Brachytherapy: Current Status and Future Strategies — Can High Dose Rate Replace Low Dose Rate and External Beam Radiotherapy?

Brachytherapy, results in rapid fall-off in dose and sparing of neighbouring organs, allows for much higher dose excalation as what can be acheiveed by EBRT (which is limited to OAR). Two types, low dose rate (LDR), involving the permanent implantation of radioactive seeds, and high dose rate (HDR). This study reviews the “current status of prostate brachytherapy, describe emerging trends and address the question of whether HDR can replace LDR and EBRT” LDR Started with I-125, and the development of TRUS guidance. Now standard treatment for men with low- and intermediate-risk disease prostate cancers. A multicentre clinical trial from the Radiation Therapy Oncology Group (RTOG 9805) reported a 92% biochemical disease-free survival after 8 years, with no deaths from disease. With good-quality implants, patients with low-risk disease can expect a long-term disease-free survival in excess of 90% after brachytherapy alone. However other studies do show much higher variation of OS and DFS, this maybe due to differing protocols (i.e. differing planning systems and patients treated with or without ADT). Brachy and EBRT is usally combined to give better dose escalation, but this is reported to increase the rate of grade 3 unrinenary toxicities. There is less knowledge about whether brachy monotherapy can be used in intermedicate risk patients, there is much more evidence regarding its use in higher risk patients. >high-grade prostate cancer managed with radiotherapy. Compared with treatment with EBRT alone, the addition of brachytherapy was associated with a 23% reduction in cause-specific mortality HDR Via temporarily implanted catheters via TRUS placement. “Images are then acquired with the catheters in place and transferred to a planning system”. “Anatomy-based inverse planning is used to optimise the dwell time at each position along the catheters to sculpt the resultant dose to achieve target coverage while limiting the dose to organs at risk”. HDR is most commonly used as a method of local dose escalation in combination with EBRT to treat patients with intermediate- and high-risk disease, with >85% DFS for patients with low/inter risk disease. There is now a trend of using fewer fractions, with several series reporting favourable results with the use of a single large HDR dose, esp for prostate which has lower a/b ratio. Morton et al (cited in article) reported no difference in biochemical control or toxicity between an HDR boost dose delivered as either two fractions of 10 Gy each or as a single dose of 15 Gy. Adding HDR to EBRT as a boost results in much higher DFS (Hoskins et al, cited in article). Use of HDR alone = Selected high-risk patients have also been treated with HDR monotherapy, with reported recurrence-free survival of 79–93%. The biggest challenge with HDR monotherapy is to define the optimum dose fractionation schedule. HDR v LDR HDR also has some cost advantages, as unlike LDR, the same radioactive source is used to treat many patients over several months. dose distribution is a more accurate due to the catheters afterloading and MRI/CT planning (thus seed placement each time is more accurate). Target coverage and normal tissue sparing is more consistently achieved with HDR than with LDR. However HDR delivers a large dose of radiation over several minutes, whereas with LDR implants, the radiation dose is delivered over several weeks or months. Prostate cancer seems to be particularly suited to radiation treatment delivered at a large dose per fraction. LDR brachytherapy, almost all patients experience significant obstructive and irritative urinary symptoms that last several months. This article does give good details into rationale regarding LDR/HDR in low or high risk patients. But does not pick a side when comparing HDR v LDR or if protocols locally can be changed to include brachy monothreapy. Morton & Hoskin 2013. Clinical Oncology.