The goal of this study was to investigate the variability of target volume and parotid gland dose distribution for nasopharyngeal carcinoma (NPC), and to explore the shifting patterns of parotid gland centroid and neck radius during radiotherapy. Twenty patients with NPC were enrolled. The target volume dose difference between planning dose and recalculated dose on weekly CT was analyzed. The recalculated doses on every weekly CT were cumulated to assess the difference between delivered dose and planning dose. The relationship of parotid gland centroid deviation with dose was studied, and the shrinking distances of neck radius were calculated for cervical vertebra 1, 2, 3 levels (C1, C2, C3). The ratio of GTVs and CTVs doses on weekly CTs to the doses on planning CT was all above 0.98; the dose of PTVs on weekly CT tended to decrease compared with planning. RMD was defined as the ratio of the mean dose of the left and right parotid glands (L-PG, R-PG) to the planning mean dose. The fitted relationships of RMD and the deviation of centroid (D) for L-PG and R-PG were: RMD=0.37*D+0.98 (R = 0.62, p < 0.001) and RMD = 0.33*D+0.97 (R = 0.72, p < 0.001), respectively. The order of neck radius shrinking distance at different levels was C1>C2=C3. In this study, we quantitatively analyzed the dosimetric variabilities of target volumes, and established linear models of parotid gland dose and its centroid deviation, which provides fractional and full-course dose evaluation during radiotherapy for NPC.

To investigate the dosimetric impact of laterality-specific RapidPlan models for nonsmall cell lung cancer. Three RapidPlan models were developed and validated for Right, Left, and General conventional lung radiotherapy. Each model was trained using 50 plans. The right and left models consisted of plans corresponding to their respective laterality. Twenty-five cases were randomly chosen from each laterality-specific model to craft a general model. All models shared identical optimization objectives and the same target and OAR structures. Validation included 13 right-sided and 13 left-sided cases optimized using each RapidPlan model without intervention and normalized such that the prescription dose covered 95% of the target volume. Statistical analysis using a paired sample t-test (p < 0.01) assessed dosimetric endpoints based on RTOG 0617 criteria. For right-sided cases, spinal cord Dmax and D0.03cc were lowest in the left model and highest in the right model (21.08 Gy and 21.22 Gy vs 23.67 Gy and 24.08 Gy). D and D esophagus mean dose was also lower in the left model compared to the right model (p < 0.01) for both left and right-sided cases. However, overall plan quality exhibited no substantial difference between general and laterality-specific models. Despite observing small but statistically significant differences, there is no discernible difference in plan quality between laterality-specific and general models, suggesting that a single RapidPlan model is sufficient.

To study dosimetric effects of leaf positioning errors (LPEs) of the Halcyon(2.0) dual-layer MLC on the long-course chemoradiotherapy (LCCRT) with 45∼50.4 Gy in 25∼28 fractions for rectal cancer. Nine Halcyon(2.0)-based LCCRT plans of rectal cancer were retrospectively involved. Four types of LPEs were introduced: (1) Uniformly distributed dual-layer random LPEs (Dual-R); (2) Proximal-layer systemic LPEs (P-S); (3) Distal-layer systemic LPEs (D-S); (4) Dual-layer systemic LPEs (Dual-S). The sensitivities of D, D and the Equivalent Uniform Dose (EUD) of PTV to various LPEs were investigated as well as varying ranges of EUDs of OARs. The sensitivities of D and EUD of PTV to Dual-R was -0.65%/mm and -0.38%/mm; the sensitivities of both indices to the P-S and D-S were similar to each other, ranging from 1.92%/mm to 2.87%/mm; both indices were more sensitive to the Dual-S and values were 4.97%/mm and 3.84%/mm respectively. The EUD changes of the bladder, and left and right femoral heads were from -13.23% to 14.82%. Single-side systemic LPEs lower than 0.7 mm are acceptable for Halcyon(2.0)-based LCCRT, while dual-layer systemic LPEs lower than 0.4 mm are acceptable, considering relative changes of 2% for D of PTV as threshold.

The virtual cone is an innovative MLC-based technique for generating dose distributions comparable to those of physical stereotactic cones. Initially designed for functional radiosurgery applications using a high-definition multileaf collimator (MLC) with 2.5 mm leaf width, this technique has been adapted to a standard 5 mm MLC system for treating small brain metastases. The adapted technique uses preconfigured location-specific control point sequences to produce spherical dose distributions with sharp dose gradients, and facilitates efficient planning through parallelizable template-based workflows. This report highlights the use of the adapted virtual cone technique for treating a 57-year-old patient with a 3 mm brain metastasis from metastatic papillary thyroid carcinoma using a standard multileaf collimator.

This study evaluated the accuracy of a commercial deep learning (DL)-based algorithm for segmenting the prostate, seminal vesicles (SV), and organs at risk (OAR) in patients with prostate cancer.

Head and Neck (H&N) cancer accounts for 3% of cancer cases in the United States. Precise tumor segmentation in H&N is of utmost importance for treatment planning and administering personalized treatment dose. We aimed to develop an automatic tumor localization and segmentation method in enhancing the clinical efficiency and ultimately improving treatment outcomes.

The present study aimed to improve the dose distribution of radiotherapy planning for nasopharyngeal carcinoma (NPC) by comparing the effects of various minimum monitor units (MUs) per dynamic control point (MMCP) values on the quality and execution efficiency of dynamic intensity-modulated radiotherapy (IMRT) planning. Thirty-four clinically implemented dynamic IMRT plans for patients with NPC were retrospectively selected. In total, 170 plans were obtained by modifying only the MMCP values (set as 1, 3, 5, 7, and 9) in the treatment planning system's (TPS) optimization parameters. These plans were divided into 5 groups. Analyzing the effects of MMCP on the target and organ dose at risk (OAR), also the execution efficiency of the treatment plan in each group and using a quality score system, we conducted an objective quantitative study of the dose distribution and execution efficiency. The target dose evaluation indicators (target coverage (TC), homogeneity index (HI), and conformity index (CI)) of all IMRT plans showed a trend of variation with an increase in MMCP values, and the difference was statistically significant when MMCP values were 5, 7, 9, and 1 (p < 0.05). With an increase in MMCP, the dose to OAR slightly increased, but the difference was not statistically significant (p > 0.05). With an increase in MMCP, the average number of MUs per segment significantly increased (p < 0.01). The groups based on MMCP values of 1, 3, 5, 7, and 9 received quality score system of 1.188, 1.180, 1.171, 0.987, and 1.184, respectively, with the MMCP7 group achieving the lowest score, indicating that this plan had the highest overall quality. The MMCP value for dynamic IMRT planning in the Monaco TPS for patients with NPC should be set to 7 to achieve fewer segments, the best execution efficiency without significantly deteriorating the target and OAR dose.

There has been no published work characterizing the attenuation of silicone breast implants in MV energy photon beams. As a result of systematic out of tolerance in-vivo dosimetry results, this report investigates whether the CT Hounsfield Units to electron density curve provides an accurate estimate of attenuation in silicone implants. A CT scan of a silicone breast implant centered on top of WT1 blocks was acquired with simple 6 MV and 10 MV plans created. Dose was calculated using the CT and a collapsed cone algorithm. The predicted dose was compared to doses measured with ionization chamber at 2 points downstream of the implant. Predicted dose from the treatment planning system was 0.9-1.7% lower than measured. The use of a density override on the implant of water (1 g/cm) improved agreement to less than 1% for all energies and measurement depths. We conclude that the use of CT Hounsfield Units for silicone breast implants leads to an under-estimation of dose in MV photon fields. Dose accuracy has been shown to be improved in the treatment planning system when silicone breast implants have a density override of water.

This study investigated a straightforward treatment planning technique for definitive stereotactic body radiation therapy (SBRT) for patients with early-stage lung cancer aimed at increasing dose to gross disease by strategically penalizing the normal tissue objective (NTO) in the Eclipse treatment planning system. Twenty-five SBRT cases were replanned to 50 Gy in 5 fractions using static and dynamic NTO methods (50 plans total). The NTO had a start dose of 100% at the target border, end dose of 20%, fall-off rate of 0.4/mm, and a priority of 150. For the static NTO plans, a lower planning target volume (PTV) objective was placed at 52 Gy with a priority of 100. Maximum dose was not penalized. Optimization was performed without user interaction. In contrast, the planner incrementally increased the priority of the NTO on the dynamic NTO plans until 95% of the target volume was covered by the prescription dose. Further, the dynamic NTO plans used both PTV lower and upper objectives at 63-64 Gy with priorities of 50. Maximum dose was penalized to ensure that the hot spot was within ± 2% of the static NTO global maximum dose. Following optimization, all plans were normalized so that the prescription dose covered 95% of the PTV. Plans were scored based on RTOG 0813 criteria, and dose to the internal target volume (ITV) and PTV was evaluated. The Wilcoxon signed-rank test (threshold = 0.05) was used to evaluate differences between the static and dynamic NTO plans. All plans met RTOG 0813 planning guidelines. In comparison to the static NTO plans, the dynamic NTO plans exhibited statistically significant increases in PTV mean dose, ITV mean dose, and PTV-ITV mean dose. Notably, the dynamic NTO plans more effectively concentrated the high dose on gross disease at the center of the PTV. As compared to the static NTO plans, the mean dose was 4.6 Gy higher in the ITV while only 1.3 Gy higher in the PTV-ITV rind of the dynamic NTO plans. Global maximum doses were similar. There were some small yet statistically significant differences in dose conformity between plan types. Furthermore, the dynamic NTO plans demonstrated a significant reduction in total monitor units (MU). This study demonstrated an efficient optimization strategy for lung SBRT plans that concentrates the highest dose in the gross disease, which may improve local control.

This study investigated optimization settings that steepen the dose gradient as a function of target size for lung stereotactic body radiation therapy (SBRT). Sixty-eight lung SBRT patients with planning target volumes (PTVs) ranging from 2-203 cc were categorized into small (<20 cc), medium (20-50 cc), and large (>50 cc) groups. VMAT plans were generated using the normal tissue objective (NTO) to penalize the dose gradient at progressively steeper NTO fall-off values (0.1, 0.2, 0.3, 0.4, 0.5 mm). Dose was calculated using the AcurosXB algorithm and was normalized so the prescription dose covered 95% of the PTV. Mann-Whitney, Kruskal-Wallis and ANOVA tests were used to assess for statistical differences in the Conformity Index at the 50% isodose level (CI50%), global maximum dose (D), and monitor units (MU) across the various NTO settings. All plans adhered to institutional criteria and met the guidelines of the Radiation Therapy Oncology Group 0813. Steeper NTO fall-off values significantly increased D and MUs across all groups (p < 0.05). CI50% significantly differed with fall-off values in small (0.3 mm) and medium (0.2 mm) targets, indicating steeper NTO fall-off values improve CI50% for small and medium targets (p < 0.05). Large targets showed no significant CI50% difference across these fall-off values. As target size increases, the importance of fall-off values in achieving an acceptable CI50% diminishes. Smaller targets benefit from steeper fall-off values despite increased D and MUs. Consideration of fall-off value relative to target size is crucial to limit dose spillage outside the target.

To assess the impact of Strut Adjusted Volume Implant (SAVI) catheter digitization variability on dosimetric evaluation parameters of HDR breast brachytherapy treatment plans. Four clinically approved SAVI cases were chosen for this digitization variability analysis. All patients were implanted with 6-1 SAVI device. Six experienced physicists independently digitized SAVI catheters. Plans utilizing significant peripheral loading were used for this study where SAVI catheters were near the chest wall and/or skin. After digitization was completed for each case by each physicist, the original clinical dwell times were copied over for comparison. This ensured that only variability among plans is the digitization of SAVI catheters by different users. The original plan that went through two physicists' checks and one physician's review was considered the "ground truth" plan to which all other plans were compared. Plans were evaluated on planning parameters for lumpectomy cavity's PTV_Eval D90, V150, V200 and for the OARs (Chest-Wall/Ribs and Skin), on D, D, D, D. Additionally, a visualization window setting-based uncertainty test was performed on the same 4 cases. Our results showed that the average and maximum dwell positional digitization uncertainties were 0.36 and 0.75 mm, respectively. Average PTV_Eval D90 was 97.11+/-2.93 %, V150 was 23.10+/-4.25 cc, V200 was 11.88+/-1.93 cc. All OAR constraints were met on all plans - Chest-Wall/Ribs (CW/Ribs) and Skin D was 103.40+/-9.23 % and 93.60+/-6.14 %, respectively. Aggregate analysis across all plans shows a clinically nonsignificant spread around the mean for all parameters considered. The robustness of SAVI treatment plans to minor variation in catheter digitization was proved through our multiuser study. Our study showed that SAVI planning constraints are stable within reasonable variation of digitization differences. Such uncertainty analysis is useful in standardization of digitization practices in a department and in defining action levels on digitization fixing request during a 2nd check.

To develop a Knowledge Based Planning (KBP) model for creating quantifiably high quality VMAT treatment plans in a single click for head and neck cases treated Simultaneous Integrated Boost (SIB) with bilateral parotid involvement (BPI) where both parotids are near, abutting or partially overlapping target volume. Eclipse RapidPlan and the publicly available PlanScorecard tool were used to assess existing Head and Neck RapidPlan models on two representative cases. The best performer was used as a foundation model to assist in creating new initial training set doses from previously treated cases. Those initial 27 cases were first replanned using only the selected foundation model, then further improved based on manual replanning, informed by dosimetric scorecard assessment. A new, initial model was trained from those 27 foundation model created cases that had been manually improved. Then, that initial model was used to replan those cases again, resulting in higher scores. Additional cases were also replanned using the initial model along with some manual changes to the optimization objectives to increase the score. This resulted in a total of 66 cases from which the final, released, HN-SIB-BPI was trained. A 27 case subset of the full training set was replanned and rescored at each phase of the process with a 260 total point 3-target scorecard. The average score increased: 210.5 foundation model; 226.96 manually improved plans; 230.1 initial model; 231.7 HN-SIB-BPI. On the same 27 case subset, mean ipsilateral and contralateral parotid dose decreased by 1.05Gy and 1.58Gy respectively from the foundation model to HN-SIB-BP. Eight external cases were created from HN-SIB-BPI with dosimetric scorecard validation on Halcyon (3-PTV:221.38/260; 2-PTV:196.1/228.5) and TrueBeam (3-PTV:222.01/260; 2-PTV:202.24/228.5). A specific clinical intent (ie: max parotid sparing) can be articulated in a comprehensive and precise manner by creating a dosimetric scorecard with individual metrics points assigned to each OAR and target metric reflecting their relative importance. This process improved the KBP model (HN-SIB-BPI) in several quantifiable ways including further sparing of parotid dose. All results and tools in this work are shared publicly.

In planning the treatment of spinal metastases using stereotactic body radiotherapy (SBRT), the optimal blocking of the spinal cord to match the leaf travel can be achieved with a first-arc collimator angle of approximately 90°. We aim to clarify the optimal second-arc collimator angles when the first-arc collimator angle is fixed to 90° in dual-arc volumetric modulated arc therapy (VMAT). For this retrospective study, we considered 37 spinal segments with spinal metastases and created dual-arc VMAT plans. In the plans, 24 Gy in 2 fractions were prescribed, and the first-arc collimator angle was fixed to 90° while varying the second-arc collimator angle in increments of 15° from 0° to 90°. All the plans were normalized such that the planning organ-at-risk volume for the spinal cord D = 17 Gy and satisfied other dose constraints. D for the planning target volume (PTV), V for the overlap between the PTV and 10 mm expansion of the spinal cord, modified gradient index, monitor unit, and 3%/1 mm gamma passing rates were compared between different second-arc collimator angles using the Wilcoxon signed-rank test and Bonferroni correction. PTV D and overlap V were the highest for a second-arc collimator angle of 45° and decreased as the angle approached either 0° or 90°. The maximum mean differences of PTV D and overlap V were -2.66% (90° vs 45°, p < 0.0024) and -5.49% (90° vs 45°, p < 0.0024), respectively. Moreover, the second-arc collimator angle of 45° was the least suitable in terms of the modified gradient index. The required monitor unit increased from the second-arc collimator angle of 15° to 45°, and the 3%/1 mm gamma passing rates reached over 95% for the evaluated second-arc collimator angles of 15°, 30°, and 45°. We found that in the dual-arc VMAT plan for spine SBRT, second-arc collimator angles other than 90° were suitable, and 45° was the optimal angle in terms of target coverage including the area around the spinal cord.

C-arm linacs have been used widely to treat multiple cranial metastases using stereotactic radiosurgery (SRS). A new generation of O-ring linacs offer several workflow advantages when compared to C-arm platforms. However, O-ring linacs are not able to employ couch rotations for noncoplanar beams used in SRS treatments. This study was conducted in order to simulate further possible developments of O-ring treatment units by assessing their geometrical efficiency. In this work we compare the plan quality for C-arm versus an O-ring platform including metrics that are relevant to SRS for multiple metastases. The comparison is conducted by incorporating tilted arcs on the O-ring platform therefore introducing noncoplanarity. Total 40 patients previously treated for SRS with 20 Gy single fraction were replanned for C-arm with a standard noncoplanar 5-arc arrangement and O-ring with both coplanar and noncoplanar beams. For the O-ring plans, we considered a default 3-arc coplanar arrangement, as well as 3- and 5-arc arrangements with arcs tipped up to 10 degrees from the axial plane. Target coverage, organ-at-risk (OAR) doses, monitor unit (MU) efficiency, conformity and gradient indices were assessed for all plans. For most metrics the O-ring geometries, even the coplanar arrangement, produced statistically comparable results to the C-arm. Small but significant differences were found for the 3 arc O-ring for PTV: D90%, D2% and MU/Gy and for the 5 arc O-ring at D2% when both were compared to the C-arm. Cumulative dose volume histograms (DVHs) for normal brain showed a cross-over between the C-arm and coplanar O-ring geometry at a low dose (2.3 ± 1.8 Gy), with O-ring associated with higher volumes above this cross-over dose. However, no statistical difference was seen in the brainstem, optic pathway and volumes of normal brain receiving 12 Gy or 20 Gy. This study has found that O-ring geometry linacs can produce SRS plans of comparable quality to those from a C-arm for multiple cranial metastases.

Oligometastatic breast cancer patients can today could benefit from a multimodal approach, combining systemic therapy with metastasis-directed treatment using stereotactic body radiotherapy (SBRT). However, the possibility to synchronously treat multiple lesions is still challenging, needing the ability to generate complex dose distributions with steep dose gradients outside the lesions and major sparing of surrounding organs at risk and accurately track and reproduce the patient's position before and during radiation therapy. We report the case of an oligometastatic patient from left breast cancer, which occurred after a full course of whole breast radiotherapy, treated using the potential of modern technology including single-isocenter setup, plan automation, breath-hold technique and surface guided tracking and reproducibility of patient's position before and during radiation therapy. A 44-year-old female patient with a history of left breast cancer, specifically a luminal-B-like invasive ductal carcinoma with Her2 overexpression, was admitted to our department. The patient previously underwent a left mastectomy (pT2N0M0), 4 cycles of adjuvant chemotherapy, adjuvant radiotherapy on the chest wall and lymph nodes drainage, and 5 years of hormonal therapy. A chest wall ultrasound and positron emission tomography revealed the presence of new lesions in the area of the surgical scar from the previous mastectomy, internal mammary, axillary and retropectoral levels. The 3 lesions were simultaneously treated with a mono-isocentric VMAT plan using SBRT technique with a total dose of 30 Gy delivered in 5 fractions. Due to the technical challenges, this treatment was supported by the use of planning automation, breath-hold technique and surface-guided radiation therapy to improve the accuracy of the dose delivery. Two different plans were generated and compared to pursue the best dosimetric result, including a summed plan obtained from 3 individual SBRT plans for each lesion with a separate isocenter placed in each of them (MIP), and a single-isocenter SBRT plan able to treat multiple lesions synchronously (SIP). Because of the advantages in terms of dosimetry and dose delivery efficiency, the patient was successfully treated with the SIP plan. The treatment time was reduced to about 4.5 minutes, allowing the comfortably use of breath-hold technique. After treatment, the condition of the patient was normal, and no toxicities have been observed in follow-up. SBRT with mono isocentric VMAT planning represents the recommended approach to simultaneously treat multiple lesions in close proximity in the thoracic district.

Radiotherapy planning for nasopharyngeal carcinoma is a complex process due to the proximity of critical structures. Volumetric modulated arc therapy (VMAT) can improve the therapeutic ratio. However, multiple treatment delivery systems offer VMAT with varying technical specifications. This study compares the dosimetric plan quality of 2 systems, Clinac-iX and Halcyon in nasopharyngeal carcinoma. We utilized contrast-enhanced computed tomography (CECT) simulation and magnetic resonance (MR) image datasets from thirty patients with nasopharyngeal carcinoma to contour target volumes and organs at risk (OARs). Two medical physicists independently performed dosimetric planning for Clinac-iX and Halcyon machines, following standard international dosimetric constraints for OARs. We compared plan quality for dosimetric profiles, indices, and plan complexity parameters from both machines. Dosimetric coverage for target volumes and plan quality indices, such as homogeneity, conformity, and coverage, showed no significant differences between Clinac-iX and Halcyon. However, Halcyon demonstrated significantly better OAR sparing, particularly for the spinal cord, optic chiasm, lenses, eyeballs and lower brain volume integral dose (BVID) (p < 0.05). Complexity parameters showed that both systems used a similar number of arcs, but Halcyon had higher monitor units and lower treatment time per fraction owing to higher dose rate. Our study results favor Halcyon for better plan quality regarding critical organ sparing, low brain volume integral dose, and fast treatment delivery. This study can be used as a reference for selecting an optimal treatment delivery system for nasopharyngeal carcinoma patients in centres equipped with multiple linear accelerators.

This study assesses the dosimetric effectiveness of the commercial trade-off optimization (TO) module in comparison to iterative optimization for volumetric modulated arc therapy (VMAT) in craniospinal irradiation technique.Fifteen patients who had previously undergone VMAT-based craniospinal irradiation (CSI) using manual optimization (TP) underwent re-optimization with trade-off optimization (MCO). All patients were treated using the Halcyon-E O-ring linear accelerator, with maximum field size of 28×28 cm², a 6MV unflattened beam, and adjacent isocenter field overlap of 10 cm. Plans were compared based on PTV dose coverage (D95%), maximum dose (Dmax), conformity index (CI), heterogeneity index (HI), maximum and mean dose to serial and parallel organs, respectively. Statistical evaluation was conducted using paired sample t-tests. The PTVD95% for TO and MCO plans were 98.0% ± 1.0% and 97.4% ± 0.7%, respectively. In the same sequence, HIs were 1.06 ± 0.01 and 1.07 ± 0.01. CIs for both arms were 0.9 ± 0.0 and its variation was statistically significant (p = 0.027). The differences in dose for bilateral cochlea and left optic nerves were statistically significant (0.022≤ p ≤0.049). The ΔDmax for serial organs and mean dose for parallel organs did not exceed 1%, except for the bilateral optic nerve, mandible, oral cavity, right parotid, and stomach. No parallel organ showed a statistically significant dose variation. Clinically significant reductions in dose were noted for three organs; the average dose reduction in MCO plans for bilateral optic nerves was 3.9%, and for the larynx, it was 8.5%. In this study, trade-off optimization did not demonstrate any significant improvement over the iteratively optimized plans, primarily because the planners were highly skilled and could already generate high-quality plans using iterative optimization alone. However, this finding may not necessarily apply universally to all treatment planners or clinical settings.

Dose-volume histograms (DVH), along with dose and volume metrics, are central to radiotherapy planning. As such, errors have the potential to significantly impact the selection of appropriate treatment plans. Dose distributions that pass tests in one TPS may fail the same tests when transferred to another, even if using identical structures and dose grid information. This work shows the design and implementation of methods for assessing the accuracy of dose and volume computations performed by treatment planning systems (TPS), and other analytical tools. We demonstrate examples where differences in calculations between systems can change the assessment of a plan's clinical acceptability. Our work also provides a more detailed DVH analysis of single targets than earlier published studies. This is relevant for SRS plans and small structure dose assessments. Very small structures are a particular problem because of their coarse digital representation, and the impact of this is thoroughly examined. Reference DVH curves were derived mathematically, based on Gaussian dose distributions centered on spherical structures. The structures and dose distributions were generated synthetically, and imported into RayStation, MasterPlan, and ProKnow. Corresponding DVHs were analytically derived and taken as ground truth references, for comparison with the commercial DVH calculations. Two commonly used dose metrics PCI and MGI were used to determine the limit of calculation accuracy for small structures. In addition, to measure the DVH differences between a larger range of commercial DVH calculators, the D95 metric from a set of real clinical plans was compared across both the 3 DVH calculators under test, and across a further six TPSs from other hospitals. We show that even slight deviations between the results of DVH calculators can lead to plan check failures, and we illustrate this with the commonly used D95 planning metric. We present clinical data across eight planning systems that highlight instances where plan checks would pass in one software and fail in another due to DVH calculation differences. For the smallest volumes tested, errors of up to 20% were observed in the DVHs. RayStation was tested down to a 3 mm radius sphere (≈0.1 cc) and this showed close to 10% error, reducing to 1% for 10 mm radius (≈4.0 cc) and 0.1% for 20 mm radius (≈33 cc). In clinical plans, the variation in D95 was up to 9% for the smallest volumes, and typically around 2% in the range 0.5 cc-20 cc, and 1% in 20 cc-70 cc, falling to <0.1% for large volumes. Paddick Conformity Index (PCI) and Modified Gradient Index (MGI) are commonly used plan quality indicators for very small volumes. For volumes ≈0.1 cc we observed errors of up to 40% in PCI, and up to 75% in MGI. Our study extends the range of tested DVH calculators in published work, and shows their performance over a wider range of volume sizes. We provide quantitative evidence of the critical need to test the accuracy of DVH calculators in the TPS before clinical use. This work is particularly relevant for both stereotactic plan evaluation and for assessment of small volume doses in published dose constraint recommendations. We demonstrate that significant errors can occur in DVHs for volumes less than 1 cc, even if the volumes themselves are calculated accurately. Even for large structures, deviations between the outputs of DVH calculators can lead to indicated or reported plan check failures if they do not include appropriate tolerances. We urge caution in the use of DVH metrics for these very small volumes and recommend that appropriate DVH uncertainty tolerances are set in organ dose constraints when using them to evaluate clinical plans.

Automated planning has surged in popularity within external beam radiation therapy in recent times. Leveraging insights from previous clinical knowledge could enhance auto-planning quality. In this work, we evaluated the performance of Ethos automated planning with knowledge-based guidance, specifically using Rapidplan (RP). Seventy-four patients with head-and-neck (HN) cancer and 37 patients with prostate cancer were used to construct separate RP models. Additionally, 16 patients from each group (HN and prostate) were selected to assess the performance of Ethos auto-planning results. Initially, a template-based Ethos plan (Non-RP plan) was generated, followed by integrating the corresponding RP model's DVH estimates into the optimization process to generate another plan (RP plan). We compared the target coverage, OAR doses, and total monitor units between the non-RP and RP plans. Both RP and non-RP plans achieved comparable target coverage in HN and Prostate cases, with a negligible difference of less than 0.5% (p > 0.2). RP plans consistently demonstrated lower doses of OARs in both HN and prostate cases. Specifically, the mean doses of OARs were significantly reduced by 9% (p < 0.05). RP plans required slightly higher monitor units in both HN and prostate sites (p < 0.05), however, the plan generation time was almost similar (p > 0.07). The inclusion of the RP model reduced the OAR doses, particularly reducing the mean dose to critical organs compared to non-RP plans while maintaining similar target coverage. Our findings provide valuable insights for clinics adopting Ethos planning, potentially enhancing the auto-planning to operate optimally.

Deep inspiration breath-hold (DIBH) has proven effective in minimizing radiation exposure to organs at risk (OARs) in right-sided breast cancer patients requiring regional nodal irradiation (RNI). However, there has been no dosimetric evaluation comparing DIBH techniques to free-breathing (FB) conditions on the TrueBeam (TB) HD linear accelerator (LINAC). To address this gap and accommodate breast cancer patients requiring RNI on the TB HD LINAC, an innovative method involving a 90-degree rotation of the regional lymph nodes' field during treatment planning was devised.

To compare the dosimetric differences in volumetric modulated arc therapy (VMAT) and intensity modulated proton therapy (IMPT) in stereotactic body radiation therapy (SBRT) of multiple lung lesions and determine a normal tissue complication probability (NTCP) model-based decision strategy that determines which treatment modality the patient will use. A total of 41 patients were retrospectively selected for this study. The number of patients with 1-6 lesions was 5, 16, 7, 6, 3, and 4, respectively. A prescription dose of 70 Gy in 10 fractions was given to each lesion. SBRT plans were generated using VMAT and IMPT. All the IMPT plans used robustness optimization with ± 3.5% range uncertainties and 5 mm setup uncertainties. Dosimetric metrics and the predicted NTCP value of radiation pneumonitis (RP), esophagitis, and pericarditis were analyzed to evaluate the potential clinical benefits between different planning groups. In addition, a threshold for the ratio of PTV to lungs (%) to determine whether a patient would benefit highly from IMPT was determined using receiver operating characteristic curves. All plans reached target coverage (V70Gy ≥ 95%). Compared with VMAT, IMPT resulted in a significantly lower dose of most thoracic normal tissues. For the 1-2, 3-4 and 5-6 lesion groups, the lung V5 was 29.90 ± 9.44%, 58.33 ± 13.35%, and 81.02 ± 5.91% for VMAT and 11.34 ± 3.11% (p < 0.001), 21.45 ± 3.80% (p < 0.001), and 32.48 ± 4.90% (p < 0.001) for IMPT, respectively. The lung V20 was 12.07 ± 4.94%, 25.57 ± 6.54%, and 43.99 ± 11.83% for VMAT and 6.76 ± 1.80% (p < 0.001), 13.14 ± 2.27% (p < 0.01), and 19.62 ± 3.48% (p < 0.01) for IMPT. The D of the total lung was 7.65 ± 2.47 Gy, 14.78 ± 2.75 Gy, and 21.64 ± 4.07 Gy for VMAT and 3.69 ± 1.04 Gy (p < 0.001), 7.13 ± 1.41 Gy (p < 0.001), and 10.69 ± 1.81 Gy (p < 0.001) for IMPT. Additionally, in the VMAT group, the maximum NTCP value of radiation pneumonitis was 73.91%, whereas it was significantly lower in the IMPT group at 10.73%. The accuracy of our NTCP model-based decision model, which combines the number of lesions and PTV/Lungs (%), was 97.6%. The study demonstrated that the IMPT SBRT for multiple lung lesions had satisfactory dosimetry results, even when the number of lesions reached 6. The NTCP model-based decision strategy presented in our study could serve as an effective tool in clinical practice, aiding in the selection of the optimal treatment modality between VMAT and IMPT.