Volumetric Modulated Arc Therapy Technique Research Articles

Minimizing normal tissue low dose bath for left breast Volumetric Modulated Arc Therapy (VMAT) using jaw offset.

With proper beam setup and optimization constraints in the treatment planning system, volumetric modulated arc therapy (VMAT) can improve target dose coverage and conformity while reducing doses to adjacent structures for whole breast radiation therapy. However, the low-dose bath effect on critical structures, especially the heart and the ipsilateral lung, remains a concern. In this study, we present a VMAT technique with the jaw offset VMAT (JO-VMAT) to reduce the leakage and scatter doses to critical structures for whole breast radiation therapy. The data of 10 left breast cancer patients were retrospectively used for this study. CT images were acquired on a CT scanner (GE, Discovery) with the deep-inspiration breath hold (DIBH) technique. The planning target volumes (PTVs) and the normal structures (the lungs, the heart, and the contralateral breast) were contoured on the DIBH scan. A 3D field-in-field plan (3D-FiF), a tangential VMAT (tVMAT) plan, and a JO-VMAT plan were created with the Eclipse treatment planning system. An arc treatment field with the x-jaw closed across the central axis creates a donut-shaped high-dose distribution and a cylinder-shaped low-dose volume along the central axis of gantry rotation. Applying this setup with proper multi-leaf collimator (MLC) modulation, the optimized plan potentially can provide sufficient target coverage and reduce unnecessary irradiation to critical structures. The JO-VMAT plans involve 5-6 tangential arcs (3 clockwise arcs and 2-3 counterclockwise arcs) with jaw offsets. The plans were optimized with objective functions specified to achieve PTV dose coverage and homogeneity; For organs at risk (OARs), objective functions were specified individually for each patient to accomplish the best achievable treatment plan. For tVMAT plans, optimization constraints were kept the same except that the jaw offset was removed from the initial beam setup. The dose volume histogram (DVH) parameters were generated for dosimetric evaluation of PTV and OARs. The D95% to the PTV was greater than the prescription dose of 42.56Gy for all the plans. With both VMAT techniques, the PTV conformity index (CI) was statistically improved from 0.62 (3D-FiF) to 0.83 for tVMAT and 0.84 for JO-VMAT plans. The difference in the homogeneity index (HI) was not significant. The Dmax to the heart was reduced from 12.15Gy for 3D-FiF to 8.26Gy for tVMAT and 7.20Gy for JO-VMAT plans. However, a low-dose bath effect was observed with tVMAT plans to all the critical structures including the lungs, the heart, and the contralateral breast. With JO-VMAT, the V5Gy and V2Gy of the heart were reduced by 32.7% and 15.4% compared to 3D-FiF plans. Significantly, the ipsilateral lung showed a reduction in mean dose (4.65-3.44Gy) and low dose parameters (23.4% reduction for V5Gy and 10.7% reduction for V2Gy) for JO-VMAT plans compared to the 3D-FiF plans. The V2Gy dose to the contralateral lung and breast was minimal with JO-VMAT techniques. A JO-VMAT technique was evaluated in this study and compared with 3D-FiF and tVMAT techniques. Our results showed that the JO-VMAT technique can achieve clinically comparable coverage and homogeneity and significantly improve dose conformity within PTV. Additionally, JO-VMAT eliminated the low-dose bath effect at all OARs evaluation metrics including the ipsilateral/contralateral lung, the heart, and the contralateral breast compared to 3D-FiF and tVMAT. This technique is feasible for the whole breast radiation therapy of left breast cancers.

A Prospective Study on the Use of Deep Inspiration Breath-Hold Technique in External Beam Radiotherapy for Breast Cancer

Background Breast cancer is the most common cancer and the leading cause of death in women. The deep inspiration breath-hold (DIBH) technique helps reduce the dose received by the heart and lungs in breast cancers during adjuvant radiotherapy (RT). We present the dosimetry of heart and lungs with DIBH technique, reproducibility, and ease of execution. Materials and Methods This is a prospective study among breast cancer patients planned for adjuvant RT following either breast conservation or mastectomy. Patients received adjuvant RT to a dose of 42.5 Gy/16 Fr to the chest wall/whole breast followed by a boost of 10 Gy/5 Fr for breast conservation surgery patients with either three-dimensional conformal RT or volumetric modulated arc therapy technique. The dosimetric parameters such as lung mean dose, heart mean dose, and V25 Gy were compared between DIBH and free-breathing (FB) scans. Data were analyzed using SPSS software, and p-value <0.05 was considered statistically significant. Results The study was conducted from September 2018 to August 2020, and 32 patients were included. The compliance to the DIBH technique was good. The dose received by ipsilateral lung V20 (17 vs. 25%) and mean dose (9 vs. 12 Gy) were significantly lower in DIBH compared with FB (p < 0.001). The V5 (31 vs. 15%), V25 (9 vs. 2%), and mean dose (7 vs. 3.3 Gy) to the heart were much higher in FB compared with DIBH (p < 0.001). Conclusion DIBH-based RT treatment delivery for breast cancer patients requiring adjuvant RT showed good compliance and offers a significant reduction in radiation dose to the heart and lung.

Comprehensively evaluating the performance of Elekta high-definition dynamic radiosurgery for hypofractionated stereotactic radiotherapy of multiple brain metastases

PurposeTo evaluate the dosimetric and delivery performance of Elekta high-definition dynamic radiosurgery (HDRS) in hypofractionated stereotactic radiotherapy (HSRT) for multiple brain metastases (BMs) by comparison with a conventional single-isocenter noncoplanar volumetric modulated arc therapy (VMAT) technique using the RayStation treatment planning system (TPS). Materials and methodsFrom June 2022 to October 2023, thirty-two patients (a total of 140 BMs) treated with HSRT (30–48 Gy/3-6f) via HDRS-based single-isocenter noncoplanar VMAT (HDRS-VMAT) were retrospectively selected for this study. Each patient was replanned using RayStation TPS-based single-isocenter noncoplanar VMAT (RayStation-VMAT). HDRS-VMAT and RayStation-VMAT plans were compared in terms of the gradient index (GI), conformity index (CI), normal brain tissue (NBT) dose exposure, monitor units (MUs), homogeneity index (HI), delivery accuracy, and beam-on time (BOT). ResultsCompared with the RayStation-VMAT plan, the HDRS-VMAT plan achieved superior CI (1.14 ± 0.09 vs. 1.23 ± 0.12, P < 0.001) and GI (5.23 ± 1.18 vs. 7.83 ± 2.75, p < 0.001) but had greater HI values. Compared with the RyaStation-VMAT plan, the HDRS-VMAT plan also yielded significantly lower NBT dose exposures (V23Gy, V21Gy, V18Gy, V12Gy and Dmean) but at the cost of increased MUs (3659.16 ± 1225.28 vs. 2536.23 ± 785.80, p < 0.001). The difference in BOTs was minimal (<1 min), which was not considered clinically significant. Furthermore, the HDRS-VMAT exhibited a higher gamma passing rate across all criteria (P < 0.001), particularly under stricter criteria (2%/1 mm), achieving an approximately 3% increase. ConclusionCompared with RaySation-VMAT, HDRS-VMAT offers superior target conformity, better NBT sparing, and higher delivery accuracy while maintaining comparable delivery efficiency. This represents a promising approach for HSRT of multiple BMs.

Intensity Modulated Therapy for Patients With Breast Cancer. Practical Guidelines and Tips for an Effective Treatment Planning Strategy

PurposePractical guidelines and tips for effective and robust radiotherapy treatment planning for breast cancer patients are addressed for intensity-modulated fixed field or volumetric modulated arc therapy techniques. The concepts described here are general and valid on all the treatment planning systems. However, some details have been shown here applied to the Varian platforms used at the authors’ institutions. MethodsThe specific aspects of using C-arm or O-ring mounted linear accelerators are covered in the document, as well as tips for dealing with certain resource constraints, target cropping and skin flash aiming to reduce risks of skin toxicity and to manage (residual after breath control) respiration motion or oedema. ResultsA decision tree is presented, and practical solutions are discussed for cases where a target volume is contoured or not; where volumetric modulated arc therapy or fixed beams intensity modulation should be applied and details about the technical implementation (tangential IMRT, butterfly IMRT or VMAT, large partial VMAT arcs). Target cropping and skin flash implications are discussed in detail, and links to plan robustness are outlined. ConclusionsPractical guidelines for breast planning are presented and summarized with a decision tree and technical summaries.

DOSIMETRIC COMPARISON OF INTENSITY-MODULATED RADIATION THERAPY (IMRT) AND VOLUMETRIC-MODULATED ARC THERAPY (VMAT) IN RECTAL CANCER PATIENTS: A COMPREHENSIVE ANALYSIS

This study aimed to conduct a thorough dosimetric comparison between two advanced radiotherapy techniques, Intensity-Modulated Radiation Therapy (IMRT) and Volumetric-Modulated Arc Therapy (VMAT), to ascertain the superior modality in terms of dose distribution and organ-at-risk sparing for rectal cancer patients. Thirty-three patients with ECOG performance status 1, aged between 18 to 60 years, diagnosed with Stage II to III rectal cancer, were included in this prospective study. Each patient underwent treatment planning with IMRT and VMAT techniques using Varian system simulation computed tomography scans. The dosimetric analysis encompassed the evaluation of target volume dose homogeneity, conformity, and doses to at-risk organs. The dosimetric comparison was conducted utilizing seven-field IMRT and dual arc VMAT plans. Statistical analysis was performed using paired t-tests and SPSS 20 software. Treatment plan constraints adhered to the RTOG 9406 guidelines, ensuring adequate planning target volume (PTV) coverage, homogeneity index, conformity index, and dose limits for organs at risk, including small bowel V20 (&lt;200cc), bladder V45 (&lt;21Gy), and femoral head V50 (≤30 Gy). Volumetric arc therapy plans demonstrated superior dose homogeneity to fixed-field intensity-modulated plans (p-value = 0.04), particularly in femoral head dose-limiting toxicity (p-value = 0.00). However, intensity-modulated therapy exhibited equivalent or superior performance in other evaluated parameters. Our findings suggest that while VMAT offers advantages in PTV coverage homogeneity and femoral head dose-limiting toxicity, IMRT remains competitive and potentially preferable in certain dosimetric aspects. The choice between IMRT and VMAT should be carefully considered based on individual patient characteristics and treatment goals. This comprehensive dosimetric comparison contributes valuable insights into optimizing radiotherapy planning for rectal cancer patients, potentially guiding clinical decision-making and improving treatment outcomes.

Measurement and Incorporation of Laryngeal Motion Using cine-MRI on an MR-Linear Accelerator to Generate Radiation Therapy Plans for Early-stage Squamous Cell Cancers of the Glottis

IntroductionSwallow-related motion of the larynx is most significant in the cranio-caudal directions and of short duration. Conventional target definition for radical radiotherapy includes coverage of the whole larynx. This study longitudinally examined respiration- and swallow-related laryngeal motions using cine-MRI. We further analysed the dosimetry to organs at risk by comparing 3D-conformal radiotherapy (3D-CRT), Volumetric-Modulated Arc Therapy (VMAT) and Intensity-Modulated Radiotherapy (IMRT) techniques. MethodsFifteen patients with T1-2 N0 glottic squamous cell carcinomas were prospectively recruited for up to three cine-MRI scans on the Elekta Unity MR-Linear accelerator, at the beginning, middle and end of a course of radical radiotherapy. Swallow frequency and motion of the hyoid bone, cricoid and thyroid cartilages and vocal cords were recorded during swallow and rest. Adapted treatment volumes consisted of GTV + 0.5-1 cm to a CTV with an additional ITV for personalised resting-motion. Swallow-related motion was deemed infrequent and was not accounted for in the ITV. We compared radiotherapy plans for 3D-CRT (whole larynx), VMAT (whole larynx), VMAT and IMRT (ITV for resting motion). ResultsResting- and swallow- motions were most prominent in the craniocaudal plane. There were no significant changes in the magnitudes of motions over the course of radiotherapy. There was a trend for a progressive reduction in the frequency of swallow. Treatment of partial-larynx volumes with intensity-modulated methods significantly reduced the dose to carotid arteries compared to whole-larynx. Robustness analysis demonstrated that when accounting for intra-fraction swallow, the total dose delivered to the ITV/PTV was maintained above 95%. ConclusionsSwallow-related motions are infrequent and accounting for resting motion in an ITV is sufficient. VMAT/IMRT techniques that treat more conformal targets can significantly spare critical organs at risk such as the carotid arteries and thyroid gland, potentially reducing the risk of carotid artery stenosis related and other complications long-term.

A phantom study investigating effective strategies for reducing fetal dose in pregnant patients with head and neck cancer

PurposeTo measure the out-of-field doses for various treatment planning techniques and assess the impact on fetal dose with and without the use of custom shielding. Materials and methodsA total of six treatment plans were generated with different treatment techniques such as 3-dimensional conformal radiation therapy (3DCRT), intensity modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT), utilizing both 6 MV flattened beams and flattening filter-free (FFF) beams. The measurements were carried out both out-of-field at the surface and at depth to assess the dose reduction achieved by removing the flattening filter and incorporating shielding. ResultsThe custom-made frame shielding can effectively reduce the surface dose with a maximum reduction of 15.2% observed in VMAT plans and achieve a maximum reduction of 100% for cone beam computed tomography (CBCT) imaging. Out-of-field dose measurements conducted at depth, positioned 58 cm inferior to the target isocenter, reveal that the shielding effectiveness consistently remains the greatest for 3DCRT technique. A maximum reduction of 21% is observed when utilizing a flattening filter-free beam. ConclusionThe results of this study indicate that the 3DCRT technique exhibits the least amount of scatter radiation both near and far from the treatment isocenter, which is the most suitable approach for radiation therapy of pregnant patients. In cases where meeting dose constraints for critical organs becomes challenging, VMAT technique emerges as the most suitable treatment technique for reducing out-of-field doses. Additionally, a flattening filter-free beam significantly reduces out-of-field doses due to lower contributions from head scatter.

The Accessible Clinical Application Progress of Supine Fixation Technique in Radiotherapy After Breast Conserving Surgery for Early Breast Cancer in China

Radiation therapy (radiotherapy) is one of the important methods for comprehensive treatment of breast cancer. Radiotherapy after breast conserving surgery for early breast cancer can not only achieve local control rate and long-term survival rate similar to total mastectomy, but also meet patients&amp;apos; pursuit of higher quality of life. With the development of intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), helical tomotherapy (HT), and other advanced radiotherapy technique, the consistency of patient position fixation during radiotherapy is the key to ensure the implementation of accurate radiotherapy. Due to the special and high activity of breast organs, there is no unified fixation method for breast conserving postoperative radiotherapy. This article reviews the clinical application and research progress of various accessible supine fixation techniques in early breast cancer postoperative radiotherapy in recent years. This paper analyzes the clinical application method and clinical application effect of various techniques, compares the advantages and disadvantages of each technology. It is found that breast bracket is the most widely used for classical breast cancer radiotherapy. In any fixation technique, it is still a practical problem for the clinic to solve the problem of the normal location of the breast activity and the consistency of the radiation. It is recommended that the position of the supposition fixation technique should be selected according to the patient&amp;apos;s BMI, breast size and target area.

Biological Dose Escalation—Do We Have a New Window of Opportunity in High-Grade Glioma?—A Feasibility Study

Despite multimodality treatment in high-grade glioma (HGG) involving maximal safe resection and adjuvant chemoradiotherapy, the prognosis remains dismal. In this study, we aimed to evaluate a method of biological enhancement by combining dose escalation with a condensed overall treatment time, aiming for maximal cytoreduction as a surrogate for improved outcomes. Hypofractionation has the dual advantage of enhanced cell kill with reduced overall treatment time. To this effect, we have employed a study involving hypofractionated simultaneous integrated boost (SIB) versus conventional treatment. As a secondary objective, we evaluated volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) in terms of optimal delivery technique for SIB boost. Forty patients were randomized into two arms, the study arm received 60 Gy in 25 fractions and the standard arm received 60 Gy in 30 fractions with concurrent and adjuvant temozolomide. The patients were assessed radiologically for tumor cytoreduction and acute toxicity parameters weekly during treatment, 6 weeks post-treatment, and 3 monthly follow-up. All patients were planned using VMAT and IMRT techniques in the study arm for the comparison of treatment time and dosimetric efficiency. However, the treatment was performed through VMAT technique. Data were analyzed using simple descriptive statistics including Student's t-tests, proportion tests, and Pearson correlation for association. The total sample size was estimated at 40, with 20 samples per group, providing a statistical power of 81% and a significance level (p-value) of 0.05. It was observed that tumor cytoreduction was significantly enhanced in a subgroup of patients in the study arm with smaller volume residual disease (p = 0.04) that was found at 6 weeks post-treatment evaluation. The tolerance, toxicity, and compliance were comparable in both arms. During the dosimetric evaluation, it was determined that VMAT had a significantly lower hot spot compared to the IMRT plan (64.22 Gy vs. 64.75 Gy, p = 0.02). It was also observed that the delivery with VMAT was faster and involved a lesser number of monitor units (555.7 MU vs. 679.6MU, p = 0.001). The hypofractionated SIB radiotherapy using the VMAT technique can provide a feasible method of biological dose enhancement without compromising toxicity and might have the future potential to improve local control in HGG.

Radiotherapy Planning in Synchronous Bilateral Breast Cancer Irradiation: A Dosimetric Study

Background: The large radiation field and surrounding normal structures make treatment planning and dose delivery of synchronous bilateral breast cancer (SBBC) much more difficult than it is for unilateral breast cancer. Intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT) can produce acceptable normal tissue sparing while improving target dose coverage compared to 3D-CRT. With this context in mind, we carried out a study to examine the dosimetric variations of IMRT and VMAT techniques using a single isocenter for planning cases of SBBC. Patients and methods: Five patients were considered for this study. All the patients had undergone bilateral mastectomy. Dose prescribed was 50 Gy in 25 fractions. VMAT and IMRT plans were created for each patient. All the plans made were mono-isocentric. Dosimetric data of the target and organs at risk (OAR) were compared. Results: There is a trend towards better PTV coverage using VMAT compared to IMRT (V95 IMRT=94.8720, V95 VMAT=95.8740; P=0.316). VMAT plans significantly improved the dose homogeneity as V105% decreased from 2.886% to 0.312% using VMAT plans (P=0.001). IMRT plans showed trend towards higher lung Dmean and V20Gy than VMAT plans. The irradiation dose to the heart was significantly higher in the IMRT plan than VMAT plan, resulting in Dmean of 15.836 Gy vs 13.580 Gy (P=0.026), V25Gy of 16.498% vs 13.832% (P=0.046) and V30 Gy of 9.774% vs 7.022% (P= 0.043). Conclusion: The single isocentric VMAT technique can be performed conveniently in SBBC. It improves target volume coverage with optimal normal tissue sparing. It is a feasible approach while planning synchronous bilateral breast irradiation.&#x0D;

Comparison of photon energies and field techniques for ovarian dose reduction in volumetric modulated arc therapy

For fertility preservation in young female patients undergoing pelvic radiotherapy for cervical cancer, lateral ovarian transposition (LOT) is a procedure that moves the ovaries away from the radiation field. However, it is still challenging to fully protect the ovaries from radiation damage in volumetric modulated arc therapy (VMAT). In this study, we optimized VMAT techniques and simulated the effect of the LOT position on the ovarian dose. Ten cervical cancer patients who received pelvic radiotherapy after LOT were retrospectively analyzed. A restricted arc plus split field technique, which incorporated beam avoidance sectors, split field, fixed jaw, and orthogonal collimator orientation with 10 MV energy (rasf-10MV-VMAT), was designed to minimize the dose to the ovaries. This technique was compared with dual-arc conventional VMAT (dac-6MV-VMAT) and restricted arc and field VMAT (raf-6MV-VMAT) techniques with 6 MV energy. Ovarian dose, target coverage, and organs at risk (OAR) sparing were compared. The location of the ovaries in the anterior-posterior and superior-inferior directions was changed to simulate the effect of the LOT position on the ovarian dose. Compared to dac-6MV-VMAT and raf-6MV-VMAT, rasf-10MV-VMAT decreased the ovarian dose significantly more, especially for a low-dose volume. Both ovaries, received a 44.0–52.1 % lower volume of >3 Gy dose, and (0.5–1.9 Gy) lower maximum and mean doses with rasf-10MV-VMAT (p < 0.05). Rasf-10MV-VMAT also improved target conformity and coverage more than raf-6MV-VMAT (p < 0.05) and reduced the bladder mean dose more than dac-6MV-VMAT (p < 0.05). The ovarian dose decreased with the distance from the target contour, and placing the ovaries near the mid-frontal plane or as high as possible after the LOT lowered ovarian exposure. This technique, using 10 MV photon energy combined with field technique optimization, reduced the ovarian dose, particularly by decreasing the low-dose exposure of ovarian tissue and improving the target conformity simultaneously. The ovarian dose could be minimized by a proper LOT position. This optimized technique could enhance ovarian protection and fertility preservation for young female survivors of cervical cancer.

A comparative study of boost dose delivery techniques in breast cancer radiotherapy optimising efficacy and minimising toxicity.

The present study aims to compare three techniques for delivering a boost absorbed dose: conventional reduced tangential (3D), volumetric modulated arc therapy (VMAT) and fields forward-planned technique boost (3DF). The study included 15 postoperative breast cancer patients who received a boost absorbed dose following breast-conserving surgery. The conformity index and homogeneity index were used to evaluate treatment outcomes, along with the average absorbed dose received by organs at risk (OAR). All the calculated dosimetric plans are carried out using Monaco Treatment Planning System (TPS). VMAT offers superior conformity, dose homogeneity and target coverage, it is associated with higher absorbed doses to OAR such as the heart and lung. In contrast, the 3D and 3DF techniques exhibit advantages in reducing absorbed doses to critical structures, potentially minimising the risk of cardiac and pulmonary complications. Each technique has its advantages and disadvantages. The choice of technique should be individualised, taking into account patient-specific factors and treatment goals and involves a multidisciplinary approach.

Off-isocentric VMAT technique for breast cancer: Effective dose reduction to organs at risk and its applicability based on patient anatomy.

This study aims to explore the off-isocentric volumetric modulated arc therapy (offVMAT) technique for breast cancer and determine its applicability based on patient anatomical parameters. We retrospectively analyzed 44 breast cancer patients with varied lymph node involvement using different arc designs. Off-isocentric techniques were benchmarked against previously published arc techniques: classic arcs (clVMAT), tangential arcs (tVMAT), and split arcs (spVMAT). During optimization, target coverage was made for all plans as close as possible to the criteria D99%> 95% and Dmax< 110% of the prescribed dose. A novel patient categorization, based on anatomical parameters (auxiliary structures) rather than lymph node involvement, is introduced. This categorization considers the volume of ipsilateral organs at risk (OARs) adjacent to the target. A binary regression model was developed on these anatomical parameters. It predicts the likelihood of offVMAT (P[offVMAT]) achieving better criteria. Using the regression model, patients were divided into two groups: P(offVMAT)> 0.5 and P(offVMAT)< 0.5. For the P(offVMAT)> 0.5 group, most tVMAT plans are unable to achieve the clinical objectives. Comparing offVMAT with spVMAT, offVMAT exhibited better dose parameters for the heart (V20, V10, and D2 are 7.1, 2.4, and 1.5 times lower respectively), ipsilateral lung (V20, V10, V5 and the mean dose are 1.4, 1.3, 1.2, and 1.2 times lower respectively). The average doses to the contralateral side are consistent. In the P(offVMAT)< 0.5 group, the tVMAT technique showed increased doses at medium and high levels, yet reduced doses in contralateral OARs compared to spVMAT and offVMAT. spVMAT showed lower doses in the contralateral lung relative to the offVMAT technique, while clVMAT trailed in both groups. Validation of the model yielded a 90% accuracy rate. The new off-isocentric breast planning technique effectively reduces doses to ipsilateral OARs, maintaining acceptable contralateral mean doses. This technique has an advantage over other techniques for patients with intricate anatomies. It is evaluated using anatomical parameters, which are also used to build binary regression model, which shows the dependence of anatomical parameters on whether offVMAT is preferred for individual patients. Also, such anatomical parameters provide a more objective and precise comparison between different planning techniques.

Multi-institutional investigation into the robustness of intra-cranial multi-target stereotactic radiosurgery plans to delivery errors.

The use of modulated techniques for intra-cranial stereotactic radiosurgery (SRS) results in highly modulated fields with small apertures, which may be susceptible to uncertainties in the delivery device. This study aimed to quantify the impact of simulated delivery errors on treatment plan dosimetry and how this is affected by treatment planning system (TPS), plan geometry, delivery technique, and plan complexity. A beam modelling error was also included as context to the dose uncertainties due to treatment delivery errors. Delivery errors were assessed for multiple-target brain SRS plans obtained through the Trans-Tasman Radiation Oncology Group (TROG) international treatment planning challenge (2018). The challenge dataset consisted of five intra-cranial targets, each with a prescription of 20Gy. Of the final dataset of 54 plans, 51 were created using the volumetric modulated arc therapy (VMAT) technique and three used intensity modulated arc therapy (IMRT). Thirty-five plans were from the Varian Eclipse TPS, 17 from Elekta Monaco TPS, and one plan each from RayStation and Philips Pinnacle TPS. The errors introduced included: monitor unit calibration errors, multi-leaf collimator (MLC) bank offset, single MLC leaf offset, couch rotations, and collimator rotations. Dosimetric leaf gap (DLG) error was also included as a beam modelling error. Dose to targets was assessed via dose covering 98% of planning target volume (PTV) (D98%), dose covering 2% of PTV (D2%), and dose covering 99% of gross tumor volume (GTV) (D99%). Dose to organs at risk (OARs) was assessed using the volume of normal brain receiving 12Gy (V12Gy), mean dose to normal brain, and maximum dose covering 0.03cc brainstem (D0.03cc). Plan complexity was also assessed via edge metric, modulation complexity score (MCS), mean MLC gap, mean MLC speed, and plan modulation (PM). PTV D98% showed high robustness on average to most errors with the exception of a bank shift of 1.0mm and large rotational errors ≥1.0° for either the couch or collimator. However, in some cases, errors close to or within generally accepted machine tolerances resulted in clinically relevant impacts. The greatest impact upon normal brain V12Gy, mean dose to normal brain, and D0.03cc brainstem was found for DLG error in alignment with other recent studies. All delivery errors had on average a minimal impact across these parameters. Comparing plans from the Monaco TPS and the Eclipse TPS, showed a lesser increase to V12Gy, mean dose to normal brain, and D0.03cc brainstem for Monaco plans (p<0.01) when DLG error was simulated. Monaco plans also correlated to lower plan complexity. Using Spearman's correlation coefficient (r) a strong negative correlation (r≤-0.8) was found between the mean MLC gap and dose to OARs for DLG errors. Reducing MLC complexity and using larger mean MLC gaps is recommended to improve plan robustness and reduce sensitivity to delivery and modelling errors. For cases in which the calculated dose distribution or dose indices are close to the clinically acceptable limits, this is especially important.

Breast Volume Is a Predictor of Higher Heart Dose in Whole-Breast Supine Free-Breathing Volumetric-Modulated Arc Therapy Planning.

In breast cancer volumetric-modulated arc therapy (VMAT) planning, the rotation of the gantry around the target implies a greater dose spreading to the whole heart, compared to tangential-field standard treatment. A consecutive cohort of 121 breast cancer patients treated with the VMAT technique was investigated. The correlation of breast volume, heart volume and lung volume with mean heart dose (mHD) and mean and maximum LAD dose (mLAD dose, MLAD dose) was tested, and a subsequent a linear regression analysis was carried out. VMAT treatment plans from 56 left breast cancer and 65 right breast cancer patients were analyzed. For right-sided patients, breast volume was significantly correlated with mHD, mLAD and MLAD dose, while for left-sided patients, breast volume was significantly correlated with mHD and mLAD, while heart volume and lung volume were correlated with mHD, mLAD and MLAD dose. Breast volume was the only predictor of increased heart and LAD dose (p ≤ 0.001) for right-sided patients. In left-sided patients, heart and lung were also predictors of increased mHD (p = 0.005, p ≤ 0.001) and mean LAD dose (p = 0.009, p ≤ 0.001). In this study, we observed an increase in heart and LAD doses in larger-breasted patients treated with VMAT planning. In right-sided patients, breast volume was shown to be the only predictor of increased heart dose and LAD dose.

Is bilateral radiotherapy necessary for patients with unilateral squamous cell carcinoma of unknown primary of the head and neck region?

Background and PurposeSquamous cell carcinoma of unknown primary (SCC-CUP) of the head and neck region remains a clinical challenge, with uncertainty surrounding the necessity of contralateral irradiation of cervical lymphatic drainage in cases of unilateral involvement. Materials and MethodsA retrospective study was conducted at the Department of Radiation Oncology, University Medical Center Mainz, on a cohort of 50 patients with unilateral SCC-CUP of the head and neck region treated between 2005 and 2019. 30 patients received bilateral and 20 received unilateral cervical radiotherapy. The majority (n = 38, 76 %) were treated with modern IMRT/ VMAT (Intensity-modulated Radiation Therapy/ Volumetric Modulated Arc Therapy) techniques. ResultsAfter a median follow-up of 64.5 months, locoregional recurrences occurred in 26 % of cases (n = 13/50), all of which were ipsilateral and predominantly within the volume of the previous irradiated CTV (clinical target volume) (85 %, n = 11/13). No patient treated unilaterally developed a contralateral recurrence in the neck. After 3 years, we observed 7 locoregional recurrences in the bilateral irradiated group (n = 7/30, 23 %), and 5 locoregional recurrences in the unilateral irradiated group (n = 5/20, 25 %). After 3 years, 12 patients had died in the bilateral irradiated group (n = 12/30, 40 %), and 7 in the unilateral irradiated group (n = 7/20, 35 %). 7 Patients showed distant metastases after 3 years in the bilateral irradiated group (n = 7/30, 23 %), and 2 in the unilateral irradiated group (n = 2/20, 10 %). Locoregional control (LRC) at 5 years was 66.2 % in the bilaterally irradiated group, and 70.0 % in the unilaterally irradiated group. Overall survival (OS) was 52.6 % (bilateral) and 64.0 % (unilateral). Distant metastasis-free survival (DMFS) was 74.7 % (bilateral) and 84.4 % (unilateral). No significant differences were observed in OS (p = 0.37), LRC (p = 0.91), and DMFS (p = 0.91) between the groups.Acute toxicity ≥ °2 accordingly CTCAE (Common Terminology Criteria of Adverse Events) was high with 97% while late toxicity ≥ °2 was moderate with 31%. There was no statistically significant difference between the group of unilateral and bilateral irradiated patients. ConclusionThese data suggest that contralateral cervical irradiation may be of limited benefit in patients with SCC-CUP, as recurrences occured ipsilaterally, and predominantly within the area of prior irradiation. Unilateral irradiation seems to be adequate for carefully selected patients.

Comparison of volumetric modulated arc therapy and helical tomotherapy for prostate cancer using Pareto fronts.

Studies comparing different radiotherapy treatment techniques-such as volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT)-typically compare one treatment plan per technique. Often, some dose metrics favor one plan and others favor the other, so the final plan decision involves subjective preferences. Pareto front comparisons provide a more objective framework for comparing different treatment techniques. A Pareto front is the set of all treatment plans where improvement in one criterion is possible only by worsening another criterion. However, different Pareto fronts can be obtained depending on the chosen machine settings. To compare VMAT and HT using Pareto fronts and blind expert evaluation, to explain the observed differences, and to illustrate limitations of using Pareto fronts. We generated Pareto fronts for twenty-four prostate cancer patients treated at our clinic for VMAT and HT techniques using an in-house script that controlled a commercial treatment planning system. We varied the PTV under-coverage (100%-V95%) and the rectum mean dose, and fixed the mean doses to the bladder and femoral heads. In order to ensure a fair comparison, those fixed mean doses were the same for the two treatment techniques and the sets of objective functions were chosen so that the conformity indexes of the two treatment techniques were also the same. We used the same machine settings as are used in our clinic. Then, we compared the VMAT and HT Pareto fronts using a specific metric (clinical distance measure) and validated the comparison using a blinded expert evaluation of treatment plans on these fronts for all patients in the cohort. Furthermore, we investigated the observed differences between VMAT and HT and pointed out limitations of using Pareto fronts. Both clinical distance and blind treatment plan comparison showed that VMAT Pareto fronts were better than HT fronts. VMAT fronts for 10 and 6MV beam energy were almost identical. HT fronts improved with different machine settings, but were still inferior to VMAT fronts. That VMAT Pareto fronts are better than HT fronts may be explained by the fact that the linear accelerator can rapidly vary the dose rate. This is an advantage in simple geometries that might vanish in more complex geometries. Furthermore, one should be cautious when speaking about Pareto optimal plans as the best possible plans, as their calculation depends on many parameters.

Dosimetry of intensity-modulated radiation therapy and volumetric-modulated arc therapy techniques after modified radical mastectomy for breast cancer and hypofractionated intensity-modulated radiotherapy.

The aim of this study was to compare the advantages and disadvantages of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) in patients with left-sided breast cancer who underwent hypofractionated IMRT after a modified radical mastectomy. Twenty patients who required adjuvant radiotherapy after modified radical mastectomy were randomly selected, and a specified dose of 43.5 Gy/15 F was used to plan for IMRT or VMAT. Dose-volume histograms (DVHs) were utilized to evaluate the dose distribution of the planning target volumes (PTVs) and organs at risk (OARs). VMAT demonstrated a greater and more uniform dose distribution of PTVs and lower number of monitor units. No significant differences were found in V5 of the affected lung and heart between the two techniques (P > 0.05). The V10, V20, V30, and Dmean of the affected lung and V10, V20, V30, V40, Dmean, and Dmax of the whole heart were better in the VMAT than in the IMRT (P < 0.05). The Dmean and Dmax of the left anterior descending (LAD) branch of the coronary artery of the heart were better in the VMAT (P < 0.05), and the use of the VMAT effectively reduced the cardiopulmonary dose. A significant advantage of V30 and Dmean was also found in VMAT (P < 0.05). These findings indicate that VMAT has higher clinical significance than IMRT, because it improved the dose distribution in the target area, reduced the cardiopulmonary dose, protected the OARs (e.g. thyroid), and shortened the treatment duration.

Dosimetric comparison of postoperative interstitial high-dose-rate brachytherapy and modern external beam radiotherapy modalities in tongue and floor of the mouth tumours in terms of doses to critical organs.

The aim of the study was to dosimetrically compare interstitial high-dose-rate (HDR) brachytherapy (BT) and modern external beam radiotherapy modalities, as volumetric modulated arc therapy (VMAT) and stereotactic radiotherapy with Cyberknife (CK) of tumours of the tongue and floor of the mouth in terms of dose to the critical organs. In National Institute of Oncology, Budapest, between March 2013 and August 2022 twenty patients (11 male/9 female) with stage T1-3N0M0 tongue (n = 14) and floor of mouth (n = 6) tumours received postoperative radiotherapy because of close/positive surgical margin and/or lymphovascular and/or perineural invasion. High-dose-rate interstitial brachytherapy applying flexible plastic catheters with a total dose of 15 × 3 Gy was used for treatment. In addition to BT plans VMAT and stereotactic CK plans were also made in all cases, using the same fractionation scheme and dose prescription. As for the organs at risk, the doses to the mandible, the ipsilateral and the contralateral salivary glands were compared. The mean volume of the planning target volume (PTV) was 12.5 cm3, 26.5 cm3 and 17.5 cm3 in BT, VMAT and CK techniques, respectively, due to different safety margin protocols. The dose to the mandible was the most favourable with BT, as for the salivary glands (parotid and submandibular) the CK technique resulted in the lowest dose. The highest dose to the critical organs was observed with the VMAT technique. The mean values of D2cm3 and D0.1cm3 for the critical organs were as follows for BT, VMAT and CK plans: 47.4% and 73.9%, 92.2% and 101.8%, 68.4% and 92.3% for the mandible, 4.8% and 6.7%, 7.3% and 13.8%, 2.3% and 5.1% for the ipsilateral parotid gland, 3.5% and 4.9%, 6.8% and 10.9%, 1.5% and 3.3% for the contralateral parotid gland, 7.3% and 9.4%, 9.0% and 14.3%, 3.6% and 5.6% for the contralateral submandibular gland. The present results confirm that BT, despite being an invasive technique, is dosimetrically clearly beneficial in the treatment of oral cavity tumours and is a modality worth considering when applying radiotherapy, not only as definitive treatment, but also postoperatively. The use of the CK in the head and neck region requires further investigation.

Radiotherapy of prostate and head-and-neck tumour: An optimal treatment planning comparison for intensity modulated radiotherapy and volumetric modulated arctherapy techniques.

To evaluate and compare merits between intensity modulated radiotherapy and volumetric modulated arc-therapy radiotherapy techniques to determine which technique can achieve better treatment plan quality and efficient delivery. The retrospective study was conducted at the Radiation Oncology Department of SanBorotlo Hospital, Vicenza, Italy, in 2019, and comprised data from Jan 2019 to Dec 2019 related to prostate and head-and-neck patients in whom Pinnacle³ treatment planning system was used for optimisation with different prescribed doses and target geometries for intensity modulated radiotherapy and volumetric modulated arc-therapy techniques. Treatment plans were simulated using 6MV photon beam of SynergyS® Linac (Linear accelerator). The plan quality was evaluated using dose-volume indices for planning target-volume and organs-at-risk. ArcCHECK™ phantom was used for dose agreement verification between planed and delivered doses. Data of 8 patients was analysed. Intensity modulated radiotherapy and volumetric modulated arc-therapy treatment plan quality for prostate was found to be similar, but volumetric modulated arc-therapy had significant results for maximum dose (p=0.005). Intensity modulated radiotherapy and volumetric modulated arc-therapy plans for head-and-neck achieved adequate target coverage and sparing of organs at risk, and produced clinically acceptable treatment plans. The percentage of target coverage (p=0.001), dose maximum (p=0.013) and conformity index (p=0.000) were significant. A significant gain for all planning target volume dose-volume indices was noted (p<0.05). Volumetric modulated arc-therapy obtained better plan with significant values and improved sparing of organs at risk compared to intensity modulated radiotherapy for both prostate and head-and-neck treatments while maintaining doses to the organs at risk (p<0.05). Dynamic arc mode of beam delivery provided increased degrees of freedom of volumetric modulated arc-therapy beam intensity modulation, depicting superior dose distribution than intensity modulated radiotherapy.