Elizabeth Watt

Evaluation of target and cardiac position during visually monitored deep inspiration breath-hold for breast radiotherapy

A low-resource visually monitored deep inspiration breath-hold (VM-DIBH) technique was successfully implemented in our clinic to reduce cardiac dose in left-sided breast radiotherapy. In this study, we retrospectively characterized the chest wall and heart positioning accuracy of VM-DIBH using cine portal images from 42 patients. Central chest wall position from field edge and in-field maximum heart distance (MHD) were manually measured on cine images and compared to the planned positions based on the digitally reconstructed radiographs (DRRs). An in-house program was designed to measure left anterior descending artery (LAD) and chest wall separation on the planning DIBH CT scan with respect to breath-hold level (BHL) during simulation to determine a minimum BHL for VM-DIBH eligibility. Systematic and random setup uncertainties of 3.0 mm and 2.6 mm, respectively, were found for VM-DIBH treatment from the chest wall measurements. Intrabeam breath-hold stability was found to be good, with over 96% of delivered fields within 3 mm. Average treatment MHD was significantly larger for those patients where some of the heart was planned in the field compared to patients whose heart was completely shielded in the plan (p < 0.001). No evidence for a minimum BHL was found, suggesting that all patients who can tolerate DIBH may yield a benefit from it. PACS number(s): 87.53.Jw, 87.53.Kn, 87.55.D.A low‐resource visually monitored deep inspiration breath‐hold (VM‐DIBH) technique was successfully implemented in our clinic to reduce cardiac dose in left‐sided breast radiotherapy. In this study, we retrospectively characterized the chest wall and heart positioning accuracy of VM‐DIBH using cine portal images from 42 patients. Central chest wall position from field edge and in‐field maximum heart distance (MHD) were manually measured on cine images and compared to the planned positions based on the digitally reconstructed radiographs (DRRs). An in‐house program was designed to measure left anterior descending artery (LAD) and chest wall separation on the planning DIBH CT scan with respect to breath‐hold level (BHL) during simulation to determine a minimum BHL for VM‐DIBH eligibility. Systematic and random setup uncertainties of 3.0 mm and 2.6 mm, respectively, were found for VM‐DIBH treatment from the chest wall measurements. Intrabeam breath‐hold stability was found to be good, with over 96% of delivered fields within 3 mm. Average treatment MHD was significantly larger for those patients where some of the heart was planned in the field compared to patients whose heart was completely shielded in the plan (p < 0.001). No evidence for a minimum BHL was found, suggesting that all patients who can tolerate DIBH may yield a benefit from it. PACS number(s): 87.53.Jw, 87.53.Kn, 87.55.D‐

Dosimetric variations in permanent breast seed implant due to patient arm position.

PURPOSE Planning and delivery for permanent breast seed implant (PBSI) are performed with the ipsilateral arm raised; however, changes in implant geometry can be expected because of healing and anatomical motion as the patient resumes her daily activities. The purpose of this study is to quantify the effect of ipsilateral arm position on postplan dosimetry. METHODS AND MATERIALS Twelve patients treated at the Tom Baker Cancer Centre were included in this study. Patients underwent two postimplant CT scans on the day of implant (Day 0) and two scans approximately 8 weeks later (Day 60). One scan at each time was taken with the ipsilateral arm raised, recreating the planning scan position, and the other with both arms down in a relaxed position beside the body, recreating a more realistic postimplant arm position. Postplans were completed on all four scans using deformable image registration (MIM Maestro). RESULTS On the Day 0 scan, the V200 for the evaluation planning target volume was significantly increased in the arm-down position compared with the arm-up position. Lung, rib, and chest wall dose were significantly reduced at both time points. Left anterior descending coronary artery, heart, and skin dose showed no significant differences at either time point. CONCLUSIONS Although some dosimetric indices show significant differences between the arm-up and arm-down positions, the magnitude of these differences is small and the values remain indicative of implant quality. Despite the delivery of the majority of dose with the arm down, it is reasonable to use CT scans taken in the arm-up position for postplanning.

Is there a ‘Leaky Pipeline’ for Women in Clinical Medical Physics in Canada?

We examined the role of women in academic medical physics departments in Canada through various stages of a representative career path.

Technical Note: Empirical altitude correction factors for well chamber measurements of permanent prostate and breast seed implant sources

Purpose: Previous studies in the literature have measured an altitude effect for low‐energy brachytherapy seeds; a correction factor applied in addition to PTP to account for the breakdown of Bragg–Gray cavity theory at low energies in well‐type ionization chambers. In clinical practice, many centers use altitude correction factors that are not seed‐model‐specific. The purpose of this work is to present altitude correction factors for several seed models without documented factors in the literature. Methods: An in‐house constructed pressure vessel was used with a well‐type ionization chamber to measure the air‐kerma strength of the IsoAid Advantage (Pd‐103), Theragenics AgX100 (I‐125), and Nucletron selectSeed (I‐125) at a pressure range representative of those encountered worldwide. The TheraSeed 200 (Pd‐103) was also measured for comparison to the originally published correction factor for validation of the experimental process. When correction factors derived in this work were within experimental uncertainties of those published, no new correction factors were proposed. Results: The three seed models measured herein all demonstrated a similar response to change in pressure as previously documented in the literature with the HDR 1000 Plus well‐type ionization chamber. Correction factors of the functional form Symbol, consistent with those previously published, were found to be appropriate for these seed models. A new correction factor is proposed for the Theragenics AgX100 and Nucletron selectSeed (k1 = 0.0417, k2 = 0.479). The IsoAid Advantage, however, agreed to within uncertainty with the published altitude correction factor for the TheraSeed 200; thus the application of the same correction factor is appropriate (k1 = 0.0241, k2 = 0.562). Symbol. No Caption available. Conclusions: This work presents altitude correction factors for three permanent implant brachytherapy seed models in clinical use. This will allow clinics to utilize model‐specific factors, reducing systematic errors in their air‐kerma strength verifications.

114: Patient Positioning and Mark-Up Optimization for Permanent Breast Seed Implant (PBSI)

S43 _________________________________________________________________________________________________________ in Ontario (ONT) and to develop recommendations to ensure all patients to have equitable access to MR-guided brachytherapy (MRgBT) for cervical cancer. Methods: A qualitative phone interview was designed by the GYN CoP working group to survey the current state of ccBT in the province. Questions were developed to inquire about the current use of image-guided ccBT and the associated referral processes, the usage of MR imaging in ccBT and the current use of imageguided interstitial GYN BT. All ONT cancer centres offering radiation treatments to GYN cancers were included. Two group members conducted and audio recorded the telephone interviews from May to November 2015 and analyzed all recordings and summarized the data. Results: Thirteen (n = 13) ONT cancer centres were interviewed. Of these, three centres do not offer ccBT, five centres offer CTguided ccBT, four centres offer a combination of CT-MR-guided ccBT and one centre offers strictly MR-guided ccBT. The three centres that do not offer ccBT have established referral processes with three tertiary cancer centres in ONT respectively. However, there is no standardized referral process, referral timing, or method of communication. Other practices vary throughout the centres. Three of 13 centres suggested developing a file portal to standardize and facilitate the sharing of external beam and BT plans, distributions and images. All CTguided ccBT centres except one have plans to develop MRgBT. The tertiary centres mentioned above are also the only centres that offer interstitial GYN BT. They are located in the southwestern part of the province. Of these, one centre offers CT-guided and two centres offer MR-guided interstitial GYN BT. There is currently no standardized guideline to identify patient candidates for interstitial GYN BT. Conclusions: This study demonstrated that models of shared care exist and are functioning in ONT. While referral processes are functioning well, some areas represent opportunities for improvement. Future work is needed by the GYN CoP to improve referral processes and to develop consensus on indications for interstitial brachytherapy. This will ensure all patients in ONT have access to this high quality brachytherapy.

Sci—Fri PM: Topics — 02: Evaluation of Dosimetric Variations in Partial Breast Seed Implant (PBSI) due to Patient Arm Position (Up vs. Down)

The planning for PBSI is done with the patients ipsilateral arm raised, however, anatomical changes and variations are unavoidable as the patient resumes her daily activities, potentially resulting in significant deviations in implant geometry from the treatment plan. This study aims to quantify the impact of the ipsilateral arm position on the geometry and dosimetry of the implant at eight weeks, evaluated on post-plans using the MIM Symphony™ software (MIM Software, Cleveland, OH). The average dose metrics for the three patients treated at the TBCC thus far using rigid fusion and contour transfer for the arms up position were 76% for the CTV V100, 61% for the PTV V100, and 37% for the PTV V200; and for the arms down position 81% for the CTV V100, 64% for the PTV V100, and 42% for the PTV V200. Qualitative analysis of the post-implant CT for one of the three patients showed poor agreement between the seroma contour transferred from the pre-implant CT and the seroma visible on the post-implant CT. To obtain a clinically accurate plan for that patient, contour modifications were used, yielding improved dose metric averages for the arms-up position for all three patients of 87% for the CTV V100, 68% for the PTV V100, and 39% for the PTV V200. Overall, the data available shows that dosimetric parameters increase with the patients arm down, both in terms of coverage and in terms of the hot spot, and accrual of more patients may confirm this in a larger population.