Benefit of using biologic parameters (EUD and NTCP) in IMRT optimization for treatment of intrahepatic tumors

Potential Defects and Improvements of Equivalent Uniform Dose Prediction Model Based on the Analysis of Radiation-Induced Brain Injury

PURPOSE

To study the impact of dose distribution on volume-effect parameter and predictive ability of equivalent uniform dose (EUD) model, and to explore the improvements.

METHODS AND MATERIALS

The brains of 103 nasopharyngeal carcinoma patients treated with IMRT were segmented according to dose distribution (brain and left/right half-brain for similar distributions but different sizes; V _D with different D for different distributions). Predictive ability of EUD_{V D} (EUD of V _D ) for radiation-induced brain injury was assessed by receiver operating characteristics curve (ROC) and area under the curve (AUC). The optimal volume-effect parameter a of EUD was selected when AUC was maximal (mAUC). Correlations between mAUC, a and D were analyzed by Pearson correlation analysis. Both mAUC and a in brain and half-brain were compared by using paired samples t-tests. The optimal D _V and V _D points were selected for a simple comparison.

RESULTS

The mAUC of brain/half-brain EUD was 0.819/0.821 and the optimal a value was 21.5/22. When D increased, mAUC of EUD_{V D} increased, while a decreased. The mAUC reached the maximum value when D was 50-55 Gy, and a was always 1 when D ≥55 Gy. The difference of mAUC/a between brain and half-brain was not significant. If a was in range of 1 to 22, AUC of brain/half-brain EUD_{V55 Gy} (0.857-0.830/0.845-0.830) was always larger than that of brain/half-brain EUD (0.681-0.819/0.691-0.821). The AUCs of optimal dose/volume points were 0.801 (brain D_{2.5 cc}), 0.823 (brain V_{70 Gy}), 0.818 (half-brain D_{1 cc}), and 0.827 (half-brain V_{69 Gy}), respectively. Mean dose (equal to EUD_{V D} with a = 1) of high-dose volume (V_{50 Gy}-V_{60 Gy}) was superior to traditional EUD and dose/volume points.

CONCLUSION

Volume-effect parameter of EUD is variable and related to dose distribution. EUD with large low-dose volume may not be better than simple dose/volume points. Critical-dose-volume EUD could improve the predictive ability and has an invariant volume-effect parameter. Mean dose may be the case in which critical-dose-volume EUD has the best predictive ability.

Comparing Multi-Objective Local Search Algorithms for the Beam Angle Selection Problem

In intensity-modulated radiation therapy, treatment planners aim to irradiate the tumour according to a medical prescription while sparing surrounding organs at risk as much as possible. Although this problem is inherently a multi-objective optimisation (MO) problem, most of the models in the literature are single-objective ones. For this reason, a large number of single-objective algorithms have been proposed in the literature to solve such single-objective models rather than multi-objective ones. Further, a difficulty that one has to face when solving the MO version of the problem is that the algorithms take too long before converging to a set of (approximately) non-dominated points. In this paper, we propose and compare three different strategies, namely random PLS (rPLS), judgement-function-guided PLS (jPLS) and neighbour-first PLS (nPLS), to accelerate a previously proposed Pareto local search (PLS) algorithm to solve the beam angle selection problem in IMRT. A distinctive feature of these strategies when compared to the PLS algorithms in the literature is that they do not evaluate their entire neighbourhood before performing the dominance analysis. The rPLS algorithm randomly chooses the next non-dominated solution in the archive and it is used as a baseline for the other implemented algorithms. The jPLS algorithm first chooses the non-dominated solution in the archive that has the best objective function value. Finally, the nPLS algorithm first chooses the solutions that are within the neighbourhood of the current solution. All these strategies prevent us from evaluating a large set of BACs, without any major impairment in the obtained solutions’ quality. We apply our algorithms to a prostate case and compare the obtained results to those obtained by the PLS from the literature. The results show that algorithms proposed in this paper reach a similar performance than PLS and require fewer function evaluations.

Indications of IMRT, PRT and CIRT for HCC from comparisons of dosimetry and normal tissue complication possibility

PURPOSE

To identify the indications for hepatocellular carcinoma (HCC) irradiated by intensity-modulated photon radiotherapy (IMRT), proton radiotherapy (PRT) or carbon-ion radiotherapy (CIRT) by comparing of dosimetric parameters and incidences of classic radiation-induced liver disease (RILD).

METHODS

In all, 40 HCCs were divided into group A (tumors located > 1 cm away from gastrointestinal [GI] tract), and group B (tumors located < 1 cm away from GI tract). The prescribed curative doses were 60 Gy (relative biological effectiveness [RBE]) in 10 fractions for group A, and 67.5 Gy (RBE) in 15 fractions for group B. IMRT, PRT and CIRT plans were separately generated to reach the curative doses and coverage. Dosimetric parameters evaluated were mean dose to normal liver (MDTNL) and the volume of normal liver receiving more than 1 Gy (RBE) (V1). Lyman-Kutcher-Burman model was used to determine the incidences of classic RILD, and Power model of non-linear regression, to estimate the tumor volume that could be irradiated with the curative doses within dose constraint of MDTNL.

RESULTS

With comparable target doses, the MDTNL (Gy [RBE]) were 18.8 ± 3.7, 13.5 ± 3.1 and 12.8 ± 2.7 in group A and 24.9 ± 7.1, 18.2 ± 3.7 and 17.5 ± 3.7 in group B, respectively, for IMRT, PRT and CIRT. The classic RILD incidences (%) were 22.3 ± 30.0 in IMRT, 2.3 ± 4.9 in PRT and 1.2 ± 2.4 in CIRT. V1 (%) were 89.9 ± 8.8, 43.0 ± 10.2 and 45.9 ± 8.8, respectively, for IMRT, PRT and CIRT.

CONCLUSIONS

PRT and CIRT could spare the liver more than IMRT. IMRT could deliver the curative doses to HCC up to a diameter of 7.9 cm; PRT, up to 13.2 cm; and CIRT, up to 14.8 cm.

Dose verification for liver target volumes undergoing respiratory motion

Respiratory motion has a significant impact on dose delivered to abdominal targets during radiotherapy treatment. Accurate treatment of liver tumours adjacent to the diaphragm is complicated by large respiratory movement, as well as differing tissue densities at the lung-liver interface. This study aims to evaluate the accuracy of dose delivered to superior liver tumours using passive respiratory monitoring, in the absence of gating technology, for a range of treatment techniques. An in-house respiratory phantom was designed and constructed to simulate the lung and liver anatomy. The phantom consisted of adjacent slabs of lung and liver equivalent materials and a cam drive system to emulate respiratory motion. A CC04 ionisation chamber and Gafchromic EBT3 film were used to perform point dose and dose plane measurements respectively. Plans were calculated using an Elekta Monaco treatment planning system (TPS) on exhale phase study sets for conformal, volume modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) techniques, with breathing rates of 8, 14 and 23 bpm. Analysis confirmed the conformal delivery protocol currently used for this site within the department is suitable. The experiments also determined that VMAT is a viable alternative technique for treatment of superior liver lesions undergoing respiratory motion and was superior to IMRT. Furthermore, the measurements highlighted the need for respiratory management in these cases. Displacements due to respiration exceeding planned margins could result in reduced coverage of the clinical target volume and much higher doses to the lung than anticipated.

Stereotactic body proton therapy for liver tumors: Dosimetric advantages and their radiobiological and clinical implications

Background and Purpose

Photon Stereotactic Body Radiotherapy (SBRT) for primary and metastatic tumors of the liver is challenging for larger lesions. An in silico comparison of paired SBRT and Stereotactic Body Proton Therapy (SBPT) plans was performed to understand the potential advantages of SBPT as a function of tumor size and location.

Methods and materials

Theoretical tumor volumes with maximum diameter of 1–10 cm were contoured in the dome, right inferior, left medial, and central locations. SBRT and SBPT plans were generated to deliver 50 Gy in 5 fractions, max dose <135%. When organs-at-risk (OAR) constraints were exceeded, hypothetical plans (not clinically acceptable) were generated for comparison. Liver normal tissue complication probability (NTCP) models were applied to evaluate differences between treatment modalities.

Results

SBRT and SBPT were able to meet target goals and OAR constraints for lesions up to 7 cm and 9 cm diameter, respectively. SBPT plans resulted in a higher integral gross target dose for all lesions up to 7 cm (mean dose 57.8 ± 2.3 Gy to 64.1 ± 2.2 Gy, p < 0.01). Simultaneously, SBPT spared dose to the uninvolved liver in all locations (from 11.5 ± 5.3 Gy to 8.6 ± 4.4 Gy, p < 0.01), resulting in lower NTCP particularly for larger targets in the dome and central locations. SBPT also spared duodenal dose across all sizes and positions (from 7.3 ± 1.1 Gy to 1.1 ± 0.3 Gy, p < 0.05).

Conclusion

The main advantages of SBPT over SBRT is meeting plan goals and constrains for larger targets, particularly dome and central locations, and sparing dose to uninvolved liver. For such patients, SBPT may allow improvements in tumor control and treatment safety.

Local Control After Stereotactic Body Radiation Therapy for Liver Tumors

PURPOSE

To quantitatively evaluate published experiences with hepatic stereotactic body radiation therapy (SBRT), to determine local control rates after treatment of primary and metastatic liver tumors and to examine whether outcomes are affected by SBRT dosing regimen.

METHODS AND MATERIALS

We identified published articles that reported local control rates after SBRT for primary or metastatic liver tumors. Biologically effective doses (BEDs) were calculated for each dosing regimen using the linear-quadratic equation. We excluded series in which a wide range of BEDs was used. Individual lesion data for local control were extracted from actuarial survival curves, and data were aggregated to form a single dataset. Actuarial local control curves were generated using the Kaplan-Meier method after grouping lesions by disease type and BED (<100 Gy₁₀ vs >100 Gy₁₀). Comparisons were made using log-rank testing.

RESULTS

Thirteen articles met all inclusion criteria and formed the dataset for this analysis. The 1-, 2-, and 3-year actuarial local control rates after SBRT for primary liver tumors (n = 431) were 93%, 89%, and 86%, respectively. Lower 1- (90%), 2- (79%), and 3-year (76%) actuarial local control rates were observed for liver metastases (n = 290, log-rank P = .011). Among patients treated with SBRT for primary liver tumors, there was no evidence that local control is influenced by BED within the range of schedules used. For liver metastases, on the other hand, outcomes were significantly better for lesions treated with BEDs exceeding 100 Gy₁₀ (3-year local control 93%) than for those treated with BEDs of ≤100 Gy₁₀ (3-year local control 65%, P < .001).

CONCLUSIONS

Stereotactic body radiation therapy for primary liver tumors provides high rates of durable local control, with no clear evidence for a dose-response relationship among commonly utilized schedules. Excellent local control rates are also seen after SBRT for liver metastases when BEDs of >100 Gy₁₀ are utilized.

Viability of Non-Coplanar VMAT for Liver SBRT as Compared to Coplanar VMAT and Beam Orientation Optimized 4π IMRT

Purpose

The 4π static noncoplanar radiation therapy delivery technique has demonstrated better normal tissue sparing and dose conformity than the clinically used volumetric modulated arc therapy (VMAT). It is unclear whether this is a fundamental limitation of VMAT delivery or the coplanar nature of its typical clinical plans. The dosimetry and the limits of normal tissue toxicity constrained dose escalation of coplanar VMAT, noncoplanar VMAT and 4π radiation therapy are quantified in this study.

Methods and materials

Clinical stereotactic body radiation therapy plans for 20 liver patients receiving 30 to 60 Gy using coplanar VMAT (cVMAT) were replanned using 3 to 4 partial noncoplanar arcs (nVMAT) and 4π with 20 intensity modulated noncoplanar fields. The conformity number, homogeneity index, 50% dose spillage volume, normal liver volume receiving >15 Gy, dose to organs at risk (OARs), and tumor control probability were compared for all 3 treatment plans. The maximum tolerable dose yielding a normal liver normal tissue control probability <1%, 5%, and 10% was calculated with the Lyman-Kutcher-Burman model for each plan as well as the resulting survival fractions at 1, 2, 3, and 4 years.

Results

Compared with cVMAT, the nVMAT and 4π plans reduced liver volume receiving >15 Gy by an average of 5 cm³ and 80 cm³, respectively. 4π reduced the 50% dose spillage volume by ∼23% compared with both VMAT plans, and either significantly decreased or maintained OAR doses. The 4π maximum tolerable doses and survival fractions were significantly higher than both cVMAT and nVMAT (P < .05) for all normal liver normal tissue control probability limits used in this study.

Conclusions

The 4π technique provides significantly better OAR sparing than both cVMAT and nVMAT and enables more clinically relevant dose escalation for tumor local control. Therefore, despite the current accessibility of nVMAT, it is not a viable alternative to 4π for liver SBRT.

Stereotactic Body Radiation Therapy for Liver Cancer: A Review of the Technology

Stereotactic body radiation therapy has been adopted in the treatment of liver cancer because of its highly conformal dose distribution when compared with other conventional approaches, and many studies have been published to report the positive clinical outcome associated with this technique. To achieve the precision needed to maintain or to improve the therapeutic ratio, various strategies are applied in different components in the stereotactic body radiation therapy process. Immobilization devices are used in minimizing geometric uncertainty induced by treatment positioning and internal organ motion. Along with a better definition of target by the integration of multimodality imaging, planning target volume margin to compensate for the uncertainty can be reduced to minimize inclusion of normal tissue in the treatment volume. In addition, sparing of normal tissue from irradiation is improved by the use of high precision treatment delivery technologies such as intensity-modulated radiotherapy or volumetric modulated arc therapy. Target localization before treatment delivery with image guidance enables reproduction of the patient's geometry for delivering the planned dose. The application of these advanced technologies contributes to the evolution of the role of radiation therapy in the treatment of liver cancer, making it an important radical or palliative treatment modality.

The Feasibility and Efficiency of Volumetric Modulated Arc Therapy-Based Breath Control Stereotactic Body Radiotherapy for Liver Tumors

There are strong evidences showing the promising oncologic results of stereotactic body radiotherapy for liver tumors. This study aims to investigate the feasibility, plan quality, and delivery efficiency of image-guided volumetric modulated arc therapy-based voluntary deep exhale breath-holding technique in the stereotactic body radiotherapy for liver tumors. Treatment was planned using volumetric modulated arc therapy with 2 modified partial arc and replanned using intensity modulated radiation therapy technique for comparison. Dosimetric parameters were calculated for plan quality assessment. Quality assurance studies included both point and multiple planar dose verifications. Daily cone beam computed tomography imaging was used to measure and correct positional errors for target volumes and critical structures immediately prior to and during treatment delivery. Total monitor units and delivery times were also evaluated. No significant dosimetric difference was found between volumetric-modulated arc therapy and conventional intensity modulated radiation therapy plans. Both techniques were able to minimize doses to organs at risk including normal liver, kidneys, spinal cord, and stomach. However, the average monitor units with volumetric-modulated arc therapy were significantly lower (29.2%) than those with intensity modulated radiation therapy (P = .012). The average beam-on time in volumetric-modulated arc therapy plans was 22.2% shorter than that in intensity modulated radiation therapy plans. In conclusion, it is feasible to utilize volumetric modulated arc therapy in the treatment planning of stereotactic body radiotherapy for liver tumors under breath control mode. In comparison to conventional intensity modulated radiation therapy plans, volumetric modulated arc therapy plans are of high efficiency with less monitor units, shorter beam-on time, tolerable intrafractional errors as well as better dosimetrics, meriting further investigations, and clinical evaluations.

Risk-optimized proton therapy to minimize radiogenic second cancers

Proton therapy confers substantially lower predicted risk of second cancer compared with photon therapy. However, no previous studies have used an algorithmic approach to optimize beam angle or fluence-modulation for proton therapy to minimize those risks. The objectives of this study were to demonstrate the feasibility of risk-optimized proton therapy and to determine the combination of beam angles and fluence weights that minimizes the risk of second cancer in the bladder and rectum for a prostate cancer patient. We used 6 risk models to predict excess relative risk of second cancer. Treatment planning utilized a combination of a commercial treatment planning system and an in-house risk-optimization algorithm. When normal-tissue dose constraints were incorporated in treatment planning, the risk model that incorporated the effects of fractionation, initiation, inactivation, repopulation and promotion selected a combination of anterior and lateral beams, which lowered the relative risk by 21% for the bladder and 30% for the rectum compared to the lateral-opposed beam arrangement. Other results were found for other risk models.

The Importance of Quasi-4D Path-Integrated Dose Accumulation for More Accurate Risk Estimation in Stereotactic Liver Radiotherapy

Intrafraction organ deformation may be accounted for by inclusion of temporal information in dose calculation models. In this article, we demonstrate a quasi-4-dimensional method for improved risk estimation. Conventional 3-dimensional and quasi-4-dimensional calculations employing dose warping for dose accumulation were undertaken for patients with liver metastases planned for 42 Gy in 6 fractions of stereotactic body radiotherapy. Normal tissue complication probabilities and stochastic risks for radiation-induced carcinogenesis and cardiac complications were evaluated for healthy peripheral structures. Hypothetical assessments of other commonly employed dose/fractionation schedules on normal tissue complication probability estimates were explored. Conventional 3-dimensional dose computation may result in significant under- or overestimation of doses to organ at risk. For instance, doses differ (on average) by 17% (σ = 14%) for the left kidney, by 14% (σ = 7%) for the right kidney, by 7% (σ = 9%) for the large bowel, and by 10% (σ = 14%) for the duodenum. Discrepancies in the excess relative risk range up to about 30%. The 3-dimensional approach was shown to result in cardiac complication risks underestimated by >20%. For liver stereotactic body radiotherapy, we have shown that conventional 3-dimensional dose calculation may significantly over-/underestimate dose to organ at risk (90%-120% of the 4-dimensional estimate for the mean dose and 20%-150% for D2%). Providing dose estimates that most closely represent the actual dose delivered will provide valuable information to improve our understanding of the dose response for partial volume irradiation using hypofractionated schedules. Excess relative risks of radiocarcinogenesis were shown to range up to approximately excess relative risk = 4 and the prediction thereof depends greatly on the use of either 3-dimensional or 4-dimensional methods (with corresponding results differing by tens of percent).

What is the appropriate size criterion for proton radiotherapy for hepatocellular carcinoma? A dosimetric comparison of spot-scanning proton therapy versus intensity-modulated radiation therapy

BACKGROUND

We performed a dosimetric comparison of spot-scanning proton therapy (SSPT) and intensity-modulated radiation therapy (IMRT) for hepatocellular carcinoma (HCC) to investigate the impact of tumor size on the risk of radiation induced liver disease (RILD).

METHODS

A number of alternative plans were generated for 10 patients with HCC. The gross tumor volumes (GTV) varied from 20.1 to 2194.5 cm3. Assuming all GTVs were spherical, the nominal diameter was calculated and ranged from 3.4 to 16.1 cm. The prescription dose was 60 Gy for IMRT or 60 cobalt Gy-equivalents for SSPT with 95% planning target volume (PTV) coverage. Using IMRT and SSPT techniques, extensive comparative planning was conducted. All plans were evaluated by the risk of RILD estimated using the Lyman-normal-tissue complication probability model.

RESULTS

For IMRT the risk of RILD increased drastically between 6.3-7.8 cm nominal diameter of GTV. When the nominal diameter of GTV was more than 6.3 cm, the average risk of RILD was 94.5% for IMRT and 6.2% for SSPT.

CONCLUSIONS

Regarding the risk of RILD, HCC can be more safely treated with SSPT, especially if its nominal diameter is more than 6.3 cm.

Four-dimensional CT-based evaluation of volumetric modulated arc therapy for abdominal lymph node metastasis from hepatocellular carcinoma

This study aimed to identify the potential benefits and limitations of a new volumetric modulated arc therapy (VMAT) planning system in Monaco, compared with conventional intensity-modulated radiotherapy (IMRT) and three-dimensional conformal radiotherapy (3DCRT). Four-dimensional CT scans of 13 patients with abdominal lymph node metastasis from hepatocellular carcinoma were selected. Internal target volume was defined as the combined volume of clinical target volumes (CTVs) in the multiple 4DCT phases. Dose prescription was set to 45 Gy for the planning target volume (PTV) in daily 3.0-Gy fractions. The PTV dose coverage, organs at risk (OAR) doses, delivery parameters and treatment accuracy were assessed. Compared with 3DCRT, both VMAT and IMRT provided a systematic improvement in PTV coverage and homogeneity. Planning objectives were not fulfilled for the right kidney, in which the 3DCRT plans exceeded the dose constraints in two patients. Equivalent target coverage and sparing of OARs were achieved with VMAT compared with IMRT. The number of MU/fraction was 462 ± 68 (3DCRT), 564 ± 105 (IMRT) and 601 ± 134 (VMAT), respectively. Effective treatment times were as follows: 1.8 ± 0.2 min (3DCRT), 6.1 ± 1.5 min (IMRT) and 4.8 ± 1.0 min (VMAT). This study suggests that the VMAT plans generated in Monaco improved delivery efficiency for equivalent dosimetric quality to IMRT, and were superior to 3DCRT in target coverage and sparing of most OARs. However, the superiority of VMAT over IMRT in delivery efficiency is limited.

Dosimetric analysis of radiation-induced gastric bleeding

PURPOSE

Radiation-induced gastric bleeding has been poorly understood. In this study, we described dosimetric predictors for gastric bleeding after fractionated radiation therapy.

METHODS AND MATERIALS

The records of 139 sequential patients treated with 3-dimensional conformal radiation therapy (3D-CRT) for intrahepatic malignancies were reviewed. Median follow-up was 7.4 months. The parameters of a Lyman normal tissue complication probability (NTCP) model for the occurrence of ≥grade 3 gastric bleed, adjusted for cirrhosis, were fitted to the data. The principle of maximum likelihood was used to estimate parameters for NTCP models.

RESULTS

Sixteen of 116 evaluable patients (14%) developed gastric bleeds at a median time of 4.0 months (mean, 6.5 months; range, 2.1-28.3 months) following completion of RT. The median and mean maximum doses to the stomach were 61 and 63 Gy (range, 46-86 Gy), respectively, after biocorrection of each part of the 3D dose distributions to equivalent 2-Gy daily fractions. The Lyman NTCP model with parameters adjusted for cirrhosis predicted gastric bleed. Best-fit Lyman NTCP model parameters were n=0.10 and m=0.21 and with TD₅₀ (normal) = 56 Gy and TD₅₀ (cirrhosis) = 22 Gy. The low n value is consistent with the importance of maximum dose; a lower TD₅₀ value for the cirrhosis patients points out their greater sensitivity.

CONCLUSIONS

This study demonstrates that the Lyman NTCP model has utility for predicting gastric bleeding and that the presence of cirrhosis greatly increases this risk. These findings should facilitate the design of future clinical trials involving high-dose upper abdominal radiation.

Boron neutron capture therapy (BNCT) for liver metastasis: therapeutic efficacy in an experimental model

Boron neutron capture therapy (BNCT) was proposed for untreatable colorectal liver metastases. The present study evaluates tumor control and potential radiotoxicity of BNCT in an experimental model of liver metastasis. BDIX rats were inoculated with syngeneic colon cancer cells DHD/K12/TRb. Tumor-bearing animals were divided into three groups: BPA-BNCT, boronophenylalanine (BPA) + neutron irradiation; Beam only, neutron irradiation; Sham, matched manipulation. The total absorbed dose administered with BPA-BNCT was 13 ± 3 Gy in tumor and 9 ± 2 Gy in healthy liver. Three weeks post-treatment, the tumor surface area post-treatment/pre-treatment ratio was 0.46 ± 0.20 for BPA-BNCT, 2.7 ± 1.8 for Beam only and 4.5 ± 3.1 for Sham. The pre-treatment tumor nodule mass of 48 ± 19 mg fell significantly to 19 ± 16 mg for BPA-BNCT, but rose significantly to 140 ± 106 mg for Beam only and to 346 ± 302 mg for Sham. For both end points, the differences between the BPA-BNCT group and each of the other groups were statistically significant (ANOVA). No clinical, macroscopic or histological normal liver radiotoxicity was observed. It is concluded that BPA-BNCT induced a significant remission of experimental colorectal tumor nodules in liver with no contributory liver toxicity.

Radiation therapy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common malignancy worldwide, and its incidence is on the rise. The primary therapy is resection or liver transplant, but only a minority of patients present with resectable disease. Historically, radiotherapy has not played a significant role in the treatment of liver malignancies because of the low tolerance of the whole liver to radiation. With improvements in 3-dimensional conformal radiotherapy and intensity-modulated radiotherapy, higher doses of radiation can be delivered to target lesions with low doses to the noninvolved liver; thus, experience in the use of radiation for the treatment of focal HCC has increased. At the same time, our understanding of the relationships between radiation dose and volume and the risk of classic radiation-induced liver disease and other toxicities more likely to occur in HCC patients has improved considerably. These developments have led to a body of evidence that now supports the careful use of radiotherapy for unresectable HCC. The rationale for studying radiotherapy in a randomized trial is strong.

Hepatic arterial iodine-131-labeled metuximab injection combined with chemoembolization for unresectable hepatocellular carcinoma: interim safety and survival data from 110 patients

Few options are available to treat patients with hepatocellular carcinoma (HCC). It was tested whether the combination of iodine-131(¹³¹I)-metuximab with chemoembolization could improve outcomes in patients with intermediate HCC. Between April 2008 and April 2009, 110 patients with unresectable HCC were treated with 113 intra-arterial ¹³¹I-metuximab injections combined with chemoembolization (mean, 1.03 per patient; median, 1; range, 1-2), followed by 264 sessions of transcatheter arterial chemoembolization (mean, 2.4 per patient; median, 3; range, 1-6). The survival rates at 6, 12, and 18 months were 88.2%, 79.1%, and 57.4%, respectively, by the Kaplan-Meier method. Of these patients, 12% exhibited grade 3/4 bilirubin toxicity, 5% exhibited grade 3/4 white blood count toxicity, and 7% exhibited grade 3/4 platelet toxicity. Response rates based on World Health Organization and European Association for the Study of the Liver criteria were 42.73% and 61.82%, respectively. The combination of ¹³¹I-metuximab and chemoembolization appeared to extend survival in patients with unresectable HCC compared with historical controls, as well as being well tolerated by patients with Child-Pugh A and B. This combination may represent a promising treatment modality for patients with intermediate HCC.

Biological optimization in volumetric modulated arc radiotherapy for prostate carcinoma

PURPOSE

To investigate the potential benefits achievable with biological optimization for modulated volumetric arc (VMAT) treatments of prostate carcinoma.

METHODS AND MATERIALS

Fifteen prostate patient plans were studied retrospectively. For each case, planning target volume, rectum, and bladder were considered. Three optimization schemes were used: dose-volume histogram (DVH) based, generalized equivalent uniform dose (gEUD) based, and mixed DVH/gEUD based. For each scheme, a single or dual 6-MV, 356° VMAT arc was used. The plans were optimized with Pinnacle(3) (v. 9.0 beta) treatment planning system. For each patient, the optimized dose distributions were normalized to deliver the same prescription dose. The quality of the plans was evaluated by dose indices (DIs) and gEUDs for rectum and bladder. The tallied DIs were D(1%), D(15%), D(25%), and D(40%), and the tallied gEUDs were for a values of 1 and 6. Statistical tests were used to quantify the magnitude and the significance of the observed differences. Monitor units and treatment times for each optimization scheme were also assessed.

RESULTS

All optimization schemes generated clinically acceptable plans. The statistical tests indicated that biological optimization yielded increased organs-at-risk sparing, ranging from ~1% to more than ~27% depending on the tallied DI, gEUD, and anatomical structure. The increased sparing was at the expense of longer treatment times and increased number of monitor units.

CONCLUSIONS

Biological optimization can significantly increase the organs-at-risk sparing in VMAT optimization for prostate carcinoma. In some particular cases, however, the DVH-based optimization resulted in superior treatment plans.

Radiotherapy and chemotherapy as therapeutic strategies in extrahepatic biliary duct carcinoma

PURPOSE

this report aims to provide an overview on radiotherapy and chemotherapy in extrahepatic biliary duct carcinoma (BDC).

PATIENTS AND METHODS

a PubMed research identified clinical trials in BDC through April 1, 2010 including randomised controlled trials, SEER analyses and retrospective trials. Additionally, publications on the technical progress of radiotherapy in or close to the liver were analysed.

RESULTS

most patients with cholangiocarcinoma present with unresectable disease (80-90%), and more than half of the resected patients relapse within 1 year. Adjuvant and palliative treatment options need to be chosen carefully since 50% of the patients are older than 70 years at diagnosis. Adjuvant radiotherapy or chemotherapy after complete resection (R0) has not convincingly shown a prolongation of survival but radiotherapy did after R1 resection. However, data suggest that liver transplantation could offer long-term survival in selected patients when combined with neoadjuvant chemoradiotherapy in patients with marginally resectable disease. For patients with unresectable biliary tract carcinoma (BTC), palliative stenting was previously the treatment of choice. But recent SEER analyses show that radiotherapy prolongs survival, relieves symptoms and contributes to biliary decompression and should be regarded as the new standard. Novel technical advances in radiotherapy may allow for dose-escalation and could significantly improve outcome for patients with cholangiocarcinoma.

CONCLUSION

both the literature and recent technical progress corroborate the role of radiotherapy in BDC offering chances for novel clinical trials. Progress is less pronounced in chemotherapy.

Comparison of simple and complex liver intensity modulated radiotherapy

BACKGROUND

Intensity-modulated radiotherapy (IMRT) may allow improvement in plan quality for treatment of liver cancer, however increasing radiation modulation complexity can lead to increased uncertainties and requirements for quality assurance. This study assesses whether target coverage and normal tissue avoidance can be maintained in liver cancer intensity-modulated radiotherapy (IMRT) plans by systematically reducing the complexity of the delivered fluence.

METHODS

An optimal baseline six fraction individualized IMRT plan for 27 patients with 45 liver cancers was developed which provided a median minimum dose to 0.5 cc of the planning target volume (PTV) of 38.3 Gy (range, 25.9-59.5 Gy), in 6 fractions, while maintaining liver toxicity risk <5% and maximum luminal gastrointestinal structure doses of 30 Gy. The number of segments was systematically reduced until normal tissue constraints were exceeded while maintaining equivalent dose coverage to 95% of PTV (PTVD95). Radiotherapy doses were compared between the plans.

RESULTS

Reduction in the number of segments was achieved for all 27 plans from a median of 48 segments (range 34-52) to 19 segments (range 6-30), without exceeding normal tissue dose objectives and maintaining equivalent PTVD95 and similar PTV Equivalent Uniform Dose (EUD(-20)) IMRT plans with fewer segments had significantly less monitor units (mean, 1892 reduced to 1695, p = 0.012), but also reduced dose conformity (mean, RTOG Conformity Index 1.42 increased to 1.53 p = 0.001).

CONCLUSIONS

Tumour coverage and normal tissue objectives were maintained with simplified liver IMRT, at the expense of reduced conformity.

Three-dimensional conformal radiation therapy and intensity-modulated radiation therapy combined with transcatheter arterial chemoembolization for locally advanced hepatocellular carcinoma: an irradiation dose escalation study

PURPOSE

To determine the maximum tolerated dose (MTD) of three-dimensional conformal radiation therapy (3DCRT)/intensity-modulated radiation therapy (IMRT) combined with transcatheter arterial chemoembolization for locally advanced hepatocellular carcinoma.

METHODS AND MATERIALS

Patients were assigned to two subgroups based on tumor diameter: Group 1 had tumors <10 cm; Group II had tumors ≥10 cm. Escalation was achieved by increments of 4.0 Gy for each cohort in both groups. Dose-limiting toxicity (DLT) was defined as a grade of ≥3 acute liver or gastrointestinal toxicity or any grade 5 acute toxicity in other organs at risk or radiation-induced liver disease. The dose escalation would be terminated when ≥2 of 8 patients in a cohort experienced DLT.

RESULTS

From April 2005 to May 2008, 40 patients were enrolled. In Group I, 11 patients had grade ≤2 acute treatment-related toxicities, and no patient experienced DLT; and in Group II, 10 patients had grade ≤2 acute toxicity, and 1 patient in the group receiving 52 Gy developed radiation-induced liver disease. MTD was 62 Gy for Group I and 52 Gy for Group II. In-field progression-free and local progression-free rates were 100% and 69% at 1 year, and 93% and 44% at 2 years, respectively. Distant metastasis rates were 6% at 1 year and 15% at 2 years. Overall survival rates for 1-year and 2-years were 72% and 62%, respectively.

CONCLUSIONS

The irradiation dose was safely escalated in hepatocellular carcinoma patients by using 3DCRT/IMRT with an active breathing coordinator. MTD was 62 Gy and 52 Gy for patients with tumor diameters of <10 cm and ≥10 cm, respectively.

Intensity-modulated radiotherapy plan optimisation for skull base lesions: practical class solutions for dose escalation

AIMS

To identify practical intensity-modulated radiotherapy planning solutions when attempting dose escalation in the skull base.

MATERIALS AND METHODS

Twenty cases of skull base meningioma were re-planned using a variation of beam number (three, five, seven and nine), beam arrangement (coplanar vs non-coplanar) and multileaf collimator (MLC) width (2.5 mm vs 10 mm) to 60 Gy/30 fractions. Plan quality and planning target volume coverage was assessed using planning target volume V(95%), equivalent uniform dose (EUD) and integral dose.

RESULTS

Critical structures were maintained below clinical tolerance levels. The 2.5 mm MLC achieved an average improvement in V(95%) by 22.8% (P=0.0003), EUD by 3.7 Gy (P=0.002) and reduced the integral dose by 13.4 Gy (P=0.0001). V(95%) and the integral dose improved with five vs three beams and seven vs five beams, but did not change with nine vs seven beams. There was no effect of beam number on EUD. There was no difference in V(95%) (P=0.54), integral dose (P=0.44) or EUD (P=0.47) for beam arrangement used. Segments per plan increased by a factor of 1.5 with each addition of two beams to a plan, and by a factor of 2.5 for 2.5 mm MLC plans vs 10 mm MLC plans.

CONCLUSIONS

We present evidence-based planning solutions for skull base intensity-modulated radiotherapy, and show that 2.5 mm MLC and five to seven beams can achieve safe dose escalation up to 60 Gy. This must be balanced with an increase in segmentation, which will increase treatment times.

Critical appraisal of volumetric modulated arc therapy in stereotactic body radiation therapy for metastases to abdominal lymph nodes

PURPOSE

A planning study was performed comparing volumetric modulated arcs, RapidArc (RA), fixed beam IMRT (IM), and conformal radiotherapy (CRT) with multiple static fields or short conformal arcs in a series of patients treated with hypofractionated stereotactic body radiation therapy (SBRT) for solitary or oligo-metastases from different tumors to abdominal lymph nodes.

METHODS AND MATERIALS

Fourteen patients were included in the study. Dose prescription was set to 45 Gy (mean dose to clinical target volume [CTV]) in six fractions of 7.5 Gy. Objectives for CTV and planning target volume (PTV) were as follows: Dose(min) >95%, Dose(max) <107%. For organs at risk the following objectives were used: Maximum dose to spine <18 Gy; V(15Gy) <35% for both kidneys, V(36Gy) <1% for duodenum, V(36Gy) <3% for stomach and small bowel, V(15Gy) <(total liver volume--700 cm(3)) for liver. Dose-volume histograms were evaluated to assess plan quality.

RESULTS

Planning objectives on CTV and PTV were achieved by all techniques. Use of RA improved PTV coverage (V(95%) = 90.2% +/- 5.2% for RA compared with 82.5% +/- 9.6% and 84.5% +/- 8.2% for CRT and IM, respectively). Most planning objectives for organs at risk were met by all techniques except for the duodenum, small bowel, and stomach, in which the CRT plans exceeded the dose/volume constraints in some patients. The MU/fraction values were as follows: 2186 +/- 211 for RA, 2583 +/- 699 for IM, and 1554 +/- 153 for CRT. Effective treatment time resulted as follows: 3.7 +/- 0.4 min for RA, 10.6 +/- 1.2 min for IM, and 6.3 +/- 0.5 min for CRT.

CONCLUSIONS

Delivery of SBRT by RA showed improvements in conformal avoidance with respect to standard conformal irradiation. Delivery parameters confirmed logistical advantages of RA, particularly compared with IM.

Treatment planning study to determine potential benefit of intensity-modulated radiotherapy versus conformal radiotherapy for unresectable hepatic malignancies

PURPOSE

To compare intensity-modulated radiotherapy (IMRT) with conformal RT (CRT) for hypofractionated isotoxicity liver RT and explore dose escalation using IMRT for the same/improved nominal risk of liver toxicity in a treatment planning study.

METHODS AND MATERIALS

A total of 26 CRT plans were evaluated. Prescription doses (24-54 Gy within six fractions) were individualized on the basis of the effective liver volume irradiated maintaining < or =5% risk of radiation-induced liver disease. The dose constraints included bowel (0.5 cm(3)) and stomach (0.5 cm(3)) to < or =30 Gy, spinal cord to < or =25 Gy, and planning target volume (PTV) to < or =140% of the prescribed dose. Two groups were evaluated: (1) PTV overlapping or directly adjacent to serial functioning normal tissues (n = 14), and (2) the liver as the dose-limiting normal tissue (n = 12). IMRT plans using direct machine parameter optimization maintained the CRT plan beam arrangements, an estimated radiation-induced liver disease risk of 5%, and underwent dose escalation, if all normal tissue constraints were maintained.

RESULTS

IMRT improved PTV coverage in 19 of 26 plans (73%). Dose escalation was feasible in 9 cases by an average of 3.8 Gy (range, 0.6-13.2) in six fractions. Three of seven plans without improved PTV coverage had small gross tumor volumes (< or =105 cm(3)) already receiving 54 Gy, the maximal prescription dose allowed. In the remaining cases, the PTV range was 9.6-689 cm(3); two had overlapped organs at risk; and one had four targets. IMRT did not improve these plans owing to poor target coverage (n = 2) and nonliver (n = 2) dose limits.

CONCLUSION

Direct machine parameter optimization IMRT improved PTV coverage while maintaining normal tissue tolerances in most CRT liver plans. Dose escalation was possible in a minority of patients.

Automated non-coplanar beam direction optimization improves IMRT in SBRT of liver metastasis

PURPOSE

To investigate whether automatically optimized coplanar, or non-coplanar beam setups improve intensity modulated radiotherapy (IMRT) treatment plans for stereotactic body radiotherapy (SBRT) of liver tumors, compared to a reference equi-angular IMRT plan.

METHODS

For a group of 13 liver patients, an in-house developed beam selection algorithm (Cycle) was used for generation of 3D-CRT plans with either optimized coplanar-, or non-coplanar beam setups. These 10 field, coplanar and non-coplanar setups, and an 11 field, equi-angular coplanar reference setup were then used as input for generation of IMRT plans. For all plans, the PTV dose was maximized in an iterative procedure by increasing the prescribed PTV dose in small steps until further increase was prevented by constraint violation(s).

RESULTS

For optimized non-coplanar setups, D(PTV, max) increased by on average 30% (range 8-64%) compared to the corresponding reference IMRT plan. Similar increases were observed for D(PTV, 99%) and gEUD(a). For optimized coplanar setups, mean PTV dose increases were only approximately 4%. After re-scaling all plans to the clinically applied dose, optimized non-coplanar configurations resulted in the best sparing of organs at risk (healthy liver, spinal cord, bowel).

CONCLUSION

Compared to an equi-angular beam setup, computer optimized non-coplanar setups do result in substantial improvements in IMRT plans for SBRT of liver tumors.

Simultaneous tumour dose escalation and liver sparing in Stereotactic Body Radiation Therapy (SBRT) for liver tumours due to CTV-to-PTV margin reduction

PURPOSE

To quantify potential benefits of CTV-to-PTV margin reduction for SBRT of liver tumours, as allowed by enhanced treatment precision.

MATERIALS AND METHODS

For 14 patients plans were generated for the clinical margin and for 3 tighter margins. An in-house developed algorithm was used to optimise beam directions, shapes, and weights for generation of the plan with the highest isocenter dose (D(iso)), while keeping the minimum PTV dose at least 65%xD(iso) and strictly adhering to all imposed hard OAR constraints. Each plan contains 10 optimal beam directions, automatically selected from up to 252 coplanar and non-coplanar input directions.

RESULTS

Apart from the expected tumour dose escalation (D(iso), EUD(PTV), gEUD(PTV)) with decreasing margin, a simultaneous improved sparing of the normal liver (D33%, D50%, D(mean)) was also observed. The smaller the margin was, the bigger both effects were. For renormalized plans with D(iso) equal to the clinical value (3x19.2Gy), and a margin reduction of 50% (2.5mm laterally, 5mm longitudinally), normal liver D33% and D50% reduced on average by 22% (maximum 38%), and 26% (maximum 47%), respectively.

CONCLUSIONS

Using an algorithm for beam direction, shape and weight optimisation, large increases in the therapeutic ratio of liver plans could be obtained for reduced margins.

PTV dose prescription strategies for SBRT of metastatic liver tumours

PURPOSE

Recently we have demonstrated that our in-house developed algorithm for automated plan generation for fully non-coplanar SBRT of liver patients (designated Cycle) yields plans that are superior to conventionally generated plans of experienced dosimetrists. Here we use Cycle in the comparison of plans with prescription isodoses of 65% or 80% of the isocentre dose.

METHODS

Plans were generated using CT-data of 15 previously treated patients. For each patient, both for the 65%- and the 80% strategy, Cycle was used to generate a plan with the maximum isocentre dose, D(isoc), while strictly obeying a set of hard constraints for the organs at risk (OAR). Plans for the two strategies were compared using D(isoc), D(PTV,99%) (the minimum dose delivered to 99% of the PTV), and the generalised equivalent uniform dose, gEUD(PTV)(a), for several values of the parameter a. Moreover, for the OARs, the distance to the constraint values was analysed.

RESULTS

The 65% strategy resulted in treatment plans with a higher D(isoc) (average 17.6%, range 7.6-31.1%) than the 80% strategy, at the cost of a somewhat lower D(PTV,99%) (average -2.0%, range -9.6% to 9.3%). On average, voxels with a dose in the 65% strategy, lower than the minimum PTV dose in the 80% strategy, were within 0.2cm from the PTV surface. For a-10, the 65% strategy yielded on average a significantly (P<0.01) higher gEUD(PTV)(a) than the 80% strategy, whereas for highly negative a-values the 80% approach was slightly better, although not significantly. Large variations between patients were observed. Generally, for the OAR the approach to the constraint levels was similar for the two strategies.

CONCLUSION

On average, PTV dose delivery is superior with the 65% strategy. However, apart from the isocentre dose, for each applied PTV dose parameter at least one patient would have been better off with the 80% dose prescription strategy.

CalcNTCP: a simple tool for computation of normal tissue complication probability (NTCP) associated with cancer radiotherapy

PURPOSE

This study was aimed to develop a simple and user-friendly software for fast and accurate computation of normal tissue complication probability (NTCP) in accordance with the Lyman model.

MATERIALS AND METHODS

The software CalcNTCP has been developed in Visual Basic and is equipped with two functional modes. Mode 1 is based on pre-stored values of various parameters for 27 different organ systems and the user has only to input the values of volume fraction (v) and radiation dose (D), whereas Mode 2 is designed for the customized entries.

RESULTS

The results of software validation have demonstrated that CalcNTCP is more efficient and time-saving as compared to manual or semi-manual procedures. The shapes and locations of representative survival curves generated by CalcNTCP-based computations for various radiation doses (10 - 100 Gy) and reference volumes (0.33 - 1.00) absolutely matched with optimal curves.

CONCLUSION

CalcNTCP is a simple, fast and accurate tool for the computation of NTCP with a direct implication in the evaluation or optimization of radiotherapy treatment plans.

Towards an objective evaluation of tolerances for beam modeling in a treatment planning system

The performance of a convolution/superposition based treatment planning system depends on the ability of the dose calculation algorithm to accurately account for physical interactions taking place in the tissue, key components of the linac head and on the accuracy of the photon beam model. Generally the user has little or no control over the performance of the dose calculation algorithm but is responsible for the accuracy of the beam model within the constraints imposed by the system. This study explores the dosimetric impact of limitations in photon beam modeling accuracy on complex 3D clinical treatment plans. A total of 70 photon beam models was created in the Pinnacle treatment planning system. Two of the models served as references for 6 MV and 15 MV beams, while the rest were created by perturbing the reference models in order to produce specific deviations in specific regions of the calculated dose profiles (central axis and transverse). The beam models were then used to generate 3D plans on seven CT data sets each for four different treatment sites (breast and conformal prostate, lung and brain). The equivalent uniform doses (EUD) of the targets and the principal organs at risk (OARs) of all plans ( approximately 1000) were calculated and compared to the EUDs delivered by the reference beam models. In general, accurate dosimetry of the target is most greatly compromised by poor modeling of the central axis depth dose and the horns, while the EUDs of the OARs exhibited the greatest sensitivity to beam width accuracy. Based on the results of this analysis we suggest a set of tolerances to be met during commissioning of the beam models in a treatment planning system that are consistent in terms of clinical outcomes as predicted by the EUD.

First Attempt of Boron Neutron Capture Therapy (BNCT) for Hepatocellular Carcinoma

A 60-year-old man with multiple hepatocellular carcinomas (HCCs) was enrolled as the first patient in a pilot study for treating multiple liver tumors with boron neutron capture therapy (BNCT). Because of compromised liver function, the multiple tumors in the right liver lobe were treated with BNCT and those in the left lobe with hepatic arterial chemoembolization. The feasibility and clinical outcome of this first case was assessed. During the treatment and follow-up period, no adverse effect as a result of BNCT was observed except for temporary temperature elevation to 38.3 degrees C, and the AST and ALT being higher than 200 IU/l. For 1 month, the tumors treated with BNCT remained stable in size. The BNCT-treated tumors showed regrowth 3.5 months after BNCT and the patient died of liver dysfunction caused by progression of HCC 10 months after BNCT. The feasibility of BNCT for HCC is confirmed in this first case.

Self-consistent tumor control probability and normal tissue complication probability models based on generalized EUDa)

Traditional methods to compute the tumor control probability (TCP) or normal tissue complication probability (NTCP) typically require a heterogeneous radiation dose distribution to be converted into a simple uniform dose distribution with an equivalent biological effect. Several power-law type dose-volume-histogram reduction schemes, particularly Niemierko's generalized equivalent uniform dose model [Med. Phys. 26, 1000 (1999)], have been proposed to achieve this goal. In this study, we carefully examine the mathematical outcome of these schemes. We demonstrate that (1) for tumors, with each tumor cell independently responding to local radiation dose, a closed-form analytical solution for tumor survival fraction and TCP can be obtained; (2) for serial structured normal tissues, an exponential power-law form relating survival to functional sub-unit (FSU) radiation is required, and a closed-form analytical solution for the related NTCP is provided; (3) in the case of a parallel structured normal tissue, when NTCP is determined solely by the number of the surviving FSUs, a mathematical solution is available only when there is a non-zero threshold dose and/or a finite critical dose defining the radiotherapy response. Some discussion is offered for the partial irradiation effect on normal tissues in this category; (4) for normal tissues with alternative architectures, where the radiation response of FSU is inhomogeneous, there is no exact global mathematical solution for SF or NTCP within the available schemes. Finally, numerical fits of our models to some experimental data are also presented.

Potential for dose-escalation and reduction of risk in pancreatic cancer using IMRT optimization with lexicographic ordering and gEUD-based cost functions

Radiotherapy for pancreatic cancer is limited by the tolerance of local organs at risk (OARs) and frequent overlap of the planning target volume (PTV) and OAR volumes. Using lexicographic ordering (LO), a hierarchical optimization technique, with generalized equivalent uniform dose (gEUD) cost functions, we studied the potential of intensity modulated radiation therapy (IMRT) to increase the dose to pancreatic tumors and to areas of vascular involvement that preclude surgical resection [surgical boost volume (SBV)]. We compared 15 forward planned three-dimensional conformal (3DCRT) and IMRT treatment plans for locally advanced unresectable pancreatic cancer. We created IMRT plans optimized using LO with gEUD-based cost functions that account for the contribution of each part of the resulting inhomogeneous dose distribution. LO-IMRT plans allowed substantial PTV dose escalation compared with 3DCRT; median increase from 52 Gy to 66 Gy (a=-5,p<0.005) and median increase from 50 Gy to 59 Gy (a=-15,p<0.005). LO-IMRT also allowed increases to 85 Gy in the SBV, regardless of a value, along with significant dose reductions in OARs. We conclude that LO-IMRT with gEUD cost functions could allow dose escalation in pancreas tumors with concomitant reduction in doses to organs at risk as compared with traditional 3DCRT.

On relating the generalized equivalent uniform dose formalism to the linear-quadratic model

Two main approaches are commonly used in the literature for computing the equivalent uniform dose (EUD) in radiotherapy. The first approach is based on the cell-survival curve as defined in the linear-quadratic model. The second approach assumes that EUD can be computed as the generalized mean of the dose distribution with an appropriate fitting parameter. We have analyzed the connection between these two formalisms by deriving explicit formulas for the EUD which are applicable to normal distributions. From these formulas we have established an explicit connection between the two formalisms. We found that the EUD parameter has strong dependence on the parameters that characterize the distribution, namely the mean dose and the standard deviation around the mean. By computing the corresponding parameters for clinical dose distributions, which in general do not follow the normal distribution, we have shown that our results are also applicable to actual dose distributions. Our analysis suggests that caution should be used in using generalized EUD approach for reporting and analyzing dose distributions.

Computer optimization of noncoplanar beam setups improves stereotactic treatment of liver tumors

PURPOSE

To investigate whether computer-optimized fully noncoplanar beam setups may improve treatment plans for the stereotactic treatment of liver tumors.

METHODS

An algorithm for automated beam orientation and weight selection (Cycle) was extended for noncoplanar stereotactic treatments. For 8 liver patients previously treated in our clinic using a prescription isodose of 65%, Cycle was used to generate noncoplanar and coplanar plans with the highest achievable minimum planning target volume (PTV) dose for the clinically delivered isocenter and mean liver doses, while not violating the clinically applied hard planning constraints. The clinical and the optimized coplanar and noncoplanar plans were compared, with respect to D(PTV,99%), the dose received by 99% of the PTV, the PTV generalized equivalent uniform dose (gEUD), and the compliance with the clinical constraints.

RESULTS

For each patient, the ratio between D(PTV,99%) and D(isoc), and the gEUD(-5) and gEUD(-20) values of the optimized noncoplanar plan were higher than for the clinical plan with an average increase of respectively 18.8% (range, 7.8-24.0%), 6.4 Gy (range, 3.4-11.8 Gy), and 10.3 Gy (range, 6.7-12.5). D(PTV,99%)/D(isoc), gEUD(-5), and gEUD(-20) of the optimized noncoplanar plan was always higher than for the optimized coplanar plan with an average increase of, respectively, 4.5% (range, 0.2-9.7%), 2.7 Gy (range, 0.6-9.7 Gy), and 3.4 Gy (range, 0.6-9.9 Gy). All plans were within the imposed hard constraints. On average, the organs at risk were better spared with the optimized noncoplanar plan than with the optimized coplanar plan and the clinical plan.

CONCLUSIONS

The use of automatically generated, fully noncoplanar beam setups results in plans that are favorable compared with coplanar techniques. Because of the automation, we found that the planning workload can be decreased from 1 to 2 days to 1 to 2 h.

The Clinical Application of Intensity-Modulated Radiation Therapy

Intensity-modulated radiation therapy is a delivery system that, when coupled with a treatment-planning optimization system, presents the opportunity to conform the dose to the target better than 3-dimensional conformal therapy, particularly in the case of concave targets. Appropriate clinical applications of this technology to challenging patient treatment scenarios requires careful consideration of issues related to target volume-dose heterogeneity and the influence of patient setup uncertainties. These issues are reviewed and illustrated. To date, clinical reports of these treatments for prostate and head and neck cancers have the most mature data. Those results are summarized here. Future applications of this technology can be expected to take careful, considered advantage of this technology to further rearrange dose distributions across target volumes to produce an integrated overall gain in treatment objectives. However, these innovative applications need to be approached with caution, preferably in prospective clinical trials that would help determine if the hypothetical clinical benefits are in fact realizable.

Radiation therapy for hepatocellular carcinoma: from palliation to cure

Technologic advances have provided the means to deliver tumoricidal doses of radiation therapy (RT) to patients with unresectable hepatocellular carcinoma (HCC) while avoiding critical normal tissues, providing the opportunity to use RT for curative intent treatment of HCC. For the current report, the expanded role of external beam RT in the setting of HCC from palliation to cure was reviewed. A systematic literature search was undertaken using the MEDLINE data base and secondary references to identify peer-reviewed, English-language articles that reported clinical outcomes after external beam RT alone or in combination with other treatments for HCC. Abstracts from the 2005 American Society of Clinical Oncology, American Society for Therapeutic Radiology and Oncology, American Gastrointestinal Association, and Society of Surgical Oncology Gastrointestinal Cancer Symposium also were included in the search. More than 60 articles reporting on clinical outcomes among patients who received RT for HCC have been published since 1990, including 20 articles that described unique sets of at least 15 patients. RT was used for palliation, to improve local control, and with curative intent in a wide spectrum of patients who most often were unsuitable for surgery and other treatments. Pain reduction following RT was noted in approximately 75% of patients with bone metastases from HCC who received RT. For patients with liver-confined disease treated with conformal RT, proton beam RT, and/or image guided RT with or without transarterial chemoembolization (TACE), local control response rates ranged from 40% to 90%, and the median survival ranges from 10 months to 25 months. For patients with HCC who had portal vein thrombus, the median survival after RT to treat the thrombus and/or the hepatic tumor with or without TACE ranged from 5.3 months to 9.7 months. Although outcomes after high-dose conformal RT for liver-confined HCC were excellent, the potential survival benefit of RT should be tested in randomized controlled trials that require international collaboration.

Multiple fields may offer better esophagus sparing without increased probability of lung toxicity in optimized IMRT of lung tumors

PURPOSE

To evaluate whether increasing numbers of intensity-modulated radiation therapy (IMRT) fields enhance lung-tumor dose without additional predicted toxicity for difficult planning geometries.

METHODS AND MATERIALS

Data from 8 previous three dimensional conformal radiation therapy (3D-CRT) patients with tumors located in various regions of each lung, but with planning target volumes (PTVs) overlapping part of the esophagus, were used as input. Four optimized-beamlet IMRT plans (1 plan that used the 3D-CRT beam arrangement and 3 plans with 3, 5, or 7 axial, but predominantly one-sided, fields) were compared. For IMRT, the equivalent uniform dose (EUD) in the whole PTV was optimized simultaneously with that in a reduced PTV exclusive of the esophagus. Normal-tissue complication probability-based costlets were used for the esophagus, heart, and lung.

RESULTS

Overall, IMRT plans (optimized by use of EUD to judiciously allow relaxed PTV dose homogeneity) result in better minimum PTV isodose surface coverage and better average EUD values than does conformal planning; dose generally increases with the number of fields. Even 7-field plans do not significantly alter normal-lung mean-dose values or lung volumes that receive more than 13, 20, or 30 Gy.

CONCLUSION

Optimized many-field IMRT plans can lead to escalated lung-tumor dose in the special case of esophagus overlapping PTV, without unacceptable alteration in the dose distribution to normal lung.

Dose–volume based ranking of incident beam direction and its utility in facilitating IMRT beam placement

PURPOSE

Beam orientation optimization in intensity-modulated radiation therapy (IMRT) is computationally intensive, and various single beam ranking techniques have been proposed to reduce the search space. Up to this point, none of the existing ranking techniques considers the clinically important dose-volume effects of the involved structures, which may lead to clinically irrelevant angular ranking. The purpose of this work is to develop a clinically sensible angular ranking model with incorporation of dose-volume effects and to show its utility for IMRT beam placement.

METHODS AND MATERIALS

The general consideration in constructing this angular ranking function is that a beamlet/beam is preferable if it can deliver a higher dose to the target without exceeding the tolerance of the sensitive structures located on the path of the beamlet/beam. In the previously proposed dose-based approach, the beamlets are treated independently and, to compute the maximally deliverable dose to the target volume, the intensity of each beamlet is pushed to its maximum intensity without considering the values of other beamlets. When volumetric structures are involved, the complication arises from the fact that there are numerous dose distributions corresponding to the same dose-volume tolerance. In this situation, the beamlets are not independent and an optimization algorithm is required to find the intensity profile that delivers the maximum target dose while satisfying the volumetric constraints. In this study, the behavior of a volumetric organ was modeled by using the equivalent uniform dose (EUD). A constrained sequential quadratic programming algorithm (CFSQP) was used to find the beam profile that delivers the maximum dose to the target volume without violating the EUD constraint or constraints. To assess the utility of the proposed technique, we planned a head-and-neck and abdominal case with and without the guidance of the angular ranking information. The qualities of the two types of IMRT plans were compared quantitatively.

RESULTS

An effective angular ranking model with consideration of volumetric effect has been developed. It is shown that the previously reported dose-based angular ranking represents a special case of the general formalism proposed here. Application of the technique to a abdominal and a head-and-neck IMRT case indicated that the proposed technique is capable of producing clinically sensible angular ranking. In both cases, we found that the IMRT plans obtained under the guidance of EUD-based angular ranking were improved in comparison with that obtained using the conventional uniformly spaced beams.

CONCLUSIONS

The EUD-based function is a general approach for angular ranking and allows us to identify the potentially good and bad angles for clinically complicated cases. The ranking can be used either as a guidance to facilitate the manual beam placement or as prior information to speed up the computer search for the optimal beam configuration. Thus the proposed technique should have positive clinical impact in facilitating the IMRT planning process.