Multi-helix rotating shield brachytherapy (RSBT) applicator and multi-source RSBT apparatus are two novel intensity-modulated brachytherapy techniques for the treatment of cervical and prostate cancer, respectively. The use of imaging techniques such as magnetic resonance imaging guided brachytherapy has enabled the precise identification and contouring of tumor volumes for treatment planning, as well as demonstrated the challenges associated with using conventional high dose rate brachytherapy (HDR-BT) approaches to conform the radiation dose to the target and avoid surrounding sensitive healthy tissues. The target conformity of conventional HDR-BT dose distributions is restricted based on the geometrical constraints imposed by the position and shape of the tube-shaped applicators, as well as the radially-symmetric radiation dose distributions produced by the radiation sources. Dose distribution conformity for cervical and prostate cancer can be significantly improved relative to conventional HDR-BT through the use of multi-helix and multi-source RSBT techniques, respectively. In this study, two novel RSBT concepts for treating cervical and prostate cancer were introduced and the dosimetric impact was evaluated. A Henschke-type cervical cancer applicator, designed for an electronic brachytherapy (eBx) source (Xoft AxxentTM) and a 0.5 mm thick tungsten partial shield with 180° or 45° azimuthal emission angles, is proposed. The interior wall of the applicator contains six evenly-spaced helical keyways that rigidly define the emission direction of the partial radiation shield as a function of depth in the applicator. The shield contains three uniformly-distributed protruding keys on its exterior wall and is attached to the source such that it rotates freely, thus longitudinal translational motion of the source is transferred to rotational motion of the shield. RSBT treatment plans were generated for five cervical cancer patients with a diverse range of high-risk target volume (HR-CTV) shapes and applicator positions. Treatment delivery time and tumor coverage (D90 of HR-CTV) were the two metrics used as the basis for evaluation and comparison. With multi-source RSBT apparatus, precise angular and linear positioning of partially-shielded 153Gd brachytherapy sources in interstitial needles for the treatment of locally-advanced prostate cancer is carried out. Following needle implantation through the patient template, an angular drive mechanism is docked to the patient template. Each needle is coupled to a multisource afterloader catheter by a connector passing through a shaft. The shafts are rotated about their axes by translating a moving template between two stationary templates. Shafts’ surfaces and moving template holes are helically threaded with the same pattern such that translation of the moving template causes simultaneous rotation of the shafts. The catheter angles are simultaneously incremented throughout treatment. For each rotation angle, source depth in each needle is controlled by a multisource afterloader, which is proposed as an array of belt-driven linear actuators, each of which drives a wire that controls catheter depth in a needle. In conclusion, the helical RSBT approach for treating cervical cancer and the multi-catheter RSBT approach for treating prostate cancer, powered with novel radiation sources amenable to shielding, are clinically- and mechanically-feasible techniques that dosimetrically outperform conventional brachytherapy methods while minimizing damage to healthy tissues inside and/or adjacent to the target.

Intensity-modulated brachytherapy techniques, compensator-based intensity modulated brachytherapy (CBT) and interstitial rotating shield brachytherapy (I-RSBT), are two novel conceptual radiation therapies for treating cervical and prostate cancer, respectively. Compared to conventional brachytherapy techniques for treating cervical cancer, CBT can potentially improve the dose conformity to the high-risk clinical target volume (CTV) of the cervix in a less invasive approach. I-RSBT can reduce the dose delivered to the prostate organ at risks (OARs) with the same radiation dose delivered to the prostate CTV. In this work, concepts and prototypes for CBT and I-RSBT were introduced and developed. Preliminary dosimetric measurements were performed for CBT and I-RSBT, respectively. A CBT prototype system was constructed and experimentally validated. A prototype cylindrical compensator with eight octants, each with different thicknesses, was designed. Direct metal laser sintering (DMLS) was used to construct CoCr and Ti compensator prototypes, and a 4-D milling technique was used to construct a Ti compensator prototype. Gafchromic EBT2 films, held by an acrylic quality assurance (QA) phantom, were irradiated to approximately 125 cGy with an electronic brachytherapy (eBT) source for both shielded and unshielded cases. The dose at each point on the films were calculated using a TG-43 calculation model that was modified to account for the presence of a compensator prototype by ray-tracing. With I-RSBT, a multi-pass dose delivery mechanism with prototypes was developed. Dosimetric measurements for a Gd-153 radioisotope was performed to demonstrate that using multiple partially shielded Gd-153 sources for I-RSBT is feasible. A treatment planning model was developed for applying I-RSBT clinically. A custom-built, stainless steel encapsulated 150 mCi Gd-153 capsule with an outer length of 12.8 mm, outer diameter of 2.10 mm, active length of 9.98 mm, and active diameter of 1.53 mm was used. A partially shielded catheter was constructed with a 500 micron platinum shield and a 500 micron aluminum emission window, both with 180° azimuthal coverage. An acrylic phantom was constructed to measure the dose distributions from the shielded catheter in the transverse plane using Gafchromic EBT3 films. Film calibration curves were generated from 50, 70, and 100 kVp x-ray beams with NIST-traceable air kerma values to account for energy variation. In conclusion, CBT, which is a non-invasive alternative to supplementary interstitial brachytherapy, is expected to improve dose conformity to bulky cervical tumors relative to conventional intracavitary brachytherapy. However, at the current stage, it would be time-consuming to construct a patient-specific compensator using DMLS, and the quality assurance of the compensator would be difficult. I-RSBT is a promising approach to reducing radiation dose delivered to prostate OARs. The next step in making Gd-153 based I-RSBT feasible in clinic is developing a Gd-153 source that is small enough such that the source, shield, and catheter all fit within a 16 guage needle, which has a 1.65 mm diameter.