A new plan quality index for nasopharyngeal cancer SIB IMRT

A new plan quality index integrating dosimetric and radiobiological indices was proposed to facilitate the evaluation and comparison of simultaneous integrated boost (SIB) intensity modulated radiotherapy (IMRT) plans for nasopharyngeal cancer (NPC) patients.Ten NPC patients treated by SIB-IMRT were enrolled in the study. Custom software was developed to read dose–volume histogram (DVH) curves from the treatment planning system (TPS). A plan filtering matrix was introduced to filter plans that fail to satisfy treatment protocol. Target plan quality indices and organ at risk (OAR) plan quality indices were calculated for qualified plans. A unique composite plan quality index (CPQI) was proposed based on the relative weight of these indices to evaluate and compare competing plans. Plan ranking results were compared with detailed statistical analysis, radiation oncology quality system (ROQS) scoring results and physician's evaluation results to verify the accuracy of this new plan quality index.The average CPQI values for plans with OAR priority of low, normal, high, and PTV only were 0.22 ± 0.08, 0.49 ± 0.077, 0.71 ± 0.062, and −0.21 ± 0.16, respectively. There were significant differences among these plan quality indices (One-way ANOVA test, p < 0.01). This was consistent with statistical analysis, ROQS results and physician's ranking results in which 90% OAR high plans were selected.Plan filtering matrix was able to speed up the plan evaluation process. The new matrix plan quality index CPQI showed good consistence with physician ranking results. It is a promising index for NPC SIB-IMRT plan evaluation.     

Integrated scoring approach to assess radiotherapy plan quality for breast cancer treatment

BackgroundProposal of an integrated scoring approach assessing the quality of different treatment techniques in a radiotherapy planning comparison. This scoring method incorporates all dosimetric indices of planning target volumes (PTVs) as well as organs at risk (OARs) and provides a single quantitative measure to select an ideal plan.Materials and methodsThe radiotherapy planning techniques compared were field-in-field (FinF), intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), hybrid IMRT (H-IMRT), and hybrid VMAT (H-VMAT). These plans were generated for twenty-five locally advanced left-sided breast cancer patients. The PTVs were prescribed a hypofractionation dose of 40.5 Gy in 15 fractions. The integrated score for each planning technique was calculated using the proposed formula.ResultsAn integrated score value that is close to zero indicates a superior plan. The integrated score that incorporates all dosimetric indices (PTVs and OARs) were 1.37, 1.64, 1.72, 1.18, and 1.24 for FinF, IMRT, VMAT, H-IMRT, and H-VMAT plans, respectively.ConclusionThe proposed integrated scoring approach is scientific to select a better plan and flexible to incorporate the patient-specific clinical demands. This simple tool is useful to quantify the treatment techniques and able to differentiate the acceptable and unacceptable plans.     

Influence of segment width on plan quality for volumetric modulated arc based stereotactic body radiotherapy

Aim

To study the influence of segment width on plan quality for volumetric modulated arc based stereotactic body radiotherapy.

Background

The redundancy of modulation for regularly shaped small volume tumors results in creation of many small segments and an increase of monitor units, with a consequent prolongation of treatment and uncertainty in treatment delivery.

Materials and methods

Six cases each in lung, abdomen and liver were taken for the study. For each case, three VMAT SBRT plans were generated with different penalties on minimum segment width of 0.5, 1.0 and 1.5 cm. A comparison was made on the metrics of dose volume histogram, dosimetric indices, monitor units (MUs) and delivery accuracy.

Results

The mean reduction of total MUs when compared with 0.5 cm plan was observed as 12.7 ± 6.0% and 17.5 ± 7.2% for 1.0 cm and 1.5 cm of minimum segment width, respectively. The p value showed a significant degradation in dosimetric indices for 1.5 cm plans when compared with 0.5 cm and 1.0 cm plans. The average deviation of measured dose with TPS calculated was 3.0 ± 1.1%, 2.1 ± 0.84% and 1.8 ± 0.9% for 0.5, 1.0 and 1.5 cm, respectively. The calculated gamma index with pass criteria of 2% dose difference and 2 mm distance to agreement was 95.9 ± 2.8%, 96.5 ± 2.6% and 97.8 ± 1.6% as calculated for 0.5, 1.0 and 1.5 cm of penalties, respectively. In view of the trade off between delivery efficiency and plan quality, 1 cm minimum segment width plans showed an improvement.

Conclusions

VMAT SBRT plans with increased optimal value of minimum segment width showed better plan quality and delivery efficiency for stereotactic body radiotherapy.     

Characterization of phenolic pellets for ESR dosimetry in photon beam radiotherapy

This work deals with the dosimetric features of a particular phenolic compound (IRGANOX 1076^®) for dosimetry of clinical photon beams by using electron spin resonance (ESR) spectroscopy. After the optimization of the ESR readout parameters (namely modulation amplitude and microwave power) to maximise the signal without excessive spectrum distortions, basic dosimetric properties of laboratory-made phenolic dosimeters in pellet form, such as reproducibility, dose–response, sensitivity, linearity and dose rate dependence were investigated. The dosimeters were tested by measuring the depth dose profile of a 6 MV photon beam. A satisfactory intra-batch reproducibility of the ESR signal of the manufactured dosimeters was obtained. The ESR signal proved to increase linearly with increasing dose in the investigated dose range 1–13 Gy. The presence of an intrinsic background signal limits the minimum detectable dose to a value of approximately 0.6 Gy. Reliable and accurate assessment of the dose was achieved, independently of the dose rate. Such characteristics, together with the fact that IRGANOX 1076^® is almost tissue-equivalent, and the stability of the ESR signal, make these dosimeters promising materials for ESR dosimetric applications in radiotherapy.     

Boosting runtime-performance of photon pencil beam algorithms for radiotherapy treatment planning

Pencil beam algorithms are still considered as standard photon dose calculation methods in Radiotherapy treatment planning for many clinical applications. Despite their established role in radiotherapy planning their performance and clinical applicability has to be continuously adapted to evolving complex treatment techniques such as adaptive radiation therapy (ART). We herewith report on a new highly efficient version of a well-established pencil beam convolution algorithm which relies purely on measured input data. A method was developed that improves raytracing efficiency by exploiting the capability of modern CPU architecture for a runtime reduction. Since most of the current desktop computers provide more than one calculation unit we used symmetric multiprocessing extensively to parallelize the workload and thus decreasing the algorithmic runtime. To maximize the advantage of code parallelization, we present two implementation strategies – one for the dose calculation in inverse planning software, and one for traditional forward planning. As a result, we could achieve on a 16-core personal computer with AMD processors a superlinear speedup factor of approx. 18 for calculating the dose distribution of typical forward IMRT treatment plans.     

A comparison of a moderately hypofractionated IMRT planning technique used in a randomised UK external beam radiotherapy trial with an in-house technique for localised prostate cancer

AimTo compare the radiotherapy technique used in a randomised trial with VMAT and an in-house technique for prostate cancer.BackgroundTechniques are evolving with volumetric modulated arc therapy (VMAT) commonly used. The CHHiP trial used a 3 PTV forward planned IMRT technique (FP_CH). Our centre has adopted a simpler two PTV technique with locally calculated margins.Materials and methods25 patients treated with FP_CH to 60 Gy in 20 fractions were re-planned with VMAT (VMAT_CH) and a two PTV protocol (VMAT_60/52 and VMAT_60/48). Target coverage, conformity index (CI), homogeneity index (HI), monitor units (MU) and dose to the rectum, bladder, hips and penile bulb were compared.ResultsPTV coverage was high for all techniques. VMAT_CH plans had better CI than FP_CH (p ≤  0.05). VMAT_60/52/48 plans had better CI than VMAT_CH. FP_CH had better HI and fewer MU than VMAT (p ≤  0.05). More favourable rectum doses were found for VMAT _CH than FP_CH (V_48.6, V_52.8, V₅₇, p ≤  0.05) with less difference for bladder (p ≥  0.05). Comparing VMAT_CH to VMAT_60/52/48 showed little differences for the bladder and rectum but VMAT_CH had larger penile bulb doses (V_40.8, V_48.6, mean, D_2, p ≤  0.05). Femoral head doses (V_40.8) were similarly low for all techniques (p = ≥ 0.05).ConclusionVMAT produced more conformal plans with smaller rectum doses compared to FP_CH albeit worse HI and more MU. VMAT_60/52 and VMAT_60/48 plans had similar rectal and bladder doses to VMAT_CH but better CI and penile bulb doses which may reduce toxicity.     

Dosimetric study of a hybrid plan technique for external beam radiotherapy in patients with cervical cancer

The aim of this study was to investigate the effect of a hybrid technique which results from combining intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for the treatment of cervical cancer patients. Plans made with the hybrid technique and pure IMRT and VMAT were retrospectively compared in 20 patients with cervical cancer at different stages. All plans were made using the same contours based on the original computed tomography (CT) scans. Conformity (CI) and homogeneity (HI) indices of the planning target volumes (PTVs) were calculated for each technique in order to evaluate plan quality. All techniques were compared in terms of dose to organs at risk (OARs), number of monitor units (MUs) and treatment time. It turned out that plans made with the hybrid technique had improved dose conformity and homogeneity compared to plans made only with IMRT and VMAT (p < 0.001). Regarding the OARs, the maximum dose (D_max) delivered to the bladder, rectum and femoral heads was lower for the hybrid plans compared to the IMRT and VMAT plans (p < 0.001). The volumes irradiated to doses of 50 Gy (V_50Gy) for rectum, bladder and bowel were lower for the hybrid plans (p < 0.001, p = 0.002). Furthermore, the treatment time and MU values for the hybrid plans were found to be between of the values for the IMRT and VMAT plans. It is concluded that, as compared to IMRT and VMAT plans, the hybrid plan technique allowed a better conformity and homogeneity for the dose distribution in the PTV and a dose reduction to the OARs.

     

Predicting toxicity in radiotherapy for prostate cancer

This comprehensive review addresses most organs at risk involved in planning optimization for prostate cancer. It can be considered an update of a previous educational review that was published in 2009 (Fiorino et al., 2009).The literature was reviewed based on PubMed and MEDLINE database searches (from January 2009 up to September 2015), including papers in press; for each section/subsection, key title words were used and possibly combined with other more general key-words (such as radiotherapy, dose-volume effects, NTCP, DVH, and predictive model). Publications generally dealing with toxicity without any association with dose–volume effects or correlations with clinical risk factors were disregarded, being outside the aim of the review.A focus was on external beam radiotherapy, including post-prostatectomy, with conventional fractionation or moderate hypofractionation (<4 Gy/fraction); extreme hypofractionation is the topic of another paper in this special issue. Gastrointestinal and urinary toxicity are the most investigated endpoints, with quantitative data published in the last 5 years suggesting both a dose–response relationship and the existence of a number of clinical/patient related risk factors acting as dose–response modifiers. Some results on erectile dysfunction, bowel toxicity and hematological toxicity are also presented.     

Magnetic resonance imaging for prostate cancer radiotherapy

For radiotherapy of prostate cancer, MRI is used increasingly for delineation of the prostate gland. For focal treatment of low-risk prostate cancer or focal dose escalation for intermediate and high-risk cancer, delineation of the tumor is also required. While multi-parametric MRI is well established for detection of tumors and for staging of the disease, delineation of the tumor inside the prostate is not common practice.Guidelines, such as the PI-RADS classification, exist for tumor detection and staging, but no such guidelines are available for tumor delineation. Indeed, interobserver studies show substantial variation in tumor contours. Computer-aided tumor detection and delineation may help improve the robustness of the interpretation of multi-parametric MRI data. Comparing the performance of an earlier developed model for tumor segmentation with expert delineations, we found a significant correlation between tumor probability in a voxel and the number of experts identifying this voxel as tumor. This suggests that the model agrees with ‘the wisdom of the crowd’, and thus could serve as a reference for individual physicians in their decision making.With multi-parametric MRI it becomes feasible to revisit the GTV-CTV concept in radiotherapy of prostate cancer. While detection of index lesions is quite reliable, contouring variability and the low sensitivity to small lesions suggest that the remainder of the prostate should be treated as CTV. Clinical trials that investigate the options for dose differentiation, for example with dose escalation to the visible tumor or dose reduction to the CTV, are therefore warranted.     

Conversion of the helical tomotherapy plans to the step-and-shoot IMRT plans for patients with hip prosthesis during radiotherapy for prostate cancer

PurposeTo evaluate the SharePlan software in conversion of helical tomotherapy (HT) to a step and shoot IMRT (sIMRT) for patients with high-risk prostate cancer and hip prosthesis.MethodsAnalysis was performed for 16 consecutive patients treated on HT. The HT plans were converted to sIMRT plans. 3DCRT, sliding window IMRT (dIMRT) and VMAT plans for a c-arm linear accelerator (CLA) were created manually. The doses in planning target volume (PTV), bladder, rectum, bowels, femoral heads and hip prosthesis were compared using: (i) a qualitative analysis of doses in averaged dose–volume histograms, (ii) a quantitative, ranking procedure performed for each patient separately, and (iii) statistical testing based on the Friedman ANOVA and Nemenyi method.ResultsFor the bladder, rectum, and femoral head, the best dose distributions were observed for HT and sIMRT and then for dIMRT, VMAT, and finally for 3DCRT (p-values were, respectively, 0.002, 0.004 and p = 0.024). For the bowels, 3DCRT was significantly different from the rest of the techniques (p = 0.009). For the hip prosthesis, the differences were only between 3DCRT and HT/sIMRT (p = 0.038).ConclusionThe SharePlan is an efficient tool for the conversion of HT plans for patients with prostate cancer and hip prosthesis. Dose distributions in sIMRT and in HT plans are similar and are generally better than in CLA plans.     

Stereotactic ablative radiotherapy for oligometastatic prostate cancer

BackgroundThe present study assessed clinical outcomes of stereotactic body radiotherapy (SBRT) in oligometastatic prostate cancer patients.Materials and methodsBetween 2017 and 2020, 37 lesions (12 osseous and 25 nodal targets) detected with conventional and/or functional imaging, were treated in 29 patients (pts), in different clinical settings: de novo oligometastatic (2 pts), oligorecurrent castration-sensitive (19 pts), castration-resistant (6 pts) prostate cancers and oligoprogressive disease during systemic therapy (2 pts). SBRT was delivered with volumetric modulated arc therapy up to a total dose of 21 Gy given in 3 fractions for bone and 30 Gy in 5 fractions for nodal metastases. A total of 34% of pts received hormonal therapy. We evaluated biochemical control [prostate serum antigen (PSA) increase < 10%)], progression free-survival (PFS) (time from SBRT to biochemical progression), local control (LC) (time from SBRT to in-field radiologic progression), hormone/systemic therapy-free survival, acute and late toxicities.ResultsAt 3 months, biochemical response was observed in 20/29 pts (69%). At a median follow-up of 17 months (range 6–33), 8/20 (40%) of the 3-month responders remained free from progression. Two-year PFS and LC were 37% and 70%, respectively. In-field progression occurred in 3/37 (8%) lesions. Hormone/systemic therapy was delayed by an average of 11.6 months (range 3–28). No significant difference in PFS based on the type of lesion or concomitant endocrine therapy was observed and no toxicity > grade 2 was reported.ConclusionsSBRT for oligometastatic prostate cancer offers a good biochemical/local control and tangible delay of hormone/systemic therapy without major toxicities.     

Comparison of dose distribution in IMRT and RapidArc technique in prostate radiotherapy

AimThe aim was to provide a dosimetric comparison between IMRT and RapidArc treatment plans with RPI index with simultaneous comparison of the treatment delivery time.BackgroundIMRT and RapidArc provide highly conformal dose distribution with good sparing of normal tissues. However, a complex spatial dosimetry of IMRT and RapidArc plans hampers the evaluation and comparison between plans calculated for the two modalities. RPI was used in this paper for treatment plan comparisons. The duration of the therapeutic session in RapidArc is reported to be shorter in comparison to therapeutic time of the other dynamic techniques. For this reasons, total treatment delivery time in both techniques was compared and discussed.Materials and methods15 patients with prostate carcinoma were randomly selected for the analysis. Two competitive treatment plans using respectively the IMRT and RapidArc techniques were computed for each patient in Eclipse planning system v. 8.6.15. RPIwin^® application was used for RPI calculations for each treatment plan.Additionally, total treatment time was compared between IMRT and RapidArc plans. Total treatment time was a sum of monitor units (MU) for each treated field.ResultsThe mean values of the RPI indices were insignificantly higher for IMRT plans in comparison to rotational therapy. Comparison of the mean numbers of monitor units confirmed that the use of rotational technique instead of conventional static field IMRT can significantly reduce the treatment time.ConclusionAnalysis presented in this paper, demonstrated that RapidArc can compete with the IMRT technique in the field of treatment plan dosimetry reducing the time required for dose delivery.     

Three-dimensional quality assurance of IMRT prostate plans using gel dosimetry

Intensity modulated radiotherapy (IMRT) is one of the most modern radiation therapy treatment techniques. Although IMRT can deliver high and complex conformational doses to the tumor volume, its implementation requires rigorous quality assurance (QA) procedures that include a dosimetric pre-treatment verification of individual patient planning. This verification usually involves measuring a small volume of absolute dose with an ionization chamber and checking bi-dimensional fluency with an array of detectors. The planning technique has tri-dimensional characteristics, but no tridimensional dosimetry has been established in the clinical routine. One strategy to perform three-dimensional dosimetry is to use polymeric gels associated with magnetic resonance imaging to evaluate dose distribution. Here, we have compared the results of conventional QA procedures involving one- and two-dimensional dosimetry to the results of three-dimensional dosimetry conducted with MAGIC-f gel in 10 cases of prostate cancer IMRT planning. More specifically, we used the gamma index (3%/3 mm) to compare the results of three-dimensional dosimetry to the expected dose distributions obtained with the treatment planning system. Except for one IMRT treatment plan, the gel dosimetry results agreed with the conventional quality control and provided an overview of dose distribution in the target volume.     

The importance of an exponential prostate-specific antigen decline after external beam radiotherapy for intermediate risk prostate cancer

Background: To study the influence of an exponential prostate-specific antigen (PSA) decline on biochemical failure after external-beam radiotherapy (EBRT). Methods: We analyzed 114 patients with intermediate risk prostate cancer (Gleason ≤ 6 and PSA 10–20 or Gleason 7 and PSA <10). Patients were randomized between EBRT doses of either 70.2 Gy or 79.2 Gy (1.8 Gy per day). All patients had a follow up of at least six PSA measurements post-EBRT. Exponential decline and PSA half life were included in a Cox regression analysis for factors associated with biochemical failure. Results: A total of 80/114 (70.2%) patterns were classified as having an exponential PSA decline. Both exponential decline (HR 0.115, 95%CI 0.03–0.44, p = 0.0016) and PSA half life ratio were statistically significant predictors (HR 1.03 (95% CI 1.01–1.06)) of biochemical failure. In the model predicting for exponential decline, none of the factors were significant. Conclusion: Patients with an exponential PSA decline show a better biochemical outcome in the long term.     

Dosimetry quality control based on percent depth dose rate variation for checking beam quality in radiotherapy

Recently, the quality management inside a radiotherapy department has been crucial to treat cancer efficiently. Thus, many international bodies recommend multiple methods to check in periodically the dosimetry quality beyond the depth of 10 cm as the beam quality index. However, they evade checking out the beam dosimetry quality on both the build-up dose and the electronic equilibrium regions. The objective of this study is to cover the overall variation of the percent depth dose (PDD) by including all sub-regions in the procedure evaluation of the beam quality.In this work, we have studied and examined the dosimetry quality by considering the whole PDD variation. The PDD rate is therefore introduced to determine accurately the quality as an overall notion in external beam radiotherapy according to the field size and photon beam energy. We have presented the reasons and methods to introduce particles contamination, such as electrons and low photon energy in this new approach. The latter enables us to figure the dosimetry quality by extending the International Atomic Energy Agency (IAEA) procedure at any field size less than 25 × 25 cm² under the current conditions without being limited to 10 × 10 cm² on the exponential decay region.     

Dosimetric characterization of 3D printed bolus at different infill percentage for external photon beam radiotherapy

Background and purpose3D printing is rapidly evolving and further assessment of materials and technique is required for clinical applications. We evaluated 3D printed boluses with acrylonitrile butadiene styrene (ABS) and polylactide (PLA) at different infill percentage.Material and methodsA low-cost 3D printer was used. The influence of the air inclusion within the 3D printed boluses was assessed thoroughly both with treatment planning system (TPS) and with physical measurements. For each bolus, two treatment plans were calculated with Monte Carlo algorithm, considering the computed tomography (CT) scan of the 3D printed bolus or modelling the 3D printed bolus as a virtual bolus structure with a homogeneous density. Depth dose measurements were performed with Gafchromic films.ResultsHigh infill percentage corresponds to high density and high homogeneity within bolus material. The approximation of the bolus in the TPS as a homogeneous material is satisfying for infill percentages greater than 20%. Measurements performed with PLA boluses are more comparable to the TPS calculated profiles. For boluses printed at 40% and 60% infill, the discrepancies between calculated and measured dose distribution are within 5%.Conclusions3D printing technology allows modulating the shift of the build-up region by tuning the infill percentage of the 3D printed bolus in order to improve superficial target coverage.     

An institutional experience of quality assurance of a treatment planning system on photon beam

Aim

The purpose of the present study is to show the application of the IAEA TRS-430 QA procedures of Eclipse™v7.5 TPS for photon energies. In addition, the trends of the deviations found in the conducted tests were determined.

Background

In the past, the lack of complete TPS QA procedures led to some serious accidents. So, QA in the radiotherapy treatment planning process is essential for determination of accuracy in the radiotherapy process and avoidance of treatment errors.

Materials and methods

The calculations of TPS and measurements of irradiations of the treatment device were compared in the study. As a result, the local dose deviation values (δ₁: central beam axis, δ₂: penumbra and build up region, δ₃: inside field, δ₄: outside beam edges, δ_50–90: beam fringe, RW₅₀: radiological width) and their confidence limit values (including systematic and random errors) were obtained.

Results

The confidence limit values of δ₄ were detected to increase with expanding field size. The values of δ₁ and δ₃ of hard wedge were larger than open fields. The values of δ₂ and δ_50–90 of the inhomogeneity effect test were larger, especially than other tests of this study. The average deviation was showed to increase with the rise of the wedge angle. The values of δ₃ and δ₄ of lung irradiation were outside tolerance.

Conclusions

The QA of TPS was done and it was found that there were no reservations in its use in patient treatment. The trend of the deviations is shown.