Curative breast radiotherapy typically leaves patients with varying degrees of cosmetic damage. One problem interfering with cosmetically acceptable breast radiotherapy is the external contour for large pendulous breasts which often results in high doses to skin folds. Thermoplastic casts are often employed to secure the breasts to maintain setup reproducibility and limit the presence of skin folds. This paper aims to determine changes in surface dose that can be attributed to the use of thermoplastic immobilization casts. Skin dose for a clinical hybrid conformal/IMRT breast plan was measured using radiochromic film and MOSFET detectors at a range of water equivalent depths representative of the different skin layers. The radiochromic film was used as an integrating dosimeter, while the MOSFETs were used for real-time dosimetry to isolate the contribution of skin dose from individual IMRT segments. Strips of film were placed at various locations on the breast and the MOSFETs were used to measure skin dose at 16 positions spaced along the film strips for comparison of data. The results showed an increase in skin dose in the presence of the immobilization cast of up to 45.7% and 62.3% of the skin dose without the immobilization cast present as measured with Gafchromic EBT film and MOSFETs, respectively. The increase in skin dose due to the immobilization cast varied with the angle of beam incidence and was greatest when the beam was normally incident on the phantom. The increase in surface dose with the immobilization cast was greater under entrance dose conditions compared to exit dose conditions.

Introduction Inter‐observer variability (IOV) in target volume delineation is a source of error in head and neck radiotherapy. Diffusion‐weighted imaging (DWI) has been shown to be useful in detecting recurrent head and neck cancer. This study aims to determine whether DWI improves target volume delineation and IOV. Methods Four radiation oncologists delineated the gross tumour volume (GTV) for ten head and neck cancer patients. Delineation was performed on CT alone as well as fused image sets which incorporated fluorodeoxyglucose (FDG)‐positron emission tomography (PET) and magnetic resonance imaging (MRI) in the form of CT/PET, CT/PET/T2W and CT/PET/T2W/DWI image sets. Analysis of the variability of contour volumes was completed by comparison to the simultaneous truth and performance level estimation (STAPLE) volumes. The DICE Similarity Coefficient (DSC) and other IOV metrics for each observer's contour were compared to the STAPLE for each patient and image dataset. A DWI usability scoresheet for delineation was completed. Results The CT/PET/T2W/DWI mean GTV volume of 13.37 (10.35–16.39)cm3 was shown to be different to the mean GTV of 10.92 (8.32–13.51)cm3 when using CT alone (P < 0.001). The GTV DSC amongst observers for CT alone was 0.72 (0.65–0.79), CT/PET was 0.73 (0.67–0.80), CT/PET/T2W was 0.71 (0.64–0.77) and CT/PET/T2W/DWI was 0.69 (0.61–0.75). Conclusion Mean GTVs with the addition of DWI had slightly larger volumes compared to standard CT and CT/PET volumes. DWI may add supplemental visual information for GTV delineation while having a small impact on IOV, therefore potentially improving target volume delineation.

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GI toxicity at 6 months or 1 year. There were no reported episodes of rectal bleeding. Four patients (14.8%), 5 patients (17.9%) and 5 patients (21.7%) reported grade 2 GU toxicity at 6 weeks, 6 months and 1 year, respectively. The most common toxicities were nocturia and urinary frequency/urgency. Rectal maximum point dose, D20 and D50 decreased from 40.7Gy, 29.6Gy and 20.8Gy in FASTR to 35.0Gy, 22.2Gy and 11.1Gy in FASTR-2 (p<0.001). Bladder point dose, D20 and D50 decreased from 40.9Gy, 28.1Gy and 21.5Gy in FASTR to 35.7Gy, 15.7Gy and 6.3Gy in FASTR-2 (p<0.001). Conclusion: FASTR-2 was more tolerable than FASTR, with no grade 3 toxicities reported, in keeping with expectations based on our previous FASTR analysis.(2) Advantages to FASTR-2 include image guidance without fiducials and a weekly treatment schedule which is more convenient for some patients. Trade-offs with FASTR-2 include a lower dose to the prostate (but still in keeping with ASTRO guidelines) and elimination of pelvic nodal irradiation (but need for routine pelvic radiotherapy still remains debated). Long-term follow-up is necessary to ensure disease control is comparable to conventional high risk treatment paradigms.

Introduction Magnetic resonance imaging (MRI) demonstrates superior soft tissue contrast and is increasingly being used in radiotherapy planning. This study evaluated the impact of an education workshop in minimising inter‐observer variation (IOV) for nasopharyngeal organs at risk (OAR) delineation on MRI. Methods Ten observers delineated 14 OARs on 4 retrospective nasopharyngeal MRI data sets. Standard contouring guidelines were provided pre‐workshop. Following an education workshop on MRI OAR delineation, observers blinded to their original contours repeated the 14 OAR delineations. For comparison, reference volumes were delineated by two head and neck radiation oncologists. IOV was evaluated using dice similarity coefficient (DSC), Hausdorff distance (HD) and relative volume. Location of largest deviations was evaluated with centroid values. Observer confidence pre‐ and post‐workshop was also recorded using a 6‐point Likert scale. The workshop was deemed beneficial for an OAR if ≥50% of observers mean scores improved in any metric and ≥50% of observers' confidence improved. Results All OARs had ≥50% of observers improve in at least one metric. Base of tongue, larynx, spinal cord and right temporal lobe were the only OARs achieving a mean DSC score of ≥0.7. Base of tongue, left and right lacrimal glands, larynx, left optic nerve and right parotid gland all exhibited statistically significant HD improvements post‐workshop ( P < 0.05). Brainstem and left and right temporal lobes all had statistically significant relative volume improvements post‐workshop ( P < 0.05). Post‐workshop observer confidence improvement was observed for all OARs ( P < 0.001). Conclusions The educational workshop reduced IOV and improved observers' confidence when delineating nasopharyngeal OARs on MRI.

Introduction: To evaluate the feasibility of prostate intrafraction motion monitoring using the SeedTracker real-time image guidance system in order to improve targeting accuracy in prostate radiotherapy. Methods: SeedTracker was used to monitor prostate gold fiducial seeds with kV x-ray imaging during radiotherapy in 30 patients. Feedback from radiation therapists was collected via the use of a user evaluation form. The impact on treatment time was established by using a record and verify system. The effective dose and a risk of exposure-induced cancer death (REID) were estimated for a 60-year-old patient when using the SeedTracker system. Results: A total of 22 radiation therapists completed user evaluation forms. The time taken to prepare a reference data set for one patient varied with three (13.6%) radiation therapists taking less than 2 min, 10 (45.5%) between 2 and 4 min, eight (36.4%) between 4 and 6 min and one (4.5%) between 6 and 8 min. The useability of the SeedTracker system was reported as 'easy' by 21 (95.5%) radiation therapists and 'hard' by 1 (4.5%) radiation therapist. Mean treatment time changed from 6 to 7 min with prostate-only radiotherapy treatment and from 6.9 to 10.2 min with prostate and whole pelvis radiotherapy treatments. The maximum effective dose with the Seed-Tracker was 1.6276 mSv, and increase in REID was 0.007%. Conclusion:The SeedTracker real-time image guidance system is a feasible tool to use in radiotherapy departments to monitor and correct for prostate intrafraction motion.

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