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Background: During prostate stereotactic body radiation therapy (SBRT), prostate tumor translational motion may deteriorate the planned dose distribution. Most of the major advances in motion management to date have focused on correcting this one aspect of the tumor motion, translation. However, large prostate rotation up to 30° has been measured. As the technological innovation evolves toward delivering increasingly precise radiotherapy, it is important to quantify the clinical benefit of translational and rotational motion correction over translational motion correction alone. Purpose: The purpose of this work was to quantify the dosimetric impact of intrafractional dynamic rotation of the prostate measured with a six degrees-of-freedom tumor motion monitoring technology. Methods: The delivered dose was reconstructed including (a) translational and rotational motion and (b) only translational motion of the tumor for 32 prostate cancer patients recruited on a 5-fraction prostate SBRT clinical trial. Patients on the trial received 7.25 Gy in a treatment fraction. A 5 mm clinical target volume (CTV) to planning target volume (PTV) margin was applied in all directions except the posterior direction where a 3 mm expansion was used. Prostate intrafractional translational motion was managed using a gating strategy, and any translation above the gating threshold was corrected by applying an equivalent couch shift. The residual translational motion is denoted as (Formula presented.). Prostate intrafractional rotational motion (Formula presented.) was recorded but not corrected. The dose differences from the planned dose due to (Formula presented.) + (Formula presented.), ΔD((Formula presented.) + (Formula presented.)) and due to (Formula presented.) alone, ΔD((Formula presented.)), were then determined for CTV D98, PTV D95, bladder V6Gy, and rectum V6Gy. The residual dose error due to uncorrected rotation, (Formula presented.) was then quantified: (Formula presented.) = ΔD((Formula presented.) + (Formula presented.)) - ΔD((Formula presented.)). Results: Fractional data analysis shows that the dose differences from the plan (both ΔD((Formula presented.) + (Formula presented.)) and ΔD((Formula presented.))) for CTV D98 was less than 5% in all treatment fractions. ΔD((Formula presented.) + (Formula presented.)) was larger than 5% in one fraction for PTV D95, in one fraction for bladder V6Gy, and in five fractions for rectum V6Gy. Uncorrected rotation, (Formula presented.) induced residual dose error, (Formula presented.), resulted in less dose to CTV and PTV in 43% and 59% treatment fractions, respectively, and more dose to bladder and rectum in 51% and 53% treatment fractions, respectively. The cumulative dose over five fractions, ∑D((Formula presented.) + (Formula presented.)) and ∑D((Formula presented.)), was always within 5% of the planned dose for all four structures for every patient. Conclusions: The dosimetric impact of tumor rotation on a large prostate cancer patient cohort was quantified in this study. These results suggest that the standard 3–5 mm CTV-PTV margin was sufficient to account for the intrafraction prostate rotation observed for this cohort of patients, provided an appropriate gating threshold was applied to correct for translational motion. Residual dose errors due to uncorrected prostate rotation were small in magnitude, which may be corrected using different treatment adaptation strategies to further improve the dosimetric accuracy.

Background Stereotactic Ablative Body Radiotherapy (SABR) is a non-invasive treatment which allows delivery of an ablative radiation dose with high accuracy and precision. SABR is an established treatment for both primary and secondary liver malignancies, and technological advances have improved its efficacy and safety. Respiratory motion management to reduce tumour motion and image guidance to achieve targeting accuracy are crucial elements of liver SABR. This phase II multi-institutional TROG 17.03 study, Liver Ablative Radiotherapy using Kilovoltage intrafraction monitoring (LARK), aims to investigate and assess the dosimetric impact of the KIM real-time image guidance technology. KIM utilises standard linear accelerator equipment and therefore has the potential to be a widely available real-time image guidance technology for liver SABR. Methods Forty-six patients with either hepatocellular carcinoma or oligometastatic disease to the liver suitable for and treated with SABR using Kilovoltage Intrafraction Monitoring (KIM) guidance will be included in the study. The dosimetric impact will be assessed by quantifying accumulated patient dose distribution with or without the KIM intervention. The patient treatment outcomes of local control, toxicity and quality of life will be measured. Discussion Liver SABR is a highly effective treatment, but precise dose delivery is challenging due to organ motion. Currently, there is a lack of widely available options for performing real-time tumour localisation to assist with accurate delivery of liver SABR. This study will provide an assessment of the impact of KIM as a potential solution for real-time image guidance in liver SABR. Trial registration This trial was registered on December 7th 2016 on ClinicalTrials.gov under the trial-ID NCT02984566.

PurposeStereotactic Ablative Radiotherapy (SABR) has recently emerged as a favourable treatment option for prostate cancer patients. With higher doses delivered over fewer fractions, motion adaptation is a requirement for accurate delivery of SABR. This study compared the efficacy of multileaf collimator (MLC) tracking vs. gating as a real-time motion adaptation strategy for prostate SABR patients enrolled in a clinical trial.MethodsForty-four prostate cancer patients treated over five fractions in the TROG 15.01 SPARK trial were analysed in this study. Forty-nine fractions were treated using MLC tracking and 166 fractions were treated using beam gating and couch shifts. A time-resolved motion-encoded dose reconstruction method was used to evaluate the dose delivered using each motion adaptation strategy and compared to an estimation of what would have been delivered with no motion adaptation strategy implemented.ResultsMLC tracking and gating both delivered doses closer to the plan compared to when no motion adaptation strategy was used. Differences between MLC tracking and gating were small with differences in the mean discrepancy from the plan of -0.3% (CTV D98%), 1.4% (CTV D2%), 0.4% (PTV D95%), 0.2% (rectum V30Gy) and 0.0% (bladder V30Gy). On average, 0.5 couch shifts were required per gated fractions with a mean interruption duration of 1.8 ± 2.6 min per fraction treated using gating.ConclusionBoth MLC tracking and gating were effective strategies at improving the accuracy of the dose delivered to the target and organs at risk. While dosimetric performance was comparable, gating resulted in interruptions to treatment.Clinical trial registration numberNCT02397317.

Purpose The Trans-Tasman Radiation Oncology Group (TROG) 15.01 Stereotactic Prostate Adaptive Radiotherapy utilizing Kilovoltage intrafraction monitoring (SPARK) trial is a multicenter trial using Kilovoltage Intrafraction Monitoring (KIM) to monitor prostate position during the delivery of prostate radiation therapy. KIM increases the accuracy of prostate radiation therapy treatments and allows for hypofractionation. However, an additional imaging dose is delivered to the patient. A standardized procedure to determine the imaging dose per frame delivered using KIM was developed and applied at four radiation therapy centers on three different types of linear accelerator. Methods Dose per frame for kilovoltage imaging in fluoroscopy mode was measured in air at isocenter using an ion chamber. Beam quality and dose were determined for a Varian Clinac iX linear accelerator, a Varian Trilogy, four Varian Truebeams and one Elekta Synergy at four different radiation therapy centers. The imaging parameters used on the Varian machines were 125 kV, 80 mA, and 13 ms. The Elekta machine was measured at 120 kV, 80 mA, and 12 ms. Absorbed doses to the skin and the prostate for a typical SBRT prostate treatment length were estimated according to the IPEMB protocol. Results The average dose per kV frame to the skin was 0.24 ± 0.03 mGy. The average estimated absorbed dose to the prostate for all five treatment fractions across all machines measured was 39.9 ± 2.6 mGy for 1 Hz imaging, 199.7 ± 13.2 mGy for 5 Hz imaging and 439.3 ± 29.0 mGy for 11 Hz imaging. Conclusions All machines measured agreed to within 20%. Additional dose to the prostate from using KIM is at most 1.3% of the prescribed dose of 36.25 Gy in five fractions delivered during the trial.

PurposeKilovoltage intrafraction monitoring (KIM) is a novel software platform implemented on standard radiation therapy systems and enabling real-time image guided radiation therapy (IGRT). In a multi-institutional prospective trial, we investigated whether real-time IGRT improved the accuracy of the dose patients with prostate cancer received during radiation therapy.Methods and materialsForty-eight patients with prostate cancer were treated with KIM-guided SABR with 36.25 Gy in 5 fractions. During KIM-guided treatment, the prostate motion was corrected for by either beam gating with couch shifts or multileaf collimator tracking. A dose reconstruction method was used to evaluate the dose delivered to the target and organs at risk with and without real-time IGRT. Primary outcome was the effect of real-time IGRT on dose distributions. Secondary outcomes included patient-reported outcomes and toxicity.ResultsMotion correction occurred in ≥1 treatment for 88% of patients (42 of 48) and 51% of treatments (121 of 235). With real-time IGRT, no treatments had prostate clinical target volume (CTV) D98% dose 5% less than planned. Without real-time IGRT, 13 treatments (5.5%) had prostate CTV D98% doses 5% less than planned. The prostate CTV D98% dose with real-time IGRT was closer to the plan by an average of 1.0% (range, -2.8% to 20.3%). Patient outcomes showed no change in the 12-month patient-reported outcomes compared with baseline and no grade ≥3 genitourinary or gastrointestinal toxicities.ConclusionsReal-time IGRT is clinically effective for prostate cancer SABR.

© 2019 American Association of Physicists in Medicine Purpose: Kilovoltage intrafraction monitoring (KIM) allows for real-time image guidance for tracking tumor motion in six-degrees-of-freedom (6DoF) on a standard linear accelerator. This study assessed the geometric accuracy and precision of KIM used to guide patient treatments in the TROG 15.01 multi-institutional Stereotactic Prostate Ablative Radiotherapy with KIM trial and investigated factors affecting accuracy and precision. Methods: Fractions from 44 patients with prostate cancer treated using KIM-guided SBRT were analyzed across four institutions, on two different linear accelerator models and two different beam models (6 MV and 10 MV FFF). The geometric accuracy and precision of KIM was assessed from over 33 000 images (translation) and over 9000 images (rotation) by comparing the real-time measured motion to retrospective kV/MV triangulation. Factors potentially affecting accuracy, including contrast-to-noise ratio (CNR) of kV images and incorrect marker segmentation, were also investigated. Results: The geometric accuracy and precision did not depend on treatment institution, beam model or motion magnitude, but was correlated with gantry angle. The centroid geometric accuracy and precision of the KIM system for SABR prostate treatments was 0.0 ± 0.5, 0.0 ± 0.4 and 0.1 ± 0.3 mm for translation, and −0.1 ± 0.6°, −0.1 ± 1.4° and −0.1 ± 1.0° for rotation in the AP, LR and SI directions respectively. Centroid geometric error exceeded 2 mm for 0.05% of this dataset. No significant relationship was found between large geometric error and CNR or marker segmentation correlation. Conclusions: This study demonstrated the ability of KIM to locate the prostate with accuracy below other uncertainties in radiotherapy treatments, and the feasibility for KIM to be implemented across multiple institutions.

Lymphoedema following axillary radiotherapy for breast cancer causes significant morbidity. Our goal was to evaluate the feasibility of sparing the lymph node that drains the arm's lymphatics (ARM node) while achieving standard dose constraints for whole breast and comprehensive lymph node irradiation.Six patients underwent lymphoscintigraphy and SPECT CT to identify the breast sentinel node (SN) and ARM node. The ARM node was contoured on the SPECT CT and deformably registered to the radiotherapy treatment planning CT. Radiotherapy plans (50 Gy in 25 fractions) with VMAT technique were generated, with the aim to spare the ARM node (Mean dose25 Gy) and achieve adequate coverage to the remaining axilla. The plan required the breast SN site (clip + 10 mm surrounding the clip) to achieve D98%47.5 Gy, and axillary nodal CTV excluding ARM node to achieve D90%45 Gy.In one patient, the ARM node was within the volume of breast SN site and sparing was not possible. For the remaining 5 patients, an ARM node-sparing plan could be successfully generated; the mean dose to the ARM node ranged from 11.2 to 23.1 Gy (median 13.8 Gy). In these 5 subjects, D90%45 Gy of axillary nodal CTV (range, 44.9-48.5 Gy, median 46.2 Gy) and D98%47.5 Gy of breast SN site were achieved.In this planning study, ARM node-sparing VMAT of the breast and lymph nodes was feasible, while maintaining adequate dosimetric coverage. However, in some individuals, localization of the ARM node in close proximity to breast SN site precluded the generation of an ARM node-sparing treatment plan.

Background Lymphoedema of the arm following axillary surgery or radiotherapy remains a significant side effect affecting some women after breast cancer treatment. Axillary reverse mapping (ARM) is a technique used to identify the lymph node draining the arm (ARM node). Our study aim was to examine the location of the ARM nodes in relation to target volumes and treatment fields for breast cancer radiotherapy. Materials and methods Eighteen breast cancer patients underwent lymphoscintigraphy of contralateral arm (left 10, right 8) and SPECT CT scan on a research study. Patient position for the SPECT CT scan approximated the position used for radiotherapy. Using MIM software™, the ARM node for each subject was contoured on the SPECT CT and verified by a nuclear medicine physician. The CT component of the SPECT CT was then transferred to ECLIPSE™ radiotherapy planning software, and the contralateral breast and axilla were contoured on this CT scan according to the ESTRO contouring guideline. Two radiotherapy plans were generated for each subject using standard tangential IMRT technique at a dose of 50 Gy in 25 fractions, one treating contralateral breast alone, the other treating contralateral breast and contralateral axilla level 1–4. The ARM node was considered “within the radiotherapy field” if the mean dose received by the ARM node was more than 50% of the prescribed dose: i.e., 25 Gy. Results One right-sided subject had 2 ARM nodes, all others had 1 ARM node. All ARM nodes (left 10, right 9) were located within level 1 of the axilla. For the subject with 2 ARM nodes, the node that received a higher dose was used for the analysis. The mean dose received by the ARM node in the whole breast radiotherapy plans ranged from 0.8 to 45.5 Gy, with a median of 10.9 Gy. The mean dose received by the ARM node in the whole breast and axilla plans ranged from 43.4 to 52.5 Gy, with a median of 49.3 Gy. In the whole breast radiotherapy plans, only 5 out of 18 ARM nodes were found to be “within radiotherapy field”, and only 2 ARM nodes received more than 40 Gy. In the breast and axilla plans, all 18 ARM nodes were “within radiotherapy field” and all received more than 40 Gy. To better visualise the locations of ARM nodes, all left sided ARM nodes were then mapped onto a CT set from one of the left-sided subjects, and all the right sided ARM nodes mapped onto one of the right-sided subjects, and digitally reconstructed radiograph (DRR) for radiotherapy fields were produced. Conclusions Our study demonstrates that the vast majority of ARM nodes (72%) are outside the tangential whole breast radiotherapy fields. In our study, all the ARM nodes were within the axillary radiotherapy fields covering level 1–4 axillary volumes according to the ESTRO contouring guideline, and complete shielding of the humeral head according to the EORTC consensus did not lead to sparing of the ARM nodes. A prospective study is needed to examine the oncological safety of ARM node-sparing axillary radiotherapy and its potential to reduce the risk of arm lymphoedema.

The Chi index described in the article 'A revision of the γ-evaluation concept for the comparison of dose distributions' by Bakai et al (Phys. Med. Biol. 2003 48 3543-53) indicates that smooth acceptance tubes, defining upper and lower limits of dose difference and distance to agreement, can be pre-defined for a given dose distribution based on the local dose gradient. Mathematical analysis and simulations indicate that the Chi index as described by Bakai et al does not produce smooth acceptance criteria in rapidly varying dose gradients. Instead, 'horns' are generated in the acceptance tubes which lead to the production of unacceptably large acceptance criteria and the possibility of false negatives.