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Proposal of a post-prostatectomy clinical target volume based on pre-operative MRI: volumetric and dosimetric comparison to the RTOG guidelines.

Croke J, Maclean J, Nyiri B, Li Y, Malone K, Avruch L, Kayser C, Malone S - Radiat Oncol (2014)

Bottom Line: Previous work from our institution demonstrated that published prostate bed CTV guidelines frequently do not cover the pre-operative MRI defined prostate.CTV MRI spares more of the lower anterior bladder wall than CTV RTOG but increases coverage of the superior lateral bladder walls.CTV contours based upon the patient's co-registered pre-operative MRI in the post-prostatectomy setting may improve coverage of the individual's prostate bed without substantially increasing the PTV size or dose to bladder/ rectum compared to RTOG CTV guidelines.

View Article: PubMed Central - PubMed

Affiliation: The Ottawa Hospital Cancer Centre, K1H 8 L6, Ottawa, Ontario, Canada. jcroke@toh.on.ca.

ABSTRACT

Background: Recurrence rates following radiotherapy for prostate cancer in the post-operative adjuvant or salvage setting remain substantial. Previous work from our institution demonstrated that published prostate bed CTV guidelines frequently do not cover the pre-operative MRI defined prostate. Inadequate target delineation may contribute to the high recurrence rates, but increasing target volumes may increase dose to organs at risk.

Methods: We propose guidelines for delineating post-prostatectomy target volumes based upon an individual's co-registered pre-operative MRI. MRI-based CTVs and PTVs were compared to those created using the RTOG guidelines in 30 patients. Contours were analysed in terms of absolute volume, intersection volume (Jaccard Index) and the ability to meet the RADICALS and QUANTEC rectal and bladder constraints (tomotherapy IMRT plans with PTV coverage of V98% ≥98%).

Results: CTV MRI was a mean of 18.6% larger than CTV RTOG: CTV MRI mean 138 cc (range 72.3 - 222.2 cc), CTV RTOG mean 116.3 cc (range 62.1 - 176.6 cc), (p < 0.0001). The difference in mean PTV was only 4.6%: PTV MRI mean 386.9 cc (range 254.4 - 551.2), PTV RTOG mean 370 cc (range 232.3 - 501.6) (p = 0.05). The mean Jaccard Index representing intersection volume between CTVs was 0.72 and 0.84 for PTVs. Both criteria had a similar ability to meet rectal and bladder constraints. Rectal DVH: 77% of CTV RTOG cases passed all RADICALS criteria and 37% all QUANTEC criteria; versus 73% and 40% for CTV MRI (p = 1.0 for both). Bladder DVH; 47% of CTV RTOG cases passed all RADICALS criteria and 67% all QUANTEC criteria, versus 57% and 60% for CTV MRI (p = 0.61for RADICALS, p = 0.79 for QUANTEC). CTV MRI spares more of the lower anterior bladder wall than CTV RTOG but increases coverage of the superior lateral bladder walls.

Conclusion: CTV contours based upon the patient's co-registered pre-operative MRI in the post-prostatectomy setting may improve coverage of the individual's prostate bed without substantially increasing the PTV size or dose to bladder/ rectum compared to RTOG CTV guidelines. Further evaluation of whether the use of pre-operative MRI improves local control rates is warranted.

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Related in: MedlinePlus

Typical case depicting the differences in shape and coverage between CTV RTOG and CTV MRI. Key - Purple: pre-op prostate, Blue: pre-op visible tumour, Red: CTV RTOG, Green: CTV MRI, Yellow: bladder. (a) pre-operative T2 MRI (b) planning CT scan (post-operative); the bladder neck has been pulled down. (c) CTV RTOG does not completely cover the region of the pre-operative prostate/ tumour. Although the bladder will now largely fill the location of the original prostate, the lateral soft tissue lateral remains at risk of microscopic disease. (d) CTV MRI extends 5 mm around the original prostate to cover the soft tissue that was adjacent to the prostate (e) Inferiorly the CTV RTOG treats more of the anterior bladder wall than CTV MRI where coverage may not be required in view of the original prostate location. (f) Superiorly the CTV MRI increases dose to the lateral bladder walls because it covers the soft tissue beside the bladder that remains at risk of microscopic disease in view of the original prostate/tumour location. CTV RTOG misses these areas.
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Fig2: Typical case depicting the differences in shape and coverage between CTV RTOG and CTV MRI. Key - Purple: pre-op prostate, Blue: pre-op visible tumour, Red: CTV RTOG, Green: CTV MRI, Yellow: bladder. (a) pre-operative T2 MRI (b) planning CT scan (post-operative); the bladder neck has been pulled down. (c) CTV RTOG does not completely cover the region of the pre-operative prostate/ tumour. Although the bladder will now largely fill the location of the original prostate, the lateral soft tissue lateral remains at risk of microscopic disease. (d) CTV MRI extends 5 mm around the original prostate to cover the soft tissue that was adjacent to the prostate (e) Inferiorly the CTV RTOG treats more of the anterior bladder wall than CTV MRI where coverage may not be required in view of the original prostate location. (f) Superiorly the CTV MRI increases dose to the lateral bladder walls because it covers the soft tissue beside the bladder that remains at risk of microscopic disease in view of the original prostate/tumour location. CTV RTOG misses these areas.

Mentions: The CTV MRI was a mean of 18.6% larger than CTV RTOG (larger in 26 cases): CTV MRI mean 138 cc (range 72.3 - 222.2 cc), CTV RTOG mean 116.3 cc (range 62.1 - 176.6 cc), (p < 0.0001). The addition of the isotropic PTV margins reduced this difference to only 4.6% (PTV MRI larger in 21 cases); PTV MRI mean 386.9 cc (range 254.4 – 551.2), PTV RTOG mean 370 cc (range 232.3 - 501.6), (p = 0.05). The mean Jaccard Index was 0.72 for CTV (standard deviation 0.09) and 0.84 for PTV (SD 0.06). Graphical depiction of absolute and overlap volumes is shown in Figure 1. Figure 2 shows a typical example of differences in the volumes for one case.Figure 1


Proposal of a post-prostatectomy clinical target volume based on pre-operative MRI: volumetric and dosimetric comparison to the RTOG guidelines.

Croke J, Maclean J, Nyiri B, Li Y, Malone K, Avruch L, Kayser C, Malone S - Radiat Oncol (2014)

Typical case depicting the differences in shape and coverage between CTV RTOG and CTV MRI. Key - Purple: pre-op prostate, Blue: pre-op visible tumour, Red: CTV RTOG, Green: CTV MRI, Yellow: bladder. (a) pre-operative T2 MRI (b) planning CT scan (post-operative); the bladder neck has been pulled down. (c) CTV RTOG does not completely cover the region of the pre-operative prostate/ tumour. Although the bladder will now largely fill the location of the original prostate, the lateral soft tissue lateral remains at risk of microscopic disease. (d) CTV MRI extends 5 mm around the original prostate to cover the soft tissue that was adjacent to the prostate (e) Inferiorly the CTV RTOG treats more of the anterior bladder wall than CTV MRI where coverage may not be required in view of the original prostate location. (f) Superiorly the CTV MRI increases dose to the lateral bladder walls because it covers the soft tissue beside the bladder that remains at risk of microscopic disease in view of the original prostate/tumour location. CTV RTOG misses these areas.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4307684&req=5

Fig2: Typical case depicting the differences in shape and coverage between CTV RTOG and CTV MRI. Key - Purple: pre-op prostate, Blue: pre-op visible tumour, Red: CTV RTOG, Green: CTV MRI, Yellow: bladder. (a) pre-operative T2 MRI (b) planning CT scan (post-operative); the bladder neck has been pulled down. (c) CTV RTOG does not completely cover the region of the pre-operative prostate/ tumour. Although the bladder will now largely fill the location of the original prostate, the lateral soft tissue lateral remains at risk of microscopic disease. (d) CTV MRI extends 5 mm around the original prostate to cover the soft tissue that was adjacent to the prostate (e) Inferiorly the CTV RTOG treats more of the anterior bladder wall than CTV MRI where coverage may not be required in view of the original prostate location. (f) Superiorly the CTV MRI increases dose to the lateral bladder walls because it covers the soft tissue beside the bladder that remains at risk of microscopic disease in view of the original prostate/tumour location. CTV RTOG misses these areas.
Mentions: The CTV MRI was a mean of 18.6% larger than CTV RTOG (larger in 26 cases): CTV MRI mean 138 cc (range 72.3 - 222.2 cc), CTV RTOG mean 116.3 cc (range 62.1 - 176.6 cc), (p < 0.0001). The addition of the isotropic PTV margins reduced this difference to only 4.6% (PTV MRI larger in 21 cases); PTV MRI mean 386.9 cc (range 254.4 – 551.2), PTV RTOG mean 370 cc (range 232.3 - 501.6), (p = 0.05). The mean Jaccard Index was 0.72 for CTV (standard deviation 0.09) and 0.84 for PTV (SD 0.06). Graphical depiction of absolute and overlap volumes is shown in Figure 1. Figure 2 shows a typical example of differences in the volumes for one case.Figure 1

Bottom Line: Previous work from our institution demonstrated that published prostate bed CTV guidelines frequently do not cover the pre-operative MRI defined prostate.CTV MRI spares more of the lower anterior bladder wall than CTV RTOG but increases coverage of the superior lateral bladder walls.CTV contours based upon the patient's co-registered pre-operative MRI in the post-prostatectomy setting may improve coverage of the individual's prostate bed without substantially increasing the PTV size or dose to bladder/ rectum compared to RTOG CTV guidelines.

View Article: PubMed Central - PubMed

Affiliation: The Ottawa Hospital Cancer Centre, K1H 8 L6, Ottawa, Ontario, Canada. jcroke@toh.on.ca.

ABSTRACT

Background: Recurrence rates following radiotherapy for prostate cancer in the post-operative adjuvant or salvage setting remain substantial. Previous work from our institution demonstrated that published prostate bed CTV guidelines frequently do not cover the pre-operative MRI defined prostate. Inadequate target delineation may contribute to the high recurrence rates, but increasing target volumes may increase dose to organs at risk.

Methods: We propose guidelines for delineating post-prostatectomy target volumes based upon an individual's co-registered pre-operative MRI. MRI-based CTVs and PTVs were compared to those created using the RTOG guidelines in 30 patients. Contours were analysed in terms of absolute volume, intersection volume (Jaccard Index) and the ability to meet the RADICALS and QUANTEC rectal and bladder constraints (tomotherapy IMRT plans with PTV coverage of V98% ≥98%).

Results: CTV MRI was a mean of 18.6% larger than CTV RTOG: CTV MRI mean 138 cc (range 72.3 - 222.2 cc), CTV RTOG mean 116.3 cc (range 62.1 - 176.6 cc), (p < 0.0001). The difference in mean PTV was only 4.6%: PTV MRI mean 386.9 cc (range 254.4 - 551.2), PTV RTOG mean 370 cc (range 232.3 - 501.6) (p = 0.05). The mean Jaccard Index representing intersection volume between CTVs was 0.72 and 0.84 for PTVs. Both criteria had a similar ability to meet rectal and bladder constraints. Rectal DVH: 77% of CTV RTOG cases passed all RADICALS criteria and 37% all QUANTEC criteria; versus 73% and 40% for CTV MRI (p = 1.0 for both). Bladder DVH; 47% of CTV RTOG cases passed all RADICALS criteria and 67% all QUANTEC criteria, versus 57% and 60% for CTV MRI (p = 0.61for RADICALS, p = 0.79 for QUANTEC). CTV MRI spares more of the lower anterior bladder wall than CTV RTOG but increases coverage of the superior lateral bladder walls.

Conclusion: CTV contours based upon the patient's co-registered pre-operative MRI in the post-prostatectomy setting may improve coverage of the individual's prostate bed without substantially increasing the PTV size or dose to bladder/ rectum compared to RTOG CTV guidelines. Further evaluation of whether the use of pre-operative MRI improves local control rates is warranted.

Show MeSH
Related in: MedlinePlus