A study of the clinical, treatment planning and dosimetric feasibility of dose painting in external beam radiotherapy of prostate cancer

Abstract

Background and purpose: Radiotherapy dose painting is a promising technique which enables dose escalation to areas of higher tumour cell density within the prostate which are associated with radioresistance, known as dominant intraprostatic lesions (DILs). The aim of this study was to determine factors affecting the feasibility of radiotherapy dose painting in patients with high and intermediate risk prostate cancer. Materials & Methods: Twenty patients were recruited into the study for imaging using a 3 T magnetic resonance imaging (MRI) scanner. Identified DILs were outlined and the scan registered with the planning computed tomography (CT) dataset. Intensity-modulated plans were produced and evaluated to determine the effect of the organ-at-risk constraints on the dose that could be delivered to the DILs. Measurements were made to verify that the distribution could be safely delivered. Results: MRI scans were obtained for nineteen patients. Fourteen patients had one to two DILs with ten overlapping the urethra and/or rectum. The target boost of 86 Gy was achieved in seven plans but was limited to 80 Gy for five patients whose boost volume overlapped or abutted the urethra. Dosimetric measurements gave a satisfactory gamma pass rate at 3%/3 mm. Conclusions: It was feasible to produce dose-painted plans for a boost of 86 Gy for approximately half the patients with DILs. The main limiting factor was the proximity of the urethra to the boost volumes. For a small proportion of patients, rigid registration between CT and MRI images was not adequate for planning purposes.

Focal Boost in Prostate Cancer Radiotherapy: A Review of Planning Studies and Clinical Trials

“…One of the leading reasons for the focal boost approach not being feasible was in instances of overlap between the boost volume and OARs. In the research undertaken by Blake et al [60], the boost volume of 83% of patients overlapped with surrounding OARs. In 42% of patients, the intended boost dose of 86 Gy was limited due to the overlap between the boost volume and the urethra.…”

“…The longest reported follow-up time was 124 months [49]. In the planning studies, as shown in Table 2, the majority of studies utilized mpMRI for GTV delineation [10,18,45,[57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75]. Five studies utilized PET-CT [12,[76][77][78][79][80], and four studies used "other methods" such as histopathology data or hypothetical IPLs [81][82][83][84].…”

Towards optimal heterogeneous prostate radiotherapy dose prescriptions based on patient‐specific or population‐based biological features

“…The dose redistribution can also be achieved by dose escalation to the detected IPLs. Boosting IPLs without violating the dose constrains of OARs has been shown to be feasible, [59][60][61] and an increased tumor control relative to uniform dose prescription has been reported. 38 However, the undetected lesions or the uncertainty in delineating IPLs from MRI or PET images 62 may lead to underdosing of sub-volumes of the prostate.…”

Patient‐specific voxel‐level dose prescription for prostate cancer radiotherapy considering tumor cell density and grade distribution

“…Ling et al 1 introduced the concept of a biological target volume (BTV) and proposed the idea of delivering radiation dose distributions based on functional sub-volumes within a target. This has led to multiple studies introducing the concept of a "boost volume" in prostate cancer (PCa) radiotherapy, [2][3][4][5][6][7] whereby a sub-region within the prostate gland is defined to receive an escalated dose of radiation whilst preserving standard doses to the remaining target to minimize risk of increased toxicity. In current standard boost-dose strategies,there is no deliberate attempt to vary the dose distribution through the boost volume, however, in practice, a non-uniform distribution arises as a result of dose gradients generated in an attempt to maintain dose to organs at risk below threshold levels.…”