D D'Souza

Targeted intra-operative radiotherapy (Targit): An innovative method of treatment for early breast cancer

INTRODUCTION We believe that conservative treatment of early breast cancer may not require radiotherapy that encompasses the whole breast. We present here the clinico-pathological basis for this view, as well as a novel therapeutic approach that allows intra-operative radiotherapy to be safely and accurately delivered to the target tissues in a standard operating theatre. THE RATIONALE: Whole-organ analysis of mastectomy specimens reveals that 80% of occult cancer foci are situated remote from the index quadrant. In contrast, over 90% of local recurrences after breast conservative therapy occur near the original tumour, even when radiotherapy is not given. Therefore, the remote occult cancer foci may be clinically irrelevant and radiotherapy to the index quadrant alone might be sufficient. A NOVEL TECHNIQUE: The Photon Radiosurgery System (PRS) is an ingenious portable electron-beam driven device that can typically deliver intra-operative doses of 5-20 Gy, respectively, to 1 cm and 0.2 cm from the tumour bed over about 22 min. The pliable breast tissue--the target--wraps around the source, providing perfect conformal radiotherapy. Being soft X-rays, the dose attenuates rapidly (alpha approximately 1/r3), reducing distant damage. RESULTS In our pilot study of 25 patients (age 30-80 years, T = 0.42-4.0 cm), we replaced the routine post-operative tumour bed boost with targeted intra-operative radiotherapy. There have been no major complications and no patient has developed local recurrence, although the median follow-up time is short, at 24 months. CONCLUSION It is safe and feasible to deliver targeted intraoperative radiotherapy (Targit) for early breast cancer. We have begun a randomised trial--the first of its kind--comparing Targit with conventional six-week course of radiotherapy. If proven equivalent in terms of local recurrence and cosmesis, it could eliminate the need for the usual six-week course of post-operative radiotherapy.

Percutaneous minimally invasive stereotactic primary radiotherapy for breast cancer

A 73-year old lady, admitted to our breast clinic, was found to have a lump in the left breast. She had recently been diagnosed with motor neurone disease and pseudobulbar palsy with a generally poor prognosis. Physical examination, mammography, and fine-needle-aspiration cytology (triple assessment) showed a 2·5 cm infiltrating duct-carcinoma. Since she was too frail for conventional surgery, the usual option would have been to treat her with tamoxifen. However, there is some evidence that local treatment is effective, in combination with tamoxifen, because it reduces breast cancer morbidity and deaths (risk reduction=0·62, 95% CI 0·41‐0·94) and may improve survival. 1

A comparison of the dose distributions from three proton treatment planning systems in the planning of meningioma patients with single-field uniform dose pencil beam scanning.

With the number of new proton centers increasing rapidly, there is a need for an assessment of the available proton treatment planning systems (TPSs). This study compares the dose distributions of complex meningioma plans produced by three proton TPSs: Eclipse, Pinnacle3, and XiO. All three systems were commissioned with the same beam data and, as best as possible, matched configuration settings. Proton treatment plans for ten patients were produced on each system with a pencil beam scanning, single‐field uniform dose approach, using a fixed horizontal beamline. All 30 plans were subjected to identical dose constraints, both for the target coverage and organ at risk (OAR) sparing, with a consistent order of priority. Beam geometry, lateral field margins, and lateral spot resolutions were made consistent across all systems. Few statistically significant differences were found between the target coverage and OAR sparing of each system, with all optimizers managing to produce plans within clinical tolerances (D2<107% of prescribed dose, D5<105%, D95>95%, D99>90%, and OAR maximum doses) despite strict constraints and overlapping structures. PACS number: 87.55.D‐With the number of new proton centers increasing rapidly, there is a need for an assessment of the available proton treatment planning systems (TPSs). This study compares the dose distributions of complex meningioma plans produced by three proton TPSs: Eclipse, Pinnacle3 , and XiO. All three systems were commissioned with the same beam data and, as best as possible, matched configuration settings. Proton treatment plans for ten patients were produced on each system with a pencil beam scanning, single-field uniform dose approach, using a fixed horizontal beamline. All 30 plans were subjected to identical dose constraints, both for the target coverage and organ at risk (OAR) sparing, with a consistent order of priority. Beam geometry, lateral field margins, and lateral spot resolutions were made consistent across all systems. Few statistically significant differences were found between the target coverage and OAR sparing of each system, with all optimizers managing to produce plans within clinical tolerances (D2<107% of prescribed dose, D5<105%, D95>95%, D99>90%, and OAR maximum doses) despite strict constraints and overlapping structures. PACS number: 87.55.D.

MO‐D‐AUD B‐09: The Role of the Radiotherapy Physicist in Intraoperative Partial Breast Irradiation Using a Low Energy X‐Ray Source, Based On 10 Years Clinical Experience

Purpose: To describe the role of the radiotherapyphysicist in the clinical implementation of the Intrabeam™ system for intraoperative radiotherapy (Carl Zeiss, Germany), based on 10 years experience at University College London Hospital. Method and Materials: On delivery of the 50kVp electronic X‐Ray system, the Radiotherapy Physics Group undertook acceptance and commissioning. Half‐value layer measurements were made using a PTW 23342 0.02cc ion chamber. A dedicated water phantom was employed to measure variation of dose rate with radial distance from the X‐Ray source in 5 orthogonal directions and in one direction for each of 8 spherical applicators. These measurements were compared with the manufacturer supplied QA peripherals and with radiochromic film to assess radial isotropy and output constancy and stability. A radiation protection survey and risk assessment was performed for unshielded operating rooms (OR) prior to clinical introduction. The routine physics requirement comprises: pre‐treatment QA and calculation of applicator treatment times; in the OR: actively delivering and monitoring the radiation treatment, monitoring and enforcement of staff radiation protection in and around the OR and measurement of patient skindose by TLD.Results: UCLH physicists have commissioned 4 such X‐Ray sources for clinical use. We have treated 134 patients over a period of 10 years. To date, dose rate surveys during treatment have demonstrated the safe usage of the system under controlled conditions and no member of staff has had a recordable radiationdose.Conclusion: The Intrabeam™ device has been shown to be very stable dosimetrically and also practical within a standard clinical environment. The involvement of the radiotherapyphysicist in the commissioning and clinical implementation of this intraoperative radiotherapy system is imperative to ensure safe treatment delivery and radiation protection of staff and patients.

Cerenkov optical emissions in particle radiotherapy

We present simulations and measurements of Cerenkov optical radiation in electron and proton radiotherapy. Photographs of Cerenkov emission from electrons can predict the range to ±1.5mm, but underestimate superficial dose.