Electronic intracavitary brachytherapy quality management based on risk analysis: The report of AAPM TG 182.

PURPOSE: The purpose of this study was to provide guidance on quality management for electronic brachytherapy. MATERIALS AND METHODS: The task group used the risk-assessment approach of Task Group 100 of the American Association of Physicists in Medicine. Because the quality management program for a device is intimately tied to the procedure in which it is used, the task group first designed quality interventions for intracavitary brachytherapy for both commercial electronic brachytherapy units in the setting of accelerated partial-breast irradiation. To demonstrate the methodology to extend an existing risk analysis for a different application, the task group modified the analysis for the case of post-hysterectomy, vaginal cuff irradiation for one of the devices. RESULTS: The analysis illustrated how the TG-100 methodology can lead to interventions to reduce risks and improve quality for each unit and procedure addressed. CONCLUSION: This report provides a model to guide facilities establishing a quality management program for electronic brachytherapy.

Understanding the impact of pelvic organ motion on dose delivered to target volumes during IMRT for cervical cancer.

BACKGROUND: Advanced radiotherapy techniques reduce normal tissue dose by conforming closely to target volumes. In cervical cancer radiotherapy, organ filling affects clinical target volume (CTV; cervix, uterus) position. This study estimates the dosimetric effect of this primary CTV position variation during chemoradiation. METHODS/MATERIALS: Twice weekly cone-beam computed tomography (CBCT) images of ten patients undergoing cervical chemoradiation were retrospectively analysed. Primary CTV, bladder and rectum were delineated. RapidArc plans were created using 10-15mm CTV-PTV margins and dose delivered to CTV based on each CBCT position was calculated using a novel vector approach. Dose delivered along the central uterine, mid-uterus and cervix vectors were analysed as well as dose delivered to points at uterine tip, anterior mid-uterus and anterior cervix. Additional RapidArc plans were created for large planning bladder volume cases using the CTV acquired with bladder volume at 150-300cc. RESULTS: 105 scans for 10 patients were analysed. Vector analysis revealed CTV underdosing in certain cases. Below 95% average vector coverage was found for all three vectors in 2 cases and one vector in 1 case. Volumetric analysis revealed D99<95% in 48% of fractions. Patients with large planning bladder volumes (>300cc) demonstrated the largest variation. Replanning improved this coverage. The anterior mid-uterus point was least well-covered; median 98.7% dose, reducing to 91.4% in cases with large planning bladder volumes. Again, replanning significantly improved this. D99>95% was maintained in 93% of fractions when bladder volume was 50cc below to 150cc above planning volume compared to 24% of fractions if bladder volume was outside this range. Similarly, D95>95% was 100% versus 84%. CONCLUSION: Organ position variation detrimentally affected dose delivered to CTV including cervix. Large planning bladder volumes (>300cc) led to more variation. We recommend bladder volumes of 150-300cc at planning and a range of 50cc below to 150cc above planning for treatment.

The dosimetric impact of target volume delineation variation for cervical cancer radiotherapy.

BACKGROUND: Cervical cancer inter-observer delineation variation has been demonstrated. This article addresses its dosimetric impact. METHODS: 21 centres outlined two INTERLACE trial quality assurance test cases. A gold standard clinical target volume (GSCTV) was created from a consensus and STAPLE outline. RapidArc plans were created for all centres' planning target volumes (PTVs; PTV1+2). Gold standard PTVs (GSPTVs) were created for each plan by applying each centre's CTV-PTV margins to GSCTV. DVH parameters including D95% and Dmean for each PTV1+2 and GSPTV were compared, representing planned versus GSPTV delivered dose. PTV1+2 and GSPTV V95% was also calculated. RESULTS: Reviewing all parameters, no plans achieved acceptable GSPTV coverage. GSPTV V95%⩾95% was not achieved for any plan. GSPTV V95%<90% in 15/21 (case 1) and 14/22 (case 2) and <80% in 2 plans from both cases. GSPTV V95% is on average 10-15% lower than planned and GSPTV D95% is 10-20% lower than planned. Most common GSCTV anatomical areas not receiving 95% dose were vagina, obturator and external iliac nodes and, in case 1, the superior nodal aspect. CONCLUSION: Cervical cancer CTV delineation variation leads to significant reductions in dose delivered to GSPTV. This highlights the ongoing importance of standardising delineation in the IMRT era.

Intensity-modulated arc therapy to improve radiation dose delivery in the treatment of abdominal neuroblastoma.

The standard European radiotherapy technique for children with neuroblastoma is a conventional parallel opposed pair. This frequently results in compromise on planning target volume coverage to stay within normal tissue tolerances. This study investigates the use of an intensity-modulated arc therapy (IMAT) technique to improve dose distribution and allow better protocol compliance. Among 20 previously treated patients, ten had received the full prescribed dose with conventional planning (protocol compliant) and ten had a compromise on planning target volume coverage (protocol noncompliant). All patients were replanned with IMAT. Dosimetric parameters of the conventional radiotherapy and IMAT were compared. The dose received by 98% of the planning target volume, homogeneity and conformity indices were all improved with IMAT (p < 0.001). IMAT would have enabled delivery of the full protocol dose in eight out of ten protocol-noncompliant patients. IMAT may improve outcomes through improved protocol compliance and better dose distributions.