Dosimetric and radiobiological characterizations of prostate intensity-modulated radiotherapy and volumetric-modulated arc therapy: A single-institution review of ninety cases

Assessment of Bioprotect's Biodegradable Balloon System as a Rectal Spacer in Radiotherapy: An Animal Study on Tissue Response and Biocompatibility

Prostate cancer is a significant health concern for men, emphasizing the need for effective treatment strategies. Dose-escalated external beam radiotherapy shows promise in improving outcomes but presents challenges due to radiation effects on nearby structures, such as the rectum. Innovative techniques, including rectal spacers, have emerged to mitigate these effects. This study comprehensively assessed tissue responses following the implantation of the Bioprotect biodegradable fillable balloon as a rectal spacer in a rat model. Evaluation occurred at multiple time points (4, 26, and 52 weeks) post-implantation. Results revealed localized tissue responses consistent with the expected reaction to biodegradable materials, characterized by mild to moderate fibrotic reactions and encapsulation, underscoring the safety and biocompatibility of the balloon. Importantly, no other adverse events occurred, and the animals remained healthy throughout the study. These findings support its potential clinical utility in radiotherapy treatments to enhance patient outcomes and minimize long-term implant-related complications, serving as a benchmark for future similar studies and offering valuable insights for researchers in the field. In conclusion, the findings from this study highlight the safety, biocompatibility, and potential clinical applicability of the Bioprotect biodegradable fillable balloon as a promising rectal spacer in mitigating radiation-induced complications during prostate cancer radiotherapy.

Dosimetric and radiobiological comparison in head-and-neck radiotherapy using JO-IMRT and 3D-CRT

Introduction

Dosimetric and radiobiological evaluations for the Jaws-only Intensity-modulated radiotherapy (JO-IMRT) technique for head and neck jaws-only intensity-modulated radiation therapy (JO-IMRT) and 3D conformal radiation therapy (3D-CRT). To compare the head-and-neck therapeutic approaches utilizing JO-IMRT and 3D-CRT techniques, different radiation dose indices were calculated, including: conformity index (CI), homogeneity index (HI), and radiobiological variables like Niemierko's equivalent uniform dose based tumor control probability (TCP) of planning target volume (PTV), normal tissue complication probability (NTCP) of organs at risk (OAR) (brainstem, spinal cord, and parotid grand).

Materials and methods

Twenty-five nasopharynx patients were studied using the Prowess Panther Treatment Planning System (Prowess Inc). The results were compared with the dose distribution obtained using 3D-CRT.

Results

Regarding tumor coverage and CI, JO-IMRT showed better results than 3D-CRT. The average doses received by the PTVs were quite similar: 72.1 ± 0.8 Gy by 3D-CRT and 72.5 ± 0.6 Gy by JO-IMRT plans (p > 0.05). The mean doses received by the parotid gland were 56.7 ± 0.7 Gy by 3D-CRT and 26.8 ± 0.3 Gy by JO-IMRT (p > 0.05). The HI and CI were 0.13 ± 0.01 and 0.14 ± 0.05 and (p > 0.05) by 3D-CRT and 0.83 ± 0.05 and 0.73 ± 0.10 by JO-IMRT (p < 0.05). The average TCP of PTV was 0.82 ± 0.08 by 3D-CRT and 0.92 ± 0.02 by JO-IMRT. Moreover, the NTCP of the parotid glands, brain stem, and spinal cord were lower using the JO-IMRT than 3D-CRT plans. In comparison to the 3D-CRT approach, the JO-IMRT technique was able to boost dose coverage to the PTV, improve the target's CI and HI, and spare the parotid glands. This suggests the power of the JO-IMRT over 3D-CRT in head-and-neck radiotherapy.

Use of a Biodegradable, Contrast-Filled Rectal Spacer Balloon in Intensity-Modulated Radiotherapy for Intermediate-Risk Prostate Cancer Patients: Dosimetric Gains in the BioPro-RCMI-1505 Study

Background/purpose

Dose-escalated external beam radiotherapy (RT) is effective in the control of prostate cancer but is associated with a greater incidence of rectal adverse events. We assessed the dosimetric gain and safety profile associated with implantation of a new biodegradable rectal spacer balloon.

Materials/methods

Patients scheduled for image-guided, intensity-modulated RT for intermediate-risk prostate cancer were prospectively included in the French multicenter BioPro-RCMI-1505 study (NCT02478112). We evaluated the dosimetric gain, implantation feasibility, adverse events (AEs), and prostate-cancer-specific quality of life associated with use of the balloon spacer.

Results

After a scheduled review of the initial recruitment target of 50 patients by the study's independent data monitoring committee (IDMC), a total of 24 patients (including 22 with dosimetry data) were included by a single center between November 2016 and May 2018. The interventional radiologist who implanted the balloons considered that 86% of the procedures were easy. 20 of the 24 patients (83.3%) received IMRT and 4 (16.7%) received volumetric modulated arc therapy (78-80 Gy delivered in 39 fractions). The dosimetric gains associated with spacer implantation were highly significant (p<0.001) for most variables. For the rectum, the median (range) relative gain ranged from 15.4% (-9.2-47.5) for D20cc to 91.4% (36.8-100.0) for V70 Gy (%). 15 patients (62%) experienced an acute grade 1 AE, 8 (33%) experienced a late grade 1 AE, 1 (4.2%) experienced an acute grade 2 AE, and 3 experienced a late grade 2 AE. No grade 3 AEs were reported. Quality of life was good at baseline (except for sexual activity) and did not markedly worsen during RT and up to 24 months afterwards.

Conclusion

The use of a biodegradable rectal spacer balloon is safe, effective and associated with dosimetric gains in modern RT for intermediate-risk prostate cancer.

Dosimetric comparison of MR-linac-based IMRT and conventional VMAT treatment plans for prostate cancer

Background

The aim of this study was to evaluate and compare the performance of intensity modulated radiation therapy (IMRT) plans, planned for low-field strength magnetic resonance (MR) guided linear accelerator (linac) delivery (labelled IMRT MRL plans), and clinical conventional volumetric modulated arc therapy (VMAT) plans, for the treatment of prostate cancer (PCa). Both plans used the original planning target volume (PTV) margins. Additionally, the potential dosimetric benefits of MR-guidance were estimated, by creating IMRT MRL plans using smaller PTV margins.

Materials and methods

20 PCa patients previously treated with conventional VMAT were considered. For each patient, two different IMRT MRL plans using the low-field MR-linac treatment planning system were created: one with original (orig.) PTV margins and the other with reduced (red.) PTV margins. Dose indices related to target coverage, as well as dose-volume histogram (DVH) parameters for the target and organs at risk (OAR) were compared. Additionally, the estimated treatment delivery times and the number of monitor units (MU) of each plan were evaluated.

Results

The dose distribution in the high dose region and the target volume DVH parameters (D_98%, D_50%, D_2% and V_95%) were similar for all three types of treatment plans, with deviations below 1% in most cases. Both IMRT MRL plans (orig. and red. PTV margins) showed similar homogeneity indices (HI), however worse values for the conformity index (CI) were also found when compared to VMAT. The IMRT MRL plans showed similar OAR sparing when the orig. PTV margins were used but a significantly better sparing was feasible when red. PTV margins were applied. Higher number of MU and longer predicted treatment delivery times were seen for both IMRT MRL plans.

Conclusions

A comparable plan quality between VMAT and IMRT MRL plans was achieved, when applying the same PTV margin. However, online MR-guided adaptive radiotherapy allows for a reduction of PTV margins. With a red. PTV margin, better sparing of the surrounding tissues can be achieved, while maintaining adequate target coverage. Nonetheless, longer treatment delivery times, characteristic for the IMRT technique, have to be expected.

Estimation of monitor unit through analytical method for dynamic IMRT using control points as an effective parameter

Introduction:

The control points (CP) play a significant role in the delivery of segmented based Intensity-Modulated Radiation Therapy (IMRT) delivery, particularly in dynamic mode. The number of segments is determined by control points and these segments will transfer from one to the other either during beam ON called dynamic delivery or during beam OFF called static delivery or step and shoot. This study was aimed at indirect estimation of the total monitor units (MU) to be delivered per field by exploiting the control points and also to find the MUs at any nth segment.

Materials and methods:

This study was performed in the Eclipse treatment planning software version 13.8.0. The details of control points, metre set weight per segment, leaf positions for each segment, field size, etc. were taken into consideration.

Results:

TPS calculated MU value and analytically estimated MU value were compared and the percentage of difference was estimated. The overall mean percentage of deviation was 1·03% between the TPS calculated method and the analytical method. The paired sample t-test was performed and, p-value <0·05, no significant difference was found. The analytical relationship determined to estimate the total number of MU delivered for any nth control point was also evaluated.

Conclusion:

The control points are a potential parameter in the conventional IMRT delivery. Through this study, we have addressed the indirect method to estimate the monitor units delivered per segment.

Volumetric Modulated Arc Therapy (VMAT): A modern radiotherapy technique - A single institutional experience

OBJECTIVE

To evaluate VMAT plans for conformity and homogeneity of radiation dose to the target in order to share our experience as a pioneering institute to use VMAT technology in Pakistan.

METHODS

Since December 2014 to January 2018, 530 patients of various anatomical sites were treated by VMAT technique at Neurospinal Cancer Care Institute (NCCI) Karachi Pakistan. ERGO++ planning system (Version 1.7.2) was used to develop VMAT plans with single or multiple arcs by the rotation of couch and gantry. The plans were evaluated by calculating Conformity Index (CI) and Homogeneity Index (HI) and critical organ (OARs) doses of individual tumor sites.

RESULTS

The average CI of various sites was 1.4 (range: 1.0-2.0) and average HI of various sites was 1.20 (range: 1.07-1.374), respective critical organ doses were adequately achieved.

CONCLUSIONS

VMAT treatment planning technique showed good conformal and homogeneous target coverage with sparing of organs at risk and reduced treatment delivery time. With these features, safety of VMAT technique may allow its routine clinical use, though it is still under investigation in many areas.

Dosimetric and radiobiological comparison of prostate VMAT plans optimized using the photon and progressive resolution algorithm

This study compared the dosimetric and radiobiological parameters of prostate volumetric modulated arc therapy (VMAT) plans using different prescriptions optimized by the photon optimization (PO) and progressive resolution optimization (PRO) algorithm. A total of 20 prostate patients were selected retrospectively and divided into 2 groups of VMAT plans using prescriptions of 60 Gy/20 fx and 79 Gy/38 fx. Inverse treatment planning optimized by the PO and PRO algorithm based on the dual-arc technique was carried out by the Eclipse treatment planning system. The maximum dose, minimum dose, mean dose, dose-volume points, and dose-volume indices of the targets and organs at risk (OAR) were calculated from the plans. In addition, radiobiological parameters such as tumor control probability (TCP), normal tissue complication probability (NTCP), and equivalent uniform dose (EUD) of the targets and OAR were determined based on their dose-volume histograms (DVHs). A paired Student's t-test was carried out to compare the difference between mean dose-volume points, radiobiological parameters, and dose-volume indices. Two-tailed p < 0.05 was defined as having statistical difference. For prostate VMAT plans optimized by the PO algorithm, equal or slightly larger mean dose and TCP of the PTV (1% for 60 Gy/20 fx and 0.2% for 78 Gy/39 fx) were found by comparing to the PRO. These were followed by finding the slightly larger conformity index (CI; 0.927 vs 0.895 and 0.910 vs 0.904), larger or equal homogeneity index (HI; 0.054 vs 0.052 and 0.058 vs 0.058), and smaller gradient index (GI; 1.366 vs 2.288 and 1.585 vs 1.742) of the PTV using plans optimized by the PO vs PRO using prescriptions of 60 Gy/20 fx and 78 Gy/39 fx. For the OAR, we found that the mean doses, NTCPs, and EUDs of the rectum, bladder, and femur were slightly larger for plans optimized by the PO algorithm compared to the PRO, though both optimization algorithms satisfied all the dose-volume criteria and objectives in the inverse planning. Both the PO and PRO algorithm can generate prostate VMAT plans fulfilling the required dose-volume criteria. It is concluded that plans optimized by the PO algorithm can produce prostate plan with very similar quality compared to PRO.

Evaluation of plan optimisers in prostate VMAT using the dose distribution index

Purpose:

Dose distribution index (DDI) is a treatment planning evaluation parameter, reflecting dosimetric information of target coverage that can help to spare organs at risk (OARs) and remaining volume at risk (RVR). The index has been used to evaluate and compare prostate volumetric modulated arc therapy (VMAT) plans using two different plan optimisers, namely photon optimisation (PO) and its predecessor, progressive resolution optimisation (PRO).

Materials and methods:

Twenty prostate VMAT treatment plans were created using the PO and PRO in this retrospective study. The 6 MV photon beams and a dose prescription of 78 Gy/39 fractions were used in plans with the same dose–volume criteria for plan optimisation. Dose–volume histograms (DVHs) of the planning target volume (PTV), as well as of OARs such as the rectum, bladder, left and right femur were determined in each plan. DDIs were calculated and compared for plans created by the PO and PRO based on DVHs of the PTV and all OARs.

Results:

The mean DDI values were 0·784 and 0·810 for prostate VMAT plans created by the PO and PRO, respectively. It was found that the DDI of the PRO plan was about 3·3% larger than the PO plan, which means that the dose distribution of the target coverage and sparing of OARs in the PRO plan was slightly better. Changing the weighting factors in different OARs would vary the DDI value by ∼7%. However, for plan comparison based on the same set of dose–volume criteria, the effect of weighting factor can be neglected because they were the same in the PO and PRO.

Conclusions:

Based on the very similar DDI values calculated from the PO and PRO plans, with the DDI value in the PRO plan slightly larger than that of the PO, it may be concluded that the PRO can create a prostate VMAT plan with slightly better dose distribution regarding the target coverage and sparing of OARs. Moreover, we found that the DDI is a simple and comprehensive dose–volume parameter for plan evaluation considering the target, OARs and RVR.

Evaluation of various common prostate IMRT techniques based on estimated tumor control and normal tissue complication probabilities in correlation with patients anatomical parameters derived from the CT scans

Background: The relationship between the prostate IMRT techniques and patients anatomical parameters has been rarely investigated.

Objective: to evaluate various prostate IMRT techniques based on tumor control and normal tissue complication probability (TCP and NTCP) values and also the correlation of such techniques with patients anatomical parameters. Methods: Four IMRT techniques (9, 7 and 5 fields and also automatic) were planned on the CT scans of 63 prostate cancer patients. The sum of distances between the organs at risk (OARs) and target tissue and also their average joint volumes were measured and assumed as anatomical parameters. Selected dosimetric and radiobiological parameters (TCP and NTCP) values were compared among various techniques and the correlation with the above anatomical parameters were assessed using Pearsons’ correlation.

Results: High correlations were found between the dosimetric/radiobiological parameters of OARs with the joint volumes and with the distances between the OARs and target tissue in all the techniques. The TCP and complication free tumor control probability (P+) values were decreased with increasing the joint volume and decreasing the distances between the OARs and target tissue (as poly-nominal functions). The NTCP values were increased with increasing the joint volumes and decreasing the distances (3-degree poly-nominal functions). For the low percent joint volumes (<20%) and high distances (>7 cm), The TCP, NTCP and P+ showed no statistical differences between various techniques (P-value>0.07). However, 9 and 7 fields techniques indicated better radiobiological results (P-value<0.05) in almost other ranges (>20% joint volumes and <7 cm distances).

Conclusion: Based on our results, it would be possible to compare radiobiological effects of various common IMRT techniques and choose the best one regarding to patients anatomical parameters derived from the CT scans.

Retrospective dosimetric evaluation of VMAT plans for prostate cancer treatment

Background

Radiation therapy (RT) remains a common and effective treatment modality for patients with locally advanced prostate cancer. Technological advancements over the past decade have resulted in the introduction of intensity-modulated radiation therapy (IMRT) planning and delivery techniques that maximise the dose of radiation delivered to the prostate while sparing organs at risk (OAR). A more recent and evolving IMRT technique, called volumetric-modulated arc therapy (VMAT), involves a continuous irradiation at a constant or variable dose rate when the gantry rotates around the prostate using one or more arcs.

Materials and methods

This paper reports on a dosimetric evaluation of our implementation of VMAT technique for prostate cancer treatment. A retrospective analysis of VMAT plans was performed for 300 prostate cancer patients treated during the period of January 2013 to December 2014. Two prescription cohorts of patients treated to a dose of 78 Gy in 39 fractions as the primary radiation therapy treatment (XRT) and 66 Gy in 33 fractions as a post-op or salvage XRT were considered.

Results

The mean and maximal doses, dose inhomogeneities and conformity indexes for the planning target volumes were evaluated for each prescription cohort of patients. Similarly, the doses to OAR such as rectum, bladder and femoral heads were also assessed for various dose levels.

Conclusion

This study shows that highly conformal radiation dose distribution for the treatment of prostate cancer is achievable with the VMAT technique. It provides evidence to support the adoption of such conformal technology in many disease sites such as the prostate. We believe that our experience reported here could help form the foundation for individual institutions to evaluate and develop the most suitable planning criteria tailored to their own needs and priority. This endeavour hopefully will provide further improvement in the planning process and, therefore, help achieve an effective and efficient delivery of radiotherapy for prostate cancer.

Analysis of a volumetric-modulated arc therapy (VMAT) single phase prostate template as a class solution

Aim

To assess a class solution template for volumetric-modulated arc therapy (VMAT) for prostate cancer using plan analysis software.

Background

VMAT is a development of intensity-modulated radiotherapy (IMRT) with potential advantages for the delivery of radiotherapy (RT) in prostate cancer. Class solutions are increasingly used for facilitating RT planning. Plan analysis software provides an objective tool for evaluating class solutions.

Materials and methods

The class solution for VMAT was based on the current static field IMRT template. The plans of 77 prostate cancer patients were evaluated using a set of in-house plan quality metrics (scores) (PlanIQ™, Sun Nuclear Corporation). The metrics compared the class solution for VMAT planning with the IMRT template and the delivered clinical plan (CP). Eight metrics were associated with target coverage and ten with organs-at-risk (OAR). Individual metrics were summed and the combined scores were subjected to non-parametric analysis. The low-dose wash for both static IMRT and VMAT plans were evaluated using 40 Gy and 25 Gy isodose volumes.

Results

VMAT plans were of equal or better quality than the IMRT template and CP for target coverage (combined score) and OAR combined score. The 40 Gy isodose volume was marginally higher with VMAT than IMRT (4.9%) but lower than CP (-6.6%)(P = 0.0074). The 25 Gy volume was significantly lower with VMAT than both IMRT (-32.7%) and CP (-34.4%)(P < 0.00001).

Conclusions

Automated VMAT planning for prostate cancer is feasible and the plans are equal to or better than the current IMRT class solution and the delivered clinical plan.

Dosimetric variations in calculation grid size in prostate VMAT: a dose-volume histogram analysis using the Gaussian error function

Background

Varying the calculation grid size can change the results of dose-volume and radiobiological parameters in a treatment plan, and therefore has an impact on the treatment planning quality assurance.

Purpose

This study investigated the dosimetric influence of the calculation grid size variation in the prostate volumetric modulated arc therapy (VMAT) plan.

Methods and materials

Dose distributions of 10 prostate VMAT plans were acquired using calculation grid sizes of 1–5 mm. Dose-volume histogram (DVH) analysis was carried out to determine the dose-volume variation corresponding to the grid size change using the Gaussian error function (GEF). At the same time, dose-volume points, dose-volume parameters and radiobiological parameters were calculated based on DVHs of targets and organs at risk (OARs) for each grid size.

Results

Comparing percentage variations of GEF parameters between the planning target volume (PTV) and clinical target volume (CTV), GEF parameters of the PTV were found varied more significantly than the CTV. This resulted in larger variations of dose-volume (%ΔCI=40·02 versus 13·55%, %ΔHI=12·45 versus 2·93% and %ΔGI=0·22 versus 0·06%) and radiobiological parameters (%ΔTCP=0·61 versus 0·25% and %ΔEUD=2·11 versus 0·26%) of the PTV compared with CTV. For OARs, the rectal wall showed a larger dose-volume variation than the rectum. However, similar dose-volume variation due to grid size change was not found in the bladder, bladder wall and femur.

Conclusions

Knowing the dosimetric variation in this study is important to the radiotherapy staff in the quality assurance for the prostate VMAT planning.

Dose-volume and radiobiological dependence on the calculation grid size in prostate VMAT planning

This study evaluated the effects of dose-volume and radiobiological dependence on the calculation grid size in prostate volumetric-modulated arc therapy (VMAT) planning. Ten patients with prostate cancer were selected for this retrospective treatment planning study. Prostate VMAT plans were created for the patients using the 6 MV photon beam produced by a Varian TrueBEAM linac with the calculation grid size equal to 1, 2, 2.5, 3, 4, and 5 mm. Dose-volume histograms (DVHs) of targets and organs at risk were generated for different grid sizes. We calculated the radiobiological parameters of the tumor control probability (TCP) of clinical target volume (CTV) and planning target volume (PTV), and the normal tissue complication probability (NTCP) of organs at risk (rectal wall, rectum, bladder wall, bladder, left femur, and right femur). The homogeneity, conformity, and gradient indexes of CTV and PTV were calculated for different grid sizes. The TCP of PTV was found decreasing with a rate of 0.06%/mm when the calculation grid size increased from 1 to 5 mm. On the other hand, both NTCPs of rectal wall and rectum were found decreasing with rates of 0.03%/mm and 0.05%/mm, respectively, with an increase of grid size. The homogeneity index of PTV increased with a rate of 0.57/mm of the calculation grid size, whereas the conformity index of PTV decreased with a rate of 0.0075/mm. The gradient index of PTV was found increasing with a rate equal to 0.05/mm. In prostate VMAT planning, variations of dose-volume and radiobiological parameters with calculation grid size on PTV, rectal wall, and rectum were more significant than those of CTV and other organs at risk such as bladder wall, bladder, and femurs. Results in this study are important in the treatment planning quality assurance when the calculation grid size is varied to compromise a shorter dose computing time.

Variations in dosimetric distribution and plan complexity with collimator angles in hypofractionated volumetric arc radiotherapy for treating prostate cancer

Purpose

Hypofractionated radiotherapy can reduce treatment durations and produce effects identical to those of conventionally fractionated radiotherapy for treating prostate cancer. Volumetric arc radiotherapy (VMAT) can decrease the treatment machine monitor units (MUs). Previous studies have shown that VMAT with multileaf collimator (MLC) rotation exhibits better target dose distribution. Thus, VMAT with MLC rotation warrants further investigation.

Methods and materials

Ten patients with prostate cancer were included in this study. The prostate gland and seminal vesicle received 68.75 and 55 Gy, respectively, in 25 fractions. A dual‐arc VMAT plan with a collimator angle of 0° was generated and the same constraints were used to reoptimize VMAT plans with different collimator angles. The conformity index (CI), homogeneity index (HI), gradient index (GI), normalized dose contrast (NDC), MU, and modulation complexity score (MCS_V) of the target were analyzed. The dose–volume histogram of the adjacent organs was analyzed. A Wilcoxon signed‐rank test was used to compare different collimator angles.

Results

Optimum values of CI, HI, and MCS_V were obtained with a collimator angle of 45°. The optimum values of GI, and NDC were observed with a collimator angle of 0°. In the rectum, the highest values of maximum dose and volume receiving 60 Gy (V_60 Gy) were obtained with a collimator angle of 0°, and the lowest value of mean dose (D_mean) was obtained with a collimator angle of 45°. In the bladder, high values of D_mean were obtained with collimator angles of 75° and 90°. In the rectum and bladder, the values of V_60 Gy obtained with the other tested angles were not significantly higher than those obtained with an angle of 0°.

Conclusion

This study found that MLC rotation affects VMAT plan complexity and dosimetric distribution. A collimator angle of 45° exhibited the optimal values of CI, HI, and MCSv among all the tested collimator angles. Late side effects of the rectum and bladder are associated with high‐dose volumes by previous studies. MLC rotation did not have statistically significantly higher values of V_60 Gy in the rectum and bladder than did the 0° angle. We thought a collimator angle of 45° was an optimal angle for the prostate VMAT treatment plan. The findings can serve as a guide for collimator angle selection in prostate hypofractionated VMAT planning.