respectively (SE 10). No complications to the laparoscopic guided implantation were encountered. Late grade 2 (CTC v 3.0) complications were recorded in nine (32%) patients. One patient had a grade 3 vaginal complication. No grade 4-5 complications have been recorded so far.

Conclusion

Image and laparoscopic guided interstitial PDR-BT using the GEC ESTRO target concept is applicable for locally advanced primary vaginal or recurrent endometrial and cervical cancer resulting in an excellent local control rate and limited morbidity.     

The use of probability maps to deal with the uncertainties in prostate cancer delineation

Background and purpose

The use of dynamic contrast-enhanced (DCE) imaging for delineation of prostate tumors requires that decisions are made on a voxel wise basis about the presence of tumor. While the sensitivity and specificity of this technique is high, we propose a probabilistic approach to deal with the intrinsic imaging uncertainty.

Material and methods

Twenty-nine patients with biopsy-proven prostate cancer underwent a DCE-CT exam prior to radiotherapy. From a logistic regression on K^trans values from healthy and diseased appearing prostate regions we obtained a probability function for the presence of tumor. K^trans parameter maps were converted into probability maps and a stratification was applied at the 5% and 95% probability level, to identify low-, intermediate-, and high-risk areas for the presence of tumor.

Results

In all patients, regions with high-, intermediate-, and low-risk were identified, with median volume percentages of 7.6%, 40.0%, and 52.1%, respectively. The contiguous areas that resulted from the voxel wise stratification can be interpreted as GTV, high-risk CTV, and CTV.

Conclusions

K^trans parameter maps from a DCE-CT exam can be converted into probability maps for the presence of tumor. In this way, the intrinsic uncertainty that a voxel contains tumor can be incorporated into the treatment planning process.     

Intrafraction motion in patients with cervical cancer: The benefit of soft tissue registration using MRI

Background and purpose

During radiation delivery, target volumes change their position and shape due to intrafraction motion. The extent of these changes and the capability to correct for them will contribute to the benefit of an MRI-accelerator in terms of PTV margin reduction. Therefore, we investigated the primary CTV motion within a typical IMRT delivery time for cervical cancer patients for various correction techniques: no registration, rigid bony anatomy registration, and rigid soft tissue registration.

Materials and methods

Twenty-two patients underwent 2-3 offline MRI exams before and during their radiation treatment. Each MRI exam included four sagittal and four axial MRI scans alternately within 16 min. We addressed the CTV motion by comparing subsequent midsagittal CTV delineations and investigated the correlation with intrafraction bladder filling.

Results

The maximum (residual) motions within 16 min for all points on the CTV contour for 90% of the MRI exams without registration, with rigid bony anatomy registration, and with rigid soft tissue registration were 10.6, 9.9, and 4.0 mm. A significant but weak correlation was found between intrafraction bladder filling and CTV motion.

Conclusions

Considerable intrafraction CTV motion is observed in cervical cancer patients. Intrafraction MRI-guided soft tissue registration using an MRI-accelerator will correct for this motion.     

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.     

Dosimetric predictor identification for radiation-induced liver disease after hypofractionated conformal radiotherapy for primary liver carcinoma patients with Child-Pugh Grade A cirrhosis

Purpose

Radiation-induced liver disease (RILD) is the most severe complication in liver cancer treatment. The aim of this study was to identify dosimetric predictors for RILD in primary liver carcinoma (PLC) patients with Child-Pugh Grade A cirrhosis after hypofractionated conformal radiotherapy (CRT).

Methods and materials

A total of 114 eligible patients (mean age 45 years old) were enrolled and treated. The mean gross tumor volume (GTV) was (378.3 ± 308.1) cm³. A median dose of 53 Gy was delivered to the PLC by hypofractionated CRT (three fractions/week) with a median fraction size of 4.6 Gy (range: 4-6 Gy).

Results

Patients were followed up for 1-79 months (median 19 months) after the completion of irradiation. RILD was diagnosed in nine (7.9%) patients. Univariate analyses revealed that GTV and the percentage of normal liver volume receiving more than 5-40 Gy irradiations (V_5-40) were related to the risk of developing RILD. Multivariate analyses demonstrated that only GTV and V₂₀ were independent predictors. Using V₂₀ as the predictor for RILD, the accuracy, sensitivity, and specificity was 76.3%, 88.9%, and 75.2%, respectively.

Conclusions

Our data suggest that V₂₀ is the unique significant dosimetric predictor for RILD risks in PLC patients with Child-Pugh Grade A cirrhosis after hypofractionated CRT.     

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.     

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.