AimAlthough manual adjustment of automatic cone beam computed tomography (CBCT) matching may improve the target coverage in certain points of interest, concerns exist that this may lead to dosimetric uncertainties which would negate the theoretical benefit of this approach. The objective of this study is to evaluate the dosimetric impact of manual adjustments made after automatic bony registration on CBCT in prostate patients.MethodsA total of 50 CBCT datasets of ten high-risk prostate cancer patients were randomly chosen. Each CBCT dataset was registered three times. Method (A): Automatic registration, Method (M1): Manual adjustment carried out by two experienced radiation therapists, Method (M2): Manual adjustment carried out by different radiation therapists with varying levels of experience. The clinical target volume (CTV), planning target volume (PTV), the bladder and the rectum were subsequently contoured on each CBCT dataset by a radiation oncologist blinded to the registration methods. The absolute difference of various dosimetric parameters were then analysed and compared with the original planning doses. A comparison of the three matching methods employed was also carried out.ResultsThere was a statistically significant difference in the magnitude of move taken in the inferior superior direction between M1 and M2 method. There were no significant differences observed in any of the dosimetric parameters examined in relation to the rectum, bladder or CTV. The only significant difference observed was the volume of PTV covered by the prescription isodose (95%) which was statistically significant lower in method A compared with both M1 and M2. There was no difference observed between M1 and M2 methods. The mean duration of the automated registration and subsequent analysis was 64 seconds compared with 91 seconds for automated registrations which included the additional manual adjustment.FindingsCBCT-based manual adjustments of automated bony-based registrations during the image-guided radiotherapy verification of prostate cancer patients can improve PTV coverage without impacting negatively on the doses received by the organs at risk. This strategy is associated with a small increase in overall treatment time.

Background: Ependymoma of the fourth ventricle is a challenging disease. Brain stem tolerance dose usually hinders the delivery of adequate radiation dose to target volumes. Aim: To present the treatment outcome of pediatric ependymoma of the fourth ventricle using combined CyberKnife and volumetric modulated arc therapy (VMAT) and compare it to VMAT plans. Methods: The medical charts of 15 patients were retrospectively reviewed. All patients underwent surgery and received radiotherapy in 2 phases using combined plans of VMAT and CyberKnife boost aiming for a total prescription dose of 59.4 Gy in 33 fractions. These plans were compared to a cone-down two-phase VMAT plans. At least 95% of the target volume was required to be encompassed by the 95% isodose level of prescription dose. Results: It was not feasible to achieve adequate target coverage using VMAT without exceeding the brain stem tolerance doses in all but one case. Brain stem maximum point dose, V59 Gy, V55.8 Gy and mean doses were 60.46 ± 0.3 Gy, 1.62 ± 0.42 cc, 37.49 ± 5.78% and 54.79 ± 0.64 Gy in VMAT plans compared to 59.67 ± 0.21 Gy, 0.55 ± 0.22 cc, 25.49 ± 3.84% and 52.86 ± 0.88 Gy in combined technique plans (p = 0.002, 0.001, 0.001 and 0.001; respectively). The estimated 5-year progression-free and overall survival rates were 53.3% and 63.6%. Performance status and extent of surgery significantly influenced overall survival. None of the patients had serious toxicities. Conclusion: On the contrary to VMAT cone-down plans, it was possible to achieve adequate target coverage without violating brain stem constraints using the combination of VMAT and CyberKnife techniques in pediatric ependymoma of the fourth ventricle. The treatment protocol was well tolerated with no reported serious radiation toxicities.

AimEvolving data are showing the need of considering smaller planning target volume (PTV) margin in paediatrics compared with adults treated for the same body site. This study proposed to evaluate the current patterns of practice regarding the PTV margin in paediatric patients compared with adult patients through an international survey.Materials and methodsA four-item questionnaire was created to address the PTV margins for paediatrics and adults as part of a comprehensive survey. International Paediatric Radiation Oncology Society (PROS) members were selected to partake and were contacted via email.ResultsIn total, 43 responded to the survey. The majority of the responders have written guidelines for PTV margin while the majority of those who have guidelines do not have separate guidelines for paediatrics. The implemented PTV margin for paediatric patients was in the majority 3–5 mm for the head region and 5–10 mm for the torso region and the difference from the PTV margin implemented in adults was not statistically significant.ConclusionThe majority of responders employ a series of site-specific PTV margin protocols that are applied to both adults and paediatrics, and do not take into consideration patient age or size. These results highlight the need of a separate policy for PTV margin in adults and paediatrics in every institution.

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