The aim of this study is to improve the characterization and modeling of the radiation field surrounding the Leksell Gamma Knife®-Perfexion^TM. The improved characterization of the radiation field enables more accurate shielding calculations to be performed for the areas adjacent to the treatment room. With the aid of a high-purity germanium detector and a satellite dose rate meter, 𝛾-ray spectra and ambient dose equivalent H*(10) data were acquired at various locations in the field of a Leksell Gamma Knife unit in a treatment room at Karolinska University Hospital, Sweden. These measurements were used to validate the results of the PEGASOS Monte Carlo simulation system with a PENELOPE kernel. The levels of the radiation that passes through the shielding of the machine (leakage radiation) are shown to be much lower than what is suggested by various bodies, e.g. the National Council on Radiation Protection and Measurements, to be used when calculating radiation shielding barriers. The results clearly indicate that Monte Carlo simulations may be used in structural shielding design calculations for γ𝛾 rays from the Leksell Gamma Knife.

Most practical guidelines for design of shielding against photon radiotherapy equipment may be retrieved from the National Council on Radiation Protection and Measurements (NCRP) report 151. The NCRP report No. 151 formalism describes structural shielding design techniques for megavoltage x- and gamma-ray radiotherapy facilities with the aim to limit radiation exposures to members of the public, employees, and the environment to an acceptable level. The implemetaion of NCRP report No. 151 recommendations may be straightforward for linear accelerators and conventional Co-60 machines which have singular source of radiation in contrast to the Leksell Gamma Knife, which has a complex multisource configuration. To harness the full potential of the NCRP 151 methodology, complementary transmission measurements may be required. In the NCRP report No. 151 the primary barriers are designed to attenuate photons emanating directly from the treatment unit while secondary barriers are calculated to shield radiation leakage and scattered photons by the patient and objects inside the treatment room. Here it is assumed that a primary radiation barrier should at the same time shield against secondary radiation. In this work the gamma-ray spectra in the vicinity of the Elekta Leksell Gamma Knife-Perfexion were acquired using a High Purity Germanium detector. It has been observed that the proportion of high energetic photons is lower in comparison with photons with low energy. This corroborates with the fact that the Leksell Gamma Knife has been designed in order to prevent any primary radiation from exiting the unit without impinging on an internal interceptor shield during all states of the machine. Therefore, the need to adapt the NCRP methodology for the Gamma Knife appeared to be justified.

Linear accelerator downtimes are common and problematic in many African countries and may jeopardise the outcome of affected radiation treatments. The predicted increase in cancer incidence and prevalence on the African continent will require, inter alia, improved response with regard to a reduction in linear accelerator downtimes. Here we discuss the problems associated with the maintenance and repair of linear accelerators and propose alternative solutions relevant for local conditions in African countries. The paper is based on about four decades of experience in capacity building, installing, commissioning, calibrating, servicing and repairing linear accelerators in Africa, where about 40% of the low and middle income countries in the world are geographically located. Linear accelerators can successfully be operated, maintained and repaired in African countries provided proper maintenance and repair plans are put in place and executed.

Aim: To compare manual graphical optimization (GrO) with hybrid inverse planning optimization (HIPO) of cervical cancer brachytherapy treatment plans using physical and radiobiological tools. Patients and Methods: Ten patients suffering from cervical cancer, treated with pulsed brachytherapy using GrO plans, were included in the study. For each patient, four different HIPO class solutions with different dose objectives to the target and constraints to the organs at risk (OAR) produced four optimized plans, that were each compared to the corresponding GrO plan. Class solution in HIPO is a set of parameters consisting of dose constraints and penalty weights, which are used for optimization. The comparison was based on the following dosimetric parameters: conformity index (COIN), minimum dose received by 98% and 90% of the high-risk clinical target volume (represented by D98 and D90, respectively), and the minimum dose imparted to 2 cm³ (D_2cm³) of the most exposed OAR i.e. bladder, sigmoid colon or rectum. The HIPO class solution which produced plans with overall better dosimetric parameters was selected and its plans were compared with manual GrO plans from a radiobiological viewpoint based on the calculated complication-free tumour control probability, P₊. Results: The average COIN for the GrO and the selected HIPO plans were 0.22 and 0.30, respectively. The median COIN of the GrO and the HIPO plans were not statistically different (p>0.05, Wilcoxon test). The relative percentage difference of the averaged P₊ values between the HIPO and GrO plans evaluated together with the external beam radiation therapy plans was 0.01%, 0.37% and 0.98% for the bladder, sigmoid colon and rectum, respectively. The lowest P₊ value for all the plans was 98.44% for sigmoid colon. Conclusion: HIPO presented comparable results in relation to manual planning with respect to dosimetric and radiobiological parameters.

Carcinoma of the cervix is a global problem. Brachytherapy (BT) is one of the main

radiation therapy components used in the management of cervical cancer. With the

advent of scientific and technological developments in treatment planning, inverse optimization

in BT has been imposed; however, to harness the full potential of inverse

planning in brachytherapy, its thorough comparison with manual optimization methods

is warranted.

Although inverse optimization algorithms are based on different mathematical approaches,

their goals are similar. The underlying principles of these algorithms will

allow them to be applied with the aim of respecting normal structures absorbed dose

limits while delivering high enough tumouricidal dose.

In this work, the physical parameters minimum dose received by 98% and 90% of

the target volume represented by D98 and D90, respectively, were used to evaluate the

treatment plans with respect to the target while the minimum dose received by 2cm3

volume, D2cm3 , was used to investigate complications in organs at risk (OARs). The

conformity index (COIN), was used to describe the coverage of the target by the prescribed

dose (PD) and the fraction of each OAR volume that receives a critical dose,

which may cause complication. The treatment plan evaluation was also performed

in terms of the complication-free tumour control probability, P+. The physical and

radiobiological evaluation corresponding to plans obtained by the inverse planning

simulated annealing algorithm (IPSA) and the hybrid inverse planning optimization

(HIPO) have been compared with corresponding ones for plans obtained using a manual

graphical optimization method.

The main observations of this work are that well tuned class solutions of inverse

optimization methods are able to produce similar dose volume histograms to those

produced with manual graphical optimization and inverse methods have the potential

to spare organs at risk while delivering acceptable dose to the target. In addition, radiobiological

indexes such as the P+ can be useful complements to physical parameters

in treatment plan evaluation.

Aim: To compare five inverse treatment plans with one conventional manually optimized plan for cervical cancer brachytherapy (BT) using radiobiological parameters combined with dosimetric and volumetric parameters.

Materials and Methods: Five inverse treatment plans were calculated using an inverse planning simulated annealing (IPSA) algorithm for each of four fractions for 12 cervical cancer patients treated with high-dose-rate (HDR) brachytherapy. The inverse treatment plans were compared with a manually optimized plan used for the actual treatment of the patients. The comparison of the plans was performed with respect to the probability of cure without complication.

Results: Overall, the manually optimized plan scored the best results; however, the probability of cure without complication is within an acceptable clinical range for all the plans.

Conclusion: Although there are still considerable uncertainties in the radiobiological parameters, the radiobiological plan evaluation method presents itself as a potential complement to physical dosimetric methods.